Late oligocene to pliocene evolution of the central portion of the south Florida platform

DEPARTMENT

STATE OF FLORIDA
OF ENVIRONMENTAL PROTECTION
David Struhs, Secretary

DIVISION OF RESOURCE ASSESSMENT AND MANAGEMENT
Edwin J. Conklin, Director

FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief

Bulletin No. 65

LATE OLIGOCENE TO PLIOCENE EVOLUTION
OF THE CENTRAL PORTION OF THE
SOUTH FLORIDA PLATFORM:
MIXING OF SILICICLASTIC AND CARBONATE SEDIMENTS

By

Thomas M. Missimer

Published for the

FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
2002

METRIC CONVERSION FACTORS

To eliminate duplication of parenthetical conversion of units in the text of reports, the
Florida Geological Survey has adopted the practice of inserting a tabular listing of conver-
sion factors. For readers who prefer U.S. units to the metric units used in this report, the
following conversion factors are provided.

MULTIPLY BY TO OBTAIN

meters (m) 3.281 feet
kilometers (km) 0.6214 miles

DEPARTMENT

STATE OF FLORIDA
OF ENVIRONMENTAL PROTECTION
David Struhs, Secretary

DIVISION OF RESOURCE ASSESSMENT AND MANAGEMENT
Edwin J. Conklin, Director

FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief

Bulletin No. 65

LATE OLIGOCENE TO PLIOCENE EVOLUTION
OF THE CENTRAL PORTION OF THE
SOUTH FLORIDA PLATFORM:
MIXING OF SILICICLASTIC AND CARBONATE SEDIMENTS

By

Thomas M. Missimer

Published for the

FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
2002

Printed for the
Florida Geological Survey

Tallahassee
2002

ISSN 0271-7832

II

PREFACE

FLORIDA GEOLOGICAL SURVEY

Tallahassee, Florida
2002

The Florida Geological Survey, Division of Resource Assessment and Management,
Department of Environmental Protection, is publishing as its Bulletin 65, Late Oligocene to
Pliocene Evolution of the Central Portion of the South Florida Platform: MIi.xing of
Siliciclastic and Carbonate Sediments, by Thomas M. Missimer. This report summarizes
the results of a multi-year investigation of the lithostratigraphy, paleoenvironments, and
chronostratigraphy of the upper Paleogene and Neogene sediments underlying the central
part of southern Florida. The data presented will be useful to scientists, planners, and cit-
izens in understanding the stratigraphy and geologic history of the strata containing
Florida's groundwater aquifers.

Walter Schmidt, Ph.D.
State Geologist and Chief
Florida Geological Survey

iv

TABLE OF CONTENTS

Page
.. .1

Abstract .....
Acknow ledgem ents ........................................
In trodu action .............................................
Statem ent of Problem s ..................................
M ethods of Investigation ................................
Introduction ........................................
Lithologic and Stratigraphic Investigations ...............
Chronostratigraphy ..................................
Paleontological Age Determinations .....................
Seismic and Sequence Stratigraphy .....................
Mixed Siliciclastic and Carbonate Sediments of the Hawthorn Group,
South Florida Platform .................................

Introduction ..............................
M ethods .................................
Previous Investigations .....................
Geologic and Stratigraphic Setting ............
Stratigraphy ............................
Formation Boundaries ....................
Suwannee Arcadia .................
Arcadia Peace River ................
Peace River Tamiami ...............
Age of the Hawthorn Group and Bounding
Variations in Composition of Sediment .........
Total Carbonate Variation: Results .........
Variations in Carbonate Mineralogy .........
Introduction ............ .........

. . .. .3
..... . .3
. . .. . .5

. . . . .6
..... . .6
........ .9
..... . .9

....... .10
.......10
. .. . .. 11
....... .12
. . ....15
.......15

Formations

Large Scale Variation in Dolomite Occurrence

Variation in
Variation of

Carbonate Mineralogy in the Arcadia Formation
Carbonate Mineralogy in the Peace River Formati

Variation in Francolite (Phosphorite) Occurrence . .
Non-Carbonate Sediment Composition Variation ........
Introduction ................................
Variation in Quartz Sand Occurrence ............
Variation in Clay Occurrence ...................
Variation in Glauconite Occurrence ..............
Composition Influence on Interpretation of Sediment Facies .
Introduction .....................................
Siliciclastic Components ...........................
Q u artz . . . . . . . . . . . . . . . . . . .
Clay ................. ...................
Other Non-Carbonate Components ...............
Carbonate Components ............................
Introduction ................................
G rainstone .................................
P ackstone ..................................
W ackestone .................................

