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The lithostratigraphy of the Hawthorn Group (Miocene) of Florida ( FGS: Bulletin 59)

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Title:
The lithostratigraphy of the Hawthorn Group (Miocene) of Florida ( FGS: Bulletin 59)
Series Title:
Florida Geological Survey: Bulletin
Creator:
Scott, Thomas M.
Florida Geological Survey
Place of Publication:
Tallahassee, Fla.
Publisher:
Florida Geological Survey
State of Florida, Dept. of Natural Resources, Division of Resource Management, Florida Geological Survey
Publication Date:
Language:
English
Physical Description:
xiv, 148 p. : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Geology -- Florida ( lcsh )
Geology, Stratigraphic -- Miocene ( lcsh )
City of Tampa ( local )
City of Ocala ( local )
City of Jacksonville ( local )
Town of Suwannee ( local )
Greater Orlando ( local )
City of Sanford ( local )
Genre:
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
General Note:
Bulletin - Florida Geological Survey ; 59
Statement of Responsibility:
by Thomas M. Scott.

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
AAA2301 ( LTQF )
AHE3941 ( NOTIS )
001530559 ( AlephBibNum )
19907496 ( OCLC )
89622679 ( LCCN )

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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Tom Gardner, Executive Director




DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director





FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist









BULLETIN NO. 59

THE LITHOSTRATIGRAPHY OF THE
HAWTHORN GROUP (MIOCENE)
OF FLORIDA

By
Thomas M. Scott
















Published for the
FLORIDA GEOLOGICAL SURVEY
TALLAHASSEE
1988


UItIERRITY OF FLORIDA LIBRARIES










DEPARTMENT
OF
NATURAL RESOURCES


DEPARTMENT
OF
NATURAL RESOURCES

BOB MARTINEZ
Governor


Jim Smith
Secretary of State


Bill Gunter
Treasurer


Bob Butterworth
Attorney General


Gerald Lewis
Comptroller


Betty Castor
Commissioner of Education


Doyle Conner
Commissioner of Agriculture


Tom Gardner
Executive- Director










LETTER OF TRANSMITTAL


Bureau of Geology
August 1988


Governor Bob Martinez, Chairman
Florida Department of Natural Resources
Tallahassee, Florida 32301

Dear Governor Martinez:

The Florida Geological Survey, Bureau of Geology, Division of Resource Management, Department
of Natural Resources, is publishing as its Bulletin No. 59, The Lithostratigraphy of the Hawthorn Group
(Miocene) of Florida. This is the culmination of a study of the Hawthorn sediments which exist throughout
much of Florida. The Hawthorn Group is of great importance to the state since it constitutes the confining
unit over the Floridan aquifer system. It is also of economic importance to the state due to its inclusion of
major phosphorite deposits. This publication will be an important reference for future geological in-
vestigations in Florida.

Respectfully yours,



Walter Schmidt, Chief
Florida Geological Survey



























































Printed for the
Florida Geological Survey

Tallahassee
1988

ISSN 0271-7832


iv










TABLE OF CONTENTS

Page

Abstract ............................ .. ......................... ..... ............xii
Acknowledgements .................. .......................................... xiv
Introduction ...................... ............................. ......... 1
Purpose and Scope ............................................................ 1
Method of Investigation ....................... .. ............................... 5
Previous Investigations ............... .. ............................................ .. 5
Geologic Structure .......... ............... ........ ............ 11
Introduction to Lithostratigraphy ....................... ... ........................ 13
Hawthorn Formation to Group Status:
Justification, recognition and subdivision in Florida ............ ... .................. 13
Present Occurrence ......................... ................................ 15
North Florida ......................... .... ... .. . ........... 15
Introduction ...................... .............................. 15
Penney Farms Formation ............... ......... ............. .. . .. 18
Definition and type locality ............................. .......... ........ 18
Lithology ................. ... ............... ... ................ .......... 21
Subjacent and suprajacent units ................. .. .. ................ ............ 24
Thickness and areal extent ............. .... .................................. 24
Age and correlation ................... ....................................... 30
Discussion .................. ................ .............. ... ............34
Marks Head Formation ........................... ...................................34
Definition and reference section ................ .................................34
Lithology .................... .. ... .............. .... ..... ........ ...........34
Subjacent and suprajacent units ................ . .................. .............. 37
Thickness and areal extent ................. ........ .......................... 39
Age and correlation .............. .......................................... 39
Discussion ................ ............. .................. ............41
Coosawhatchie Formation ................... ................ ...... .............. 41
Definition and reference section ................ .................. .............. .. 41
Lithology ................................................ .... ......... ..... 41
Subjacent and suprajacent units ................ ................... .............. 43
Thickness and areal extent ................ ................... .................. 43
Age and correlation ..................... .............. .......... .............. 43
Discussion .............. ... .................................................. 46
Charlton Member of the Coosawhatchie Formation ................ ................... 46
Definition and reference section .............. ............................... ....... 46
Lithology ....................... ... .. ......................... 46
Subjacent and suprajacent units ......................................... .............. .46
Thickness and areal extent ................. .. ............................ 46
Age and correlation ....................... ....................... 48
Discussion .................... ... .. ........... ........ ........... 49
Statenville Formation ................... . .......... 50
Definition and type locality .. . .......................... ............. . 50
Lithology ................. .. ..... ....................... ............ 50
Subjacent and suprajacent units ................ .................................... 52
Thickness and areal extent ................. ................................ 53
Age and correlation ........................... .. ...... ........... 53










Discussion .................................... ................................. 54
Alachua Formation .................................... ............................ 54
South Florida .......................................... ..........................56
Arcadia Formation ..................................... ........................... 56
Definition and type section ....................... ............................. 56
Lithology ......................................... ............................ 56
Subjacent and suprajacent units ....................................... ............. 58
Thickness and areal extent ...................................... ................. 60
Age and correlation ....................................... ....................... 65
Discussion ............................................. ........................ 65
Tampa Member of the Arcadia Formation ................ ................ . ........ 65
Definition and type section ........................................... ............ 65
Lithology ................................... .................................. 70
Subjacent and suprajacent units ................... ........................ ...... .70
Thickness and areal extent ........................................................ 70
Age and correlation ........................................................... 72
Discussion ......................................... ............................ 73
Nocatee Member of the Arcadia Formation ............................................ .73
Definition and type section ........................................................ 73
Lithology .................. ... .. .................................... 73
Subjacent and suprajacent units .................................................... 76
Thickness and real extent ........................................................ 76
Age and correlation ..................................... ......................... 76
Discussion .................................................... 79
Peace River Formation ............................................................. 79
Definition and type section ........................................................ 79
Lithology ....................... ..............................................79
Subjacent and suprajacent units ................................................... 81
Thickness and areal extent ....................................................... 81
Age and correlation ...................................... ........................84
Discussion ................ ................................... ..................84
Bone Valley Member of the Peace River Formation ..................................... 86
Definition and type locality ................... .............. .... ................. 86
Lithology ......................................................... ............. 87
Subjacent and suprajacent units ...................................... ..............88
Thickness and real extent ..................................................... 88
Age and correlation .............................................................. 88
Discussion ............................... ...... .............................. 90
Eastern Florida Panhandle ...........................................................91
Torreya Formation .................. ............................................. 91
Definition and type section ................................... ...... .......... 91
Lithology .................................. .................................. 91
Subjacent and suprajacent units .................................................. 96
Thickness and real extent .................. .................................... 100
Age and correlation .............................................................100
Discussion ......... ........................................ ....... 100
Dogtown Member of the Torreya Formation ............................................ 100
Definition and type locality ................. ................................... 100
Lithology ..................................................................... 100
Subjacent and suprajacent units .................................................101
Thickness and real extent ...................................................... .101


vi











A ge ....................... .........
Discussion ..............................
Sopchoppy Member of the Torreya Formation ....
Definition and type locality .................
Lithology ...........................
Subjacent and suprajacent units .............
Thickness and areal extent .................
Age and correlation .......................
Discussion ...........................
Hawthorn Group Mineralogy ...................
Phosphate ................................
Occurrence in the Hawthorn Group ..........
Phosphate Genesis .....................
Post-depositional modification ..............
Hard rock phosphate deposits ............ .
Palygorskite and Sepiolite ...................
Dolomite ........................ ...

Geologic History .............................

Paleoenvironments ........................

Hawthorn Group Gamma Ray Log Interpretation ...
North Florida .............. .............
South Florida ............... ...........
Eastern Panhandle ... ...................


Summary ................... .. ...... .........


. .. . . . . . . . . . . . . . . . 1 1 1

. . . . . . . . . . . . . . . . . . 1 18


. .123
. 123
..123
..130


............................ 130


Conclusions .....................................................................138

References ...................... ........... ...... . ........... 139



APPENDIX

Appendix A. Lithologic legend for stratigraphic columns ................................. 148

FIGURES


Figure
1 Study area and areas of discussion ...............


. . . . . . . . . . . . . . 2


2 Location of cores............. ..................... ........ .............3

3 Cross section location map. ................. .................... ............ 4

4 Structures affecting the Hawthorn Group................ ..... ................... 12


5 Statewide map of the elevation of the upper Hawthorn Group surface. .....


.......... 16


6 Statewide isopach map of the Hawthorn Group ......


....101
....101
.. .101
.. .101
.... 102
.... 102
... 102
....102
....102
... 102
.... 103
.... 103
.... 103
... 107
... 108
.... 108
....110


. .17










7 Lithostratigraphic units of the Hawthorn Group in north Florida. ....................... 19

8 Geologic map of the pre-Hawthorn Group surface ... . ... ...... ............. . . 20

9 Type section of the Penney Farms Formation, Harris #1, W-13769, Clay County (Lithologic
legend Appendix A) ...................... ............... ................. 22

10 Intraclasts with phosphatic rims from Penney Farms Formation, St. Johns County, W-13844...... 23

11 Cross section A-A' (see figure 3 for location) (See Scott (1983) for discussion of faults) ........ 25

12 Cross section B-B' (see figure 3 for location) (See Scott (1983) for discussion of faults)........ 26

13 Cross section C-C' (see figure 3 for location) (See Scott (1983) for discussion of faults)........ 27

14 Cross section D-D' (see figure 3 for location) (See Scott (1983) for discussion of faults)........ 28

15 Cross section E-E' (see figure 3 for location) (See Scott (1983) for discussion of faults) ........ 29

16 Cross section F-F' (see figure 3 for location) (See Scott (1983) for discussion of faults)........ .30

17 Top of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group......31

18 Isopach of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn
Group ..... ..... .... ................................................ . 32

19 Formational correlations (modified from unpublished C.O.S.U.N.A. Chart, 1985).............. 33

20 Reference section for the Marks Head Formation, Jennings #1, W-14219, Clay County
(Lithologic legend Appendix A) ................. ................................... 35

21 Reference section for the Marks Head Formation, N.L. #1, W-12360, Bradford County
(Lithologic legend Appendix A) .. . .................... ... ... ................ 36

22 Top of the Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group..... 38

23 Isopach of Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group...... 40

24 Reference section for the Coosawhatchie Formation, Harris #1, W-13769, Clay County
(Lithologic legend Appendix A) ................ ................... ................ 42

25 Top of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group..... 44

26 Isopach of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn
Group................ ............. .............................45

27 Reference core for the Charlton Member of the Coosawhatchie Formation, Cassidy #1,
Nassau County (Lithologic legend Appendix A). ................. ................... 47

28 Top of the Charlton Member (dashed line indicates extent of Charlton).................... 48

29 Isopach of the Charlton Member (dashed line indicates extent of Charlton) .................. 49

30 Reference core for the Statenville Formation, W-15121, Betty #1, Hamilton County
(Lithologic legend Appendix A) ............................................ 51










31 Photograph of Statenville Formation outcrops showing distinct cross bedding ............... 52

32 Area of occurrence of the Statenville Formation ................. . ................... 53

33 Lithostratigraphic units of the Hawthorn Group in southern Florida........................ 55

34 Type core for the Arcadia Formation, Hogan #1, W-12050, DeSoto County (Lithologic legend
Appendix A) ............. . .. ..................................... 57

35 Cross section G-G' (see figure 3 for location) ....................................59

36 Cross section H-H' (see figure 3 for location) .................. .................. ... 60

37 Cross section I-I' (see figure 3 for location). .................. ....................... 61

38 Cross section J-J' (see figure 3 for location) ................. ........................ 62

39 Cross section K-K' (see figure 3 for location)......................... ................ ............ 63

40 Cross section L-L' (see figure 3 for location). .................. ...................... 64

41 Top of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group........... 66

42 Isopach of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group........67

43 Reference core for the Tampa Member of the Arcadia Formation, Ballast Point #1, W-11541,
Hillsborough County (Lithologic legend Appendix A).............. .... ................... 68

44 Reference core for the Tampa Member of the Arcadia Formation, R.O.M.P. 7-1, W-15166,
Manatee County (Lithologic legend Appendix A). ................. ................... 69

45 Top of Tampa Member ............. ..... ........................................ 71

46 Isopach of Tampa Member............. .......................................... 72

47 Type core for the Nocatee Member of the Arcadia Formation, Hogan #1, W-12050, DeSoto
County (Lithologic legend Appendix A)................... ......................... 74

48 Reference core for the Nocatee Member of the Arcadia Formation, R.O.M.P. 17, W-15303,
DeSoto County (Lithologic legend Appendix A). .................. .................... .75

49 Isopach of Nocatee Member............ ..........................................77

50 Top of Nocatee Member. ................................. ................... .78

51 Type core of the Peace River Formation, Hogan #1, W-12050, DeSoto County (Lithologic
legend Appendix A)............. ...................................... 80

52 Top of Peace River Formation. Shaded area indicates undifferentiated Hawthorn Group ....... 82

53 Isopach of Peace River Formation. Shaded area indicates undifferentiated Hawthorn Group..... 83

54 Reference core for the Bone Valley Member of Peace River Formation, Griffin #2, W-8879,
Polk County (Lithologic legend Appendix A) ............... ........................ 85

55 Schematic diagram showing relationship of lithostratigraphic units in southern Florida......... 86










56 Top of Bone Valley Member..................... ............. ...... ........... 89

57 Isopach of Bone Valley Member. ............. ...... .............. ................. 90

58 Lithostratigraphic units of the Hawthorn Group in the eastern Florida panhandle ............. 92

59 Reference core for the Torreya Formation, Rock Bluff #1, W-6611, Liberty County (Lithologic
legend A ppendix A). .......................................... ..................... 93

60 Reference core for the Torreya Formation, Owenby #1, W-7472, Gadsden County (Lithologic
legend Appendix A). ................................................ 94

61 Reference core for the Torreya Formation, Goode #1, W-6998, Leon County (Lithologic
legend Appendix A) ............ ........................................... 95

62 Cross section M-M' (see figure 3 for location). .................. ................... .. 97

63 Isopach of the Torreya Formation ................... ...................... 98

64 Top of the Torreya Formation................. ....................... ............99

65 Location of phosphate deposits in Florida ................ ......................... 104

66 Structural features of the southeast United States (after Riggs, 1979) ..................... 106

67 Lithostratigraphic units in relation to proposed sea level fluctuations (after Vail and Mitchum,
1979)......... ...........................................................113

68 Cross section showing reconstructed stratigraphic sequence at the end of Late Oligocene.... 115

69 Cross section showing reconstructed stratigraphic sequence at the end of the Early
Miocene .................................... ................... ...........116

70 Cross section showing reconstructed stratigraphic sequence at the end of Middle Miocene .... 117

71 Cross section showing reconstructed stratigraphic sequence at the end of the Early
Pliocene ......................................................119

72 Cross section showing stratigraphic sequence occurring at present ................. .. .120

73 Relation of Mammal ages to planktonic foraminifera time scale (after Webb and Crissinger,
1983).......... ............................................................122

74 Gamma-ray log, Jennings #1, W-14219, Clay County. ............. .. ............. 124

75 Gamma-ray log, R.O.M.P. 17, W-15303, DeSoto County ................ ........... 125

76 Gamma-ray log, R.O.M.P. 45-2, Polk County. ................ .................... .126

77 Gamma-ray log, Osceola #7, W-13534, Osceola County ......................... 127

78 Gamma-ray log, Phred #1, W-13958, Indian River County............ ... .......... 128

79 Gamma-ray log, Cape Coral #1, W-15487, Lee County. .......................... 129

80 Gamma-ray log, Owenby #1, W-7472, Gadsden County.... ........ ................... 131










81 Gamma-ray log, Howard #1, W-15515, Madison County ............... ............... 132

TABLE

1 Nomenclatural changes that have occurred in relation to the Hawthorn Group................. 6










ABSTRACT


The Hawthorn Formation has been a problematic unit for geologists since its inception by Dall and Har-
ris (1892). It is a complex unit consisting of interbedded and intermixed carbonate and siliciclastic
sediments containing varying percentages of phosphate grains. These sediments have been widely
studied by geologists due to their economic and hydrologic importance in the southeastern United
States. Economically, the Hawthorn sediments contain vast quantities of phosphate and clay and limited
amounts of uranium. Hydrologically, the Hawthorn contains secondary artesian aquifers, provides an
aquiclude for the Floridan aquifer system and, in some ares, makes up the upper portion of the Floridan
aquifer system.
The Hawthorn Formation of previous investigators has been raised to group status in Georgia by Hud-
dlestun (in press). The present investigation extends the formations recognized in southern Georgia into
northern Florida with some modifications, and accepts Huddlestun's concept of the Hawthorn Group.
SThe Hawthorn Group and its component formations in southern Florida represent a new lithostratigraphic
nomenclature applied to these sediments. The elevation of the Hawthorn to group status in Florida is
justified by the Hawthorn's complex nature and the presence of really extensive, mappable lithologic
units.
The Hawthorn Group in northern peninsular Florida consists of, in ascending order, the Penney Farms
Formation, the Marks Head Formation and the Coosawhatchie Formation. The Coosawhatchie Forma-
tion grades laterally and, in a limited area, upwards into the Statenville Formatioh.
Lithologically, the Hawthorn Group in northern Florida is made up of a basal carbonate with interbedd-
ed siliciclastics (Penney Farms), a complexly interbedded siliciclastic-carbonate sequence (Marks
Head), a siliciclastic unit with varying percentages of carbonate in both the matrix and individual beds
(Coosawhatchie) and a crossbedded, predominantly siliciclastic unit (Statenville). Phosphate grains are
present throughout these sediments, varying in percentage up to 50 percent of the rock.
Sediments of the Hawthorn Group in northern peninsular Florida range in age from Early Miocene
(Aquitanian) to Middle Miocene (Serravalian). This represents a significant extension of the previously
accepted Middle Miocene age.
In southern Florida, the group includes two formations, in ascending order, the Arcadia Formation and
the Peace River Formation. The Tampa Formation or Limestone of former usage is included as a lower
member of the Arcadia Formation due to the Tampa's limited areal extent, lithologic similarities, and
lateral relationship with the undifferentiated Arcadia. Similarly, the Bone Valley Formation of former
usage is incorporated as a member in the Peace River Formation.
Lithologically, the Arcadia Formation is composed of carbonate with varying amounts of included and
interbedded siliciclastics. Siliciclastic sediments in the Arcadia are most prevalent in its basal Nocatee
Member. The Peace River Formation is predominantly a siliciclastic unit with some interbedded car-
bonates. Phosphorite gravel is most common in the Bone Valley Member. Sand-sized phosphate grains
are virtually ubiquitous in the southern Florida sediments with the exception of the Tampa Member where
it is often absent.
The southern Florida Hawthorn sediments range in age from Early Miocene (Aquitanian) to Early
Pliocene (Zanclian).
The Hawthorn Group in the eastern Florida panhandle is composed of the Torreya Formation and, in a
few areas, a Middle (?) Miocene unnamed siliciclastic unit. Lithologically, the Torreya consists of a
carbonate-rich basal section with interbedded clays and sands, and a dominantly siliciclastic, often
massive, plastic clayey upper unit (Dogtown Member). Phosphate grains are noticeably less common in
the Hawthorn of the panhandle.
Hawthorn Group sediments are characterized by the occurrence of an unusual suite of minerals.
Apatite (phosphate grains) is virtually ubiquitous in the peninsular Hawthorn sediments. Palygorskite,
sepiolite and dolomite occur throughout the group statewide.
Miocene sea level fluctuations were the primary controlling factor determining the extent of Hawthorn
deposition in Florida. During the maximum Miocene transgression, sediments of the Hawthorn Group










were probably deposited over the entire Florida platform. Hawthorn sediments were subsequently
removed from the crest of the Ocala Platform (Ocala Uplift) and the Sanford High by erosion.
The Hawthorn Group appears to have been deposited under shallow marine conditions. These condi-
tions are suggested by the occurrence of molds of shallow water mollusks and a limited benthic
foraminifera fauna. The deepest water conditions apparently existed in the Jacksonville and
Okeechobee Basins.
The gamma-ray signature of the Hawthorn Group is quite distinctive, providing a useful tool for iden-
tification and correlation in areas of limited data. The Hawthorn signature consists of distinctly different
patterns in northern and southern peninsular and eastern panhandle Florida.










ACKNOWLEDGEMENTS


The author wishes to acknowledge the assistance of many individuals during the course of this study.
The assistance of these individuals was invaluable in the successful completion of this investigation.
The author thanks C.W. "Bud" Hendry, Jr., former State Geologist of Florida, and Steve Windham,
former Bureau Chief of the Florida Bureau of Geology for allowing the author to attend Florida State
University under the state's job related courses program. Discussions and support from the staff of the
Florida Geological Survey were greatly appreciated. Of particular assistance were Ken Campbell,
Paulette Bond and Walt Schmidt, State Geologist. Justin Hodges, former driller for theFlorida Geological
Survey, was invaluable to this study. Mr. Hodges' expertise was responsible for the recovery of excellent
quality cores, many of which were used in this research. Draftsmen Jim Jones and Ted Kiper spent many
hours laboring over the figures for the text.
Thanks are due to a number of individuals around the state for their help during this project. These in-
clude: Jim Lavender, Tony Gilboy, Jim Clayton, John Decker, Greg Henderson and Kim Preedom of the
Southwest Florida Water Management District who provided cores and geophysical data; Mike "50-50"
Knapp from the South Florida Water Management District; Drs. Sam Upchurch and Richard Strom of the
University of South Florida; and to Tom Missimer of Missimer and Associates.
Special thanks are due to Dr. Paul Huddlestun of the Georgia Geologic Survey for many hours of
discussion and data sharing. Muriel Hunter also shared freely her knowledge of Florida stratigraphy.
The author is very appreciative of the very competent assistance of Cindy Collier, secretary from the
Geological Investigations Section of the Florida Geological Survey. The final form of this manuscript
would have been significantly more difficult to achieve without her assistance.
The author greatly appreciates the guidance and assistance of his faculty committee, Drs. Sherwood
Wise (Chairman), William Parker, J.K. Osmond, Steve Winters, and William Burnett. Their time and effort
assisted in an improved final draft. The author also appreciates the many hours of discussion and the
assistance provided by former FSU graduate students and Florida Geological Survey graduate
assistants Andy LeRoy and Barry Reik.
Reviews of this manuscript by a number of geologists aided the author in presenting this study in a
more concise manner. This author greatly appreciates the efforts of the following reviewers: Walt
Schmidt, Bill Yon, Ken Campbell, Ed Lane, Jackie Lloyd, Paulette Bond and Alison Lewis of the Florida
Geological Survey; Drs. Wise, Parker, Osmond, Winters, and Burnett of Florida State University; Dr. Sam
Upchurch of the University of South Florida; and Ms. Muriel Hunter, independent geologist.
Finally, and most importantly, are the thanks due to my family for their support during this endeavor.
My wife of 17 years has lived with this research for more than one third of our married life. This research
would not have been completed without her support.










THE LITHOSTRATIGRAPHY OF THE HAWTHORN
GROUP (MIOCENE) OF FLORIDA

By
Thomas M. Scott

INTRODUCTION

The late Tertiary (Miocene-Pliocene) stratigraphy of the southeastern Coastal Plain provides
geologists with many interesting and challenging problems. Much of the interest has been generated by
the occurrence of scattered phosphorite from North Carolina to Florida. The existence of phosphate in
the late Tertiary rocks of Florida was recognized in the late 1800's and provided an impetus to investigate
these sediments. More recently, the hydrologic importance of these units has led to further investigations
of the stratigraphy and lithology to determine their effectiveness as an aquiclude, aquitard and aquifer.
The Hawthorn Formation in Florida has long been a problematic unit. Geologists often disagree about
the boundaries of the formation. The resulting inconsistencies have rendered accurate correlation be-
tween authors virtually impossible.
The biggest problem hindering the investigation of the Hawthorn strata has been a paucity of quality
subsurface data. Since the mid-1960's, the Florida Geological Survey has been gathering core data from
much of the state, providing a unique opportunity to investigate the extent of, and facies relationships in
the Hawthorn of the subsurface.
This investigation is an attempt to provide an understanding of the Hawthorn Group, its lithologies,
stratigraphy and relation to subjacent and suprajacent units. A greater understanding of the Hawthorn is
imperative to deciphering the late Tertiary geologic history of Florida.


PURPOSE AND SCOPE

The purpose of this investigation is to provide a coherent lithostratigraphic framework facilitating a bet-
ter understanding of the Hawthorn Group in Florida. The internal framework of the Hawthorn, its lateral
continuity, and relation to subjacent and suprajacent units were investigated in order to provide this
knowledge.
The area covered by this study extends from the Apalachicola River in the Florida Panhandle on the
west to the Atlantic Coast on the east and from the Georgia-Florida border on the north, south to the
Florida Keys (Figure 1). The study area encompasses all or portions of 56 counties. Data points outside
the study area, particularly in Georgia, were used to assist in providing a more accurate picture within the
study area boundaries.
The study area boundaries were chosen based on several criteria. In the past, the western limits of the
Hawthorn were drawn at the Apalachicola River. The western boundary was chosen both to coincide with
the historical boundary and to avoid overlap with the investigation of equivalent sediments in the
Apalachicola Embayment by Schmidt (1984).
More than 100 cores provided the data base for the present study. The locations of cored data points
are shown on Figure 2. Figure 3 delineates cross section transects.













AREA NOT INCLUDED IN STUDY


1
-N-

i
0 25 50 MILES
0 40 80 KILOMETERS
SCALE


Figure 1. Study area and areas of discussion.


C~~dd
Q 4








*---1



747 71- --15515155377 28 13815
-.--- 7472 .0- 15728
8,7 48 ,q t2 6933 \-- ---
21 7 52 8 6998,- 6911i-'58 10480 15121 71
g *6906 \ --.-6836 / 14619
S7536 I 380 380-- /
/ .----------i / ,/10473
I T 115162 13812 1417
/ I !12360 WI141 93
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EXPLANATION
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Figure 3. Cross section location map.


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METHOD OF INVESTIGATION


The Hawthorn Group is predominantly a subsurface unit. As a result, the principal data sources for this
study were the cores drilled by the Florida Geological Survey from 1964 through the present. The cores
were obtained using a Failing 1500 Drillmaster with a capacity to drill in excess of 1000 feet (305 meters).
Under most conditions, nearly continuous recovery of 1-34 inch (4.5 cm) diameter cores was obtained.
Losses in core recovery were minimized due to the expertise of driller Justin Hodges. The cores
recovered were placed in boxes and are stored at the Geological Survey in Tallahassee. Additional cores
were obtained from the Southwest Florida Water Management District and the St. Johns River Water
Management District. All cores are available for inspection by the public.
Supplemental lithologic data sources included samples obtained from water wells drilled by private
contractors who provide cuttings to the Geological Survey. Unfortunately, the cuttings do not necessarily
provide accurate-lithologic information. This circumstance is due to the loss of fine grained (clay, silt and
very fine sand-sized), poorly consolidated to nonindurated sediments. The drilling method, sample col-
lection, and subsequent removal of drill mud by washing facilitates the loss of this material. The net result
is to skew the sediment types toward sands and more indurated materials. The use of cuttings does,
however, allow the extrapolation of lithologies and contacts in areas of limited core control. Water-well
cuttings were thus used only to supplement core data.
All cores and well cuttings were examined using a binocular microscope. Examinations were normally
made at magnification of 10x to approximate the use of a hand lens in field identification. Higher
magnifications (up to 45x) were employed for the identification of the finer grained constituents of the
sediments. Geologist's logs of the samples were recorded according to the Florida Geological Survey
format which aids in producing a concise, standardized lithologic description. Coded lithologic data were
stored on magnetic tape for later retrieval and use. These data were run through the Florida Geological
Survey's FBGO1 program on the Florida State University computer which provided a full English printout
of the lithologic information. The data were also run through the Stratlog program to provide a lithologic
column of each core analyzed.
Samples collected for x-ray analysis were taken primarily from cores, although outcrops along the
Suwannee and Alapaha Rivers were also sampled. Since clay minerals present in the sediments were of
primary interest, samples were taken from the more clayey portions of the cores. Samples were mounted
for x-ray analysis by standard techniques and analyzed with CuKoradiation.
Gamma-ray logs were run on most core holes. Numerous gamma-ray logs run in water wells are also
available for correlation purposes. All geophysical logs are on permanent file at the Geological Survey
and are open to the public.


PREVIOUS INVESTIGATIONS

Interest in the general stratigraphic framework of the southeastern Coastal Plain and the occurrence of
phosphate in the sediments now assigned to the Hawthorn Group prompted geologists to investigate
these sediments in Florida. Table 1 indicates the important nomenclatural changes that have occurred in
relation to the Hawthorn Group.
The discovery of phosphatic rock in Florida first occurred in the late 1870's near the town of Hawthorne
in Alachua County (Day, 1886). By 1883, Dr. C.A. Simmons quarried and ground the phosphatic rocks for
fertilizer (Sellards, 1910). During the 1880's phosphate was also discovered in central Florida.
Smith (1881) noted the phosphatic rocks exposed along the Suwannee River from the Okefenokee
Swamp downstream and placed them in the Vicksburg Stage. Hawes (1882), in discussing the
"phosphatic sandstones from Hawthorne," described them as containing sharks' teeth and bones
belonging to the Tertiary Age. Smith (1885) and Johnson (1885) discussed the stratigraphy and occur-
rence of the phosphatic rocks of Florida. Johnson (1885) applied the name Fort Harlee marl to the
phosphatic sediments at Waldo in Alachua County. He mentioned the occurrence of Ostrea and silicified
corals within the sediments. Johnson also mentioned that those rocks are rather widespread in the state.
















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Smith (1885) examined samples sent to him by L.C. Johnson and thought the phosphatic limestone at
Hawthorne was Eocene or Oligocene, as was the rest of the limestone in the peninsula. However,
fossiliferous samples from the Waldo area indicated to Smith that the rocks were Miocene. He con-
sidered the rocks near Waldo to be the same as those exposed at Rock Springs in Orange County. Kost
(1887), in the first report of the Florida Geological Survey, mentioned the recognition of phosphatic rocks
in several locations throughout the state. Penrose (1888) briefly discussed the phosphatic sediments of
Alachua County. Johnson (1888) named the Waldo Formation for the phosphatic sediments exposed in
eastern Alachua County.
The first major contribution to the understanding of the Miocene phosphatic sediments of Flordia was
published by Dall and Harris (1892). Relying upon unpublished data from L.C. Johnson and their own
field information, Dall and Harris applied the name "Hawthorne beds" for the phosphatic sediments ex-
posed and quarried near Hawthorne, Alachua County. They reproduced sections and descriptions ob-
tained from Johnson. Dall and Harris placed the "Hawthorne beds" in the "newer" Miocene. Johnson's
Waldo Formation was thought to be in the "older" Miocene although Dall and Harris state (p. 111), "Old
Miocene phosphatic deposits These rocks were among those referred by Johnson to his Waldo forma-
tion, though typical exposures at Waldo belong to the newer or Chesapeake Miocene." Dall and Harris
placed the "Hawthorne beds" in their "Chattahoochee group" which overlies the Vicksburg Group and
underlies the "Tampa group" (including their "Tampa limestone" which they felt was younger than the
"Hawthorne beds").
The name "Jacksonville limestone" was applied by Dall and Harris (1892) to a "porous, slightly
phosphatic, yellowish rock" first recognized by Smith (1885). They thought the "Jacksonville limestone"
covered a large area from Duval County to at least Rock Springs in Orange County and included it in the
"newer Miocene" above the "Hawthorne beds."
Dall and Harris (1892) examined the sediments in the phosphate mining area on the Peace River and
referred to the phosphate-producing horizon as the "Peace Creek bone bed." Underlying the producing
zone was a "yellowish sandy marl" containing phosphate grains and mollusk molds which they named
the "Arcadia marl." Both units were considered to be Pliocene in age.
Dall and Harris also named the "Alachua clays" stating these clays "occur in sinks, gullies, and other
depressions... ." They assigned the Alachua clays to the Pliocene based on vertebrate remains.
Matson and Clapp (1909) considered the Hawthorn to be Oligocene following Dall (1896) who began
referring to the "older Miocene" as Oligocene. They considered the Hawthorn to be contemporaneous
with the Chattahoochee Formation of west Florida and the Tampa Formation of south Florida. The
Hawthorn was referred to as a formation rather than "beds" without formally making the change or
designating a type section. Matson and Clapp placed the Hawthorn in their "Apalachicola group." Chert
belonging to the "Suwannee limestone" was also included in the Hawthorn Formation at this time.
Matson and Clapp (1909) named the "Bone Valley gravel," replacing the "Peace Creek bone bed" of
Dall and Harris (1892). They believed, as did Dall and Harris, that this unit was Pliocene. Matson and
Clapp thought that the Bone Valley was predominantly of fluviatile origin and was derived from pre-
existing formations, especially the "Hawthorn formation." The Bone Valley gravels were believed to be
younger than Dall and Harris' "Arcadia marl," older than the Caloosahatchee marl and in part contem-
poraneous with the "Alachua clays."
Veatch and Stephenson (1911) did not use the term "Hawthorn formation" in describing the sediments
in Georgia. Instead the sediments were included in the "Alum Bluff formation" and described as strata
lying between the top of the Chattahoochee formation and the base of the Miocene. Overlying their
"Alum Bluff" sediments was an argillaceous sand that was in places a friable phosphatic sand which
Veatch and Stephenson named the Marks Head marl. The Duplin marl, a coarse phosphatic sand with
shells, overlies the Marks Head or the Alum Bluff when the Marks Head is absent.
Sellards (1910, 1913, 1914, 1915) discussed the lithology of the sediments associated with hard rock
and pebble phosphate deposits. He presented a review of the origins of the phosphate and their relation
to older formations. Sellards (1915) published the section exposed at Brooks Sink in a discussion of the
incorporated pebble phosphates.










Matson and Sanford (1913) dropped the "e" from the end of Hawthorne (as Dall and Harris had used
it). They state (p. 64), "The name of this formation is printed on the map as Hawthorne, the spelling used
in some previously published reports, but as the geographic name from which it is derived is spelled
Hawthorn, the final "e" has been dropped in the text." This began a debate of minor importance that
continues to the present. Currently the Florida Geological Survey accepts the name without the "e."
Vaughan and Cooke (1914) established that the Hawthorn is not equivalent to or contemporaneous
with, any part of the Chattahoochee Formation but is essentially equivalent to the "Alum Bluff
formation." They suppressed the name Hawthorn and recommended the use of the name "Alum Bluff
formation" and retained the Oligocene age.
Matson (1915) believed that the "Alum Bluff" (Hawthorn) phosphatic limestones formed the bed rock
beneath the pebble phosphates of central Florida. This unit had previously been called the "Arcadia
marl" (Dall and Harris, 1892). Matson added the sands of the "Big Scrub" in what is now the Ocala Na-
tional Forest and the sands of the ridge west of Kissimmee (Lake Wales Ridge) to the "Alum Bluff forma-
tion." He thought also that the sequence of sediments called the "Jacksonville formation" (formerly the
"Jacksonville limestone" of Dall and Harris, 1892) contained units equivalent to the "Alum Bluff forma-
tion." Matson thought that the "Bone Valley gravel" and "Alachua clays" were Miocene. He based this
on the belief that the elevation of the "Bone Valley gravel" was too high to be Pliocene.
Sellards (1919) considered the "Alum Bluff" to be Miocene rather than Oligocene based on the
vertebrate and invertebrate faunas. He stated (p. 294): "In the southern part of the state the deposits
which are believed to represent the equivalent of the Alum Bluff formation are distinctly phosphatic." He
felt that the deposits referred to the "Jacksonville formation" are lithologically similar to the "Alum Bluff"
sediments as developed in south Florida and contain similar phosphatic pebbles. According to Sellards
(1919), phosphate first appears in the Miocene "Alum Bluff" rocks, and the "Bone Valley gravels" and
the "Alachua clays" represent the accumulation of reworked Miocene sediments.
Mossom (1925, p. 86) first referred the "Alum Bluff" to group status citing "The Alum Bluff is now con-
sidered by Miss Gardner as a group... ." Gardner did not publish this until 1926. Gardner (1926), in rais-
ing the Alum Bluff to a group, also raised the three members, Shoal River, Oak Grove, and Chipola, to
formational status. Mossom (1926) felt the Chipola Formation was the most important and widespread
subdivision of the group. He included the fuller's earth beds in north Florida and the phosphatic sands
throughout the state in this formation. However, the phosphatic sands were generally referred simply to
the Alum Bluff Group. Mossom also believed that the red, sandy clay sediments forming the hills in north
Florida belonged in the Chipola Formation.
The Hawthorn Formation was reinstated by Cooke and Mossom (1929), since Gardner (1926) had rais-
ed the Alum Bluff to group status. Cooke and Mossom (1929) defined the Hawthorn Formation to include
the original Hawthorn "beds" of Dall and Harris (1892) excluding the "Cassidulus-bearing limestones"
and chert which Matson and Clapp (1909) had placed in the unit. Cooke and Mossom believed the
"Cassidulus-bearing limestones" and the chert should be placed in the Tampa Limestone (which at that
time included strata now assigned to the Suwannee Limestone). They included the "Jacksonville
limestone" and the "Manatee River marl" (Dall and Harris, 1892) in the Hawthorn even though they felt
the faunas may be slightly younger than typical Hawthorn. They also included Dall and Harris' "Sop-
choppy limestone" in the Hawthorn. Cooke and Mossom felt that a white to cream-colored, sandy
limestone with brown phosphate grains was the most persistent component of this unit.
Stringfield (1933) provided one of the first, although brief, descriptions of the Hawthorn Formation in
central-southern Florida. He noted that the Hawthorn contained more limestone in the lower portion
toward the southern part of his study area.
Cooke (1936) extended the Hawthorn Formation as far northeastward as Berkeley County, South
Carolina. Cooke (1943, p. 90) states, "The Hawthorn Formation underlies an enormous area that stret-
ches from near Arcadia, Florida, to the vicinity of Charleston, South Carolina." Cooke (1945) discussed
the Hawthorn and its occurrence in Florida. The only change suggested by Cooke (1945, p. 192) was to
tentatively include the Jacksonville Formation of Dall and Harris (1892) into the Duplin Marl rather than in
the Hawthorn as Cooke and Mossom (1929) had done. Cooke (1945) also believed that the Apalachicola










River was the western boundary of the Hawthorn.
Parker and Cooke (1944) investigated the surface and shallow subsurface geology of southernmost
Florida. The plates accompanying their report showed the Hawthorn Formation ranging from -10 feet
MSL (-3 meters) to -120 feet MSL (-37 meters) overlain by the Tamiami Formation, Caloosahatchee Marl,
and Buckingham Marl. Parker (1951) reassigned the upper sequence of Hawthorn sediments to the
Tamiami Formation based on his belief that the fauna was Late Miocene rather than Middle Miocene.
This significantly altered the concept of Mansfield's (1939) Tamiami Limestone and of the Hawthorn in
southern Florida. Parker et al. (1955) continued this concept of the formations.
Cathcart (1950) and Cathcart and Davidson (1952) described the Hawthorn phosphates, their relation-
ship to the enclosing sediments and the lithostratigraphy. Also mentioned is the variation in lithologies
and thickness of the Hawthorn within the land pebble district. An excellent description of the Bone Valley
Formation was presented by Cathcart (1950).
Vernon (1951) published a very informative discussion of the Miocene sediments and associated pro-
blems. Beyond providing data on the limited area of Citrus and Levy Counties, Vernon provided a propos-
ed geologic history of Miocene events. He believed that the Alachua Formation was a terrestrial facies of
the Hawthorn and also was, in part, younger than Hawthorn.
Puri (1953) in his study of the Flordia panhandle Miocene referred to the Middle Miocene as the Alum
Bluff Stage. He considered the Hawthorn to be one of the four lithofacies of the Alum Bluff Stage.
Yon (1953) investigated the Hawthorn between Chattahoochee in the panhandle and Ellaville on the
Suwannee River. Yon included in the Hawthorn the sand and clay unit that was later formally placed in
the Miccosukee by Hendry and Yon (1967).
Bishop (1956), in a study of the groundwater and geology of Highlands County, Florida, concluded that
the "Citronelle" sands which overlie the Hawthorn graded downward into the Hawthorn. He suggested
that these sands be included in the Hawthorn as a non-marine, continental facies deposited as a delta to
a large river which existed in Florida during the Miocene.
Pirkle (1956 a, 1956 b, 1957) discussed the sediments of the Hawthorn Formation from Alachua Coun-
ty, Florida. He considered the Hawthorn as a unit of highly variable marine sediments which locally con-
tained important amounts of phosphate. He also regarded the sediments of the Alachua Formation as
terrestrial reworked sediments ranging from Lower Miocene to Pleistocene. Later studies by Pirkle,
Yoho, and Allen (1965) and Pirkle, Yoho, and Webb (1967) characterized the sediments of the Hawthorn
and Bone Valley Formations.
The interest of the United States Geological Survey in the Hawthorn and Bone Valley Formations for
their economic deposits of phosphate and related uranium concentrations resulted in a number of
publications including Bergendal (1956), Espenshade (1958), Carr and Alverson (1959), Cathcart and
McGreevy (1959), Ketner and McGreevy (1959), Cathcart (1963 a, b; 1964; 1966), Espenshade and
Spencer (1963), and Altschuler, Cathcart, and Young (1964). With the exception of Espenshade (1958)
and Espenshade and Spencer (1963), the studies investigated the strata in the Central Florida
Phosphate District and adjacent areas. Espenshade (1958) and Espenshade and Spencer (1963) con-
ducted investigations in north Florida.
Goodell and Yon (1960) provide a discussion of the lithostratigraphy of the post-Eocene rocks from
much of the state. They provide a regional lithostratigraphic view of the Miocene sediments in Florida.
The occurrence of magnesian (Mg) rich clays (palygorskite) within the Hawthorn Formation has been
investigated by several authors. McClellan (1964) studied the petrology and occurrence of the palygor-
skite (attapulgite). Gremillion (1965) investigated the origin of the clays. Ogden (1978) suggested deposi-
tional environments and the mode of formation of the clays.
Puri and Vernon (1964) summarized the geology of the Hawthorn. They discussed the status of the
knowledge of the Hawthorn but added very little new information.
Brooks (1966, 1967) suggested that the Hawthorn should be raised to group status in the future. He
further discussed the existence of the Hawthorn across the Ocala Uplift and its subsequent erosional
removal. Brooks believed Middle Miocene strata were absent from the Ocala Uplift but were present
downdip from the arch. He felt that Lower Miocene beds were present on the arch.










Sever, Cathcart, and Patterson (1967) investigated the phosphate resources and the associated
stratigraphy of the Hawthorn Formation in northern Florida and southern Georgia.
Riggs (1967) suggested raising the Hawthorn Formation to group status based on his research in the
phosphate district. The rocks of Riggs' "Hawthorn group" were related by containing greater than one
percent phosphate grains. The Bone'Valley Formation was included as the uppermost unit of the group.
Riggs and Freas (1965) and Freas and Riggs (1968) also discussed the stratigraphy of the central Florida
phosphate district and its relation to phosphorite genesis.
The geology and geochemistry of the northern peninsular Florida phosphate deposits were in-
vestigated by Williams (1971). Clark (1972) investigated the stratigraphy, genesis and economic potential
of the phosphorites in the southern extension of the Central Florida Phosphate District.
Weaver and Beck (1977) published a wide ranging discussion of the Coastal Plain Miocene sediments
in the southeast. Emphasis was placed on the depositional environments and the resulting sediments,
particularly the clays.
Wilson (1977) mapped the Hawthorn and part of the Tampa together. He separated the upper Tampa,
termed the Tampa Limestone unit, from the lower "sand and clay" unit of the Tampa Limestone.
Missimer (1978) discussed the Tamiami-Hawthorn contact in southwest Florida and the inherent pro-
blems with the current stratigraphic nomenclature. Peck et al. (1979) believed that the definition of the
Tamiami by Parker et al. (1955) added to the previously existing stratigraphic problems. Hunter and Wise
(1980 a, 1980 b) also addressed this problem suggesting a restriction and redefinition of the Tamiami
Formation.
King and Wright (1979) in an effort to alleviate some of the stratigraphic problems associated with the
Tampa and Hawthorn formations redefined the Tampa and erected a type section from a core at Ballast
Point. Their redefinition restricted the Tampa to the quartz sandy carbonates with greater than 10 per-
cent quartz sand and less than 1 percent phosphate grains. King (1979) presented a discussion of the
previous investigations of the Tampa to which the reader is referred. The discussion is not repeated here.
Riggs (1979 a, 1979 b; 1980) described the phosphorites of the Hawthorn and their mode of deposition.
Riggs (1979 a) suggested a model for phosphorite sedimentation in the Hawthorn of Florida.
Scott and MacGill (1981) discussed the Hawthorn Formation in the Central Florida Phosphate District
and its southern extension. Scott (1983) provided a lithostratigraphic description of the Hawthorn in
northeast Florida. Both studies were in cooperation with the United States Bureau of Mines.
T.M. Scott (1981) suggested the Hawthorn Formation had covered much of the Ocala Arch and was
subsequently removed by erosion. Scott (1982) designated reference cores for the Hawthorn Formation
and compared these to the reference localities previously designated. Scott's (1982) discussion was
limited to the northeastern part of the state.
Cyclic sedimentation in the sediments of the Hawthorn was proposed by Missimer and Banks (1982).
Their study suggested that reoccurring sediment groups occurred within the formation in Lee County.
Also Missimer and Banks followed the suggestions of Hunter and Wise (1980 a, 1980 b) in restricting the
definition ofthe Tamiami. This is also the case in Wedderburn et al. (1982).
Hall (1983) presented a description of the general geology and stratigraphy of the Hawthorn and adja-
cent sediments in the southern extension of the Central Florida Phosphate District. An excellent discus-
sion of the stratigraphy and vertebrate paleontology of this area was provided by Webb and Crissinger
(1983).
Silicification of the Miocene sediments in Florida has been the focus of a number of studies. Strom, Up-
church and Rosenweig (1981), Upchurch, Strom and Nuckles (1982), and McFadden, Upchurch, and
Strom (1983) discussed the origin and occurrence of the opaline cherts in Florida. Related to the cherts
are palygorskite clays that were also discussed in these papers and by Strom and Upchurch (1983,
1985).
There have been a number of theses completed on various aspects of the Hawthorn Group. These in-
clude McClellan (1962), Reynolds (1962), Isphording (1963), Mitchell (1965), Assefa (1969), Huang
(1977), Liu (1978), King (1979), Reik (1980), Leroy (1981), Peacock (1981), and McFadden (1982).
Many water resource investigations include a section on the Hawthorn Formation but do not add new
geologic or stratigraphic data. These are not included here.










GEOLOGIC STRUCTURE


The geologic structures of peninsular Florida have played an important role in the geologic history of
the Hawthorn Group. These features affected the depositional environments and the post-depositional
occurrence of the Hawthorn sediments. Due to the nature of the Tertiary sediments in peninsular Florida,
it is difficult to ascertain a true structural origin for some of these features. Depositional and erosional
processes may have played a role in their development.
The most prominent of the structures in peninsular Florida is the Ocala Platform (often referred to as
Ocala Arch or Uplift) (Figure 4). The term platform rather than uplift or arch is preferred here since it does
not have a structural connotation.
Originally named the Ocala Uplift by O.B. Hopkins in a 1920 U.S. Geological Survey press release, this
feature was formally described by Vernon in 1951. Vernon described it as a gentle flexure developed in
Tertiary sediments with a northwest-southeast trending crest. He believed that the crest of the platform
has been flattened by faulting. Vernon (1951) dated the formation of the uplift as being Early Miocene
based on the involvement of basal Miocene sediments in the faulting and the wedging out of younger
Miocene sediments against the flanks of the platform. Cooke (1945) thought that warping began prior to
the Late Eocene and continued into the Late Miocene or later. Ketner and McGreevy (1959) suggested
that the platform formed prior to Late Miocene since undeformed beds of Late Miocene overlie warped
beds of the Ocala Platform. Cooke (1945), Espenshade and Spencer (1963) and T.M. Scott (1981) believ-
ed that the Hawthorn once covered most or all of the Ocala Platform. Vernon (1951) believed the Platform
was an island area throughout much of the Miocene and the Hawthorn sediments did not extend across
the structure. Brooks (1966) believed the feature formed prior to the early Late Miocene. He also agrees
with Pirkle (1956 b) that the Hawthorn once extended across the platform.
Riggs (1979 a, b) stated that the Ocala Upland (his term for the Ocala Platform) was a major structural
feature controlling the formation and deposition of the phosphorites in the Florida Miocene.
The Sanford High is another important positive feature in the northern half of peninsular Florida
(Figure 4). Vernon (1951) proposed the name for a feature located in Seminole and Volusia Counties,
Florida. He describes the feature as "a closed fold that has been faulted, the Sanford High being located
on the upthrown side." The Hawthorn Group and the Ocala Group are missing from the crest of the San-
ford High. The Avon Park Formation lies immediately below post-Hawthorn sediments. The missing sec-
tion presumably was removed by erosion. Meisburger and Field (1976), using high-resolution seismic
reflection profiling, identified a structural high offshore from Daytona Beach in Volusia County and sug-
gested that this feature may be an offshore extension of the Sanford High. Meisburger and Field believed
that the seismic evidence indicated uplift that ended prior to Pliocene time. Vernon (1951) believed the
feature to be a pre-Miocene structure. Riggs (1979 a, b) considered the Sanford High the "other positive
element of extreme importance" in relation to phosphorite deposition.
Extending from the Sanford High are the St. Johns Platform to the north and the Brevard Platform to
the south (Figure 4). Both are low, broad ridges or platforms expressed on the erosional surface of the
Ocala Group. The St. Johns Platform plunges gently to the north-northwest towards the Jacksonville
Basin. The Brevard Platform plunges gently to the south-southeast and southeast. The names of both
features were introduced by Riggs (1979 a, b).
The Jacksonville Basin, located in northwest Florida, is the most prominent low in the northern half of
the peninsula. In the deepest part of the basin the Hawthorn Group sediments exceed 500 feet (150
meters) in thickness. The name Jacksonville Basin was first used by Goodell and Yon (1960). Leve (1965)
believed the basin was at least in part fault controlled.
Previously, many authors included the Jacksonville Basin in the Southeast Georgia Embayment. As
more data became available it became apparent that an eastward dipping positive feature, informally
named the Nassau Nose (Scott, 1983), separated the Jacksonville Basin from the rest of the Southeast
Georgia Embayment. The Jacksonville Basin should still be considered as a subbasin of the larger em-
bayment. The Southeast Georgia Embayment was named by Toulmin (1955) and appears to have been
active from Middle Eocene through Miocene time (Herrick and Vorhis, 1963).













I
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ALABAMA


GEORGIA


I: - -


JACKSONVILLE
BASIN


APALACHICOLA
EMBAYMENT

Q


40


0 50 100 150 MILES
iI I
0 80 160 240 KILOMETERS
SCALE
Figure 4. Structures affecting the Hawthorn Group.


GULF
TROUGH


SOUTHEAST
GEORGIA
EMBAYMENT


ST. JOHNS
PLATFORM


SANFORD










The Gulf Trough or Channel extends from the Southeast Georgia Embayment to the Apalachicola Em-
bayment (Figure 4). It is the Miocene expression of the older Suwannee Straits. The Suwannee Straits ef-
fectively separated the siliciclastic facies to the north from the carbonate facies to the south during the
Early Cretaceous. The Gulf Trough was nearly full of sediments by the Late Oligocene and Early Miocene
time, allowing increasing amounts of siliciclastic material to invade the carbonate environments of the
peninsular area. Schmidt (1984) provided an excellent discussion of the history of both the Suwannee
Strait and the Apalachicola Embayment.
In central peninsular Florida between the southern end of the Ocala Platform and the Brevard Platform
are two important features in relation to the Hawthorn Group. The Osceola Low and the Kissimmee
Faulted Flexture (Figure 4) were both named by Vernon (1951). Vernon considered the Kissimmee
Faulted Flexure to be "a fault-bounded, tilted, and rotated block" with "many small folds, faults, and
structural irregularities." His "flexure" is actually a high on the Avon Park surface with the Ocala and
Hawthorn Groups absent over part of it due to erosion.
The Osceola Low, as described by Vernon (1951), is a fault-bounded low with as much as 350 feet (106
meters) of Miocene sediments. This author has investigated the Osceola Low using cores, well cuttings
and geophysical data (Florida Geological Survey, unpublished data). The data does not indicate the
presence of a discrete fault. They do suggest a possible flexure or perhaps a zone of displacement with
"up" on the east, "down" on the west. This zone also appears to be the site of increased frequency of
karst features developed in the Ocala Group limestone. Scott and Hajishafie (1980) indicated that the
Osceola Low trends from north-south to northeast-southwest.
The Okeechobee Basin as named by Riggs (1979 a, 1979 b) encompasses most of southern Florida
(Figure 4). It is an area where the strata generally gently dips to the south and southeast. Pressler (1947)
referred to this area as the South Florida Embayment stating that its synclinal axis plunged towards the
Gulf (to the southwest and/or west). Since this differs significantly from the Okeechobee Basin, the term
Okeechobee Basin is preferred and utilized in this study. Within the basin there have been postulated
episodes of faulting (Sproul et al., 1972) and folding (Missimer and Gardner, 1976).

INTRODUCTION TO LITHOSTRATIGRAPHY

The Hawthorn Group has long been considered a very complex unit. Puri and Vernon (1964) declared
the Hawthorn "the most misunderstood formational unit in the southeastern United States." They further
considered it as "a dumping ground for alluvial, terrestrial, marine, deltaic, and pro-deltaic beds of
diverse lithologic units... ." Pirkle (1956b) found the dominant sediments to be quite variable stating,
"The proportions of these materials vary from bed to bed and, in cases, even within a few feet both
horizontally and vertically in individual strata."

HAWTHORN FORMATION TO GROUP STATUS: JUSTIFICATION,
RECOGNITION AND SUBDIVISION IN FLORIDA

Formational status has been applied to the Hawthorn since Dall and Harris named the "Hawthorne
beds" in 1892. As is evident from the Previous Investigations section, there has been much confusion
concerning this unit. The complex nature of the Hawthorn caused many authors to suggest that the
Hawthorn Formation should be raised to group status although none formally did so (Pirkle, 1956b;
Espenshade and Spencer, 1963; Brooks, 1966, 1967; Riggs, 1967). The Hawthorn was referred to as a
group in Georgia for several years on an informal basis until Huddlestun (in press) formalized the status
change in the southeastern United States, recognizing its component formations in Georgia. The
recognition of formations within the Hawthorn Group in Florida is warranted due to the lithologic com-
plexity of the sediments previously referred to as the Hawthorn Formation. The extension of several
Georgia units into Florida and the creation of new Florida units is based on the expectation that Hud-
dlestun will validly publish the status change from formation to group. If he fails to do so, this text will be
amended to validate the necessary changes in the proper manner according to the North American Code










of Stratigraphic Nomenclature (1983).
An original type locality for the Hawthorn Group was not defined within the limits of our present
stratigraphic code. However, it appears that Dall and Harris' (1892) intention was to use the old Simmons
pits near Hawthorne in Alachua County as the type locality (holostratotype). The other sections referred
to by Dall and Harris (1892) at Devil's Millhopper, Newnansville well, and White Springs were reference
sections. The old Simmons pit is no longer accessible indicating the need for a new type locality
(neostratotype). The Hawthorne #1 core W-11486, located in Alachua County drilled in the vicinity of the
old Simmons pit should fill this gap. As such the Hawthorne #1 core is designated as a neostratotype or
replacement (accessible) type section for the Hawthorn Group.
Although many authors have agreed that the Hawthorn deserves group status, questions remain. What
should be included in the group and what should be the stratigraphic status of the units (i.e., formations
with or without members)? The approach used in this study has been to identify lithostratigraphic units
within the study area, determine their areal extent and thickness and, based on these findings, assign a
formational status where appropriate. Having done that, as detailed subsequently in this report, the
Hawthorn Formation of Florida is herein raised to group status. Its formations are described and type
sections or cores are designated in accordance with the North American Stratigraphic Code (North
American Commission on Stratigraphic Nomenclature (NACSN), 1983). Utilizing the group concept will
enable geologists to better understand the framework of the Miocene sediments in Florida and much of
the southeastern Coastal Plain.
The sediments placed in the Hawthorn Group are related by the occurrence of phosphate, a palygor-
skite-sepiolite-smectite clay mineral suite and the mixed carbonate-siliciclastic nature of the entire se-
quence. Color, particularly in the siliciclastic portions, is often distinctive in the sediments of this group.
In some regions and in specific intervals, lithologic heterogeneity provides a diagnostic trait of the
Hawthorn Group.
The component formations of the Hawthorn Group vary from region to region within the State. The
variation is the result of the depositional and environmental controls exerted on the Hawthorn sediments
by features such as the Ocala Platform, the Sanford High, the St. Johns Platform, and the Brevard Plat-
form. The variation in component formations of a group is discussed in and accepted by the North
American Commission on Stratigraphic Nomenclature (Article 28b, North American Stratigraphic Code,
1983).
The name Hawthorn is retained for the group since the group represents a series of units that had been
recognized as the Hawthorn Formation. Only a few changes (additions) are proposed in this report that
alter the overall boundaries of the former Hawthorn Formation. Due to its wide use and acceptance, drop-
ping the term Hawthorn and providing a new group name would cause unnecessary confusion.
Once the lithostratigraphic units were determined, names were selected for the respective sections.
These are listed in Table 1 along with reference to the original author. When possible, names currently in
use, or proposed in a bordering State (Georgia), were used in Florida. Examples of these are the Marks
Head, Coosawhatchie and Statenville Formations currently recommended for use in Georgia (Hud-
dlestun, in press). Where a sediment package exhibited significant variation in Florida from the
equivalent unit in Georgia, a new name is proposed (i.e., the Penney Farms Formation).
In the eastern panhandle the name Torreya Formation is used since it is already in the literature (Banks
and Hunter, 1973; Huddlestun and Hunter, 1982; Hunter and Huddlestun, 1982; Huddlestun, in press)
and there is insufficient evidence to suggest any changes. Future research, however, may suggest fur-
ther changes.
The names of the formational units of the Hawthorn Group in southern Florida were selected based on
historical perspective and current usage. The name Arcadia Formation is reintroduced for the Hawthorn
carbonate unit. The use of Arcadia is similar to the use suggested by Riggs (1967). Two members are
named in the Arcadia, the Tampa Member and the Nocatee Member. These members do not comprise
the entire Arcadia but only represent the lower Arcadia where they are identifiable.
The Tampa Member represents a reduction in status for the Tampa from formation to member. Since
this reduction represents only a minor alteration of the Tampa definition and since the name Tampa is










widely used and recognized, a new name is not suggested for this member. The most prominent reasons
for reducing the Tampa to member status is the limited area of recognition and its lithologic affinities with
the rest of the Arcadia Formation of the Hawthorn Group.
A new name, the Peace River Formation, is proposed for the upper Hawthorn siliciclastic section, in-
cluding the Bone Valley Formation of former usage. The Bone Valley Formation is reduced to member
status and the name is retained for the same reasons discussed for the Tampa Member. There has been
some discussion and disagreement concerning including the entire Bone Valley in the Hawthorn Group
due to the presence of a major, Late Miocene unconformity. This unconformity separates the upper
gravel bed of the Bone Valley.from the remainder of the unit and often is recognizable only on a
biostratigraphic basis using vertebrate faunas. The unconformity is generally not recognized on a
lithostratigraphic basis. The North American Stratigraphic Code (NACSN, 1983) recognizes this pro-
blem. Article 23d states "...a sequence of similar rocks may include an obscure unconformity so that
separation into two units may be desirable but impractical. If no lithic distinction adequate to define a
widely recognizable boundary can be made, only one unit should be recognized, even though it may in-
clude rock that accumulated in different epochs, periods or eras (NACSN, 1983)."
The formations of the Hawthorn Group are similar yet different in northern and southern Florida and in
the eastern panhandle. Also, within southern Florida, the group varies from east to west. As a result the
discussion of the Hawthorn will be presented separately for northern and southern Florida and the
eastern Florida panhandle (Figure 1).


PRESENT OCCURRENCE

The Hawthorn Group underlies much of peninsular Florida (Figures 5 and 6). It is absent from most of
the Ocala Platform and Sanford High due to erosion. Outliers of Hawthorn sediments and residuum oc-
cur scattered along the platform in lows and in some karst features. The Hawthorn Group sediments are
also absent from part of Vernon's (1951) Kissimmee Faulted Flexure in Osceola County presumably due
to erosion.
The Hawthorn Group dips gently away from the Ocala Platform and Sanford High at generally less than
6 feet per mile (1.1 meters per kilometer) (Figure 5). In north Florida, the Hawthorn dips generally to the
east and northeast towards the Jacksonville Basin and the east coast. Locally the dip may become
greater and may reverse in some areas. This is due to postdepositional movement related to karst activi-
ty, subsidence, possible faulting, and tilting of the platform. Scott (1983) indicated this on structure maps
of the Ocala Group (p. 29) and the Hawthorn Formation (p. 32).
In central and south Florida the Hawthorn Group dips gently to the south and southeast with local
variations (Figure 5). Generally, further south in the state the dip is more southeasterly. The strata dip to
the west and southwest along the western edge of the state from Pasco County south to Lee County.
The Hawthorn Group ranges in thickness from a feather edge along the positive features to greater
than 500 feet (160 meters) in the Jacksonville Basin and greater than 700 feet (210 meters) in the
Okeechobee Basin (Figures 4 and 6). The Hawthorn generally thickens to the northeast in north Florida
toward the Jacksonville Basin and southward into the Okeechobee Basin (Figure 6).


NORTH FLORIDA

INTRODUCTION

The Hawthorn Group in Florida, north of Orange County and west through Hamilton County, has
distinct affinities to the Hawthorn in Georgia. The sediments of the upper two-thirds of the group are very
similar to those in Georgia, facilitating the use of the same terminology in both states. The basal one-third
of the group changes significantly into Florida and, therefore, a new formational name is proposed.











... _- \ o.50

o i

FACIES' --- rf*
CHANGE





-50








i Bi ,l
--N-
1 a 50
-.,









0 10 2 3.0 40M\
10 2o0 3 0 405 M- 3_ ..
SCALE
-- -
APPROXIMATE LIMITS OF THE HAWTHORN GROUP * I /


CONTOUR INTERVAL 50 FT./ ---
CORE AND WELL CUTTING LOCATIONS
DATA BASE CORES FROM FIG. 2
WITH ADDITIONAL CUTTINGS
-550
-100 ----

-150

-150 -- --
-100





Figure 5. Statewide map of the elevation of the upper Hawthorn Group surface.

*- ,; ... ^
10o 3, '

















































0 1 2,0 30 40 MI.
SO 10 4'oo KM.
SCALE


APPROXIMATE LIMITS OF THE HAWTHORN GROUP
11111111111111T11
CONTOUR INTERVAL 50 FT.
CORES AND WELLCUTTINGS LOCATIONS
DATA BASE CORES FROM FIG. 2
WITH ADDITIONAL CUTTINGS


700

750


800


Figure 6. Statewide isopach map of the Hawthorn Group.


