The lithostratigraphy of the Hawthorn Group (Miocene) of Florida /

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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
S ` N-- 13751
S------- 1381 I 14219
S.. 1483 *-13769 13744
) ., o .l/--14280 010488 014476 13765
\ -,'14255 ... 14521

S-- 14566 j14376
S, f --L' _11486!1.-.-.i
S --r----. _,.s1 _-14353 ",,
143- 14318 r
F- .147510 L._.-

_-.ri
15127 0)14764
S> 15290
< f 112700 . /r.
-i -, i5312699 5334
N j---'J 15334 0
N J -- r 13534 3489

S L 136761 3676
r L 135510 13490
S....... 13055 \ 1138081
1 I '40 2M 1 ', ..** SWFWMD *
10 0TO o o 40 0o Kilo.tr. 13-2X. 08879 13942 13957
SCALE -MM- 3 MS18
scALE 11541 14883 15261' -'a7.
S4888 13269 13958\
1 3331 *1 13245
o 15205 11570 0 13238 I /--
CORE LOCATION 298*5 0112906
15166 11946
0 14882 14882 11908 112942
-- FGS "W" NUMBER 0 *---115303 12050
15168 j 12
153 3 / 015246
14873 011907 l
153320 I
1l-5289 --
15286 I
015487 0 -.

-- I

Figure 2. Location of cores.

15493

flAY P

k

0 20 40 MILES

0 20 40 KILOMETERS
SCALE

EXPLANATION
* CUTTINGS
* CORES

Figure 3. Cross section location map.

4 o'oo

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
I \

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

LO 0il N IA S S

M AD S 0 N H~p ~d l~~

BA K

i I I I ~ Cch alB io

L FAYETTE

IE

-N- 6

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

LIMITS OF HAWTHORN
GROUP
HAWTHORN GP.
UNDIFFERENTIATED

-v

"-v.

IJ

U NhL N Y \
; RPORD,

A L RC H U 0
I NA

Q\\r~

A/RI I CY N
0r^VT

1- I

oOLWI5a-. IIII

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

I

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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

/

MAD ISON
- I

S ~ U IA A
i24L

ij

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-N-

SCALE cl = 25 FEET
0 20 4(
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LEGEND
CORES

j>W LIMITS OF HAWTH

HAWTHORN GP.
UNDIFFERENTIA1

LO

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ORI

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GROUP

I

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1--7,

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HILL DO OUC

-*
_

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

COUMB'A A

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100
75
50
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I FAY TT "

(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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-80

-90

-100

-110 -

-120

-130

-140

-150

-160__

-170 _

-180-

-190__

-200__

-210

-220

pqW-1376
SRND
SRANO
SAND
PHOSPHATE SAND
DOLOHITE
PHOSPHATE OOLOMITE
PHOSPHATE DOLOMITE
PHOSPHRTE
PHOSPHATE
PHOSPHRTE CLAY
PHOSPHATE CLAY
PHOSPHATE MARKS HEAD FORMATION
PHOSPHATE CLAY
PHOSPHATE CLAY
CLAY
OOLOMITE CLAY

SAND OOLDOITE
SAND
- auD

---------

- -' - -'

-----------
---------------
-----------
I%_-%_
-------
-------
-------
~-------
-------
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'-' '-' '-' -'
'-' '-' '-' '-'
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-------
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-' '-' '-' '-'

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PHOSPHATE
PHOSPHATE
PHOSPHATE
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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~~~~~~_~~__~~ ___~~_

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AWTHORN GROUP

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>9

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

oICOUMB A 0

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0 20 40 KILOMETERS
LEGEND HER ANDO
CORES -

LIMITS OF HAWTHORN
GROUP
P A S
HAWTHORN GP.
UNDIFFERENTIATED

I-4- C-A=

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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.

''

S A

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 -

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

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////

-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

-- ^ -/ _
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- -.-.,, -_, .- -.
.'7" 7

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-.- -.- .-.- -.--.

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
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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-,

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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
8P 0 ~ T7 ,q~0 o0 300
-P 44 2 N N 0 0 40 0 a 0
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I I I'7 '7 7 47 47 r
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I I

40S O 0 0 4 40 MO
C 0 7 7 7 7 7 7 7 7
N N N ("4 0 40 04 40 0
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

'so
'%

a'
0

""t^

25c
300S

1?