. . . . . .19
........ 22
........ 22
on ....... 22
........ 23
........ 26
..........26
........ 28
. . . . . .3 1
........ 32
. .. . .. .32
.. . .. . ..32
. . .. . . .32
.. . .. . ..32
.......... 34
........ 35
. . .. . . .35
. . .. . .. .35
. . .. . .. 36
. . .. . .. 3 7
. . .. . .. 37

II

M udstone ....................
Faunal Occurrence and Interpretation of Water Depth
Introduction ...............................
Faunal Characteristics and Water Depth ........
Description of the Hawthorn Group Subfacies .......
Introduction ...............................
Subfacies Descriptions .......................
Introduction ..........................
Subfacies 1 ...........................
Subfacies 2 ...........................
Subfacies 3 ...........................
Subfacies 4 ...........................
Subfacies 5 ...........................
Subfacies 6 ...........................
Subfacies 7 ...........................
Subfacies 8 ...........................
Subfacies 9 ...........................
Subfacies 10 ..........................
Subfacies 11 ..........................
Subfacies 12 ..........................
Subfacies 13 ..........................
Subfacies 14 ..........................
Interpretation of Subfacies ......................

Introduction .........

Discontinuity Deposits, Subfacies 1 ............
Restricted Facies, Subfacies 3, 4, 5, 6, and 7 .....

Beach Facies: Laminated Sands, Grainstones and Packstor
Quartz Sand, Subfacies 2 ......................
Inner Ramp Facies, Subfacies 8 and 9 .................
Outer Ramp Facies, Subfacies 10, 11, 12, and 13 ........
Inner and Outer Ramp, Subfacies 14 .................
Discussion ...................................... ...
Depositional Model for the Hawthorn Group on the
South Florida Platform ........................
Timing of the Transition from Pure Carbonate to Mixed
Carbonate/Siliciclastic Sediment Deposition
on the South Florida Platform ..................
Siliciclastic and Carbonate Sediment Mixes and the
Process of Sediment Mixing ....................
Late Paleogene and Neogene Chronostratigraphy of the
Central Part of the South Florida Platform .............
Introduction .......................................
M ethods ......................... .. ... ............
Strontium and Stable Isotope Sample Preparation .......
Paleomagnetic Measurements .......................
Foraminifera .......................................
Introduction ........... ........ ... .........
Age of the Arcadia Formation Based on Foraminifera ...
Age of the Peace River Formation Based on Foraminifera .

tes with

. . . . . . . . .. 7 1

. . . . . . . . .. 79

. . . . . . . . .. 8 0

. . . . . . .. . 8 1
................ 81
. . . . . . . . 8 2
. . . . . . . . .. 8 2
. . . . . . . . .. 8 3
................ 83
................ 83
. . . . . . . . .. 8 3
. . . . . . . . 8 4

.

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

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

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

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

Calcareous N annofossils .......................................
Introduction .............................................
Calcareous Nannofossil Stratigraphy of Core W-16242 .............
Calcareous Nannofossil Stratigraphy of Core W-16523 .............
Discussion of Formation Ages from the Calcareous Nannofossil Data .
Diatom s ..................................................
Strontium -Isotope Stratigraphy .................................
Introduction ............................................
Results .................... ...... .....................
Strontium-Isotope Age Constraints on Stratigraphic Units ............
Introduction .............................................
Age of the Suwannee Limestone Based on Strontium Isotopes .......
Age of the Arcadia Formation Based on Strontium Isotopes .........
Age of the Peace River Formation Based on Strontium Isotopes .....
Age of the Tamiami Formation Based on Strontium Isotopes ........
M agnetostratigraphy .........................................
Introduction ............................................
Laboratory Methods ......................................
Rock M agnetic Analysis ................................
Paleomagnetic Methodology and Sample Classification ........
Results ............................................. ...
Magnetic Remanence Intensity ..........................
Rock M agnetic Results ..............................
Coercivity Spectral Data ............................
ARM Results ....................................
Paleom agnetic Results ......................................
Magnetostratigraphy and Age Implications ........................
Magnetostratigraphy and Age of the Suwannee Limestone .........
Magnetostratigraphy and Age of the Arcadia Formation ...........
Magnetostratigraphy and Age of the Peace River Formation ........
Magnetostratigraphy and Age of the Tamiami Formation ..........
Magnetostratigraphy and the Ages of the Caloosahatchee and
the Fort Thompson Formations ..........................
Oxygen and Carbon Isotope Stratigraphy .........................
Introduction ......................................... ...
Oxygen Isotope Variations and Age Considerations ...............
Carbon Isotope Variations and Age Considerations ...............
Discussion .................. ...............................
Ages of late Paleogene and Neogene Stratigraphic Units ...........
Introduction ........................................
Suwannee Lim estone ..................................
Hawthorn Group-Arcadia Formation ......................
Hawthorn Group-Peace River Formation ...................
Tam iam i Form ation ...................................
Caloosahatchee Form ation ..............................
Conclusions............ .....................................
Late Paleogene and Neogene Sea Level History of the South Florida Platform
Based on Sequence Stratigraphy ..............................
Introduction ..............................................