**- .- ..










The Hawthorn Group in north Florida can be subdivided into four formations as indicated in Figure 7.
From oldest to youngest, these are the Penney Farms Formation, the Marks Head Formation, the
Coosawhatchie Formation, and the Statenville Formation. The Penney Farms Formation can be divided
into two informal members referred to simply as upper and lower members. The Coosawhatchie Forma-
tion also has upper and lower informal members and the Charlton Member (Huddlestun, in press) (Figure
7).
The formational breakdown of the Hawthorn Group in north Florida is recognizable in cores. However,
due to the highly variable nature of the north Florida Hawthorn sediments, the individual units are very
difficult to identify in well cuttings. Therefore it is recommended that when using well cuttings in this area
these sediments simply be referred to as Hawthorn Group undifferentiated.
The sediments of the Hawthorn Group are significantly different west of the crest of the Ocala Platform
(west of Hamilton County). These units will be discussed separately from those east of the crest in north
Florida.
The Hawthorn Group in north Florida shows significant variation when traced into central Florida. In
the area between the Sanford High and the Ocala Platform, the Hawthorn is thinned both depositionally
and erosionally (Figure 6). Within this zone the upper part of the group changes character, such that it is
difficult to correlate with the formations to the north. The basal unit of the group carries through this area,
and is apparent in east central Florida where it grades into the lower part of the Arcadia Formation of
southern Florida.
Throughout most of the north Florida region the Hawthorn Group unconformably overlies the Upper
Eocene Ocala Group (Figure 8). The Crystal River Formation of the Ocala Group underlies the Hawthorn
in most of the area where the Ocala Group occurs. However, in areas peripheral to the Sanford High and
in portions of the transition zone, the Hawthorn overlies the lower Ocala Group (Williston Formation). The
author has not encountered any instances of the Hawthorn overlying the Avon Park Formation when the
Ocala Group is absent since the Hawthorn Group is also absent in these cases (Sanford High, for in-
stance). The sediments of the subjacent Ocala Group are typically cream to white, foraminiferal
grainstone to wackestone, containing no quartz sand. The limestones are often recrystallized just below
the contact with the Hawthorn Group. This contrast of lithologies with the basal Hawthorn Group is
generally dramatic, resulting in little confusion in identifying the contact.
The Suwannee Limestone of Oligocene age unconformably underlies the Hawthorn Group on the
northeastern-most portion of the Ocala Platform in Hamilton and Columbia Counties. Typically, the
Suwannee is a granular, microfossiliferous, cream, white, to very pale orange grainstone to wackestone.
It is sometimes recrystallized below the contact with the Hawthorn and rarely may be a dolostone. The
lithologic differences between the basal Hawthorn Group sediments and the Suwannee Limestone are
quite distinctive; confusion concerning the contact is unlikely.
The St. Marks Formation of Early Miocene age underlies the Hawthorn in an extremely limited area in
the western half of Hamilton County. The St. Marks occurs sporadically and generally is less than 30 feet
(9 meters) thick (Colton, 1978). Lithologically, the St. Marks is a quartz sandy, silty, sometimes clayey
limestone (wackestone to mudstone). Occasionally, it may be dolomitized. The lithology of this unit is
similar to the basal Hawthorn sediments except for the lack of phosphate grains in the St. Marks. The St.
Marks lithology may occur within the basal Hawthorn carbonates, creating possible confusion concern-
ing the contact. Although the contact is unconformable, it is often not apparent. As a result, the top of the
St. Marks is placed below the last occurence of phosphatic sediments. This datum is traceable from
western Hamilton County westward into the eastern panhandle in Madison, Jefferson, and Leon Coun-
ties.

PENNEY FARMS FORMATION

Definition and Type Locality

The Penney Farms Formation is a new lithostratigraphic name proposed here for the predominantly
subsurface basal unit of the Hawthorn Group in north and central Florida. It is named after the town of











POST-HAWTHORN
UNDIFFERENTIATED


STATENVILLE
FORMATION
CHARLTON
MEMBER

COOSAWHATCHIE c.
FORMATION 3

z
MARKS HEAD C
0
FORMATION

4

PENNEY FARMS
FORMATION

SUWANNEE
LIMESTONE ASEN

2 SWANEEV1 N


OCALA GROUP


Figure 7. Lithostratigrapnmc units of the Hawthorn Group in north Florida.









































SCALE
0 20 40 MILES

0 20 40 60 KILOMETERS


EXPLANATION
1 MIOCENE ST. MARKS FM.
AND CHATTAHOOCHEE FM.
M OLIGOCENE SUWANNEE LS.
AND "SUWANNEE' LS.
EOCENE OCALA GROUP


* CORE LOCATIONS


sN


LIMITS OF HAWTHORN GROUP


Figure 8. Geologic map of the pre-Hawthorn Group surface.










Penney Farms in central Clay County, Florida. The type core, W-13769 Harris #1, is located near Penney
Farms (SW/4, SE/4, Section 7, Township 6S, Range 25E) with a surface elevation of 97 feet (30 meters).
The type core was drilled by the Florida Geological Survey in December 1977 and is permanently stored
in the Survey's core library. The type Penney Farms Formation occurs between -118 feet MSL (-36
meters) and -205 feet MSL (-63 meters) (Figure 9).

Lithology

The Penney Farms Formation consists of two informal, unnamed members which are distinguished
from each other based on the abundance of carbonate beds. Figure 9 graphically shows the variable
nature of this formation and its general two member framework. Each member consists of lithologies
similar to the other but the proportions of the lithologies are dissimilar. In the lower member, carbonates
predominate with sands and clays interbedded in varying proportions. The upper member is a
predominantly siliciclastic unit with interbedded carbonate beds. The interbedded sands and clays of the
lower member generally increase in abundance upward in the section causing the contact with the upper
member to be gradational in nature. The top of the lower member is placed where carbonate beds
become dominant over the siliciclastic beds. The North American Code of Stratigraphic Nomenclature
(NACSN, 1983) (Article 23) allows for this arbitrary placement of a boundary in a gradational sequence.
Occasionally, the siliciclastic beds are abundant enough in the lower member to obscure the contact
altogether thus the separation of the informal members within the Penney Farms Formation is not always
possible.
The carbonates are variably quartz sandy, phosphatic, clayey dolostones. Sand content is variable to
the point that the sediment may become a dolomitic sand. Phosphate grains may be present in amounts
greater than 25 percent with an average of approximately 5 to 10 percent. Clay percentages are general-
ly minor (below 5 percent) but often increase in the dolostones of the upper member. The dolostones are
medium gray (N5) to pale yellowish brown (10 YR 6/2). They are generally moderately to well indurated
and finely to coarsely crystalline in the lower member. The dolostones of the upper member are generally
less indurated. Thicker, more massive beds predominate in the lower unit while thinner beds are most
common in the upper section. Mollusk molds are common in the dolostones, particularly in the more
coarsely crystalline type.
Zones of intraclasts are common in the hard, finer grained dolostones of the lower part of the Penney
Farms. The intraclasts are composed of dolomite that is essentially the same as the enclosing matrix.
The intraclasts are recognizable due to a rim of phosphate replacement along the edges of the clasts
(Figure 10). Edges of the clasts vary from angular to subrounded indicating very little to no transport of
the fragments. They also may be bored, indicating at least a semi-lithified state prior to being
redeposited.
Limestone, in the basal portion of the Penney Farms Formation, occurs sporadically. When it does oc-
cur, it is generally dolomitic, quartz sandy and phosphatic.
The quartz sands are fine to coarse grained, moderately to poorly sorted, variably phosphatic,
dolomitic, silty and clayey. The phosphate grain content varies considerably, sometimes to the point of
being classified as phosphorite sand (50 percent or greater phosphate grains). In general, however, the
phosphate grain content averages between 5 and 10 percent. The sands are typically olive gray (5 Y 3/2)
or grayish olive (10 Y 4/2) to medium light gray (N 6). Clay content varies considerably in the sands.
Clay beds in the Penney Farms Formation are typically quartz sandy, phosphatic, silty and dolomitic.
The proportions of the accessory minerals vary from nearly zero to more than 50 percent. Nearly pure
clay beds are uncommon. Dolomite is very common in the clays, often being the most abundant ac-
cessory mineral. Olive gray (5 Y 3/2) and grayish olive green (5 GY 3/2) colors generally predominate, but
colors may range into the lighter shades. Smectite typically dominates the clay mineralogy of this unit
with palygorskite, illite and sepiolite also present. X-ray analyses by Hettrick and Friddell (1984) indicate
that palygorskite may become predominant over smectite in some samples. Reik (1982) indicated that
palygorskite dominates in the lower part of the Penney Farms while smectite dominates in the upper por-




















LAND SURFACE


CLAY


UNDIFFERENTIATED


-110 -



-120 -



-130 _


PHOSPHATE SAHO HAWTHORN GROUP
PHOSPHRTE SAND
PHOILT PHTE SPHTE DOLITE
SILT PHOSPHATE DOLOMITE
SILT PHOSPHATE DOLOMITE
PSILT PHA TE OLOE
PHOSPHATE
PHOSPHATE CL
PHOSPHRTE CLRY
PHOSPHRTE CLAY
PHOSPHATE CLRY
PHOSPHRTE CLRY Z
PHOSPHATE DCLAY 0
PHOSPHATE DOLDAITE
PHOSPHRTE 00LONITE
PHOSPHATE SRND LOTE
PHOSPHATE SANO
PHOSPHATE CLHY
PHOSPHATE CLRY 0
PHOSPHATE CLRY O
PHOSPHATE CLRY
PHOSPHATE EOLOMITE
PHOSPHATE DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHRTE DOLOMITE C
PHOSPHATE DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOHITE
PHOSPHATE 00
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE SAND DOLOMITE
PHOSPHATE SRND 0
PHOSPHATE SAND O
PHOSPHTE
PHOSPHATE 0
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
CLAY


-150 _














-190 -



-200 _



-210



-220


- -- - PHfI PHATE


5NO -- ----------------_ I -__ )\

SRNO
SAND W-137
SAND
PHOSPHATE SAND
DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHRTE DOLOHITE
PHOSPHATES
PHOSPHRTE
PHOSPHRTE
PHOSPHRTE CLRY
PHOSPHRTE CLRYMARKS HEAD FORMATION
PHOSPHATE CLRY
PHOSPHATE CLAY
CLAY
OSLOMITE CLRY
SANO OOLOMITE
SANO
VInn


80 -



70 _



60



50 -



40 -


7------7
.. . .. ..
Z'.Z Z. Z
...... ...













4' 4* 4*





4 z z--



z z ZI-


OCALA GROUP



CRYSTAL RIVER FORMATION


... ... ... ...


Figure 9. Type section of the Penney Farms Formation, Harris #1, W-13769, Clay County (Lithologic

legend Appendix A).


PHOSPHRTE
PHOSPHATE
PHOSPHATE
CLRY
PHOSPHATE DOLOMITE
PHOSPHRTE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOHITE
PHOSPHATE CLAY
PHOSPHATE CLAY
SRND
SRNO
SRND
PHOSPHATE SARN
PHOSPHATE
PHOSPHRTE
SAND
5SNO
PHOSPHRTE
PHOSPHATE
PHOSPHRTE
PHOSPHATE SHND DOLOMITE
PHOSPHATE CLAY
PHOSPHRTE CLAY
PHOSPHATE CLAY
PHOSPHRTE CLRY
PHOSPHATE SAND
PHOSPHATE SRND
PHOSPHRTE SRND
PHOSPHATE SRND
PHOSPHRTE SRND
PHOSPHATE SRND
PHOSPHRTE SRND
PHOSPHATE SRND
PHOSPHATE SRNA
PHOSPHATE SRND
PHOSPHRTE SAND
PHOSPHATE SRNO
PHOSPHATE SANO
PHOSPHATE SAND
PHOSPHATE SARNO H,
PHOSPHATE SARN
~U1~LBE 0L~I H


69


h --


AWTHORN GROUP


PHOSPHRTE
















































'4L
p q .

-l A.

p
' a tA a


>~T'QK

*1_-


*0,

42.t


- 4bCt
4
I,'
a, V


!' 0 v, ':
S." *

,4r.- '


Figure 10. Intraclasts with phosphatic rims from Penney Farms Formation, St. Johns County,
W-13844.


I

'a










tion in Clay County. Other minor mineralogic constituents include mica, K-feldspar and opal ct. Clinop-
tilolite has been identified in a few samples (Huddlestun, in press).
When abundant silt-sized, unconsolidated dolomite occurs, difficulty arises in determining whether the
actual rock type is a very dolomitic clay or a very clayey dolostone. Insoluble residue analysis is the only
accurate method of determining the clay and dolostone contents. Rough analysis indicates that, in
general, the lighter the color of the sediment, the higher the dolomite content. This method was
employed for determining the sediment type in these situations.
The siliciclastic beds of the Penney Farms Formation are lithologically very similar to those in the
Parachucla Formation in southeastern Georgia (Huddlestun, in press). As the Penney Farms Formation
begins to lose its carbonate units northward and northwestward into Georgia, the characteristic
lithologies are no longer apparent and the formation can no longer be identified as the Penney Farms.
These sediments in Georgia are included in the Parachucla Formation (Huddlestun, in press).
Southward into central Florida, the Penney Farms contains more carbonate than in the type area. Be-
tween the Sanford High and the Ocala Platform in portions of Lake and western Orange Counties, the
percentage of siliciclastic beds decreases to the point that the separation of upper and lower members
becomes unfeasible. The carbonates in this area contain coarser sand and a noticeably coarser
phosphate grain fraction.
Further to the east, in Orange County, and southward into eastern Osceola and Brevard Counties, the
basal Hawthorn Group consists predominantly of dolostone. This basal unit is tentatively placed in the
Arcadia Formation until further investigations can be conducted.

Subjacent and Suprajacent Units

The Penney Farms Formation unconformably overlies limestones of the Eocene Ocala Group or the
Oligocene Suwannee Limestone. Figure 8 indicates the areas in which each occurs.The unconformity is
very apparent due to the drastically different lithologies. Previous discussion of the base of the Hawthorn
Group in north Florida describes the lithologic differences in greater detail.
The Marks Head Formation unconformably overlies the Penney Farms Formation throughout north
Florida except in those areas where it has been removed by erosion. In areas where the Marks Head has
been eroded, the Penney Farms is overlain by sands and clays classified as undifferentiated post-
Hawthorn deposits.
The top of the Penney Farms is placed at the break between the lighter colored sediments of the Marks
Head and the darker colored sands and clays of the upper part of the Penney Farms. Occasionally, a rub-
ble zone marks the break between the Marks Head and the Penney Farms Formations. When it occurs,
the rubble consists of clasts of phosphatized carbonate.
The relationship of the Penney Farms Formation and to the underlying and overlying sediments is il-
lustrated in Figures 11 through 16.

Thickness and Areal Extent

The Penney Farms Formation of the Hawthorn Group occurs primarily as a subsurface unit. The top of
the Penney Farms Formation ranges in cores from -333 feet MSL (-101 meters) in Carter #1, W-14619,
Duval County to +80 feet MSL (24.3 meters) in Devils Millhopper #1, W-14641, Alachua County (Figure
17). Limited data from one outcrop in Marion County (Martin-Anthony roadcut, NE/4, NEi/4, NE/4, Sec.
12, Township 14S, Range 21E) indicates the sediments assigned to the Penney Farms occur at +140 to
+ 150 feet MSL (43 to 46 meters). This is the only recognized occurrence of the basal Hawthorn Group at
elevations this high.
The Penney Farms Formation dips in a general northeasterly direction from the flanks of the Ocala
Platform toward the Jacksonville Basin with an average dip of 4 feet per mile (0.8 meters per kilometer).
The direction of dip of the Penney Farms trends toward the north into the Jacksonville Basin from the St.
Johns Platform (Figure 17). Locally, both the direction and angle of dip may vary.




















S o o '- A '
Su W-12360 A'
WBf-4S-22E-25bd
W-15121 W-13812 60 ,200
WHm- N-12E-3ba W-15162 WBk-2S-19E-30c
WCo-2S-17E-23dc
W-6836 .175
WHm-1N-15E-36C 5
150 UNDIFF. SUWANNEE RIVER
.130

40 ALAPAHA RIVER UNDIFF
12s -125


io, 3 UNDIFFERENTIATED 30 -iM

0ArC"-E VI. _7'

.-2 HEAD FM. 70
5 O-1 1 CHARLTON 2
00"I1_KLOMET MEMBERS


2- ,PENNEY FARMS FM. 25


MSL MSL

ST. MARKS FM. SUWA NEE

SUWANNEE LS. -10

OCALA GROUP









EXPLANATION -40 o
IaiS HAWTHORN GROUP BOUNDARIES


SCALE -so
5 10O MILES

0 5 10 15 KILOMETERS
0,0, -200





-250
















Figure 11. Cross section A-A' (see figure 3 for location) (See Scott (1983) for discussion of faults).















































Figure 12. Cross section B-B' (see figure 3 for location) (See Scott (1983) for discussion of faults).



















1 \_ X .... o I
00 r 0 0 0 1
,


C 0














', ..w / / /
10
oYN( 0Y)








.o "o




ivNha
















n V B V N I I
10 0 C S
00 0?0
4 0


























1 50w
W-13769
1/ V WCy-S-25E-7cd


n0 oCHA O ST. JOHNS RIVER 40 25



IM 10 W-14476
WCy-6S-2gE-17ab
S"W-137"4
2\ / WS -S-128E-3 8 -7




10




MSL* 7" MSL

SST 1 UNDIFFERENTIATED


-10


-20 \ -2 +
-507











SOCALA GROUP 00


0-50,


- EXPLANATION -
,ll HAWTHORN GROUP BOUNDARIES



5 5 10 MILES

0 5 10 15 KILOMETERS
-00 -0O






-325. 325




-110 I 10










Figure 14. Cross section D-D' (see figure 3 for location) (See Scott (1983) for discussion of faults).
Figure 14. Cross section D-D' (see figure 3 for location) (See Scott (1983) for discussion of faults).

















E < W- 400
W 1441 WPu -2E-18ca
WA.-9S-19E-15ad 601 0
0W-14594 "0 1* 200
WPu-9S-23E-18bb W1434
75 W-148 WPu-9S-24E-9ab
WAa-10S-22E-31cb
-550



.2. 40

ST. JOHNS RIVER



W-14413
75 w-14477 WSJ-8S-28E-20bb 7
20 -4. WPu-8S-27E-26cc
W-13844
50. a WSJi-10OS-30E-37

.. -.o-"0



MSL I"
SSL

-25 2





1 \"
UNDIFFERENTIATED -0








4.0 EXPLANATION -4 5
iVWIA HAWTHORN GROUP BOUNDARIES 4


--o SCALE \/
,a 1; 0 "MILES o
-17. 1 I --- 4
5 5 10 15 KILOMETERS


.0 -OCALA GROUP

S-70

-"F 0 -2SO







Figure 15. Cross section E-E' (see figure 3 for location) (See Scott (1983) for discussion of faults).














PUTNAM CO MARION CO
F


MARION CO LAKE CO
MARION CO LAKE CO


W-15127
WMr-17S-26E-36cd


LAKE CO I POLK CO
SF'

W-13055
WPo-27S-25E-21da

W-5055 (cuttings)
WLk-24S-25E-20bd


W-14751
W-14318 WMr-16S-26E-13ab


FORMATION


OCALA GP.


EXPLANATION
Wr A HAWTHORN GROUP BOUNDARIES

SCALE
0 5 10 MILES
0 5 10 15 KILOMETERS


FEET


OCALA GP.


Figure 16. Cross section F-F' (see figure 3 for location) (See Scott (1983) for discussion of faults).




The Penney Farms Formation varies in thickness from being absent on the crests of the Ocala Platform
and Sanford High to more than 155 feet (47 meters) in Carter #1, W-14619, Duval County in the Jackson-
ville Basin (Figure 18). The total thickness of this unit was not determined in this core as the core ter-
minated in the Penney Farms Formation after penetrating 155 feet (47 meters). This author estimates
that the base of the Penney Farms should occur near -575 feet (-175 meters) MSL based on nearby water
wells. This suggests that approximately 230 feet (70 meters) of the unit should be present in the deepest
portion of the Jacksonville Basin. The informal upper member attains its maximum observed thickness of
88 feet (27 meters) in Cassidy #1, W-13815, Nassau County. Seventy-five feet (23 meters) of the lower in-
formal member were penetrated in W-14619. This author estimates that approximately 150 feet (46
meters) of this member should be present based on previously discussed criteria.
The Penney Farms Formation of the Hawthorn Group occurs throughout much of north and central
Florida. It is absent from the crest of the Ocala Platform and the Sanford High due to erosion and
nondeposition. The Penney Farms Formation thins on the St. Johns Platform and is absent from the
highest part of the structure, the area where the Sanford High and the St. Johns Platform merge (Figure
4).


Age and Correlation


The Hawthorn Group sediments of northern Florida have yielded very few dateable fossils or fossil
assemblages. Diagenetic overprinting on the sediments has obliterated the vast majority of fossils leav-
ing mainly molds and casts. Diatom and mollusk molds are the most frequently encountered fossil re-
mains.


METERS FEET
-150
40-
30 -100
20
50
10
0 -MSL
-10
--50
-20
-30 -100
-40
--150
-50



























































-N-



SCALE c 25 FEET
0 20 40 Mil

0 20 40 KILOMETERS
LEGEND
CORES


LIMITS OF HAWTHORN GRC


i HAWTHORN GP.
UNDIFFERENTIATED









}0


M AD IS5 C










RR


v 0L SI




.ES

C I T J









I 1.~1II- -o-~ --- -------~
"SN MT E


,UP H HE R MA NDO I.

r-~ R A I IE I~~



P IA S Itc







7<--L Act O JH
7T F~r t I i P


Figure 17. Top of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group.


k. T -225
LO 10


Sr\ b c vv- \D V -2-75
H^AN ^Ar^^^VN \u \ ^S-250




-175






G_ CHRST

I -L f CTN j All






F L A GL ER

L E I v y




B-h A-


25



-100
-75
-50
-25


I

















S-- SN ASS


MA DISON H T

B- D




SCOL BIA
SU AN IF I
-- -- '^ ^ A^FJL --- ^_- --.Il*
__ f ^51^^


. I A


I


FAYETTE


UN~i7jejI/ Ic1~


/r
ii I U I N 1 0 L Y



?GI I S -25


-N- jA'



SCALE cl = 25 FEET
0 20 40

S 20 40 KILOMETER:
LEGEND
CORES

L LIMITS OF HAWTH(
GROUP

HAWTHORN GP.
UNDIFFERENTIATED


MILES

S


v y













C ITRU R1


S U MT R
)RN

HE RI A N DO

D



P A S ,C







Hl S-.'O OUC H


Or
U)


P NA

25


T~~ gl JV\ F L A G L E R




N .
" \\ RI r-^:


v 0 L U S I A









EMIN N LE


0


0P 1 CL
P o S _


4 F-I--4-+--I


Figure 18. Isopach of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn
Group.


10


L E


T


I


~I I *~


' '


I


i


' "'


'


- I -


q


~J,


r u I 1


\_


AU





50
V ]S3 125

100

75




T. JOH NS 50


*^
~9


1


--L-L










At the present time, dateable fossils from the Penney Farms Formation have been obtained from only
two sites. The first is from the Cassidy #1 core, W-13815, Nassau County in the interval from -450 to -455
feet LSD (-137 to -138.7 meters LSD). The sediment, a calcareous, quartz sandy clay, contained benthic
and planktonic foraminifera, ostracods, spicules (sponge?), echinoid fragments and bryozoans. The
planktonic foraminifera indicate an Aquitanian age upper Zone N.4 or lower N.5 of Blow (1969) for this in-
terval (Huddlestun, personal communications, 1983).
The second site encompasses the Martin-Anthony roadcut in north central Marion County (NE/4,
NE1/4, NE1/4, of Section 12, Township 14S, Range 21E). An oreodont jaw collected from the hard car-
bonates exposed in the roadcut was dated as Late Arikareen (equates to Early to Middle Aquitanian)
(MacFadden, 1982).
The few ages obtained in north Florida correlate well with dates obtained by Huddlestun (personal
communication, 1983) in the Hawthorn Group of Georgia. The age suggested for the Penney Farms For-
mation correlates with the age of the upper part of the Parachucla Formation in Georgia (Figure 19).
Lithologically, the Penney Farms Formation grades laterally into the Parachucla Formation through a
transition zone north of the Jacksonville Basin. These ages indicate that the basal portion of the Penney
Farms Formation is slightly older (1-2 million years) than the base of the Pungo River Formation in the
Miocene of North Carolina as indicated by Gibson (1982) and Riggs (1984).
The type Penney Farms appears to be equivalent to at least part of the Tampa Member of the Arcadia
Formation (as described in this report). Based on Huddlestun's (in press) suggestion that the Parachucla
Formation correlates with the Chattahoochee Formation of western Florida and southwest Georgia, the
Penney Farms Formation is also equivalent to part of the Chattahoochee Formation (Figure 19). The Pen-
ney Farms appears to equate with Miller's (1978) unit E from the Osceola National Forest.


EASTERN EASTERN SE AND E EASTERN NORTHERN SOUTHERN
SERIES NORTH SOUTH
SERIES CAROLINA CAROLINA GEORGIA PANHANDLE FLORIDA FLORIDA SERIES

RAYSOR CYPRESSHEAD FM. MICCOSUKEE FM. CYPRESSHEAD FM. TAMIAMI FM. PLOCENE
PLIOCENE YORK TOWN FM / YORK TOWN FMS. /DUPLIN FM. /CITRONELLE FM. / NASHUA FM.
REWORKED
UPPER SEDIMENT O WABASSO UPPER
m beds
PEACE
w COOSAW- COOSAW- RIVER I
HATCHEE HATCHEE La. MBR. > FM. 3 u
w FM. FM. 3 STATE NV LLE 0 Z
O PUNGO FM S I i
PUNGO COOSAW-
z os HATCHEE Z


EC NENOCATEE MBR.
PARACHUCLA PARA- CHATTA- PENNEY I TAMPA MBR.


RIM FM.W
0 09 CHUCLA HOOCHEE AND FARMS 0CA 0
J '*FM. ST. MARKS fms. FM. F

*LRGICENEVEN FM. SUWANNEE SUWANNEE SUWANNEE
OLIGOCENE BEND FM. LS. LS OUGOCENE



E OCENE SANTEE AVONM
SCOOPERFM. OCALAGP. OCALANGP. OCALAGP. OCALAGP. UPPE0

CASTLE HAYNE SANTEE LS. AVON PARK FM. AVON PARK FM. M. AVON PARK FM. MIDDLE



Figure 19. Formational correlations (modified from unpublished C.O.S.U.N.A. Chart, 1985).










The Penney Farms Formation of the Hawthorn Group is older than the commonly accepted age for the
Hawthorn Formation as described by Puri and Vernon (1964). This age, Middle Miocene, was accepted
for the Hawthorn Formation by the Florida Geologic Survey for sometime. The data presented here in-
dicate this should be revised (see Figure 19). Armstrong et al. (1985) have even suggested a latest
Oligocene age for the base of the Hawthorn in southeastern Florida.

Discussion

As stated previously, the Penney Farms Formation in northern Florida is equivalent to the Parachucla
Formation in southeastern Georgia. The Penney Farms represents a southern extension of the
Parachucla siliciclastics, but contains a significant amount of dolostone which is not present in the
Parachucla. The two units are laterally gradational with each other. Within the gradational sequence the
lateral boundary between the units is arbitrarily placed where carbonate becomes an important lithologic
factor. This boundary usually occurs just north of the state line in Georgia; however, the Parachucla oc-
curs in northernmost Nassau County, Florida. The Penney Farms Formation also grades laterally, to the
south, into undifferentiated Hawthorn Group.
The carbonate section of the Penney Farms Formation has often been referred to as the basal
Hawthorn dolostone in northern Florida. It is lithologically distinctive enough to be recognizable in well
cuttings, even in relatively poor quality cuttings. The gamma-ray signature also is quite distinctive, con-
sisting of a number of very high counts per second (cps) peaks (see section on gamma-ray logs).
The full areal extent of the Penney Farms deposition on the Ocala Platform is not presently known. The
occurrence of sediments assigned to this unit at the Martin-Anthony road cut in Marion County (elevation
140 to 150 feet [43-46 meters] above MSL) suggest deposition on a significant portion of the platform.



MARKS HEAD FORMATION

Definition and Reference Section

Huddlestun (in press) reintroduced the Marks Head Formation as part of the Hawthorn Group in
Georgia. The Marks Head Formation is extended here to encompass the middle unit of the Hawthorn
Group in north Florida. The lithologic similarities between the Marks Head Formation in southeast
Georgia and in north Florida warrants the use of the same nomenclature.
Huddlestun (in press) describes the type locality of the Marks Head Formation in Georgia from out-
crops at and near Porters Landing in northern Effingham County, Georgia. The reader is referred to Hud-
dlestun (in press) for descriptions of these localities and for a historical summary of the Marks Head For-
mation in Georgia.
The proposed reference section for the Marks Head Formation in Florida lies between -89 feet (-29
meters) MSL and -190 feet (-58 meters) MSL in the Jennings #1 core, W-14219, Clay County, Florida
(SE/4, SE/4, Section 27, Township 4S, Range 24E) (Figure 20). The land surface elevation is 90 feet (27
meters) MSL.

Lithology

The Marks Head Formation in Florida consists of interbedded sands, clays and dolostones throughout
its extent. Carbonate beds are more common in the Marks Head Formation in Florida than in Georgia;
the proportion of carbonate, both as a rock type and an accessory (matrix) mineral, gradually increases
into Florida. This unit is the most lithologically variable formation of the Hawthorn Group in north Florida.
Miller (1978) defined his Unit D (equivalent to the Marks Head Formation) as being "complexly interbedd-
ed shell limestone, clay, clayey sand and fine grained sandstone." The variable nature of the Marks















W- 1t219


LAND SURFACE







w

cI-

I-


z


PHOSPHATE CLRY
PHDSPHRTE CLRY
PHOSPHATE CLAY HAWTHORN
PHOSPHATE CLAY
PHOSPHATE CLRY
PHOSPHATE CLRY
PHOSPHATE CLRY
PHOSPHATE CALCITE GROUP
PHOSPHATE CRLCITE
CLAY
CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE DOLOMITE
PHOSPHRTE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE SRNO DOLOMITE

CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE Z
PHOSPHATE 0
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE 0
PHOSPHATE LL
PHOSPHATE CLRY
PHOSPHATE CLAY S U
PHOSPHATE CLRY
PHOSPHATE CLRY A
PHOSPHATE CLAY




DOLOMITE
OOLOMITr .
DOLOMITE 0
DOLOMITE
DOLOMITE
PHOSPHATE DOLOMITE 0
PHOSPHRTE DOLOMITE
PHOSPHATE DOOLMITE
PHOSPHATE
PHOSPHRTE
PHOSPHATE


I


-180 -
-L9B


-19C


-200


-210


-230


-240


-250


-260


-270


-280


-290


-300


-310


-320 I


-330 _


-34t0


-350


-360


-370 -


-:7


-..-. 7 .. .,



.- z











r..:-.-, -- -









.. -. -,









-/ -/ -/ -/
:: -: :

7-
-_. -- .




-I.- -


Z -380 W
OOLOMITE 0 >
OOLOMITE
DOLOMITE C 1
DOLOMITE
DOLO MITE -390 -
C II--
PHOSPHRTE SRND DOLOMITE 0
SONO OLOMITE LL I I
SANO DOLOMITE -400
PHOSPHATE
PHOSPHATE wL
PHOSPHATE
PHOSPHATE I

= Figure 20. Reference section for the Marks Head Formation.
P Jennings #1, W-14219, Clay County
PHOSPHATE DOLOMITE C
PHOSPHATE OOLOMITE (Lithologic legend Appendix A).
PHOSPHATE OSLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOHMITE



35


PHOSPHATE RNO DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLONITE
PHOSPHATE DOLOMITE
PHOSPHRTE OOLOMITE
PHOSPHRTE OOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE DOLOMITE


-90


-100 --


-120


-130


-150


-160 _


-170 _


I L


-
-


OCALA GROUP


_


F


- PHOSPHATE DOULUMJI
PHOSPHATE DOLOMITE
-.-." -. PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
S-2- ~ PHOSPHATE SRNO CLRY
SRND DOLODMTE


l-1 l PHOSPHATE CLAY

2
0



DOLOMITE
DOLOHITE 0
-.- ---,. DOLOMITE 1L
DOLOMITE
DOLOMITE W
SHAND
= SANO
SRAND OLOMITE
L.
PHOSPHRTE SAND
PHOSPHATE SRND W
PHOSPHATE SAND
PHOSPHATE SRAND

DHOSPHRLOMITE N

--- *- DOLOMITE
S DOLOMITE
S DOLOMITE
DOLOMITE


DOLO ITE CLY
DOLOMITE
-..-- .'O-T. EDOLOMITE

SRNO DOLOMITE CLAY
OOLDHITE



DOLO LMTE


- DOLOMITE




C LAY- /7- 5
SRN DOLOM ITE CLAY
SOOLOMITE




OLOITE CLAY HAWTHORN GROUP
PHOSPHATE SRHD
PHOSPHATE SRD OL ITE
RNPHDSPMTE SRMO OOLOMITE
SRND OOLOMITE CLRY
SRND
SRND
SRND DOLOMITE
OOLOMITE
CLAY
CLRY
DOLOMITE CLAY HAWTHORN GROUP

PHOSPHRTE
Fculr

















W-12360


LAND SURFACE


CLAY
HERVY MINS.
HERVY MINS.CLRY


:_


















































.-'.-'.i'.
.i'.i'.i'.
.-'.i'.i'.
.-'.i'.-'.
.i'.i'.i'.
.i'.i'.i
.i'.i'.i'.
.-'.-'.i'.






























=7


HEAVY HINS.CLAY
HEAVY HINS.
HEAVY MINS.


RSANO


UNDIFFERENTIATED


EYPSUM
GYPSUM
CLAY


CALCITE
CALCITE
CALCITE
CALCITE
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
CALCITE
CALCITE
CALCITE CLRY


-L50 -



-160



-170 -



-180



-190 -



-200-



-210 -


CALCITE
CRLCITE HAWTHORN GROUP
CALCITE
CALCITE
CALCITE
CALCITE

CALCITE CHARLTON MEMBER
CALCITE
CALCITE
CALCITE
CALCITE
CALCITE
CALCITE
CALCITE


PHUSPHATE SANU
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SANO
PHOSPHATE SAND OOLOMI
PHOSPHATE DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOMITE
0OLOMITE CLAY
nninmITE rI nr


-230 _



-2'0 -



-250-



-260



-270



-280__



-290


./. /.. /. /









S--/ -/ -































-








-7-
-/ -/ -/ -/

























S--'--.









7 7
.-_,. -. -,., ,,.
































7
-.- _. -.... .




























:
-. -I: -I- -

































-7 -
/ / / -/




'-'-'-'





















P/ P/ P/ 7
/ / / /P






.'. '-7. ",- .'-



.-7' '.- ''
."'.-.7..".'7





















1-.7'.'-..'
- r-' '-'.r

I- '- '- /-
i / i i /


PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLRY
PHOSPHATE OILOMITE
PHOSPHATE OiLOAITE COOSAWHATCHIE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE FORMATION
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE OOLOAITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOHITE
PHOSPHATE OOLOMITE
PHOSPHRTE OOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLONITE
PHOSPHATE DOLOMITE
PHOSPHATE CRLCITE DOLOMITE
PHOSPHATE CALCITE
PHOSPHATE CALCITE
..M.N....... FgiT


PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE CALCITE
PHOSPHATE CALCITE CLAY
PHOSPHATE CALCITE
PHOSPHATE CRLCITE CLAY
CALCITE
CALCITE
CALCITE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE
SANO CALCITE
SRANO CALCITE
SAND CALCITE
SANO CALCITE
PHOSPHATE SANO
PHOSPHATE SANO
PHOSPHATE SRNO
PHOSPHATE SARN
PHOSPHATE SANO CLAY
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE
PHOSPHATE
PHOSPHATE SRANO
PHOSPHATE SAND
PHOSPHATE SANO
SAHRN CALCITE
SAND CALCITE

5ANO

DOLOMITE
PHOSPHATE SANO
PHOSPHATE SANO
PHOSPHATE SAND
PHOSPHATE SAND CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE SAND
PHOSPHATE SARN


MARKS HEAD

FORMATION


PHUbPHRTE SANO
PHOSPHATE SAND
PSPOHATE SAND
PHOSPHATE SAND CLAY
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHATE OOLOMITE PENNEY FARMS
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE
;"j8g" O0LDHITE FORMATION
PHOSPHATE
PHOSPHATE SARN
PHOSPHATE SANO
PHOSPHATE CALCITE
PHOSPHATE CALCITE
PHOSPHATE CALCITE
PHOSPHATE CALCITE
PHOSPHATE CALCITE
PHOSPHATE CALCITE
PHOSPHATE SAND
PHOSPHATE SRNO
PHOSPHATE SASS HAWTHORN GROUP
PHOSPHATE SANS


OCALA GROUP
OCALA GROUP


Figure 21. Reference section for the Marks Head Formation, N.L. #1, W-12360, Bradford County

(Lithologic legend Appendix A).


110 __



100



90 -


-'40


-100 _



-110 -



-120 -


f t


... ... ... ...

0 0 5










Head is readily apparent when comparing the lithologic columns of W-14219 (Figure 20) and W-12360
(Figure 21).
The carbonate portion of the Marks Head Formation is typically dolostone; limestone is uncommon but
does occur sporadically as is the case throughout the Hawthorn Group. The Marks Head dolostones are
generally quartz sandy, phosphatic and clayey. The dolostones vary in induration from poorly con-
solidated to well indurated. The induration varies in inverse relationship to the amount of clay present
within the sediment. Phosphate grains normally comprise up to 5 percent; however occasional beds may
contain significantly higher percentages. Quartz sand content varies from less than 5 percent to greater
than 50 percent where it grades into a dolomite cemented quartz sand. The dolostones range from
yellowish gray (5 Y 7/2) to olive gray (5 Y 4/1) in color. Crystallinity varies from micro- to very finely
crystalline with occasional more coarsely crystalline zones. Molds of mollusk shells are often present.
The occurrence of limestone within the Marks Head Formation in Florida is quite rare. The majority of
the "limestone" reported from this part of the section by other workers is actually dolostone. The
limestone that does occur is characteristically dolomitic, quartz sandy, phosphatic, clayey, and fine
grained.
The quartz sands from the Marks Head Formation are generally fine to medium grained (occasionally
coarse grained), dolomitic, silty, clayey and phosphatic. The dolomite, silt and clay contents are highly
variable and the quartz sands are gradational with the other lithologies. Phosphate sand is usually pre-
sent in amounts ranging from 1 to 5 percent; however, phosphate grain percentages may range con-
siderably higher in thin and localized beds. The quartz sands are typically light gray (N 7) to olive gray (5
Y 4/1) in color. Induration varies from poor to moderate.
Clay beds are quite common in the Marks Head Formation, occasionally comprising a large portion of
the section. The clays are quartz sandy, silty, dolomitic and phosphatic. As is the case in the Penney
Farms Formation, the Marks Head clays contain highly variable percentages of accessory minerals;
relatively pure clays do occur but are not common. The clays range from greenish gray (5 GY 6/1) to olive
gray (5 Y 4/1) in.color and are typically lighter colored than the clays of the underlying unit.
Phosphate grains are present virtually throughout the Marks Head Formation. They characteristically
occur as brown to black, sand-sized grains scattered throughout the sediments. The phosphate grains
are rounded and often in the same size range as the associated quartz sands. Phosphate pebbles occur
rarely.
Mineralogically, the Marks Head Formation clays contain palygorskite, sepiolite, smectite and illite;
kaolinite is present only in the weathered section (Hettrick and Friddell, 1984). Hettrick and Friddell
(1984) indicated that palygorskite is often the dominant clay mineral in this unit; smectite is the second
most abundant clay mineral. Smectite becomes the most abundant clay mineral when palygorskite con-
tent decreases. Other minor mineralogic constituents include mica, opal-ct, and feldspar. Huddlestun (in
press) reports the occurrence of zeolite in the Marks Head Formation in Georgia.
The Marks Head Formation becomes difficult to identify in the southern portion of the area between the
Sanford High and the Ocala Platform (Figure 22). Within this transition zone the Marks Head loses most
of the dolostone beds. The distinction between this unit and the overlying Coosawhatchie Formation
becomes problematic. As a result, the Hawthorn Group in this area is referred to as undifferentiated. Ad-
ditional coring in the transition zone may delineate the facies changes through this zone and more ac-
curately determine the correlation of this unit into central and south Florida.

Subjacent and Suprajacent Units

The Marks Head Formation is underlain disconformably throughout most of its extent by the Penney
Farms Formation. The upper member of the Penney Farms Formation consists predominantly of darker,
olive gray (5 Y 3/2) colored sands and clays with occasional dolostone beds. The base of the Marks Head
Formation is placed at the contact between the darker colored sands and clays of the upper Penney
Farms and the generally lighter colored, more complexly interbedded sands, clays and dolostone of the
Marks Head. Occasionally, the contact is marked by a rubble zone containing phosphatized carbonate
















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LEGEND
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LIMITS OF HAWTHORN
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HAWTHORN GP.
UNDIFFERENTIATED


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Figure 22. Top of the Marks Head Formation. Shaded area indicates undifferentiated Hawthorn
Group.


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clasts but the unconformity is often difficult to recognize in cores. In the western-most portion of Hamilton
County, the Marks Head is underlain by the sandy carbonates of the Penney Farms Formation.
The Coosawhatchie Formation disconformably overlies the Marks Head Formation throughout north
Florida except where it has been removed by erosion. In these areas the Marks Head is overlain by
sediments referred to as undifferentiated, post-Hawthorn deposits.
The Coosawhatchie-Marks Head contact is generally placed at the top of the first hard carbonate bed
or light colored clay unit below the darker colored clayey, dolomitic, quartz sands and dolostones of the
basal Coosawhatchie Formation. Occasionally, the contact appears gradational in a sequence of
dolostones and interbedded sands. In this case the top of the upper-most dolostone bed is regarded as
the boundary. Occasionally a rubble bed marks the unconformity.
The relationship of the Marks Head Formation to the underlying and overlying units is graphically il-
lustrated in Figures 11 through 16.

Thickness and Areal Extent

The Marks Head Formation of the Hawthorn Group in Florida occurs primarily as a subsurface unit.
The top of the Marks Head Formation in the subsurface varies from -260 feet MSL (-79 meters) in Carter
#1, W-14619, Duval County to +114 feet MSL (+35 meters) in Devil's Millhopper #1, W-14641, in
Alachua County (Figure 22).
The Marks Head Formation dips to the northeast from the flanks of the Ocala Platform toward the
Jacksonville Basin with an average dip of 4 feet per mile (0.8 meters per kilometer) (Figure 22). The direc-
tion of dip of the Marks Head Formation trends towards the north from the St. Johns Platform into the
Jacksonville Basin (Figure 4). The direction and angle of dip may vary locally.
The thickness of the Marks Head Formation varies from being absent on the crest of the Ocala and
Sanford Highs to 130 feet (40 meters) in N.L. #1, W-12360, Bradford County (Figure 23). It is interesting
to note that this well is not in the Jacksonville Basin but to the southeast of it.
The Marks Head Formation is present throughout much of north Florida. It apparently has been remov-
ed by erosion from the Sanford High (Figures 4 and 23) and has not been identified on the Ocala Platform
possibly being absent as a result of erosion or non-deposition. In the area between the Ocala and San-
ford Highs, the Marks Head is very thin and becomes difficult to recognize, merging southward into the
undifferentiated Hawthorn Group.

Age and Correlation

Dateable fossil assemblages within the Marks Head Formation have not been found in north Florida.
The only fossils noted were scattered molds of mollusk shells and occasional diatom molds. Lithologic
correlation between these sediments and those in Georgia, where fossiliferous sediments are found, in-
dicates that the Marks Head Formation is late Early Miocene (Burdigalian) age (Huddlestun, personal
communication, 1983). Planktonic foraminifera in Georgia indicate Zone N.6 or early N.7 of Blow (1969).
Huddlestun (in press) suggests that the Marks Head Formation in Georgia is correlative with the Tor-
reya Formation (Banks and Hunter, 1973) in the eastern panhandle of Florida (Figure 19). Huddlestun (in
press) considers both formations to be slightly older than the Chipola Formation in the Florida panhandle
which has been correlated with the upper part of planktonic zone N.7 of Blow (1969). It is suggested here
that the Marks Head Formation of north Florida is correlated with at least the upper part of the Arcadia
Formation and is younger than the Arcadia's Tampa Member in southwest Florida. The Marks Head For-
mation is thought to be a time equivalent of the lower part of the downdip Bruce Creek Limestone in the
southern part of the Apalachicola Embayment. It appears that the Marks Head Formation may be cor-
relative with the lower Pungo River Formation in North Carolina, based on ages suggested for the Pungo
River by Gibson (1982).
As is the case for the Penney Farms Formation, the Marks Head Formation is older (see Figure 19)
than the previously accepted age for the "Hawthorn Formation" in Florida as interpreted by Cooke


















/


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- I


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SCALE cl = 25 FEET
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Figure 23. Isopach of Marks Head Formation. Shaded area indicates undifferentiated Hawthorn
Group.


COUMB'A A

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(1945) and Purl and Vernon (1964). Puri and Vernon suggested a strictly Middle Miocene age for their
"Hawthorn."

Discussion

The extension of the name Marks Head Formation into Florida was based on the general lithologic
similarities between the sediments in Georgia and those in Florida. Despite an increased carbonate con-
tent in the Florida section, the units are quite similar and the Georgia lithostratigraphic nomenclature is
used to avoid stratigraphic confusion.
The Marks Head Formation, like the time-equivalent unit in the panhandle, the Torreya Formation, con-
tains significant amounts of clay. As reported by Hetrick and Friddell (1984), palygorskite is generally the
dominant clay mineral with subordinate amounts of smectite. The occurrence of large amounts of
palygorskite is suggestive of an unusual set of environmental circumstances which prevailed over large
areas of the southeastern coastal plain. The exact conditions are not well understood. However, whether
palygorskite is a product of brackish water lagoons (Weaver and Beck, 1977) or ephemeral (alkaline)
lakes (Upchurch, et al., 1982), the fluctuating sea levels in late Early Miocene could have reworked these
deposits, incorporating vast amounts of palygorskite into the Marks Head sediments. Future detailed
clay mineralogy investigations may facilitate a better understanding of the genesis of the clays and of the
depositional environments of the Marks Head Formation.



COOSAWHATCHIE FORMATION

Definition and Reference Section

The Coosawhatchie Formation of the Hawthorn Group is used in this paper for the upper unit of the
group in much of north Florida. Huddlestun (in press) proposed the Coosawhatchie as a formal
lihtostratigraphic unit in Georgia. It extends into north Florida with only minor lithologic changes.
The Coosawhatchie Formation in Florida consists of three members: informal lower and upper
members and the Charlton Member, as defined by Huddlestun (in press). The Charlton Member will be
discussed separately. A basal clay bed occurs in a few cores in St. Johns County and may equate with
the Berryville Clay (Huddlestun, in press).
The type locality for the Coosawhatchie Formation is at Dawsons Landing on the Coosawhatchie River
in Jasper County, South Carolina, as described by Heron and Johnson (1966). Huddlestun (in press) sug-
gests a reference locality in Georgia along the Savannah River in Effingham County.
The reference section for north Florida is in the Harris #1 core, W-13769, Clay County (SW/4, SE1/4,
Sec. 7, T6S, R25E) (Figure 24). The surface elevation of the core is 97 feet (30 meters) MSL. The top of
the Coosawhatchie Formation in Harris #1 is at +37 feet (+ 11 meters) MSL (Figure 24), the base is at
-74 feet (-23 meters) MSL.

Lithology

The Coosawhatchie Formation in Florida consists of quartz sands, dolostones and clays.
Characteristically, sandy to very sandy dolostone is the most common lithology in the upper informal
member, where it is interbedded with quartz sands and clays. In the lower informal member, the quartz
sands and clays predominate with interbedded dolostones.
The quartz sands are dolomitic, clayey and phosphatic. The sand grains are fine to medium grained,
poorly to moderately sorted, and subangular to subrounded. The proportions of accessory materials vary
greatly. The sands grade into the dolostones and clays in many instances. The phosphate grain content
is quite variable ranging from a trace to more than 20 percent. Clay content varies from less than 5 per-



















LAND SURFACE


CLRY


UNDIFFERENTIATED


PHOSPHATE SHND HAWTHORN GROUP
PHOSPHATE SAND
PHOSPHATE SAND
SILT PHOSPHATE DOLOMITE
SILT PHOSPHATE DOLOMITE
SILT PHOSPHATE DOLOMITE
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY Z
PHOSPHRTE CLAY 0
PHOSPHATE DOLOMITE
PHOSPHATE DOLOHITE
PHOSPHRTE SAND DOLOMITE
PHOSPHATE SRNO
PHOSPHATE SRNO
PHOSPHATE CLAY
PHOSPHATE CLRY O
PHOSPHATE CLAY LL
PHOSPHATE CLAY
PHOSPHRAE DOLOHITE W
PHOSPHATE DOLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOHITE 0
PHOSPHATE DOLOMITE I
PHOSPHATE DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE Z
PHOSPHRTE
PHOSPHATE
PHOSPHRTE
PHOSPHATE SANO DOLOMITE 0
PHOSPHATE SANO 0
PHOSPHATE SAND O
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPH A TE
PHOSPHATE
CLAY


----


-' '-' '-' '-'

-' '-' '-' '-'





-' '-' '-' '-'
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----
---




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pqW-1376
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SRANO
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PHOSPHATE OOLOMITE
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PHOSPHRTE
PHOSPHATE
PHOSPHRTE CLAY
PHOSPHATE CLAY
PHOSPHATE MARKS HEAD FORMATION
PHOSPHATE CLAY
PHOSPHATE CLAY
CLAY
OOLOMITE CLAY

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---------




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-----------
---------------
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PHOSPHATE
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CLAY
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOMITE
PHOSPHRTE CLRY
PHOSPHATE CLAY
SAND
SAND
SAND
PHOSPHATE SANO
PHOSPHATE
PHOSPHATE
SAND
5RND
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE SRNO DOLOMITE
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHRTE CLAY
PHOSPHATE SANS
PHOSPHATE SRND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SRND
PHOSPHATE SRND
PHOSPHATE SRND
PHOSPHATE SRND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SRNO H
PHOSPHATE SAND
PHSHR E SANO


OCALA GROUP



CRYSTAL RIVER FORMATION


Figure 24. Reference section for the Coosawhatchie Formation,

Harris #1, W-13769, Clay County

(Lithologic legend Appendix A).


cent to greater than 30 percent. The sands are often lighter colored in the upper member where there is

more carbonate in the matrix and darker in the lower member. Colors range from greenish gray (5 GY

6/1) and light gray (N 7) to olive gray (5 Y 4/1). Induration is generally poor.

The dolostones of the Coosawhatchie Formation are quartz sandy, clayey and phosphatic. The

percentages of quartz sand and clay vary widely and may be as much as 50 percent in transitional zones.

Phosphate grain content is quite variable also, but is generally less than 10 percent. The dolostones are

micro- to fine crystalline, poorly to moderately indurated and occasionally contain molds of fossils. They

range in color from light gray (N 7) and greenish gray (5 GY 6/1) to olive gray (5 Y 6/1). The dolostones of

the upper member appear to become more calcareous in the Jacksonville Basin.

The clays in the Coosawhatchie Formation are typically quartz sandy, silty, dolomitic and phosphatic.

The clays are light olive gray (5 Y 6/1) to olive gray (5 Y 4/1). Clay beds are most common in the lower

member (Scott, 1983). The clay mineralogy is dominated by smectite (Hetrick and Friddell, 1984). The

clay beds often contain diatoms (Hoenstine, 1984).

The phosphate grains present in the Coosawhatchie Formation are normally amber colored to brown

or black; lighter colors occur near the land surface. The phosphate grains are usually well rounded and in


U


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AWTHORN GROUP


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PHOSPHATE










the same size range as the associated quartz sands. Coarser phosphate sands and phosphate pebbles
or rubble are not common but are present.

Subjacent and Suprajacent Formations

The Coosawhatchie Formation disconformably overlies the Marks Head Formation but the disconfor-
mity is often not readily apparent. It is, however, recognized biostratigraphically in Georgia (Huddlestun,
personal communication, 1983). The contact often occurs in a thin gradational sequence of interbedded
sands and dolostones. Occasionally, the contact is marked by a rubble bed.
The Statenville Formation of the Hawthorn Group overlies and interfingers with the Coosawhatchie in
Hamilton and Columbia Counties and possibly a small portion of Baker County. The contact is confor-
mable and is recognized by the occurrence of more phosphate grains and less carbonate in the Staten-
ville and the thin bedded nature of the Statenville.
With the exception of the area described above, the Coosawhatchie in Florida is overlain unconfor-
mably by undifferentiated post-Hawthorn deposits. These include sands, clays, shell beds and occa-
sional limestones. The relationship of the Coosawhatchie to the underlying and overlying units is in-
dicated in Figures 11 through 16.

Thickness and Areal Extent

The Coosawhatchie Formation occurs throughout much of north Florida. The top of the Coosawhatchie
ranges from -93 feet MSL (-28 meters) in Bostwick #1, W-14477, Putnam County to + 168 feet MSL (51
meters) in Devils Millhopper #1, W-14641, Alachua County (Figure 25). It attains a maximum thickness in
Florida (including the Charlton Member) of 222 feet (68 meters) in Carter #1, W-14619, Duval County
(Figure 26). The Charlton Member in this core is 23 feet (7 meters) thick. Huddlestun (in press) indicates
that the Coosawhatchie attains a maximum thickness of 284 feet (87 meters) in the southeast Georgia
Embayment.
The Coosawhatchie Formation dips in a northeasterly direction from the flanks of the Ocala Platform
toward the Jacksonville Basin (Figures 4 and 26). From the St. Johns Platform it dips to the west off the
structure and to the north into the Jacksonville Basin (Figures 4 and 26). The average dip is approximate-
ly 4 feet per mile (0.8 meters per kilometer). Variations in the angle and direction of dip are evident from
Figures 11 through 16.
The Coosawhatchie Formation is not known to occur over the Ocala and Sanford Highs or in the im-
mediately surrounding areas. This is thought to be due primarily to erosion; nondeposition may also have
played a role. The Coosawhatchie extends from Georgia southward into central Flordia. In central Florida
(between the Ocala and Sanford Highs) it becomes difficult to distinguish and is included in the undif-
ferentiated Hawthorn Group.

Age and Correlation

Huddlestun (in press) suggests a Middle Miocene (Early Serravallian) age for the Coosawhatchie For-
mation based on planktonic foraminifera. Huddlestun placed it in Zone N.11 of Blow (1969).
Hoenstine (1984) studied diatoms from a few selected cores through the Hawthorn. He recognized a
Middle Miocene assemblage in Florida sediments assigned in this paper to the Coosawhatchie Forma-
tion.
The Coosawhatchie Formation is thought to be correlative with the lower portion of the Intracoastal
Limestone in the Apalachicola Embayment (Schmidt, 1984) and the lower Shoal River Formation in the
Florida panhandle (Huddlestun, pers. comm., 1983). In the peninsular area of Florida, it appears to cor-
relate with the lower part of the Peace River Formation of this paper. The Coosawhatchie was correlated
with much of the Pungo River Formation in North Carolina by Gibson (1982) and Riggs (1984) (Figure 19).

















MADISON H T I


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LIMITS OF HAWTHORN
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Figure 25. Top of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group.


a


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Figure 26. Isopach of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn
Group.


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175
A 150

125

100
75
50

HNS









Discussion


The Coosawhatchie Formation is widespread in northern Florida and throughout most of this area it is
the uppermost Hawthorn sediment encountered in the subsurface. In limited areas it is shallow enough
to be exposed in some foundation excavations. The Coosawhatchie Formation in the Jacksonville Basin
contains a lower clay bed of variable thickness. This clay bed correlates with the Berryville Clay Member
of the Coosawhatchie Formation in southeastern Georgia.
The Coosawhatchie Formation is quite similar to the Peace River Formation of southern Florida in that
both are predominantly siliciclastic units. However, the Coosawhatchie contains significantly more car-
bonate in the matrix than the Peace River. The formations are gradational with each other through the
zone of undifferentiated Hawthorn Group sediments in central Florida.



CHARLTON MEMBER OF THE COOSAWHATCHIE FORMATION

Definition and Reference Section

Huddlestun (in press) redefined the "Charlton formation" of Veatch and Stephenson (1911) as a for-
mal member of the Coosawhatchie Formation in Georgia. He found that the Charlton Member is a
lithofacies of the upper part of the Coosawhatchie (Huddlestun's Ebenezer Member) in south Georgia
and north Florida. Huddlestun (in press) discussed the reference localities in some detail. A reference
section for the Charlton Member of the Coosawhatchie Formation in Florida is the Cassidy #1 core,
W-13815, Nassau County (NW/4, NW/4, Sec. 32, T3N, R24E). The surface elevation is 80 feet (24
meters) MSL. The Charlton Member occurs from +3 feet (+1 meter) MSL to -43 feet (-13 meters) MSL
(Figure 27).

Lithology

The Charlton Member characteristically consists of interbedded carbonates and clays. It is less sandy
than the upper member of the Coosawhatchie, into which it grades laterally and vertically and typically
contains less sand and phosphate grains. It contains a clay component that is often very conspicuous in
the cores (Huddlestun, in press). This has been found to be true in Florida also.
The carbonate beds of the Charlton Member are often dolostones but range into limestone. They are
slightly sandy, slightly phosphatic to non-phosphatic and clayey. They often contain abundant molds of
fossil mollusks. The dolostones are finely crystalline, light olive gray (5 Y 6/1) and poorly to moderately in-
durated. The limestones are characteristically very fine grained, slightly sandy, clayey, poorly to
moderately indurated, and yellowish gray (5 Y 8/1).
The clays are dolomitic to calcareous, with poor to moderate induration, silty, and light gray (N 7) to
greenish gray (5 GY 6/1). The clay minerals present include smectite, palygorskite, illite and kaolinite
(Hetrick and Friddell, 1984).

Subjacent and Suprajacent Units

The Charlton Member both overlies and interfingers laterally with the upper informal member of the
Coosawhatchie Formation. The Charlton is simply a distinctive facies of the upper informal member. The
Charlton is disconformably overlain by the sediments discussed as overlying the Coosawhatchie Forma-
tion.

Thickness and Areal Extent

Sediments assigned to the Charlton occur at Brooks Sink (SW/4, SW/4, Sec. 12, T7S, R20E, Bradford














W-13815


LAND SURFACE


CLAY
HEAVY MINS.
HEAVY MINS.


UNDIFFERENTIATED


70 -



60



50 -







30 -



20



10



0



-10



-20



-30



-40



-50


PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE

PHOSPHATF SRNn
PHOSPHATE SANO
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE SANH
SAND DOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOHITE



PHOSPHATE DOLOMITE
PHOSPHATE DOLOHITE
DOLOHITE CLAY


U.


-360



-370


SANO CLAY
DOLOHITE

PHOSPHATE DOLOMITE
PHOSPHATE 0OLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE DOLOMITE
punRPATF nnl HTT, P


PHOSPHATE


z

I-



0
UL
PHOSPHATE DOLOMITE
PHOSPHATE
PHOSPHATE
PHOSPHATE A L
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SANO OLOMITE
PHOSPHATE OOLOAITE CLAY P
PHOSPHATE CLRY
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE


-190



-200



-210



-220



-230



-240



-250



-260



-270



-280



-290



-300



-310



-320



-330


HAWTHORN GROUP


OCALA GROUP


CRYSTAL RIVER FORMATION


Figure 27. Reference core for the Charlton Member of the Coosawhatchie Formation, Cassidy #1,

Nassau County (Lithologic legend Appendix A).


1 HAWTHORN GROUP
SAND


CALCITE
CALCITE CHARLTON MEMBER
CALCITE


PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
SILT PHOSPHATE SANO
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE
SRNO CLAY
CLRY
CLAY
CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE SAND
PHOSPHATE SANO
PHOSPHATE SAND
PHOSPHATE SANO
CLAY
CLAY
CLAY
CLAY
CLAY
CLAY
SANHO
SRNO
SANO
SANO
SANO
SANO
CALCITE CLAY
CLRY
CLAY
SAND CLAY


-70



-80



-90



-L00 _



-110



-120-



-130-



-140



-150



-160



-170 _


--- -- --- ---














-7 -7 -

--/ --/ -
-/ -/-/-/


..-:, ..? ---: ,-- -,
."-."Z --- .'2:- ': "-:


;"- -- ..'TL.'-"' '


////









































-N-


SCALE CI 25 FEET
0 20 40 MILES
I I I I
0 20 40 KILOMETERS
LEGEND
CORES


~.4I, LIMITS OF HAWTHORN GROUP

-_ / LIMITS OF CHARLTON


Figure 28. Top of the Charlton Member (dashed line indicates extent of Charlton).

County) at an elevation of + 145 feet (44 meters) MSL (Figure 28). The highest elevation for the top of the
Charlton in a core was in Wainwright #1, W-14283, Bradford County where it occurred at + 109 feet (+ 33
meters) MSL. The deepest that the top of the Charlton Member was found is in Carter #1, W-14619,
Duval County, where it is -38 feet MSL (-12 meters).
The Charlton Member of the Coosawhatchie Formation reaches its maximum recognized thickness in
Florida in Cassidy #1, W-13815, Nassau County, where it is 40 feet (13 meters) thick (Figure 29). It is very
spotty in its occurrence, as is evident from the cross-sections (Figures 11 through 16).

Age and Correlation

The Charlton Member, as originally defined by Veatch and Stephenson (1911), was considered
Pliocene. Huddlestun (in press) postulates that, based on his observations of the molluskan fauna and







































-N- t 1


SCALECI 10 FEET
0 20 40 MILES
0 20 40 KILOMETERS -
LEGEND
CORES |U

LIMITS OF HAWTHORN GROUP

"'/ LIMITS OF CHARLTON

Figure 29. Isopach of the Charlton Member (dashed line indicates extent of Charlton).


the lithostratigraphy of the unit, it is Middle Miocene (Seravallian) in age (Figure 19).
The Charlton Member correlates with at least part of the informal upper member of the Coosawhatchie
Formation. Correlations for the Coosawhatchie Formation are discussed in the previous section.

Discussion

The sediments assigned to the Charlton Member of the Coosawhatchie Formation were referred to as
the "Jacksonville limestone" by Dall and Harris (1892). Dall and Harris suggested that the "Jacksonville
limestone" was Pliocene in age. Matson (1915) changed the Jacksonville Limestone to the "Jacksonville
formation." Cooke (1945) suggested placing the "Jacksonville formation" in the Duplin Marl. No type
section was ever formally designated for the Jacksonville formation.
The lithologic relationship of these sediments,to the rest of the Coosawhatchie Formation as recogniz-










ed in this study supports the work of Huddlestun (in press). The use of the Charlton Member rather than
reintroducing the "Jacksonville limestone (or formation)" is suggested here to aid in nomenclatural con-
sistency between the Georgia coastal plain and peninsular Florida. The reduction in status of the
Charlton is necessary due to its limited extent.

STATENVILLE FORMATION

Definition and Type Location

The Statenville Formation is a new lithostratigraphic name proposed by Huddlestun (in press) for in-
terbedded phosphatic sands, dolostones and clays at the top of the Hawthorn Group in the type section
along the Alapaha River near Statenville, Georgia, north of Georgia Highway 94. The Statenville Forma-
tion extends southward into Hamilton and Columbia Counties area of Florida.
Reference localities listed by Huddlestun (in press) include exposures along the Alapahoochee Creek
between the Georgia Highway 135 bridge in southwest Echols County and at the bridge over the river
1.25 miles (2 km) northeast of Jennings in Hamilton County, Florida; and exposures along the Suwannee
River approximately one mile (1.6 km) above and below the site of the former Cones Bridge (now a boat
landing) in Sec. 36, T1N, R16E in Hamilton and Columbia Counties, Florida. None of these outcrop sec-
tions expose the entire unit. The best section available is present in the designated reference core Betty
#1, W-15121, Hamilton County (NE/4, NW/4, Sec. 3, T2N, R12E), Florida. This core provides the only
complete section available. The Statenville Formation extends from the surface to 87 feet (26 meters)
MSL. Surface elevation is 150 feet (46 meters) MSL (Figure 30).


Lithology

The Statenville Formation of the Hawthorn Group consists of interbedded sands, clays and dolostones
with common to abundant phosphate grains. The diagnostic feature of the Statenville Formation is its
thin bedded, often crossbedded, nature that is exhibited in outcrop (Figure 31). Outcrops generally con-
sist of thin beds of dolostone and clay alternating with thin beds of sand.
Quartz sands predominate in much of the unit. The sands are fine to coarse grained (with occasional
quartz gravel present), clayey to dolomitic, poorly indurated, poorly to moderately sorted, and subangular
to angular. Colors range from very light gray (N 8) to light olive gray (5 Y 6/1). The sands are quite
phosphatic with thin zones grading into phosphorite sands. The average phosphate grain percentage is
approximately 10 percent.
The dolostones, which occur commonly as thin beds within the Statenville, are sandy, clayey,
phosphatic and poorly to well indurated. The dolostones are typically yellowish gray (5 Y 8/1) to very light
orange (10 YR 8/2). The percentages of sand, phosphate, and clay in the dolomites vary widely.
Sediments in the Betty #1 core indicate that dolostone is most common in the lower portion of the unit.
Clay beds are not readily apparent in the outcrop sections. However, in the Betty #1 core they are quite
common and are more abundant in the upper portion of the Statenville (Figure 30). The clay beds are
characteristically sandy, dolomitic, phosphatic, light olive gray (5 Y 6/1) to yellowish gray (5 Y 8/1) and
poorly indurated. The clay minerals present are characteristically smectite, palygorskite and illite.
Phosphate grains are abundant in the Statenville Formation. The phosphate grains are tan, amber,
and brown to black, rounded, and generally are in a similar size range as the associated quartz sands.
Huddlestun (in press) discusses phosphate pebbles and clasts (conglomerate) as being present in
dolomite beds along the Suwannee River and also along the Alapaha River. Phosphorite from the Staten-
ville Formation is presently being mined by Occidental Chemical Company in Hamilton County, Florida.
These phosphorite sands occur in the upper, less dolomitic portion of the unit.
The thin bedded nature of the Statenville sediments is quite distinctive in outcrop. Huddlestun (in
press) reports that the bedding ranges from horizontal to undulatory to variously cross bedded, with












150



140



130



120



ito



100



90



80



70



60



50



40



30



20


---
t- t-


LAND SURFACE


-- ^ -/ _
-M M
,- -- .


__' --._, .-_, ---,
- -.-.,, -_, .- -.
.'7" 7








-- -. -. -
_,_ -- _. -- _,..' .
,-- -- , _






-,- --- --- --, .
-,-, ,--- -.-,-,
-.- -.- .-.- -.--.