Figure

rR 1

TTE

P SCIO

_j_0I

L Ks

20 1

it
TST

E 1 150
T I

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

-28 __ z, z x
PHOSPHATE
PHOSPHI 0
-260 PHOSPHRTE
1- 1 .I PHOSPHPf E cc

PHOSPHATE
-270 _PHOSPHR'E
I I I PHOSPHR;[
PHOSPHRAT
PHPSPHIITE
_r i __i PHOSPHAT

-280 _

-290 -

-300 -

-310 -

-320 -

-330 -

-30 __

-350 _

-360 _

-370 _

-380

-390__

-450 _

-460 _

-470 _

-480 __

-490 -

-500 _

-510 __

-520 _

-530 _

I T~

-T, T.
T. T.

T T
*r-^J'^r--'

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:7:7
:'. : :.:: : ': ...
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7
._*- *.^
.,,.^-. -
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.-,.*.,*.,*
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IB'

PHOSPHATE
PHOSPHATE SA
PAHOPHATE
PHOSPHATE
PHDSPH7TE
SHOT SPOLOE SO
PHOSPHATE
PHOSPHATE

PAAO
PHOSPHATE
PHOSPHATE
SDOLPHAT E
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE

SANO CLAY

0
SRNO
SRMD

SANO CALCITE Z

N 0

CLAY
CLAY A
CALCITE CLAY 0 g

PHOSPHATE Z
PHOSPHATE SAND
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRATE
PHOSPHATE
PHOSPHRATE
CLAY
CLAY
CLAY
CLAY
CLARY
SANO CALCITE
SANO
PHOSPHATE
PHOSPHATE
PHOSPHATE
CLAY
0OLO.ITE
DOLODITE
ODLOHITE
OOLHITIE
SOLOAITE
DOLONITE
SILT DOLOlHITE CLAY
DOLDMITE CLAY

CLAY
CLAY

CLAY
DOLO.ITE

PHOSPHATE OOLOMITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE SOLOHITE
PHOSPHATE DOLOMITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOHITE
PHOSPHATE OOLOMITE
PHOSPHTAE OOLOHITE
PHOSPHATE DOLOHTTE
PHOSPHATE SOLOAHTE
PHOSPHATE OOLOAHTE
PHOSPHATE HOLOHTTE
PHOSPHSPHATE OOLOHE
PHSSPHRTE OOLOH]TE
PHOSPHRTE OOLOHITE
PHOSPHATE
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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---

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LAND SURFACE

CLUY
PHOSPHRFIE
PHOSPHRIE
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHSSPHATE UNDIFFERENTIATED
P US SP fl S

20

10 _

0

-10

-20

-30

-40 __

-50

-60

-70

-80

-90

-100__

-110

-120

-130

-140

PHOSPHlATE SNO
PHOSPHATE SANS
PHOSPHATE SRAN
PHOSPHATE SRND CLAY
PHOSPHRTE SANS
PHOSPHATE SANO
PHOSPHATE SNSO
PHOSPHRTE SRND
POSPHATS"" ARCADIA FORMATION
PSPHRTE ARCADIA
PHOSPHATE
PHOSPHATE
PHOSPHRTE SAND
P OSPHATE SRNO
PHOSPHATE SANS
PHOSPHURT
PHOSPHATE CL 2
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPNATS CLAY
PHOSPHRTE CLRA
PHOSPHATE SAND OOLONITE
PHOSPHATE SOLOHISTE
PHOSPHATE NOL DOLOITE
PHOSPHRTE CLA I
PHOSPHRTE SRNO OOLOM1TE
PHOSPHATE CLRY
PHOSPHATE CLAY
PHOSPHATE SAND
PHOSPHATE SAND
PHOSPHflTE SANS
PHOSPHfTE DOLOMITE CLAY
PHOSPHRTE SRNO
SAND ODLOM1TE CLAY
PHOSPHRIE SRNS
PHNSPHRTE SAND
PHOSPHATE SANS
PHOSPHATE DOLOMITE CLAY
SUNO CLAY
PHOSPHAIE SANS
PHOSPHATE SANS
PHSPHARTE SRND
PHOSPHATE SAND
PHOSPHATE SRNS
PHOSPHARIE IRN
PHOSPHRTE SUNO
SANS
SRND
SAND