....... 87
........87
....... 87
....... 89
....... 89
........89
....... 92
........92
........92
....... 97
........9 7
...... 100
...... 100
...... 104
...... 106
...... 106
.......106
.......107
...... 107
...... 107
.......108
...... 108
...... 116
...... 116
.......116
...... 116
...... 116
...... 123
...... 123
...... 124
...... 125

...... 126
...... 127
.......127
...... 127
...... 130
.......134
...... 134
.......134
...... 134
...... 137
...... 138
...... 139
...... 140
.......141

...... 142
.......142

Regional Lithostratigraphy Patterns of the Arcadia and Peace River Formations .142
Sequence Stratigraphy ..............................................146
Definitions ................ ......................................146
Recognition of Supersequence, Sequence, and Sediment Packages
in the Arcadia and Peace River Formations ........................ 149
Sequence Stratigraphy of Arcadia Formation ........................ 149
Introduction ................. ............................. 149
Supersequence A ................. ...........................150
Supersequence B ................. ...........................150
Supersequence C ................................... ...........157
Supersequence D ..................................... ........157
Sequence Stratigraphy of the Peace River Formation .................... .157
Introduction ................. ............................. 157
LPR Supersequence ..........................................157
UPR Sequence ...............................................157
Sea Level History of the South Florida Platform from
Late Oligocene to Early Pliocene ................................ 161
Introduction ..................... .................................161
Sea Level History ..................................................161
Comparison of the South Florida Ramp Sea Level Curve to the
Haq et al. (1988) Global Sea Level Curve .......................... 164
Discussion ...................................... ................... 165
R eferences ........................................................ 167

FIGURES
Figure

1. Map showing the southern part of the Florida Platform, the land area, shelf area,
and the principal area of investigation ................................. .4

2. Map of South Florida showing the location of all cores and wells used in the
investigation ............................................ ..........8

3. A general stratigraphic section for the study area based on the previous
work of Scott (1988) .................................... ............ 13

4. Variation of total carbonate percentage with depth in core W-16242
based on 760 measurements ......................................... 18

5. Variation of total carbonate percentage within the Arcadia Formation
in core W-16242 ................................................... 20

6. Variation of total carbonate percentage in the Peace River Formation
in core W-16242 ................................................... 21

7. Calcite percentage with depth in the Peace River Formation in core W-16242 ..... 24

8. Dolomite percentage with depth in the Peace River Formation in core W-16242 .. .25

9. Non-carbonate sediment percentage with depth in core W-16242
based on 760 analyses .................................... ...........27

10. Non-carbonate sediment percentage with depth in the Arcadia Formation
in core W -16242 ..................................................29

11. Non-carbonate sediment percentage with depth in the Peace River Formation
in core W -16242 ..................................................30

12. Subfacies 1. Discontinuity deposits within the Hawthorn Group ............... 49

13. Subfacies 2. Quartz sand and shell deposits in the Peace River Formation in
core W-17115 ....................................................50

14. Subfacies 3. Example ofbrecciated texture in subfacies 3 from core W-17115
at a depth of 236.77 to 236.86 m (776.8 to 777.1 ft) ...................... .51

15. Subfacies 4. Mixed siliciclastic/carbonate deposits from Estero Bay, Florida and
an example of subfacies 4 from the Peace River Formation ................. 52

16. Subfacies 5. Laminated clay ........................................... .54

17. Subfacies 6. Example of subfacies 6 in core W-16242 from a depth of
131 to 133.5 m .......................................... .......... 55

18. Subfacies 8 in the Arcadia Formation ................................... 56

19. Examples of subfacies 9 in core W -16242 ................................. .58

20. Examples of subfacies 10 from the Arcadia Formation in core W-16242 ......... .59

21. Subfacies 11. Examples of the relatively deep water mollusk Hyotissa
subfacies from the Arcadia Formation in core W-16242 .................... .60