PHOSPHATE SRND7O CI
PHOSPHATE SAND
PHOSPHATE SAND
SAND DOLOMITE
SAND
n:nn


W-15121


HAWTHORN GROUF

CLAY




PHOSPHATE
PHOSPHATE SAND
PHOSPHATE
PHOSPHATE
PHSSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE DOLOMITE CLAY
PHOSPHATE SRND
PHOSPHATE SAND
CLAY
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHATE SAND
UnCoDuarC ca.n


HOSPHRTE
PHOSPHATE
SAND CLAY
DOLOMITE
SAND DOLOMITE _


HAWTHORN GROUP
PHnflPHPTF ri rY


SRND
SAND


SRND
SAND
SAND
saun rI nv


ST. MARKS FORMATION


SUWANNEE LIMESTONE


Figure 30. Reference core for the Statenville Formation, W-15121, Betty #1, Hamilton County
(Lithologic legend Appendix A). 51


-/ -'/ -*/ /\






- -^- --
- ~z 7 -~ 7z
-:7 :7--





--:r --






/ / / /
/ /
/ / / /l
/ :7--
:7-- -:7
::7 z2"--


0



-10


I X/ z


7// /


OHP Phil F


I


I


IIIlill I I II I


z
0




0
IL
L.
.
..I
-I

z
w
I-









COOSAWHATCHIE

FORMATION









































" .. &."."".".."3U


Figure 31. Photograph of Statenville Formation outcrop showing distinct cross bedding.


locally common cut and fill structures. The thin dolostone and clay beds remain as small ledges while the
sands erode deeper into the outcrop (Figure 31). This distinctive bedding is also exposed in the
phosphate pits in Hamilton County. A reworked zone with more parallel bedding is present above the
crossbedded and thinbedded section.

Subjacent and Suprajacent Units

The Statenville Formation is underlain throughout its extent in north Florida by the Coosawhatchie For-
mation with which it also interfingers. The contact between the formations is conformable. The contact is
placed at the base of the section of thinbedded, significantly ( >15 percent) phosphatic sands, clays and
dolostones.
The Statenville Formation occurs from very near the ground surface to the top of the Coosawhatchie
Formation throughout most of its occurrence. The uppermost portion of the section is often weathered
and has lost its dolomite and phosphate content. Near its eastern limit, it may be overlain by undifferen-
tiated post-Hawthorn deposits (Figures 11 through 16).













































AJA LIMITS OF HAWTHORN GROUP
AREA OF STATENVILLE OCCURRENCE

Figure 32. Area of occurrence of the Statenville Formation.


Thickness and Areal Extent

The Statenville Formation is recognized in three cores in north Florida (Figure 32). It also crops out
along rivers and streams in the Hamilton and Columbia County area. Figure 32 shows the area where the
Statenville is known to be present; lateral limits of the formation are poorly defined at this time.
The thickness of the Statenville Formation ranges up to 87 feet (26.5 meters) as recognized in Betty #1,
W-15121, Hamilton County. This represents the greatest known thickness.

Age and Correlation

Brooks (1966) believed that these sediments were Late Miocene in age based on what he referred to as
inconclusive paleontologic evidence. Limited collections of terrestrial vertebrate fossils from the Staten-










ville Formation indicate a Middle Miocene age (Huddlestun, in press). Webb (personal communication,
1983 in Huddlestun, in press) states that the Statenville mammal fauna is late Barstovian (late Middle
Miocene) and is between 14 million and 12 million years old. Huddlestun (in press) believes this unit to be
of Serravallian age, possibly in part equivalent to Zone N.11 of Blow (1969). The reworked zone at the top
of the Statenville section appears to be Late Miocene based on vertebrate fossils (Cathcart, 1985, per-
sonal communication).
The Statenville Formation appears equivalent to the upper part of the Coosawhatchie Formation. Hud-
dlestun's (in press) zonal correlation indicates an equivalence to the upper part of the Pungo River For-
mation in North Carolina. The Statenville is also correlative with part of the Intracoastal Formation in the
Florida panhandle (Schmidt, 1984) and part of the Peace River Formation in southern Florida.

Discussion

The Statenville Formation of northern Florida is recognized primarily in outcrops along the Alapaha
and Suwannee Rivers in Hamilton County and northward into Georgia. The Statenville's limited extent in
north Florida is at least in part due to a rather limited data base. Additional cores and further research will
be necessary to better define the limits and relationships of the Statenville and associated units.


ALACHUA FORMATION

The Alachua Formation, originally called the "Alachua clays" by Dall and Harris (1892), is an often
misused and misunderstood unit. The original definition included sands and clays filling in karst depres-
sions or stream channels related to sinkholes.
Sellards (1914) greatly expanded the definition of the Alachua Formation by including the hardrock
phosphate-bearing deposits of the "Dunnellon formation" in the Alachua. He felt that the sands of the
"Dunnellon" were a facies of the "Alachua clays." Later authors (Cooke and Mossom, 1929; Cooke,
1945) followed the expanded definition of the Alachua.
Vernon (1951) discussed the Alachua as "a mixture of interbedded, irregular deposits of clay, sand
and sandy clay of the most diverse characteristics." Puri and Vernon (1964) also used this definition.
Discussions of the origin of the Alachua Formation have yielded a number of theories. Cooke (1945)
believed that this unit was a residual, in situ accumulation of weathered Hawthorn sediments. Puri and
Vernon (1964) felt the Alachua Formation was terrestrial and in part lacustrine and fluviatile. Brooks
(1966, in Teleki, 1966) suggested that the Alachua was formed by deposition in an estuarine environment
and included residual Hawthorn deposits overlain by slumped Pliocene fluvial and sinkhole accumula-
tions. Based on the occurrence of the hard rock phosphates, the paleoextent of the Hawthorn Group
sediments (Scott, 1981), field inspection of outcrops and the existing literature, the present author feels
that this unit resulted from the weathering and/or reworking of Hawthorn Group sediments. The Alachua
Formation at this time is not considered as part of the Hawthorn Group in peninsular Florida.
Suggested ages of the Alachua Formation range from as old as Middle Miocene (Vernon, 1951) to as
young as Plio-Pleistocene (Pirkle, 1956b). The range in suggested ages can be attributed to a multiple
phase development for this deposit. For example, different generations of karst or different cycles of
reworking can incorporate similar lithologic packages with differing vertebrate faunas enclosed. As a
result sediments assigned to the Alachua Formation may range in age from the Miocene to the
Pleistocene.
It is readily apparent that the Alachua Formation is a complex unit. Further research is necessary to
better understand and delineate this complex unit.












POST HAWTHORN
UNDIFFERENTIATED

BONE
VALLEY
MEMBER

PEACE RIVER
FORMATION 0
O
C!-
(r

Z
CC
ARCADIA
FORMATION
<


TAMP-
MEMBER
NOCATEE
MEMBER


"SUWANNEE" /
LIMESTONE /S



OCALA GROUP


CRYSTAL RIVER
AND
WILLISTON
FORMATIONS


Figure 33. Lithostratigraphic units of the Hawthorn Group in southern Florida.










SOUTH FLORIDA
Although the Hawthorn Group in south Florida consists of the same general sediment types (car-
bonate, quartz sand, clay and phosphate), the variability and complexity of the section is different from
the strata in northern Florida. In the south Florida area (Figure 1), particularly the western half of the area,
the Hawthorn Group consists of a lower, predominantly carbonate unit and an upper, predominantly
siliciclastic unit. Eastward the section becomes more complex due to a greater percentage of siliciclastic
beds present in the lower portion of the Hawthorn Group.
The differences that exist between the northern and southern sections of the Hawthorn Group require
separate formational nomenclature. In southern Florida, the Hawthorn Group consists of in ascending
order, the Arcadia Formation (new name) with the Tampa and Nocatee (new name) Members and the
Peace River Formation (new name) with the Bone Valley Member (Figure 33). The new nomenclature
helps alleviate many of the previously existing problems associated with the relationship of the Bone
Valley, Tamiami, Hawthorn, and Tampa units in the south Florida region.

ARCADIA FORMATION
Definition and Type Section
The Arcadia Formation is a new formational name proposed here for the lower Hawthorn carbonate
section in south Florida. This unit includes sediments formerly assigned to the Tampa Formation or
Limestone (King and Wright, 1979) and the "Tampa sand and clay" unit of Wilson (1977).
Dall and Harris (1892) used the term "Arcadia marl" to describe beds along the Peace River. This term
was never widely used and did not appear in the literature again except in reference to Dall and Harris. It
appears that their use of the "Arcadia marl" described a carbonate bed now belonging in the Peace
River Formation of the upper Hawthorn Group. Riggs (1967) used the term "Arcadia formation" for the
carbonate beds often exposed at the bottom of the phosphate pits in the Central Florida Phosphate
District. Riggs' use of this name was never formalized. The "Lexicon of Geologic Names" (U.S.G.S.,
1966) listed the name Arcadia as being used as a member of the Cambrian Trempealeau Formation in
Wisconsin and Minnesota, thereby precluding its use elsewhere. Investigations into the current status of
this name indicated that the Arcadia member has not been used in some 25 years and does not fit the
current Cambrian stratigraphic framework. The Lexicon also indicates Arcadia clays as an Eocene
(Claibornian) unit in Louisiana. This name also has been dropped from the stratigraphic nomenclature of
Louisiana (Louisiana Geological Survey, 1984, personal communication). Since these former usages of
this name are no longer viable, the term can be used for the lower Hawthorn Group sediments in
southern Florida in accordance with Article 20 of the North American Code of Stratigraphic
Nomenclature (NACSN, 1983).
The Arcadia Formation is named after the town of Arcadia in DeSoto County, Florida. The type section
is located in core W-12050, Hogan #1, DeSoto County (SE/4, NW1/4, Section 16, Township 38S, Range
26E, surface elevation 62 feet (19 meters)) drilled in 1973 by the Florida Geological Survey. The type Ar-
cadia Formation occurs between -97 feet MSL (-30 meters MSL) to -520 feet MSL (-159 meters) (Figure
34).
Two members can be recognized within the Arcadia Formation in portions of south Florida. These are
the Tampa Member and the Nocatee Member (Figure 33). The members are not recognized throughout
the entire area. When the Tampa and Nocatee are not recognized, the section is simply referred to as the
Arcadia Formation.
Lithology

The Arcadia Formation, with the exception of the Nocatee Member, consists predominantly of
limestone and dolostone containing varying amounts of quartz sand, clay and phosphate grains. Thin
beds of quartz sand and clay often are present scattered throughout the section. These thin sands and
clays are generally very calcareous or dolomitic and phosphatic. Figure 34 graphically illustrates the
lithologies of the Arcadia Formation including the Tampa and Nocatee Members. The lithologies of the


















LAND SURFACE





UNDIFFERENTIATED

-PHOSPHATE
PHOSPHATE HAWTHORN GROUP
PHOSPHATE
PHOSPHATE
- PHOSPHATE



PHOSPHATE
PHOSPHATE
PHOSPHATE
- PHOSPHATE
CLRA
PHOSPHATE
PHOSPHMRE
SAND

CLAY


CLAY Z

---- - PHOSPHRTE CLR NB
PHOSPHATE CLRY 4
PHOSPARIE CLAY K
PHOSPHATE CLAY -
PHOSPHATE CLRO T
PHOSPHATE CLAY 0
S PHOSPHATE CLAY U
PHOSPHAlTE I
PHOSPHRTE UA
PHOSPHATE >
PHOSPHATE =
PHOSPHATE 1C
PHOSPHRTE
PHOSPHATE
PHOSPHATE U
PHOSPHATE O
PHOSPHRTE
PHOSPHAIE
PHOSPHRIE .
PHOSPHATE
S PHOSPHATE




PHOSPHATE
PHOSPHTE
SAWO CRLCITE
| . . PHOSPHATE
PHOSPHRIE

PHOSPHATE
SPHOSPHATE
PHOSPHRIE

PHOSPHITE


PHOSPHATE SRNO CLAR
SfNO


PHOSPHAI SOO
PHOSPHATE SRHO
PHOSPHATE SAND


PHOPHOPTE SHD
PHOSPHATE 0AHO
PHOSPHATE SAHO
PHOSPHATEOSPH SAHO
SPHOEPHR RNO

PHOSPHATE SANS
PHOSPHAYE SYHO
PHOSPHATE 0RA0
PHOSPHATE SAOND
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLRY
PHOSPHRIE CLAY
PHOSPHATE CLAY
PHOSPHARE CLAY
PHOSPHATE CLAY
PHOSPHATE CLRY
PHOSPHATE SAHO
PHOSPRRfl BRAD
PHOSPHATE SAHO
PHOSPHRt SflHO
PHOSPHATE
PHOSPHRIE SRNO
PHOSPHRATE SANHO
PHOSPHATE SRHO
PHOSPHATE SANE
PHOSPHAIR SAND
PHOSPHRTE SONO CLAY
PHOSPHAEl SAND
PHOSPHRI SHRAD
PHOSPHR CLAY
PHOSPHYTE CLAY
PHDBPHAI SARNO
PHOSPHATE SANO
SH.E


-280


-290


-300


-310-



-320


-330



-3t40


-350


-360


-370


-380



-390


-400



-410


-450 _



-460 -


-470 __



-480 __


-490 __



-500 -



-510 -


-520



-530 _


-1 r I







T T-,


















*H- -
EAK:7







:ii:7












. .


:::
T-**T-**


PHOSPHATE
PHOSPHA TE
PHOSPHATE w -
PHOSPHATE
PHOSPHATE
PHOSPHRTE SAHO
PHOSPHATE
PHOSPHRTE



PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPMATE
PHOSPHATE
SRNO CLAY



SA1O
SRHO
SRAO CALCITE Z
0

SNOA CRLCITE 0 P
U I

CLRY ;
CLAY

CLAY

CALCITE CLAY
CLRY I r


PHOSPHATE Z 4
PHOSPHATE SREO
PHQSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
CLAY
CLAY
CL.,

SlAKO CALCITE
PRO PHRTE
PHOSPHATE
PHOSPHATE
CLAY
DOLONITE
DOLOMITE
OOLOAITE
OLONEITE
OOLOAITE
SILT OOL..ITE CLAY
DOLOMITE CLHY




CLAY
CLAY



CLRY
DOLOYITE



PHOSPHATE OOLOMHTE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOI1TE
PHOSPHATE OOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOPOTE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOHITE
PHOSPHATE OOLO ITE
PHOSPHATE DDLOHIIE
PHOSPHATE DOLON7IE
PHOSPHATE OOLO" TE
PHOSPRHATE DOLOHITE
PHOSPHATEOO E
PHOSPHATE
PHOSPHATE
PHOSPHRATE


"SUWANNEE" LIMESTONE


'R'.EC Figure 34. Type core for the Arcadia Formation, Hogan #1,


SA.. 0 W-12050, DeSoto County (Lithologic
SRHOE 0 leen

.. U legend Appendix A).

U 0
ai 4
U.

PHOSPHATE a
PH05PHRI J ;
PHOS PH H H T
PHOSPHAIS O
PHOSPHHIE I
PHOSPHR I


PHOSPHATE
PHOSPHAIE
PHOSPHR IE
PHDSPHAIE
PHOSPHATE
P HE SP TA P


12050


10



0 -



-10 _


-20



-30 --


-90



-100__



-110


-120


-130






-150



-160



-170


-1B0


-190


-200 -



-210


-220



-230



-240 -


-250 -



-260 _


-270__


P i5P5P5

















L-- -





7r'=Lr-L










Tampa and Nocatee Members will be discussed separately from the undifferentiated Arcadia Formation.
Dolomite is generally the most abundant carbonate component of the Arcadia Formation except in the
Tampa Member. Limestone is common and occasionally is the dominant carbonate type. The dolostones
are quartz sandy, phosphatic, often slightly clayey to clayey, soft to hard, moderately to highly altered,
slightly porous to very porous (moldic porosity) and micro- to fine crystalline. The dolostones range in col-
or from yellowish gray (5 Y 8/1) to light olive gray (5 Y 6/1). The phosphate grain content is highly variable
ranging up to 25 percent but is more commonly in the 10 percent range. The limestones of the Arcadia
are typically quartz sandy, phosphatic, slightly clayey to clayey, soft to hard, low to highly recrystallized,
variably porous and very fine to fine grained. The limestones are typically a wackestone to mudstone with
few beds of packstone. They range in color from white (N 9) to yellowish gray (5 Y 8/1). The phosphate
grain content is similar to that described for the dolostones. Fossils are generally present only as molds
in the carbonate rocks.
Clay beds occur sporadically throughout the Arcadia Formation. They are thin, generally less than 5
feet thick, and of limited areal extent. The clays are quartz sandy, silty, phosphatic, dolomitic and poorly
to moderately indurated. Color of the clay ranges from yellowish gray (5 Y 8/1) to light olive gray (5 Y 6/1).
Lithoclasts of clay are often found in other lithologies. Smectite, illite, palygorskite, and sepiolite com-
prise the clay mineral suite (Reynolds, 1962).
Quartz sand beds also occur sporadically and are generally less than 5 feet thick. They are very fine to
medium grained (characteristically fine grained), poorly to moderately indurated, clayey, dolomitic and
phosphatic. The sands are usually yellowish gray (5 Y 8/1) in color.
Chert is also sporadically presently in the Arcadia Formation in the updip areas (portions of Polk,
Hillsborough, Manatee and Hardee Counties). In many instances the chert appears to be silicified clays
and dolosilts.

Subjacent and Suprajacent Units

The Arcadia Formation overlies either the Ocala Group or the "Suwannee" Limestone in the south
Florida region (Figure 8). The contact between the basal Arcadia and the Ocala Group is an easily
recognized unconformity. In the north central and northeastern portions of southern Florida, where the
Hawthorn Group overlies the Ocala Group (Figures 8 and 41), the Arcadia is characteristically a gray,
hard, quartz sandy, phosphatic dolostone with a few siliciclastic interbeds. This is in contrast to the Ocala
Group, which is a cream to white, fossiliferous, soft to hard limestone (packstone to wackestone).
Throughout most of south Florida, the Hawthorn Group overlies limestones most often referred to as
the "Suwannee" Limestone (Figure 33). In much of this area the contact is recognizably unconformable.
The contrast between the sandy, phosphatic, fine-grained to finely crystalline carbonates of the Arcadia
and the coarser grained nonphosphatic, non-quartz-sandy limestones of the "Suwannee" Limestone
allow the contact to be easily placed. However, in the downdip areas (e.g., Lee and Charlotte Counties
and further south) the contact becomes more obscure. In this area the contact is placed at the base of the
last occurrence of a sandy, variably phosphatic carbonate.
The limestones underlying the Arcadia are referred to as "Suwannee" limestone due to the uncertain-
ty of the formational assignment. These sediments have characteristically been called "Suwannee" by
previous workers despite the fact that they have never been accurately correlated with the typical Suwan-
nee Limestone in northern Florida. Hunter (personal communication, 1984) believes that these car-
bonates are not Suwannee or the equivalent but are an unnamed limestone of Chickasawhayan Age
(Late Oligocene).
Unconformably overlying the Arcadia Formation is the Peace River Formation (Figure 33). The Peace
River Formation is predominantly a siliciclastic unit with varying amounts of carbonate beds. The percen-
tage of carbonate beds is higher near the base of the Peace River, resulting in a transitional or grada-
tional contact with the Arcadia. In some areas the contact is often marked by a phosphatic rubble zone
and/or a phosphatized dolostone hardground. In the more gradational sequence the contact is placed
where the carbonate beds become significantly more abundant than the siliciclastic beds.














- -a --0
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MANATEE CO. HARDEECO.


W-11570
WMa-33S-22E-01


HAROE CO.c IIGMANS CO.
I


W-12906
WHd-35S-27E-23ad


METERS FEET
S150
40

30 100

20
50
10

0 MSL
-10
-50
-20

-30 -100

-40
-150
-50

-60 -200

-70
-250
-60

-90 -300

-100
-350
-110

-120 -400

-130

-140 -450
-140

-150,
-500
-160

-170 -550

-180
-600
-190

-200 -650

-210
-700
-220

-750


The relationship of the subjacent and suprajacent units to the Arcadia Formation can be seen in the

cross sections shown in Figures 35 through 40.


Thickness and Areal Extent


The Arcadia Formation occurs primarily as a subsurface unit throughout its extent. The top of the Ar-

cadia Formation in cores ranges from -440 feet MSL (134 meters) in W-15493 Monroe County to greater

than + 100 feet MSL (30 meters) in several cores in Polk County (Figure 41). Data obtained from well cut-

tings in areas lacking core data indicated that the top of the Arcadia may be greater than -750 feet MSL

(229 meters) in Palm Beach and Martin Counties (Figure 41).

The Arcadia Formation appears to be absent from the southern nose of the Ocala Platform, the San-

ford High and part of the Brevard Platform (Figures 41 and 42). It increases in thickness away from these

features, reaching a maximum of 593 feet (181 meters) in a core in Charlotte County (Southeast Florida

Water Management District R.O.M.P. 3-3) and more than 650 feet (198 meters) in a well in southern Dade


Figure 36. Cross section H-H' (see figure 3 for location).


-






0g 3 0 0 0 0 0
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Psosse~o--$Ex
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County (Figure 42).
The dip of the Arcadia Formation exhibits some variability in the northern portion of the south Florida
area (Figure 41). This is primarily due to the occurrence of the Ocala Platform, Osceola Low, Sanford
High and the Brevard Platform (Figure 4). In general, however, the dip is to the southeast at approximate-
ly 5 feet per mile (0.9 meters per kilometer).
The basal unit of the Hawthorn Group is present throughout the south Florida area. It is apparently ab-
sent from the southern flanks of the Ocala Platform and the Sanford High and from part of the Brevard
Platform. This is at least partially due to erosion prior to Peace River deposition. The Arcadia Formation
is not identifiable in the area between the Ocala Platform and the Sanford High. A carbonate unit is pre-
sent in this area, but it has characteristics attributable to both the Arcadia and Penney Farms Forma-
tions. Until further research can be conducted, the Hawthorn Group remains undifferentiated in this area.
In the southern portion of south Florida, the Arcadia contains an increasing percentage of very moldic
(mollusk shell molds) limestones and the entire carbonate section becomes less phosphatic to the south.
The Arcadia Formation was tentatively identified in the Port Bougainville core, W-15493, Monroe
County (upper Keys). The transition from the typical Arcadia in southwest Florida to that in the upper
Keys is difficult to ascertain due to the nearly complete lack of core data and paucity of well cuttings in
the area. Further research, when the data become available, will be necessary to clarify these questions.

Age and Correlation

The sediments of the Arcadia Formation have yielded few dateable fossil assemblages. Diagenesis of
the original carbonate sediments has destroyed most fossil material leaving only casts and molds. From
mollusk samples collected by Hunter (personal communication, 1984) in portions of southwest Florida,
the upper part of the Arcadia correlates with part of the Marks Head Formation of north Florida and
Georgia and the Torreya Formation of the Florida panhandle. This suggests that the upper Arcadia is no
younger than mid-Burdigalian (late Eary Miocene) (Figure 19). The lower Arcadia seems to be equivalent
to the Penney Farms Formation and part of the Parachucla Formation Georgia (Figure 19) (Huddlestun,
personal communications, 1983; Hunter, personal communication, 1984). The base of the Arcadia may
be as old as early to middle Aquitanian (early Early Miocene) (Figure 19).

Discussion

The Arcadia Formation as described in this report is important from both a hydrologic and economic
viewpoint. Hydrologically, it incorporates several aquifers and confining units identified within the
Hawthorn Group. Economically, the carbonates of the Arcadia form the base of the mineable phosphorite
throughout much of the Central Florida Phosphate District. The Arcadia Formation as used here provide
a coherent picture of the early part of the Miocene in southern Florida.


TAMPA MEMBER OF THE ARCADIA FORMATION

Definition and Type Section

The Tampa Member of the Arcadia Formation represents a lithostratigraphic change in status from for-
mation to member. The Tampa has long been a problematic unit due to facies changes and apparent
gradational contacts with overlying and underlying units. The change from formation to member is
necessary due to the limited areal extent of the Tampa and its lithologic similarities and relationships with
the remainder of the Arcadia Formation of the Hawthorn Group. The Tampa Member is predominantly a
subsurface unit throughout its extent cropping out only in the Tampa area.
King (1979) and King and Wright (1979) thoroughly discussed the Tampa Member (their Tampa Forma-
tion) and its type locality. They designated Ballast Point core W-11541, Hillsborough County as the prin-














TR



H ER AND A










P sco0









-1508 ~
'300 -
L A A T S EN





















ARCORE 0 EOBE
SHAWTHORN G AUNDIERENTIATED
50 ARCADIA FORMATION ABSENT


0


NDJOI N R ER













PA l CE A OC















8 RO0 W0 RD.
- 47 0


A ADE








Figure 41. Top of Arcadia Formation. Shaded area r
indicates undifferentiated Hawthorn Group.

k

l:i';I


0
Io







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'%


a'
0


""t^


































25c
300S

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Figure


rR 1

TTE



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20 1

it
TST


E 1 150
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lwt 200
5 0 0 TT G- "


11000


P A LM B E C




d P~ I I~._]_i ., I 17350


IT. 450 80 450





SCORE



HAWTHORN GROUP UNDIFFERENTIATED
SARCADIA FORMATION ABSENT -0


42. Isopach of Arcadia Formation. 10
Shaded area indicates undifferentiated ~~
Hawthorn Group.IS




Q'7












1 15L 1.


0


-10


-20


-30


-'40


UNNAMED LIMESTONE OR

SUWANNEE LIMESTONE


Figure 43. Reference core for the Tampa Member of the Arcadia Formation, Ballast Point #1,
W-11541, Hillsborough County (Lithologic legend Appendix A).


cipal reference core (SE1/4, NW/4, of Section 11, Township 30S, Range 18E). The Tampa Member oc-
curs from -9 feet (-2.7 meters) MSL to -74 feet (-22.5 meters) MSL in this core (Figure 43). They also refer-
red to two other cores (Duette #1, W-11570, Manatee County and Brandon #1, W-11531, Hillsborough
County) as reference cores. This author also recognizes core W-15166 (Bradenton R.O.M.P. TR 7-1,
W1/4 of Section 26, Township 35S, Range 17E, Manatee County) as an excellent reference section for the
Tampa Member. W-15166 contains the Tampa Member from -285 feet (-87 meters) MSL to -423 feet (-129
meters) MSL (Figure 44).
The classical type area of the Tampa Member lies around Tampa Bay at Ballast Point and Six Mile
Creek (Dall and Harris, 1892). Unfortunately the type exposures do not completely or accurately repre-
sent the Tampa as it occurs in the subsurface. As a result the Tampa Member discussed in this paper as
a formal member of the Arcadia Formation of the Hawthorn Group is described from the previously men-
tioned reference cores.


LAND SURFACE


HAWTHORN GROUF




ARCADIA FORMATION


TAMPA MEMBER


-60


-70


-80


-80


-100


SAND
SAND




CLAY
CLAY
CLAY


























-to



-20



-30



-40



-50



-60



-70



-80



-90



-[00



-110



-120



- 30



-14"0



-150



-160



-170



-180



-190



-200



-210



-220



-230



-2f0



-250


PHOSPHATE
PHOSPHATE
PHOSPHATE SRNO CLAY
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE


TAMPA MEMBER


N-15166
-260


UNDIFFERENTIATED -270




?-? --280
HAWTHORN GROUP
SRND
CLAY -290


PHOSPHATE
PHOSPHATE -300
PHOSPHATE
PHOSPHATE SAND
PHOSPHATE
PHOSPHATE
PHOSPHATE -310
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE -320
PHOSPHATE SAND
PHOSPHATE
PHOSPHATE DOLOMITE
PHOSPHATE ODLOHITE
PHOSPHRTE SANO DOLOMITE -330
SAND
SAND
PHOSPHATE SAND
PHOSPHRTE SRNO
PHOSPHATE SAND -3400
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE -
PHOSPHATE SAND -350
PHOSPHATE SAND
PHOSPHATE CLRY
PHOSPHATE
PHOSPHRTE
PHOSPHATE SARN OOLOHITE -360
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE SAND DOLOMITE -
PHOSPHATE DOLOMITE
PHOSPHATE SRNO 0
PHOSPHRTE S flNO 5
PHOSPHATE SAND -
PHOSPHRTE SaRN -380
PHOSPHATE SRNH
PHOSPHRTE SRND
PHOSPHATE SAND
PHOSPHATE SRNO
PHOSPHATE SAND
PHOSPHATE SAN DOLOMITE 0 -3980
UL
PHOSPHATE SAND OLOMITE
SfNO 5 -400
SaND
SRND 0 -LIfl
SAND
SRNo
PHOSPHATE SRND
PHOSPHATE SAND C -410
SAND
SAND
SRNO
OLOMITE CLARY
PHOSPHATE SRND -420
PHOSPHATE SAND
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE --430
PHOSPHRIE
PHOSPHRATE
PHOSPHRIE
PHOSPHATE CLARY
PHSPHRATE CLRY -44L0
PHOSPHATE CLAY
PHOSPHATE CLRY
PNOSPHAI E CLAY
PHOSPHATE CLAY
PHOSPHATE CLR'
PHOSPHRTE SRND
PHOSPHATE
SRNA OQLOMITE CLAT
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
PHOSPHATE DOLOMITE
.PHOSPHRTE DOLOMITE
SAND
SAND


SHNO
SANO
SAND
SAND
SANO
SRNO
SRNO
SRNO
PHOSPHATE
5RNO CLAY
CLAY
CLRY

SANO


ARCADIA FORMATION


TAMPA MEMBER


PHOSPHATE SARN
PHOSPHATE
PHOSPHATE

SRNO
SHAD1


SUWANNEE LIMESTONE


SAND
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHRIE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE


Figure 44. Reference core for the Tampa Member of the Arcadia Formation, R.O.M.P. 7-1, W-15166,

Manatee County (Lithologic legend Appendix A).


SAND

SAND
PHOSPHATE
PHOSPHATE
PHOSPHATE









Lithology


The Tampa Member consists predominantly of limestone with subordinate dolostone, sands, and
clays. The lithology of the Tampa is very similar to the limestone portion of the Arcadia Formation with
the exception of its phosphate content which is almost always noticeably less than in the Arcadia.
Phosphate grains generally are present in the Tampa in amounts less than 3 percent although beds con-
taining greater percentages do occur, particularly near the facies change limits of the member.
Lithologically, the limestones are variably quartz sandy and clayey with minor to no phosphate. Fossil
molds are often present and include mollusks, foraminifera and algae. Colors range from white (N 9) to
yellowish gray (5 Y 8/1). The limestones range from mudstones to packstones but are most often
wackestones. The dolostones are variably quartz sandy and clayey with minor to no phosphate. They are
typically microcrystalline to very fine grained and range in color from pinkish gray (5 YR 8/1) to light olive
gray (5 Y 6/1). The dolostones often contain fossil molds similar to those in the limestones.
Sand and clay beds occur sporadically within the Tampa Member. Lithologically, they are identical to
those described for the Arcadia Formation except for the phosphate content which is significantly lower
in the Tampa Member.
Siliceous beds are often present in the more updip portions of the Tampa. In the type area near Tampa
Bay the unit is well known for silicified corals, siliceous pseudomorphs of many different fossils and chert
boulders.

Subjacent and Suprajacent Units

The Tampa Member overlies the "Suwannee" Limestone in areas where the Nocatee Member is not
present and the Tampa Member forms the base of the Arcadia. The boundary often appears gradational
as discussed by King (1979) and King and Wright (1979). Figure 19 indicates an unconformable time rela-
tionship with the "Suwannee" Limestone which often is not apparent lithologically. This indicates a pro-
bable reworking of underlying materials into the Tampa Member obscuring the unconformity.
The Tampa Member overlies the Nocatee Member in the area where both are present (Figure 33). The
contact appears conformable and is easily recognized. In a few areas where the Nocatee is absent, the
Tampa may overlie undifferentiated Arcadia Formation sediments. The Tampa Member may be both
overlain and underlain by undifferentiated Arcadia.
The Tampa Member is overlain throughout most of its extent by carbonates of the undifferentiated Ar-
cadia Formation. The contact often appears gradational over one or two feet. An increase in phosphate
grain content is the dominant factor in defining the lithologic break. In updip areas the Tampa may be
overlain by siliciclastic sediments of the Peace River Formation. Further updip it may be exposed at the
surface or covered by a thin veneer of unconsolidated sands and clays which may represent residuum of
the Hawthorn sediments. Figure 35 through 39 show the relationship of the Tampa Member to the overly-
ing and underlying units.

Thickness and Areal Extent

The Tampa Member is quite variable in thickness throughout its extent. It thins updip to its northern
limit where it is absent due to erosion and possibly nondeposition. The thickest section of Tampa en-
countered is in W-14882 in Sarasota County where 270 feet (82 meters) of section are assigned to this
member (Figure 45). More typically an average thickness is approximately 100 feet (30.5 meters).
The top of the Tampa Member (Figure 46) ranges in elevation from as high as +75 feet (23 meters)
MSL in northeastern Hillsborough County to -323 feet (-98.5 meters) MSL in northern Sarasota County.
The lowest elevation for the top of the unit occurs in a rather large depression that encompasses part of
northern Sarasota County and southern Manatee County.
The Tampa dips towards the south in the northern half of the area of occurrence (Figure 46). Dip direc-
tion in the southern half is more to the southwest and west. Dip angle varies from place to place but the













































SCALE ., -ou rc-c= LEGEND
0 20 40 MILES CORES
I I I N CUTTINGS
O 20 40 KILOMETERS
S 20 40 KILOMETERS LIMITS OF HAWTHORN GROUP

Figure 45. Top of Tampa Member.



average from highest to lowest point is approximately 8 feet per mile (1.5 meters per kilometer). The dip
appears steeper in the northern and central area (Figure 46).
Figures 45 and 46 show the area of occurrence for the Tampa Member. North of this area, the Tampa
has been removed by erosion and only a few, isolated, erosional remnants are present. In some areas its
absence may be due to nondeposition. East and south of the area of occurrence, the Tampa grades
laterally into the undifferentiated Arcadia Formation. It is important to note that relatively thin beds of
Tampa lithology occur within the Arcadia Formation outside the area in which Tampa is mapped. These
beds often occur sporadically throughout the lower Arcadia but are not thick enough and are too com-
plexly interbedded with Arcadia lithologies to be mapped as Tampa Member. Characteristically, the Tam-
pa is recognized when there are few beds of Arcadia lithologies interbedded with Tampa lithologies and
the sequence of Tampa lithologies is sufficiently thick. Further data may permit more accurate definition
of the limits of the Tampa Member.












































LEGEND

SCALE CI =50 FEET S CORE
0 20 40 MILES CTINGS
I ., I I LA LIMITSOF
0 20 40 KILOMETERS HAWTHORN
GROUP
Figure 46. Isopach of Tampa Member.


Age and Correlation

The Tampa Member is characteristically variably fossiliferous. Mollusks are most common with corals
and foraminifera also present. Despite the presence of these fossils, no age diagnostic species have yet
been recognized.
MacNeil (1944) suggested the correlation of the Tampa with the Paynes Hammock Formation of
Mississippi based on the mollusk fauna present in each. Poag (1972) dated the Paynes Hammock For-
mation using planktic foraminifera and suggested a Late Oligocene age (N2-N3 of Blow, 1969). Hud-
dlestun (personal communication, 1984) indicates that the Tampa Member equates with part of the
Parachucla Formation in Georgia and straddles the boundary between the Oligocene and Miocene.
Hunter (personal communication, 1984) agrees with Huddlestun and correlates the Tampa with part of
the lower Parachucla. Hunter also feels that much of what is incorporated into the Tampa Member in this









paper is older than the original type Tampa (Silex Beds) at Ballast Point and Six Mile Creek. The Tampa
is also correlated with part of the Penney Farms Formation in north Florida (Figure 19).

Discussion

The introduction of the Tampa as a member of the Arcadia Formation represents a status reduction
from formation. The reduction is necessary due to the limited area extent of the Tampa and its inter-
fingering, gradational nature with part of the Arcadia Formation. The historical significance of the Tampa
and its widespread use suggest a retention of the name. This revision of the Tampa hopefully will provide
an understandable, useable unit of local extent and places it within a regional perspective.


NOCATEE MEMBER OF THE ARCADIA FORMATION

Definition and Type Section

The Nocatee Member is a new name introduced here for sediments at the base of the Arcadia Forma-
tion in parts of southwest Florida. Previously, this interval had been informally called the "sand and clay
unit" of the Tampa Limestone by Wilson (1977). This unit is recognized only in the subsurface. The
Nocatee Member is named for the town of Nocatee in central DeSoto County, Florida. The type core is
W-12050, Hogan #1, located in the SE 1/4, NW 1/4, Section 16, Township 38S, Range 26E, with a surface
elevation of 62 feet (19 meters). The type Nocatee occurs between -294 feet (-89.5 meters) MSL and -520
feet (-158.5 meters) MSL (Figure 47). The type core was drilled by the Florida Geological Survey.

Lithology

The Nocatee Member is a complexly interbedded sequence of quartz sands, clays, and carbonates, all
containing variable percentages of phosphate. Figure 47 shows the nature of the Nocatee in W-12050 in
central Desoto County.
The Nocatee is a predominantly siliciclastic unit in the type core (W-12050). This is a noticeable
change from the remainder of the Arcadia Formation including the Tampa Member, which are
predominantly carbonates with variable percentages of included siliciclastics. The quartz sands in the
Nocatee are typically fine to coarse grained, occasionally silty, clayey and calcareous to dolomitic. The
quartz sands range in color from white (N 9) to light olive gray (5 Y 6/1). Phosphate grain content is quite
variable. In the type core, phosphate grain content is generally low (1-3 percent) with scattered beds with
greater concentrations (up to 10 percent). However, in the Nocatee Member in other cores (W-15303, for
example, Figure 48), phosphate grains are more common, averaging about 7-8 percent.
Clay beds are quite common in the Nocatee Member and are variably quartz sandy, silty, phosphatic,
and calcareous to dolomitic. The colors characteristically range from yellowish gray (5 Y 8/1) to light olive
gray (5 Y 6/1) and olive gray (5 Y 4/1). Limited x-ray data suggest that the characteristic clay mineral pre-
sent is smectite, with palygorskite common. Illite and sepiolite are also present. Further analyses are
needed to confirm the identifications and relative abundances of these clay minerals within the Nocatee
Member.
Limestone and dolostone are both present in this member. The ratio of limestone to dolostone is
variable, as can be seen by comparing W-12050 (Figure 47) with W-15303 (Figure 48). The limestones
are generally fine grained, soft to hard, quartz sandy and phosphatic. The percentage of clay present is
quite variable and grades into the clay lithology. Colors of the limestone vary from white (N 9) to yellowish
gray (5 Y 8/1) and light olive gray (5 Y 6/1), generally in response to clay content. The limestones are
usually wackestones with varying degrees of recrystallization and cementation.
The dolostones are quartz sandy, phosphatic, soft to hard, and micro- to very finely crystalline.
Variable amounts of clay are present. Colors range from yellowish gray (5 Y 8/1) to light gray (N 7), light
olive gray (5 Y 6/1) and grayish brown (5 Y 3/2).

























































-30 -



-40 __



-50 _



-60



-70



-80 _



-90 _



-1t8 __



-1108 __



-120 __





-138 __

-LtB __



-150







-170 __



-1801



-190


LAND SURFACE






UNDIFFERENTIATED

} PHOSPHATE
:P.oSI"TE HAWTHORN GROUP
PHOSPHATE
PHOSPHATE
*- PHOSPHATE




PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE

SPHATE
PHOSPHATE
00
7 PHOSPHATE
PHOSPHATE
T- CLAY


P OPCLAY Z

PHOSPHATE CLAY
PHOSPHATE CLAY
P- HOSPHATE CLAY
PHOSPHAIE CLAY
PHOSPHATE CL4Y O
PHOSPHOSPHE CLAY LL
PHOSPHATE
PHOSPHATE C 0
PHOSPHATE A IL

PHOSPHIE
PHOSPHATE
PHOSPHRATE
PHOSPHATE L
PHOSPHATE
PHOSPHATE ,
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
OOLONITTE
SANO
s.. ,
SANO CALCITE
PHOSPHPTE
POSPH.ATE
PHOSPHATE
PHOSPHATE
SRIO CALCITE
PHOSPHATE
SPHOSPHRTE
_I .*.*(_. PHOSPHATE
.% :. I. P.OSPHr.lE
.... .. PHOSPH
--- n TT. ---'f-pn________________


SNAHO
SAND
PHOSPHRTF
PHOSPHATE SRHO
PHOSPHATE SRAO

PHOSPHATE SAND
PHOSPHATE SANO
PHOSPHATE SAND
PHOSPHATE SRAN
PHOSPHATE SAND
PHOSPHATE SRANO
SAND
'a"'
SRHD
SANO
PHOSPHATE SANO
PHOSPHATE S1NO
PHOSPHRTE SfRNO
PHOSPHATE SlNO I
PHOSPHATE CLAY
PHOSPHATE CLRI
PHOSPHRTE CLy I
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHAIT CLAY
PHOSPHATE CLAY
PHOSPHATE SAO I
PHOSPHATE SRO
PHOSPHATE SANO
PHOSPHRTE
PHOSPHATE SANO
PHOSPHATE SRAN
PHOSPHATE SAND
PHOSPHATE SGAD
PHOSPHATE SITD
PHOSPHTE SAND CLAY
PHOSPHRTE SR
PHOSPHATE SRAN
PHOSPHATE CLAY
PHOSPHRTE CLAI
PHOSPHRTE SRNO
PHOSPHRTE SANO
SAND


CLfl
CLAY

-210 SAN



-220 I 1 f

'. D
-2
26H




-2'0 --

SPATE

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PHOSPHATE OOLOHITE
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PHOSPHATE OOLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOMITE
PHOSPHTAE OOLOHITE
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PHOSPHATE SOLOAHTE
PHOSPHATE OOLOAHTE
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PHOSPHSPHATE OOLOHE
PHSSPHRTE OOLOH]TE
PHOSPHRTE OOLOHITE
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PHOSPHATE
PHOSPHATE


"SUWANNEE" LIMESTONE


Figure 47. Type core for the Nocatee Member of the Arcadia

Formation, Hogan #1, W-12050, DeSoto

County (Lithologic legend Appendix A).


-12050


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LAND SURFACE


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PSPHRTE ARCADIA
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PHOSPHATE CLAY
PHOSPHATE CLAY
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PHOSPHRTE CLRA
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PHOSPHATE SOLOHISTE
PHOSPHATE NOL DOLOITE
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PHOSPHRTE SRNO OOLOM1TE
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PHOSPHATE CLAY
PHOSPHATE SAND
PHOSPHATE SAND
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PHOSPHfTE DOLOMITE CLAY
PHOSPHRTE SRNO
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PHOSPHAIE SANS
PHOSPHATE SANS
PHSPHARTE SRND
PHOSPHATE SAND
PHOSPHATE SRNS
PHOSPHARIE IRN
PHOSPHRTE SUNO
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SAND


..... .....
PHOSPUHAI SUNO CLAU HAWTHORN GROUP
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PHOSPHATE
PHOSPHATE
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PHOSPHATE SRUO RIER


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PHOSPHATE SANS
PHOSPHATE SANO
PHOSPHATE SAND CLRY
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SPHOSPHRTE CLAY 507
-310 __ PHOSPHATE CLRAY ,
S PHOSPHATE SRHO CRLCIIE .- I-
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Figure 48. Reference core for the Nocatee Member of the Arcadia Formation, R.O.M.P. 17, W-15303,

DeSoto County (Lithologic legend Appendix A).


75


J


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-150



-160


-170__



-180 _


-190 -



-200 _


-210 _


-220



-230


-2t0


-250


-260



-270 _


-320


-330


-340


-350


-360


-370


-380


-390


-400


-410


-420



-430


-440


-450.


-460



-470


-490



-490



-500


-510


-520


-530


-50 .


-550


-560


-570


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-590


-600 -


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SUNO

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SANO
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SAND


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PHOSPHArE 15303
PHOSPHATE SANO CLAY
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PH SPHRTE CLRY
PHOSPHART CLRY
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PHOSPHATE SANL CALCITE
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PHOSPHRTE
PHOSPHATE SRNO DOLOMTE
PHOSPHRTE SRNO
PHOSPHA TE
PUNOSPHRIE SRNO
PHOSPHATE SRNO
PHOSPHRIE
PHOSPHRIE
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PHOSPH RTE SN
PHOSPHATE ODLOUITS
PHNSPUDTS oLUO.S! ARCADIA FORMATION
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PHOSPHATE
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SAND
SANS

SAUN SUWANNEE LIMESTONE


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I


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I


PHOSPHATE
PHOSPHATE
PHOSPHATE
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PHOSPHATE
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PHOSPHATE SRNS
PHOSPHRTE SRAND
SANS
SRND
PHOSPHATE SRND
PHOSPHATE
PHOSPHA E
PHOSPHATE
POSPHAE TAMPA MEMBER
PHOSPHATE SUNS
PHOSPHATE SRNO
PHSPHRATE SAND

PHOSPHA TEPAN
PHOSPHATE
PHOSPHRATE
PHOSPHATE
PHOSPHRATE
PHOSPHATE
PH SPHRITE
PHOSPHITE
PHOPHRTEA
PHONPHRAE
PHOSPHATE
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PHOSPHRTE
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P USS PUU S















P USN PUU A


-










Fossils are often present in the Nocatee, most often as molds. However, in some of the clay beds
diatoms are present but have not been identified. Fossils present include mollusks, algae, foraminifera
and corals.

Subjacent and Suprajacent Units

The Nocatee Member overlies limestones currently assigned to the "Suwannee" Limestone. The con-
tact between the units often appears gradational from the basal, quartz-sandy, phosphatic, occasionally
clayey carbonates of the Nocatee into the slightly quartz sandy, non-phosphatic limestones of the
"Suwannee" (Figures 47 and 48). Occasionally, the basal Nocatee is a siliciclastic unit and it is easily dif-
ferentiated from the limestones of the "Suwannee." The contact is suggested to be a disconformity bas-
ed on paleontology (Huddlestun, personal communication, 1984).
The Tampa Member overlies the Nocatee throughout much of the area. The top of the Nocatee is
generally placed at the top of the siliciclastic section below the Tampa (as in W-12050, Figure 47).
However, occasionally there is a carbonate bed at the top of the Nocatee which contains too much
phosphate to be included in the Tampa. This bed is taken as the top of the Nocatee Member. Occasional-
ly, the Nocatee is overlain by carbonates of the undifferentiated Arcadia Formation. The relationships of
the Nocatee with the subjacent and suprajacent units are shown in Figures 36, 37, and 39.

Thickness and Areal Extent

The Nocatee Member ranges in thickness up to 226 feet (70 meters) in W-12050 DeSoto County
(Figure 49). Other cores in Charlotte County stopped in the Nocatee, in areas where it may be thicker.
Further coring or properly sampled cuttings are needed to delinate the thickness and, possibly, the ex-
tent of the Nocatee in this area.
The top of the Nocatee ranges in depth from -81 feet (-24.5 meters) MSL in Polk County to -639 feet
(-195 meters) MSL in Charlotte County (Figure 50). In general the upper surface dips to the south and
southeast at an average of 7.5 feet per mile (1.7 meters per kilometer).
The Nocatee Member is of rather limited areal extent as is the Tampa Member. It has been identified in
parts of Polk, Hardee, DeSoto, Charlotte, Manatee, Hillsborough, Sarasota, and possibly Highlands
Counties. The lateral limits of this unit in most cases are the result of facies changes (Figures 49 and 50).
In portions of the updip area, the Nocatee may be represented by a clay unit present in the Tampa, as
discussed by Gilboy (1983). The extent of the Nocatee to the south and east is questionable at this time
due to a lack of subsurface data (Figures 49 and 50).

Age and Correlation

The age of the Nocatee Member is based completely on its subjacent positioning to the Tampa
Member and its suprajacent position to the "Suwannee" Limestone of south Florida. It is older than part
of the Tampa Member, equivalent to part of the Tampa, and younger than the underlying Oligocene car-
bonates. This suggests an earliest Miocene age for the unit. At the present time there have been no at-
tempts to date the unit paleontologically.
The Nocatee grades laterally westward and southward into very quartz-sandy, phosphatic carbonates
of the undifferentiated Arcadia Formation. Eastward the unit grades into a more siliciclastic-rich east
coast faces of the undifferentiated Arcadia. Northward, it appears that the Nocatee grades into the basal
Tampa Member. The Nocatee correlates with the lower part of the type Tampa Member. It is also cor-
relative with part of the lower Penney Farms Formation of north Florida and the lower Parachucla of
southeast Georgia (Figure 19).





























































PALM BEACH
U


S -N-



SCALE I


20 40


Cl 25 FEET


40 MILES

KILOMETERS
KILOMETERS


LEGEND
CORES
CUTTINGS
.J%, LIMITS OF HAWTHORN GROUP


Figure 49. Isopach of Nocatee Member.


0


0
0











--4


PA SCO -1, I



L LS BROGH E LA


S. P 0 L K BREVARD

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Cl = 25 FEET
SCALE B E COE
0 20 40 MILES 0 CUTTINGS

0 20 40 KILOMETERS LIMITS OF HAWTHORN GROUP













Figure 50. Top of Nocatee Member.










Discussion


The sediments of the Nocatee Member have been recognized for some time. The name "Tampa sand
and clay unit" represents the first published name applied to these sediments (Wilson, 1977). Although
these sediments are of limited areal extent, their distinctive lithology suggests the formal recognition of
these sediments as a member of the Arcadia Formation. Outside the recognized area of occurrence
equivalent carbonate sediments of the Arcadia Formation are often very sandy and may contain thin clay
beds. The equivalence of the two units is recognized by the stratigraphic position.

PEACE RIVER FORMATION

Definition and Type Section

The Peace River Formation is a new formational rank name proposed for the combined upper
Hawthorn siliciclastic strata and the Bone Valley Formation. The upper Hawthorn siliciclastic strata in-
clude siliciclastic beds previously placed in the Tamiami Formation (Parker, 1951) and the Murdock Sta-
tion and Bayshore Clay members of the Tamiami Formation (Hunter, 1968). The formation is named for
the Peace River which occurs in the vicinity of the type section in core W-12050.
The type section for the Peace River Formation is designated as core W-12050, Hogan #1, located in
east central DeSoto County, Florida (SE 1/4, NW 1/4 Section 16, Township 38S, Range 26E) with a surface
elevation of 62 feet (19 meters). The type Peace River Formation occurs between +41 feet (+12.5
meters) MSL and -97 feet (-29.5 meters) MSL (Figure 51).
W-15303, R.O.M.P. #17, is suggested as a reference section (Figure 48). R.O.M.P. #17 is located west
of W-12050 in the west central part of DeSoto County (NE 1/4, NE 1/4 Section 14, Township 38S, Range
23E, surface elevation 22 feet (6.5 meters)). The Peace River Formation occurs between -3 feet (-1 meter)
MSL and -77 feet (-23.5 meters) MSL in W-15303.


Lithology

The Peace River Formation consists of interbedded quartz sands, clays and carbonates. The
siliciclastic component predominates and is the distinguishing lithologic feature of the unit. Typically the
siliciclastics comprise two-thirds or more of the formation.
The quartz sands are characteristically clayey, calcareous to dolomitic, phosphatic, very fine to
medium grained, and poorly consolidated. Their color ranges from light gray (N 7) and yellowish gray (5 Y
8/1) to olive gray (5 Y 4/1). The phosphate content of the sands is highly variable. In the type section
(W-12050), the phosphate content is lowest in the upper part of the section and greatest near the base.
The same is true for the reference section in W-15303. The phosphate occurs both as sand- and gravel-
sized particles. The gravels are most abundant in the Bone Valley Member, although they may occur
elsewhere in the unit.
Clay beds are quite common in the Peace River Formation. The clays are quartz sandy, silty,
calcareous to dolomitic, phosphatic, and poorly to moderately indurated. Color ranges from yellowish
gray (5 Y 8/1) to olive gray (5 Y 4/1). Reynolds (1962) characterized the clay minerals as consisting of
smectite (montmorillonite), palygorskite (attapulgite) and sepiolite. Strom (personal communication,
1984) and Barwood (personal communication, 1984) agree that smectite and palygorskite are the domi-
nant clay minerals in the formation.
Carbonates occur throughout the Peace River Formation. Characteristically they comprise less than
33 percent of the Peace River section. The carbonates may be either limestone or dolostone. Updip
(northward), dolostone occurs more frequently. The limestones are characteristically variably sandy,
clayey and phosphatic, poorly to well indurated, mudstones to wackestones. They vary in color from
yellowish gray (5 Y 8/1) to white (N 9). Dolostones are micro- to very finely crystalline, variably sandy,
clayey and phosphatic, and poorly to well indurated. Colors range from light gray (N 7) to yellowish gray








































-------
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-320 _



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-370 -



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-400 __



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Figure 51. Type core of the Peace River Formation, Hogan #1,


W-12050, DeSoto County (Lithologic

legend Appendix A).


















80


W-12050


-50



-60 _



-70 _



-80 __



-90



-100 _




-L10 _



-120



-130








-150



-160 _



-170 __



-180



-190 _


-200 __



-210



-220



-230








-250



-260



-270


PHOSPHATE
SAIN DOLOMITE
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CLAY 1

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PHOSPHATE SANO
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PHOSPHATE
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DOLONITEITE






PSPATCL E L TE





PH0SPHATE OOLOATTE

PHOSPHATE OOLOHTE
PHOISPHATE DOLOMTE
PHOSPHATE OOLOAYTE
HOSPHATE OLOHE


HOSPHATE DOLOHTE
PHOSPHATE OLOH E




PHOSPH TE 0LOM E
PHOSPHATE OOLOMTE




PHOSPHATE DOLOHMTE
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PHOSPHATE
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---
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----

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(5 Y 8/1). Mollusk molds are common throughout the carbonates. Occasionally dolomite occurs as a
dolosilt (composed of unconsolidated, silt-sized dolomite rhombs). The dolosilts contain variable
amounts of clay, are generally only slightly sandy and phosphatic, and do not contain fossil molds or
fragments.
Chert occurs sporadically in the Peace River Formation. Characteristically it appears to be a replace-
ment of the carbonates although silicified clays do occur. The cherts are opaline and are suggestive of
localized "alkaline lake" deposition, as described by Upchurch, Strom and Nuckels (1982) and Strom
and Upchurch (1983).

Subjacent and Suprajacent Units

The Peace River Formation disconformably overlies the Arcadia Formation throughout its extent. The
contact often appears unconformable updip and conformable gradationall) downdip (Figure 35 through
40). The gradational appearance is due to the repetition of similar lithologies in both formations. When
the boundary appears gradational the base of the Peace River Formation is placed where the carbonates
become dominant over the siliciclastic beds (Figures 48 and 51). As was previously mentioned in the
discussion of the Arcadia Formation, the contact may also be marked by a rubble zone.
The sediments overlying the Peace River Formation are assigned to several formations. In the south
Florida area and the southern part of east central Florida, the limestone and sand facies of the Tamiami
Formation unconformably overlie the Peace River. Sediments disconformably suprajacent to the Peace
River Formation in the west central Florida area (Polk, Hillsborough, Manatee, Sarasota, and Charlotte
Counties) and parts of east central Florida are generally unnamed, nonphosphatic sands (often surficial)
and unnamed fossiliferous sands and shell beds. The contact with the surficial sands is often obscure
due to leaching of the phosphate and clays in the upper portion of the Peace River Formation. In the
central and south central section, unfossiliferous non-phosphatic to very slightly phosphatic sands
overlie the Peace River. These sands have been called "Citronelle" Formation (Cooke and Mossom,
1929; Cooke, 1945) and "Fort Preston" Formation (Puri and Vernon, 1964). In Georgia, these sands are
currently assigned to the Cypresshead Formation by Huddlestun (personal communication, 1984). These
sediments are assigned here, for convenience, to the post-Hawthorn sediments.
Problems in identifying the upper limits of the Peace River arise in areas of extensive reworking of the
sediments. In such a case the sediment may be completely reworked and the resultant lithology only
slightly different than the unreworked sediments. When this occurs minor changes in lithology such as
an increase in shell material, change in clay mineralogy, or change in sorting provide the necessary
lithologic criteria for separating the units.

Thickness and Areal Extent

Sediments assigned to the Peace River Formation occur over much of the southern half of the Florida
peninsula. The top of the unit ranges from a maximum known elevation of + 175 feet (+53 meters) MSL
in Polk County to greater than -150 feet (-46 meters) MSL in part of Collier, Dade, Broward, and Palm
Beach Counties (Figure 52). The thickness of this unit varies to more than 650 feet (198 meters) in parts
of Martin and Palm Beach Counties (Figure 53). This thickness, which is taken from several sets of cut-
tings in the area, seems anomalously thick. Thicknesses of 400 feet (122 meters) or greater occur in
eastern Glades County along the western edge of Lake Okeechobee (Figure 53).
Although the Peace River Formation occurs over most of the southern portion of the state, it is absent
from the Ocala Platform and the Sanford High (Figures 4, 52 and 53). It is also absent, possibly due to
erosion, from portions of Hillsborough, Pinellas, Manatee and Sarasota Counties (Figures 52 and 53). It
dips east, south and west off the southern nose of the Ocala Platform (an area referred to as the Central
Florida Platform by Hall [1983]). South of this area, the dip is primarily south and southeast at approx-
imately 8 feet per mile (1.3 meters per kilometer) (Figure 52). Local variations of dip direction and degree
are common.






















































































Figure 52. To
ind


I


IYAI E A










IS
O L E 0 EE E HO









O GOUP U' i S FI ET A D E




AE -- TE AGH IN0
C TI 1 __ __/--- __ I I /I \ MART IN



CH LIIT OT A AO -
























-------
IH E N




-ep























p of Peaoe River Formation. Shaded area a" i "l. "l
SCALE

CORE o,. L | BR 0 W P
CUTTINGS uip0
LIMITS OF HAWTHORN GROUP
HAWTHORN GROUP UNDIFFERENTIATED---
PEACE RIVER FORMATION ABSENT


D D E








\. -



p of Peace River Formation. Shaded area
icates undifferentiated Hawthorn Group.