..... .....
PHOSPUHAI SUNO CLAU HAWTHORN GROUP
PHOSPHATE SAND CLAY
PHOSPHATE
PHOSPHATE
PHOSPHASTE
PHOSPHASE
PHOSPHATE SUAND
PHOSPHATE SRUO RIER

PHOSPHNRTE SRNS
PHOSPHATE 5RNO
PHOSPHATE SRUO
PPOSPH"TE SANS
PHOSPHATE SNSO
PHOSPHATE SAND CALCITE
PHOSPHATE SANO
PHOSPHATE OOLOMITE
PHOSPHATE SOLOMITE
PHOSPHATE DOLOITE

PHOSPHRTE SA O
PHOSPHATE SANS
PHOSPHATE SANO
PHOSPHATE SAND CLRY
PHOSPHATE SRNO CLAY
PHOSPHATE CLRY
PHOSPHATE SANS
PHOSPHATE SAND
PHOSPHATE SANS DOLOUITE

EEE7

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SPHOSPHTE
PHOSPHATE
-20 PHOSPHTE SN -62
---'2- PHOSPHATE -- tN
PHOSPHATE ,-63
SI HOSPHIE SACO NOCATEE MEMBER
PUOSPURNE CLUY
-20 PHOSPHA TE
-290 POSPHIE -630
PHOSPHATE
PHOSPHATE
S PHOSPHRTE SAND
PHOSPHATE CLAY
-300 0 PHOSPHATE CLAY -640
PHOSPHATE CLRY
Fige 4. R e PHO PHe CLY ....
PDe HOSPHATE CLAY( l A A.
SPHOSPHRTE CLAY 507
-310 __ PHOSPHATE CLRAY ,
S PHOSPHATE SRHO CRLCIIE .- I-
pHOSPHATE ,- | I SRNO
PHI SPHATE 1 SANO

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

~--

-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

-5B0

-590

-600 -

-610

SANS
SUNO

SRNO
SANO
SAND
PHOSPHRTE SAND
PHOSPHATE
SAND
SlNO
SRNO
SUNO
SUNS
SAHO
SANS

SAUN
SRAN CLAY

SAND

PHOSPHATE
PHOSPHArE 15303
PHOSPHATE SANO CLAY
PHOSPHRTE CLRY
PH SPHRTE CLRY
PHOSPHART CLRY
PHOSPHATE CLAY
PHOSPHATE SANL CALCITE
PHOSPHRTE
PHOSPHRTE
PHOSPHRTE
PHOSPHATE SRNO DOLOMTE
PHOSPHRTE SRNO
PHOSPHA TE
PUNOSPHRIE SRNO
PHOSPHATE SRNO
PHOSPHRIE
PHOSPHRIE
PHOSPHRVE
PHOSPH RTE SN
PHOSPHATE ODLOUITS
PHNSPUDTS oLUO.S! ARCADIA FORMATION
PHOSPHATE CLAY
PHOSPHATE
PHOSPHATE SAND
PHS PHRTE SRND
PHOSPH TE
PHOSPHAlTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHS E NOCATEE MEMBER
PHOSPHRTE n Ic M
PHOSPHATE SANO
PH OSPHATE SAND
PH SPHRTE SUNO
PHOSPHRTE
PHOSPHRTE
PHOSPHATE
PHOSPHATE
PHUNP .. E
PHOSPHATE
PHOSPHATE
PHOSPHATE CLAY HAWTHORN GROUP .

SAND
SANS

SAUN SUWANNEE LIMESTONE

; "

I

I

I

PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHATE
PUOSPHRTE
PHOSPHRTE SAND
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
PHOSPHA TE
PHOSPHRTE
PHOSPHATE
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

In_ vL_^_ ---- -- _

S" NDIN RIVER

M8 7 -4 m 1 5
Q .-- l / ,00 1-1 AP R _E E OBEE
M A N20 T E K I G H LL A ND

i.-u 50. -o---e- -Mme

SN -------- O --

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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LAND SURFACE