22. Examples of subfacies 12 and 13 from the Arcadia Formation in core W-17115 ... .62

23. High-resolution seismic reflection profile (modified boomer source) in the
Caloosahatchee River illustrating subfacies 14, labeled as
Peace River Formation .............................................63

24. Diagram showing a typical graded bed sequence in the Peace River Formation
in core W-16242 from a depth of 208 to 213 feet ......................... .64

25. Diagram showing the relative water depths of the 14 primary subfacies described
from shallow to deep water .......................................... 76

26. South Florida mixed carbonate/siliciclastic ramp .......................... .77

27. A profile across the Suwannee Limestone shallow-water carbonate ramp displaying
the dominant occurrences of major grain types, sedimentary structures, and
biological and textural attributes .................................... .78

28. Distribution of planktonic foraminifers and calcareous nannofossils in
well L-1849 adjacent to seismic line connecting to core W-16242 ............. .84

29. Distribution of planktonic foraminifers and calcareous nannofossils in
well L-1984 near core W -16523 ...................................... .85

30. Correlation of well L-1984 to core W-16523 along section D-D' ................ .86

31. Calcareous nannofossil selected species range chart for core W-16242 ........... 88

32. Calcareous nannofossil selected species range chart for core W-16523 ........... 90

33. 7"Sr/16Sr ratios with depth in core W-16242 showing a general reduction
w ith age ...................................... ................... 96

34. 87Sr/6Sr ratios with depth in core W-16523 ................. ............ .98

35. "'Sr/6Sr ratios with depth in core W -17115 ............................... .99

36. Age ranges of strontium-isotope samples with depth in core W-16242 .......... 101

37. Age ranges of strontium-isotope samples with depth in core W-16523 .......... 102

38. Age ranges of strontium-isotope samples with depth in core W-17115 .......... 103

39. Strontium-isotope ratios versus age range using the Berggren (1985) time scale .105

40. Magnetic susceptibility with depth in core W-16242 ........................ 109

41. Natural remanent magnetization, magnetization after exposure of samples to a
30 mT Alternating Field, and magnetization after thermal treatment of samples
to 300C with depth in core W -16242 .................................. 111

42. J/Jo plots for class A samples from core W-16242 .......................... 112

43. J/Jo plots for class B samples from core W-16242 .......................... 113

44. J/Jo plots for class C samples from core W-16242 .......................... 114

45. J/Jo plots for class D samples from core W-16242 .......................... 115

46. Coercivity spectral analysis plots of mixed carbonate/siliciclastic sediment
samples from core W-16242 ........................................ 117

47. Coercivity spectral analysis plots of mixed carbonate/siliciclastic sediment
samples from core W-16242 ........................................ 118

48. ARM plots of mixed carbonate/siliciclastic sediments from core W-16242 ....... .119

49. ARM plots of mixed carbonate/siliciclastic sediments from core W-16242 ....... .120

50. Representative vector component plots of class A, B, C, and D samples collected
from mixed carbonate and siliciclastic sediments of core W-16242 ........... 121

51. Magnetic inclination versus depth in core W-16242 ........................ 122

52. A composite benthic 6180 record of the world ocean from Miller
and Fairbanks (1985) ...............................................128

53. Variation of stable oxygen and carbon isotopes with depth in core W-16242 ..... 129

54. Variation of stable oxygen and carbon isotopes with depth in core W-16523 ..... .131

55. Variation of stable oxygen and carbon isotopes with depth in core W-17115 ..... .132

56. A comparison of the stable oxygen isotope data from cores W-16242, W-16523,
and W-17115 to the generalized late Paleogene and Neogene variation from
the A tlantic O cean ................................................ 133

57. A comparison of the stable carbon isotope data from cores W-16242, W-16523,
and W-17115 with the late Paleogene and Neogene data from the
Atlantic Ocean ...................................................135

58. Comparison of the new chronostratigraphy in this paper to previous age estimates
for the Neogene and late Paleogene formations on the South Florida Platform .136

59. Map of southern Florida showing locations of cores, wells, and cross-sections .... 143

60. Section A-A' from central Charlotte County to Marco Island .................. 144

61. Section B-B' from Captiva Island to west-central Charlotte County ........... .145

62. Block diagram of the Hawthorn Group in the study area from Charlotte County
to Collier County based on sections A-A' and B-B' ...................... .147