Full Text

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STATEOFFLORIDA DEPARTMENTOFNATURAL RESOURCES.Tom Gardner,Executive Director DIVISION OF RESOURCE MANAGEMENTJeremyA.Craft,Director FLORIDA GEOLOGICAL SURVEYWalter Schmidt,State GeologistBULLETIN NO. 59THE LITHOSTRATIGRAPHYOFTHE HAWTHORN GROUP (MIOCENE) OF FLORIDABy ThomasM.Scott Published for theFLORIDA GEOLOGICAL SURVEYTALLAHASSEE 1988 unIVERSITY OFFLORIDAL1B.RARIES

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Jim Smith Secretary of State Bill Gunter. TreasurerDEPARTMENTOFNATURAL RESOURCES DEPARTMENTOFNATURAL RESOURCESBOB MARTINEZ Governor Bob Butterworth Attorney General Gerald Lewis Comptroller Betty Castor Commissioner of Education Tom Gardner ExecutiveDirector ii Doyle Conner Commissioner of Agriculture

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LETTER OF TRANSMITTAL Bureau of Geology August 1988 Governor Bob Martinez, Chairman Florida Departmentof Natural Resources Tallahassee, Florida 32301 Dear Governor Martinez:TheFlorida Geological Survey, BureauofGeology, Division of Resource Management, DepartmentofNatural Resources, is publishing as its Bulletin No.59,TheLithostratigraphyofthe Hawthorn Group (Miocene)ofFlorida. This is the culmination of a study of the Hawthorn sediments which exist throughout muchofFlorida. The Hawthorn Group is of great importance to the state since it constitutes the confining unit over the Floridan aquifer system. It is also of economic importance to the state due to its inclusionofmajor phosphorite deposits. This publication will be an important reference for future geological in vestigations in Florida. Respectfully yours, Walter Schmidt, Chief Florida Geological Survey iii

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Printed for the Florida Geological Survey Tallahassee 1988 ISSN 0271-7832 iv

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TABLE OF CONTENTSPage Abstract xii Acknowledgements xiv Introduction 1 Purpose and Scope 1 Method of Investigation 5 Previous Investigations 5 Geologic Structure11Introduction to Lithostratigraphy 13 Hawthorn Formation to Group Status: Justification, recognition and subdivisioninFlorida 13 Present Occurrence : ..15 North Florida 15 Introduction.1-5 Penney Farms Formation 18 Definition and type locality18Lithology21Subjacent and suprajacent units 24 Thickness and areal extent 24 Age and correlation 30 Discussion 34 Marks Head Formation 34 Definition and reference section 34 Lithology 34 Subjacent and suprajacent units 37 Thickness and areal extent 39 Age and correlation 39 Discussion41Coosawhatchie Formation41Definition and reference section41Lithology41Subjacent and suprajacent units 43 Thickness and areal extent 43 Age and correlation 43 Discussion 46 Charlton Member of the Coosawhatchie Formation.46Definition and reference section ; 46Lithology 46 Subjacent and suprajacent units 46 Thickness and areal extent 46 Age and correlation 48 Discussion49Statenville Formation 50 Definition and type locality 50 Lithology 50 Subjacent and suprajacent units 52 Thickness and areal extent 53 Age and correlation 53v

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Discussion54Alachua Formation 54 South Florida56Arcadia Formation56Definition and type section56Lithology56. Subjacent and suprajacent units58Thickness and areal extent60Age and correlation65Discussion65Tampa Memberofthe Arcadia Formation 65Definition and type section65Lithology70Subjacent and suprajacent units70Thickness and areal extent70Age and correlation72Discussion73Nocatee Member of the Arcadia Formation73Definition and type section73Lithology73Subjacent and suprajacent units76Thickness and areal extent76Age and correlation76Discussion79Peace River Formation79Definition and type section79Lithology79Subjacent and suprajacent units81Thickness and areal extent81Age and correlation84Discussion '84Bone Valley Member of the Peace River Formation86Definition and type locality _ 86Lithology87Subjacent and suprajacent units88Thickness and areal extent88Age and correlation88Discussion90Eastern Florida Panhandle91Torreya Formation91Definition and type section91Lithology91Subjacent and suprajacent units96Thickness and areal extent100Age and correlation100Discussion100Dogtown Member of the Torreya Formation100Definition and type locality100Lithology100Subjacent and suprajacent units101Thickness and areal extent101vi

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Age101Discussion101Sopchoppy Member of the Torreya Formation101Definition and type locality101Lithology102Subjacent and suprajacent units102Thickness and areal extent102Age and correlation-.102Discussion102Hawthorn Group Mineralogy102Phosphate103Occurrence in the Hawthorn Group103Phosphate Genesis103Post-depositional modification107Hard rock phosphate deposits108Palygorskite and Sepiolite108Dolomite11 P Geologic History111Paleoenvironments118Hawthorn Group Gamma Ray Log Interpretation1,23North Florida123South Florida123Eastern Panhandle130Summary130Conclusions138References139 APPENDIXAppendixA.Lithologic legend for stratigraphic columns ,148 FIGURESFigure 1 Study area and areas of discussion 22Location of cores33Cross section location map :4 4Structures affecting the Hawthorn Group12 5Statewide map of the elevation of the upper Hawthorn Group surface16 6Statewide isopach map of the Hawthorn Group ''.-17vii

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7 Lithostratigraphic units of the Hawthorn Groupinnorth Florida 19 8 Geologic map of the pre-Hawthorn Group surface 20 9 Type section of the Penney Farms Formation, Harris #1, W-13769, Clay County (Lithologic legend AppendixA)22 10 Intraclasts with phosphatic rims from Penney Farms Formation, St. Johns County, W-13844 2311Cross section A-A' (see figure 3 for location) (See Scott (1983) for discussion of faults) 25 12 Cross section B-B' (see figure 3 for location) (See Scott (1983) for discussion of faults) 26 13 Cross section C-C' (see figure 3 for location) (See Scott (1983) for discussion of faults) 27 14 Cross section0-0'(see figure 3 for location) (See Scott (1983) for offaults) 28 15 Cross section E-E' (see figure 3 for location) (See Scott (1983) for discussionoffaults) 29 16 Cross section F-F' (see figure 3 for location) (See Scott (1983) for discussion of faults) 30 17 Top of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group3118 Isopach of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group 32 19 Formational correlations (modified from unpublished C.O.S.U.N.A. Chart, 1985) 33 20 Reference section for the Marks Head Formation, Jennings#1,W-14219, Clay County (Lithologic legend AppendixA)3521Reference section for the Marks Head Formation, N.L.#1,W-12360, Bradford County (Lithologic legend AppendixA)36 22 Top of the Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group 38 23 Isopach of Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group 40 24 Reference section for the Coosawhatchie Formation, Harris #1, W-13769, Clay County (Lithologic legend AppendixA)42 25 Top of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group 44 26 Isopach of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group 45 27 Reference core for the Charlton Member of the Coosawhatchie Formation, Cassidy #1, Nassau County (Lithologic legend AppendixA)47 28 Top of the Charlton Member (dashed line indicates extent of Charlton) 48 29 Isopach of the Charlton Member (dashed line indicates extent of Charlton) 49 30 Reference core for the Statenville Formation, W-15121, Betty #1, Hamilton County (Lithologic legend AppendixA)51viii

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31Photograph of-Statenville Formation outcrops showing distinct cross bedding 52 32 Area of occurrence of the Statenville Formation 53 33 Lithostratigraphic units of the Hawthorn Group in southern Florida 55 34 Type core for the Arcadia Formation, Hogan #1, W-12050, DeSoto County (Lithologic legend AppendixA)57 35 Cross section G-G' (see figure 3 for location) 59 36 Cross section H-H' (see figure 3 for location) 60 37 Cross section I-I' (see figure 3 for location)6138 Cross sectionJ-J'(see figure 3 for location) 62 39 Cross section K-K' (see figure 3 for location) : 63 40 Cross section L-L' (see figure 3 for location) 6441Top of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group 66 42 Isopach of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group 67 43 Reference core for the Tampa Member of the Arcadia Formation, Ballast Point#1, W-11541, Hillsborough County (Lithologic legend AppendiXA)68 44 Reference core for the Tampa Member of the Arcadia Formation, R.O.M.P. 7-1, W-15166, Manatee County (Lithologic legend AppendixA)69 45 Top of Tampa Member7146 Isopach of Tampa Member 72 47 Type core for the Nocatee Member of the Arcadia Formation, Hogan #1, W-12050, DeSoto County (Lithologic legend AppendiXA)74 48 Reference core for the Nocatee Member of the Arcadia Formation, R.O.M.P. 17, W-15303, DeSoto County (Lithologic legend AppendixA)7549 Isopach of Nocatee Member.7750 Top of Nocatee Member. 7851Type core of the Peace River Formation, Iilogan #1,W-12050, DeSoto County (Lithologic legend AppendixA)80 52 Top of Peace River Formation. Shaded area indicates undifferentiated Hawthorn Group 82 53 Isopach of Peace River Formation. Shaded area indicates undifferentiated Hawthorn Group.....83 54 Reference core for the Bone Valley Member of Peace River Formation, Griffin #2, W-8879, Polk County (Lithologic legend AppendixA)8555 Schematic diagram showing relationship of lithostratigraphic unitsinsouthern Florida 86ix

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56 Top of Bone Valley Member 89 57 Isopach of Bone Valley Member 90 58 Lithostratigraphic units of the Hawthorn Groupinthe eastern Florida panhandle 92 59 Reference core for the Torreya Formation, Rock Bluff#1,W-6611, Liberty County (lithologic legend AppendixA)93 60 Reference core for the Torreya Formation, Owenby#1,W-7472, Gadsden County (Lithologic legend AppendixA)9461Reference core for the Torreya Formation, Goode#1,W-6998, Leon County (Lithologic legend AppendixA)95 62 Cross section M-M' (see figure 3 for location) 97 63 Isopach of the Torreya Formation 98 64 Top of the Torreya Formation 99 65 Location of phosphate depositsinFlorida 104 66 Structural features of the southeast United States (after Riggs, 1979) 106 67 Lithostratigraphic unitsinrelation to proposed sea level fluctuations (after Vail and Mitchum, 1979) 11368Cross section showing reconstructed stratigraphic sequence at the end of Late Oligocene....11569Cross section showing reconstructed stratigraphic sequence at the end of the Early Miocene 116 70 Cross section showing reconstructed stratigraphic sequence at the end of Middle Miocene....11771Cross section showing reconstructed stratigraphic sequenceatthe end of the Early Pliocene 119 72 Cross section showing stratigraphic sequence occurringatpresent 120 73 Relation of Mammal ages to planktonic foraminifera time scale (after Webb and Crissinger, 1983) 122 74 Gamma-ray log, Jennings#1,W-14219, Clay County 12475Gamma-ray log, R.O.M.P.17,W-15303, DeSoto County 125 76 Gamma-ray log, R.O.M.P. 45-2, Polk County 126 77 Gamma-ray log, Osceola#7,W-13534, Osceola County 12778Gamma-ray log, Phred#1,W-13958, Indian River County 128 79 Gamma-ray log, Cape Coral#1,W-15487, Lee County 129 80 Gamma-ray log, Owenby#1,W-7472, Gadsden County131x

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81Gamma-ray log, Howard#1,W-15515, Madison County 132TABLE1 Nomenclatural changes that have occurredinrelation to the Hawthorn Group 6 xi

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ABSTRACTThe Hawthorn Formation has been a problematic unit for geologists since its inception by Dall and Har ris (1892). It is a complex unit consisting of interbedded and intermixed carbonate and siliciclastic sediments containing varying percentages of phosphate grains. These sediments have been widely studied by geologists due to their economic and hydrologic importanceinthe southeastern United States. Economically, the Hawthorn sediments contain vast quantities of phosphate and clay and limited amounts of uranium. Hydrologically, the Hawthorn contains secondary artesian aquifers,providesanaquiclude for the Floridan aquifer system and,insome ares, makes up the upper portion of the Floridan aquifer system. The Hawthorn Formation of previous investigators has been raised to group status in Georgia by Hud dlestun (in press). The present investigation extends the formations recognizedinsouthern Georgia into northern Florida with some modifications, and accepts Huddlestun's concept of the Hawthorn Group. / The Hawthorn Group and its component formationsin Florida represent a new nomenclature applied to these sediments. The elevation of the Hawthorn to group status InFlorida ISjustified by the Hawthorn's complex nature and the presence of areally extensive, mappable lithologic units. The Hawthorn Group in northern peninsular Florida consists of,inascending order, the Penney Farms Formation, the Marks Head Formation and the Coosawhatchie Formation. The Coosawhatchie Forma tion grades laterally and,ina limited area, upwards into the Statenville Formation. Lithologically, the Hawthorn Group in northern Florida is made up of a basal carbonate with interbedd ed siliciclastics (Penney Farms), a complexly interbedded siliciclastic-carbonate sequence (Marks Head), a siliciclastic unit with varying percentages of carbonateinboth the matrix and individual beds (CoosaWhatchie) and a crossbedded, predominantly siliciclastic unit (Statenville). Phosphate grains are present throughout these sediments,varyinginpercentage up to 50 percent of the rock. Sediments of the Hawthorn Groupinnorthern peninsular Florida rangeinage from Early Miocene (Aquitanian) to Middle Miocene (Serravalian). This represents a significant extension of the previously accepted Middle Miocene age.Insouthern Florida, the group includes two formations,inascending order,the Arcadia Formation and the Peace River Formation. The Tampa Formation or Limestone of former usage is included as a lower member of the Arcadia Formation due to the Tampa's limited areal extent, lithologic similarities, and lateral relationship with the undifferentiated Arcadia. Similarly, the Bone Valley Formation of former usage is incorporatedasa memberinthe Peace River Formation. Lithologically, the Arcadia Formation is composed of carbonate with varying amounts of included and interbedded siliciclastics. Siliciclastic sedimentsinthe Arcadia are most prevalantinits basal Nocatee Member. The Peace River Formation is predominantly a siliciclastic unit with some interbedded car bonates. Phosphorite gravel is most commoninthe Bone Valley Member. Sand-sized phosphate grains are virtually ubiquitous in the southern Florida sediments with the exception of the Tampa Member where it is often absent. The southern Florida Hawthorn sediments rangeinage from Early Miocene (Aquitanian) to Early Pliocene (Zanclian). The Hawthorn Groupinthe eastern Florida panhandle is composed of the Torreya Formation and,ina few areas, a Middle(?)Miocene unnamed siliciclastic unit. Lithologically, the Torreya consists of a carbonate-rich basal section with interbedded clays and sands, and a dominantly siliciclastic, often massive, plastic clayey upper unit (Dogtown Member). Phosphate grains are noticeably less commoninthe Hawthorn of the panhandle. Hawthorn Group sediments are characterized by the occurrence ofanunusual suite of minerals. Apatite (phosphate grains) is virtually ubiquitousinthe peninsular Hawthorn sediments. Palygorskite, sepiolite and dolomite occur throughout the group statewide. Miocene sea level fluctuations were the primary controlling factor determining the extent of Hawthorn depositioninFlorida. During the maximum Miocene transgression, sediments of the Hawthorn Group xii

PAGE 17

were probably deposited over the entire Florida platform. Hawthorn sediments were subsequently removed from the crest of the Ocala Platform (Ocala Uplift) and the Sanford High by erosion. The Hawthorn Group appears to have been deposited under shallow marine conditions. These condi tions are suggested by the occurrence of molds of shallow water mollusks and a limited benthic foraminifera fauna. The deepest water conditions apparently existedinthe Jacksonville and Okeechobee Basins. The gamma-ray signature of the Hawthorn Group is quite distinctive, providing a useful tool for iden tification and correlationinareas of limited data. The Hawthorn signature consists of distinctly different patternsinnorthern and southern peninsular and eastern panhandle Florida. xiii

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ACKNOWLEDGEMENTSThe author wishes to acknowledge the assistance of many individuals during the course of this study. The assistance of these individuals was invaluableinthe successful completion of this investigation. The author thanks C.W."Bud"Hendry, Jr., former State Geologist of Florida, and Steve Windham, former Bureau Chief of the Florida Bureau of Geology for allowing the author to attend Florida State University under the state's job related courses program. Discussions and support from the staff of the Florida Geological Survey were greatly appreciated. Of particular assistance wereKenCampbell, Paulette Bond and Walt Schmidt, State Geologist. Justin Hodges, former.driller for the Florida Geological Survey, was invaluable to this study. Mr. Hodges' expertise was responsible for the recovery of excellent quality cores, many of which were usedinthis research. Draftsmen Jim Jones and Ted Kiper spent many hours laboring over the figures for the text. Thanks are due to a number of individuals around thestate for their help during this project. These in clude: Jim Lavender, Tony Gilboy, Jim Clayton, John Decker, Greg Henderson and Kim Preedom of the Southwest Florida Water Management District who provided cores and geophysical data; Mike"50-50"Knapp from the South Florida Water Management District; Drs. Sam Upchurch and Richard Strom of the University of South Florida; and to Tom Missimer of Missimer and Associates. Special thanks are due toDr.Paul Huddlestun of the Georgia Geologic Survey for many hours of discussion and data sharing. Muriel Hunter also shared freely her knowledge of Florida stratigraphy. The authorisvery appreciative of the very competent assistance of Cindy Collier, secretary from the Geological Investigations Section of the Florida Geological Survey. The final form of this manuscript would have been significantly more difficult to achieve without her assistance. The author greatly appreciates the guidanceandassistance of his faculty committee, Drs. Sherwood Wise (Chairman), William Parker, J.K. Osmond, Steve Winters, and William Burnett. Their time and effort assisted inanimproved final draft. The author also appreciates the many hours of discussion and the assistance provided by formerFSUgraduate students and Florida Geological Survey graduate assistants Andy LeRoy and Barry Reik. Reviews of this manuscript by a number of geologists aided the authorinpresenting this studyina more concise manner. This author greatly appreciates the efforts of the following reviewers: Walt Schmidt, Bill Yon,KenCampbell,EdLane, Jackie Lloyd, Paulette Bond and Alison Lewis of the Florida Geological Survey;Drs.Wise, Parker, Osmond, Winters, and Burnett of Florida State University;Dr.Sam Upchurch of the University of South Florida; andMs.Muriel Hunter, independent geologist. Finally, and most importantly, are the thanks due to my family for their support during this endeavor.I My wife of 17 years has lived with this research for more than one third of our married life. This research would not have been completed without her support. xiv

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THE LITHOSTRATIGRAPHY OF THE HAWTHORN GROUP (MIOCENE) OF FLORIDAByThomasM.ScottINTRODUCTION Thelate Tertiary (Miocene-Pliocene) stratigraphy ofthe southeastern Coastal Plain provides geologists with many interesting and challenging problems. Much of the interest has been generated by the occurrence of scattered phosphorite from North Carolina to Florida. The existence of phosphate in the late Tertiary rocks of Florida was recognized in the late 1800's and providedanimpetus to investigate these sediments. More recently, the hydrologicimportance of these units has led to further investigations ofthe stratigraphy and lithology to determine their effectivenessasanaquiclude, aquitard and aquifer. The Hawthorn Formation in Florida has long been a problematic unit. Geologists often disagree about the boundaries ofthe formation. The resulting inconsistencies have rendered accurate correlationbetween authors virtually impossible. The biggest problem hindering the investigation of the Hawthorn strata has been a paucity of quality subsurface data. Since the mid-1960's, the Florida Geological Survey has been gathering core data from much ofthe state, proViding a unique opportunity to investigate the extent of, and facies relationships in theHawthornofthe subsurface. This investigation isanattempt to provideanunderstanding of the Hawthorn Group, its lithologies, stratigraphy and relation to subjacent and suprajacent units. A greater understanding of the Hawthorn is imperative to deciphering the late Tertiary geologichistory of Florida.PURPOSE AND SCOPEThe purpose of this investigation is to provide a coherent lithostratigraphic framework facilitating a bet ter understanding ofthe Hawthorn Group in Florida. The internal framework of the Hawthorn, its lateral continuity, and relation to subjacent and suprajacent units were investigated in order to provide this knowledge. The area covered by this study extends from the Apalachicola River in the Florida Panhandleonthe west to the Atlantic Coastonthe east and from the Georgia-Florida borderonthe north, south to the Florida Keys (Figure1).The study area encompasses all or portions of 56 counties. Data points outside the study area, particularly in Georgia, were used to assist in providing a more accurate picture within the study area boundaries. The study area boundaries were chosen based on several criteria.Inthe past, the western limits of the Hawthorn were drawn at the Apalachicola River. The western boundary was chosen both to coincide with the historical boundary and to avoid overlap with the investigation of equivalent sedimentsinthe Apalachicola Embayment by Schmidt (1984). More than 100 cores provided the data base for the present study. The locations of cored data points are shownonFigure2.Figure 3 delineates cross section transects.1

PAGE 20

AREANOTINCLUDEDINSTUDYo2550MILESIIIo4080KILOMETERSSCALEFigure1.Study area and areas of discussion.2

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1375113744 1376514871FGS "W" NUMBERLocation of cores,SCALE14882 '--Figure2. '\.. •3.. _----\\.C )-----.------T-----,1551515537 15728 . :13815 [--_ . ..L. 7472.7180i6933 -,...----=-\e lei 7458ee /ee)....\_0 6998j.l 10480115121 \,r /.'/''-.Jy.f e (' e6906) l..,r-----.!!836e'\! :i/14619 t (7536I)' r'...-13809.13805'-"-i /eJ C---------------j..-----,-.fr' ee , e "/10473-...r \ f\ 115162'13812 rJ \ !Ii \iL._.2.23llO !'\ I ,)"') e1 "\ I "-, 'l/ 13814/., 14219ib?-I "';J r7 14\283 e-1 3769'Jl !e14476..... I 1e _ )ll-----"'...... 14255 1143.ll.l-------,14521"'V-r<... (i 1'-.-----14346",e1441---., . 14641e ee144717 -...J )!ee8400e 'j------. !e!14566e j14376i '--"l.. e (( r .L/ I '-114318 I ,I 14751e\ LJr-i ' , .. ji \,#.....r........ \ "------------e ) \15127e.14764" .{ 15290 ') ( e.-I" 12700 ei----j \! ----1' 12699" er " ! --i TL.._. U, \10830 \'-l I . ---J'---l I15334e ? ---,13534 \3489 e, '. 13551e!13490--r----------.1.1e13055\ _13881 1'I-,-'? r<;-,..'-. 13957 .... e8879 <. 13942e + 13964.lee\.,e!11541 .1488315261 . .JJUl7fi __ r e1'..14888ei13269\ \ 13958e If? ;1.:lQll.' '!,.-15205 e13238I/ '-_1_ eel12906 \! -----111946! l."" 11 \ i11908\112942, ',.r e 12050! ,--:"-, ..e15168iee! .-l ., II _!Ji_:M3 . ee11907I jL _15332ei.'e15289._ // u ---L_------------. \ 15286e i i l 15487 l-----II '1iI '___ .JL.-----.f------------iI i --------III i CORELOCATION

PAGE 22

Figure3.o2040MILESIiii'o2040KILOMETERSSCALEEXPLANATI0N•CUTTINGS•CORESCross sectio!1 location map.4__11iI____L _ iK' J' iII-I1III I-----1Iiii ii-,__. ---J-'--

PAGE 23

METHOD OF INVESTIGATION The Hawthorn Group is predominantly a subsurface unit. As a result, the principal data sources for this study were the cores drilled by the Florida Geological Survey from 1964 through the present. The cores were obtained using a Failing 1500 Drillmaster with a capacity to drill in excess of 1000 feet (305 meters). Under most conditions, nearly continuous recovery of 1-3,4 inch (4.5 em) diameter cores was obtained. Losses in core recovery were minimized due to the expertise of driller Justin Hodges. The cores recovered were placedinboxes and are stored at the Geological SurveyinTallahassee. Additional cores were obtained from the Southwest Florida Water Management District and the St. Johns River Water Management District. All cores are available for inspection by the public. Supplemental lithologic data sources included samples obtained from water wells drilled by private contractors who provide cuttings to the Geological Survey. Unfortunately, the cuttings do not necessarily provide accurate lithologic information. This circumstanceisdue to the loss of fine grained (clay, silt and very fine sand-sized), poorly consolidated to nonindurated sediments. The drilling method, sample col lection, and subsequent removal of drill mud by washing facilitates the loss of this material. The net resultisto skew the sediment types toward sands and more indurated materials. The use of cuttingsdoes, however, allow the extrapolation of lithologies and contactsinareas of limited core control. Water-well cuttings were thus used only to supplement core data. All cores and well cuttings were examined using a binocular microscope. Examinations were normally made at magnification of 10x to approximate the use of a hand lens in field indentification. Higher magnifications (up to 45x) were employed for the identification of the finer grained constituents of the sediments. Geologist's logs of the samples were recorded according to the Florida Geological Survey format which aids in producing a concise, standardized lithologic description. Coded lithologic data were stored on magnetic tape for later retrieval and use. These data were run through the Florida Geological Survey's FBG01 program on the Florida State University computer which provided a full English printout of the lithologic information. The data were also run through the Stratlog program to provide a lithologic column of each core analyzed. Samples collected for x-ray analysis were taken primarily from cores, although outcrops along the Suwannee and Alapaha Rivers were also sampled. Since clay minerals present in the sediments were of primary interest, samples were taken from the more clayey portions of the cores. Samples were mounted for x-ray analysis by standard techniques and analyzed with CuKo<.radiation. Gamma-ray logs were runonmost core holes. Numerous gamma-ray logs run in water wells are also available for correlation purposes. All geophysical logs areonpermanent file at the Geological Survey and are open to the public. . PREVIOUS INVESTIGATIONS Interest in the general stratigraphic framework of the southeastern Coastal Plain and the occurrence of phosphate in the sediments now assigned to the Hawthorn Group prompted geologists to investigate these sediments in Florida. Table 1 indicates the important nomenclatural changes that have occurredinrelation to the Hawthorn Group. . The discovery of phosphatic rockinFlorida first occurredinthe late 1870's near the town of HawthorneinAlachua County (Day, 1886).By 1883, Dr.CASimmons quarried and ground the phosphatic rocks for fertilizer (Sellards, 1910). During the 1880's phosphate was also discovered in central Florida. Smith (1881) noted the phosphatic rocks exposed along the Suwannee River from the Okefenokee Swamp downstream and placed theminthe Vicksburg Stage. Hawes (1882),indiscussing the "phosphatic sandstones from Hawthorne," described themascontaining sharks' teeth and bones belonging to the Tertiary Age. Smith (1885) and Johnson (1885) discussed the stratigraphy and occur rence of the phosphatic rocks of Florida. Johnson (1885) applied the name Fort Harlee marl to the phosphatic sediments at WaldoinAlachua County.Hementioned the occurrence ofOstreaand silicified corals within the sediments. Johnson also mentioned that those rocks are rather widespreadinthe state. 5

PAGE 24

OALLIIIHAIIIS.189Z lAUD IIIICLAPP.U09COOlEIII10SSOI,U29 COOlE,lU5 nPURlIII YEIlOR,1115 IILSOR,II17IITHISSTUOI 1 IlIOlTH FlO!IDA I saUTH flO110 A Bon. Valty..-., . S Eunnamed GravelClayi . P'IttCrHkbonebed!...,:; pho.phodt. ! unit .. !.. . " .. > .. iiArcadia Marlti!.. Jadilonvlll, "_.,.tlo I M.... I.. FormationUpp.rUpper "Chacta.lI,teh ..Fm.noPlloctn. G,,,,,P l'm ... ' ..... I A ..., ",.,1 "" .. _ ..Duplin Marll Alum Bluff bed, 5ftOOIRI_ R.work,dH .... ttlorn Formation C ....lll'.... ,l .......bet Shoal RIYIT Shoal River .,dlnllnteTamp. Alum Bluff' 10 .... 0 _ r••lamland limestone unit" I T":I FOTlllatlonFormationHawthorn iof rampaLim..ton..Ebed, H••thornHa.thornFormation 10",,,,'_ Formation <>rael ..E !" . i;;;(PenlnlUlar . ... .. tuoot.. , Oak Gran Florida)•E 0..<11......,...ilForlllationland For ... tlon ":; il Sand mtllb"Chlpot. .....<> Chlpol... • <>iiia; r.eI.. "COOl ••hatchl, 0: > • E'H••thorn ".Ha.thornFormation ""'"'*' ""'"'*' .(Panhandl.)For••tlon> ,,' •= . ;:;( Chipol. ;; Chlpola ,,'': "" Statenville "'_. .Florkfa> Florida) ;; . '""beds0:;; (C.ntralFlorida). i ForlllationFormationChlpol. .." Formallons...= . For.aUon I-unn.mad +--!=!-o ........... .unit '" C.. lllvh .... Chattahoochee Formation.Chattahooch.e r---'"OcheUlta:OwIn""""r(W..tFlorida). !he I... i;Mark. H.ad <>, bed. ;; (Panhandl.) oJ Cl ........ ;\Formation ArcadiaW.t ..._i"9 St. Mark •• a._ St. Mark,eolTonIPITorr.)'aTampaLhlll.ton.TampaLlm••ton.. LlmetlOM Formation -,. andTampaFormation :fael ..ForllaUonFormation ::; . FormationHawthorne (Penln.ular..P.nny ,(SouthFlorida) IFlorida) oJ • FarIA' beds '"FUMatlon Tampa Mbr.til . "",NocatuMbr •Table1.Nomenclatural changes that have occurredinrelation to the Hawthorn Group.6

PAGE 25

Smith (1885) examined samples sent to him by L.C. Johnson and thought the phosphatic limestone at Hawthorne was Eocene or Oligocene, as was the rest of the limestone in the peninsula. However, fossiliferous samples from the Waldo area indicated to Smith that the rocks were Miocene. He con sidered the rocks near Waldo to be the same as those exposed at Rock SpringsinOrange County. Kost (1887), in the first report of the Florida Geological Survey, mentioned the recognition of phosphatic rocks in several locations throughout the state. Penrose (1888) briefly discussed the phosphatic sediments of Alachua County. Johnson (1888) named the Waldo Formation for the phosphatic sediments exposed in eastern Alachua County. The first major contribution to the understanding of the Miocene phosphatic sediments of Flordia was published by Dall and Harris (1892). Relying upon unpublished data from L.C. Johnson and their own field information, Dall and Harris applied the name "Hawthornebeds"for the phosphatic sediments ex posed and quarried near Hawthorne, Alachua County. They reproduced sections and descriptions ob tained from Johnson. Dall and Harris placed the "Hawthornebeds"inthe"newer"Miocene. Johnson's Waldo Formation was thought to beinthe"older"Miocene although Dall and Harris state (p. 111),"OldMiocene phosphatic deposits These rocks were among those referred by Johnson to his Waldo forma tion, though typical exposures at Waldo belong to the newer or Chesapeake Miocene." Dall and Harris placed the"Hawthornebeds"intheir "Chattahoocheegroup"which overlies the Vicksburg Group and underlies the"Tampagroup"(including their"Tampalimestone" which they felt was younger than the"Hawthornebeds"). The name "Jacksonville limestone" was applied by Dall and Harris (1892) to a "porous, slightly phosphatic, yellowishrock"first recognized by Smith (1885). They thought the "Jacksonville limestone" covered a large area from Duval County to at least Rock SpringsinOrange County and included it in the"newerMiocene"above the "Hawthornebeds."Dall and Harris (1892) examined the sediments in the phosphate mining areaonthe Peace River and referred to the phosphate-producing horizon as the "Peace Creek bonebed."Underlying the producing zone was a "yellowish sandymarl"containing phosphate grains and mollusk molds which they named the"Arcadiamarl."Both units were considered to be Pliocene in age. Dall and Harris also named the "Alachuaclays"stating these clays"occurinsinks, gullies, and other depressions...." They assigned the Alachua clays to the Pliocene based on vertebrate remains. Matson and Clapp (1909) considered the Hawthorn to be Oligocene following Dall (1896) who began referring to the"olderMiocene" as Oligocene. They considered theHawthorn to be contemporaneous with the Chattahoochee Formation of west Florida and the Tampa Formation of south Florida. The Hawthorn was referred toasa formation rather than"beds"without formally making the change or designating a type section. Matson and Clapp placed theHawthornintheir "Apalachicola group." Chert belonging to the "Suwannee limestone" was also included in theHawthorn Formation at this time. Matson and Clapp (1909) named the"BoneValley gravel," replacing the"PeaceCreek bonebed"of Dall and Harris (1892). They believed,asdid Dall and Harris, that this unit was Pliocene. Matsonand Clapp thought that the Bone Valley was predominantly of fluviatile origin and was derived from pre existing formations, especially the "Hawthorn formation." The Bone Valley gravels were believed to be younger than Dall and Harris' "Arcadia marl," older than the Caloosahatchee marl andinpart contem poraneous with the"Alachuaclays." Veatch and Stephenson (1911) did not use the term "Hawthorn formation"indescribing the sediments in Georgia. Instead the sediments were included in the"AlumBluff formation" and described as strata lying between thetop of the Chattahoochee formation and the base of the Miocene. Overlying their"AlumBluff"sediments wasanargillaceous sand that wasinplaces a friable phosphatic sand which Veatch and Stephenson named the Marks Head marl. The Duplin marl, a coarse phosphatic sand with shells, overlies the Marks Head or the Alum Bluff when the Marks Head is absent. Sellards (1910, 1913,1914, 1915) discussed the lithology of the sediments associated with hard rock and pebble phosphate deposits. He presented a review of the origins of the phosphate and their relation to older formations. Sellards (1915) published the section exposed at Brooks Sink in a discussion of the incorporated pebble phosphates. 7

PAGE 26

Matson and Sanford (1913) dropped the"e"from the end of Hawthorne(asOalland Harris had used it). They state(p.64),"Thename of this formation is printedonthe mapasHawthorne, the spelling usedinsome previously published reports, but as the geographic name from which itisderived is spelled Hawthorn, the final"e"has been droppedinthe text." This began a debate of minor importance that continues to the present. Currently the Florida Geological Survey accepts the name without the"e."Vaughan and Cooke (1914) established that the Hawthornisnot equivalent to or contemporaneous with, any part of the Chattahoochee Formation butisessentially equivalent to the "Alum Bluff formation." They suppressed the name Hawthorn and recommended the use of the name"AlumBluff formation" and retained the Oligocene age. Matson (1915) believed that the "Alum Bluff" (Hawthorn) phosphatic limestones formed the bed rock beneath the pebble phosphates of central Florida. This unit had previously been called the "Arcadia marl" (Oall and Harris, 1892). Matson added the sands of the"BigScrub"inwhatisnow the Ocala Na tional Forest and the sands of the ridge west of Kissimmee (Lake Wales Ridge) to the"AlumBluff forma tion."Hethought also that the sequence of sediments called the "Jacksonville formation" (formerly the "Jacksonville limestone" ofOalland Harris, 1892) contained units equivalent to the "Alum Bluff forma tion." Matson thought that the "Bone Valley gravel" and "Alachua clays" were Miocene.Hebased thisonthe belief that the elevation of the "Bone Valley gravel" was too high to be Pliocene. Sellards (1919) considered the "Alum Bluff" to be Miocene rather than Oligocene basedonthe vertebrate and invertebrate faunas.Hestated(p.294):"Inthe southern part of the state the deposits which are believed to represent the equivalent of the Alum Bluff formation are distinctly phosphatic."Hefelt that the deposits referred to the "Jacksonville formation" are lithologically similar to the"AlumBluff"sedimentsasdevelopedinsouth Florida and contain similar phosphatic pebbles. According to Sellards (1919), phosphate first appearsinthe Miocene "Alum Bluff" rocks, and the "Bone Valley gravels" and the "Alachua clays" represent the accumulation of reworked Miocene sediments. Mossom (1925,p.86)first referred the "Alum Bluff" to group status citing"TheAlum Bluffisnow con sidered by Miss Gardnerasa group...." Gardner did not publish this until 1926. Gardner (1926), in rais ing the Alum Bluff to a group, also raised the three members, Shoal River, Oak Grove, and Chipola, to formational status. Mossom (1926) felt the Chipola Formation was the most important and widespread subdivision of the group.Heincluded the fuller's earth bedsinnorth Florida and thephosphatic sands throughout thestateinthis formation. However, the phosphatic sands were generally referred simply to the Alum Bluff Group. Mossom also believed that the red, sandy clay sediments forming the hills in north Florida belongedinthe Chipola Formation. The Hawthorn Formation was reinstated by Cooke and Mossom (1929), since Gardner (1926) had raisedthe Alum Bluff to group status. Cooke and Mossom (1929) defined the Hawthorn Formation to include the original Hawthorn"beds"ofOalland Harris (1892) excluding the "Cassidulus-bearing limestones" and chert which Matson and Clapp (1909) had placedinthe unit. Cooke and Mossom believed the "Cassidulus-bearing limestones" and the chert should be placedinthe Tampa Limestone (which at that time included strata now assigned to the Suwannee Limestone). They included the "Jacksonville limestone" and the "Manatee River marl" (Oall and Harris, 1892)inthe Hawthorn even though they felt the faunas may be slightly younger than typical Hawthorn. They also includedOalland Harris' "Sop choppy limestone"inthe Hawthorn. Cooke and Mossom felt that a white to cream-colored, sandy limestone with brown phosphate grains was the most persistent component of this unit. Stringfield (1933) provided one of the first, although brief, descriptions of the Hawthorn Formationincentral-southern Florida.Henoted that the Hawthorn contained more limestoneinthe lower portion toward the southern part of his study area. Cooke (1936) extended the Hawthorn Formation as far northeastwardasBerkeley County, South Carolina. Cooke (1943,p.90)states, "The Hawthorn Formation underliesanenormous area that stret ches from near Arcadia, Florida, to the vicinity of Charleston, South Carolina." Cooke (1945) discussed the Hawthorn and its occurrenceinFlorida. The only change suggested by Cooke (1945,p.192) was to tentatively include the Jacksonville Formation ofOalland Harris (1892) into the Ouplin Marl rather than in the HawthornasCooke and Mossom (1929) had done. Cooke (1945) also believed that the Apalachicola8

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River was the western boundary of the Hawthorn. Parker and Cooke (1944) investigated the surface and shallow subsurfacegeology,ofsouthernmost Florida. The plates accompanying their report showed the Hawthorn Formation ranging from -10 feet MSL(-3meters) to -120 feet MSL (-37 meters) overlain by the Tamiami Formation, Caloosahatchee Marl, and Buckingham Marl. Parker (1951) reassigned the upper sequence of Hawthorn sediments to the Tamiami Formation basedonhis belief that the fauna was Late Miocene rather than Middle Miocene. This significantly altered the concept of Mansfield's (1939) Tamiami Limestone and of the Hawthorninsouthern Florida. Parker et al. (1955) continued this concept of the formations. Cathcart (1950) and Cathcart and Davidson (1952) described the Hawthorn phosphates, their relation ship to the enclosing sediments and the lithostratigraphy. Also mentioned is the variation in lithologies and thickness ofthe Hawthorn within the land pebble district.Anexcellent description of the Bone Valley Formation was presented by Cathcart (1950). . Vernon (1951) published a very informative discussion of the Miocene sediments and associated pro blems. Beyond providing dataonthe limited area of Citrus and Levy Counties, Vernon provid.ed a proposedgeologic history of Miocene events.Hebelieved that the Alachua Formation was a terrestrial facies of the Hawthorn and also was,inpart, younger than Hawthorn. Puri (1953) in his study of the Flordia panhandle Miocene referred to the Middle Mioceneasthe Alum Bluff Stage.Heconsidered the Hawthorn tobeone of the four lithofacies ofthe Alum Bluff Stage. Yon (1953) investigated the Hawthorn between Chattahoocheeinthe panhandle and Ellavilleonthe Suwannee River. Yon includedinthe Hawthorn the sand and clay unit that was later formally placedinthe Miccosukee by Hendry and Yon (1967). Bishop (1956), in a study of the groundwater and geology of Highlands County, Florida, concluded that the"Citronelle"sands which overlie the Hawthorn graded downward into the Hawthorn.Hesuggested that these sands be included in the Hawthornasa non-marine, continental facies depositedasa delta to a large river which existed in Florida during the Miocene. Pirkle (1956a,1956b,1957) discussed the sediments ofthe Hawthorn Formation from Alachua Coun ty, Florida.Heconsidered the Hawthornasa unit of highly variable marine sediments which locally con tained important amounts of phosphate.Healso regarded the sediments of the Alachua Formationasterrestrial reworked sediments ranging from Lower Miocene to Pleistocene. Later studies by Pirkle, Yoho, and Allen (1965) and Pirkle, Yoho, and Webb (1967) characterized the sediments of the Hawthorn and Bone Valley Formations. The interest ofthe United States Geological Surveyinthe Hawthorn and Bone Valley Formations for their economic deposits of phosphate and related uranium concentrations resultedina number of publications including Bergendal (1956), Espenshade (1958), Carr and Alverson (1959), Cathcart and McGreevy (1959), Ketner and McGreevy (1959), Cathcart (1963a,b;1964; 1966), Espenshade and Spencer (1963), and Altschuler, Cathcart, and Young (1964). With the exception of Espenshade (1958) and Espenshade and Spencer (1963), the studies investigated the stratainthe Central Florida Phosphate District and adjacent areas. Espenshade (1958) and Espenshade and Spencer (1963) con ducted investigations in north Florida. Goodell and Yon (1960) provide a discussion of the lithostratigraphy of the post-Eocene rocks from much of the state. They provide a regional lithostratigraphic view of the Miocene sedimentsinFlorida. The occurrence of magnesian (Mg) rich clays (palygorskite) within the Hawthorn Formation has been investigated by several authors. McClellan (1964) studied the petrology and occurrence of the palygor skite (attapulgite). Gremillion (1965) investigated the origin of the clays. Ogden (1978) suggested deposi tional environments and the mode of formation of the clays. Puri and Vernon (1964) summarized the geology of the Hawthorn. They discussed the status of the knowledge ofthe Hawthorn but added very little new information. Brooks (1966, 1967) suggested that the Hawthorn shouldberaised to group status in the future.Hefurther discussed the existence of the Hawthorn across the Ocala Uplift and its subsequent erosional removal. Brooks believed Middle Miocene strata were absent from the Ocala Uplift but were present downdip from the arch.Hefelt that Lower Miocene beds were presentonthe arch.9

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Sever, Cathcart, and Patterson (1967) investigated the phosphate resources and the associated stratigraphy of the Hawthorn Formation in northern Florida and southern Georgia. Riggs (1967) suggested raising theHawthorn Formation to group status basedonhis research in the phosphate district. The rocks of Riggs' "Hawthorngroup"were related by containing greater than one percent phosphate grains. The Formation was includedasthe uppermost unit of the group. Riggs and Freas (1965) and Freas and Riggs (1968) also discussed the stratigraphy ofthe central Florida phosphate district and its relation to phosphorite genesis. The geology and geochemistry ofthe northern peninsular Florida phosphate deposits were in vestigated by Williams (1971). Clark (1972) investigated the stratigraphy, genesis and economic potential of the phosphoritesinthe southern extension of the Central Florida Phosphate District. Weaver and Beck (1977) published a wide ranging discussion of the Coastal Plain Miocene sediments in the southeast. Emphasis was placedonthe depositional environments and the resulting sediments, particularly the clays. Wilson (1977) mapped theHawthorn and part of the Tampa together. He separated the upper Tampa, termed the Tampa Limestone unit, from the lower "sand andclay"unit of the Tampa Limestone. Missimer (1978) discussed the Tamiami-Hawthorn contact in southwest Florida and the inherent pro blems with the current stratigraphic nomenclature. Peck et al. (1979) believed that the definition ofthe Tamiami by Parker etal.(1955) added to the previously existing stratigraphic problems. Hunter and Wise (1980a,1980b)also addressed this problem suggesting a restriction and redefinition of the Tamiami Formation. King and Wright (1979) inaneffort to alleviate some of the stratigraphic problems associated with the Tampa and Hawthorn formations redefined the Tampa and erected a type section from a core at Ballast Point. Their redefinition restricted the Tampa to the quartz sandy carbonates with greater than 10 per cent quartz sand and less than 1 percent phosphate grains. King (1979) presented a discussion ofthe previous investigations ofthe Tampa to which the reader is referred. The discussion is not repeated here. Riggs (1979a,1979b;1980) described the phosphorites of the Hawthorn and their mode of deposition. Riggs (1979a)suggested a model for phosphorite sedimentation in the Hawthorn of Florida. Scott and MacGili (1981) discussed the Hawthorn Formation in the Central Florida Phosphate District and its southern extension. Scott (1983) provided a lithostratigraphic description of the Hawthorn in northeast Florida. Both studies wereincooperation with the United States Bureau of Mines. T.M. Scott (1981) suggested the Hawthorn Formation had covered much ofthe Ocala Arch and was subsequently removed by erosion. Scott (1982) designated reference cores for the Hawthorn Formation and compared these to the reference localities previously designated. Scott's (1982) discussion was limited to the northeastern part of the state. Cyclic sedimentation in the sediments of the Hawthorn was proposed by Missimer and Banks (1982). Their study suggested that reoccurring sediment groups occurred within the formation in Lee County. Also Missimer and Banks followed the suggestions of Hunter and Wise (1980a,1980b)inrestricting the definition0the Tamiami. This is also the caseinWedderburn et al. (1982). Hall (1983) presented a description of the general geology and stratigraphy oftheHawthorn and adja cent sediments in the southern extension ofthe Central Florida Phosphate District.Anexcellent discus sion of the stratigraphy and vertebrate paleontology of this area was provided by Webb and Crissinger (1983). Silicification of the Miocene sedimentsinFlorida has been the focus of a number of studies. Strom, Up church and Rosenweig (1981), Upchurch, Strom and Nuckles (1982), and McFadden, Upchurch, and Strom (1983) discussed the origin and occurrence of the opaline chertsinFlorida. Related to the cherts are palygorskite clays that were also discussed in these papers and by Strom and Upchurch (1983, 1985). There have been a number of theses completedonvarious aspects of the Hawthorn Group. These in clude McClellan (1962), Reynolds (1962), Isphording (1963), Mitchell (1965), Assefa (1969), Huang (1977), Liu (1978), King (1979), Reik (1980), Leroy (1981), (1981), and McFadden (1982). Many water resource investigations include a sectiononthe Hawthorn Formation but do not add new geologic or stratigraphic data. These are not included here. 10

PAGE 29

GEOLOGIC STRUCTUREThe geologic structures of peninsular Florida have playedanimportant role in the geologic history of the Hawthorn Group. These features affected the depositional environments and the post-depositional occurrence of the Hawthorn sediments. Due to the nature of the Tertiary sediments in peninsular Florida, it is difficult to ascertain a true structural origin for some of these features. Depositional and erosional processes may have played a role in their development. The most prominent ofthe structures in peninsular Florida is the Ocala Platform (often referred toasOcala Arch or Uplift) (Figure4).The term platform rather than uplift or arch is preferred here since it does not have a structural connotation. Originally named the Ocala Uplift by O.B. Hopkins in a 1920U.S. Geological Survey press release, this feature was formally described by Vernon in 1951. Vernon described itasa gentle flexure developed in Tertiary sediments with a northwest-southeast trending crest.Hebelieved that the crest ofthe platform has been flattened by faulting. Vernon (1951) dated the formation of the upliftasb.eingEarly Miocene basedonthe involvement of basal Miocene sediments in the faulting and the wedging out of younger Miocene sediments against the flanks of the platform. Cooke (1945) thought that warping began prior to the Late Eocene and continued into the Late Miocene or later. Ketner and McGreevy (1959) suggested that the platform formed prior-to Late Miocene since undeformed beds of Late Miocene overlie warped beds ofthe Ocala Platform. Cooke (1945), Espenshade and Spencer (1963) and T.M. Scott (1981) believedthat theHawthorn once covered most or all of the Ocala Platform. Vernon (1951) believed the Platform wasanisland area throughout much of the Miocene and the Hawthorn sediments did not extend across the structure. Brooks (1966) believed the feature formed prior to the early Late Miocene.Healso agrees with Pirkle (1956b)that the Hawthorn once extended across the platform. Riggs (1979a,b)stated that the Ocala Upland (his term for the Ocala Platform) was a major structural feature controlling the formation and deposition of the phosphorites in the Florida Miocene. The Sanford Highisanother important positive featureinthe northern half of peninsular Florida (Figure4).Vernon (1951) proposed the name for a feature located in Seminole andVolusia Counties, Florida. He describes the featureas"aclosed fold that has been faulted, the Sanford High being locatedonthe upthrown side." The Hawthorn Group and the Ocala Group are missing from the crest of the San ford High. The Avon Park Formation lies immediately below post-Hawthorn sediments. The missing sec tion presumably was removed by erosion. Meisburger and Field (1976), using high-resolution seismic reflection profiling, identified a structural high offshore from Daytona BeachinVolusia County and sug gested that this feature maybeanoffshore extension of the Sanford High. Meisburger and Field believed that the seismic evidence indicated uplift that ended prior to Pliocene time. Vernon (1951) believed the feature tobea pre-Miocene structure. Riggs (1979a,b)considered the Sanford High the"otherpositive element of extreme importance" in relation to phosphorite deposition. Extending from the Sanford High are theSt.Johns Platform to the north and the Brevard Platform to the south (Figure4).Both are low, broad ridges or platforms expressedonthe erosional surface of the Ocala Group. The St. Johns Platform plunges gently to the north-northwest towards the Jacksonville Basin. The Brevard Platform plunges gently to the south-southeast and southeast. The names of both features were introduced by Riggs (1979a,b).The Jacksonville Basin, locatedinnorthwest Florida, is the most prominent lowinthe northern half of the peninsula.Inthe deepest part of the basin the Hawthorn Group sediments exceed 500 feet (150 meters) in thickness. The name Jacksonville Basin was first used by Goodell and Yon (1960). Leve (1965) believed the basin was at least in part fault controlled. Previously, many authors included the Jacksonville Basininthe Southeast Georgia Embayment.Asmore data became available it became apparent thataneastward dipping positive feature, informally named the Nassau Nose (Scott, 1983), separated the Jacksonville Basin from the rest of the Southeast Georgia Embayment. The Jacksonville Basin should stillbeconsideredasa subbasin of the larger em bayment. The Southeast Georgia Eml?ayment was named by Toulmin (1955) and appears to have been active from Middle Eocene through Miocene time (Herrick and Vorhis, 1963).11

PAGE 30

y# • # SOUTHEAST GEORGIA EMBAYMENT OSCEOLA LOWFLORIDA "\ OKEECHOBEE BASIN '\ GULF TROUGHGEORGIA150 MILESI\\ 1 II I \\o50 100 1""---1 I'o80160SCALEStructures affecting the Hawthorn Group.ALABAMAFigure4.29 G V -N027 35T---,I I J IIIII12

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The Gulf Trough or Channel extends from the Southeast Georgia Embayment to the ApalachicolaEmbayment (Figure4).Itis the Miocene expression of the older Suwannee Straits. The Suwannee Straits ef fectively separated the siliciclastic facies to the north from the carbonate facies to the south during the Early Cretaceous. The Gulf Trough was nearly full of sediments by the Late Oligocene and Early Miocene time, allowing increasing amounts of siliciclastic material to invade the carbonate environments of the peninsular area. Schmidt (1984) providedanexcellent discussion of the history of both the Suwannee Strait and the Apalachicola Embayment.Incentral peninsular Florida between the southern end ofthe Ocala Platform and the Brevard Platform are two important features in relation to the Hawthorn Group. The Osceola Low and the Kissimmee Faulted Flexture (Figure4)were both named by Vernon (1951). Vernon considered the Kissimmee Faulted Flexure tobe"afault-bounded, tilted, and rotated block" with"manysmall folds, faults, and structural irregularities." His"flexure"is actually a highonthe Avon Park surface with the Ocala and Hawthorn Groups absent over part of it due to erosion. The Osceola Low,asdescribed by Vernon (1951), is a fault-bounded low withasmuchas350 feet (106 meters) of Miocene sediments. This author has investigated the Osceola Low using cores, well cuttings and geophysical data (Florida Geological Survey, unpublished data). The data does not indicate the presence of a discrete fault. They do suggest a possible flexure or perhaps a zone of displacement with"up"on the east,"down"onthe west. This zone also appears tobethe site of increased frequency of karst features developed in the Ocala Group limestone. Scott and Hajishafie (1980) indicated that the Osceola Low trends from north-south to northeast-southwest. The Okeechobee Basinasnamed by Riggs (1979a,1979b)encompasses most of southern Florida (Figure4).It isanarea where the strata generally gently dips to the south and southeast.Pressler (1947) referred to this areaasthe South Florida Embayment stating that its synclinal axis plunged towards the Gulf (to the southwest and/or west). Since this differs significantly from the Okeechobee Basin, the term Okeechobee Basin is preferred and utilizedinthis study. Within the basin there have been postulated episodes of faulting (Sproul et aI., 1972) and folding (Missimer and Gardner, 1976).INTRODUCTION TO LITHOSTRATIGRAPHYThe Hawthorn Group has long been considered a very complex unit. Puri and Vernon (1964) declared theHawthorn"themost misunderstood formational unitinthe,southeastern United States." They further considered itas"adumping ground for alluvial, terrestrial, marine, deltaic, and pro-deltaic beds of diverse lithologic units...."Pirkle (1956b) found the dominant sediments tobequite variable stating,"Theproportions of these materials vary from bed to bed and, in cases, even within a few feet both horizontally and vertically in individual strata."HAWTHORN FORMATION TO GROUP STATUS: JUSTIFICATION, RECOGNITION AND SUBDIVISIONINFLORIDAFormational status has been applied to the Hawthorn since Dall and Harris named the "Hawthornebeds"in 1892. As is evident from the Previous Investigations section, there has been much confusion concerning this unit. The complex nature of the Hawthorn caused many authors to suggest that the Hawthorn Formation shouldberaised to group status although none formally didso(Pirkle, 1956b; Espenshade and Spencer, 1963; Brooks, 1966, 1967; Riggs, 1967). The Hawthorn was referred toasa groupinGeorgia for several yearsonaninformal basis until Huddlestun (in press) formalized the status changeinthe southeastern United States, recognizing its component formationsinGeorgia. The recognition of formations within the Hawthorn Group in Florida is warranted due to the lithologic com plexity ofthe sediments previously referred toasthe Hawthorn Formation. The extension of several Georgia units into Florida and the creation of new Florida units is basedonthe expectation that Hud dlestun will validly publish the status change from formation to group.Ifhe fails to doso,this text willbeamended to validate the necessary changesinthe proper manner according to the North American Code 13

PAGE 32

of Stratigraphic Nomenclature (1983).Anoriginal type locality for the Hawthorn Group was not defined within the limits of our present stratigraphic code. However, it appears that Dall and Harris' (1892) intention was to use the old Simmons pits near HawthorneinAlachua Countyasthe type locality (holostratotype). The other sections referred tobyDall and Harris (1892) at Devil's Millhopper, Newnansville well, and White Springs were reference sections. The old Simmons pit isnolonger accessible indicating the need for a new type locality (neostratotype). The Hawthorne#1core W-11486, locatedinAlachua County drilledinthe vicinity of the old Simmons pit should fill this gap.Assuch the Hawthorne#1core is designatedasa neostratotype or replacement (accessible) type section for the Hawthorn Group. Although many authors have agreed that the Hawthorn deserves group status, questions remain. What should be includedinthe group and what should be the stratigraphic status of the units (Le., formations with or without members)? The approach usedinthis study has been to identify lithostratigraphic units within the study area, determine their areal extent and thickness and, basedonthese findings, assign a formational status where appropriate. Having done that,asdetailed subsequentlyinthis report, the Hawthorn Formation of Floridaisherein raised to group status. Its formations are described and type sections or cores are designatedinaccordance with the North American Stratigraphic Code (North American CommissiononStratigraphic Nomenclature (NACSN), 1983). Utilizing the group concept will enable geologists to better understand the framework of the Miocene sedimentsinFlorida and much of the southeastern Coastal Plain. The sediments placedinthe Hawthorn Group are related by the occurrence of phosphate, a palygor skite-sepiolite-smectite clay mineral suite and the mixed carbonate-siliciclastic nature of the entire se quence. Color, particularlyinthe siliciclastic portions, is often distinctiveinthe sediments of this group.Insome regions andinspecific intervals, lithologic heterogeneity provides a diagnostic trait of the Hawthorn Group. The component formations of the Hawthorn Group vary from region to region within the State. The variation is the result of the depositional and environmental controls exertedonthe Hawthorn sedimentsbyfeatures suchas the Ocala Platform, the Sanford High, the St. Johns Platform, and the Brevard Plat form. The variationincomponent formations of a group is discussedinand accepted by the North American CommissiononStratigraphic Nomenclature (Article 28b, North American Stratigraphic Code, 1983). The name Hawthorn is retained for the group since the group represents a series of units that had been recognizedasthe Hawthorn Formation. Only a few changes (additions) are proposedinthis report that alter the overall boundaries of the former Hawthorn Formation. Due to its wide use and acceptance, drop ping the term Hawthorn and providing a new group namewould cause unnecessary confusion. Once the lithostratigraphic .units were determined, names were selected for the respective sections. These are listedinTable 1 along with reference to the original author. When possible, names currentlyinuse, or proposedina bordering State (Georgia), were usedinFlorida. Examples of these are the Marks Head, Coosawhatchie and Statenville Formations currently recommended for useinGeorgia (Hud dlestun,inpress). Where a sediment package exhibited significant variationinFlorida from the equivalent unitinGeorgia, a new name is proposed (Le., the Penney Farms Formation).Inthe eastern panhandle the name Torreya Formation is used since it is alreadyinthe literature (Banks and Hunter, 1973; Huddlestun and Hunter, 1982; Hunter and Huddlestun, 1982; Huddlestun,inpress) and there is insufficient evidence to suggest any changes. Future research, however, may suggest fur ther changes. The names of the formational units of the Hawthorn Groupinsouthern Florida were selected basedonhistorical perspective and current usage. The name Arcadia Formation is reintroduced for the Hawthorn carbonate unit. The use of Arcadia is similar to the use suggested by Riggs (1967). Two members are namedinthe Arcadia, the Tampa Member and the Nocatee Member. These members do not comprise the entire Arcadia but only represent the lower Arcadia where they are identifiable. The Tampa Member represents a reductioninstatus for the Tampa from formation to member. Since this reduction represents only a minor alteration of the Tampa definition and since the name Tampa is 14

PAGE 33

widely used and recognized, a new name is not suggested for this member. The most prominent reasons for reducing the Tampa to member status is the limited area of recognition and its lithologic affinities with the rest ofthe Arcadia Formation of the Hawthorn Group. A new name, the Peace River Formation, is proposed for the upper Hawthorn siliciclastic section, in cluding the Bone Valley Formation of former usage. The Bone Valley Formation is reduced to member status and the name is retained for the same reasons discussed for the Tampa Member. There has been some discussion and disagreement concerning including the entire Bone Valley in the Hawthorn Group due to the presence of a major, Late Miocene unconformity. This unconformity separates the upper gravel bed ofthe Bone Valley.from the remainder ofthe unit and often is recognizable onlyona biostratigraphic basis using vertebrate faunas. The unconformity is generally not recognizedona lithostratigraphic basis. The North American Stratigraphic Code (NACSN, 1983) recognizes this pro blem. Article 23dstates"... a sequence of similar rocks may includeanobscure unconformitysothat separation into two units maybedesirable but impractical. If no lithic distinction adequate to define a widely recognizable boundary canbemade, only one unit shouldberecognized, even though it may in clude rock that accumulated in different epochs, periods or eras (NACSN, 1983)." The formations ofthe Hawthorn Group are similar yet different in northern and southern Florida and in the eastern panhandle. Also, within southern Florida, the group varies from east to west.Asa result the discussion of the Hawthorn willbepresented separately for northern and southern Florida and the eastern Florida panhandle (Figure1).PRESENT OCCURRENCEThe Hawthorn Group underlies much of peninsular Florida (Figures 5 and6).Itisabsent from most of the Ocala Platform and Sanford High due to erosion. Outliers of Hawthorn sediments and residuumoc-.cur scattered along the platforminlows andinsome karst features. The Hawthorn Group sediments are also absent from part of Vernon's (1951) Kissimmee Faulted FlexureinOsceola County presumably due to erosion. The Hawthorn Group dips gently away from the Ocala Platform and Sanford High at generally less than 6 feet per mile(1.1meters per kilometer) (Figure5).Innorth Florida, the Hawthorn dips generally to the east and northeast towards the Jacksonville Basin and the east coast. Locally the dip may become greater and may reverseinsome areas. This is due to postdepositional movement related to karst activi ty, subsidence, possible faulting, and tilting of the platform. Scott (1983) indicated thisonstructure maps of the Ocala Group(p.29)and the Hawthorn Formation(p.32).Incentral and south Florida the Hawthorn Group dips gently to the south and southeast with local variations (Figure5).Generally, further southinthe state the dip is more southeasterly. The strata dip to the west and southwest along the western edge ofthe state from Pasco County south toLeeCounty. The Hawthorn Group rangesinthickness from a feather edge along the positive features to greater than 500 feet (160 meters)inthe Jacksonville Basin and greater than 700 feet (210 meters)inthe Okeechobee Basin (Figures 4 and6).The Hawthorn generally thickens to the northeastinnorth Florida toward the Jacksonville Basin and southward into the Okeechobee Basin (Figure6).NORTH FLORIDAINTRODUCTION The Hawthorn GroupinFlorida, north of Orange County and west through Hamilton County, has distinct affinities to the Hawthorn in Georgia. The sediments of the upper two-thirds of the group are very similar to those in Georgia, facilitating the use ofthe same terminologyinboth states. The basal one-third ofthe group changes significantly into Florida and, therefore, a new formational name is proposed.15

PAGE 34

APPROXIMATE LIMITS OF THE HAWTHORNGROUP-iiiiiiiiiiiiiiIiiCONTOUR INTERVAL50FT . • CORE AND WELL CUTTING LOCATIONS DATA BASE CORES FROM FIG. 2 WITH ADDITIONALCUTTINGS•o10203040MI.II""i"Io1020304050KM.SCALE-100Statewide map of the elevation of the upper Hawthorn Group surface. -;.. 0,16 0 0 : Figure5.

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APPROXIMATELIMITSOF THEHAWTHORNGROUPiiiiiiiiiiiiiiiiiCONTOUR INTERVAL 50 FT . • CORES AND WELLCUTTINGS LOCATIONSDATABASE CORES FROM FIG. 2 WITH ADDITIONAL CUTTINGS.' 0, 17Statewide isopach map of the Hawthorn Group .o 1,0 2,030 .,0 MI. 1'02b3'0 4'0JoKM. SCALEFigure6.

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The Hawthorn Group in north Florida can be subdivided into four formationsasindicated in Figure7.From oldest to youngest, these are the Penney Farms Formation, the Marks Head Formation, the Coosawhatchie Formation, and the Statenville Formation. The Penney Farms Formation canbedivided into two informal members referred to simplyasupper and lower members. The Coosawhatchie Forma tion also has upper and lower informal members and the Charlton Member (Huddlestun, in press) (Figure7).The formational breakdown of the Hawthorn Groupinnorth Floridaisrecognizable in cores. However, due to the highly variable nature of the north Florida Hawthorn sediments, the individual units are very difficult to identifyinwell cuttings. Therefore it is recommended that when using well cuttings in this area these sediments simply be referred toasHawthorn Group undifferentiated. The sediments of the Hawthorn Group are significantly different west of the crest ofthe Ocala Platform (west of Hamilton County). These units will be discussed separately from those east ofthe crest in north Florida. The Hawthorn Group in north Florida shows significant variation when traced into central Florida.Inthe area between the Sanford High and the Ocala Platform, the Hawthorn is thinned both depositionally and erosionally (Figure6).Within this zone the upper part of the group changes character, such that it is difficult to correlate with the formations to the north. The basal unit of the group carries through this area, and is apparent in east central Florida where it grades into the lower part of the Arcadia Formation of southern Florida. Throughout most of the north Florida region the Hawthorn Group unconformably overlies the Upper Eocene Ocala Group (Figure8).The Crystal River Formation of the Ocala Group underlies the Hawthorn in most of the area where the Ocala Group occurs. However,inareas peripheral to the Sanford High andinportions of the transition zone, the Hawthorn overlies the lower Ocala Group (Williston Formation). The author has not encountered any instances ofthe Hawthorn overlying the Avon Park Formation when the Ocala Group is absent since the Hawthorn Group is also absent in these cases (Sanford High, for in stance). :rhe sediments of the subjacent Ocala Group are typically cream to white, foraminiferal grainstone to wackestone, containing no quartz sand. The limestones are often recrystallized just below the contact with the Hawthorn Group. This contrast of lithologies with the basal Hawthorn Group is generally dramatic, resultinginlittle confusioninidentifying the contact. The Suwannee Limestone of Oligocene age unconformably underlies the Hawthorn Grouponthe northeastern-most portion of the Ocala PlatforminHamilton and Columbia Counties. Typically, the Suwannee is a granular, microfossiliferous, cream, white, to very pale orange grainstone to wackestone.Itis sometimes recrystallized below the contact with the Hawthorn and rarely maybea dolostone. The lithologic differences between the basal Hawthorn Group sediments and the Suwannee Limestone are quite distinctive; confusion concerning the contact is unlikely. The St. Marks Formation of Early Miocene age underlies the Hawthorninanextremely limited area in the western half of Hamilton County. The St. Marks occurs sporadically and generally is less than 30 feet(9meters) thick (Colton, 1978). Lithologically, theSt.Marks is a quartz sandy, silty, sometimes clayey limestone (wackestone to mudstone). Occasionally, it maybedolomitized. The lithology of this unit is similar to the basal Hawthorn sediments except for the lack of phosphate grains in the St. Marks. The St. Marks lithology may occur within the basal Hawthorn carbonates, creating possible confusion concern ing the contact. Although the contact is unconformable, itisoften not apparent.Asa result, thetop of the St. Marksisplaced below the last occurence of phosphatic sediments. This datum is traceable from western Hamilton County westward into the eastern panhandle in Madison, Jefferson, and Leon Coun ties. PENNEY FARMS FORMATION Definition and Type Locality The Penney Farms Formation is a new lithostratigraphic name proposed here for the predominantly subsurface basal unit of the Hawthorn Group in north and central Florida. Itisnamed after the town of 18

PAGE 37

POST-HAWTHORNUNDIFFERENTIATEDSTATENVILLEFORMATIONMARKSHEADFORMATIONCOOSAWHATCHIE Cl.::>t--C) Z 0:::: o :I:r-
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....."--Geologic map of the pre-Hawthorn Group surface. ....p ."..40MILES"60KILOMETERSCORELOCATIONSLIMITSOFHAWTHORNGROUPEOCENEOCALAGROUP20..MIOCENEST.MARKSF M.ANDCHATTAHOOCHEEFM.OLIGOCENESUWANNEELS.AND'SUWANNEE'LS.2040SCALE'-"._.--i ! 20'.IIIEXPLANATION•o oIFigure8.I-'-' I f( -/ \.