UNDIFFERENTIATED

PHOSPHATE

POSP'TE HAWTHORN GROUP
PHOSPHRTE
PHOSPHTE
PHOSPHATE

POSPHATE
POSPH ATE
PHOSPHATE
PHOSPHATE

PHOSPHRATE
PHOSPHATE
SAWl
PHOSPHATE
PHOSPHATE
CLRAY

Z
CLAY -

PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY IC
PHOSPHATE CLAY 0
PHOSPHRIE CLAY O
PHOSPHATE CLA U
PHOSPHATE
PHOSPHATE -
PHOSPHRIE U
PHOSPHATE >
PHOSPHATE
PHOSPHATE rE
PHOSPHMTE
PHOSPHATE U
PHOSPHATE
PHOSPHRIE
PHOSPHATE
PHOSPHATE
PHOSPHATE -
POSPHATE
OOLOMITE
SANO

SANO CRLCITE
PHOSPHATE
PHOSPHATE
PHOSPHRTE
PHOSPHRTE
PHOSPHRTE
SRND CRLCITE
PHOSPHARTE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE

PHOSPHATE SATm CLAY
SAND
SANa
SAWO
PHOSPHATE
PATSPHRTE SAWO
PHOSPHATE STMO

PHOSPHATE SATW
PHOSPHATE SRMA
PHOSPHATE SARN
PHOSPHATE SAWO
PHOSPHARTE SAN0

SRHO

PHOSPHATE SLAO
PHOSPHATE S5RO
PHOSPHRTE SRNO I
PHOSPAAIE AND

PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHATE CLAY I
PHOSPHATE CLAY
PHOSPHATE CLAY
PHOSPHRTE SCLAY
PHOSPHATE CLAY
PHOSPHRTE CLAY
PHOSPHATE CLTA I
PHOSPHATE RC AT
PHOSPHATE SAMO
PHOSPHATE SATO
PHOSPHATE CAY
PHOSPHATE SAYD

PHOSPHATE SRNO
PHOSPHATE SAWN
PHOSPHATE SRANO
PHOSPHRTE SRO CLR
PHOSPHATE SANO CLAY
PHOSPHATE SRND
PHOSPHATE CLRAY
PHOSPHATE CLRAT
PHOSPHATE SfNo
PHOSPHATE SAND
SRANO
'YnqP.arr

SAN0
SAWN
SAHS
SA 0

SAT
SA I
AHO

2 0
U.
I. 4
PHOSPHATE 3
PHOSPHATE
PHOSPHA 1
PHWSPH.IE
PH0SPHIpTE
PHOSPHRATE c

PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHATE
PHOSPHRTE

-510 -

-520

-530

-280 -

-290 _

-300 -

-310 -

-320 _

-330 -

-3'0 _

-350 _

-360 _

-370 -

-380 -

-390 -

-400 __

-410 -

-420 -

-430 _-

PHOSPHATE

PHOSPHATE
PHOSPHATE
PHOSPHAE SAWO
PHOSPHRT
..!= .

PEISPAITE

ST:t
T T

Ty:::I:?: ::
T T

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^y~-,I

"SUWANNEE" LIMESTONE

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
SAHO
SOAW
PHOSP ATE
PHOSPHATE
PHOSPHARTE

PHOSPHATE
PHOSPHATE
PHOSPHCALCITE

LU
CLAY CLAY
SAW

SRO ALCITE Z

CLAY 4
CLAY 1

CLAY I

CALCITE CLAY 0
AHOSPHATE Z
PHOSPHATE SANO
PHOSPHATE
PHOISPHIATE
PHSPHATE

CLIAY
CLRY ATE

CLAY
SLHO LCIT E
PHOSPHATE

PHOSPHATE
PHOSPHRTE

CLAY
OOLOHTE

PHOSPHATE
OOLOPHTE

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
PHOSPHATE OOLO TE
PHOSPHATE
PHOSPHATE
PHOSPHRTE

PHOSPHATE

" ' ' '"""'"""

I

---
-------
-------
r-------

----

----
- - - -

----

-------
-------
-------
~-p-p-p

(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.

	Front Cover
	Front Matter
	Title Page
	Letter of transmittal
	Table of Contents
	Abstract
	Acknowledgement
	Introduction
	Method of investigation and previous...
	Geologic structure
	Hawthorn formation to group status:...
	North Florida
	South Florida
	Eastern Florida Panhandle
	Hawthorn group mineralogy
	Geologic history
	Paleoenvironments
	Hawthorn group gamma ray log...
	Summary
	Conclusions
	References
	Appendix A: Lithologic legend for...
	Back Cover
	Spine

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