63. Section from Captiva Island (core W-16242) to north Palm Beach County ....... 148

64. Some examples of the 59 sediment packages found in the Arcadia Formation .... 155

65. Some selected examples of sediment packages from the Peace River Formation .159

66. Comparison of the new chronostratigraphy in this paper to previous age estimates
for the Neogene and late Paleogene formations on the South Florida Platform .162

67. Sea-level curve for the South Florida Platform from late Oligocene to early Pliocene
with a comparison to the global sea-levelcurve of Haq et al. (1988) .......... 163

TABLES

Table

1. W ell and Core Information ............................................. .7

2. Comparison of Total Carbonate Percentages by Formation in the
South Seas Plantation Core (W-16242) ............................... 17

3. Comparison of the Calcite and Dolomite occurrence in the Arcadia Formation
In Cores W-16242, W-16523, and W-17115 (North to South) ................ 23

4. Occurrence of Glauconite in Core W-16242 .......................... .. 33

5. Subfacies Type Descriptions and Microfacies Grouped Within Each Subfacies .... 40

6. Subfacies Types, Water Depths, and Probable Depositional Environments ....... 72

7. 87Sr/ 6Sr Measurements and Calculated Ages of Samples from Cores W-16242,
W -16523, and W -17115 ................. ................ ......... 93

8. Possible Ages of Selected Neogene and Late Paleogene Formations on the
South Florida Platform ................ ................. ...... 137

9. Sediment Packages in the Arcadia Formation ...........................151

10. Thickness of Sequences and Number of Sediment Packages within Sequences .. .154

11. Sediment Packages in the Peace River Formation ......................... 158

12. Summary of Global Sea Level Events and Effects on the Florida Platform ..... .161

PLATES
(see separate pdf files on CD)

1. Core W-16242 geology, composition, paleomagnetic and isotope data.

2. Core W-16523 geology, composition and isotope data.

3. Core W-17115 geology, composition and isotope data.

4. Chronostratigraphy of core W-16242.

5. Arcadia Formation sequence stratigraphy.

6. Peace River Formation sequence stratigraphy.

BULLETIN NO. 65

LATE OLIGOCENE TO PLIOCENE EVOLUTION
OF THE CENTRAL PORTION OF THE SOUTH FLORIDA PLATFORM:
MIXING OF SILICICLASTIC AND CARBONATE SEDIMENTS

By
Thomas M. Missimer, P.G. No. 144

ABSTRACT

Synchronous deposition of carbonate
and siliciclastic sediments occurred on the
South Florida Platform during the late
Oligocene to early Pliocene, producing a
large number of complex mixed carbon-
ate/siliciclastic lithologies, some perhaps
unique to the region. All 14 defined subfa-
cies contain a mix of carbonate and silici-
clastic sediments along with phosphorite
grains. Only a small percentage of the
stratigraphic section contains sediments
with a solely carbonate or solely siliciclastic
composition. Transitions between subfa-
cies are both transitional and abrupt. The
hypothesis that carbonate and siliciclastic
mixed sediment sequences show mostly
abrupt boundaries (Mount, 1984) is not
supported.
Based on the interpretations of the
depositional environments for the 14 subfa-
cies found in the Hawthorn Group, the
entire stratigraphic section was deposited
on a ramp with a high percentage of the
sediments containing a carbonate mud
component. Homoclinal ramp deposits are
characterized by low, rather uniform slopes
from shallow water into the basin with con-
tinuous grading of sediment types from
nearshore sands to deep water sands and
muds. Many described ramp deposits con-
tain little or no mud in the open inner or
outer ramp subfacies, such as the eastern
Florida ramp, the current west Florida
ramp, and other wave-dominated ramps,
such as southern Australia, (James and
Von der Borch, 1991); (James et al., 1994;
Boreen and James, 1993). Modern ramp
deposits bordering restricted water bodies,
such as the Arabian Gulf, do contain a belt