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Penney Farms in central Clay County, Florida. The type core, W-13769 Harris#1, is located near Penney Farms (SWV4,SEV4, Section7,Township6S,Range 25E) with a surface elevation of97feet (30 meters). The type core was drilled by the Florida Geological SurveyinDecember 1977 andispermanently stored in the Survey's core library. The type Penney Farms Formation occurs between -118 feet MSL(-36meters) and -205 feet MSL (-63 meters) (Figure9).Lithology The Penney Farms Formation consists of two informal, unnamed members which are distinguished from each other basedonthe abundance of carbonate beds. Figure 9 graphically shows the variable nature of this formation and its general two member framework. Each member consists of lithologies similar to the other but the proportions of the lithologies are dissimilar.Inthe lower member, carbonates predominate with sands and clays interbedded in varying proportions. The upper member is a predominantly siliciclastic unit with interbedded carbonate beds. The interbedded sands and clays of the lower member generally increaseinabundance upwardinthe section causing the contact with the upper member tobegradational in nature. The topofthe lower memberisplaced where carbonate beds become dominant over the siliciclastic beds. The North American Code of Stratigraphic Nomenclature (NACSN, 1983) (Article23)allows for this arbitrary placement of a boundaryina gradational sequence. Occasionally, the siliciclastic beds are abundant enoughinthe lower member to obscure the contact altogether thus the separation ofthe informal members within the Penney Farms Formation is not always possible. The carbonates are variably quartz sandy, phosphatic, clayey dolostones. Sand content is variable to the point that the sediment may become a dolomitic sand. Phosphate grains maybepresentinamounts greater than25percent withanaverage of approximately 5 to10percent. Clay percentages are general ly minor (below 5 percent) but often increaseinthe dolostones of the upper member. The dolostones are medium gray (N5) to pale yellowish brown(10YR6/2). They are generally moderately to well indurated and finely to coarsely crystallineinthe lower member. The dolostones of the upper member are generally less indurated. Thicker, more massive beds predominateinthe lower unit while thinner beds are most common in the upper section. Mollusk molds are common in the dolostones, particularlyinthe more coarsely crystalline type. Zones of intraclasts are commoninthe hard, finer grained dolostones of the lower part of the Penney Farms. The intraclasts are composed of dolomite thatisessentially the sameasthe enclosing matrix. The intraclasts are recognizable due to a rim of phosphate replacement along the edges ofthe clasts (Figure10). Edges of the clasts vary from angular to subrounded indicating very little to no transport of the fragments. They also maybebored, indicating at least a semi-lithified state prior to being redeposited. Limestone, in the basal portion ofthe Penney Farms Formation, occurs sporadically. When it does oc cur, it is generally dolomitic, quartz sandy and phosphatic. The quartz sands are fine to coarse grained, moderately to poorly sorted, variably phosphatic, dolomitic, silty and clayey. The phosphate grain content varies considerably, sometimes to the point of being classifiedasphosphorite sand(50percent or greater phosphate grains).Ingeneral, however, the phosphate grain content averages between 5 and10percent. The sands are typically olive gray(5Y 3/2) or grayish olive (10 Y 4/2) to medium light gray(N6).Clay content varies considerably in the sands. Clay beds in the Penney Farms Formation are typically quartz sandy, phosphatic, silty and dolomitic. The proportions of the accessory minerals vary from nearly zero to more than 50 percent. Nearly pure clay beds are uncommon. Dolomite is very common in the clays, often being the most abundant ac cessory mineral. Olive gray(5Y 3/2) and grayish olive green(5GY 3/2) colors generally predominate, but colors may range into the lighter shades. Smectite typically dominates the clay mineralogy of this unit with palygorskite, illite and sepiolite also present. X-ray analyses by Hettrick and Friddell (1984) indicate that palygorskite may become predominant over smectiteinsome samples. Reik (1982) indicated that palygorskite dominatesinthe lower part of the Penney Farms while smectite dominates in the upper por-21

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90 -I 80 CLRY70 60 -10 -20 -30 -40 -50 -60 -70 -UNDIFFERENTIATEDzo II: o u.enII:: >wz zW 11. HAWTHORN GROUP OCALAGROUPPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATE PHlSPHATE PHOSPHATE PHOSPHATE CLAY HEAD FORMATIONPHOSPHRTE CLRY PHOSPHATE CLAY CLAY OOLOHITE CLAY PHnSPHRTE W-13769 SANDSANDPHOSPHATE SAND OOLCI1TTE PHOSPHATE DOLOHITE PHOSPHRTE DOLOMITECRYSTALRIVERFORMATIONSANDDOLOMITE .-:-.:::--:-. :• ..;..:.-:-. : PHOSPHATE """';""_'7'_"""';""-':7' • PHOSPHATE CLAY PHOSPHATEOOLOHITEPHOSPHATE DOLOMITE PHOSPHATEDOLOHITEPHOSPHATE DOLOMITE PHOSPHATE CLAY PHOSPHATE CLAYSAND SAND SANDPHOSPHRTE SAND PHOSPHATE PHOSPHRTESANDSRNDPHOSPHRTE PHOSPHRTE PHOSPHATE PHOSPHATESANDDOLOMITE PHOSPHRTE CLAY PHOSPHRTE CLRY PHOSPHRTE CLAY CLAY PHOSPHATESANDPHOSPHATE SAND PHOSPHRTE SAND PHOSPHATE SAND PHOSPHATE SAND PHOSPHATESANDPHOSPHATESANDPHOSPHATE SAHD PHOSPHATESANDPHOSPHATESAND...:..-. ...:.....:..-...:... .-:-.::-.;.. ::-.;.. :. ..;.. :-------1]0 _ -210 -l20 _ -l30 _ -l't0 _ -80 -90-100 -220 -200 -160-190-170 -150 -180zo j:ceII: o U. w :f ol ce:J:ceen oooPHOSPHATE HAWTHORN GROUPLAND SURFACEPHOSPHATE SANOSILTPHOSPHATEOOLOMBESILTPHOSPHATE DOLOMITESILT PHOSPHATE DOLOMITE PHOSPHATE PHOSPHATE PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHFHE CLAY PHOSPHATE DOLOHITE PHOSPHATE DOLOMITE PHOSPHATESANDDOLOMITE PHOSPHATESANDPHOSPHATESANDPHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHAtEDOLOHITEPHOSPHATE OOLOMITE PHOSPHRTE DOLOMITE PHOSPHATE DOLOMITE PHOSPHRTEDOLDHITEPHOSPHATE DOLOHITEPHOSPHATEDOLOHITEPHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHATE PHOSPHf'lTE SANDOOLOHITE PHOSPHATESANDPHOSPHRTESANDPHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHATE PHOSPHRTE PHOSPHRTE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE CLAY'''''''''''''''. .-;"" ...... -; . ..,:-; ...... -;. _.'-''-'._...........,......_.. _ .. _ .. _ ..................'-''-''-''-'................'-''-''-''-'.........._..........,......._.._.._.._.................'-''-'._.. _. .................0-'._.,_,,_,.................'-''-''-''-'...............,_.._.. _ .._...................'-''-''-''-' '-;'-:. '....' ,'-':,'. _.'-''-''-'.....,............._.._.._.._. .":'.-.":".-.-=..-.":'. ...........,...., '-;""'-':-;-' .... '-;'-':-;', '-'._.'-''-'.":".-.":'.-.":'.-.":'.'''''''''''''''''.'-''-''-''-'.........._..'-''-''-''-'_......................._.'-''-''-'........,,:.-.,,:.-.,,:,.-.,,:,,' ................'-''-'._.'-'..................._.._.'-''-'..........,...... ................".".".................._.._.._.._.-1020'103050 Figure9.Type section of the Penney Farms Formation, Harris#1,W-13769, Clay County (Lithologic legend AppendixA).22

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..\.,, '.\....." . ,.'ft...'"......, ...;e. 1j..' , .. . .."\,., '... " Figure10.Intraclasts with phosphatic rims from Penney Farms Formation,St.Johns County,W-13844.23

PAGE 42

tioninClay County. Other minor mineralogic constituents include mica, K-feldspar and opal ct. Clinop tilolite has been identifiedina few samples (Huddlestun,inpress). When abundant silt-sized, unconsolidated dolomite occurs, difficulty arises in determining whether the actual rock typeisa very dolomitic clay or a very clayey dolostone. Insoluble residue analysis is the only accurate method of determining the clay and dolostone contents. Rough analysis indicates that,ingeneral, the lighter the color of the sediment, the higher the dolomite content. This method was employed for determining the sediment typeinthese situations. The siliciclastic beds of the Penney Farms Formation are lithologically very similar to thoseinthe Parachucla Formationinsoutheastern Georgia (Huddlestun,Inpress).Asthe Penney Farms Formation begins to lose its carbonate units northward and northwestward into Georgia, the characteristic lithologies are no longer apparent and the formation cannolonger be identified as the Penney Farms. These sedimentsinGeorgia are includedinthe Parachucla Formation (Huddlestun,inpress). Southward into central Florida, the Penney Farms contains more carbonate thaninthe type area. Be tween the Sanford High and the Ocala Platforminportions of Lake and western Orange Counties, the percentage of siliciclastic beds decreases to the point that the separation of upper and lower members becomes unfeasible. The carbonatesinthis area contain coarser sand and a noticeably coarser phosphate grain fraction. Further to the east,inOrange County, and southward into eastern Osceola and Brevard Counties, the basal Hawthorn Group consists predominantly of dolostone. This basal unitistentatively placedinthe Arcadia Formation until further investigations can be conducted. Subjacent and Suprajacent Units The Penney Farms Formation unconformably overlies limestones of the Eocene Ocala Group or the Oligocene Suwannee Limestone. Figure 8 indicates the areasinwhich each occurs.The unconformity is very apparent due to the drastically different lithologies. Previous discussion of the base of the Hawthorn Groupinnorth Florida descibes the lithologic differencesingreater detail. The Marks Head Formation unconformably overlies the Penney Farms Formation throughout north Florida exceptinthose areas where it has been removed by erosion.Inareas where the Marks Head has been eroded, the Penney Farms is overlain by sands and clays classifiedasundifferentiated post Hawthorn deposits. The top of the Penney Farms is placed at the break between the lighter colored sediments of the Marks Head and the darker colored sands and clays of the upper part of the Penney Farms. Occasionally, a rub ble zone marks the break between the Marks Head and the Penney Farms Formations. When it occurs, the rubble consists of clasts of phosphatized carbonate. The relationship of the Penney Farms Formation and to the underlying and overlying sediments is il lustratedinFigures11through16.Thickness and Areal Extent The Penney Farms Formation of the Hawthorn Group occurs primarilyasa subsurface unit. The top of the Penney Farms Formation rangesincores from -333 feet MSL(-101meters)inCarter#1,W-14619, Duval County to+80feet MSL (24.3 meters) in Devils Millhopper#1,W-14641, Alachua County (Figure17).Limited data from one outcropinMarion County (Martin-Anthony roadcut, NEY4,NEY4,NEY4, Sec.12,Township 14S, Range21E)indicates the sediments assigned to the Penney Farms occur at+140 to+150 feet MSL (43 to 46 meters). This is the only recognized occurrence of the basal Hawthorn Group at elevations this high. The Penney Farms Formation dipsina general northeasterlydirection from the flanks of the Ocala Platform toward the Jacksonville Basin withanaverage dip of 4 feet per mile (0.8 meters per kilometer). The direction of dip of the Penney Farms trends toward the north into the Jacksonville Basin from the St. Johns Platform (Figure17).Locally, both the direction and angle of dip may vary. 24

PAGE 43

A''0100 30"t; 20 w.,.....5052 '0 " MSL W WCo-2SE-23dcW-6836SUWANNEELS. -----------_ ---_ ----OCALAGROUPEXPLANATION W"..... HAWTHORNGROUP BOUNDARIESSCALE510MILES I--r--"-r, ...... , '1015KILOMETERS g.. 10 .IU.'liCOICOC(JICUCDI: W-12380WBI-4S-22E-25bdI ... ".,""0_i A' 110 200'0.0100 " MSL'0 .:502 w-20 -100-60-200Figure 11. Cross section A-A' (see figure 3 for location) (See Scott (1983) for discussion of faults).25

PAGE 44

B B'W-14594wpueS-23E-18bbEXPLANATION W"...... HAWTHORNGROUP BOUNDARIESIT,.00 .'"7
PAGE 45

MSL.0 "10 -"-10C' '00 -170-000-00-'00-'20-21'5_4'"000 -'0 "I Ww -2U-ISO -110,W-14318WPu-13$-2BE-07c.5O...100PENNEY FARMS FM.MARK'SHEADFM.LOWER MEMSER (L.COOS.) "A':...L-COOSAWHATCHIEFM. W-14353WPu-ll S-28e-2 7cbiEXPLANATION SCALEo 5 10MILESII""o510 115 KILOMETERS ........ HAWTHORN GROUP BOUNDARIES lllll","'W-14183 we, ,,"!"f'ffff ff.f••.'••.'.'.'•• ••flOCALA OROUP Il••.;>.>O.CO " ,U ..•.,",," 0 0 " ST.JOHNSRIVERiii? :>c .•-' z .",oot"''''ot)4,8"...."......"...... W-13815WHa-3H-24E-32 ••---__ (1) -_ F... -......................... ______CHARLTONMEMSERC-'0 -00 -'0-'0'0100,.'0'0 -150 I" w 2 -'0 _250_100--",-'0 MSL I\:)--J Figure13.Cross section C-C' (see figure 3 for location) (See Scott (1983) for discussion of faults).

PAGE 46

->DO-175 .0IISL-00'00It.D''0 110 100., .. .. -toO -'00 -30-100...."'wWw:;; .. a-IU -'0to-,."W-13744 I10 .. IZ >.1: . COIOO.... U COOSAWHATCHIE'".ST.JOHNSRIVER\ \ \ \ \ \\\\ '!<"'\'\'\'\ OCALAGROUP '\'\'\'\'\'\'\ EXPLANATIONSCALE 5 10MILES .... .... ..l'I-r,-....... ,,1015KILOMETERS lIJI....1:' HAWTHORNGROUP BOUNDARIESW-14283WBd-8S-Z2E-24dc '"\'"MARKS 111 '" -10-'0D 7ll"-7ll -'0 -125..40WonW","wtuZ-3211 -100 -225 IISL -350 -110Figure 14. Cross section0-0'(see figure 3 for location) (See Scott (1983) for discussion of faults).28

PAGE 47

IISL 3D 100,.. ,.-eo -200."-to l..::: '"-!OS'" .,.-E'UNDIFFERENTIATED W-14413 W-13844I -'OS-30E-37 ST.JOHNSRIYER .uOlZO .co .... u I"C EXPLANATION SCALE5 10MILES t--r--""'-r,--T.' 10 Hi KILOMETERS ... HAWTHORN GROUP BOUNDARIESW-14841E,. " ,.IISL....Figure 15. Cross section E-E' (see figure 3 for location) (See Scott (1983) for discussion of faults). 29

PAGE 48

IIPUTNAMCO ! MARlON COFIIMARION COILAKE COIIILAKECO l POLK COIF'W-13055WPo-27S-25E-21daMETERSFEET1504030100205010 0 MSL , -10 -50 -20-30-100-40-150-50 -60 -200-70-250-80-90-300W-12700WLk-20S-26E-17bbOCALA GP.W-15127WMr-17S-26E-36cdUNDIFFERElmATEO1015KilOMETERSSCALE510MILESIII'EXPLANATIONW-14751WMr-16S-26E-13ab ...,....., HAWTHORNGROUPBOUNDARIESW-14318WPu-13S-28E-7ca '"........ AVON .... PARKFORMATION !oETBlS FEET15040301002050100 MSL-10-50-20-30-100-40-150-50 -60 -200-70-250-80-90-300 -100 -350-110Figure 16. Cross section F-F' (see figure 3 for location) (See Scott (1983) for discussion of faults). The Penney Farms Formation varies in thickness from being absentonthe crests of the Ocala Platform and Sanford High to more than 155 feet(47meters) in Carter #1, W-14619, Duval County in the Jackson ville Basin (Figure 18). The total thickness of this unit was not determined in this core as the core ter minated in the Penney Farms Formation after penetrating 155 feet (47 meters). This author estimates that the base of the Penney Farms should occur near -575 feet (-175 meters) MSL based on nearby water wells. This suggests that approximately 230 feet (70 meters) of the unit should be present in the deepest portion of the Jacksonville Basin. The informal upper member attains its maximum observed thickness of 88 feet (27 meters) in Cassidy #1, W-13815, Nassau County. Seventy-five feet (23 meters) of the lower in formal member were penetrated in W-14619. This author estimates that approximately 150 feet (46 meters) of this member should be present basedonpreviously discussed criteria. The Penney Farms Formation of the Hawthorn Group occurs throughout much of north and central Florida. It is absent from the crest of the Ocala Platform and the Sanford High due to erosion and nondeposition. The Penney FarmsFormation thinsontheS1.Johns Platform and is absent from the highest part of the structure, the area where the Sanford High and theS1.Johns Platform merge (Figure4).Age and Correlation The Hawthorn Group sediments of northernFlorida have yielded very few dateable fossils or fossil assemblages. Diagenetic overprintingonthe sediments has obliterated the vast majority of fossils leav ing mainly molds and casts. Diatom and mollusk molds are the most frequently encountered fossil re mains. 30

PAGE 49

tr--l M ""J)__ ,-1--+-_-1-'( )R -N-SCALE CIFEETo2040MILES1-1-,........' .,.-...",.&'-r ........__.J'o2040KILOMETERS • CORES OFHAWTHORN GROUPHAWTHORN GP. UNDIFFERENTIATEDFigure 17. Top of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group.31

PAGE 50

.'-.1"', HAWTHORN GP. EiI UNDIFFERENTIATED LIMITSOF HAWTHORN GROUP • CORES CIFEETSCALEo2040MILESI'j"jIo2040KILOMETERSFigure18.Isopach of Penney Farms Formation. Shaded area indicates undifferentiated Hawthorn Group.32

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At the prese.nt time, dateable fossils from the Penney Farms Formation have been obtained from only two sites. The first is from the Cassidy#1core, W-13815, Nassau Countyinthe interval from -450 to -455 feet LSD (-137 to -138.7 meters LSD). The sediment, a calcareous, quartz sandy clay, contained benthic and planktonic foraminifera, ostracods, spicules (sponge?), echinoid fragments and bryozoans. The planktonic foraminifera indicateanAquitanian age upper Zone N.4 or lower N.5 of Blow (1969) for this in terval (Huddlestun, personal communications, 1983). The second site encompasses the Martin-Anthony roadcut in north central Marion County (NEV4,NEV4, NEV4, of Section 12, Township 14S, Range 21E).Anoreodont jaw collected from the hard car bonates exposed in the roadcut was dated as Late Arikareen (equates to Early to Middle Aquitanian) (MacFadden, 1982). The few ages obtained in north Florida correlate well with dates obtained by Huddlestun (personal communication, 1983) in the Hawthorn Group of Georgia. The age suggested for the Penney Farms For mation correlates with the age of the upper part of the Parachucla Formation in Georgia (Figure 19). Lithologically, the Penney FarmsFormation grades laterally into the Parachucla Formation through a transition zone north of the Jacksonville Basin. These ages indicate that the basal portion of the Penney FarmsFormation is slightly older (1-2 million years) thanthe base of the Pungo River Formation in the Miocene of North Carolina as indicated by Gibson (1982) and Riggs (1984). The type Penney Farms appears to be equivalent to at least part of the Tampa Member of the Arcadia Formation (as described in this report). Based on Huddlestun's (in press) suggestion that the Parachucla Formation correlates with the Chattahoochee Formation of western Florida and southwest Georgia, the Penney FarmsFormation is also equivalent to part of the Chattahoochee Formation (Figure 19). The Pen ney Farms appears to equate with Miller's (1978) unit E from the Osceola National Forest.EASTERN EASTERNSEAND E NORTHERN SOUTHERN NORTH SOUTH EASTERN SERIES GEORGIA PANHANDLE FLORIDA FLORIDA SERIES CAROLINA CAROLINAPLIOCENEYORK TOWN FM. CYPRESSHEAD FM. CYPRESS HEAD FM. TAMIAMI FM.PLIOCENEIDUPLINFM. INASHUAFM.UPPER a:WABASSO UPPER CD beds ::! PEACE>-W WwRIVER COOSAWCOOSAW...J ..JW..J CHARLTOM11....J11.: FM. ::::l WCHATCHEE HATCHEEMBR. ::::l >CZFM.STATENVILLE0w0CZCFM.za:WFM.a:0W-PUNGO C'CDC'. -0 :!: COOSAW:!: 0HATCHEEZ Z0RIVERFMa: a:00-MARKSTORREYAMARKS0ARCADIA J: a: FM.MARKS J: FM.Ia::!: HEADFM.HEADFM. FM.HEADFM.I== W W ==3:c(c(3: PARA-CHATTA-PENNEY J: J: PARACHUCLA0 0CHUCLAHOOCHEEANDFARMS..JFM • FM. ST.MARKSfms.FM...JSUWANNEESUWANNEEOLIGOCENELS. LS. OUGOCENE LS.OCALAGP.OCALAGP.OCALAGP.OCALAGP.UPPEREOCENESANTEEAVONAVON PARK FM. AVON PARK FM. AVON PARK FM.MIDDLECASTLEHAYNESANTEE LS.LS.PARKFM.Figure 19. Formational correlations (modified from unpublished C.O.S.U.N.A. Chart,. 1985). 33

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The Penney Farms Formation of the Hawthorn Groupisolder than the commonly accepted age for the Hawthorn Formationasdescribed by Puri and Vernon (1964).Thisage, Middle Miocene, was accepted for the Hawthorn Formation by the Florida Geologic Survey for sometime. The data presented here in dicate this should be revised (see Figure19).Armstrong et al. (1985) have even suggested a latest Oligocene age for the base of the Hawthorninsoutheastern Florida. DiscussionAsstated previously, the Penney Farms Formationinnorthern Floridaisequivalent to the Parachucla Formationinsoutheastern Georgia. The Penney Farms represents a southern extension of the Parachucla siliciclasticS, but contains a significant amount of dolostone which is not presentinthe Parachucla. The two units are laterally gradational with each other. Within the gradational sequence the lateral boundary between the unitsisarbitrarily placed where carbonate becomesanimportant lithologic factor. This boundary usually occurs just north of thestate lineinGeorgia; however, the Parachucla oc cursinnorthernmost Nassau County, Florida. The Penney Farms Formation also grades laterally, to the south, into undifferentiated Hawthorn Group. The carbonate section of the Penney Farms Formation has often been referred toasthe basal Hawthorn dolostoneinnorthern Florida.Itislithologically distinctive enough toberecognizableinwell cuttings, eveninrelatively poor quality cuttings. The gamma-ray signature also is quite distinctive, con sisting of a number of very high counts per second (cps) peaks (see sectionongamma-ray logs). The full areal extent of the Penney Farms depositiononthe Ocala Platform is not presently known. The occurrence of sediments assigned to this unit at the Martin-Anthony road cutinMarion County (elevation 140 to 150 feet [43-46 meters] above MSL) suggest depositionona significant portion of the platform. MARKS HEAD FORMATION Definition and Reference Section Huddlestun (in press) reintroduced the Marks Head Formationaspart of the Hawthorn Group in Georgia. The Marks Head Formationisextended here to encompass the middle unit of the Hawthorn Groupinnorth Florida. The lithologic similarities between the Marks Head Formationinsoutheast Georgia andinnorth Florida warrants the use of the same nomenclature. Huddlestun (in press) describes the type locality of the Marks Head Formation in Georgia from out crops at and near Porters Landinginnorthern Effingham County, Georgia. The readerisreferred to Hud dlestun(inpress) for descriptions of these localities and for a historical summary of the Marks Head For mationinGeorgia. The proposed reference section for the Marks Head FormationinFlorida lies between-89feet(-29meters) MSL and -190 feet(-58meters) MSLinthe Jennings#1core,W-14219, Clay County, Florida (SE1f4,SE1f4, Section27,Township4S,Range 24E) (Figure20).The land surface elevationis90feet (27 meters) MSL. Lithology The Marks Head FormationinFlorida consists of interbedded sands, clays and dolostones throughout its extent. Carbonate beds are more commoninthe Marks Head FormationinFlorida than in Georgia; the proportion of carbonate, bothasa rock type andanaccessory (matrix) mineral, gradually increases into Florida. This unitisthe most lithologically variable formation of the Hawthorn Groupinnorth Florida. Miller (1978) defined his Unit D (equivalent to the Marks Head Formation)asbeing "complexly interbeddedshell limestone, clay, clayey sand and fine grained sandstone." The variable nature of the Marks34

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zo 0(2:II:f(/)2:II:0(l&.> WZZW Ii. HAWTHORN GROUP 0(2:II: o l&.II: W> iz:oJ0((/) > II: ozoPHOSPHRTESRNOPHOSPHATESANDPHOSPHATESANDOOLOHITESANDODLOHlTECLAYSAND SAND SAND SANDSRNODOLDHlTE DOLDHlTECLAY CLAY CLAYDOLOHlTECLAYDOLOHITE DOlOHlTE DOLDHITESRNDDDLOHITECLAYOCALAGROUPDOLOMITEDOLOMITE OOlOHlTE DOLOHITEDOLOMITEDOLOHlTE OOLOHlTE OOLOHITE OOLDHlTE OOLOHlTESRNDCLAYSANDDOLDHlTECLRYOOLOHITE DOLOHITE DDLOHlTEPHOSPHATEDOLUM! It: PHOSPHATEDOLOHITEPHOSPHATEDOLDHITEPHOSPHATEDOLOMITEPHOSPHATEDOLOHITEPHOSPHRTESRNOCLAYSRNDDOLOMITEPHOSPHEHE CLAY PHOSPHRTE PHOSPHRTESANDPHOSPHATE SrlNO PHOSPHATESAND PHOSPHA'!'E SAN[JOOLOHITEDOLOMITEOOLOMTTE COLCI11iE OOLOHITESAND SANDSRND SRIIlD OOLOH]TE---------------------------------------------------------------------------------'-'._.._.._.. _. _._. .. .-:-.:.-:-.:--:-.:--:.. :11=======----------------.=.-.-.-.-. -:-.-. Reference section for the Marks Head Formation, Jennings#1,W-14219, Clay County (Lithologic legend AppendixA).-'100-390-360 -380 -370 -350-3't0-330-270 _ -320-260 _ :1 -=.=:=:=:-=.=:=:-1 -19(_.1.1.1.1 -250__-[80-2't0 _ -220 _-210 -230 __ .-200 Figure 20. W-I't219 zo 0(2:II: o l&. Q 0( W :z:(/)lll:II:0(2: zo 0(2:II: o l&. W o 0(:z:0((/) o ooQ zW II: W ItQ z ;:) H UCLRYPHOSPHAiEPHOSPHATE PHOSPHATE PHOSPHATEPHOSPHRTEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATFPHOSPHATECLAY PHOSPHr.TE CLAYPHOSPHATECLAYPHOSPHATEClAY PtlOSPHATE CLAYPHOSPHATECLAYPHOSPHATECLRY HAWTHORNPHOSPHATECLAYPHOSPHATECLRYPHOSPHATECLAY GROUPCLAY CLAYPHOSPHATE PHQSPHA'!E DOlDHITEPHOSPHATEDOLOH!iEPHOSPHATEDOlOH!TEPHOSPHATEDOLOHITEPHOSPHATEDOLOMITEPHOSPHATESANDDOLGHlTEOOLOMlTE OOLQ!ilTi.OOLOMi TEOGLOMITEOOLOMlTEPHOSPHATEOOLDMIlEPHOSPHATEOOLONlTE PHosrHATE OOLG:1lTEflH05PI/FiTEPH(JSPUATE PHOSPHATE PHOSPHATESANDaOLOHlTEPHOSPHnTEOOLOHlTEPHOSPHATEOOLOHJTEPHOSPHATEDOLDHlTEPIIOSPHATEODLOHJTEPHOSPHnTEOOLOHJTE PHOSPHATE OOLOHJTEPHOSPIIATEPHOSPHnTE PIIOSPHOTEPtlOSPHATE PtlOSPHATEDOLOHITE OOLOHITE OOLOHITE DOLOMITE DOLOMITE DOLOHIlEPHOSPHATESANDDOLOM]TESANDDOLDMITESANDDOLOMITEPHOSPHATE PHOSPHATE PHOSPHATEPHOSPHRTE PHOSPHRTEDOLOMITEP.tOSPHATEDOLOMITEPHOSPHATEDOLOHlTEPHOSPHATEOOLOHITEPHOSPHATEDDLOHlTELAND SURFACE-----------'-''-'._.._.--------------.... ...... ....... :t:3t:3t:3t:::=::: .... :::::....:::::-:::::7080205090'10-'10106030-90-10-60-20 -80-70-50-30-100-110 -120-130 -l't0-150-l70-160 35

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W-12360 HAWTHORN GROUPOCALAGROUP COOSAWHATCHIEMARKSHEAD FORMATION FORMATION PENNEY FARMS FORMATIONSAND SANDPHOSPHATESRNOPHOSPHATESANO. PHOSPHRTESANDCLRY PHOSPHATE ODLOHITE PHOSPHRTE OOLOHITE PHOSPHATE OOLOHITE PHOSPHATE DOLOHITE PHOSPHRTE OOLOHlTE PHOSPHATE OOLOHITE PHOSPHATE OOLOHITE PHOSPHATE DOLOHITE PHOSPHATE OOLOHITE PHOSPHATE OOLOHITEPHOSPHATE PHOSPHATE PHOSPHRTESRNDPHOSPHRTESANDPHOSPHATE CALC ITEPHOSPHATECRLCITEPHOSPHATECALCITEPHOSPHATE CALC ITEPHOSPHATECALCITEPHOSPHRTECALCITEPHOSPHATESANOPHOSPHATESANOPHOSPHATESAND SRNOOOLOHITE PHOSPHATE SAND PHOSPHATE SRND PHOSPHATE SANO PHOSPHATESRNDCLAY PHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPI-tRTE PHOSPHATE PHOSPHATE PHOSPHATESAND 7" -/ 7"-/-/. /7"/---;--=-;-=-;.":'.-.":'.-.":.-.":.' .......... . ..;. . .:..-:. ..:...-:. ..:...-:-.::f:::f:3f:::f: :-.------:p=:p=:p=:p:/ /PHOSPHRTE CLRY PHOSPHATE CLAY PHOSPHRTE CLRY PHOSPHATE CLAY PHOSPHRTE CLRY PHOSPHATEDOLOHITEPHOSPHRTE DOLOMITE PHOSPHATE OOLOHITE PHOSPHATEOOLOHlTE.'-' '-' "1PHOSPHATE '-'._••_.._.PHOSPHRTE OOLOHITE ------'i'-':---:.--:-:PHOSPHATE1.001".1.0.1 I t=" t="f-.f-PHDSPHRTE PHOSPHATE PHOSPHATECALcnEPHOSPHATECALCITECLAY PHOSPHATECALCITEPHOSPHRTECALCITECLAYCALCITE CALCITE CALCITEPHOSPHATE CLAY PHOSPHATE PHOSPHATE SANDCALCITESANDcALcnESANDCALClTESANDCALcnEPHOSPHATESANDPHOSPHATESANDPHOSPHATE SAND PHOSPHATESANDPHOSPHATE SAND CLAY PHOSPHATEDOLOHITEPHOSPHATEDDLOHlTEPHOSPHATEDOLOHITEPHOSPHATEDOLOHlTEPHOSPHATE OOLOH]TEPHOSPHATE OOLOl1l1E PHOSPHATEDOLOHITEPHOSPHATEDOLOHITEPHOSPHATE OOLOHITE PHOSPHATEOOLOHlTEPHOSPHATE PHOSPHRTE PHOSPHRTESAND"PHOSPHATESANDPHOSPHATESANDSANOCRLClTESANDCALClTE -281'1 _ -lll'1-l'l-l'1 -[31'1 _ -291'1-2'1-1'1--:--60 -70 _ -50-L61'1-260 _ -80 _ -[21'1 _ -270 -250 _ -l90-l50 _ -181'1-171'1 _ -201'1 _ ::::.7. ... 7. .. -231'1 _ w :E::E:==c(U) o ooCHARLTON MEMBERHAWTHORN GROUPPHOSPHATE SAND PHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDOOLOHI PHOSPHATE DOLDH]TEPHOSPHATEDOLOHlTEPHOSPHATEOOLDHl1EPHOSPHATEDOLOHITEPHOSPHATEDOLOHllEOOLOHITE CLAY nmnHTTF rlRYCALCITECALCITECALCITECALCITECALCITE CALCITE CALCITECALCITECALCITECALCITE CALCITECALCITE CALCITE CALCITECALcnE CALcnECALCITELANDSURFACECRLCITECALenECALCITE CALCITECLAYCLAYCLRYCLAY CLAYCLAYCLAYCLAYCLAYCLAYClAYCLAYCLRY CLRYCLAY(AlenECALCITECALCITECLAYSANDUNDIFFERENTIATEDCLAYHEAVY"INS.HEAVY"INS.CLAYCLAYCLAY GYPSUMGYPSUM CLAYHEAYY"INS.CLAYHEAVY"INS.HEAVY"INS.---------------..f-."""""'.""..-----------------'-._ .. _ .._.'-'1 :-;-:-.;-;-:-:-;-:-:-;-: I ::::::::::::::::::: .. ...... . ------I:gf:gf! gf! . : ••••••••• .• .-....'""'"To.-.,.. ••.. --... . .....,.. . ....,.. .. :::::Z:::t:::t: ::t: ::t:: ....... 191'1-40171'1181'1Ill'111'1161'1-3021'11'111'11'1-1021'1-20121'131'1151'1141'1131'151'181'171'1 61'191'1'11'1 Figure 21. Reference section for the Marks Head Formation, N.L.#1,W-12360, Bradford County (Lithologic legend AppendixA).36

PAGE 55

Head is readily apparent when comparing the lithologic columnsof W-14219 (Figure 20) and W-12360 (Figure 21). The carbonate portion ofthe Marks Head Formation is typically dolostone; limestone is uncommon but does occur sporadically as is the case throughout the Hawthorn Group. The Marks Head dolostones are generally quartz sandy, phosphatic and clayey. The dolostones varyininduration from poorly con solidated to well in,durated. The induration variesininverse relationship to the amount of clay present within the sediment. Phosphate grains normally comprise up to 5 percent; however occasional beds may contain significantly higher percentages. Quartz sand content varies from less than 5 percent to greater than 50 percent where it grades into a dolomite cemented quartz sand. The dolostones range from yellowish gray(5Y 7/2) to olive gray(5Y 4/1)incolor. Crystallinity varies from microto very finely crystalline with occasional more coarsely crystalline zones. Molds of mollusk shells are often present. The occurrence of limestone within the Marks Head Formation in Florida is quite rare. The majority of the"limestone"reported from this part ofthe section by other workers is actually dolostone. The limestone that does occur is characteristically dolomitic, quartz sandy, phosphatic, clayey, and fine grained. The quartz sands from the Marks Head Formation are generally fine to medium grained (occasionally coarse grained), dolomitic, silty, clayey and phosphatic. The dolomite, silt and clay contents are highly variable and the quartz sands are gradational with the other lithologies. Phosphate sand is usually pre sent in amounts ranging from 1 to 5 percent; however, phosphate grain percentages may range con siderably higher in thin and localized beds. The quartz sands are typically light gray(N7)to olive gray(5Y 4/1) in color. Induration varies from poor to moderate. Clay beds are quite commoninthe Marks Head Formation, occasionally comprising a large portion of the section. The clays are quartz sandy, silty, dolomitic and phosphatic. As is the case in the Penney Farms Formation, the Marks Head clays contain highly variable percentages of accessory minerals; relatively pure clays do occur but are not common. The clays range from greenish gray(5GY 6/1) to olive gray(5Y 4/1) in color and are typically lighter colored than the clays of the underlying unit. Phosphate grains are present virtually throughout the Marks Head Formation. They characteristically occur as brown to black, sand-sized grains scattered throughout the sediments. The phosphate grains are rounded and often in the same size rangeasthe associated quartz sands. Phosphate pebbles occur rarely. Mineralogically, the Marks Head Formation clays contain palygorskite, sepiolite, smectite and illite; kaolinite is present only in the weathered section (Hettrick and Friddell, 1984). Hettrick and Friddell (1984) indicated that palygorskite is often the dominant clay mineral in this unit; smectite is the second most abundant clay mineral. Smectite becomes the most abundant clay mineral when palygorskite con tent decreases. Other minor mineralogic constituents include mica, opal-ct, and feldspar. Huddlestun (in press) reports the occurrence of zeolite in the Marks Head FormationinGeorgia. The Marks Head Formation becomes difficult to identify in the southern portion ofthe area between the Sanford High and the Ocala Platform (Figure22).Within this transition zone the Marks Head loses most ofthe dolostone beds. The distinction between this unit and the overlying Coosawhatchie Formation becomes problematic. As a result, the Hawthorn Group in this area is referred toasundifferentiated. Ad ditional coring in the transition zone may delineate the facies changes through this zone and more ac curately determine the correlation of this unit into central and south Florida. Subjacent and Suprajacent Units The Marks Head Formation is underlain disconformably throughout most of its extent by the Penney Farms Formation. The upper member of the Penney Farms Formation consists predominantly of darker, olive gray(5Y 3/2) colored sands and clays with occasional dolostone beds. The base ofthe Marks Head Formation is placed at the contact between the darker colored sands and clays ofthe upper Penney Farms and the generally lighter colored, more complexly interbedded sands, clays and dolostone ofthe Marks Head. Occasionally, the contact is marked by a rubble zone containing phosphatized carbonate 37

PAGE 56

• CORESLIMITSOF HAWTHORN GROUP HAWTHORN GP.UNDIFFERENTIATEDCI •25 FEET2040MILES, I,I KILOMETERSi20SCALEIIFigure 22. Top of the Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group.38

PAGE 57

clasts but the unconformity is often difficult to recognizeincores.Inthe western-most portion of Hamilton County, the Marks Head is underlain by the sandy carbonates of the Penney Farms Formation. The Coosawhatchie Formation disconformably overlies the Marks Head Formation throughout north Florida except where it has been removed by erosion.Inthese areas the Marks Head is overlain by sediments referred toasundifferentiated, post-Hawthorn deposits. The Coosawhatchie-Marks Head contact is generally placed at thetop of the first hard carbonate bed or light colored clay unit below the darker colored clayey, dolomitic, quartz sands and dolostones of the basal Coosawhatchie Formation. Occasionally, the contact appears gradational in a sequence of dolostones and interbedded sands.Inthis case the topof the upper-most dolostone bed is regardedasthe boundary. Occasionally a rubble bed marks the unconformity. The relationship of the Marks Head Formation to the underlying and overlying units is graphically il lustrated in Figures11through 16. Thickness and Areal Extent The Marks Head Formation of the Hawthorn GroupinFlorida occurs primarilyasa subsurface unit. The topof the Marks Head Formationinthe subsurface varies from -260 feet MSL (-79 meters) in Carter#1,W-14619,Duval County to + 114 feet MSL(+35meters)inDevil's Millhopper#1,W-14641, in Alachua County (Figure 22). The Marks Head Formation dips to the northeast from the flanks of the Ocala Platform toward the Jacksonville Basin withanaverage dip of 4 feet per mile (0.8 meters per kilometer) (Figure 22). The direc tion of dip ofthe Marks Head Formation trends towards the north from theSt.Johns Platform into the Jacksonville Basin (Figure4).The direction and angle of dip may vary locally. The thickness of the Marks Head Formation varies from being absentonthe crest of the Ocala and Sanford Highs to 130 feet(40meters)inN.L.#1,W-12360, Bradford County (Figure 23). It is interesting to note that this well is not in the Jacksonville Basin but to the southeast of it. The Marks Head Formation is present throughout much of north Florida.Itapparently has been removedby erosion from the Sanford High (Figures 4 and23)and has not been identifiedonthe Ocala Platform possibly being absentasa result of erosion or non-deposition.Inthe area between the Ocala and San ford Highs, the Marks Headisvery thin and becomes difficult to recognize, merging southward into the undifferentiated Hawthorn Group. Age and Correlation Dateable fossil assemblages within the Marks Head Formation have not been foundinnorth Florida. The only fossils noted were scattered molds of mollusk shells and occasional diatom molds. Lithologic correlation between these sediments and those in Georgia, where fossiliferous sediments are found, in dicates that the Marks Head Formation is late Early Miocene (Burdigalian) age (Huddlestun, personal communication, 1983). Planktonic foraminiferainGeorgia indicate Zone N.6 or early N.7 of Blow (1969). Huddlestun (in press) suggests that the Marks Head FormationinGeorgia is correlative with the Tor reya Formation (Banks and Hunter, 1973) in the eastern panhandle of Florida (Figure19).Huddlestun (in press) considers both formations tobeslightly older than the Chipola Formation in the Florida panhandle which has been correlated with the upper part of planktonic zone N.7 of Blow (1969). It is suggested here that the Marks Head Formation of north Florida is correlated with at least the upper part of the Arcadia Formation and is younger than the Arcadia's Tampa Member in southwest Florida. The Marks Head For mation is thought to be a time equivalent of the lower part of the downdip Bruce Creek Limestone in the southern part ofthe Apalachicola Embayment. It appears that the Marks Head Formation maybecor relative with the lower Pungo River FormationinNorth Carolina, basedonages suggested for the Pungo River by Gibson (1982). As is the case for the Penney Farms Formation, the Marks Head Formation is older (see Figure19)than the previously accepted age for the "Hawthorn Formation" in Floridaasinterpreted by Cooke39

PAGE 58

HAWTHORN GP, UNDIFFERENTIATED • CORESCI•25FEET Z1 LIMITS OF HAWTHORN GROUp1RSCALEo2040MILES "I-T"""'&".,.--.,.1'-1"............. _-1'o2040KILOMETERSFigure 23. Isopach of Marks Head Formation. Shaded area indicates undifferentiated Hawthorn Group.40

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(1945) and Puri aRd Vernon (1964). Puri and Vernon suggested a strictly Middle Miocene age for their "Hawthorn." Discussion The extension of the name Marks Head Formation into Florida was basedonthe general lithologic similarities between the sediments in Georgia and those in Florida. Despiteanincreased carbonate con tent in the Florida section, the units are quite similar and the Georgia lithostratigraphic nomenclature is used to avoid stratigraphic confusion. The Marks Head Formation, like the time-equivalent unit in the panhandle, the Torreya Formation, con tains significant amounts of clay. As reported by Hetrick and Friddell (1984), palygorskite is generally the dominant clay mineral with subordinate amounts of smectite. The occurrence of large amounts of palygorskite is suggestive ofanunusual set of environmental circumstances which prevailed over large areas of the southeastern coastal plain. The exact conditions are not well understood. However, whether palygorskite is a product of brackish water lagoons (Weaver and Beck, 1977) or ephemeral (alkaline) lakes (Upchurch, et aI., 1982), the fluctuating sea levels in late Early Miocene could have reworked these deposits, incorporating vast amounts of palygorskite into the Marks Head sediments. Future detailed clay mineralogy investigations may facilitate a better understanding ofthe genesis of the clays and of the depositional environments of the Marks Head Formation. COOSAWHATCHIE FORMATION Definition and Reference Section The Coosawhatchie Formation of the Hawthorn Group is usedinthis paper for the upper unit ofthe group in much of north Florida. Huddlestun (in press) proposed the Coosawhatchie as a formal lihtostratigraphic unit in Georgia.Itextends into north Florida with only minor lithologic changes. The Coosawhatchie FormationinFlorida consists of three members: informal lower and upper members and the Charlton Member,asdefined by Huddlestun (in press). The Charlton Member will be discussed separately. A basal clay bed occurs in a few coresinSt. Johns County and may equate with the Berryville Clay (Huddlestun, in press). The type locality for the Coosawhatchie Formation is at Dawsons Landingonthe Coosawhatchie River in Jasper County, South Carolina,asdescribed by Heron and Johnson (1966). Huddlestun (in press) sug gests a reference localityinGeorgia along the Savannah River in Effingham County. The reference section for north Florida isinthe Harris#1core, W-13769, Clay County (SW1f4,SE1f4, Sec.7,T6S, R25E) (Figure 24). The surface elevation of the core is97feet(30meters) MSL. The top of the Coosawhatchie Formation in Harris#1isat+37feet (+11meters) MSL (Figure 24), the base is at -74 feet (-23 meters) MSL. Lithology The Coosawhatchie FormationinFlorida consists of quartz sands, dolostones and clays. Characteristically, sandy to very sandy dolostoneisthe most common lithologyinthe upper informal member, where it is interbedded with quartz sands and clays.Inthe lower informal member, the quartz sands and clays predominate with interbedded dolostones. The quartz sands are dolomitic, clayey and phosphatic. The sand grains are fine to medium grained, poorly to moderately sorted, and subangular to subrounded. The proportions of accessory materials vary greatly. The sands grade into the dolostones and claysinmany instances. The phosphate grain content is quite variable ranging from a trace to more than20percent. Clay content varies from less than 5 per-41

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zo :2: a: (I):2: a: it>w zz Wl1. HAWTHORN GROUP OCALAGROUPPHOSPHATEPHOSPHATEPHOSPHATECLAYPHOSPHATEDOLOHnePHOSPHATEDOLOMITePHOSPHATEDOLOMITEPHOSPHATEOOLDHlTEPHOSPHATE CLAY PHOSPHATE CLAYSANDSANDSANDPHOSPHATESANDPHOSPHATEPHOSPHATESANDSANDPHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATESANDDOLOMITEPHOSPHRTECLAYPHOSPHATECLAYPHOSPHATECLAY PHOSPHATE CLAYPHOSPHAtESANDPHOSPHATESANDPHOSPHATE SANDPHOSPHATESANDPHOSPHATE SANDPHOSPHATESANDPHOSPHATE SANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESRNDPH[lSPHATEPHOSPHATE PHOSPHATECLAY HEAD FORMATIONPHOSPHATECLAYPHOSPHATECLAYCLAYDOlOH]TECLAY'CRYSTALRIVERFORMATIONPHOSPHATESANDPHOSPHATESANDPHOSPHRTESANDPHOSPHATESANDPHOSPHATESAND SANDDOLDtHtE P""""R"W-13769 SANDSANDPHOSPHATESAND DOlQ"TTE PHOSPHATEOOI..OHITEPHOSPHATEDOtCHITE_'::._----------------------------------220 -210 -190 -200 -120 _ . .;.::0••_._.,_,._._.-'. -80 -90-160 -170-[80-150-1't0-100 Reference section for the Coosawhatchie Formation, Harris#1,W-13769, Clay County (Lithologic legend AppendixA).PHOSPHATEFigure24. HAWTHORN GROUPLAND SURFACEUNDIFFERENTIATEDCLAYPHOSPHATESANDSILTPHOSPHRTEDOLOMITESILTPHOSPHATEOOt..OMITESILTPHOSPHATEDOLOHITEPHOSPHATE PHOSPHATEPHOSPHRTECLAYPHOSPHRTECLRY ZPHOSPHATECLRY0 i= PHOSPHRTESRNDDOLOHITE ec PHOSPHRTESAND :Ea: PHOSPHATECLAY0PHOSPHRTE CLAYIL PHOSPHRTECLRYPHOSPHAtE DOLOMITE W PHOSPHATEoOLoHITE %u PHOSPHATEDOLOMITE IPHOSPHATEDOLOHITE ec PHOSPHRTEDOLOMITE %ecPHOSPHhTE SRNDOOLOt'llTE en PHOSPHATESAND0PHOSPHATESAND0 U PHOSPHATEPHOSPHRTE PHOSPHRTEPHOSPHATEPHOSPHRTEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTE CLAY _._._. .-;._.-; . ...:-;._.-;. _.._.._.._._._._..'-''-''-''-'.................---.............._._.-'. . ...:-:._.-:..-;-.-.:-; . ...:-:._.-; .. . ...:-:._.-;._.-; ..'-''-''-'._.. ..........._.-'-' 0••_.,_,._.-.....-. .;..;:.;..;:.;..;:.;.. _.'-' ._ .._.--'-'-'_.._.'-''-'--'1...... ................_. ................'-''-''-''-'..... .:::::::::::::::-///y .... . .:-:-:.:-:-:.:. -'10 -60-70-50 -3010-2030-1020 50 80 70 90 60 cent to greater than 30 percent. The sands are often lighter coloredinthe upper member where there is more carbonateinthe matrix and darkerinthe lower member. Colors range from greenish gray(5GY 6/1) and light gray(N7)to olive gray(5Y 4/1). Induration is generally poor. The dolostones of the Coosawhatchie Formation are quartz sandy, clayey and phosphatic. The percentages of quartz sand and clay vary widely and maybeasmuchas50 percentintransitional zones. Phosphate grain content is quite variable also, but is generally less than 10 percent. The dolostones are microto fine crystalline, poorly to moderately indurated and occasionally contain molds of fossils. They range in color from light gray(N7)and greenish gray(5GY 6/1) to olive gray(5Y 6/1). The dolostones of the upper member appear to become more calcareousinthe Jacksonville Basin. The claysinthe Coosawhatchie Formation are typically quartz sandy, silty, dolomitic and phosphatic. The clays are light olive gray(5Y 6/1) to olive gray(5Y 4/1). Clay beds are most common in the lower member (Scott, 1983). The clay mineralogy is dominated by smectite (Hetrick and Friddell, 1984). The clay beds often contain diatoms (Hoenstine, 1984). The phosphate grains presentinthe Coosawhatchie Formation are normally amber colored to brown or black; lighter colors occur near the land surface. The phosphate grains are usually well rounded and in42

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the same size range as the associated quartz sands. Coarser phosphate sands and phosphate pebbles or rubble are not common but are present. Subjacent and Suprajacent Formations The Coosawhatchie Formation disconformably overlies the Marks Head Formation but the disconfor mity is often not readily apparent. Itis,however, recognized biostratigraphically in Georgia (Huddlestun, personal communication, 1983). The contact often occurs in a thin gradational sequence of interbedded sands and dolostones. Occasionally, the contact is marked by a rubble bed. The Statenville Formation 9f the Hawthorn Group overlies and interfingers with the Coosawhatchie in Hamilton and Columbia Counties and possibly a small portion of Baker County. The contact is confor mable and is recognized by the occurrence of more phosphate grains and less carbonate in the Staten ville and the thin bedded nature of the Statenville. With the exception of the area described above, the Coosawhatchie in Florida is overlain unconfor mably by undifferentiated post-Hawthorn deposits. These include sands, clays, shell beds and occa sional limestones. The relationship of the Coosawhatchie to the underlying and overlying units is in dicated in Figures11through16.Thickness and Areal Extent The Coosawhatchie Formation occurs throughout much of north Florida. The top of the Coosawhatchie ranges from -93 feet MSL (-28 meters)inBostwick#1,W-14477, Putnam County to+168 feet MSL(51meters) in Devils Millhopper#1,W-14641, Alachua County (Figure25).It attains a maximum thickness in Florida (including the Charlton Member) of 222 feet (68 meters)inCarter #1, W-14619, Duval County (Figure 26). The Charlton Memberinthis coreis23 feet (7 meters) thick. Huddlestun (in press) indicates that the Coosawhatchie attains a maximum thickness of 284 feet (87 meters)inthe southeast Georgia Embayment. The Coosawhatchie Formation dipsina northeasterly direction from the flanks of the Ocala Platform toward the Jacksonville Basin (Figures 4 and26).From the St. Johns Platform it dips t9 the west off the structure and to the north into the Jacksonville Basin (Figures 4 and26).The average dip is approximate ly 4 feet per mile (0.8 meters per kilometer). Variationsinthe angle and direction of dip are evident from Figures11through16.The Coosawhatchie Formation is not known to occur over the Ocala and Sanford Highs or in the im mediately surrounding areas. This is thought tobedue primarily to erosion; nondeposition may also have played a role. The Coosawhatchie extends from Georgia southward into central Flordia.Incentral Florida (between the Ocalaand Sanford Highs) it becomes difficult to distinguish and is included in the undif ferentiated Hawthorn Group. Age and Correlation Huddlestun (in press) suggests a Middle Miocene (Early Serravallian) age for the Coosawhatchie For mation basedonplanktonic foraminifera. Huddlestun placed itinZoneN.11of Blow (1969). Hoenstine (1984) studied diatoms from a few selected cores through the Hawthorn. He recognized a Middle Miocene assemblageinFlorida sediments assignedinthis paper to the Coosawhatchie Forma tion. The Coosawhatchie Formationisthought to be correlative with the lower portion of the Intracoastal Limestone in the Apalachicola Embayment (Schmidt, 1984) and the lower Shoal River Formation in the Florida panhandle (Huddlestun, pers. comm., 1983).Inthe peninsular area of Florida, it appears to cor relate with the lower part of the Peace River Formation of this paper. The Coosawhatchie was correlated with much of the Pungo River FormationinNorth Carolina by Gibson (1982) and Riggs (1984) (Figure 19). 43

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CI • 25FEET,i40KILOMETERSI20 • CORESSCALE HAWTHORN GP.UNDIFFERENTIATED LIMITSOF HAWTHORN GROUPoIo. R Figure 25. Top of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group.44

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LIMITSOF HAWTHORN GROUP HAWTHORN GP,UNDIFFERENTIATED • CORES i. SCALEoI'Io2020ICIFEETFigure 26. Isopach of Coosawhatchie Formation. Shaded area indicates undifferentiated Hawthorn Group.45

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Discussion The Coosawhatchie Formationiswidespreadinnorthern Florida and throughout most of this area it is the uppermost Hawthorn sediment encounteredinthe subsurface.Inlimited areas it is shallow enough tobeexposedinsome foundation excavations. The Coosawhatchie Formationinthe Jacksonville Basin contains a lower clay bed of variable thickness. This clay bed correlates with the Berryville Clay Member of the Coosawhatchie Formationinsoutheastern Georgia. The Coosawhatchie Formationisquite similar to the Peace River Formation of southern Florida in that both are predominantly siliciclastic units. However, the Coosawhatchie contains significantly more car bonateinthe matrix than the Peace River. The formations are gradational with each other through the zone of undifferentiated Hawthorn Group sedimentsincentral Florida. CHARLTON MEMBER OF THE COOSAWHATCHIE FORMATION Definition and Reference Section Huddlestun(inpress) redefined the "Charltonformation" of Veatch and Stephenson (1911) as a formalmember of the Coosawhatchie FormationinGeorgia. He found that the Charlton Memberisa lithofacies of the upper part of the Coosawhatchie (Huddlestun's Ebenezer Member)insouth Georgia and north Florida. Huddlestun(inpress) discussed the reference localitiesinsome detail. A reference section for the Charlton Member of the Coosawhatchie FormationinFloridaisthe Cassidy#1core, W-13815, Nassau County (NWV4,NWV4, Sec.32,T3N, R24E). The surface elevationis80 feet (24 meters) MSL. The Charlton Member occurs from+3 feet(+1 meter) MSL to-43feet (-13 meters) MSL (Figure 27). . Lithology The Charlton Member characteristically consists of interbedded carbonates and clays. Itisless sandy than the upper member of the Coosawhatchie, into which it grades laterally and vertically and typically contains less sand and phosphate grains. It contains a clay component thatisoften very conspicuousinthe cores (Huddlestun,inpress). This has been found to be trueinFlorida also. The carbonate beds of the Charlton Member are often dolostones but range into limestone. They are slightly sandy, slightly phosphatic to non-phosphatic and clayey. They often contain abundant molds of fossil mollusks. The dolostones are finely crystalline, light olive gray(5Y 6/1) and poorly to moderately in durated. The limestones are characteristically very fine grained, slightly sandy, clayey, poorly to moderately indurated, and yellowish gray(5Y 8/1). The clays are dolomitic to calcareous, with poor to moderate induration, silty, and light gray(N7)to greenish gray(5GY 6/1). The clay minerals present include smectite, palygorskite, illite and kaolinite (Hetrick and Friddell, 1984). SUbjacent and Suprajacent Units The Charlton Member both overlies and interfingers laterally with the upper informal member of the Coosawhatchie Formation. The Charlton is simply a distinctive facies of the upper informal member. The Charlton is disconformably overlain by the sediments discussedasoverlying the Coosawhatchie Forma tion. Thickness and Areal Extent Sediments assigned to the Charlton occur at Brooks Sink (SWV4,SWV4, Sec.12,T7S, R20E, Bradford46

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W-138158070 LAND SURFACE ::::::::::::::: CLAYHEAVYMINS.HEAVYHINS. -l80_ PHOSPHATEzo en > W ZZ WQ, HAWTHORN GROUPSRNOCLRYSAND SANDCLAYPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATESILTPHOSPHATESANDPHOSPHATE PHOSPHATE PHOSPHATECLAYPHOSPHATEPHOSPHATESANDCLAYCLAYCLRYCLAYPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATECLAYPHOSPHATE PHOSPHATECLAYPHOSPHATE PHOSPHATE PHOSPHATECLAYPHOSPHATESANDPHOSPHATESANOPHOSPHATESANDPHOSPHATESANDCLRYCLAYCtAYCLAY CLAY CLAYSAND SAND SAND SAND SAND SANDCALCITECLAYCLRY-CLAYSRNDCLAY .o ..nPHOSPHATEDOLOHITEPHOSPHATE"PHOSPHATE PHOSPHATE PHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDDOLOMITEPHOSPHATEDOLOMITECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHATE PHOSPHATE -'100-370,":'.-,":'.-,":'.-.":'.-3'10 ,=-,=-,-.-270_ -310_-320 -280 _-290 _ -330 _-300 -250 -260 -380-390 --360-350-2't0 _ -230-200 _ -220-190_ ::.::.::.::.::.::.::.-1 zo a: f2wi: o :z:c(en o ooHAWTHORN GROUP UNDIFFERENTIATEDSANDCLAYSANDCLAY CLAYCLAYCLAYCLAYCLAY CLAY CLAY CLAYPHOSPHATEOOLOHITEPHOSPHATEDOLOHITEDOLOHITECLAYSANOSAND SANDSRND CHARLTONMEMBERCALCITEPHOSPHATF SANn PHOSPHATESANDPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHATESANDSANDDOlOHIfEPHOSPHATEDOLOHITEPHOSPHATEDOLOHITE PHOSPHATEDOLOMIEPHOSPHRTEOOLOHITEPHOSPHATEOOLOHlTEPHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTEPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE '-''-'._.._......._._.._.._.,_.._.-,....._.,...,..... -'._.._.._............-'.._.._.._.._._,.. . : ..........._. ._...._.'-' --6020'101030-[10_-10 -120 _50-1't0_-'10-20 _ -130_ :::-:::::-:::::-:::::.UUJUll]l!l]tJ-90-100 _ -150_-70 -60 -50 -80 -30'-;-'..,,:-;."':-;-'_'-;-' •PHOSPHATEDOLOMITE '-:-'"':-;-'_'-;-'"':-;', PHOSPHATE DOLotUTE '-;• ...:-:-."':-;-'_'-;-' •PHOSPHATEOOLOHITE ::::-:::: -::::-:::_;:..J' __ .tIllOLUOlll"!"-lTlIE'_-160_-170_.,",.SANDCLAYDOLOMITEOCALA GROUPCRYSTALRIVER FORMATIONFigure 27. Reference core for the Charlton Member of the Coosawhatchie Formation, Cassidy#1,Nassau County (Lithologic legend AppendixA).47

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SCALEoIo LIMITSOF HAWTHORN GROUP _ ...._/"LIMITSOFCHARLTONFigure 28. Top of the Charlton Member (dashed line indicates extent of Charlton). County) at an elevation of+145 feet (44 meters) MSL (Figure 28). The highest elevation for the top of the Charlton in a core wasinWainwright #1, W-14283, Bradford County where it occurred at+109 feet(+33 meters) MSL. The deepest that the top of the Charlton Member was found isinCarter#1,W-14619, Duval County, where it is -38 feet MSL (-12 meters). The Charlton Member of the Coosawhatchie Formation reaches its maximum recognized thickness in FloridainCassidy#1,W-13815, Nassau County, where it is 40 feet (13m.eters)thick (Figure 29). It is very spotty in its occurrence, as is evident from the cross-sections (Figures11through 16). Age and Correlation The Charlton Member, as originally defined by Veatch and Stephenson (1911), was considered Pliocene. Huddlestun (in press) postulates that, based onhis observations of the molluskan fauna and 48

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LIMITSOF HAWTHORN GROUP ...,_.......... LIMITSOF CHARLTONFigure 29. Isopach of the Charlton Member (dashed line indicates extent of Charlton). the lithostratigraphy of the unit, it is Middle Miocene (Seravallian) in age (Figure 19). The Charlton Member correlates with at least part of the informal upper member of the Coosawhatchie Formation. Correlations for the Coosawhatchie Formation are discussedinthe previous section. Discussion The sediments assigned to the Charlton Member of the Coosawhatchie Formation were referred to as the "Jacksonville limestone" by Dall and Harris (1892). Dall and Harris suggested that the "Jacksonville limestone" was Pliocene in age. Matson (1915) changed the jacksonville Limestone to the "Jacksonville formation." Cooke (1945) suggested placing the "Jacksonville formation"inthe Duplin Marl. No type section was ever formally designated for the Jacksonville formation. The lithologic relationship of these sediments,tothe rest of the Coosawhatchie Formation as recogniz-49

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edinthis study supports the work of Huddlestun(inpress). The use of the Charlton Member rather than reintroducing the "Jacksonville limestone (or formation)"issuggested here to aidinnomenclatural con sistency between the Georgia coastal plain and peninsular Florida. The reduction in status of the Charltonisnecessary due to its limited extent. STATENVILLE FORMATION Definition and Type Location The Statenville Formationisa new lithostratigraphic name proposed by Huddlestun(inpress) for in terbedded phosphatic sands, dolostones and clays at thetop of the Hawthorn Groupinthe type section along the Alapaha River near Statenville, Georgia, north of Georgia Highway94.The Statenville Forma tion extends southward into Hamilton and Columbia Counties area of Florida. Reference localities listed by Huddlestun(inpress) include exposures along the Alapahoochee Creek between the Georgia Highway 135 bridgeinsouthwest Echols County and at the bridge over the river 1.25 miles(2km)northeast of JenningsinHamilton County, Florida; and exposures along the Suwannee River approximately one mile (1.6km)above and below the site of theformer Cones Bridge (now a boat landing)inSec.36,T1N,R16EinHamilton and Columbia Counties, Florida. None of these outcrop sec tions expose the entire unit. The best section availableispresentinthe designated reference core Betty#1,W-15121, Hamilton County (NEV4,NWV4, Sec.3,T2N, R12E), Florida. This core provides the only complete section available. The Statenville Formation extends from the surface to 87 feet (26 meters) MSL. Surface elevationis150 feet(46meters) MSL (Figure 30). Lithology The Statenville Formation of the Hawthorn Group consists of interbedded sands, clays and dolostones with common to abundant phosphate grains. The diagnostic feature of the Statenville Formationisits thin bedded, oftencrossbedded, nature thatisexhibitedinoutcrop (Figure31).Outcrops generally con sist of thin beds of dolostone and clay alternating with thin beds of sand. Quartz sands predominateinmuch of the unit. The sands are fine to coarse grained (with occasional quartz gravel present), clayey to dolomitic, poorly indurated, poorly to moderately sorted, and subangular to angular. Colors range from very light gray(N8)to light olive gray(5Y 6/1). The sands are quite phosphatic with thin zones grading into phosphorite sands. The average phosphate grain percentage is approximately10percent. The dolostones, which occur commonlyasthin beds within the Statenville, are sandy, clayey, phosphatic and poorly to well indurated. The dolostones are typically yellowish gray(5Y 8/1) to very light orange(10YR8/2). The percentages of sand, phosphate, and clayinthe dolomites vary widely. Sedimentsinthe Betty#1core indicate that dolostoneismost commoninthe lower portion of the unit. Clay beds are not readily apparentinthe outcrop sections. However,inthe Betty#1core they are quite common and are more abundantinthe upper portion of the Statenville (Figure30).The clay beds are characteristically sandy, dolomitic, phosphatic, light olive gray(5Y 6/1) to yellowish gray(5Y 8/1) and poorly indurated. The clay minerals present are characteristically smectite, palygorskite and illite. Phosphate grains are abundantinthe Statenville Formation. The phosphate grains are tan, amber, and brown to black, rounded, and generally areina similar size rangeasthe associated quartz sands. Huddlestun (in press) discusses phosphate pebbles and clasts (conglomerate)asbeing presentindolomite beds along the Suwannee River and also along the Alapaha River. Phosphorite from the Staten ville Formation is presently being mined by Occidental Chemical CompanyinHamilton County, Florida. These phosphorite sands occurinthe upper, less dolomitic portion of the unit. The thin bedded nature of the Statenville sedimentsisquite distinctiveinoutcrop. Huddlestun (in press) reports that the bedding ranges from horizontal to undulatory to variously cross bedded, with50 '.

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ON OUPNE _ _LANDSURFACE"",7":7":7":7J,..:-;. .HAWTHORN W-15121'-:-;' .GROUPI_I"_I"_I"_"_. -._. ,.-:-;. , --=--=--=--=--=--=--=CLAY--------1--------'-;' .I_""_II_I'_I_. . -'-:::"-=-'-:::"-=.:-:::..-=.:-:::.. -I ...:-;. PHOSPHATEZ -.:=.-=-,:=-, -=-,:=-. -=-.:=-, PHOSPHATESAND0•_t_._.PHOSPHATE-=--=.=--=--=--=--=PHOSPHATE --=--=--=--=--=--=--=-Pf"lSPHATEII(-=--=--=--=--=--=--=PHOSPHATE -=-::.-=--=--=--=--=PHOSPHATE'-:-;' .PHOSPHATE a:...:-;. ,PHOSPHATE0 '-:-;' .PHOSPHATE II."':-;' -'-;' .PHOSPHATE........PHOSPHATECLAYW-::.::.-=--=--=--=--=PHOSPHATE .... ::.::. -=::. -=-=-=--.... =--=-=--=-=--=-=PHOSPHATECLAY...:-;. .PHOSPHATE> "':-;' ,PHOSPHATEZ,PHOSPHATEW -'-;' . , PHOSPHATE ,PHOSPHATE ,PHOSPHATE < --------PHOSPHATEOOLOHITECLAY I-7// //-/-/-71PHOSPHATESAND en.po • IJ ,p.,p.PHOSPHATESANDCLAY----PHOSPHATESANO--PHOSPHATESAND-PHOSPHATESANO---PHOSPHATE ?PHOSPHATE -sA-NIT CLAYCOOSAWHATCHIEPHOSPHATESANOPHOSPHATESAND f-=:i-:=-:=-=:i-:=-= SANDDOLOMITEFORMATION / / /7/ / // 1-'-'-' -' --: PHOSPHATE1-_"__"__,_PHOSPHATE SANDCLAY -/ -/ -7-71 _1-_0__"__DOLOMITE-------":".-=-=-=--=-=-=-SANDDOLOMITEQ :=-::=:=-::=-:=-::=-=< Z /. -/. /'7 W0__ en __ a: a:< 0= =::::;z.II. HAWTHORNGR (', cvSAND SANDST.MARKS FORMATISANDT 7 // / SAND / / / /C'''1n(', CV +-+-+-T-++-+I-SUWANNEE LlMESTO+-++-+-+-+-+-1020100 140 130 120 1L 015070-10305040806090 51Figure 30. Reference core for the Statenville Formation, W-15121, Betty#1,Hamilton County (Lithologic legend AppendixA).