of muddy open-water inner and outer ramp
deposits. Ancient epeiric sea ramp deposits
also produced wackestone and mudstone
deposits in the open shelf area. Therefore,
the southern Florida ramp deposited dur-
ing the late Oligocene to early Pliocene was
more similar to a restricted-sea ramp than
a wave-dominated ramp.
A new chronostratigraphy was devel-
oped for the upper Paleogene and Neogene
sediments on the central part of the South
Florida Platform. The ages of the
sediments were determined by the com-
bined use of calcareous nannofossils, plank-
tonic foraminifera, diatoms, strontium-iso-
tope stratigraphy, magnetostratigraphy,
and carbon and oxygen isotope variations.
Based on these integrated dating tech-
niques, the following age constraints using
the Berggren et al. (1995b) time scale were
placed on the formations in this region: the
Suwannee Limestone is constrained
between 33.7(?) to 28.5 Ma, the Arcadia
Formation of the Hawthorn Group is con-
strained from between 26.5 to 12.4 Ma, the
Peace River Formation of the Hawthorn
Group is constrained between 11(?) to 4.3
Ma, the Tamiami Formation is constrained
between 4.29 to 2.15 Ma, and the
Caloosahatchee Formation is constrained
from 2.14 to 0.6 Ma.
Eleven third-order sea-level events
were recognized in the stratigraphic record
between the late Oligocene and early
Pliocene. With the exception of the early
Miocene sea-level events, the remaining
seven events corresponded closely in time
with the global sea-level curve of Haq et al.
(1988). However, the depth of flooding on
the Florida Platform differed from the rela-
tive depths predicted by the Haq curve.

FLORIDA GEOLOGICAL SURVEY

During the late Aquitanian and
Burdigalian, Haq observed three third-
order sea-level events, but four events were
recorded in the cores studied. It is hypoth-
esized that two of the events correlate to
event 2.1 of Haq et al. (1988), which is a
revision of the global curve.

ACKNOWLEDGEMENTS

This research effort was conducted in
cooperation with the Florida Geological
Survey. All research efforts are accom-
plished by a team of scientists and not by
any single individual. Therefore, it is
appropriate to acknowledge and thank
many individuals and organizations that
contributed to the information and ideas
presented in this report.
For the guidance, criticism, and direc-
tion of this research effort and advice over
many years, I thank Dr. Robert N.
Ginsburg of the University of Miami. Dr.
Ginsburg is responsible for the develop-
ment of the thought process used in the
organization and ideas explored in this dis-
sertation and for improvement of my writ-
ing skills.
I thank Dr. Donald F. McNeill for his
assistance in the paleomagnetic data collec-
tion and analysis process and in the devel-
opment of the chronostratigraphy as well
as reading the first draft. Dr. Peter Swart
provided much needed input in the isotope
data collection and analysis. Dr. Gregor
Eberli helped in the analysis of the seismic
reflection data and provided much needed
criticism on sequence stratigraphic con-
cepts and terminology. Dr. Thomas M.
Scott helped reassess the stratigraphy and
provided sound criticism on terminology.
Perhaps the most fundamental infor-
mation provided was the continuous cores
collected at South Seas Plantation,
Koreshan, and Marco Island. This infor-
mation was provided by the Florida
Geological Survey. I thank Dr. Walter
Schmidt, State Geologist, Dr. Thomas
Scott, Assistant State Geologist, and their
fine staff for all of the help I received. All

of the strontium isotope analyses were per-
formed at the geochronology laboratory,
University of Florida under the direction of
Dr. Paul Mueller. Many samples were col-
lected from the cores for identification and
analysis of calcareous nannoplankton. This
work effort was conducted by Mr. J.
Mitchner Covington of Tallahassee, former-
ly with the Florida Geological Survey.
Approximately 125 km of continuous
seismic reflection profiles were obtained
using the Rice University Research vessel,
the R/V Lonestar. I thank Dr. John
Anderson of Rice University for his assis-
tance in obtaining the data and his review
of the interpretation. Another approxi-
mately 500 km of seismic reflection profile
data were obtained from the files of the
U.S. Geological Survey, Water Resources
Division in Fort Myers, Florida. I thank
Mr. Henry LaRose for his assistance in
obtaining these data.
Considerable assistance was provided
by many faculty members at the University
of Miami, Rosenstiel School of Marine and
Atmospheric Science. Dr. Larry Peterson
provided the use of his laboratory for analy-
sis of total carbonate and provided much
advice on global oceanographic data during
the Miocene. Dr. Leslie Melim provided
help using the X-ray diffraction equipment
and advice on data analysis. Dr. Robert
Warzeski provided critical reviews of many
concepts involving the interpretation of the
seismic reflection data and geophysical
logs. Dr. Andreas Pisera of the University
of Warsaw, Poland assisted in the identifi-
cation of various bryozoa and red algae in
thin sections. Dr. Donald Moore provided
considerable assistance in the interpreting
water depth data for mollusks and infor-
mation on depositional environments of
bryozoans.
I thank the Marine Geology and
Geophysics Division, Rosenstiel School of
Marine and Atmospheric Science for use of
the equipment. Mr. Allan Buck provided
much assistance in use of the equipment.

BULLETIN NO. 65

INTRODUCTION

STATEMENT OF PROBLEMS

There is considerable interest in the
evolution of carbonate platforms to mixed
carbonate-siliciclastic environments (Byers
and Dott, 1981; Doyle and Roberts, 1988;
Budd and Harris, 1990; Harris and
Lomando, 1991). Since mixed carbonate-
siliciclastic sediments tend to develop in
shoaling-upward sequences, they can pro-
vide insights into both sea-level events and
sequence stratigraphy (Sarg, 1988).
Because of its relative tectonic stability, the
Florida Platform is an exceptionally good
geographic area to study both the changes
in sediment composition with time and the
sea-level events which caused the changes.
The principal questions posed for research
in this report relate to the evolution in sed-
iment deposition with time on the central
part of the South Florida Platform (Figure
1) during Oligocene to Pliocene time.
Throughout this publication the term
"South Florida Platform" will be used to
describe the area of Florida lying south of
an east-west line running approximately
through Lake Okeechobee as commonly
used in geographic references on Florida
(see Figure 1).
A series of fundamental questions to be
answered include: where in the strati-
graphic record does the occurrence of silici-
clastic sediment begin, what rock types
were deposited and in what patterns, and
how do the mixed carbonate/siliciclastic
rock types relate to water depth and sea-
level change? In order to answer these
questions, the regional stratigraphic frame-
work of the Florida Platform was assessed
and compared to the changes in lithologies
observed in both cores and shallow, high-
resolution seismic reflection profiles, and
related global oceanographic events in real
time.
The first group of questions to be posed
involves the detailed description of the
lithologies found in the Hawthorn Group of

South Florida. Is the carbonate-siliciclastic
transition on the South Florida Platform
gradational or abrupt? What unique or
unusual sediments occur because of the
mixing of numerous lithic components of
diverse origins and what processes pro-
duced these sediment types?
Evolution of the sediment types on the
South Florida Platform involves correla-
tions to global events, which requires
knowledge of deposition in absolute time.
When did the major change occur on the
South Florida Platform causing the transi-
tion from carbonate to mixed siliciclastic
and carbonate sediments? Based on known
regional events, another question involving
time is: Was the closure of the Gulf Trough
or Apalachicola Embayment (Schmidt,
1984) by siliciclastic sediment infill the sig-
nificant event allowing movement of the
siliciclastic sediments to the south in the
late Oligocene-early Miocene or were the
siliciclastic sediments already mixed with
the carbonates earlier in time (mid-
Oligocene sea level event)? Finally, there
has been a continuing debate (Scott, 1988;
Missimer, 1992a) over the ages of the
Arcadia (Hawthorn Group), Peace River
(Hawthorn Group), Tamiami, and
Caloosahatchee Formations for many
years. Therefore, what are the ages of
these formations?
A stratigraphic technique that can be
used to organize complex sediments into a
reasonable framework for study and com-
parison is sequence stratigraphy (Van
Wagoner et al., 1990; Loucks and Sarg,
1993). Based upon the seismic reflection
data, core data and well logs studied, can
the sediments of the Hawthorn Group be
placed within a sequence stratigraphic
framework for comparison with regional
and global sediments of equivalent ages
located in other areas or to the global eusta-
tic sea-level curve? Because of the impor-
tance of these sediments for the develop-
ment of water supplies and other economic
considerations, a series of questions related
to mapping of sequences arises. Do third-