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Figure 31. Photograph of Statenville Formation outcrop showing distinct cross bedding. locally common cut and fill structures. The thin dolostone and clay beds remainassmall ledges while the sands erode deeper into the outcrop (Figure 31). This distinctive bedding is also exposed in the phosphate pits in Hamilton County. Areworked zone with more parallel bedding is present above the crossbedded and thinbedded section. Subjacent and Suprajacent Units The Statenville Formationisunderlain throughout its extentinnorth Florida by the Coosawhatchie For mation with which it also interfingers. The contact between the formations is conformable. The contact is placed at the base of the section of thinbedded, significantly ( >15 percent) phosphatic sands, clays and dolostones. The Statenville Formation occurs from very near the ground surface to thetopofthe Coosawhatchie Formation throughout most of its occurrence. The uppermost portion of the section is often weathered and has lost its dolomite and phosphate content. Near its eastern limit, it maybeoverlain by undifferentiated post-Hawthorn deposits (Figures11through16). -52

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.,\.oS .. • CORESSCALEoI'io2020Ii40 ).." LIMITSOF HAWTHORN GROUPAREAOF STATENVILLE OCCURRENCEFigure32.Area of occurrence of the Statenville Formation. Thickness and Areal Extent The Statenville Formation is recognizedinthree coresinnorth Florida (Figure32).Italso crops out along rivers and streamsinthe Hamilton and Columbia County area. Figure32shows the area where the Statenville is known to be present; lateral limits of the formation are poorly defined at this time. The thickness ofthe Statenville Formation ranges up to87feet (26.5 meters)asrecognized in Betty#1,W-15121, Hamilton County. This represents the greatest known thickness. Age and Correlation Brooks (1966) believed that these sediments were Late Mioceneinage basedonwhat he referred toasinconclusive paleontologic evidence. Limited collections of terrestrial vertebrate fossils from the Staten-53

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ville Formation indicate a Middle Miocene age (Huddlestun, in press). Webb (personal communication,1983in Huddlestun, in press) states that the Statenville mammal fauna is late Barstovian (late Middle Miocene) andisbetween14million and12million years old. Huddlestun (in press) believes this unit to be of Serravallian age, possiblyinpart equivalent to ZoneN.11of Blow (1969). The reworked zone at the top ofthe Statenville section appears tobeLate Miocene basedonvertebrate fossils (Cathcart, 1985, per sonal communication). The Statenville Formation appears equivalent to the upper part ofthe Coosawhatchie Formation. Hud dlestun's (in press) zonal correlation indicatesanequivalence to the upper part ofthe Pungo River For mation in North Carolina. The Statenvilleisalso correlative with part ofthe Intracoastal Formation in the Florida panhandle (Schmidt, 1984) and part ofthe Peace River Formationinsouthern Florida. Discussion The Statenville Formation of northern Floridaisrecognized primarilyinoutcrops along the Alapaha and Suwannee Rivers in Hamilton County and northward into Georgia. The Statenville's limited extent in north Floridaisat least in part due to a rather limited data base. Additional cores and further research willbenecessary to better define the limits and relationships of the Statenville and associated units. ALACHUA FORMATIONTheAlachua Formation, originally called the "Alachua clays" by Dall and Harris (1892), isanoften misused and misunderstood unit. The original definition included sands and clays filling in karst depres sions or stream channels related to sinkholes. Sellards (1914) greatly expanded the definition of the Alachua Formation by including the hardrock phosphate-bearing deposits of the "Dunnellon formation"inthe Alachua. He felt that the sands of the"Dunnellon"were a facies of the "Alachua clays." Later authors (Cooke and Mossom, 1929; Cooke, 1945) followed the expanded definition of the Alachua. Vernon (1951) discussed the Alachuaas"amixture of interbedded, irregular deposits of clay, sand and sandy clay of the most diverse characteristics." Puri and Vernon (1964) also used this definition. Discussions ofthe origin ofthe Alachua Formation have yielded a number of theories. Cooke (1945) believed that this unit was a residual,insitu accumulation of weathered Hawthorn sediments. Puri and Vernon (1964) felt the Alachua Formation was terrestrial and in part lacustrine and fluviatile. Brooks(1966,in Teleki, 1966) suggested that the Alachua was formed by depositioninan estuarine environment and included residual Hawthorn deposits overlain by slumped Pliocene fluvial and sinkhole accumula tions. Based on the occurrence ofthe hard rock phosphates, the paleoextent oftheHawthorn Group sediments (Scott, 1981), field inspection of outcrops and the eXisting literature, the present author feels that this unit resulted from the weathering and/or reworking ofHawthorn Group sediments. The Alachua Formation at this time is not consideredaspart of theHawthorn Groupinpeninsular Florida. Suggested ages ofthe Alachua Formation range fromasoldasMiddle Miocene (Vernon, 1951) toasyoung as Plio-Pleistocene (Pirkle, 1956b). The rangeinsuggested ages canbeattributed to a multiple phase development for this deposit. For example, different generations of karst or different cycles of reworking can incorporate similar lithologic packages with differing vertebrate faunas enclosed. As a result sediments assigned to the Alachua Formation may range in age from the Miocene to the Pleistocene.Itis readily apparent that the Alachua Formation is a complex unit. Further research is necessary to better understand and delineate this complex unit. 54

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ARCADIA FORMATION PEACE RIVER FORMATION POST HAWTHORN UNDIFFERENTIATED BONE VALLEVMEMBER 0... o t----------1ffi z a: o If-I "SUWANNEE" LIMESTONEOCALAGROUP CRYSTAL RIVER AND WILLISTON FORMATIONSFigure33.Lithostratigraphic units of the Hawthorn Groupinsouthern Florida.55

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SOUTH FLORIDAAlthough the Hawthorn Groupinsouth Florida consists of the same general sediment types (car bonate, quartz sand, clay and phosphate), the variability and complexity of the section is different from the stratainnorthern Florida.Inthe south Florida area (Figure1),particularly the western half of the area, the Hawthorn Group consists of a lower, predominantly carbonate unit andanupper, predominantly siliciclastic unit. Eastward the section becomes more complex due to a greater percentage of siliciclastic beds presentinthe lower portion of the Hawthorn Group. The differences that exist between the northern and southern sections of the Hawthorn Group require separate formational nomenclature.Insouthern Florida, the Hawthorn Group consists ofinascending order, the Arcadia Formation (new name) with the Tampa and Nocatee (new name) Members and the Peace River Formation (new name) with the Bone Valley Member (Figure33).The new nomenclature helps alleviate many of the previously existing problems associated with the relationship of the Bone Valley, Tamiami, Hawthorn, and Tampa unitsinthe south Florida region. ARCADIA FORMATION Definition and Type Section The Arcadia Formationisa new formational name proposed here for the lower Hawthorn carbonate sectioninsouth Florida. This unit includes sediments formerly assigned to the Tampa Formation or Limestone (King and Wright, 1979) and the "Tampa sand and clay" unit of Wilson (1977). Dalland Harris (1892) used the term "Arcadia marl" to describe beds along the Peace River. This term was never widely used and did not appearinthe literature again exceptinreference to Dalland Harris. It appears that their use of the "Arcadia marl" described a carbonate bed now belonging in the Peace River Formatien of the upper Hawthorn Group. Riggs (1967) used the term "Arcadia formation" for the often exposed at the bottom of the phosphate pitsinthe Central Florida Phosphate District. Riggs' use-or-this nam-ewa.Snever formalized. The "Lexicon of Geologic Names" (U.S.G.S., 1966) listed the name Arcadia as being used as a member of the Cambrian Trempealeau Formation in Wisconsin and Minnesota, thereby precluding its use elsewhere. Investigations into the current status of this name indicated that the Arcadia member has not been usedinsome 25 years and does not fit the current Cambrian stratigraphic framework. The Lexicon also indicates Arcadia clays asanEocene (Claibornian) unitinLouisiana. This name also has been dropped from the stratigraphic nomenclature of Louisiana (Louisiana Geological Survey, 1984, personal communication). Since these former usages of this name arenolonger viable, the term canbeused for the lower Hawthorn Group sedimentsinsouthern Floridainaccordance with Article20of the North American Code of Stratigraphic Nomenclature (NACSN, 1983). The Arcadia Formationisnamed after the town of ArcadiainDeSoto County, Florida. The type section is locatedincore W-12050, Hogan#1,DeSoto County (SEV4, NWY4,Section 16, Township 38S, Range 26E, surface elevation62feet (19 meters)} drilledin1973 by the Florida Geological Survey. The type Ar cadia Formation occurs between -97 feet MSL(-30meters MSL) to -520 feet MSL (-159 meters) (Figure 34). Two members can be recognized within the Arcadia Formationinportions of south Florida. These are the Tampa Member and the Nocatee Member (Figure33).The members are not recognized throughout the entire area. When the Tampa and Nocatee are not recognized, the section is simply referred to as the Arcadia Formation. Lithology The Arcadia Formation, with the exception of the Nocatee Member, consists predominantly of limestone and dolostone containing varying amounts of quartz sand, clay and phosphate grains. Thin beds of quartz sand and clay often are present scattered throughout the section. These thin sands and clays are generally very calcareous or dolomitic and phosphatic. Figure 34 graphically illustrates the lithologies of the Arcadia Formation including the Tampa and Nocatee Members. The lithologies of the56

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UNDIFFERENTIATEDLAND SURFACE PHOSPHATE HAWTHORN GROUP PHOSPKATPHOSPHATEI'HCJSPHA1E 50-._.'-'._.._.,-------------._.._.'-''-'_••_. 0-. _. -280 -29057Type core for the Arcadia Formation, Hogan#1,W-12050, DeSoto County (Lithologic legend AppendixA)."SUWANNEE" LIMESTONEzo j::err:eQeurr:err: wIII W WW leu ozCLAY CLAY [LAY tlAYCUll' CALCITECLAY[LRYCLAY CLAY CLAYCALCITE CLAY PHOSPHATE PHOSPHATESANDPHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHRTE PKOSPHPTE PHOSPHATE PHOSPHRTE PHOSPHATE CUIV CLAY CLAY CLAY[LAY5RNDCALCITESANDPHOSPHATE PHOSPHATE PHOSPHATE CLAY DOLOPlliE DOLOMITE DOLOPlITE DOLOMJTE OOLOMJTE OOLONITESlLTODLO"'ITECLAYDDLOKITECLAYSAND CALCITE" ... "SAND SA .. SR" SAMOCALCITE CLAYOOlO"'ITEPHOSPHAlE OOLOIUTEPHOSPHRlEOOLOHITE PHOSPtlATE DOLOMITE PHOSPHATE DOLONITE PHOSPHATE DOLOMITE PHOSPHATE DOLOMITE PHOSPHATE OOLOIUTE PHOSPHATE DOLOMITE PHOSPHATE DOLOMITEPHOSPHATEOOlDHITEPHOSPHATEOOLONITEPHOSPHRTEOOLONITEPHOSPHRTEOOlONITEPHOSPHRTE OOLOIUTEPHOSPHA1EOOLONITEPHDSPHATEOOLOHITEPHOSPHRTE PHOSPHATE PHDSPHA1 PHOSPHATE -410 -420 -430 -440 -450 -460 -470 -480 -490 --500--510 -530 20PHOSPHATE-------PHOSPHATE PHOSPHATE 10PHOSPHRTe -.,_.._.--CLRYPHOSPHATE_._. -.._.PHOSPHATE0SA" 'HOSPHAlE......PHOSPHATE CUlTrr-=-r-=-r-=-r-" -10-Z [LAl =======0------------j:: -20PHOSPHATECLRT e PHOSPHATEClRY PHOSPHRTECLRY rr: PHOSPHATE CLAY0-30PHOSPHATECLAYPHDSPHAlECLRY LL PHOSPHATE rr: PHOSPHATEPHOSPHRTEW -40 PHOSPHATE>-PHOSPHInE ir PHOSPHATEPHOSPHRTEWPHOSPHATE-50 PHOSPHATEU -PHOSPHATE e PHOSPHATEWPHOSPHATE II. PHOSPHATE PHOSPHATE -60 PHOSPHATeDOlOIUTESAND SAND-70 511"'0 SRNDCALCITE::T.:: -:::T.: PHOSPHP.TEPHOSPHATE PHOSPHATE-80 PHDSPlolATE PHOSPHATESAND CALCITEPHOSPHATE PHOSPHATE -90 PHOSPHATE -PHOSPHAlE PHOSPHAlE -100 PHOSPHAIESAliDCLAYSAND SANDSAND SAHD-110 PIlDf;PHAlff'HOSf'HATESAHOf'HOSPHAlt:SIINO=======: -120PHOSPHATESAHD PHOSPHAlt: SAHDPHOSPHATE SANDPHOSPHATE SANDI'HoSPHATESAND-130PHoSPHAIESANDSANDZSAND0 SAND SAND j:: PHDSPHATESAND
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Tampa and Nocatee Members willbediscussed separately from the undifferentiated Arcadia Formation. Dolomite is generally the most abundant carbonate component of the Arcadia Formation except in the Tampa Member. Limestone is common and occasionally is the dominant carbonate type. The dolostones are quartz sandy, phosphatic, often slightly clayey to clayey, soft to hard, moderately to highly altered, slightly porous to very porous (moldic porosity) and microto fine crystalline. The dolostones range in col or from yelloWish gray(5Y 8/1) to light olive gray(5Y 6/1). The phosphate grain content is highly variable ranging up to 25 percent but is more commonly in the 10 percent range. The limestones of the Arcadia are typically quartz sandy, phosphatic, slightly clayey to clayey, soft to hard, low to highly recrystallized, variably porous and very fine to fine grained. The limestones are typically a wackestone.to mudstone with few beds of packstone. They rangeincolor from white(N9)to yellowish gray(5Y 8/1). The phosphate grain content is similar to that described for the dolostones. Fossils are generally present only as moldsinthe carbonate rocks. Clay beds occur sporadically throughout the Arcadia Formation. They are thin, generally less than 5 feet thick, and of limited areal extent. The clays are quartz sandy, silty, phosphatic, dolomitic and poorly to moderately indurated. Color of the clay ranges from yellowish gray(5Y 8/1) to light olive gray(5Y 6/1). Lithoclasts of clay are often found in other lithologies. Smectite, illite, palygorskite, and sepiolite com prise the clay mineral suite (Reynolds, 1962). Quartz sand beds also occur sporadically and are generally less than 5 feet thick. They are very fine to medium grained (characteristically fine grained), poorly to moderately indurated, clayey, dolomitic and phosphatic. The sands are usually yellowish gray(5Y 8/1)incolor. Chertisalso sporadically presentlyinthe Arcadia Formationinthe updip areas (portions of Polk, Hillsborough, Manatee and Hardee Counties).Inmany instances the chert appears tobesilicified clays and dolosilts. Subjacent and Suprajacent Units The Arcadia Formation overlies either the Ocala Group or the"Suwannee"Limestone in the south Florida region (Figure8).The contact between the basal Arcadia and the Ocala Group is an easily recognized unconformity.Inthe north central and northeastern portions of southern Florida, where the Hawthorn Group overlies the Ocala Group (Figures 8 and 41), the Arcadia is characteristically a gray, hard, quartz sandy, phosphatic dolostone with a few siliciclastic interbeds. This is in contrast to the Ocala Group, which is a cream to white, fossiliferous, soft to hard limestone (packstone to wackestone). Throughout most of south Florida, the Hawthorn Group overlies limestones most often referred toasthe"Suwannee"Limestone (Figure 33).Inmuch of this area the contact is recognizably unconformable. The contrast between the sandy, phosphatic, fine-grained to finely crystalline carbonates ofthe Arcadia and the coarser grained nonphosphatic, non-quartz-sandy limestones of the"Suwannee"Limestone allow the contact tobeeasily placed. However,inthe downdip areas (e.g., Lee and Charlotte Counties and further south) the contact becomes more obscure.Inthis area the contact is placed at the base ofthe last occurrence of a sandy, variably phosphatic carbonate. The limestones underlying the Arcadia are referred toas"Suwannee"limestone due to the uncertain ty ofthe formational assignment. These sediments have characteristically been called"Suwannee"by previous workers despite the fact that they have never been accurately correlated with the typical Suwan nee Limestone in northern Florida. Hunter (personal communication, 1984) believes that these car bonates are not Suwannee or the equivalent but areanunnamed limestone of Chickasawhayan Age (Late Oligocene). Unconformably overlying the Arcadia Formation is the Peace River Formation (Figure 33). The Peace River Formation is predominantly a siliciclastic unit with varying amounts of carbonate beds. The percen tage of carbonate bedsishigher near the base ofthe Peace River, resulting in a transitional or grada tional contact with the Arcadia.Insome areas the contact is often marked by a phosphatic rubble zone and/or a phosphatized dolostone hardground.Inthe more gradational sequence the contact is placed where the carbonate beds become significantly more abundant than the siliciclastic beds.58

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------W-13942WOe-29S-33E-23ad-10 f--50 -20-30[-'00-40-150-50-60[-200-70-250-80-90,...-300.SUWANNEE-100LIMESTONE I-350 -110-120 r -400-130I I INDIANRIVERCO. IIG'METERSFEETr15040W-13958Wlr-32S-39E-16cb30 -rl00 201-5010-O-t-MSLUNDIFFERENTIATEDW-13984WBv-30S-35E-09ab/ --......'"'""-"AVONPARKLIMESTONEPEACERIVERIFORMAT10NIOSCEOLA CO.IBREVARDCO. I W-9150(CUTTINGS)WOa-31S-32E-04bIPOLKCO. I OSCEOLACO.IW-15281WPO-3QS-28E-12ccjCRYSTALRIVERFORMATIONW-14883WPO-30S-27E-04cb --EXPLANATION SCALEo510MilESIiII"o510lSKILOMETERS I;#"'...r.l:of HAWTHORNGROUP BOUNDARIESSUWANNEELIMESTONEW-148B8WHI-31S-20E-25IHILLSBOROUGHCO. :POlK CO.IIGMETERSFEET r 40W-11541WHI-30S-18E-11da3010020 50100-10 J,.-50 -20 -30I-'00-40-150-50 -60{-200-70-250-80-90 I-300 -100-350-110-120{-400-130 -140-450-150t-5OO-160Figure 35. Cross section G-G' (see figure 3 for location).59

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HMANATEECO.I HARDEE CO.I HARDEE CO.! HIGH..ANIlS CO.I H' Figure36.Cross section H-H' (see figure 3 for location).5010-10 -50 -20-30-100-0MSL METelS FEET50 W-12906WHd-35S-27E-23adW-12965 WHd-34S-24E-27aaWHI-34S-28E-18da r----::::: W-11946 \?W-437 150I \/ 100 20UNDIFFERENTIATED-150-50'" -60 -200-70-250-60 + SUWANNEE + -90-300LIMESTONE-1-350-110-120-400 -130 -450-140-150 -500W-11570 SCALE510 MILES IIII1015KILOMETERSEXPLANATION W"...... HAWTHORNGROUPBOUNDARIESARCADIAFORMATIONMETERS FEET 150 4030100 20 5010MSL--10-50-20-30-100-40-150-50-60-200-70-250-80 -90-300-100-350-110-120-400-130-140-450-150-500-160-170-550-180-600-190-200-650-210-700-220-750The relationship ofthe subjacent and suprajacent units to the Arcadia Formation canbeseen in the cross sections shown in Figures35through 40. Thickness and Areal Extent The Arcadia Formation occurs primarilyasa subsurface unit throughout its extent. The topof the Ar cadia Formationincores ranges from -440 feet MSL (134 meters) in W-15493 Monroe County to greater than+100 feet MSL (30 meters) in several cores in Polk County (Figure 41). Data obtained from well cut tingsinareas lacking core data indicated that thetopof the Arcadia maybegreater than -750 feet MSL (229 meters) in Palm Beach and Martin Counties (Figure 41). The Arcadia Formation appears tobeabsent from the southern nose of the Ocala Platform, the San ford High and part ofthe Brevard Platform (Figures41and 42). It increases in thickness away from these features, reaching a maximum of 593 feet(181meters) in a core in Charlotte County (Southeast Florida Water Management District R.O.M.P. 3-3) and more than 650 feet (198 meters) in a well in southern Dade60

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COMPOSITE METERSFEET(cutting.)W-14754r150W-1S24640WMI-39S-38E-33ca30 rl00 20 t5010TMSL-10-50 -20-30r-'00-40-150-50 -70-250-80-90{-300-100 -110-350-,20r-400-130 -140-450 -150{-500-160-170-550-180I-600-190-200-650-210 r-7OO -220IOKEECHOBEEco.I MARTIN CO.I I W-4896(cuttlnge)WOk-38S-34E-02PEACERIVER FORMATlON I H1GHLANlS CO. I OKEECHOBEECO.I lNlFFERENT1ATBlSEDlMEHTS ARCADIA FORMATlONSUWAMlEE UMESTONEW-9285lcutllngalWHI-39S-28E-4dd s= ? .......................................................... DESOTOco.I HIGHLANDS CO.I W-12050WOa-38S-28E-18dl1EXPLANATIONARCADIAFOAMATlONISARASOTAco. IDESOTO co.IISCALEo510MILESIj'i"o51015KILOMETERS HAWTHORNGROUP BOUNDARIESrI RIVER FORMATlON W-14882W-11908WSa-37S-17E-13bWSa-37S-30E-31bb 10050FEET15040102030-10 1--50 -20 -30 t -100-40-150-50-601-200-70-250-80 -90 t-3OO -100-350-110-120{-400-130-450-140-150{-SOO-160-170-550-180{-600-190-200-650-210 1"-700-220 METERSFigure 37. Cross section1-1'(see figure 3 for location).61

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I HLLS8OROUGHCO.IMANATEECO.IJIMANATEECO. : SARASOTACO.IISARASOTACO. I CHARLOTTECO.IICHARLOTTECO.ILEECO.I .f METERSFEETr5010-TMSL-10 -50-20-30r-1OO -40 -150-50 -80[200 -70-2S0-80-90[300-100.-350 -110-120 {-400 -130-450-140 -150{-500-180-SSO-170-180{-800-190-850-200 -210 1-700 -220-750W-15288WLa-44S-26E-15 " UNDIFFERENTIATED W-15289WCh-42S-23E-l1ba?ARCADIAFORMATIONPEACERIVERFORMATION G W-14871 W-15188 WSa-3BS-1BE-3Bj :I II f''1\TAMIlA MEMBERIj I W-15188WMa-35S-17E-26aW-14882WSa-37S-17E-13 ....ARCADIAFORMATIONW-15205WMa-33S-1BE-301( '1FFEREHTlA TEDEXPLANATIONHAWTHORNGROUPBduNDARIESSCALEo510MILESli'l"o51015KILOMETERS "SUWAME LIMESTONEW-llS41WHI-30S-18E-11da / METERSFEET f 150 403010020 f 10oMSL--10-50 -20-30 I -100-40-150-50 -60 {-200 -70-250-BO-90I-300-100-350-110-120{-400-130-140-450-150{-500-160-170-550-lBO{-600-190-200-650-210 {-700 -220-750Figure 38. Cross sectionJ-J'(see figure 3 for location).62

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KW-13055WPo-27S-25E-21daIPOlKCO.I HARDEE CO.II HARDEE CO.IDESOTO CO.IDESOTO CO.iCHARLOTTE CO.CHARLOTTECO.!LEECO.I IIIK' W"....... HAWTHORN GROUP BOUNDARIESSCALEo510MILESIiii" o51015KILOMETERSMETERS FEET r'5OW-1528640WLc-44S-26E-15 30.1-100 201-5010_OtMSL-10 -50 -20-30('00-40-150-50-60r-2OO-70-250-80-90t-3OO-100-350 -110 -120r-4OO-130 -450 -140 -150 {-500 -160 -170-S50-180r-6OO-190 -200-650-210r-7OO-220 -750W-11907WCh-41S-25E-05ARCAOIAFORMATIONNOCATEEMEMBERARCAOIAFORMATIONPEACERIVERFORMATIONW-120SOWOa-38S-26E-16d8ARCADIAFORMATION IN>FFERENTlATmsW-11948WHr-35S-26E-03dW-13245WHr-32S-25E-21cajSUWANNEE LIMESTONEEXPLANATION BOlE V ALI.EYMEMBER_79WPo-29$-24E-24cb iPEACERIVEA AI. PEACE RIVER FM. UNOIF. / METERS FEET1'50403D10020 r 10oMSL--10-50 -20 -30 t -100-40-150 -50 -GO{-200-70-250-80 (J) -90-"-300 (,) -100 t-350-110-120 {-400 -130 -140-450-150{-500-160-170-550-180{-GOO-190-200-650-210 f700 -220-750Figure 39. Cross section K-K' (see figure 3 for location).

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FEET50tMSL-10-so-20:r1OO-150-50 COMPOSITE W-14754W-15248WMI395-38E-33co L' -80t-2OO-70 -250-BO -90 r300-100-350-110-120 t-400 -130-4SO-140ARCAOIA FORMATIONI-150rsoo-180-5SO -170 -lBO [-800 -190 -8SO-200-210 -700ST.LUCIECOIMARTINCOPEACERIVERFORMATIONIIBREVARDCOIINDIANRIVERCOINDIANRIVERCOl ST.LUCIECOIIBREVARDCOW-13957W-13984W-13B81WBy-29S-34E-24bd W•• -:"-...-""\C OCALAGROUPCRYSTALRIVERFORMATION EXPLANATION SCALEo510MILESli'lI'o51015KILOMETERS HAWTHORNGROUP BOUNDARIESW-13489WOa-26S-34E-3.b s= IORANGECO I OSCEOLACOIL '::1=t1-'-=.•'-.""_.W-15334WOr-23S-34E-17bb c METERSFEET1'5040 30 100 20 r 10oMSL--10-50 -20 -30 I -100-40-150-50 -60 {-200 -70-250-80 -90 I-300CJ) -100 -350-110-120{-400-130-140-450-150 {-500 -160-170-550 -180 {-600-190-200-650-210 -[-700 -220-750Figure 40. Cross section L-L' (see figure 3 for location).

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County (Figure 42). The dip of the Arcadia Formation exhibits some variability in the northern portion ofthe south Florida area (Figure 41). This is primarily due to the occurrence of the Ocala Platform, Osceola Low, Sanford High and the Brevard Platform (Figure4).Ingeneral, however, the dip is to the southeast at approximate ly 5 feet per mile (0.9 meters per kilometer). The basal unit ofthe Hawthorn Groupispresent throughout the south Florida area.Itis apparently ab sent from the southern flanks of the Ocala Platform and the Sanford High and from part of the Brevard Platform. This is at least partially due to erosion prior to Peace River deposition. The Arcadia Formation is not identifiable in the area between the Ocala Platform and the Sanford High. A carbonate unit is pre sent in this area, but it has characteristics attributable to both the Arcadia and Penney Farms Forma tions. Until further research canbeconducted, the Hawthorn Group remains undifferentiatedinthis area.Inthe southern portion of south Florida, the Arcadia containsanincreasing percentage of very moldic (mollusk shell molds) limestones and the entire carbonate section becomes less phosphatic to the south. The Arcadia Formation was tentatively identified in the Port Bougainville core, W-15493, Monroe County (upper Keys). The transition from the typical Arcadia in southwest Florida to that in the upper Keys is difficult to ascertain due to the nearly complete lack of core data and paucity of well cuttings in the area. Further research, when the data become available, willbenecessary to clarify these questions. Age and Correlation The sediments ofthe Arcadia Formation have yielded few dateable fossil assemblages. Diagenesis of the original carbonate sediments has destroyed most fossil material leaving only casts and molds. From mollusk samples collected by Hunter (personal communication, 1984)inportions of southwest Florida, the upper part of the Arcadia correlates with part of the Marks Head Formation of north Florida and Georgia and the Torreya Formation of the Florida panhandle. This suggests that the upper Arcadia is no younger than mid-Burdigalian (late Eary Miocene) (Figure19).The lower Arcadia seems tobeequivalent to the Penney Farms Formation and part of the Parachucla Formation Georgia (Figure19)(Huddlestun, personal communications, 1983; Hunter, personal communication, 1984). The base of the.Arcadia maybeas old as early to middle Aquitanian (early Early Miocene) (Figure19).Discussion The Arcadia Formationasdescribedinthis report is important from both a hydrologic and economic viewpoint. Hydrologically, it incorporates several aquifers and confining units identified within the Hawthorn Group. Economically, the carbonates of the Arcadia form the base of the mineable phosphorite throughout much"@f.the Central Florida Phosphate District. The Arcadia Formationasused here provide a coherent picture ofthe early part of the Mioceneinsouthern Florida. TAMPA MEMBER OF THE ARCADIA FORMATION Definition and Type Section The Tampa Member ofthe Arcadia Formation represents a lithostratigraphic change in status from for mation to member. The Tampa has long been a problematic unit due to facies changes and apparent gradational contacts with overlying and underlying units. The change from formation to member is necessary due to the limited areal extent of the Tampa and its lithologic similarities with the remainder of the Arcadia Formation ofthe Hawthorn Group. The Tampa MemberISpredominantly a subsurface unit throughout its extent cropping out only in the Tampa area. . King (1979) and King and Wright (1979) thoroughly discussed the Member (their Tampa tion) and its type locality. They designated Ballast Point core W-11541, Hillsborough Countyasthe pnn65

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ARCADIA FORMATION ABSENT668ROWA FR-"O'-!--r"\--r-' I.-_.-j f--1_-;.i __ -,oC,J' AEICJ.so FT.-300 ... IN J Top of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group.CORE CUTTINGS LIMITSOFHAWTHORNGROUP HAWTHORNGp.UNDIFFERENTIATED SCALE, " Figure 41.

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350-600 C.I.-50fT.l{j 10 1,0ICAlllto101040 "067Isopach of Arcadia Formation. Shaded area indicates undifferentiated Hawthorn Group.• CORE • CUTTINGS <.L> LIMITS OF HAWTHORN GROUP HAWTHORN GROUP UNDIFFERENTIATED r&il ARCADIA FORMATION ABSENT5Figure 42.

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LAND SURFACE o-l0-20 -30-1.f0-50 -60 -70-80-90-l00 1-....:..-....:..-....:..-....:...UNDIFFERENTIA 11541. f-.-' _. _ .. 1-::::::-::::::-,-::::::-:::::: . f-._._._.1-:-;-'-:-;-.-:-;-.-:-;-.tt-t-tSANDHA WTHORN GROUPISANDt-t-t-t-SAND SAND t-t-t-tSAND---SAND SANDCLAYIIISAND SANDARCADIA FORMATIONISAND SANDSAND SANDTAMPA MEMBER '1'1 ICLAY CLAY:,''1. :1' ..:,''1.:,'..CLAYSAND SANDIiISAND SAND I SANDHAWTHORN GROUP• ",,,on UNNAMED LIMESTONEOR\\ ". SUW ANNEE LIMESTONEIIFigure 43. Reference core for the Tampa Member ofthe Arcadia Formation, Ballast Point#1,W-11541, Hillsborough County (Lithologic legend AppendixA).cipal reference core (SE1f4 , NW1f4, of Section11,Township 30S, Range 18E). The Tampa Member oc curs from-9feet (-2.7 meters) MSL to -74 feet (-22.5 meters) MSL in this core (Figure 43). They also referredto two other cores (Duette#1,W-11570, Manatee County and Brandon#1,W-11531, Hillsborough County)asreference cores. This author also recognizes core W-15166 (Bradenton R.O.M.P.TR7-1, W1f4 of Section 26, Township 35S, Range 17E, Manatee County)asanexcellent reference section for the Tampa Member. W-15166 contains the Tampa Member from -285 feet (-87 meters) MSL to -423 feet (-129 meters) MSL (Figure 44). The classical type area of the Tampa Member lies around Tampa Bay at Ballast Point and Six Mile Creek (Dall and Harris, 1892). Unfortunately the typeexposures do not completely or accurately repre sent the Tampaasit occurs in the subsurface.Asa result the Tampa Member discussed in this paper as a formal member of the Arcadia Formation of the Hawthorn Group is described from the previously men tioned reference cores.68

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10 -LANDSURFACE .p..Uo . -10 _ o --20 -30 NOSAMPLE =lIm-?-?SAND SAND CLAY ('L:OW-15155-260 UNDIFFERENTIATED -270 _ HAWTHORN GROUp,-280 -290 PHOSPHATE PHOSPHATE PHOSPHATESANDCLRYPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHFHE PHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHRTEPHOSPHATEPHOSPHATE PHOSPHATETAMPA MEMBER -50 -90 IARCADIA FORMATION TAMPA MEMBER HAWTHORN "IISUWANNEE LIMESTONESAND SAND PHOSPHATESANDPHOSPHATEPHOSPHATESAND SAND SAND SAND SAND SAND SAND SAND SAND SAND SANDPHOSPHATESANDCLAYCLAY CLAYSANDSAND SANDSAND SAND SAND SAND SAND SAND SAND SANDPHOSPHATEPHOSPHRTEPHOSPHATE PHOSPHQTEPHOSPHRTE-300 PHOSPHATEPHOSPHATESANDPHOSPHRTE PHOSPHRTEPHOSPHATE -310 PHOSPHATE PHOSPHATEI Or:-: PHOSPHATE ,:To:PHOSPHATE PHOSPHATE -320 PHOSPHATESANDPHOSPHRTEPHOSPHATEOOLOHI1EPHOSPHATEDOLOHITEPHOSPHRTESANDDOLOMIle -330 -SANDSAND?HQSPHRTESANDPHOSPHATESANDPHOSPHATESAND -3'1-0 PHQSPHRiEPHOSPHATEPHQSPHP.1EPHOSPHATEPHOSPHATE SAND -350 PHOSPHATESANDPHOSPHATECLAYPHOSPHATE PHOSPHATE PIolOSPHRTE SANDOOLOHITE -360 PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATESRNDODLOl'UTEZ -370 PHOSPHATEDOLOMITEPHOSPHATESAND0PHOSPHATESANDPHOSPHATESAND PHOSPHATE SAND-380 PHOSPHATE SAND'tlATE SANDPHOSPHATESANO0 -'1-10 SANOa:SAND SAND 7.:/-2'1-0_ :-:-:-:-:-:-:-::;,:::;,:::;,:::;,::SANDPIlOSPIlATE PHOSPHATEPHOSPtlATECLAYPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATE -250 Figure 44. Reference core for the Tampa Member of the Arcadia Formation, R.O.M.P, 7-1, W-15166, Manatee County (Lithologic legend AppendixA).69

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Lithology The Tampa Member consists predominantly of limestone with subordinate dolostone, sands, and clays. The lithology ofthe Tampa is very similiar to the limestone portion of the Arcadia Formation with the exception of its phosphate content which is almost always noticeably less thaninthe Arcadia. Phosphate grains generally are present in the Tampa in amounts less than 3 percent although beds con taining greater percentages do occur, particularly near the facies change limits of the member. Lithologically, the limestones are variably quartz sandy and clayey with minor to no phosphate. Fossil molds are often present and include mollusks, foraminifera and algae. Colors range from white(N9)to yellowish gray(5Y 8/1). The limestones range from mudstones to packstones but are most often wackestones. The dolostones are variably quartz sandy and clayey with minor to no phosphate. They are typically microcrystalline to very fine grained and range in color from pinkish gray(5YR 8/1) to light olive gray(5Y 6/1). The dolostones often contain fossil molds similar to those in the limestones. Sand and clay beds occur sporadically within the Tampa Member. Lithologically, they are identical to those described for the Arcadia Formation except for the phosphate content which is significantly lower in the Tampa Member. Siliceous beds are often presentinthe more updip portions ofthe Tampa.Inthe type area near Tampa Bay the unit is well known for silicified corals, siliceous pseudomorphs of many different fossils and chert boulders. Subjacent and Suprajacent Units The Tampa Member overlies the"Suwannee"Limestone in areas where the Nocatee Member is not present and the Tampa Member forms the base of the Arcadia. The boundary often appearsgradationalasdiscussed by King (1979) and King and Wright (1979). Figure19indicatesanunconformable time rela tionship with the"Suwannee"Limestone which often is not apparent lithologically. This indicates a pro bable reworking of underlying materials into the Tampa Member obscuring the unconformity. The Tampa Member overlies the Nocatee Member in the area where both are present (Figure 33). The contact appears conformable and is easily recognized.Ina few areas where the Nocatee is absent, the Tampa may overlie undifferentiated Arcadia Formation sediments. The Tampa Member may be both overlain and underlain by undifferentiated Arcadia. The Tampa Member is overlain throughout most of its extent by carbonates ofthe undifferentiated Ar cadia Formation. The contact often appears gradational over one or two feet.Anincrease in phosphate grain content is the dominant factorindefining the lithologic break.Inupdip areas the Tampa may be overlain by siliciclastic sediments ofthe Peace River Formation. Further updip it may be exposed at the surface or covered by a thin veneer of unconsolidated sands and clays which may represent residuum of the Hawthorn sediments. Figure 35 through39show the relationship ofthe Tampa Member to the overly ing and underlying units. Thickness and Areal Extent The Tampa Member is quite variable in thickness throughout its extent.Itthins updip to its northern limit where it is absent due to erosion and possibly nondeposition. The thickest section of Tampa en countered is in W-14882 in Sarasota County where 270 feet (82 meters) of section are assigned to this member (Figure 45). More typicallyanaverage thickness is approximately 100 feet (30.5 meters). The top of the Tampa Member (Figure 46) rangesinelevation fromashigh as+75 feet (23 meters) MSL in northeastern Hillsborough County to -323 feet (-98.5 meters) MSL in northern Sarasota County. The lowest elevation for the top of the unit occursina rather large depression that encompasses part of northern Sarasota County and southern Manatee County. The Tampa dips towards the southinthe northern half ofthe area of occurrence (Figure 46). Dip direc tion in the southern half is more to the southwest and west. Dip angle varies from place to place butthe70

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LEGEND• CORES • CUTTINGS LIMITSOFHAWTHORNGROUP '40 .0 -.J__ ---''-__KILOMETERS40MILESI, I ----" ... <'--"'"_CHANGE •,CHARLOTTEIGLADESCI-50FEET20Ii20SCALE! I)_I---C-"""L---f-----------,----t---+----,--',-+----1:\-fI1_. ••I\. ---0 I---"+--\ \\ T"--.\. . ' _:__0_ -.3. 0 CEOLAI i I (:-) .I'I' j -:-'--Ij---'----,.", __ -L.i .'8REVAROIooIFigure 45. Top of Tampa Member. average from highest to lowest point is approximately 8 feet per mile (1.5 meters per kilometer). The dip appears steeper in the northern and central area (Figure 46). Figures 45 and 46 show the area of occurrence for the Tampa Member. North of this area, the Tampa has been removed by erosion and only a few, isolated, erosional remnants are present.Insome areas its absence may be due to nondeposition. East and south of the area of occurrence, the Tampa grades laterally into the undifferentiated Arcadia Formation. It is important to note that relatively thin beds ofTampalithologyoccurwithin the Arcadia Formation outside the area in which Tampa is mapped. These beds oftenoccursporadically throughout the lower Arcadia but are not thick enough and are too com plexly interbedded with Arcadia lithologies to be mapped as Tampa Member. Characteristically, the Tampais recognized when there are few beds of Arcadia lithologies interbedded with Tampa lithologies and the sequence of Tampa lithologies is sufficiently thick. Further data may permit more accurate definition of the limits of the Tampa Member.71

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LIMITS OFHAWTHORNGROUPLEGEND•CORE• CUTI'INGS KILOMETERS40MILESI I-----+--+-,,/i 0 i / "" GLAi! U • i I .. __-'iCI = 50FEETj40 2' 20I,P5C0 j20SCALEi---t-<,\c\1\ !.1.I l+--j--+--f--t--+---;l--r'\.-:Y-f--t--t--___--+•! ----t----\\\ ooIFigure46.Isopach of Tampa Member. Age and Correlation The Tampa Memberischaracteristically variably fossiliferous. Mollusks are most common with corals and foraminifera also present. Despite the presence of these fossils, no age diagnostic species have yet been recognized. MacNeil (1944) suggested the correlation of the Tampa with the PaynesH-ammockFormation of Mississippi basedonthe mollusk fauna presentineach.Poag(1972) dated the Paynes Hammock For mation using planktic foraminifera and suggested a Late Oligocene age (N2-N3 of Blow, 1969). Hud dlestun (personal communication, 1984) indicates that the Tampa Member equates with part of the Parachucla FormationinGeorgia and straddles the boundary between the Oligocene and Miocene. Hunter (personal communication, 1984) agrees with Huddlestun and Gorrelates the Tampa with part of the lower Parachucla. Hunter also feels that much of whatisincorporated into the Tampa Member in this72

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is older original type Tampa (Silex Beds) at Ballast Point and Six Mile Creek. The TampaISalso correlated with part ofthe Penney Farms Formationinnorth Florida (Figure19).Discussion The introduction of the Tampaasa member of the Arcadia Formation represents a 'status reduction from formation. The reduction is necessary due to the limited areal extent of the Tampa and its inter gradational nature with part of the Arcadia Formation. The historical significance of the Tampa andItSwidespread use suggest a retention of the name. This revision of the Tampa hopefully will provideanunderstandable, useable unit of local extent and places it within a regional perspective. NOCATEE MEMBER OF THE ARCADIA FORMATION Definition and Type Section The Nocatee Member is a new name introduced here for sediments at the base of the Arcadia Forma tion in parts of southwest Florida. Previously, this interval had been informally called the "sand and clayunit"ofthe Tampa Limestone by Wilson (1977). This unitisrecognized only in the subsurface. The Nocatee Member is named for the town of Nocateeincentral DeSoto County, Florida. Tre type coreisW-12050, Hogan#1,locatedintheSE 1/4, NW V4, Section16,Township 38S, Range 26E, with a surface elevation of62feet (19 meters). The type Nocatee occurs between -294 feet (-89.5 meters) MSL and -520 feet meters) MSL (Figure 47). The type core was drilled by the Florida Geological Survey. : Lithology The Nocatee Member is a complexly interbedded sequence of quartz sands, clays, and carbonates, all containing variable percentages of phosphate. Figure 47 shows the nature of the NocateeinW-12050 in central Desoto County. The Nocatee is a predominantly siliciclastic unit in the type core (W-12050). This is a noticeable change from the remainder of the Arcadia Formation including the Tampa Member, which are predominantly carbonates with variable percentages of included siliciclastics. The quartz sandsinthe Nocatee are typically fine to coarse grained, occasionally silty, clayey and calcareous to dolomitic. The quartz sands rangeincolor from white(N9)to light olive gray(5Y6/1). Phosphate grain content is quite variable. In the type core, phosphate grain contentisgenerally low(1-3percent) with scattered beds with greater concentrations (up to 10 percent). However,inthe Nocatee Memberinother cores (W-15303, for example, Figure 48), phosphate grains are more common, averaging about7-8percent. Clay beds are quite commoninthe Nocatee Member and are variably quartz sandy, silty, phosphatic, and calcareous to dolomitic. The colors characteristically range from yellowish gray(5Y8/1) to light olive gray(5Y6/1) and olive gray(5Y4/1). Limited x-ray data suggest that the characteristic clay mineral pre sent is smectite, with palygorskite common. Illite and sepiolite are also present. Further analyses are needed to confirm the identifications and relative abundances of these clay minerals within the Nocatee Member. Limestone and dolostone are both presentinthis member. The ratio of limestone to dolostoneisvariable,ascan be seen by comparing W-12050 (Figure47)with W-15303 (Figure 48). The limestones are generally fine grained, soft to hard, quartz sandy and phosphatic. The percentage of clay present is quite variable and grades into the clay lithology. Colors ofthe limestone vary from white(N9)to yellowish gray(5Y8/1) and light olive gray(5Y6/1), generallyinresponse to clay content. The limestones are usually wackestones with varying degrees of recrystallization and cementation. The dolostones are quartz sandy, phosphatic, soft to hard, and microto very finely crystalline. Variable amounts of clay are present. Colors range from yellowish gray(5Y8/1) to light gray(N7),light olive gray(5Y6/1) and grayish brown(5Y3/2).73

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zo j:c a:o ...cCc oa: c a: w III WwI!!cg zCLAY CLAYSANDCALClTECLA.,OOlDNITESAND SANDSR .. SANDCALCJTE CLAY CLAY CLAYCALClTECLAYCLA., CLAY C .. AY CLAYCALCITECLAY PHOSPHATE PHOSPHATESANDPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHATE PHOSPHATE PHOSPHATE CLAY CLAY CLAYClRYCLAYSRHOCRLCIlESANOPHOSPHATE PHOSPHATE PHOSPHATE CLAY ODlONJiE OOlONITE OOlONITE OOlONITEOOLONlTE OOLONlTESILToDlONITECLAYODlONlTEClRYPHOSPHATEOoLOHI1EPHOSPHATEOOLOHlTE PHOSPHATE ODlONITEPHOSPHATEOOlDIIITEPHOSPHRTEODlDNITEPHOSPHATEOOlDIIITEPHDSPHATEOOlOIIlTEPHOSPHRIEOOlONlTEPHDSPHATEOOlONITEPHOSPHRTEOOlONITEPHDSPHRTEOOlONITEPHOSPHATEOOlONITE PHOSPHATEOOlONITEPHOSPHATEOOlONIlEPHOSPHAIEOOLoNlTEPHOSPHATEOOLONlTEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE'SUWANNEE'LIMESTONE-280 -310_-320_ -330-m --------500-510 -520 -530zo j:c a:o ... a: w > ii:w o cw zo j:c a:o ...cCc oa: c PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATEUNDIFFERENTIATEDSANDPHOSPHRTF'NOSPHRTESANOPHOSPHATESAHDCLAYPHoSPHATEClA.,PHOSPHATE CLAY _ PHOSPHATE CLAY PHoSPHATEClA.,PHOSPHATEClA.,PHOSPHATE CLAY PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHRTE PHOSPHRTE PHOSPHATE PHOSPHRTE PHOSPHATEDolONITESANDSRHO SA)"O SANOCRlCITEPHOSPHP.TEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATESANOCALCITEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHCSPHATE PHoSPHATESANOCLR.,SANO SANOSANDPHOSPHATE SANDPHDSPHATESAND PHOSPHATESAH;) SAND PHOSPHATE SAND PHOSPHATE SANDSANDSAND SAND SAND PHOSPHATE SAND PHOSPHATE SAND PHOSPHATESANDPHOSPNATESANDPHDSPHATEClAYPHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAY PHOSPHATE CLAYPHoSPHATEClA'fPHDSPHATESANOPHoSPHATESANOPHoSPHATESAHoPHOSPHATEPHOSPHATESAHoPHDSPHATESAHoPHDSPHATESAHDPHDSPHRTESAHoPHOSPHATESAHoPHOSPHATE SAHo CLAY PHOSPHRTESAHDPHDSPHATESAHoPHOSPHATEClA.,PHOSPHATE CLAYPHDSPHRTESANDPHOSPHAIESANOSAND CLAY PHOSPHATE PHOSPHATESANDPHOSPHATE PHOSPHATE CLAYLAND SURFACE -f:.-=-f:.-=-f:.-=-f:.---------------=::::=::::_.._.'-'_._._.'-'_. _.'-''-'._. =:=:=:=:_.._._._._.'-'._._._ ::: ::: ::::::'NOSP",," HAWTHORNGROUP --10-20-50 -60 -70-302060503010 -80-180-170 -100 -90-190 -110 -120 -130 -160 -150 -200 -210CLAY SAND-220-230 -250 -26e-270 SANOSAND SANDSAND SANDZSAND SANDa:0SAND j: SAND W SANDIII Cw a: ::E 0 C...C PHOSPHATE ::EC PHOSPHAll C PHOSPHRI[ C PHOS"HRIE I0PHOSPHf'TEa: PHO';PHRIEC PHOSPHATE ?1l05PttA1EPHOSPHRlt: PHOSPHRTE PHOSPHRIE PHOSPlml(PHOSPHI'lTE 74Type core for the Nocatee Member ofthe Arcadia Formation, Hogan#1,W-12050, DeSoto County (Lithologic legend AppendixA).

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\-.1-15303 NOCATEEMEMBER""SUWANNEE LNESTONE SANO SA"'O SAND SAND SANDSANO SAMO SANDSANOSAND SANDSANOSAND SAND SANDSAND SAND SAND SANOSANDSANO SANO SANO SANO SAHO SRNO SRNO SANDSANOPHOSPHATESANOPHOSPHATESANO SANOSAND SAND SAND SAND SAND SAND SANDSANOCLAYSAND SANDSANOSANO SANO SAHOSANDSANO SANOSANDSAND SAND SAND SANDPHOSPHIUE PHDSPHRIEPHOSPHRIE SRNO CLAYPHOSPHRTfCLAT PHOSPHAIEtLAYPHOSPHRTECLAYPHOSPHIneCLAYPHOSPHATESANDCALCITEPHOSPHATEPHOSPHATEPHQSPHRTEPHOSPHATESAHDDOlO"ITEPHOSPHATESANDPHOSPHATEPHOSPHATE SAND PHOSPHATESANDPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHR1ESRND ARCADIAFORMATIONPHOSPHATEPHOSPHRTESANDPHD5PHAIE5ANQPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATE PHOIiiPHAlE PHOSPHATEPHOSPHRIESAHDPHOSPHATE SANDPHOSPHATESAHD PHOSPHIlTE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATEPHOSPHATE PHOSPHATE CLAYHAWTHORNGROUPI -500 -520-530 -510-H0-590-600-550-350 -360 _ -370 -560 -570 -320 -580 -620-610-380-630-650-390 PEACERIVERFORMATIONHAWTHORNGROUP1UNDIFFERENTlATEDCLAYPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHATEPHOSPHRTEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTE PHOSPHRTE PHOSPHRTEPHOSPHATEPHOSPHRTE PHOSPHRTESRHDPHOSPHATESRNDPHOSPHRTESRND SA"'O SAND SANDPHOSPHATESANDPHOSPHATEPHOSPHRlE PHOSPHAlE mmm TAMPAMEMBERPHOSPHRTESflNDPHOSPHATESANDPHOSPHATESAND SAND PIlQSPHR1EPIIOSPllnTpl/OarllnTEPIIOIlPIInTE PIlOSPHA1EPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHATESRNOPHOSPHRlEPHOSPHATE PHOSPHATEPHOSPHRTE PHOSPHRTEPHOSPHATE PHOSPHATESANDCLAYPHOSPHATE PHOSPHATE fiAND CLAYPHOSPHATEPHOSPHRTEPHOSPHATE PHOSPHATE PHOSPHATESRNDPHOSPHATESANDPHOSPHATESRNOPHOSPHATESRNOPHOSPHATESRNDPHDSPHATESAHD PHDSPHATESAHD PHDSPHATESAHDPHOSPHATESAND P.,OSPHATE SANOPHOSPHATESAHDPHOSPHATESANOCALCIlEPHOSPHATESANOPHOSPHATE OOLO'HTE PHOSPHATE DOLOf1IlE PHOSPHATE PHOSPHATE PHOSPHATEPHOSPHAlE SRMO CLAYPHOSPHAlE PHOSPHAlE NOCATEEMEMBERPHOSPHRlE PHOSPHAlEPHOSPHATE PHOSPHATEPHOSPHATESANOPHOSPHATECLRYPHOSPHATECLAYPHOSPHAlECLAYPHOSPHATECLflY PHOSPHRlECLRTPHOSPHATECLAYPHOSPHATECLRTPHOSPHAIESANDCALCITE "HOSPHR1PHDSPHR1EPHOSPHATEPHOSPHATE SAND PHOSPHATESANDPHOSPHATESANDPHOSPHATESANDCLAYPHOSPHATESANDCLAYPHOSPHATECLAYPHOSPHATESANOPHOSPHRTESAND PHOSPHATESANDODLDHITE PHOSPHATESAHOPHOSPHATESANOPHOSPHATESANDPHOSPHATESANDCLAYPHOSPHATESANDPHOSPHRTESANDPHOSPHRTESRNOPHOSPHATESAND SAND ARCADIAFORMATIONPHOSPHATEPHOSPHATE PHOSPHATE PNOSPHATESANDPHOSPHATESANDPHOSPHflTESANOPHOSPHATE PHOSPHATEPHOSPHATECLRYPHOSPHATECLAYPHOSPHATECLAYPHOSPHRTECLAY PHOSPHATESflNOOOLOf1I1E PHOSPHRTEOOLOtUTEPHOSPHATEDOLOMITEPHOSPHATEDOLOMITEPHOSPHATESANDDOLOMITEPHOSPHATECLAYPHOSPHATECLAYPHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATEDOLOMitECLAYPHOSPHATESAND SAND OOLOttlTE CLAYPHOSPHATESANOPHOSPHATESANDPHOSPHATESANDPHOSPHATEODLO"ITECLAYSAHOCLAY PHOsPHR1ESRNQPHOSPHATESRNOPHOSPHATESANQ PHOSPHATESANO PHOSPHATESANO PHOSPHAtESANDPNDSPHRTESRNOSAND SANDSAHOSANDPHOSPHATELAND SURFACE:::-:::-:::-:::-I"'"--_..... .',-.',-,',-,' -310-300-29010-60 -5020-100-10 _-------20 -30-90 -70 .. :T..:-.--80o-120-110 Figure 48. Reference core for the Nocatee Member ofthe Arcadia Formation, R.O.M.P. 17, W-15303, DeSoto County (Lithologic legend AppendixA).75

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Fossils are often present in the Nocatee, most oftenasmolds. However, in some of the clay beds diatoms are present but have not been identified. Fossils present include mollusks, algae, foraminifera and corals. Subjacent and Suprajacent Units The Nocatee Member overlies limestones currently assigned to the"Suwannee"Limestone. The con tact between the units often appears gradational from the basal, quartz-sandy, phosphatic, occasionally clayey carbonates ofthe Nocatee into the slightly quartz sandy, non-phosphatic limestones ofthe"Suwannee"(Figures 47 and 48). Occasionally, the basal Nocatee is a siliciclastic unit and it is easily dif ferentiated from thelimestonesofthe"Suwannee."The contact is suggested tobea disconformity basedon paleontology (Huddlestun, personal communication, 1984). The Tampa Member overlies the Nocatee throughout much ofthe area. The topof the Nocatee is generally placed at thetopofthe siliciclastic section below the Tampa (as in W-12050, Figure 47). However, occasionally there is a carbonate bed at thetopof the Nocatee which contains too much phosphate to be includedinthe Tampa. This bed is takenasthe top ofthe Nocatee Member. Occasional ly, the Nocatee is overlain by carbonates ofthe undifferentiated Arcadia Formation. The relationships of the Nocatee with the subjacent and suprajacent units are shown in Figures 36,37, and 39. Thickness and Areal Extent The Nocatee Member ranges in thickness up to 226 feet (70 meters) in W-12050 DeSoto County (Figure 49). Other coresinCharlotte County stopped in the Nocatee,inareaswhere it may be thicker. Further coring or properly sampled cuttings are needed to delinate the thickness and, possibly, the ex tent of the Nocatee in this area. The topof the Nocatee ranges in depth from-81feet (-24.5 meters) MSL in Polk County to -639 feet (-195 meters) MSLinCharlotte County (Figure 50).Ingeneral the upper surface dips to the south and southeast atanaverage of 7.5 feet per mile (1.7 meters per kilometer). The Nocatee Member is of rather limited areal extentasis the Tampa Member.Ithas been identified in parts of Polk, Hardee, DeSoto, Charlotte, Manatee, Hillsborough, Sarasota, and possibly Highlands Counties. The lateral limits of this unitinmost cases are the result of facies changes (Figures 49 and 50).Inportions ofthe updip area, the Nocatee mayberepresented by a clay unit present in the Tampa,asdiscussed by Gilboy (1983). The extent of the Nocatee to the south and east is questionable at this time due to a lack of subsurface data (Figures49and 50). Age and Correlation The age of the Nocatee Memberisbased completelyonits subjacent positioning to the Tampa Member and its suprajacent position to the"Suwannee"Limestone of south Florida.Itis older than part of the Tampa Member, equivalent to part ofthe Tampa, and younger than the underlying Oligocene car bonates. This suggestsanearliest Miocene age for the unit. At the present time there have been no at tempts to date the unit paleontologically. The Nocatee grades laterally westward and southward into very quartz-sandy, phosphatic carbonates of the undifferentiated Arcadia Formation. Eastward the unit grades into a more siliciclastic-rich east coast facies ofthe undifferentiated Arcadia. Northward, it appears that the Nocatee grades into the basal Tampa Member. The Nocatee correlates with the lower part ofthe type Tampa Member.Itis also cor relative with part of the lower Penney Farms Formation of north Florida and the lower Parachucla of southeast Georgia (Figure19).76

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BEACH• ••PAL hi LEGEND• CORES • CUTTINGS LIMITSOF HAW;HORN GROUP'.! !I ! !I• 46 • •\ >I.i• 44 HENDRY t---t--+-,Ji 0I , ,/hi ARTIN,/.I/ , 'LAI([f;.;;;.;;;--"/,"/,,IKILOMETERSI , '1'""-1-----+,---+-.-...;.... __I__ : •iiI! -i : TJ' I .-.-•i -+_.._.'-' '-1\ •+-.---' -y----t-::----t 1 • -----t----t-t---t---+--J,.-!-\ .CIFEET 24 PSC0SCALE --r------.. ---012040MILES t--.,.......,j-.....",.I'-.,jr-----...J' o2040Figure49.Isopach of Nocatee Member. 77

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•BEACH• ••PAL M i LEGEND•CORES• CUTTINGS LIMITSOFHAWTHORN GROUP46 44NORY 1------+--+-,./1j / rr--f----+--1--1--.---.1 /,,!KILOMETERSI: . • --\----i----L-1--1-----4 ••, II ' ---L __ _ _L _ __l_ SCALEo2040MILES -....,-'&"'rj ....J1o2040Figure50.Top of Nocatee Member.78

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Discussion The sediments ofthe Nocatee Member have been recognized for some time. The name "Tampa sand and clayunit"represents the first published name applied to these sediments (Wilson, 1977). Although these sedi.ments are of limited areal extent, their distinctive lithology suggests the formal recognition of these sedimentsasa member of the Arcadia Formation. Outside the recognized area of occurrence equivalent carbonate sediments of the Arcadia Formation are often very sandy and may contain thin clay beds. The equivalence of the two unitsisrecognized by the stratigraphic position. PEACERIVERFORMATION Definition and Type Section The Peace River Formationisa new formational rank name proposed for the combined upper Hawthorn siliciclastic strata and the Bone Valley Formation. The upper Hawthorn siliciclastic strata in clude siliciclastic beds previously placedinthe Tamiami Formation (Parker, 1951) and the Murdock Sta tion and Bayshore Clay members of the Tamiami Formation (Hunter, 1968). The formationisnamed for the Peace River which occursinthe vicinity of the type sectionincore W-12050. The type section for the Peace River Formationisdesignatedascore W-12050, Hogan#1,located in east central DeSoto County, Florida(SE 1f4, NW 1f4 Section16,Township 38S, Range 26E) with a surface elevation of62feet(19meters). The type Peace River Formation occurs between+41feet(+12.5 meters) MSL and -97 feet (-29.5 meters) MSL (Figure51).W-15303, R.O.M.P. #17,issuggestedasa reference section (Figure 48). R.O.M.P. #17 is located west of W-12050 in the west central part of DeSoto County (NE 1f4, NE 1f4 Section 14, Township 38S, Range 23E, surface elevation 22 feet (6.5 meters)). The Peace River Formation occurs between-3feet(-1meter) MSL and -77 feet (-23.5 meters) MSLinW-15303. Lithology The Peace River Formation consists of interbedded quartz sands, clays and carbonates. The siliciclastic component predominates and is the distinguishing lithologic feature of the unit. Typically the siliciclastics comprise two-thirds or more of the formation. The quartz sands are characteristically clayey, calcareous to dolomitic, phosphatic, very fine to medium grained, and poorly consolidated. Their color ranges from light gray(N7)and yellowish gray(5Y8/1) to olive gray(5Y4/1). The phosphate content ofthe sandsishighly variable.Inthe type section (W-12050), the phosphate contentislowestinthe upper part of the section and greatest near the base. The same is true for the reference sectioninW-15303. The phosphate occurs bothassandand gravel sized particles. The gravels are most abundantinthe Bone Valley Member, although they may occur elsewhere in the unit. Clay beds are quite common in the Peace River Formation. The clays are quartz sandy, silty, calcareous to dolomitic, phosphatic, and poorly to moderately indurated.Color ranges from yellowish gray(5Y8/1) to olive gray(5Y4/1). Reynolds (1962) characterized the clay mineralsasconsisting of smectite (montmorillonite), palygorskite (attapulgite) and sepiolite. Strom (personal communication, 1984) and Barwood (personal communication, 1984) agree that smectite and palygorskite are the domi nant clay mineralsinthe formation. Carbonates occur throughout the Peace River Formation. Characteristically they comprise less than 33 percent of the Peace River section. The carbonates maybeeither limestone or dolostone. Updip (northward), dolostone occurs more frequently. The limestones are characteristically variably sandy, clayey and phosphatic, poorly to well indurated, mudstones to wackestones. They varyincolor from yellowish gray(5Y8/1) to white(N9).Dolostones are microto very finely crystalline, variably sandy, clayey and phosphatic, and poorly to well indurated. Colors range from light gray(N7)to yellowish gray79

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zo j::::0(::Iirr:e0(is0(urr:0(rr:w III ::Iiw::Iil:l t o(g ZSANDCALCITECLAY CLAY CLAYOOLOHITECLRYCLAY CLAYCALCITECLAYCLAY CLAYC...AYCLRYCALCITECLAYPHOSPHATE PHOSPHATESANDPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHPTE PHOSPHATE PHOSPHATEPHOSPHATECLAYCLAY CLAY CLAY CLAYSANDCALCITESANDPHOSPHRTEPHOSPHATE PHOSPHATECLAY OOLOMI7E DOLOMITEDOLOMItE DOLOMItE OOLOHItEDOLOMITESll1DOLOMItECLRYDOLOMITECLAYSANDSAHOSANDSAMOCALCItEPHOSPHATEDOLOMItE PHDSPHATEOOLDHItE PHOSPtlATE DOLOMITEPHOSPHATEDOLOMItEPHOSPHRTEDOLOMITEPHOSPHATEDOLOMITEPHOSPHATEDOLOMITEPHOSPHATEDOLOMITEPHOSPHATEOOLOMITEPHOSPHATEDOLOMITE PHDSPHATEODLOHItEPHOSPHATEDOLOMItEPHOSPHATEDOLDHIlEPHOSPHRTEOOLOHItE PHOSPHRTEOOLOHITE PHOSPHATEOOLOHITEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTE"SUWANNEE" LIMESTONE--------320 _ -310 _ W 1 21'151'1 PHOSPHATEPHOSPHATE PHOSPHATESAMOPHOSPHRTE -300 __ SAND••••••••PHOSPHATE sANOCLRY-290 -280 -500 -S10 -520 -530-330-%0 zo j::::c::Iirr: o ILCisc u rr:c z 2 t o(::Iirr:err:w > wu0(W PHOSPHATE SIUtOPMOSPMATESAMO PHOSPHATE SANtiSAMO PHOSPHATE SAND PHOSPHATE SAND SAND SAND SAMO SAHOPHOSPHATESAMO PHOSPHATESAMOPHOSPHATESANDPHOSPHATESAMOPHOSPHATECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHA1ECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHATECLAYPHOSPHATESAND PHOSPHATESAMO PHOSPHATE SF/MD PHOSPHATE PHOSPHATESANDPHOSPHATESANDPHOSPHATESANDPHOSPHATESAND PHOSPHATE SANDPHOSPHATE SAMO CLAYPHOSPHATESANDPHOSPHATESANDPHOSPHATECLAYPHOSPHRTECLAYPHOSPHF/TESANO PHOSPHATE SANDSAND "1''"' LH'CLAY SAND PHOSPHATF PHOSPHATESIINO PHOSPHATE SAMO PHOSPHATECLAYPHOSPHATECLAYPHOSPHATECLRYPHOSPHATECLAYPHOSPHATECLRY PHOSPHATECLATPHOSPHATE PHOSPHATEPHOSPHRTEPHOSPHATE PHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTEPHOSPHATEPHOSPHATEPHOSPHRTEPHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATE DDLDl'lllE SAND SAND 5AII.OSAND CALCITEPHDSPHP.TEPHOSPHATE PHOSPHATE PHOSPIlAIEPHOSPHATE SAHDCALCITEPHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATEPHOSPHRTE PHOSPHRTESRHOCLATSAND SAND SAND UNDIFFERENTIATEDLAND SURFACE-........"-".."-""-" == PHOSPHATEHAWTHORN GROUP ....t-PHOSPHATEPHOSPHAtE CLAY PHOSPHAtEPHOSPHATESANDPHOSPHATE PHOSPHATECLAY -L00 -150 -L70-200 -190-L80-160 -90 -120 -80-50 -L 1020-10-130-20-7010-60-305030 60 -210CLAY SAMO -220 -230 -250-26e -270 SANDSAND SAND SAMOSAND SAND SAND f5l1l SAND m::Ii:Pt
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(5Y Mollusk molds are common throughout the carbonates. Occasionally dolomite occursasa dolosllt (composed 'of unconsolidated, silt-sized dolomite rhombs). The dolosilts contain variable amounts of clay, are generally only slightly sandy and phosphatic, and do not contain fossil molds or fragments. Chert occurs sporadically in the Peace River Formation. Characteristically it appears tobea replace ment of the carbonates although silicified claysdooccur. The cherts are opaline and are suggestive of localized "alkaline lake" deposition,asdescribed by Upchurch, Strom and Nuckels (1982) and Strom and Upchurch (1983). SUbjacent and Suprajacent Units The Peace River Formation disconformably overlies the Arcadia Formation throughout its extent. The contact often appears unconformable updip and conformable (gradational) downdip (Figure35through 40). The gradational appearance is due to therepetition of similar lithologies in both formations. When the boundary appears gradational the base ofthe Peace River Formation is placed where the carbonates become dominant over the siliciclastic beds (Figures48and51).Aswas previously mentioned in the discussion ofthe Arcadia Formation, the contact may alsobemarked by a rubble zone. The sediments overlying the Peace River Formation are assigned to several formations.Inthe south Florida area and the southern part of east central Florida, the limestone and sand facies of the Tamiami Formation unconformably overlie the Peace River. Sediments disconformably suprajacent to the Peace River Formation in the west central Florida area (Polk, Hillsborough, Manatee, Sarasota, and Charlotte Counties) and parts of east central Florida are generally unnamed,nonphosphatic sands (often surficial) and unnamed fossiliferous sands and shell beds. The contact with the surficial sands is often obscure due to leaching ofthe phosphate and clays in the upper portion ofthe Peace River Formation.Inthe central and south central section, unfossiliferous non-phosphatic to very slightly phosphatic sands overlie the Peace River. These sands have been called "Citronelle" Formation (Cooke and Mossom, 1929; Cooke, 1945) and"FortPreston" Formation (Puri and Vernon, 1964).InGeorgia, these sands are currently assigned to the Cypresshead Formation by Huddlestun (personal communication, 1984). These sediments are assigned here, for convenience,tothe post-Hawthorn sediments. Problems in identifying the upper limits ofthe Peace River ariseinareas of extensive reworking of the sediments.Insuch a case the sediment maybecompletely reworked and the resultant lithology only slightly different than the unreworked sediments. When this occurs minor changes in lithology suchasanincreaseinshell material, changeinclay mineralogy, or changeinsorting provide the necessary lithologic criteria for separating the units. Thickness and Areal Extent Sediments assigned to the Peace River Formation occur over much of the southern half of the Florida peninsula. The top of the unit ranges from a maximum known elevation of+175 feet (+53meters) MSL in Polk County to greater than -150 feet(-46meters) MSL in part of Collier, Dade, Broward, and Palm Beacl:1 Counties (Figure52).The thicknessofthis unit varies to more than 650 feet meters) in parts of Martin and Palm Beach Counties (Figure53).This thickness, whichistaken from several sets of cut tings in the area, seems anomalously thick. Thicknesses of 400 feet (122 meters) or greater occurineastern Glades County along the western edge of Lake Okeechobee (Figure 53). Although the Peace River Formation occurs over most ofthe southern portion of the state, it is absent from the Ocala Platform and the Sanford High (Figures4,52and53).Itisalso absent, possibly due to erosion, from portions of Hillsborough, Pinellas, Manatee and Sarasota Counties (Figures52and53).Itdips east, south and west off the southern nose of the Ocala Platform(anarea referred toasthe Central Florida Platform by Hall [1983]). South of this area, the dip is an.d at approx imately 8 feet per mile (1.3 meters per kilometer) (Figure52).Local variations of dip direction and degree are common.81

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Figure 52.CJ.SO FT.10)0! 10)020.0;0 SCALE•CORE•CUTTINGS _,'50V-L...J LIMITS OF HAWTHORN GROUP HAWTHORNGROUPUNDIFFERENTIATED PEACE RIVER FORMATION ABSENTTop of Peace River Formation. Shaded area indicates undifferentiated Hawthorn Group.82.BEACH

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Isopach of Peace River Formation. Shaded area indicates undifferentiated Group. Figure53.o" N :l ),0 .,It''''''to20)04010 SCALE• CORE• CUTTINGS LIMITSOFHAWTHORNGROUP HAWTHORNGROUPUNDIFFERENTIATED 0E3/!?fIl PEACE RIVER FORMATION ABSENT83

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Age and Correlation The Peace River Formation often contains well preserved fossils that include vertebrates, diatoms, and foraminifera. As a result, the range of ages that this unit encompasses can often be documented. Vertebrate fossils are frequently exposed during mining operations in the central Florida phosphate mines. The oldest, a limited fauna tentatively assignedanearly to middle Barstovian age (late Early to late Middle Miocene) (Webb and Crissinger, 1983), was collected from the lowest strata ofthe Peace River Formation, just above its contact with the older Arcadia Formation. These fossils suggest a possi ble latest Early to early Middle Miocene age for the lowest part ofthe Peace River. This author has found no record of Late Barstovianor Clarendon ian vertebrate sites in the Peace River Formation of southern Florida. The next younger vertebrates from the phosphate mining area are those knownasthe Lower Bone Valley fauna. These are regardedasbeing of Early Hemphillian age (medial to late Late Miocene) according to MacFadden and Webb (1982). The Bone Valley Member, also contains the Upper Bone Valley Fauna, for which a Late Hemphillian age has been assigned. This fauna is discussed further in the section of the Bone Valley Member. Another assemblage of vertebrate fossils, knownasthe Manatee local fauna, was collectedinsituat the Manatee River Dam site, just east of BradentoninManatee Coun ty. These. fossils, assignedanearly Late (or medial) Hemphillian age, came from beds only 6 to 10 feet (1.8 to 3.0 meters) above present sea level (MacFadden and Webb, 1982,p.197). Marine invertebrates provide additional information about the age of the Peace River Formation in other parts of southern Florida. Diatoms identified by Hoenstine (personal communication, 1979) from core W-10761inCharlotte County indicate a Middle Miocene age for Peace River sediments at -92 feet (-28 meters) below present sea level. According to Huddlestun (personal communication, 1983), foraminifera in W-15286inLee County suggestanage no younger than earliest Pliocene for sediments at -132 feet (-40.5 meters) MSL. Huddlestun also suggests a Late Miocene age (early to middle Tortonian age) for Peace River sediments at -405 to -417 feet (-124 to 127.5 meters) MSL in W-15246 in Martin County.Healso indicatedanearliest Pliocene age for the Peace River sediments between -175 feet (-53.5 meters) MSL and -437 feet (-133.5 meters) MSLinW-15493inMonroe County. When considering the depths from which some of these invertebrates are reported, the reader should bearinmind that the southern half ofthe peninsula is known to be a subsiding area, with the degree of subsidence varying from minimalinthe northern area to maximum at the southernmost tip ofthe penin sula and in the Florida Keys. The present subsea elevation ofthe strata that contain these marine in vertebrates is therefore not necessarily the sameasthe elevation ofthe stratainrelation to sea level at time of deposition. From the preceding records, the Peace River Formation is thought to range in age from possibly latest Early or early Middle Miocene for the oldest sediments to early Pliocene for the youngest. Huddlestun et al. (1982) informally proposed the name "Indian Riverbeds"ofthe Hawthorn Group (later changed to Wabasso beds) foraninterval of sedimentsincore W-13958, Indian River County. They reported diatoms'and planktonic foraminifera indicative of a late Early Pliocene age for the strata. Their age assignment suggests that the Wabasso beds maybeslightly younger than the uppermost Peace River strata. The lower part ofthe Peace River Formation is here correlated with the Coosawhatchie and Statenville formations of northern Florida (Figure19).This is based partlyonstratigraphic position, and partly on ages suggested by the Middle Miocene diatoms, and the tentative Early to Middle Barstovian age for the vertebrates in the lowest beds of the Peace River. Huddlestun (personal communication, 1983) suggests that the upper strata ofthe Peace River are slightly older than the Jackson Bluff Formation in the Panhandle. They are also slightly older than the Tamiami Formation of southern Floridaasrestricted herein. Discussion For years the Peace River Formation has been identified and mappedasthe upper siliciclastic unit of the Hawthorn Formation in south Florida. It is simply the phosphatic quartz sands and clays that overlie 84

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z a: o :J:I-<:J: ON-8879TIATED VER ON LAND SURFACE-",,'.."PEAT........... . ...PEAT•I••••• W ....,""""""PEAT-UNDIFFERENTIATED','.',.,',',',,[CLAYI•••••••-'-;'-'-;'-'-;'-'-;' ,0_'0_00_00_0-,-,-, -, , ....:-;'-'-;'-'-;'-'-;' , r-:-;'-'-;' -'-;' -'-;' ,BONE VALLEY MEMBER .:-:-;: '.......CLAY .J, CLAYPEACE ,J,'1-'CLAYRIVER FORMATI ,J,,J, CLAY .J, CLAY-PHGSPHATECLAY,p,,p, ,p,,p.CLAY Po -, J, -. j. -, :r, CLAY , ;). CLAY, ,.,',J, CLAY 'IJO r, cv.-'-:..:.:-: ... :..:.:-:..:.:-:..:.: 'PHOSPHATEDOLOMITECLAYUNDIFFEREN-,'-,PHOSPHATEDOLOMITECLAYPEACERI rl CV/ / / PHOSITE ::>HNU PHOSPHATE PHOSPHATESANDARCADIA FORMATI---------PHOSPHATE I-,-,-,-r PHOSPHATESANOPHOSPHATESANOPHOSPHATESANDPHOSPHATESANOI' ' I' ' I' ' I' IISUWANNEE LIMESTONEIIII III1 1010080706050903010-1020o Figure 54, Reference core for the Bone Valley Member of Peace River Formation, Griffin#2,W-8879, Polk County (Lithologic legend AppendixA).and grade into the Hawthorn carbonate section (here referred to as the Arcadia Formation).Inthis report the name Peace River Formation is formally proposed for this section including the Bone Valley Forma tion of former usage, the lower Tamiami Formation of Parker, etal.(1955) and the Murdock Station and Bayshore Clay members of the Tamiami of Hunter (1968), Strata currently assigned to the Peace River Formationinsouthernmost Florida and along the southeastern coast include sediments that are Messinian to Zanclian, latest Miocene to earliest Pliocene in age, These sediments may be age equivalent with the uppermost bed of the Bone Valley Member. Ad-85

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mittedly the data baseinthese areas is relatively poor. Future investigations may provide the core data necessary to further describe the sections. BONE VALLEY MEMBER OF THE PEACE RIVER FORMATION Definition and Type Locality The Bone Valley Formation of former usage is demoted herein to member status within the Peace River Formation of the Hawthorn Group. The status reductionissuggested due to the limited areal extent of this unit, to the gradational nature of its boundaries (both lateral and vertical) with the Peace River For mation, and to its lithologic similarities to the Peace River Formation. This unit directly overlies the Ar cadia Formation in some areas but overlies and interfingers with the upper Peace River Formation in other areas (Figure 55). The type area designated by Matson and Clapp (1909) consists of phosphate mines west of Bartow in Polk County, but no individual type section was proposed. More complete sections ofthe Bone Valley Member are presently available in present-day phosphate mines than were accessible when the unit wassPLIO-PLEISTOCENE SANDSBONE VALLEYNo200SOUTHERN METE'lioI........ N .. O ..RT.H.ER..NioiP..OiiiiL.. K ,;;;;c;;;,;u;;,;,N;.;.Ty Figure55.Schematic diagram showing relationship of lithostratigraphic units in southern Florida.86

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sections are constantly being changed by the mining operations and a definite type sectionISImpossible to erect.Asa result, the Bone Valley Member type area remains designated the current exposuresinmines westofBartowinPolk County . . is interesting to note that the original "Bone Valley Gravel" of Matson and Clapp (1909) was probably limited to only the uppermost gravel bed of the Bone Valley Formationasitiscurrently used in the phosphate district. As mining methods improved deeper pits were dug exposing more of the phosphorite section and the accepted definition of the Bone Valleywasexpanded to include these sediments. A principal reference section in a core, W-8879 (NE 114, SW 114 Section24,Township 29S, Range 24E, Polk County), near Bartow is suggestedasbeing representative of this unit.Inthis core the Bone Valley Member occurs between 91.5 feet (28 meters) MSL and56feet (17 meters) MSL (surface elevationis110 feet [33.5meters]) (Figure54).Lithology Throughout its extent, the Bone Valley Memberisa clastic unit.Itconsists of pebbleor gravel-sized phosphate fragments and sand-sized phosphate grainsina matrix of quartz sand and clay. Percentages ofthe various constituents vary widely. The occurrence of phosphate gravelsinthe Bone Valleyisthe most lithologically important factor in the separation of the member from the remainder of the Peace River Formation. Phosphorite sands are also present, oftenasthe most abundant phosphate size fraction. The phosphate grains rangeincolor from white(N9),where they have been leached,toblack(N1).Commonly the larger phosphate clasts appear to be replacement of carbonate by phosphate. . The quartz sands occur intimately mixed with the phosphate and claysinthe Bone Valley Member. On ly in part ofthe leached zone are phosphate grains absent from the sands. A leached zone develops where the phosphate grains are removed by groundwater dissolution. Other phosphate minerals are often deposited in the sands, weakly cementing them. Claysinthis zone are also altered. The sands range from very fine grained to very coarse with some zones containing quartz pebbles and cobbles. Col ors ofthe sands range from white(N9)and light brown(5YR6/4) in the leached zone to light olive gray(5Y 6/1) in the more clayey sections and to dark gray(N3)inthe highly phosphatic sections. Clays characteristically occurasmatrix materials but also occurasdiscrete beds. The clay beds vary in the amount of accessory minerals present, occasionally occurringasrelatively pure clay with very little sand or phosphate grains. The clay beds often occur at the base of the Bone Valley and are referred tointhe phosphate districtas"bedclays." The "bed clays" have been interpreted by someasbeing the "residuum of the argillaceous carbonate rock of the Hawthorn ... " (Altschuler et aI., 1964). Other clay occurrences in the Bone Valley have been interpretedaspossible products of alkaline lake deposition (Strom and Upchurch, 1983). Colors of the clay beds exposedinthe mines range from white(N9)to yellowish gray(5Y 8/1), light brown(5YR6/4)andblue green(5BG7/2).Incores, the colors show a similar range plus olive grays(5Y6/1and 5Y 4/1). Beds of carbonate rubble often occur at the base of the"bedclay." Bedding in the Bone Valley Member varies from faintly stratified to strongly cross bedded. Graded bed ding is common throughout the unit, although itisoften not well developed. The poorly stratified units are typically more clayey and poorly-sorted, while the crossbedded sections are moderately to well sorted and generally lack finer grained materials (silts and clays). A mottled appearance to the sedimentisnot typical in the Bone Valley Member but becomes apparentinthe underlying undifferentiated Peace River sediments. The very phosphatic section of the Bone Valley Member grades upward into slightly phosphatictonon phosphatic clayey sands. These clayey sands havebeenreferred toasthe Upper Bone Valley (Altschuler et aI., 1964). Bedding is typically n'I?Ssive. Inthis investigation this placedinthe asthe uppermost sediments, but is given a separate bed name.ThiSsectIon often contains the leachedzone"which has been altered, often intensely, by groundwater, removing all the included phosphate. 87

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Subjacent and Suprajacent Units The Bone Valley Member disconformably overlies the Arcadia Formation throughout much of its ex tent.Inthe areas furthest updip (Figure 55), the lower Arcadia (possibly the Tampa Member in some cases) immediately underlies the Bone Valley.Insouthernmost Polk and adjacent parts of Hardee and Manatee counties, the Bone Valley grades laterally, and to some extent vertically, into the undifferen tiated Peace River Formation.Inthis area the Bone Valley often lies on the Peace River and the differen tiation between the two becomes difficult (Figure 55). These relationships and those with the overlying units are shown in Figures 35 through 40. The characteristic Bone Valley section (if such could be seenina single pit wall or core) consists of a basal gravelly unit lying on either undifferentiated Peace River Formation or Arcadia Formation. This is overlain by a "middlefeed"unit of sand-sized material with little gravel which, in turn, is overlain by the upper gravels. When the basal gravels are present it is quite simple to separate the Bone Valley from the undifferentiated Peace River Formation. However, if the basal gravels are absent and the middle unit of the Bone Valley liesonthe Peace River sediments, it often is not possible to accurately separate the two beds, and placement of the boundary becomes arbitrary. The Bone Valley Member is unconformably overlain throughout its extent by unnamed sands. These sands often appear to grade into the Bone Valley due to the obliteration ofthe contact by ground-water leaching and reworking. The unnamed sands have often been referred toasPleistocene or Plio Pleistocene in age. Thickness and Areal Extent The Bone Valley Member occurs at elevationsashighas175 feet above sea level (53 meters) in southwestern Polk County (Figure 56). Over the majority of its areal extent the Bone Valley member oc curs above 100 feet (30.5 meters) MSL. The lowest elevations of the upper surface ofthe Bone Valley oc cur near the limits ofthe memberonthe east, south and west (Figure 56). This unit attains a maximum thickness of just over50feet (15 meters) in southwest Polk County, from which it thins in all directions (Figure 57). Locally, the Bone Valley may thicken abruptly into karst features. The upper surface of the Bone Valley Member dipsinall directions away from the highest area at less than 5 feet per mile (0.9 meters per kilometer). Individual beds within the Bone Valley appear to have a slight"seaward"dip (Matson and Clapp, 1909). This unit extends over much of the western half of Polk County, the eastern one-third of Hillsborough County, northeast Manatee County and northwest to north-central Hardee County (Figures 56 and 57). Outside this area individual beds of Bone Valley lithology occur intermixed with undifferentiated Peace River sediments, but are not differentiated. Age and Correlation Vertebrate remains are frequently exposed during mining operations in the central Florida phosphate mines, and are probably the source of the name, Bone Valley. The ages assigned to the Bone Valley Member are derived entirely from these vertebrate fossils. The oldest, a limited fauna tentatively assignedanearly to Middle Barstovian age (Webb and Criss inger, 1983), was collected from the lowest strata ofthe Bone Valley Member, just above its contact with the older Arcadia Formation. These fossils suggest a possible latest Early to early Middle Miocene age for the lowest part ofthe Bone Valley. This author has found no record of Late Barstovian vertebrate sitesinthe Bone Valley Member of southern Florida. The next younger vertebrates from the phosphate mining area are those knownasthe "Lower Bone Valley Fauna." These are regardedasbeing of Early Hem phillian age (medial to late Late Miocene) (MacFadden and Webb, 1982). The youngest vertebrate assemblage, knownasthe Upper Bone Valley Fauna, occurs in marine sediments deposited aboveanunconformity thought to represent the Messinian regressive event. MacFadden and Webb (1982) in dicate a Late Hemphillian age for these animals. Because ofthe unconformity, it is suggested that the 88

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oIoSCALE-N20 20ICI 25FEETLEGEND• CORES • CUTTINGS LIMITSOFBONE VALLEY MEMBER40MILESIKILOMETERSFigure56.Top of Bone Valley Member. age of the uppermost Bone Valley strataisprobably Early Zanclian (very Early Pliocene; see Figure 73). These sediments are discussed by Webb and Crissinger (1983)asreworked channel deposits ("driftrock"of phosphate mining terminology), also being of Late Hemphillian age. They further reported that Pleistocene vertebrates have been collected from younger channel fills that contain reworked parts of the Bone Valley Member. The Early Pliocene strata of the Bone Valley Member that occur above the unconformity seem to have no exact correlatives that have been identified with certaintyinFlorida or the Southeast Georgia Embay ment. Huddlestun (personal communication, 1983) suggests a correlation of the Bone Valley Member to the hard rock phosphates of central Florida basedonvertebrate faunas. The Bone Valley also correlates to part of the Intracoastal Formationinthe Apalachicola Embayment (Schmidt, 1984). Part of the Bone Valley Member correlates with the Coosawhatchie and StatenvilleFormations of North Florida and Georgia and the Pungo River Formation of North Carolina. A portion of the Bone valley correlates with Huddlestun's (in press) Screven Formation in the Georgia Coastal Plain.89

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LEGEND• CORES " CUTTINGS LIMITSOFBONE VALLEY MEMBERKILOMETERS CI=25FEET ;______f---_":-iJ:,., N G E -.\•I ')trf--+-+---+'-" --+--1--1L r->--(r-'----e--\\fI PAS "C 0 r' _II [ Ii/I-fl ,":' \ ..l._1 [,11 ---f---"' '' l ".,!., "" 0 \._ A I iV,.,'\J. I ,;j I (t"/9. / v 0r l)V ' r-\ \Q(" I oQ: r._0 n6 5eE(IAI. 0 .\, HILL'A DueI\ ::.uJj Uv \.) 1I _ -' i/f 0 I-K\"H---=-+--+-f---:--I-t----J-lL...LJ-r-.,...---\ \1 ('" \ '\ = i ...,......."<." • 0\.'" I C""\:':--.0 -D 11 -l "/.t '\, tj)I-C-..hoC\ \i r\ / "_0"r,".ni:J"tc?30 III I ,'Ii:RIVE R t?/( --,-:__ '1'7L.r'--,,-'-'--"t.-.,MANATE"E' •V l./ 0 "-,_-..• -<':::'" "i EE H" : \ __ SlUCIE\ \ "I! '. "lf--\\\ 5 R ICH'JIrA-; •DES OJ 1--I'll . I-N-\ :.._.1--__._1--I Y 10,//\_MIA K III r SCALE 0,2040MILES t---T"""..I'-.r-_'.L.'--,.r--..I----.J. o2040Figure 57, Isopach of Bone Valley Member. Discussion The Bone Valley section has been recognized for years due to its economic importance. However,aspreviously mentioned, its limited areal extent does not warrant formational status. The preceding discus sion ofthe Bone Valley indicates distinct similarities between parts ofthe Bone Valley Member and the undifferentiated Peace River Formation. Geologists familiar with the geologic section in the phosphate district readily recognize the similarities and many have accepted the association of these units. One source of discussion concerning the placement ofthe entire Bone Valey in the Peace River For mation and theHawthorn Group is the occurrence of a major unconformity within this section. The un conformity spans much of the Late Miocene, Without the aid of dateable fossils, it is normally not possi ble to separate the pre-unconformity gravels from the post-unconformity gravels. The argument has been presented that the post-unconformity Bone Valley sediments should not be included in the Peace River Formation or theHawthorn Group, However, basedonlithologic similaritiesoneither side ofthe noncon formity and their stratigraphic position it is perfectly acceptable under the North American Stratigraphic Code, Article 23d (NACSN, 1983) to place all these sedimentsina single unit.90

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Inli.ghtof this argument it is interesting to note that the classical Bone Valley "Formation"asoriginally byM.atsonand Clapp (1909), included only the post-Messinian gravels. This was the only por of the section normally exposedasa result ofthe old mining methods.Asflotation methods began being used to concentrate the phosphate, mining went deeper into the phosphate-bearing strata.Asthe deeper lithologies were exposed, most were incorporated into the Bone Valley "Formation" thereby ex panding the time frame and the definition of the unit.EASTERN FLORIDA PANHANDLEThe Hawthorn Group extends northwestward from the Ocala Platform across the eastern portion of the Florida panhandleasfar westasthe Apalachicola RiverinGadsden and Liberty Counties. Sediments of the Hawthorn Group have not been identified west of the Apalachicola Riveronthe west side of the Gulf Trough (Huddlestun and Hunter, 1982). These sediments are thickest in the Gulf Trough and thin dramatically on the flanks. Lithologically, much of the Hawthorn Groupinthe eastern panhandleisquite different from the Hawthorn sediments of the peninsular area. The most obvious differenceisthe decreased phosphate content throughout the section.InMadison, Jefferson and part ofLeonCounties the dominant lithologyissandy clay to very clayey sand. Carbonate content increasesinthe Gulf Trough area, where the lithologies become more similar to those of the northeastern peninsular areainmany respects. Stratigraphically, the sediments under consideration here are assigned to the Torreya Formation of the Hawthorn Group (Figure58).Unfortunately, core data to further refine the stratigraphy of these sediments in the eastern panhandle do not exist at this time eitherinnorthern Florida or southern Georgia. TORREYA FORMATION Definition and Type Section The Torreya Formation was describedbyBanks and Hunter (1973)asconsisting of post-Tampa, pre Chipola (Early Miocene) age depositsinthe eastern Florida panhandle.Indefining this unit Banks and Hunter (1973) restricted the use ofthe Hawthorn Formation by removing from it the sediments of the Tor reya. However, they did not clearly distinguish between the two units lithologically due to the paucity of data available at the time. Huddlestun and Hunter (1982) suggested the revision of the definition of the Torreya to include all deposits previously referred to the Hawthorn Formationinthe eastern Florida panhandle. They regarded the Torreyaasidentical to the Hawthorn Formation of former usage. The Torreyaisthe only formation currently recognizedaspart of the Hawthorn Groupinthis area.Itincludes two named members: the Dogtown and the Sopchoppy (Figure58).The type section designated by Banks and Hunter (1973)islocated at Rock Bluff, Liberty County, Florida,inthe Torreya State Park from which the formational nameisderived. Rock Bluff is locatedonthe Apalachicola Riverinthe SW1!4, Section17,Township 2 North, Range 7 West. A complete descrip tion of this outcrop is availableinBanks and Hunter (1973). For the purpose of this study, reference sec tions are designatedincores W-6611, SE1!4,NE1!4 Section23,Township2N,Range7W,Liberty County (Figure 59); W-7472, NW1f4 , SE1f4 Section 19, Township 2N, Range3W,Gadsden County (Figure 60); and W-6998, SE1f4 , NW1f4 Section8,Township2N,Range2E,Leon County (Figure61).Lithology The Torreya Formation of the eastern Florida panhandle is typically a siliciclastic unit with increasing amounts of carbonateinthe lower portion of the section, particularlyinthe Gulf Trough area. The siliciclastic portion varies from a very fine to medium grained, clayey quartz sand to a variably quartz sandy, silty clay often containing a minor but variable carbonate component (either calcareous or91

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POST-HAWTHORNUNDIFFERENTIATED lei1:'.enI::Ef------71:'. DOG."1:'.1a. TOWN(Ill. ::> ) 0 a: 0 (!) LC/)_z a: 0TORREYA J: I-FORMATION 3: J: CHATTAHOOCHEEOR ST.MARKSFORMATIONSFigure58.Lithostratigraphic units of the Hawthorn Group in the eastern Florida panhandle.92

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j:: •HA WTHORN GROUP 2502Y0230 220 210 200190180170
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I W-7't72 zo i= wa:a:oI-HAWTHORN GROUP CHATTAHOOCHEE FORMATIONSAND SAND SAND SANDSANOSANDCLAYCLAYCLRYCLAYCLAYSAND SANDSANO SANO SANOSANOCl.AY SANO SAND SANDSANeSANOCLAYCLAYSANOSRNDSANDSRNDSAND SAND ::::'=:=::'=:=::'=:=::'-=.10 20 70 80 50 30 60'100 Z0-10 i= wa: a:0I-HA WTHORN GROUP MICCOSUKEE FORMATION LAND SURFACESRNDDOGTOWN MBR.SANDCLAYSANDCLAYPHOSPHATE PHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PI-lOSIlHATE PHOSPHATEPHOSPHATE PHOSPHRTECLAYPHOSPHRTE SAND PHOSPHRTE SANDSRNDCLAYCLRYCLAY j;j,.ll:l. SAND SANDSRNDSANDSRND.-'-''-'._.-------'-_.-_.-_.-',==.::=.==.=-------._.._.._.._..--'--'--'=.==.==.=------'-'._.._.'-' '-''-''-''-'.==.==.==.=-------, -, -, 'I :._.._.. _ .. _ ..._._._..'-''-''-''-'_._._.. CLRY JACKSON BLUFF CLRY FORMATION -I!!IELHI'II; ---------.,._.._.. _ .._.-----------------------------E-E-E-E---------------=======-1 ::.::.=-=-=-=-=-, ._.. _ .. _ .._.I_._._..._.._.._.._. _._._... _ .._.._.._._._._.. '-;-'_'7'_'7'_'-;', ._.._.._.._. 250 2'10 230 220 210 200 190 180 170 160 CD 150 .j:>.1'10 130 120 110 100 90Figure60.Reference core for the Torreya Formation, Owenby#1,W-7472, Gadsden County (Lithologic legend AppendixA).

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230 220 210 200 190.-;-.-'-;-'...:-;-.-'-;-'J 1_0"_I"_I1_."_.-._..-------=:-=:-=:-=:-=: -=:-=: -I"_00_00_00_0.._._._..I_II_II_II_I."_II_II_I"_I""""'"_._..I_I"_II_II_II .I_""_0"_00_01_._. _..I_II_I0_1"_II""""'"""",_••I_I"_,I_I1_01""""0_._••I_"I_II_II_I1_.........._••I_II_II_I1_.1_._.........t•1_0"_"0_1'_0''''''''''_._..I_I"_II_II_I_.........._..I-II_I"_I"_"1_._. _..1_0I_II_"I_I1""""0""""'"""",•I_I1_0"_"I_I_._.-..I_II_II_I,_"._.-._..I_I1_01_01_,""""'"_._.... .I•••••••....I_I1_0I_II_II........._..........."_I"_""_I0_0LANDSURFACECLAYMICCOSUKEE FORMATIONCLAY W-6998'-::'-=:'-::'-=:'-::' SAND SANDCLAYzo j:c(2a: o u.c(> w a:a: o IHA WTHORN GROUP HA WTHORN GROUPSANDCLAYSANDCLAYSAND SAND SANDPHOSPHATEPHDSPHATE PHDSPHATE PHOSPHATE PHOSPHATEPHOSPHATEPHOSPHATE PHOSPHATE PHOSPHATESANDCLAYSANDCLAYSAND SAND SAND SANDCLAY----...:.:::...:.:::...:.:::...:."':'1-------------------------------------"_"-"_"."_II_I"__"_"I_""_II_II_I1_.......... _.."_I"_I"_II_I"""""."""",..........I_II_I"_I1_"1_._...........'_0I_II_II_II .I_"0_00_01_"I_I _I _II1_,"_""_"1_'._-'-''-'._.1 • _. II_I1_'•__._.I_I_._II1_-__•I_II_II I_II1_-"__•__I__I_I_"_III_II_I1_'I_I" "_._1_'I_II_I"_"I I_"I1_-1__"_"I_1_"_.I1 10150 180 170 130 120160 140 90 ST. MARKS FORMATIONFigure 61. Reference core for the Torreya Formation, Goode#1,W-6998, Leon County (Lithologic legend AppendixA).95

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dolomitic). Phosphate grains are a common but minor lithologic component of the siliciclastic beds and are often absent. Induration varies from poor to moderate, generallyindirect relation to the relative amounts of clay and/or carbonate present. The colorsinthe unweathered siliciclastic beds range from white(N9)and yellowish gray(5Y 8/1) to light olive gray(5Y 6/1).Ina more weathered section the sediments appear mottled and are grayish-red(10R 4/2) to grayish orange(10YR 7/4)incolor. The carbonate portion of the Torreya Formation typicallyisa variably quartz-sandy, clayey limestone which occasionally maybedolomitic.Asnoted by Huddlestun and Hunter (1982), the Torreya is the only formation of the Hawthorn Groupinnorth Florida and Georgia where limestone is ao important and con sistent component of the lithology. Minor amounts of phosphate are presentinlimestones of the upper Torreya. Quartz sand content varies drastically and grades into calcareous quartz sands. Indurationisusually moderate butisvariable. Color ranges from white(N9)to light olive-gray(5Y 6/1). The carbonate sediments are often fossiliferous and commonly have abundant molds and casts of mollusks. Clays areanimportant lithologic component of the Torreya Formation particularlyinthe upper part of the unit. The clays are predominantly palygorskiteandsmectite with minor sepiolite, illite and kaolinite (Weaver and Beck, 1977). Weaver and Beck (1977) recognized the variability of the clay mineralogyinthat some intervals may be dominated by palygorskite while others may be predominantly smectite or, more rarely, sepiolite. Ogden (1978) recognized that palygorskite was the major and occasionally the sole clay mineral constituentinthe southern portion (Florida) of the fuller's earth mining district. Other minor lithologic components recognizedinthe Torreya Formation include feldspar, pyrite, opal-CT, and mica. Beddinginthe Torreya Formation ranges from thin laminae to more massive beds up to 5 feet (1.5 meters) thick (HuddlestunandHunter, 1982). Bioturbation has had a widely variable effectonthe bed ding, which ranges from undisturbed to highly bioturbated. Huddlestun and Hunter (1982) recognized the occurrence of intraformational brecciasinthe Torreya sediments. The intraclasts are composed of clay or carbonate and are enclosedina clayey or carbonate matrix. They suggest that the intraclast beds are characteristic of the inner Apalachicola Embayment and the Gulf Trough area, and are a local occurrence, not correlatable throughout the area. Lithologic variationinthe Torreya occurs both laterally and vertically. The lateral variations include1)more carbonateinthe Apalachicola Embayment-Gulf Trough area and2)the carbonates become dolomitic eastward and northwestward (Huddlestun and Hunter, 1982). Vertical variations recognized within the Torreya Formation include in ascending order1)a basal carbonate-rich zone;2)a siliciclastic (quartz sand) sequence that often contains phosphate grains;3)a clay-rich facies which contains the commercial fullers earth beds (this is the Dogtown Member);4)a calcareous facies of sandy limestone or calcareous quartz sands (Sopchoppy Member?); and5)uppermost beds of noncalcareous clays and quartz sand (Huddlestun and Hunter, 1982). SubjacentandSuprajacent Units The Torreya Formationisunderlain by carbonates that have been referred toasthe Chattahoochee Formation and/orSt.Marks Formation. Huddlestun and Hunter (1982) refer to these sediments as Chat tahoochee. Other investigators, suchasHendry and Sproul (1966) and Yon (1966), placed the sedimentsinthe St. Marks. The contact between these units appears gradationalinportions of the Gulf Trough Apalachicola Embayment area butisdisconformableinother areas. Throughout much of its extent, the Torreya Formationisdisconformably overlain by the Citronelle and Miccosukee formations. The Citronelle Formation occursinthe western portion of the area,inparts of Liberty and Gadsden Counties, and grades eastward into the Miccosukee Formation. Near Alum Bluff (W-6901),onthe Apalachicola River, the Torreyaisoverlain disconformably by the Chipola Formation (Banks and Hunter, 1973; Huddlestun and Hunter, 1982). Further south,inWakulla County, erosional outliers of Jackson Bluff Formation disconformably lieonthe Torreya (Banks and Hunter, 1973). Hud dlestun and Hunter (1982) state that elsewhereinthe eastern panhandle the Torreya Formationisoverlain by undifferentiated surficial sands. These relationships are showninFigure62.96

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M Cross section M-M' (see figure 3 for location).300200 M' 8025070150 "1 3010020 5010? "t-10SUWANNEELS ,-50 -20 -40-150 ........-50.... -70-250IMADISON CO. I HAMILTON CO. METERS FEETI , ,, I .EFI'EIlSON co. I MADISON CO.I ,'",.W-6911 WJI-2N-8E-8dll ILEON CO.IJEFFERSON CO.IIEXPLANATION SUWANlEELS SCALEo 5 10 MILES li'iI'o510 15 KILOMETERS HAWTHORN GROUP BOUNDARIESFigure62.-70 -60 70UBERTY CO. I GADSDEN CO. I METERSIW-7458 GADSDEN COILEON CO. W-71BO W-6611 IWLn-2N-1W-2.d WLb-2N-7W-23db I W-7472 60"" 250-250 "200 -10 I' 1/1 -20 #-1004--30CHATTAHOOCHEE I ....FII.'1+\r1J>. I *-'" -40• 0+",0 -50 FEET 300200. 60 50 "j 401003020 "1 I ITORREYA coFII. I II I IST. MARKS FII.--J 10MSL0_

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--.0 'I _ i \ '"-\'1. I --v' I j i i i i ILIMITSOF TORREYAFORMATION ---=k I \ II l .... ,J....."....i:I! 1II\ J' -I n-\lr,J , IIII ' -!---r-----------'-..J..-J I', ,I SCALEo10203040MI.,,',",' iIo1020304050 KM"-W--T--'t __•t/ ,jcf)cv_L.J/'j III II III'I • • I'(r8";>/'> i r')!. i ;,CD co•CORE '-'.' GROUPFigure63.Isopach of the Torreya Formation.

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•CORELIMITS OFo ... TORREYA FORMATION -N' SCALEo10203040MI.Ii',I',"'o1020304050KM . -?\ \ HAMIL TON ''t,."")...,/ ,. I ! II -1'---<-...,-'-,,'1r-----, ,.1 I$UWANNEEi (1= 'IIj. () i.JI.J --'"\ I c . i, TA I '-__ ! 6' '1""'\.,< ,'I"h..\ I .' "'--, ...Ii LAFAYETTlE -\.r"1-( __ .i-r-_--------i;./i ..4 1 _ ..., .. ' ,-'.&.'.,..,)._ LIMITSOF ..... '. . UHAWTHORNGROUPFigure64.Topofthe Torreya Formation.

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Thickness and Areal Extent The Torreya Formation varies considerablyinthickness with a maximum of 227 feet (69 meters)inW-7539, Suber#1,Gadsden County, Florida near the axis of the Apalachicola Embayment (Huddlestun and Hunter, 1982). Characteristically, through the eastern panhandle, the thickness varies from 50 feet(15meters)to100 feet(30meters) (HuddlestunandHunter, 1982) (Figure63).The Torreya Formation underlies much of the eastern panhandle as showninFigures 64 and65.It oc cursinparts of Madison, Jefferson, Leon, Wakulla, Liberty and Gadsden Counties. The Torreya extends northward into south Georgia (Huddlestun and Hunter, 1982), but its full extentisnot known. Elevation of the upper surface of the Torreya ranges from less than50feet to greater than 200 feet above MSL (Figure64).Age and Correlation Hunter and Huddlestun (1982), Huddlestun and Hunter (1982) and Huddlestun(inpress) suggest that the Torreya Formationismiddle Early Miocene (early to middle Burdigalian)inage (Figure19).The age determinationisbased-on correlation with the Marks Head Formation by molluskan faunal zones and the occurrence of two vertebrate faunas (Huddlestun,inpress). The Torreya Formation correlates with the Marks Head Formation of northeast Florida and southeast Georgia.Italso correlates with the upper part of the Arcadia Formation of southern Florida (Figure19).Northward into North Carolina the Torreya equates with the lower Pungo River Formation basedonrelative ages. Discussion Itisobvious from this discussion that future investigations,asmore data become available, may allow the Torreya Formation of the Hawthorn Group tobefurther subdivided or revised. DOGTOWN MEMBER OF THE TORREYA FORMATION Definition and Type Locality The Dogtown Member of the Torreya Formation was suggested by Huddlestun and Hunter (1982) for the clay-rich intervalinthe upper Torreyainparts of Liberty, Gadsden and Leon Counties, Florida, and Decatur County, Georgia. Commercial fuller's earth deposits occur within the Dogtown Member. The type locality of the Dogtown MemberistheLaCamelia Mine of Engelhard Corp., locatedinSec tion15,Township 3 North, Range 3 West, Gadsden County, Florida. The Owenby#1core (W-7472) locatedinSE V4, Section4,Township 2 North, Range 3 Westissuggested hereasa reference section (Figure 60). Lithology The Dogtown Member,asdescribed by Huddlestun and Hunter (1982), and Huddlestun(inpress) con sists largely of clay. The clays are often quartz sandy, silty and occasionally dolomitic (Weaver and Beck, 1977). The commercial clay beds are quite pure clay but these do not make up the entire unit. Indurationisgenerally moderate. The color of the unweathered, freshly exposed sediment varies from very light gray(N8)to pale greenish-yellowish(10Y 8/2) and light bluish-gray(5B 7/1). Beddinginthe clays ranges from thinly bedded (laminated) and somewhat fissile to massive, blocky, poorly bedded units. Where the clayisshaley, thereisoften silt or fine sand along bedding planes (Huddlestun and Hunter, 1982). The clay beds often contain clay intraclasts and show desiccation cracks (Weaver and Beck, 1977). 100

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Associated with the clay beds are sand and carbonate beds which often separate the clay zone into two beds. The sands are very fine to fine grained, variably clayey, dolomitic or calcareous and poorly to moderately indurated. Colors range from light gray(N7)to yellowish-gray(5Y 7/2). The carbonate beds are clayey, sandy, dolostones to limestones with varying percentagesofphosphate. Induration varies from poor to good. Colors range from white(N9)to light olive-gray(5Y 6/1). Mollusk molds are common in this unit. Theclay minerals associated with the Dogtown Member are predominantly palygorskite and smectite with minor but variable percentages of illite and sepiolite (Weaver and Beck, 1977). The relative percen tages of individual clay minerals vary from bed to bedinthe section. Lithologically, the Dogtown Member grades vertically both upward and downward into undifferentiated Torreya Formation. Subjacent and Suprajacent Units At this time, utilizing limited core and outcrop data, itisdifficult to accurately determine the relation ship of the Dogtown Member to the Sopchoppy Member.Itappears that, although the Dogtownisnot known to directly overlie the Sopchoppy Memberinany core or outcrop, the Dogtown Memberisyounger than the Sopchoppy and could possiblybefoundina suprajacent position to it. The Dogtown Member is unconformably overlain by the Citronelle and/or the Miccosukee Formations where the contact has been observed. Thickness and Areal Extent The thickness ofthe Dogtown varies from a maximum recognized thickness of 40.5 feet(12meters) W-7539 (Suber#1)to a minimum of 15.5 feet (4.7 meters) (Huddlestun,inpress). The Dogtown Member occurs in northern Liberty, northern Gadsden, and northern Leon CountiesinFlorida andinsouthern Decatur and Grady Counties, Georgia. Its limits in Georgia have not been ac curately defined (Huddlestun,inpress). Age As discussed under the Torreya Formation, the Dogtown is middle Early Miocene (early to middle Bur digalian) in age.Itis includedinthe Caroliaf10ridanaZone of Hunter and Huddlestun (1982). Weaver and Beck (1977) also suggestedanEarly Miocene age for the fuller's earth beds (Dogtown Member). Discussion The Dogtown Member of the Torreya Formation contains economically important fuller's earth clay deposits. Although its areal extent has not been accurately defined, it appears tobemappableina limited area.Asis the case with the Torreya Formation in general, more core data are needed to further define the Dogtown Member. SOPCHOPPY MEMBER OFTHETORREYA FORMATION Definition and type Locality Huddlestun and Hunter (1982) suggested using the "Sopchoppy limestone" of Dall and Harris (1892)asa member ofthe Torreya Formation. The type locality of the Sopchoppy Member isanexposure of fossiliferous sandy Iimstone under a bridge over Mill Creek in the center of Section34,Township 4 South, 3 West, northwest of Sopchoppy, Wakulla County, Florida.Nocore dataispresently available in this area.101

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Lithology Dall and Harris (1892) refered to the Sopchoppy Limestoneasa very soft limestone with numerous im prints of fossils.Inreferring the Sopchoppy to the Alum Bluff Formation, Matson and Clapp (1909) did not provide descriptions ofthe limestone. Huddlestun (in press) recognizes two lithofaciesinthe Sopchoppy Member:1)a sandy, fossiliferous limestone, and2)a tough, phosphatic, dolomitic sand. \ The limestone is moldic, fossiliferous, variably sandy and phosphatic and is coarsely bioclastic with a calcareous mud matrix (Huddlestun,inpress). The sand facies is a fine grained, well sorted, dolomitic, phosphatic quartz sand. This sand is often irregularly distributed through the limestone unit. Clays are presentasinterstitial material and include palygorskite and smectite (Weaver and Beck, 1977). Subjacent and Suprajacent Units Thickness and Areal Extent The only recognized occurrence of the Sopchoppy Member is near the Sopchoppy River in Wakulla County, Florida. Its relationship with the overlying and underlying units, and its thickness and extent are not clearly understood (Huddlestun and Hunter, 1982). However, it appears to grade vertically downward into undifferentiated Torreya Formation.Inthe type area, the Sopchoppy Member is overlain by undif ferentiated sands (Pleistocene?). Age and Correlation The age of the Sopchoppy Member is basedonmacrofaunal similarities with the main portion ofthe Torreya Formation (Huddlestun,inpress). This suggestsanEarly Miocene age. Correlations of the Sopchoppy with other units are not well understood at this time. Huddlestun (in press) suggests that it may correlate with the phosphatic sands below the Dogtown Member north of the Sopchoppy Member's type area. Discussion Very littleisknown about the Sopchoppy Member of the Torreya Formation outside of its type area. No core data are presently available to study the extent of the unit. Further study is required to better under stand the Sopchoppy.HAWTHORN GROUP MINERALOGYThe sediments here included in theHawthorn Group have been of interest for many years due in part to their unusual mineralogy and complex lithostratigraphy. While the Hawthorn contains a variety of com mon minerals, it also has a number of unusualminerals which developed under special conditions. The genesis of these minerals was related to oceanic chemistry, depositional environments and the effects of post-depositional, diagenetic changes. The unusualminerals present in the Hawthorn Group include francolite, palygorskite, sepiolite, and dolomite. The phosphates have been the focus of much research due to their economic importance. Development ofthe phosphate minerals and phosphorite deposits requiredanunusual set of cir cumstances that also resulted in the formation and deposition of palygorskite and sepiolite. Related to these conditions is the formation of dolomite in the Hawthorn sediments. Each of these minerals willbediscussed separately to contribute toanunderstanding of the conditions necessary for their formation. The separate discussions show that similar environmental conditions were responsible for the unusual mineral suite commonly recognized in theHawthorn sediments. 102

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PHOSPHATE Occurrenceinthe Hawthorn Group is in much of the Hawthorn Group, constituting one of the primary lithologic factors for assigning sediments to the group.Inpeninsular Florida, phosphate is virtually ubiquitous throughout the Hawthorn sediments. Nonphosphatic lithologies are not common but do occur, usuallyinthe more pure clays and carbonates orasrare, clean, quartz sand beds. However,inthe eastern Florida panhan dle on the northwest flank of the Ocala Platform (Figures4,63and64),non-phosphatic sedimentsinthe Hawthorn are quite common.Inthe Hawthorn sediments statewide, phospate typically occursassand-sized grains disseminated throughout the sediment. Pebble-sized phosphate grains are also common but generally are limited (i.e. Bone Valley Member) to localized areas or very thin zones. The concentration of phosphate within the Hawthorn sediments ranges from zero to greater than50percent. Characteristically, however, the average concentration in the Hawthorn sediments is between 2 and10percent. Economically important occurrences of phosphate are knowninseveral areas of the state (Figure65).The most productive deposit is found in the Central Florida Phosphate DistrictinPolk, Hillsborough, Manatee and Hardee Counties.Inthis district, the phosphateisproduced predominantly from the Bone Valley Member ofthe Peace River Formation with some production occurring from the undifferentiated Peace River Formation. Pebble phosphorites predominateinthe Bone Valley Member while sand-sized phosphorites dominate the undifferentiated section. Southward into the southern extension of the Cen tral Florida Phosphate District (Hardee, Manatee, Sarasota and DeSoto Counties), the production comes from the undifferentiated Peace River Formation. The southeast Florida phosphate deposit, located primarilyinBrevard and Osceola Counties (Figure65)contains phosphoriteinthe undifferentiated Peace River Formation. This deposit occursonthe flank ofthe Brevard Platform (Figure4).There has beennomininginthe southeastFlorida deposit. Phosphate productioninnorth Florida is limited toanareaineastern Hamilton County. The Northern Florida deposit extends eastward and southwardasshowninFigure65.Productioninnorth Floridaisfrom the Statenville Formation. This depositislocatedonthe northeast flank of the Ocala Platform (Figures 4 and 65). The northern Florida depositisassociated with the lower grade south Georgia deposit (Figure 65). Further east in north Floridaisthe northeast Florida deposit (Riggs, 1984) (Figure65).This deposit is unique in that it is much deeperinthe section, occurring more than 200 feet(61meters) below land sur face. These sediments are tentatively placedinthe Marks Head Formation of the Hawthorn Group based on very limited core data.Ifthe formational assignmentiscorrect, the phosphorites.mayrepresent the oldest Miocene phosphorite depositinthe southeastern United States. Currently, experimental borehole mining techniques are being used to test the feasibility of mining this deposit (Scott, L.E., 1981). One other important phosphate deposit, the Hard Rock Phosphate District, occursinnorthern Florida.Itis not currently considered part of the Hawthorn Group although weathering of the Hawthorn Group sediments was probably responsible for the formation of the hard rock phosphates. The Hard Rock District lies west ofthe present erosional scarp ofthe Hawthorn Group and occursonthe eastern flank of the Ocala Platform (Figures 4 and65).Currently the hard rock deposits are not being mined. Phosphate Genesis The abundance of phosphateinthe Hawthorn sedimentsisanomalous when compared to theremainder of the Tertiary sediments. Many questions arise concerning the genesis of phosphateinFlorida including:1)What was the source of the phosphate?;2)How was it deposited?;3)What role did topographic or structural features play? Research worldwide is producing a greater insight into the pro cesses involved in the formation of marine phosphates. However, the problemisstill far from being thoroughly understood. 103

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EXPLANATION lIiIill NORTHERN NORTHEAST [Z] HARDROCK g SOUTHEAST CENTRAL I22!J SOUTHERNCOLLIER... / ...... .>..... ............ ,., .'E! I !"-S-o _ __ \LEEIHENDRY :PALMBEACHl__,I ,I IjI -r-----\ BROWARD 1-I----i i I I \ i50MILES f 80KILOMETERS25ISCALEo oIFigure 65. Location of .phosphate deposits in Florida.104

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The phosphorite deposits in the southeastern United States are enigmatic when compared to other oc curences of phosphoritesinthe world (Riggs, 1984). Most marine phosphorite deposits occuronwestern continental shelves where upwellingisassociated with trade wind belts, or along east-west seaways by equatorial upwelling. The southeastern United States deposits do not fall into these categories. More recent research indicates, however, that similar mechanisms (upwelling and cur rents) maybeinvolved in the phosphorite formationinthe southeast(Riggs, 1984). Kazakov (1937) originally suggested that marine phosphorites were precipitated inorganically from upwelling, cold, phosphorus-rich water. The inorganic mechanism for phosphorite precipitation has been suggested tobeunlikely by more recent research (Bentor, 1980). Upwelling, however, remainsanimportant mechanisminthe formation of these deposits. Upwelling currents provide the nutrients necessary for the production of large amounts of organic matter (Sheldon, 1980). Subsequent concentration of the phosphorus may result from the action of bacteria at or above the sediment-water interface (Riggs, 1979b), orininterstitial pores withinth.esediment (Burnett, 1977). An oceanographic event of global extent was responsible for the formation ofthe Miocene phosphorite deposits in the southeastern United States (Riggs, 1984). The deposition of the phosphorites and associated phosphatic sediments was controlled by the regional structural framework and the effects of the impinging upwelling currents (Riggs, 1984). Figure66shows the structural features of the southeastern coastal plain from North Carolina to Florida that probably controlled phosphate deposition. Only Florida's structural framework willbediscussed here. The dominant positive structural featuresinthe peninsula are the Ocala Platform and the Sanford High including the Sanford High's northern and southern extensions, theSt.Johns Platform and the Brevard Platform, respectively (Figure66).The negative features include the Jacksonville Basin and the Osceola Low. These structures are all consideredaspre-Miocene features (Vernon, 1951). Riggs (1979b) con sidered the structural framework tobeone of the most important variablesinthe development of the phosphogenic system. He outlined three criteria for the development of the phosphogenic system. First is the appropriate regional setting which defines the limits of the system. Second, shoaling environments associated with structural or topographic highs and adjacent basins must occur. Third, the highs must have the appropriate topography to produce the phosphorite and accumulate itinassociated topographic lows. Florida's regional structural setting meets these criteria. According to Riggs (1984), optimum production of phosphate occurredonthe flanks of the highsinFlorida while significantly less formed elsewhereinthe marine environment. Gulf Stream-associated upwellings resulting from bathymetric (topographic) influences impingedonthe flanks ofthe structures providing the necessary constant supply of phosphorus required for phosphate deposition. Miller (1982) suggested that the upwellings associated with north Florida phosphate deposition were related to a south-flowing cold-water current that Gibson (1967) identified during a faunal study ofthe phosphorites in North Carolina. Hoenstine (1984) also recognized a cold water diatom florainportions of the Hawthorn Group inaninvestigation of the groupinnortheast Florida. Riggs (1979b) believed that phosphate deposition qccurredasa biochemically precipitated mudinthe shallow water environmentsonthe positive structural features. The microcrystalline phosphate mud (microsphorite) is not commonly preserved; however, remnants ofthe microsphorite beds maybepre sent in the Hawthorn Group sediments. Many of the zones suggested tobemicrosphorite appear tobe1)phosphatized carbonate hard grounds;2)phosphatic subaerial crusts; and3)secondary deposits of phosphate by groundwater. The microsphorite beds were reworked into pelletal and intraclastic grains that were deposited in topographic lowsonthe flanks of the positive features. Riggs (1979a) suggested that many ofthe pelletal grains originated from the ingestion of phosphate mud by organisms and the ex cretion of phosphatic fecal pellets. Miller (1982) suggests that gentle currents were responsible for the formation ofthe pelletal phosphorites in north Florida. Intraclastic and lithoclastic fragments could have resulted from the erosion and reworking of semilithified to lithified microsphorite beds and possibly phosphatized carbonate beds. Burnett (1977) suggested that the phosphorites forming off the coast of Peru and Chile are inorganical ly precipipated in the pore waters of anoxic sediments. Phosphorus-rich waters upwell onto the shelf pro105

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Structural features of the southeast United States (after Riggs, 1979). 10650a-N50I I , DELA WARE'/ EMBAYMENT / \""'I""I,"""""Figure 66.CENTRAL FLA. PLATFORM tru s.E. GEORGIA EMBAYMENT,\ " \\I\I,I \ \JI \JII, ,, ( ",........"'::::::.:_-:-===:.:'::'=-::'

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viding. the nutrients for high biologic productivity resultinginanincreased accumulation of organic bottom sediments. Burnett etal.(1980) indicated that the highest concentrationof phosphateInthe sediments occurredinthe zone of oxygen minimum. The phosphate is provided to the pore waters by the decomposition of the incorporated organic matter. The precipitation of phosphate in the pores results in the growth of nodules and, presumably, various sizes of pellets in the sediment. The resultant phosphate grains range from silt-sized to pebble-sized with the size range becoming coarser and identifiable intraclastic fragments becoming more common toward the phosphate source area. Riggs (1979b) has noted this occurrenceonthe flanks of the Ocala Platform. Away from the areas of primary phosphate deposition, the percentage of phosphate present in the Hawthorn sediments generally decreasesasdoes the ratio of pebble to sand-sized phosphate. Riggs (1979b) suggested that, away from the highs or positive structural features, fine sand-sized and silt-sized phosphates formed from a loose colloidal suspension of orthochemical phosphate occurring above the bottom. As the aggregates formed they trapped other sedimentsinthem including silts, dolomite rhombs, organic debris and clays. The resulting aggregates were subsequently incorporatedinthe bottom sediments.Itis the author's opinion that the vast majority of phosphate grainsinFlorida have been transported, or at least reworked, from their original depositional area. Throughout the Hawthorn Group, the occurrence of phosphate appears related to the occurrence of quartz sand.Itisuncommon for the percentage of phosphate to exceed the percentage of quartz sandina clay or carbonate sediment except in the case of a phosphorite suchasthose currently being mined. The lack of phosphate grainsinrelatively pure car bonates (lacking quartz sand or other siliciclastic particles)inthe Hawthorn is very common even though these units maybeoverlain and/or underlain by quartz sandy carbonates containing phosphate. The same relationship applies to relatively pure clays and sandy clays. These relationships suggest that, although phosphateinFloridaisa precipitate, it most often becomes a clastic particle which is subse quently deposited at varying distances from the source areas. Phosphorite deposits result when suffi cient quantities of phosphate are available and wave and/or current energies are sufficient to winnow and concentrate the phosphate grains. Sedimentary features, including graded bedding and cross bedding, are indicative of the higher energy conditions present during phosphorite deposition. Grain size and shape ofthe phosphate particles may alsobeindicative of reworked materials, since the grains vary from rounded and sand-sized to subangular or rounded and pebble-sized. Post-Depositional Modification Post-depositional weathering and reworking of the Hawthorn sediments have been relatively widespread. The best documented effects are those that affect the sediments of the major phosphorite deposits. Leaching, redeposition and reworking have all played a roleinthe modification of the original phosphatic material in the Hawthorn sediments. Throughout much of northern and central Florida, part of the Hawthorn Group (Figure5)has been sub jected to the effects of groundwater migration. Leaching ofthe soluble phosphates has been one of the major effects of this process, resultinginthe total loss of phosphateinextreme cases. The post depositional development of the "leached zone"inthe Central Florida phosphorite deposits has been discussed by a number of authors including Altschuler and Young (1960), Altschuler et al. (1964), Riggs (1979a) and Hall (1983). Supergene weathering ofthe phosphorite tends to upgrade or increase the phosphate content by removing the included carbonates and organic material. The deveopment of the aluminum phosphate zone is the direct result of weathering of the carbonate fluorapatites. Riggs (1979a) recognized seven zones ranging from unaltered to completely leached. These zones were gradational andallzones may befully developedinanyonesection. The typical zonation trends from: unaltered carbonate fluorapatite to mixed calcium-aluminum phosphates to aluminum phosphates and, finally, to phosphate free.,Asthe phosphate grains are leached the color changes from shiny black and dark brown to earthy-textured light colors and white. This same process of supergene weathering alters and removes claysaswell. The net 107

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resultisthe development of a clean quartz sand which constitutes part of the overburden (Altschuler and Young, 1960). Elsewhereinthe state, where the upper Hawthorn sediments do not constituteaneconomic phosphorite deposit, weathering follows a similar sequence but without the extensive development of the aluminum phosphate zone.Asthe phosphate and carbonate are removed, a vesicular sandstone develops. Hard Rock Phosphate Deposits Hard rock phosphate deposits are found scattered along the eastern flank of the Ocala Platform west of the present limits of the Hawthorn Group (Figure 65). Cooke (1945), Vernon (1951) and Puri and Ver non (1964) considered these depositsaspart of the Alachua Formation. The phosphate occurs as "plates or large boulder like masses" (Cooke, 1945) restingonthe surface of the underlying limestones of the Ocala Group or Suwannee Limestone. Cooke (1945) also reported that the phosphate has replaced portions of this underlying carbonate. These deposits were mined from 1890 until the mid-1960s, when the last operation closed. The origin of the hard rock phosphateisintimately related to the development or occurrence of a phosphorite depositinthe Hawthorn Group. Sellards (1913) believed that the phosphate was derived from overlying phosphatic sediments by dissolution and was subsequently reprecipitated to form the hard rock deposits. Cooke (1945) also supported this theory. Sellards (1913) discussed theories proposedby other authors, many of whom felt the source of the phosphate tobeguano. Vernon (1951) believed guano to be the source of the phosphate, citing the fact thathedid not believe the phosphatic materials of the Hawthorn Group were deposited that highonthe Ocala Platform. The Hawthorn Group was postulated to have extended over much of the Ocala Platform (Scott, T.M., 1981) basedonthe occurrence of chertsinthe upper part of the Ocala Group and Suwannee Limestone. The occurrence of phosphatic sands associated with the hard rock phosphates also suggests the former presence of the Hawthorn Groupinthe Hard Rock Phosphate District. Basedonthese assumptions, the present author agrees with Sellards (1913), Cooke (1945) and Up church and Lawrence (1984) that phosphates presentinthe Hawthorn Grouponthe east flank of the Ocala Platform were probably the source of the phosphorus which developed the hard rock phosphate deposits.Itissuggested here that the original Hawthorn phosphorite deposit formedinthe manner described for other Florida deposits.Itthen underwent extensive leaching, erosion and reworking to develop the hard rock phosphates and the residual Hawthorn sediments previously placedinthe Alachua Formation.Itisinteresting to note here that recent researchonthe erosional scarp of the Hawthorn GroupinColumbia County indicates that groundwaterinthe Floridan aquifer system under the Hawthorn Group near the scarpissupersaturated with respect to P04 (Upchurch and Lawrence, 1984). Upchurch and Lawrence believe that the development of karst features penetrating the Hawthorn sediments allows the phosphorus-bearing watertoenter the aqUifer system. They also feel that this mechanism may have allowed the development of the hard rock deposits and may explain the discon tinuous nature of their occurrence. PALYGORSKITEAND SEPIOLITE Palygorskite and sepiolite are not generally considered common clay minerals. Their sedimentary origin is not well known, although itisgenerally assumed that restricted conditions are often required for their formation. Their occurrenceinthe Hawthorn Group of the Florida, Georgia and South Carolina coastal plain, where they often are the dominant clay mineral,iswell documented (Reynolds, 1962; Heron and Johnson, 1966; Weaver and Beck, 1977; Reik, 1982; Hetrick and Friddell,.1984). The occur rence of these claysinassociation with dolosilts and phosphate indicates unusual depositional en vironments for tl:1e Miocene sedimentsinthe southeastern United States. 108

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Palygorskite and sepiolite are magnesium silicate clay minerals belonging to the2:1 layer group and possessing an amphibole-like chain or fibrous structure. While the two minerals differ slightlyinstruc ture, .they have similar chemical formulas. The major differenceisthat palygorskite contains some aluminum substituted for magnesium while sepiolite does not (Hathaway, 1979). For a complete discus sion of the mineralogy and chemistry of palygorskite, see Gremillion (1965), Grim (1968), Weaver and Beck (1977), Ogden (1978), and Hathaway (1979). Palygorskite and sepiolite occur throughout the Hawthorn Group mixed with variable proportionsofsmectite, illite, chlorite and some kaolinite. Hetrick and Friddell's (1984) study of the Hawthorn Group clay mineralogy indicated a highly variable clay-mineral composition that is not obviously related to stratigraphic position. However, statistical evaluation of this data indicated that the formations of the Hawthorn Group are significantly different from each otherinsmectite, palygorskite and sepiolite content (Hetrick and Friddell, 1984). They indicate that palygorskite and sepiolite are the dominant clay minerals in the Marks Head Formation of northern Florida and Georgia, while smectite dominates in the Coosawhatchie and Penney Farms (Parachucla) formations. Palygorskite and sepiolite are often closely associated with dolomitic sediments (Reynolds, 1962; Weaver and Beck, 1977; Reik, 1982). The dolomiteinthese sedimentsiscommonly the limpid dolosilt discussed in the dolomite section of this paper. The modes of formation and depositional environments of palygorskite and sepiolite have been studied by a number of authors (McClellan, 1964; Gremillion, 1965; Millot, 1970; Beck, 1977; Ogden, 1978; Strom and Upchurch, 1985) resultingina number of depositional models. The formation of these clays has been postulated to have resulted from:1)weathering (Kerr, 1937),2)alteration of volcanic ash (Gremillion, 1965),3)transformation from clay mineral precursor (Weaver and Beck 1977, Ogden, 1978), and4)neoformation or precipitation from sea water (Millot, 1970). Currently, the transfor mation of a clay mineral precursor suchasmontmorillionite by the addition of silicon and magnesiumisthe accepted mode of formation for palygorskite and sepiolite.Itshouldbenoted here that a minor amount of palygorskite probably precipitated directly from solution (Weaver and Beck, 1982). The development of palygorskite and sepiolitewasthought to occur primarily in restricted, brackish water (schizohaline) lagoons and tidal flats by Weaver and Beck (1977, 1982) and Ogden (1978). Weaver and Beck (1977) suggest that sepiolite formed under more fresh water conditionsinthis environment. The transformation of the precursor clay minerals to palygorskite and sepiolite requires a relatively high pH (8-9)assuggested by Weaver and Beck (1977), and a supply of silicon and magnesium. ThepHin creases in response to evaporationinthe restricted environments, and, perhaps seasonally, reaches the required highpHlevels.AsthepHlevels increase, the solubility of biogenic opal (foundindiatoms and siliceous sponge spicules) increases, supplying the silicon required. Magnesiumisconcentrated due to the evaporation of the brackish waters. Given these conditions, and a supply of a suitable precursor clay mineral suchassmectite, Weaver and Beck (1977) and Ogden (1978) postulate the development of palygorskite and sepiolite clays. Weaver and Beck (1977) also discuss the development of limpid dolomiteinassociation with palygor skite genesis. They suggest that dolomite forms both prior to palygorskite formation and after it. This may also indicate a seasonality to the critical nature of the depositional environments. Restricted, alkaline lagoons probably occurred over a wide area during Hawthorn deposition. The flanks ofthe Ocala Platform possibly provided ideal environments for palygorskite formationasdid parts ofthe St. Johns and Brevard Platforms and the Sanford High. The reworking of these palygorskite-rich deposits during transgression could provide vast amounts of clay that couldbeincorporatedinthemore normal marine portions of the Hawthorn Group downdip. The association of dolomiteinboth the environ ment ofthe reworked palygorskite indicates the possibility that the silt-sized dolomites were transported into depositional basins. Upchurch et al. (1982) and Strom and Upchurch (1983) discuss the development of palygorskite and opaline chert in peri marine, alkaline-lake environments. Their discussion of the palygorskite and opal forming environments suggests a somewhat more restricted environment than that discussed by other authors. It seems to this author that the more restricted environment of Upchurch, etal.(1982) may have occurred in conjunction with less restricted, palygorskite-producing, brackish water (alkaline) lagoons. However, the ephemeral lakes of these authors were less common and of smaller areal extent than the 109

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lagoonal environments. The net result is the large scale production of palygorskite with a more limited creation of opaline sediments and subsequent reworking ofthe palygorskite into the depositional basins. DOLOMITE Dolomite, like phosphate, is a rather enigmatic mineralinnature. A number of different types of dolomite are known to exist, suggesting that there is not a single, unique process by which dolomite forms or dolomitization occurs. As a result, there isnounique model to explain dolomite genesis (Zenger and Dunham, 1980).Itis important to attempt to understand the occurrence of dolomiteinthe Hawthorn Group, due to the association of dolomite with phosphate and palygorskite. The knowledge resulting from attempts to determine the origin of one mineral may shed light on the origin ofthe other minerals. Carbonate rocks dominate the Hawthorn sediments in a large portion of southern Florida. Northward, the carbonate content decreasesasthe terrigenous component increases. Even in the northern area, however, carbonate remains an important constituent, bothasa primary lithology andasanaccessory mineral. Dolomiteisthe most common carbonate componentinthe Hawthorn Group throughout much of the state. Only in portions of southern Florida does dolomite assume a subordinate position with respect to limestone in the group. Dolomite occursinseveral different modes; the predominant types are dolomitizedlimestones or secondary dolomites and dolosilts.Italso is presentasanaccessory mineral in clays, clayey sands, limestones and many phosphate grains. Secondary dolomites are presentinthe carbonates of the Hawthorn Group throughout the state. These dolomites are characterized by a coarse, anhedral dolomite replacingtheoriginal limestone. Most original depositional features are destroyed by the dolomitization, although ghost structures of pellets and fossils have been observed in thin section. Molds of mollusk shells are common and are often lined with later-phase dolomite and/or sparry calcite druses.Itappears that the original carbonate rock was a wackestone to a mudstone that contained a variable siliciclastic component, including phosphate. This type of dolomite is most commoninthe basal Hawthorn Group Penney Farms Formation in northern Florida. The dolomites of the basal Hawthorn Groupinmuch of northern and part of southern Florida lie directlyonundolomitized Eocene (Oligoceneina few cases) limestones. The development ofthe dolomite was restricted to the Miocene carbonates by some mechanism. The occurrence of a recrystallized low permeability zoneinthe upper few feet of the undolqmitized limestones below the pre-Hawthorn uncon formity may have provided enough of a permeability barrier to groundwater movement to limit dolomitiza tion to the Miocene carbonates. Further study is required to determine if the dolomitization is an early or later diagenetic event. Dolosilt is a term applied to unconsolidated, silt-sized, euhedral, rhombic, often limpid crystals of dolomite. This type of dolomite has also been referred toasmicrosucrosic dolomite when more lithified (Prasad, 1983). Dolosilts are extremely commoninthe sediments of the Hawthorn Group ranging from a minor accessory mineral to a nearly pure dolosilt sediment. The dolosilts range from fine silt-sized (10 microns) to fine sand-sized (greater than62microns). The individual crystals show sharp crystal faces and often have hollow centers. Lithologically, dolosilts are present in a wide variety of sediment types. Clays and clayey sands ofthe Hawthorn Group very commonly contain dolosilts in widely varying amounts. A complete gradation be tween the clays and dolosilt-rich sediments often occurs, causing some problems in identifying the corn-' ponents ofthe sediment, since minor amounts of clayina fine-grained dolosilt may present the ap pearance of a siliciclastic, silty clay lithology. The carbonate portions of the Hawthorn Group contain variable percentages of dolosilt. Beds vary lithologically from nearly pure dolosilt and dolostone to limestones with minor percentages of dolosilt floating in a carbonate mud matrix. Prasad (1983) has identified two types of dolomite in the Hawthorn of southern Florida. First, he recognized a dolomite fraction of microsucrosic, silt-sized rhombs (dolosilts) that show no replacement textures. Second, Prasad identified fine grained dolomite associated with dolosilts that exhibited a replacement texture. The dolomite replaced metastable fossil fragments often 110

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with a syntaxial dolomite rim (Prasad, 1983). Prasad also noted that there isaninverse relationshipbetween micrite and dolosilt in the carbonate beds suggesting a replacement of the micrite by dolosilt.Innorthern parts of central Florida, dolosilts are significantly more abundant thaninsouth Florida. This suggests that dolomite genesis (and perhaps dolomitization) was more intense or completeinthese areas than in the southern area discussed by Prasad (1983).Itis also interesting to note that the northern and central Florida dolomites are associated with greater amounts of palygorskite and,ingeneral, phosphate. Silt-sized dolomite rhombs and occasionally clastsofdolomite are often incorporatedinphosphate grains. Riggs (1979a) states that itisnot unusual ifasmuchas90percent of the phosphate grainsina deposit contain inclusions of dolomite. This associationisimportant since the two mineral phasesdonot form in the same geochemical environment. The magnesium concentrationisa controlling.factorinthe development of phosphate in that magnesium inhibits the formation of phosphateinnormal seawater (Bentor, 1980). Riggs (1979a) recognizes evidence of transportation of the dolomite rhombs. -He sug gests that the dolomite and phosphate developedinadjacent areas and that the dolomite was transported then mixed with the phosphate muds. The origin of dolomite is a confusing and enigmatic question. Even though it is a common rock-forming mineral andanaccessory mineral, the various modes of formation are not well understood. With respect to the dolomites in the Hawthorn Group, there appears to have been several types of dolomite develop ment. These types include replacement of limestones (secondary dolomite), dolomitization of metastable fossil material, and dissolution of aragonite and high-Mg calcite mud with co-precipitation of dolomite (dolosilt or microsucrosic dolomite). The replacement of limestone by dolomiteisvirtually completeinthe carbonates of the Hawthorn Group's Penney Farms and Marks Head Formationsinnorthern Florida. Dolomitizationonthis broad scale is suggestive of a mixing zone mode of formation for the dolomites.Asdescribed by Badiozamani (1973), dolomite maybeformed by the replacement of limestone by groundwaters of mixed fresh and marine origins.Itis suggested here that these dolomitesinthe Hawthorn Group resulted from the migra tion of mixed-water zones through the carbonate sedimentsassea levels fluctuated during the Late Miocene. The timing of this eventispurely speculative basedonproposed sea level curves (Vail and Mit chum, 1979). Further researchisneededtofully understand the timing and mode of formation of the replacement dolomites. Dolosilts, or microsucrosic dolomites, may also formfrom the effects of mixing-zorie watersonfine grained carbonate sediments and fossil debris. Prasad (1983, 1985) studied the microsucrosic dolomites ofthe Arcadia and Peace River Formationsinsouthern Florida.Heconcluded that dolomitizationofthe metastable fossil material (echinoderm plates) occurred prior to freshwater diagenesis. The dolosilts ap pear to have precipitated from dilute solutioninthe interstital pores. The source for the calcium car bonate to form the dolomiteinthe mixed watersisinferred to have come from dissolution of fine grained lime mud (Prasad, 1983, 1985). The fine grained, limpid, euhedral, rhombic nature of the dolosilts is con sidered indicative of growth from dilute solutionsinmixed waters (Folk and Land, 1975). Basedonthe belief that these dolomite crystals formina brackish water environment, Weaver and Beck (1977) believedthat the dolosilts formedinthe same environmentasthe palygorskites. Very small(1micron), well-formed, rhombic dolomite crystals have been recognized cementing aragonitic mudsonportions of Andros Island (Gebelein, etal.1980). Growth of these dolomite crystals concurrently with dissolution of the aragonite resultsinlimpid, inclusion-free dolosilts. These sediments may form in two ways, both of which are related to mixing of fresh and marine water. First, they may form inanintertidal or tidal flat environmentasrecognized by Gebelein, et al. (1980). Secondly, they can develop in migrating mixed water zonesinburied sediments (very shallow burial in this case) due to sea level fluctuatiolls (Prasad, 1983, 1985). Both origins seem toberepresentedinthe dolosilts of the Hawthorn Group.GEOLOGIC HISTORYSedimentationinpeninsular Florida throughout the Paleogene was dominated by carbonate deposi-111

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tion. Only minor percentages of siliciclastic materials are presentinthe pre-Miocene sediments. At the beginning of the Neogene, the influx of siliciclastic materials-increased dramatically, flooding the car bonate environments and pushing these environments southward. Carbonate deposition continued perhapsaslate as early Middle Mioceneinparts of south-central Florida to Late Miocene(?)inthe Keys. Within the carbonate units, siliciclastic material occurringasboth accessory minerals and the dominant sediment typeinthin beds generally increased in percentage with decreasing age. Chen (1965) believed that the Gulf Trough (his Suwannee Channel) (Figure4)actedasa natural bar rier to the southward movement of siliciclastic material until near the end of the Eocene. However, a large influx of siliciclastic material is not recognized until Miocene time. The assumed source for the siliciclasticsisthe southern Appalachian Mountains and the Piedmont. The reason for the dramatic in creaseinthe supply of siliciclastics has not been documented. However, itispossibly the result of a renewed upliftinthe southern Appalachiansinthe late Paleogene or early Neogene. The geologic history of the Hawthorn Groupisdirectly related to the Miocene fluctuations of global sea level.Anunderstanding of the global sea levels such as those proposed by Vail and Mitchum (1979) aidindetermining the depositional controls exerted by features suchasthe Sanford High and the Ocala Plat form. Since the proposed sea level curves are thought to be free from local tectonic influence, com parison of these curves to the present position of the Hawthorn Group sediment may shed lightonthe possibilities of tectonic influenceonthe Florida platform. Throughout the Tertiary, the Florida platform has been subjected to numerous fluctuations, transgres sions and regressions of thesea.The effects of these variationsinsea level have been most dramatic from the latest Oligocene through the Pleistocene. Coastal onlap curves published by Vail and Mitchum (1979) reflect these changes along with the apparent relative magnitudes of the fluctuations basedonrelative coastal onlap (Figure67).Incontrast to the Vail and Mitchum (1979) sea level curvesisthe classical idea of fluctuating sea levels expressed by Cooke (1945). According to Cooke (1945), thereisa three-fold subdivision of the Miocene presentinFlorida. Each subdivision was the result of a sea level rise from a previous low stand and a subsequent withdrawal of the sea at the end of each division. The subdivisions were referred to as the Early, Middle and Late Miocene. Cooke (1945) believed that sea level rose to its greatest height during the Middle Miocene. The relationships of the formations of the Hawthorn Group to the proposed sea level are shown in Figure67.The formations of the Hawthorn Groupinthe peninsular area (north and south Florida of Figure1)are predominantly related to the sea level stands of the earliest Miocene through middle Late Miocene.Inthe panhandle, Hawthorn Group depositionisthought to be restricted to the Burdigalian as recognizedinthe Torreya Formation. Correlations of the Hawthorn Group sediments to the Vail and Mitchum (1979) sea level curve indicate the following sequence of events. The earliest marine transgression thatissuggested to have affected the deposition of the Hawthorn Group beganinthe Early Miocene (Aquitanian). At least part of the Pen ney Farms Formation was deposited at this timeaswas the lower portion of the Arcadia Formation (Tam pa and Nocatee Members and undifferentiated Arcadia). Deposition was interrupted when the sea level droppedinmid-Early Miocene (Early Burdigalian).Assea level continued to rise through the Early Miocene, Hawthorn deposition resumed. Although itisnot yet documented, the upper portion of the Pen ney Farms Formation may have been deposited during this period. Much of the upper part of the Arcadia Formation was also deposited during this transgression.Inthe panhandle, the deposition of the Torreya Formation of the Hawthorn Group began during this transgression. However, the documented age for the Torreya FormationisEarly to Middle Burdigalian (Huddlestun,inpress).Assea level roseinLate Burdigalian, the Marks Head Formation, the Torreya Formation and the upper portion of the Arcadia Formation were deposited. Sea level continued the rising trend into the Middle MioceneasMarks Head and Torreya deposition ceased.Inpeninsular Florida the Coosawhatchie was depositedonthe Marks Headinnorthern Florida during the Serravalian.Insouthern Florida, the Arcadia Formation deposition endedinSerravalian and later Miocene depositioninthe panhandle Hawthorn Group has not been recognized. Thisisdue either to non-deposition or erosional removal of these 112

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GLOBAL CHART OF RELATIVE til UNCONGEOCHRONOLOGIC til COASTALONLAPw .. FORMITY UNITS til ...J (VAIL & MITCHUM,1979)WU ZAGE i= 0 z EASTERN...J>a:...Ja:STANDARD I--:>o:i PANHANDLE Uw < 0a:EPOCHS l3iEZ T .. ,.3 "''" ----------------T"'.2;:l 1--22.5-22___________ ----...;:r", ________ AOUITANIAN24T02.2Td25I I I T-,---TT:': 26 W CHATTIAN .. IP210Figure 67. Lithostratigraphic unitsinrelation to proposed sea level fluctuations (after Vail and Mit chum, 1979). 113

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sediments. Post-Serravalian (Tortonian) deposition appears tobelimited to southern Florida and perhaps some of the central east coast area where sediments assigned to the Peace River Formation have been identified. Most Hawthorn sedimentation ended by the end ofthe Tortonian upon the sea level drop of the Messinian. Huddlestun et al. (1982) recognizedaninformal unit oftheHawthorn Group which was depositedinlate Early Pliocene (Tabianian). These beds, referred toasthe Indian River beds (later changed to Wabasso beds by Huddlestun (personal communication 1984)) were deposited during the post-Messinian sea level rise. The unit is recognizable only faunally and its extent in Florida is not presently known. During this time the upper bed ofthe Bone Valley Member of the Peace River Forma tion developedinpart of Polk, Hillsborough, Hardee and Manatee Counties. This bedisthe classic Bone Valley Gravel of the earliest usage. Vail and Mitchum's (1979) sea level curve also lists a number of major and minor unconformities recognized in the seismic sections. Although there are a number of unconformities visually recognizable within the Hawthorn Group (particularlyinnorthern Florida), their correlation with those of Vail and Mit chum (1979)ishighly speculative. The difficultyincorrelating the unconformities may arise from the very poor biostratigraphic record of the Hawthorn Groupinmuch of Florida or from problems associated with the Vail and Mitchum curve. At this time no attemptismade to correlate the minorunconformities.Iffuture biostratigrahic investigations identify more complete, correlatable faunas or a refinement of Vail and Mitchum's sea level curve occurs, the minor unconformities mayberecognized and correlated. The major unconformities relating to the base ofthe Hawthorn Group in peninsular Florida are the pre Hawthorn to post-Ocala unconformity (the Oligocene absent), and the pre-Hawthorn to post-Suwannee unconformity (Latest Oligocene). Fluctuating sea levels caused varying amounts of land area tobeexposed subaerially during the Late Oligocene through Early Pliocene. During the periods of exposure terrestrial vertebrates inhabited the area. The fossil remains found in sinkholes, stream channels and nearshore sediments provide a means of determining the age ofthe enclosing sediments and therefore the age ofthe terrestrial episodes. The series of hypothetical cross sections shown in Figures68to 72 suggest a possible geologic history of the Hawthorn GroupinFlorida. The line of section extends from northern Madison County southeastward to eastern Marion County then south-southeast to Palm Beach County. This series of sec tions takes into account erosion of sediments during low sea levels and the slow downwarping of southern Florida from a hinge lineinOsceola County south. The erosional removal of sediments is shownonthe sectionsaserosional vacuities from several different periods. The earliest Neogene exposure of the platform occurred during Late Oligocene into Early Miocene (Figure 68).Itisvery probable that much of the Florida Platform was exposed during this time. Following this low stand, sea level rose but probably did not cover the entire platform. The deposition of the basal Arcadia, the Penney Farms, and the St. Marks Formations occurred during the early Early Miocene. Following this event there was a minor regression then continued transgression. During this period, as the sea levels rose, the Martin-Anthony fauna (MacFadden, 1980) and a terrestrial fauna collected along the Tampa By-Pass Canal (Dale Jackson, personal communications, 1984) were deposited. Both sites contain associated marine fossils indicating a close proximity to land. Upchurch (personal communica tion, 1986) notes that the Tampa By-Pass Canal exposed some"Tampa"sediments containing a freshwater component to the fauna. These sites are 25 to 22 million years old and are of Arikareean age (North American Land Mammal Age, NALMA) (Chattian and Aquitanian, Figure 73). Followinganearliest Miocene declineinsea level, the sea level began a rise which continued with only minor interruptions through the Early Miocene. Deposition of the upper part of the Arcadia, the Marks Head and the Torreya Formationsoccurredinthe later part of the Early Miocene. During this time (Hem ingfordian NALMA; Burdigalian and possibly Aquitanian) a diverse land mammal fauna developed. A number of localities containing this fauna occurinnorth central and panhandle Florida (see MacFadden and Webb, 1982). The number of sites and their distribution indicate thatinthe latter part ofthe Early Miocene, there was a considerable area above sea level (Figure 69).Assea level continued to rise these areas were eventually covered. Sea level continued to rise reaching its maximum height in the mid-Middle Miocene (Figure 70), when 114

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MADISONSUWANNEECOLUMBIAALACHUAMARIONLAKEORANGEOSCEOLAOKEECHOBEEMARTINIPALMBEACHPRESENTSEALEVELOKEECHOBEE BASIN " OCALAGROUPOCALA PLATFORMLOWESTLATE-------------------------------------------------------------------OLIGOCENESEALEVEL-----__--.t?--AVONPARKFM. o EROSIONAL VACUITIES UNCONFORMABLE CONTACTSFigure68.Cross section showing reconstructed stratigraphic sequence at the end of Late Oligocene.115

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MADISON SUWANNEEICOLUMBIA ALACHUA MARIONLAKEORANGEOSCEOLAOKEECHOBEE MARTINIPALM BEI.CH OCALAPLATFORM OKEECHOBEE BASINHIGHEST EARLY MIOCENE SEA LEVEL ARCADIA FM. PRESENT SEA LEVEL.?-----j -------------------------------------------------AVON PARK FM.DEROSIONAL VACUITIES UNCONFORMABLE CONTACTSFigure69.Cross section showing reconstructed stratigraphic sequence at the end of the Early Miocene.116

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MADISON SUWANNEEICOLUMBIAALACHUAMARIONLAKEORANGEOSCEOLAOKEECHOBEEMARTINIPALMBEACHOCALA PLATFORM OKEECHOBEE BASINPEACE RIVER FM. PRESENTSEALEVEL _ UNCONFORMABLE CONTACTSOCALAGROUP AVON PARK FM.------------------------------------------------------------------------HIGHESTMIDDLE MIOCENESEALEVELFigure70.Cross section showing reconstructed stratigraphic sequence at the end of Middle Miocene.117

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the peninsula was probably entirely submerged. The Peace River and Coosawhatchie Formations were depositedinthe peninsular area whileanunnamed unit was depositedinthe eastern panhandle. Mam mal faunas from this time are not well represented. MacFadden and Webb (1982) note sitesinJefferson and Alachua Counties that maybeBarstovian age NALMA (Langhian and Serravalian) with possible Barstovian faunas from the Central Florida Phosphate District.Inthe Central Florida Phosphate District this fauna was collected from sediments immediately above the Arcadia Formation. These sediments were subsequently covered by estuarine and marine sediments of the Peace River Formation (Webb and Crissinger, 1983). Following the mid-Middle Miocene high stand, sea level began to decline and more-of the Florida Plat form was exposed. The land area continued increasing into the Late Miocene as the seas continued to recede (Figure71).Thereisnorecord of deposition during this timeinthe eastern panhandle or the nor thern peninsular area.Inthe southern peninsula the upper most portions of the Peace River Formation (incuding the Bone Valley Member) were deposited. The highest sea levels of the Late Miocene and Early Pliocene did not inundate much of the peninsula. During the Late Miocene and Early Pliocene, terrestrial vertebrates were abundant,asindicated by the fauna at the Love Bone Bedinwestern Alachua Cunty (the only Clarendon ian [Tortonian] site) and the faunas at many other Hemphillian (latest Miocene and Early Pliocene) sites. During the Pliocene and Pleistocene sea levels fluctuated but, judging from data presently available, did not completely cover the state. Deposition appears to have been limited to the southern one-third of Florida and the coastal areas. Erosion breached the Hawthorn Group overlying the Ocala Platform and removed significant amounts of sediment from the peninsula (Figure72).This erosional episode con tinues today. There are problems associated with comparing the Vail and Mitchum (1979) sea level curve to the distribution of-Hawthorn Group sedimentsinFlorida. These problems arise when attempting to correlate the occurrence of some Hawthorn sediments presently well above sea level with a paleo-sea level represented as beingator very near present sea level. Further research is required concerning the ac tual elevations of paleo-sea levelsinorder to understand the relationships of these levels to the lithostratigraphic units onshore.PALEOENVIRONMENTSThe Miocene sediments of Florida were apparently depositedina number of complex depositional en vironments. Environments range from prodeltaic to open, shallow marine, carbonate bank. Previous workers (Puri 1953; Puri and Vernon, 1964) referred to continental (terrestrial), deltaic, and marine condi tions. However, the sediments assigned to the Hawthorn Group by this investigation were deposited only under marine or peri-marine conditions that seemed to have ranged from prodeltaic and shallow to sub tidal marine, to intertidal and supratidal. Terrestrial sediments occur onlyaspaleosoils and weathered residuum of the Hawthorn sediments.Innorthern peninsular Florida the Penney Farms and Marks Head Formations appear to have been deposited under shallow marineconditions. This is basedonthe occurrence of a shallow water fauna ofBalanus, Ostreaand other mollusks(Pecten, Cardium, Chione,etc). Intraclasts are commonly recognizedinthe Penney Farms and Marks Head, which suggests depositionina shallow water environment with periodic episodes of stormor tidally-induced high energies. That the shoreline was located west of the present outcrop is indicated by the occurrence of the vertebrate remainsinthe Penney Farms described by MacFadden (1980). The presence of palygorskite-rich beds within the-two formations suggests a near shore, coastal-lagoonal environments (Weaver and Beck, 1977). The Coosawhatchie Formation is also thought to have been depositedina subtidal, shallow marine en vironment. The Coosawhatchie contains significantly fewer carbonate beds and is much more sandy than the underlying units. Sea level seems to have risen to its Miocene maximum heightinthe Middle Miocene, during Coosawhatchie deposition.Asthe sea transgressed, the palygorskite-producing zones of the peri-marine environment were reworked, incorporating palygorskite throughout the unit. 118

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MADISON SUWANNEE COLUMBIAALACHUAMARIONLAKEORANGEOSCEOLAOKEECHOBEEMARTINIPALMBEACHOCALA PLATFORMOCALAGROUP AVON PARK FM. oEROSIONAL VACUITIES UNCONFORMABLE CONTACTSUNDIFFERENTIATEDHAWTHORNGROUPOKEECHOBEE BASINHIGHEST EARLY PLIOCENE :;EA LEVELFigure 71. Cross section showing reconstructed stratigraphic sequence at the end of the Early Pliocene. 119

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MADISON SUWANNEE COLUMBIA ALACHUA MARION LAKE ORANGE OSCEOLA OKEECHOBEE MARTINIPALM BEACHOCALAPLATFORM OKEECHOBEEBASINPRESENT SEA LEVEL PLIO-PLEISTOCENE DEPOSITS AVON PARK FM.DEROSIONAL VACUITIES UNCONFORMABLE CONTACTSOCALA GROUP ""..".,0 ENESEDI _..,,,,,,,f1 Figure 72. Cross section showing stratigraphic sequence occurring at present.120

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.Sediments assig.ned to the Statenville Formation crop out along parts of the Suwannee and Alapaha Rivers. These sedIments are often strongly cross bedded and contain thin dolomite laminae. Puri and Vernon (1964) thought that the laminae represented algal layers. Associated with the thin dolomite layers are mudcracks, palygorskite beds and opaline cherts. These features suggest a supratidal environment for some of the sediments, while the crossbedded zones suggested nearshore, shallow subtidal to possibly, intertidal conditions. The occurrence of the opaline chertsisinteresting since their and association with palygorskite and dolosilt (McFadden, 1982)issuggestive of the development of evaporative conditions and highly alkaline waters (Upchurch et aI., 1982).Insouthern Florida a shallow marine carbonate platformexisted throughout a large portion of the Miocene. Siliciclastics were transported onto this carbonate bank from the north and east by southward flowing longshore currents. The Arcadia Formation developedinthis environment. King (1979) sug gested a quiet water lagoon, much like the present Florida Bay, for the deposition of the Tampa Member ofthe Arcadia. Similar depositional environments probably continued throughout the deposition of the Arcadia, although the water depths may have increased towards the southeastinresponse to sub sidence ofthe platforminsouthern Florida. The Nocatee Member represents a higher energy, more open, near-shore marine environment that occurredonthe southeast edge of the carbonate bank during Tampa deposition. The Nocatee grades westward into a very sandy facies of the undifferentiated Arcadia and northwestward into the Tampa Member. The Peace River Formation represents the flood of siliciclastics that entered southern Florida during the Middle Miocene. The carbonate bank environmentwasoverrun by the siliciclastics, which restricted the deposition of carbonate beds to limited areas. This change was,inpart, a response to the riseinsea level in the Middle Miocene and the continued influx of large amounts of siliciclastics from the north.Inthe northern portion of the area of its occurrence, the Peace Riverwasdepositedina shallow marine to brackish water environmentasindicated by the occurrence of shallow water forms ofBalanusandOstreainthe carbonate beds. Further south (particularly southeasterly) open marine conditions prevailedassuggested by the abundance of planktonic foraminiferainPeace River sedimentsinMartin County. The Bone Valley Member of the Peace River Formation is a most interesting unit not only from the standpoint of its phosphate resources but also from the depositional environments it represents and the questions it raises. Early investigators (Eldridge, 1893; Matson and Clapp 1909; Matson and Sanford, 1913; and others) believed that the Bone Valley resulted from the reworking of pre-existing Hawthorn residuum by rivers and the advancing Pliocene sea. Cooke (1945) believed that it wasinpart residual from theHawthorn andinpart estuarine. Webb and Crissinger (1983) indicate a marine depositional en vironment for much of the Bone Valley Member. Portions of the Bone Valley were depositedina more nearshore, higher energy environment while others were laid down in a quieter, shallow marine environ ment suchasan or lagoon. The proximity to land is demonstrated by the occurrence of ter restrial vertebrates mixed with marine vertebrates. This author believes that the Bone Valley Member contains reworked (pre-existing) phosphate derived updip from the older parts of the Hawthorn, gravel sized clasts of phosphatized dolomite, and phosphate formed in the marine environment during Bone Valley deposition. The late phase (very Late Miocene or very Early Pliocene) gravel bed that was classically called the Bone Valley Formation or Gravel is reworked from pre-existing phosphorites. This bed was depositedinfreshwater rivers to brackish water, tidally influenced environments. The depositional environment of sediments assigned to the Torreya Formation of the Hawthorn Group in the eastern panhandle has been discussed by Weaver and Beck (1977). They suggest that these sediments and correlative sediments in southwest Georgia were depositedina tidally influenced peri marine environment. The environments present ranged from variably brackish to more normal marine waters. This interpretation is basedonthe occurrence of palygorskite and dolomite, which they believe required more brackish water conditions to form and the occurrence of marine to brackish water diatoms. There were periodic episodes of high energy (perhaps storms) which could have developed intraclast beds within the unit. Limestones presentinthe lower Torreya suggest a shallow, subtidal marine environment during deposition. . The Hawthorn Group of the Gulf Trough contains a greater abundance of carbonate beds thanISpre sent eastwardinthe panhandle.Itappears that this accumulation of carbonate with incorporated121

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...... I\) I\) ABSOLUTE CENOZOIC NORTH AMERICAN EUROPEAN PLANKTONIC TIME SCALE EPOCHS LANDMAMMALSTAGES FORAMINIFERA (MYBP)..AGES, ZONES BLANCAN N19 PLIOCENE ZANCLIAN MESSINIANN18 HEMPHILLIANN17 w I-ct-I N16 CLARENDONIAN TORTONIANI-N15 wW -I zSERRAVALLIANN10-N14l-ewl-e (.) N9 i 0LANGHIAN 1-15 i BARSTOVIANN8 N7BURDIGALIAN > N6 -Ia: HEMINGFORDIAN ct N5w AQUITANIAN N4 N3/P22 ARIKAREEAN OLIGOCENE CHATTIANIN2/P21 WHITNEYAN Figure 73. Relation of Mammal ages to planktonic foraminifera time scale (after Webb and Crissinger, 1983).

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siliciclastics was deposited in a lagoon or embayment environment prior to the time when siliciclastics flooded area. When large "amounts of siliciclastics entered the area, carbonate deposition was severely limited.HAWTHORN GROUP GAMMA-RAY LOG INTERPRETATIONGamma-ray logs are of particular importance to the investigator studying the complex section ofthe H.awthorn The activityinthe Hawthorn Group sediments is generally significantly higher than subjacent or supraJacent formations, thus allowing the delineation of this unit. Also, since these sediments are often partially or entirely cased off during well construction, the ability of gamma-ray probe to obtain information through casing is most important.Inthe course of this stUdy gamma-ray logs were the only geophysical logs used. For a discussion of resistivity logs of the Hawthorn Group sediments see Johnson (1984). The Hawthorn Group shows significant stratigraphic and lithologic variation from one area of the state to another. As a result the gamma-ray log discussionissubdivided into sectionsasshown in Figure1.NORTH FLORIDA The Hawthorn Group of northern Floridaconsists of a complex sequence of siliciclastics and car bonates containing varying percentages of uranium-bearing phosphate minerals. The resultant gamma ray log shows Widely varying peak intensities (Figure74).The patterns of peaks are similar throughout much of the area from Duval County west to western Hamilton County and from Nassau County south to southern Putnam County. The Hawthorn thins and the gamma-ray signature changes somewhat south of Putnam CountyinMarion, Lake and northwestern Orange Counties. This is due both to erosional removal of the upper sediments and to less depositioninthe area between the Ocala Uplift and the San ford High. A typical gamma-ray log from the north Florida area (Figure74)consists of five generalized zones. However, the pattern may show significant variationinthe intensities of peaks and thicknesses of peak groups. Formational correlation with the gamma-ray signatureisrelatively consistent. The upper, high in tensity zone and part ofthe subjacent lower intensity zone correlate with the Coosawhatchie Formation and, where it is present, the Statenville Formation. The Marks Head Formation correlates with part of the low intensity zone, the underlying higher intensity zone, and the upper portion of the second low intensity zone. The Penney Farms Formation incorporates the remainder of this low intensity zone and the basal, high to very high intensity zone. The underlying Ocala Group and occasionally the Suwannee Limestone have significantly lower generalizedsignatures than the sediments of the Hawthorn Group. The forma tional correlations with the gamma-ray signature are shown in Figure74.The upper and lower boun daries of theHawthorn Group are generally easily pickedonthe gamma-ray logs. However, caution must be exercised in making formational identifications based solelyonthe signatures. SOUTH FLORIDA Intensities of gamma-ray activityinthe Hawthorn Group sediments show similar ranges to those recognized in the northern portion of the peninsula. However, the generalized gamma-ray signature is quite different. Figure75shows a typical southern Florida gamma-ray log (compare with the northern Florida log, Figure 74).Asis the case in northern Florida, the Hawthorn sediments in this area have,ingeneral, significantly higher gamma-ray signatures than the subjacent or suprajacent units. The Hawthdrn Groupinsouthern Floridaissomewhat less complex than its northern counterpart.Inthis area theHawthornisgenerally composed of a siliciclastic upper unit (the Peace River Formation) and a lower carbonate unit (the Arcadia Formation). The Hawthorn becomes more complex to the east due to a greater siliciclastic influx and subsequently the gamma-ray signature changes. These variations are discussed by Gilboy (1983). Several logs showing the more typical range of variations are showninFigures 76,77,and78.123

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CLAY COUNTYW-14219LAND SURFACEUNDIFFERENTIATED-100wo IE!5 -200 en ClZ -300lL COOSAWHATCHIE FORMATION MARKS HEAD FORMATION PENNEY FARMS RMAnONOCALA GROUPo100 200 CPSFigure 74. Gamma-ray log, Jennings#1,W-14219, Clay County. The least complex area is the western half of southern Florida from Polk County southward to Lee and Collier Counties. A typical log for this area,asshown in Figure 79, consists of a number of distinct intensi ty zones. The uppermost zone is a relatively low intensity zone corresponding to the Peace River Forma tion. This is underlain by a zone of numerous higher intensity peaks which represent the upper, undif ferentiated Arcadia Formation. Below this zone, the intensity drops to the lowest point in the Hawthorn Group. The intensity increases below the low intensity zone to a moderate intensity in basal sediments of the Arcadia Formation. At the base ofthe Arcadia Formation, the base ofthe Hawthorn Group, the gamma-ray intensity drops significantly at the contact with the"Suwannee"Limestone. Variations of the gamma-ray intensity are often greatestinthe Peace River Formation. The intensity in creasesasthe phosphate content increases in the phosphate district. The gamma-ray signature of the upper section is most intense when the Bone Valley Member of the Peace River Formation is present (Figure 76).Inpart of the eastern portion of southern Florida and the extreme southern end of the penin sula, the gamma-ray activity ofthe Peace River Formation is generally low with only a few high peaks.Inparts of Osceola, Brevard and Indian River Counties the Peace River Formation may contain significant phosphate. The resultant gamma-ray signature is high. 124

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DESOTO COUNTYW-15303ARCADIA FORMATION "SUWANNEE" LIMESTONELAND SURFACEUNDIFFERENTIATED PEACE RIVER FORMATION-100-400w u.a: :::> (/)0-200z <{--J9 w COt;; -300wu.-500 -.J.,---....----,...o100200CPSFigure75.Gamma-ray log, R.O.M.P.17,W-15303, DeSoto County.Inthe eastern portion of southern Florida, south from and including Brevard County and east from the Polk-Osceola County line, the gamma-ray signature is more complex (Figure77).Inthe n.orthern part of this area, theHawthorn is thin and the signature has many high intensity peaks. South from this area the Hawthorn thickens and the generalized signature contains a wider range of intensities (Figure78).Throughout the eastern half of southern Florida, the Peace River Formation is characteristically of lower gamma-ray intensity than the underlying Arcadia Formation, although a wide variation exists (Figures77and 78). The topof the Peace River Formation is usually markedbya peak thatissignificantly higher than the background. This represents a concentration of phosphate at the post-Hawthorn unconformity. The contact between the Arcadia and Peace River Formations is generally marked byanincreaseinthe abundance of large peaksinthe Arcadia. Characteristically, the basal Hawthorn Group sediments con tain the greatest number of high intensity peaks and the most intense peaks (Figures 77 and78).Underlying theHawthorn Group throughout the eastern section are sediments with low gamma-ray ac tivities.Inportions of the eastern section, the Hawthorn is unconformably underlain by limestones of the Ocala Group which have very low activities.Inother areas the Hawthornisunderlain by "Suwannee" Limestone or, in some cases, unnamed Lower Miocene limestones both with gamma-ray signatures much lower than the overlying section. 125

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POLKCOUNTYR.O.M.P.45-2LAND SURFACE BONE VALLEYMbr.200CPSARCADIA FORMATION SUWANNEE LIMESTONE100oPEACE RIVER , FORMATION-300 -100 lI.. a: :::l CIloZ .Jg wCD-200 >wW lI.. Figure 76. Gamma-ray log, R.O.M.P. 45-2, Polk County.126

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OSCEOLA COUNTYW-13534-100wo <{ u.a: ::>CIJ oz <{..J;: -200 9 w
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INDIAN RIVERCOUNTYW-13958LAND SURFACE-100w a: ::>CIJ oz ...J g w CDt W WLL-200-300UNDIFFERENTIATED PEACE RIVER FORMATION?ARCADIA FORMATIONo100200CPSFigure 78. Gamma-ray log, Phred#1,W-13958, Indian River County. 128

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LEECOUNTYW-15487LAND SURFACEPEACE RIVER FORMATION UNDIFFERENTIATEDo-100-200 -600-500w 0 LL-300a: ::>C/) cz ...J :;: 0...JwARCADIAlD fFORMATIONw-400wLLFigure 79. Gamma-ray log, Cape Coral#1,W-15487, Lee County. 129

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EASTERN PANHANDLE The Hawthorn Group sediments of the eastern Florida panhandle are lithologically different from the Hawthorn in the northern peninsula. This difference is also recognizable when comparing gamma-ray logs from these areas (compare Figure80with Figure74).The northern axis of the Ocala Platform servesasthe line separating the two areas, with the Hawthorn Group thickening away from the axis to the east and west. The Hawthorn sediments of the eastern panhandle are predominantly clays, sandy clays and clayey sands with occasional carbonate lenses and contain minor percentages of phosphate. The percentage of carbonate beds increasesinwestern Leon County and westward intotheGulfTrough and Apalachicola Embayment. Figures80and81show the gamma-ray signature variation in the eastern panhandle. The typical gamma-ray signature of the Hawthorn Group in the area east of the Gulf Trough is shown in Figure 81. The Hawthorn Group (Torreya Formation) has a gamma-ray signature that is well above the in tensity of the subjacent and suprajacent units.Inthe Gulf Trough theHawthorn Group thickens. The gamma-ray signature there appears more like that of the peninsular Hawthorn with many higher-intensity peaks separated by low intensity zones.SUMMARY1)The Hawthorn Formation has long been considered a complex and unusual unit. The complexity of the strata is the result of interbedding and mixing of carbonate and siliciclastic componentsinassocia tion with the occurrence of phosphate and palygorskite. The complex nature ofthe Hawthorn can best be understood if the unit is raised to group status and formations are identified within it. This author formally proposes upgrading of the Hawthorn Formation to group statusinFlorida. New formations are also for mally proposed to subdivide the Hawthorn Group.2)The Hawthorn Group occurs throughout much of Florida and the Coastal Plain of Georgia.InFlorida, theHawthorn is primarily a subsurface unit, although it crops out along the flanks ofthe Ocala Platform, along the southwest coast of the state, andinlimited areas of the eastern panhandle.Itis ab sent from the crest of the Ocala Platform and the Sanford High due to erosional removal.3)Evidence suggests that sediments of the Hawthorn Group covered the Ocala Platform during Miocene time. The occurrence of outliers of these sediments, the hard rock phosphate and silicified Eocene and Oligocene carbonates, suggests the presence ofthe Hawthorn over the crest ofthe plat form.4)The formations oftheHawthorn Group vary from north Florida into south Florida and from north Florida into the eastern panhandle. The Ocala Platform and the Sanford High affected deposition of these sediments, allowing the regional grouping of the formations.5)The Hawthorn Group in north Florida occurs east ofthe crest of the Ocala Platform and north ofthe Sanford High in central Florida. The sediments of the Hawthorn thin in the area between the Ocala Plat form and the Sanford High.Itappears that the section is thinned due to both erosion and decreased deposition. South of this area the north Florida Hawthorn sediments grade into the south Florida Hawthorn throughanarea of undifferentiated Hawthorn Group.6)The area of transition between theHawthorn Group of north Florida and that of south Florida occurs inanarea from central Lake County to northwestern Orange County. This area is between the Ocala Plat form and the southern edge ofthe Sanford High. Within this zone the component formations of the Hawthorn Group are difficult to recognize and as a result, the section remains undifferentiated Hawthorn Group.7)The north Florida Hawthorn Group consists of (in ascending order) the Penney Farms Formation, the Marks Head Formation, the Coosawhatchie Formation and the Statenville Formation. All of these for mational names are new to Florida stratigraphy. The Marks Head, Coosawhatchie and Statenville Forma tions and the Charlton Member of the Coosawhatchie Formation are extended into Florida from Georgia where their use is currently being formalized (Huddlestun,inpress). 130

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GADSDEN COUNTYW-7472LAND SURFACE-100UNDIFFERENTIATEDw o lL a:::> en o z ...J-200 ;:g WlD I WWlL-300oTORREYA FORMATION--?BASAL TORREYA FORMATION CHATTAHOOCHEE FORMATION100CPSFigure80.Gamma-ray log, Owenby#1,W-7472, Gadsden County.131

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MADISON COUNTYW-15515LANDSURFACEUNDIFFERENTIATEDw ()"" u. a:::::J(/)""...J0:g w cof W WU.TORREYA FORMATION SUWANNEE LIMESTONE-200 ...... --... --------...... -----------...,o100200CPSFigure81.Gamma-ray log, Howard#1,W-15515, Madison County.8)The Penney Farms Formationisa new name proposed for the basal Hawthorn sediments in north Florida. The type section of the Penney Farms Formation is in core W-13769, Harris#1,located near Penney Farmsincentral Clay County (SWV4,SE1f4 Section7,Township 6S, Range 25E). It consists of in terbedded dolomites and siliciclastics with carbonate being most abundant in the lower portion and siliciclasticsinthe upper portion. The dolostones are variably quartz sandy, phosphatic and clayey, often containing zones of intraclasts. The siliciclastics vary from clayey sands to sandy clays with varying percentages of phosphate and dolomite. The clays present are smectite, palygorskite, illite and sepiolite. The Penney Farms Formation unconformably overlies the Ocala Group or, in a few areas, the Suwan nee Limestone.Itis overlain unconformably by the Marks Head Formation. The topcifthe Penney Farmsincores ranges from -333 feet MSL(-101meters)inW-14619 in Duval County to+80 feet MSL(+24 meters)inW-14641 in Alachua County. This unit is thickest in the Jacksonville Basin where more than 155 feet (47 meters) of it are present. The Penney Farms sediments are absent from the crest of the Ocala Platform and the Sanford High. The unit dips generally to the northeast from the Ocala Platform toward the Jacksonville Basin at approximately 4 feet per mile (0.8 meters per kilometer). Local varia tions in dip are common. Few fossils are presentinthe Penney Farms Formation. Dateable faunas encountered indicate an ear ly to middle Aquitanian age (Early Miocene) for this unit. These equate with ZoneNAand possibly early 132

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N.5 of Blow (1969). The Penney Farms Formation correlates with the Parachucla FormationinGeorgia, the lower part of the Arcadia Formationinsouth Florida and the Chattahoochee Formationinthe eastern Florida panhandle. Itisslightly older than the Pungo River Formation of North Carolina.9)The Marks Head Formationisintroduced here for sediments of the Florida Hawthorn Group that cor relate with the Marks Head FormationinGeorgiaasrecognized by Huddlestun(inpress). A reference section in Florida isincore W-14219, Jennings#1,Clay County, Florida (SE1f4 , SE1f4, Section27,Township 4S, Range 24E). The Marks Headisthe most complexly interbedded unit of the Hawthorn Group. Lithologically, it con sists of interbedded clays, quartz sands, and carbonate (usually dolostone), each with varying percen tages of quartz sand, clay, carbonate and phosphate. The clays presentinthe Marks Head are palygor skite, smectite, illite and sepiolite. The Marks Head unconformably overlies the Penney Farms Formation throughout much of its extent.Itis,in turn, overlain unconformably by the Coosawhatchie Formation. The top of the Marks Head ranges from -260 feet MSL (-79 meters)inW-14619, Duval County to+114 feet (35 meters)inW-14641 Alachua County. This unitisabsent from the crestofthe Ocala Platform and the Sanford High. It reaches a max imum thickness of 130 feet (40 meters)inW-12360, Bradford County. The Marks Head dips generally to the northeast from the flanks of the Ocala Platform toward the Jacksonville Basin at approximately 4 feet per mile (0.8 meters per kilometer). Local variations are com mon. The age of the Marks Head FormationinFloridaisinferred from the dateable faunas foundinGeorgia, since no faunas have been identifiedinthe Florida portion. The Marks HeadisBurdigalian age (late Early Zone N.6 or very early N.7 of Blow (1969). This unit correlates with the Torreya Formation of the Florida panhandle, part of the Arcadia Formation of south Florida. and the lower Pungo River Formation of North Carolina. 10) The Coosawhatchie Formationisintroduced here for the upper unit of the Hawthorn GroupinnOIthem peninsular Florida. It is a southern extension of the Coosawhatchie Formation of Georgiaasin troduced by Huddlestun (in press). A reference sectioninFloridaisincore W-13769, Clay County (SW1f4 , SE1f4, Section7,Township6S,Range 25E). Lithologically the Coosawhatchie consists of carbonates, quartz sands and clays. The upper part of the formationischaracteristically a very sandy, clayey dolostone with interbedded siliciclastics and variable percentages of phosphate. The lower partischaracteristically clayey, dolomitic sand with interbedded clay and carbonate and variable amounts of phosphate. Clay minerals present include smectite, palygorskite, sepiolite and illite. The Coosawhatchie Formation unconformably overlies the Marks Head Formation and unconformably underlies undifferentiated post-Hawthorn sediments. Its upper beds appear to grade laterally into the Statenville Formation. The top of the Coosawhatchie ranges from -93 feet MSL(-28meters)inW-14477, Putnam County to+168 feet MSL(51meters)inW-14641, Alachua County. This unitisalso absent from the Ocala Platform and the Sanford High. The thickest known occurrence of the CoosawhatchieisinW-14619, Duval County, where it attains a thickness of 222 feet (68 meters). This unit generally dips nor theasterly from the Ocala Platform toward the Jacksonville Basin at apprOXimately 4 feet per mile (0.8 meters per kilometer). Local variationsindip are common. The age of the Coosawhatchie Formationisthought to be Middle Miocene (early Serravalian) basedondiatoms and planktonic foraminifera. Itiscorrelated with the Peace River Formation of south Florida, the lower part of the shoal River Formationinthe panhandle, and much of the Pungo River FormationinNorth Carolina. 11) The Charlton Member of the Coosawhatchie Formation represents a redl,Jction of the Charlton For mation to member status, as used by Huddlestun (in press). A reference section for the Charlton MemberinFloriaa isinW-13815, Nassau County (NW1f4,NW1f4 , Section 32, Township 3N, Range 24E). It consists of interbedded carbonates and clays that are variably quartz sandy and slightly to non phosphatic. The Charlton overlies conformably and interfingers with the undifferentiated Coosawhatchie Forma tion. It unconformably underlies the undifferentiated post-Hawthorn sediments. The top of the Charlton ranges from -38 feet MSL (-12 meters)inW-14619, Duval County to+109 feet (33 meters)inW-14283, 133

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Bradford County. Its maximum thickness is approximately 40 feet (13 meters)inW-13815, Nassau Coun ty. The occurrence of the Charlton Member is spotty throughout the northeastern most part of the state. The age of the Charlton Member is considered tobeMiddle Miocene by Huddlestun (in press), basedonthe mollusk fauna and the lithostratigraphic relationships.12)The Statenville Formation is a formational name extended into Florida from Georgia where it was described by Huddlestun (in press). A reference section for Florida is in core W-15121, Hamilton County (NE1f4,NW1f4, Section3,Township 2N, Range 12E). The Statenville is characteristically quartz sand with common to abundant phosphate, interbedded with clays and dolostones. One ofthe diagnostic features of this unit is its thin bedded and cross bedded nature. The Statenville conformably overlies part ofthe Coosawhatchie Formation and unconformably underlies undifferentiated post-Hawthorn sediments.InFlorida, this formation is recognized only in the limited area of Hamilton and Columbia Counties. The maximum thickness is 87 feet (26.5 meters) in W-15121, Hamilton County. The age ofthe Statenville is believed tobeMiddle Miocene (Serravalian) by Huddlestun (in press). Vertebrate fossils collected from it suggest a late Middle Miocene age. A reworked zone at the topofthe Statenville contains Late Miocene vertebrate fossils.13)The south Florida Hawthorn Group consists of (in ascending order) the Arcadia Formation with the Nocatee and Tampa Members and the Peace River Formation with the Bone Valley Member. The Ar cadia and Peace River Formations and the Nocatee Member are new names introduced here. The Tam pa and Bone Valley Members are former formational units reduced to member status within the newly proposed Hawthorn Group framework.14)The Arcadia Formationisa new name proposed here for the lower Hawthorn carbonate section of south Florida. The type section isinthe core W-12050, DeSoto County (SE1f4,NW1f4, Section 16, Township 388, Range 26E). The Arcadia Formation, with the exception ofthe Nocatee Member, is predominantly carbonate with varying percentages of quartz sand, clay and phosphate. Thin quartz sand beds and clay beds are present but not abundant. The Arcadia Formation unconformably overlies the Ocala Groupinpart of south Florida and the"Suwannee"Limestone in the remainder.Insome areas the contact between the Arcadia and the"Suwannee"appears conformable. The Arcadia is usually overlain by the Peace River Formation but, where the Peace River is absent, the Arcadiaisoverlain by undifferentiated post-Hawthorn sediments. The topofthe Arcadia ranges from -440 feet MSL (-134 meters)inW-15493, Monroe County, to+112 feet MSL (34 meters) in W-13269, Polk County.Itranges in thickness up to more than 600 feet (183 meters).Ingeneral, the Arcadia dips to the southeast at approximately 5 feet per mile (0.9 meters per kilometer). The Arcadia Formation has yieldedfew dateable fossils. Mollusk specimens in the upper portion in dicate a correlation with the Torreya Formation of the eastern panhandle and the Marks Head Formation of north Florida and Georgia. This places the Arcadia Formationasnoyounger than mid-Burdigalian (late Early Miocene). The lower part of the Arcadia appears to equate with the Penney Farms Formation of north Florida, the Chattahoochee Formation in the eastern panhandle and the Parachucla Formationineastern Georgia.15)The Tampa Member of the Arcadia Formation represents a reduction in status for the Tampa from formation to member. The reduction is justified basedonthe limited areal extent ofthe unit and by its variable nature whichisgradational with the undifferented Arcadia Formation. The classical type area oc curs around Tampa Bay in Hillsborough County. The type core is W-11541 (SE1f4,NW1f4, Section 11, Township 30S, Range 18E, Hillsborough County). Reference cores showing regional variation include W-11570 (Section1,Township 33S, Range 22E, Manatee County) and (NW1f4, Section 22, Township 35S, Range 17E, Manatee County). The Tampa Member is predominantly limestone with varying percentages of quartz sand, clay, and minor phosphate. Dolomite is generally a minor component. Phosphate is generally present in amounts less than 3 percent. Individual beds of quartz sand and clay do occur but are infrequent. The Tampa Member overlies the"Suwannee"Limestoneinareaswhere the Nocatee Member is not 134

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present beneath the Tampa. The contact with the "Suwannee" often appears gradational butinthe up dip areas, the contact is abrupt and unconformable. When the Nocatee Member is present, it underlies the Tampa conformably. The Tampa is overlain throughout much of its extent by the undifferentiatedArcadia Formation. Where the undifferentiated Arcadia Formation is absent due to erosion, the Tampa Member is overlain by either the Peace River Formation or undifferentiated post-Hawthorn sediments. The topofthe Tampa ranges from+75feet(23meters) MSLinHillsborough County to -323 feet (-98.5 meter) MSL in Sarasota County. The thickness of the Tampa Member ranges up to 270 feet(82meters). The Tampa Member is characteristically variably fossiliferous. Most common are mollusks, with corals and foraminifera also present. Despite the presence of these fossils, no age-diagnostic species have been recognized. It is suggested that the Tampa correlates with the lower part of the Parachucla Forma tioninGeorgia. The Tampa may correlate with the basal Penney Farms Formationinnorth Florida.16)The Nocatee Member of the Arcadia Formationisa new name proposed here forthe''Tampa sand andclay"unit of Wilson (1977) which occurs entirelyinthe subsurface. The typecore is W-12050(SE1f4, NW1f4, Section 16, Township 38S, Range 26E, DeSoto County). The Nocatee Member is a complexly interbedded sequence of quartz sands, clays, and carbonates, all containing variable percentages of phosphate.Itispredominantly a siliciclastic unit but becomes more carbonate-rich near the limits of the member, where it grades into the undifferentiated Arcadia Forma tion. The Nocatee Member overlies "Suwannee" Limestone throughout the Nocatee's extent. The contact appears gradational. The Tampa Member conformably overlies the Nocatee throughout much of the Nocatee's extent. Occasionally, the Nocateeisoverlain by the undifferentiated Arcadia Formation. The topofthe Nocatee Member ranges from-81feet (-24.5 meters) MSLinPolk County to -639 feet (-195 meters) MSL in Charlotte County. The thickest section currently recognizedis226 feet(70meters) in DeSoto County. The age ofthe Nocatee is based solelyonits relationship to the Tampa Member. This suggestsanearliest Miocene age. 17) The Peace River Formationisa new name proposed for the "upper Hawthorn" clastic unitofsouthern Florida. The type sectionisin W-12050 (SE1f4,NW1f4, Section16,Township 38S, Range 26E, DeSoto County). W-15303 (NE1f4, NE1f4, Section14,Township 38S, Range 23E, DeSoto County)isa sug gested reference section. The Peace River Formation consists predominantly of siliciclastics with interbedded carbonate units. Phosphate is present in highly variable percentages that range into the economically important category. The clastics are calcareous to dolomitic, clayey, phosphatic quartz sands to sandy clays. The Peace River Formation overlies the Arcadia Formation (including the Tampa Member) throughout its extent. The contact appears unconformableinthe updip area and gradational downdip.Itisoverlain by the Tamiami Formation in parts of southern Florida and by undifferentiated post-Hawthorn sedimentsinthe remainder of the area. The top of the Peace River Formation ranges from+175 feet(53meters) MSL in Polk County to -150 feet(-46meters) MSLinparts of Dade and Collier Counties. Thicknesses range to greater than 400 feet(122meters)incentral southern Florida. The Peace River Formation often contains well preserved faunas, including foraminifera, diatoms and, in some areas, vertebrates.Asa result, the range of ages this unit encompasses oftencanbedocumented. The oldest date assigned to the Peace River Formation, basedonlimited vertebrate faunas, is early Middle Miocene (early Serravalian). The youngest age applied to the unitisnoyounger than earliest Pliocene, basedonplanktonic foraminifera faunas. The Peace River Formation correlatesinpart with the Coosawhatchie and Statenville Formations of north Florida and Georgia and the Pungo River Formation of North Carolina.18)The Bone 'Valley Member of the Peace River Formation represents a reduction from formation to member status for the Bone Valley strata. This reduction is justified basedonthe limited areal distribu tion ofthe Bone Valley, its laterally and vertically gradational relationship with the undifferentiated Peace River Formation, and lithologic similarities with the Peace River Formation. The original type locality was in the phosphate mines west of BartowinPolk County. No single sectioninthe mines remains very long, 135

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therefore, no neotype section has been erected. A reference core, W-8879 (NE1f4,SW1f4 Section 24, Township 29S, Range 24E, Polk County), is suggested here. The Bone Valley Member is a clastic unit consisting of quartz sands, clays and variable, but usually high, percentages of phosphate. Characteristically, it consists of pebbleto gravel-sized and sand-sized phosphate in a quartz sand and clay matrix. The occurrence of the phosphategravels is the most lithologically important factor in distinguishing the Bone Valley Member from the remainder ofthe Peace River Formation. Clay beds and quartz sand units are relatively common in the Bone Valley Member. The Bone Valley Member unconformably overlies the carbonates of the Arcadia Formation throughout much of its areal extent.Inthe southern area of the Bone Valley, it interfingers with and ov.erlies the un differentiated Peace River Formation. The Bone Valley is overlain by undifferentiated post-Hawthorn sediments. This contact is unconformable although weathering often obscures it, creating a gradational appearance. The topofthe Bone Valley Member ranges from+175 feet (53 meters) MSL to less than+100 feet (30.5 meters) MSL. The maximum thickness reaches just over 50 feet (15 meters). The age of the Bone Valley Memberisderived entirely from vertebrate remains. The oldest ages sug gested are late Early Miocene (mid-Barstovian; late Burdigalian). Most ofthe Bone Valley Member is late Middle to mid-Late Miocene (Clarendon ian; late Serravallian to mid-Tortonian). The uppermost phosphate gravels of the original Bone Valley "Grave,ls" are very latest Miocene to Early Pliocene (Late Hemphillian; Messinian to Zanclian). The Bone Valley Member correlates in part with the Coosawhatchie and Statenville Formations of nor thern Florida and Georgia.Italso correlates in part with the Pungo River Formation of North Carolina.19)The sediments of the eastern Florida panhandle Hawthorn Group occurinthe area between the axis of the Ocala Platform and the Apalachicola River. These sediments show significant variation from the Hawthorn Group east of the platforminnorth Florida, facilitating the use of separate formational names.Inthe panhandle the sediments ofthe Hawthorn Group are placed entirely in the Torreya Forma tion.20)The Torreya Formation of the Hawthorn Group was named by Banks and Hunter (1973) and revised by Huddlestun and Hunter (1982) and Huddlestun (in press). Their terminology is used in this paper. The type section for the Torreya Formationislocatedonthe Apalachicola River at Rock Bluff (SW1f4, Section 17, Township 2N, Range 7W, Liberty County). Reference sections designated here are in cores W-6611 (SE1f4,NE1f4, Section23,Township 2N, Range7W,Liberty County), W-7472 (SE1f4,NW1f4, Section 19, Township 2N, Range 3W, Gadsden County), and W-6998 (SE1f4,NW1f4, Section8,Township 2N, Range 2E, Leon County). The Torreya contains two named members, the Dogtown and the Sopchoppy. The Torreya Formation is characteristically a siliciclastic unit with increasing amounts of carbonate in the Gulf Trough area. Lithologically, the siliciclastic section is clayey quartz sand to quartz sandy clays with variable percentages of accessory minerals including dolomite, limestone and phosphate. Fuller's earth clays areanimportant part of the Torreya Formationinthe Gulf Trough area. Phosphate is often absent from the Torreya sediments. The carbonate portion of this unit is typically a quartz sandy limestone (occasionally dolomitic to dolostone). The Torreya Formation overlies the Chattahoochee and/orSt.Marks Formations. The contact appears gradational in part ofthe Gulf Trough but disconformableinother areas.Itis overlain unconformably by the Citronelle and Miccosukee Formations throughout much of its extent.Inlimited areas it is overlain unconformably by the Jackson Bluff Formation.Insome areas the Torreya is overlain by undifferentiated surficial sands. The age ofthe Torreya Formation based on predominantly vertebrate faunas, is mid-Early Miocene (early to mid-Burdigalian). This unit correlates with the Marks Head Formation of north Florida and south Georgia and the upper part of the Arcadia Formation of southern Florida.Inthe southern portion ofthe Apalachicola Embayment the Torreya grades into the Bruce Creek Limestone. The Torreya equates with the lower part of the Pungo River Formation of North Carolina. 21) The Dogtown Member of the TorreyaFormation is the clay-rich interval in the upper Torreya in parts of Liberty, Gadsden, and Leon Counties, Florida, and Decatur County, Georgia. The type locality is 136

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the La .Gamelia Mine of Englehard Minerals and Chemical Corp.inGadsden County (Section15,Township 3N, Range 3W). A reference corefor the Dogtown is W-7472 (SEV4,NWV4, Section 19, Township 2N, Range 3W, Gadsden County). The Dogtown Member consists predominantly of clays with thin sand and carbonate beds. The com mercial clay beds are quite pure, but the other clays of this unit are often quartz-sandy, silty and occa sionally dolomitic. The clay minerals associated with this unit are mainly palygorskite and smectite. This member ranges in thickness from15feet (4.7 meters) to 40.5 feet(12meters) where it is recognizedin cores. Its areal extent is not presently defined. The relationship of the Dogtown to overlying and underlying units has not been accurately defined. The ageisconsidered tobemid-Early Miocene (early to mid-Burdigalian). 22) The Sopchoppy Member of the Torreya Formationisa sandy, fossiliferous limestone of limited areal extent. Its type locality isonMill Creek in Wakulla County (center, Section 34, Townhip4S,Range 3W). . The Sopchoppy varies from a sandy, phosphatic, fossiliferous limestone to a dolomitic, phosphatic, quartz sand.Ithas only been recognized near the type locality at the present time and its thickness and extent are not defined. This member is.thought tobeEarly Miocene basedonfaunal similarities with the main portion ofthe Torreya Formation. 23) The Hawthorn Group, statewide, often containsanunusual mineral assemblage consisting of palygorskite and sepiolite (mixed with other clay minerals), phosphate minerals, and dolomite. Although dolomite is notanuncommon mineral, some of the types presentinthe Hawthorn are poorly understood. 24) Phosphate is present throughout the sediments of the Hawthorn Group, constituting one ofthe primary lithologic parameters for this unit.Inpeninsular Florida, the occurrence of nonphosphatic lithologiesisnot common but does occur. However,inthe eastern panhandle non-phosphatic, very clayey sediments are quite common. Phosphateisusually presentassand-sized to pebble-sized grains in concentrations ranging from less than 1 percent to greater than50percent. The average contentisgenerally between 2 and10percent. Economically important phosphate deposits are recognized in limited areas of northern and central Florida. Hard rock phosphates are also foundinwest-central Florida. 25) Palygorskite and sepiolite are not generally considered common clay minerals. The occurrence of these clays in association with dolosilts and phosphate suggests unusual depositional environments for the Miocene sedimentsinthe southeastern United States. These clays occur throughout the Hawthorn Group in association with variable amounts of smectite, illite and,insome cases, kaolinite. 26) Dolomite is the most common carbonate component of the Hawthorn Group throughout much of Florida. Replacement dolomite and dolosilts are the predominant types. Replacement dolomite is the result of dolomitization ofanoriginal limestone. Dolosilts,onthe other hand, resulted not only from the replacement of pre-existing fine grained carbonate, but also maybeprecipitated under a variety of condi tions. 27) The Alachua Formation and its relationship to the Hawthorn Group has long been debated. The present author believes the Alachuaisa weathered and/or reworkedresiduum of the Hawthorn Group. 28) Carbonate deposition dominated the Florida Plateau prior to Miocene time. During the Miocene a flood of siliciclastic sediments intermixed with and spilled over the carbonate environments. The siliciclastics filled the Gulf Trough and entered the depositional environments of Florida. This great influx of siliciclastics was possibly due to renewed upliftinthe southern Apalachians. 29) The geologic history of the Hawthorn Groupisdirectly related to the fluctuations of sea level throughout the Miocene. The highest sea levels were reachedinthe Middle Miocene during the deposi tion of the Coosawhatchie. During low stands of sea level, terrestrial vertebrate faunas migrated and developedonthe exposed land. . 30) The Miocene sediments of Florida were deposited in a series of complex depositional en vironments, resulting in the complex lithostratigraphic nature of the Hawthorn Group. The sediments of theHawthorn Group of northern Florida were depositedinshallow water to limited supratidal en vironments. This is basedonthe molluskan fauna (molds), the occurrence of intraclasts, crossbedding, 137

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and mudcracks.Asmentioned above, the deepest water environment (still shallow) occurred during Coosawhatchie Formation deposition when the sea level was at its maximum.Insouthern Florida, a carbonate bank environment existed throughout the time of deposition of the Ar cadia. Water depths and siliciclastic supply increased to the east.Assea level rose during the Middle Miocene the carbonate bank environment was overrun by siliciclastics during the deposition of the Peace River Formation. The Bone Valley Member of the Peace River Formation was deposited.inshallow water environments ranging from high energy nearshore to quieter water lagoons. Hawthorn deposition during the Mioceneinthe eastern panhandle was limited to the late Early Miocene Torreya Formation. The depositional environment suggested by Weaver and (1977) is a tidally influenced lagoon. 31) Gamma-ray logs provideanimportant tool for the correlation and interpretation ofthe Hawthorn sediments throughout Florida. The Hawthorn Group, in general, has a unique, identifiable gamma-ray signature.Ithas significantly higher (more intense) peaks than the overlying and underlying units, with gamma-ray intensities that vary from less than 50 cps to greater than 500 cps. Within each region of the state, signatures are characteristic and correlate well with the formational breakdown of the group.CONCLUSIONSThe Hawthorn Group of the southeastern Coastal Plain isanunusual and complex unit. The complex lithostratigraphy of the strata indicates that the Hawthorn shouldbedescribedasa group, rather than re taining the former formation status. The Hawthorn is formally raised herein to group status in Florida and is subdivided regionally into its component formations. Regionally, the Hawthorn Group shows significant variation. As a result, the formational subdivision of the groupisdifferent for the northern and southern peninsula and for the eastern panhandle areas of Florida. The formations of the group in northern Florida are, in ascending order: the Penney Farms; the Marks Head; the Coosawhatchie, including its Charlton Member; and the Statenville.Insouthern Florida the units are, in ascending order: the Arcadia Formation with its Tampa and Nocatee Members; and the Peace River Formation, with its Bone Valley Member. The group in the eastern panhandle is represented by the Torreya Formation, with its Dogtown and Sopchoppy Members. The formational names are, with the exception ofthe Torreya, new names to Florida stratigraphy. The Marks Head, Coosawhatchie and Statenville are names extended into Florida from Georgia, while the Penney Farms, Arcadia and Peace River are new names proposed here. The use ofthe Charlton, Tampa and Bone Valley namesasmembers represents a reduction from formational status for these units. This demotion is justified by their limited areal extent, lithologies and stratigraphic relationships with the for mations of which they are members. The lithostratigraphic units ofthe Hawthorn Group are related by the occurrence of unusual mineralogies (including phosphate, palygorskite and sepiolite clay minerals, dolomite and opaline cherts), color and stratigraphic position. The occurrence ofthe unusual mineral suite is suggestive of a unique set of environmental conditions present during the deposition oftheHawthorn Group. Further refinement and definition ofthe concept of the Hawthorn Group and its component formations will occurasnew data become available. A better understanding of the framework ofthe group will assist in determining the conditions and processes responsible for the deposition ofthe unusual mineral suite associated with the Hawthorn sediments. 138

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REFERENCESAltschuler, Z.S., and Young,EJ.,1960, Residual origin of the "Pleistocene" sand mantleincentral Florida uplands and its bearingonmarine terraces and Cenozoic uplift: U.S. Geological Survey, Professional Paper 400-B,p.B202-B207.-------,Cathcart, J.B., and Young, E.J., 1964, Geology and geochemistry of the Bone Valley Formation and its phosphate deposits, west central Florida (Geological Society of America Annual Meeting Guidebook, field trip#6):Geological Society of America 1964 Meeting,68p.Armstrong, J.R., Brown, M.P., and Wise, S.W., Jr., 1985, The geology of the Floridan aquifer systemineastern Martin andSt.Lucie Counties, Florida, Southeastern Geology,v.26,p.21-38. Assefa, G., 1969, Mineralogy and petrology of selected rocks from the Hawthorn Formation, Marion and Alachua Counties, Florida: (M.S. thesis), Gainesville, University of Florida,81p.Badiozamani,K.,1973, The Dorag dolomization modelapplication to the Middle Ordovician of Wiscon sin: Journal of Sedimentary Petrology,v.43,p.965-984. Banks,J.E,and Hunter,M.E,1973, Post-Tampa, pre-Chipola sediments exposedinLiberty, Gadsden, Leon, and Wakulla Counties, Florida: Trans., Gulf Coast Association Geological Societiesv.23,p.355-363. Bentor, Y.K., 1980, Phosphorites the unsolved problemsinBentor, Y.K., ed., Marine Phosphorites -geochemistry, occurrence and genesis: Society of Economic Paleontologists and Mineralogists Special Publication 29,p.3-18. Bergendal, M.H., 1956, Stratigraphy of parts of DeSoto and Hardee Counties: U.S. Geological Survey Bulletin 1030-B,33p.Bishop,EW.,1956, Geology and ground water resources of Highlands. County, Florida: Florida Geological Survey, Report of Investigation15,115p.Blow, W.H., 1969, Late middle Eocene to Recent planktonic foraminiferal biostratigraphy,inBron nimann,P.and Renz, H.H. (eds.), Proceedings First Int. Conf. Planktonic Microfossils (Geneva, 1967): Leiden, Holland, E.J. Brill,p.199-421. Brooks, H.K., 1966, Geological history of the Suwannee River: Southeastern Geological Society, 12th Annual Field Conference Guidebook,p.37-45._______, 1967, Miocene-Pliocene problems of peninsular Florida: Southeastern Geological Society, 13th Field Trip Guidebook,p.1-2._______, Gremillion, L.R., Olson,N.K., and Puri, H.S., 1966, Geology of the Miocene and Pliocene Seriesinthe north Florida-south Georgia area: Southeastern Geological Society, 12th An nual Field Conference,94p.Burnett, W.C., 1977, Geochemistry and origin of phosphorite deposits from off Peru and Chile: Geological Society of America Bulletinv.88,p.813-823. Burnett, W.C., Veeh, V.H., and Soutar,A.1980, U-series, oceanographic and sedimentary evidenceinsupport of recent formation of phosphate nodules off Peru:inBentor, Y.K. ed. Marine Phosphorites -geochemistry, occurrence and genesis, Society of Economic Paleontologists and Mineralogists Special Publication 29,p.61-72. Carr, W.J., and Alverson, D.C., 1959, Stratigraphy of middle Tertiary rocks in parts of west central Florida: U.S. Geological Survey Bulletin 1092,111p.139

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MARSTONSCIENCE APPENDIX A Lithologic legend for stratigraphic columns.; . r'200 _ :.;.,:;•'0 -.ft""..... .... . . ;''. oi. .;:.-. .:".": dolomiteclayeyquartzsandshellbedcalcareousquartz sa'nd . .. . ...... '.\ .....:.CIayey e;t 0 1,0mite : dolomiticquartz sand ,..,clay <. sandyc.lay,'.quartz sand .dolomit icc I ay calcareousclay------.-_.-_.-_.-------.-_.-_.-_.-........ ..........--------,--,--'--'=--=:t---ffi--::.-ffi-::. --------_ ::. -::. . -=--c ---,::/'-=-z--=--c -.• --;"0.-..... ... -.... .. ............ . -..... ... -..... .. 100 1 10 1 Lf0120 130 1501190 180 160'90 sandydolomite 80 calcareousdolomite 70 limestone 60S0..-+--l--I--+--+--l--I-'+0-+--I--+-Y-y'/y y/30 p 20 sandylimestoneclayeylimestonedolomiticlimestonephosphoritechert 10-10 -nosample148

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UNIVERSITYOFFLORIDA/1//111/111////1///111/1///1/11//1////1/1///11////11//1//1///1/131262 07019 4674