FLORIDA GEOLOGICAL SURVEY

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BULLETIN NO. 65

order cycles occur in the early to middle
Miocene sediments and, if so, are they are-
ally extensive, can these cycles be mapped
on a regional basis, and can the cycles be
distinguished and mapped in high-resolu-
tion seismic reflection profiles?
Global and regional sea-level varia-
tions through time are of fundamental
importance in producing changes in sedi-
ment types that create the stratigraphic
record (Vail et al., 1977a; 1977b). There are
both global and regional events that cause
changes in the relative position of sea level,
causing the magnitude of the changes to be
quite variable at any given geographic loca-
tion and producing different sediment
types and thicknesses for the same time
period (Vail et al., 1991). It is important to
study stratigraphy in comparison to an
overall global framework in order to com-
pare one region to another. Based on the
observations made on South Florida
Platform sediments, 1) does the global sea-
level curve of Haq et al. (1987) provide an
accurate model for the history of the area?,
and 2) can the global sea-level curve be
refined based on new information obtained
from the South Florida Platform for the
late Oligocene-Miocene time frame?
A fundamental concept with regard to
mixed carbonate/ siliciclastic sediment that
remains to be resolved is the belief amongst
many geologists that the stratigraphic con-
tacts between carbonate and siliciclastic
sediments are generally abrupt (Mount,
1984). This supposition is in conflict with
Walther's Law, which suggests that within
a vertical succession containing mixed
sediments, records of gradational transi-
tions between carbonate and siliciclastic
faces should commonly occur. Perhaps the
concept of limited mixing of end-member
compositions is real or maybe the mixed
sediment sequences have not been studied
in sufficient detail to assess if intermediate
compositional changes are common.
From a practical application point of
view, the stratigraphic units on the South
Florida Platform being studied as part of

this research are economically very impor-
tant as future sources of water supply.
Past geological studies have not defined the
units in sufficient detail to allow proper
definition of flow systems and calibration of
regional ground water models (Stringfield,
1966; Stringfield and LaGrand, 1966;
Miller, 1986; Bush and Johnson, 1988).
Also, the study of the hydrogeology was
limited in the past to the definition of large-
scale aquifer groups. Ground-water quality
information and simulations are becoming
quite important. These types of investiga-
tions, aimed at predicting the long-term
viability of public water supplies and
assessing the movement of toxic or haz-
ardous substances, require a much greater
level of detail in geologic data compared to
the past. The skeletal structure of an
aquifer must be known in order to accu-
rately predict water quality changes with
time (Missimer, 1994). Answers to these
fundamental questions will provide a
beginning to the more detailed geologic
investigations required to properly define
the upper portion of the Floridan aquifer
system on the South Florida Platform.

METHODS OF INVESTIGATION

Introduction

The primary problems posed for inves-
tigation are related to the significant
change in sediment-type deposition on the
South Florida Platform during the late
Paleogene and Neogene, the documentation
of the transition of a shallow marine plat-
form from a predominantly carbonate to a
mixed carbonate/siliciclastic environment,
and how the platform was affected by
eustatic sea-level changes. Specific ques-
tions have been posed with regard to the
effect of the eustatic sea-level changes, the
time of arrival of the siliciclastic sediments,
the overall chronology of the sediment
sequences, the cyclicity of the deposits, the
source and the mode of transport of the sili-
ciclastic sediments, and if a general deposi-

FLORIDA GEOLOGICAL SURVEY

tional model can be developed to explain
the patterns of deposition and the changes
in sediment types.
Three primary types of investigations
were made, which are: 1) investigation of
the sediment types and the stratigraphic
patterns of deposition; 2) investigation of
the chronostratigraphy; and 3) the estab-
lishment of the sequence stratigraphy of
the sediments. Each major area of investi-
gation required a number of specific studies
in order to be able to synthesize conclu-
sions.

Lithologic and Stratigraphic
Investigations

Stratigraphic investigations were
made using three cores drilled by the
Florida Geological Survey and a number of
wells (11) located between the cores. The
locations of these cores and wells are given
in Figure 2. Two detailed stratigraphic sec-
tions were constructed, section A-A' being a
dip section, and the other section, B-B',
being constructed perpendicular to the
platform dip. An additional section was
constructed between the cores to provide an
assessment of the continuity of sediment
sequences. These sections were chosen in
order to carefully evaluate the tops and bot-
toms of each formation and to have the abil-
ity to obtain continuous seismic reflection
data either parallel to the section or cutting
across it. Detailed studies of the cores and
well log data allowed some general strati-
graphic and lithologic characteristics to be
evaluated for application to broader region-
al problems on the southern part of the
Florida Platform.
The three cores that were studied were
W-16242, W-16523, and W-17115. All
three cores penetrated the full thickness of
the Hawthorn Group, the principal strati-
graphic unit of interest. These cores were
drilled using a wire-line coring device,
which allowed a high percentage of core
recovery. Geophysical logs were obtained
from the borehole of each core. Single-point

resistivity and natural gamma ray logs
were available for all cores. In addition,
core W-17115 has a neutron log and a 16/64
lateral resistivity log. Each core was stud-
ied in considerable detail by cutting the
core using a rock saw and then carefully
describing the lithology changes with depth
using a stereoscopic microscope. The lithol-
ogy changes were compared to the geophys-
ical logs to be sure that the depth intervals
written on the core boxes were correct.
Each well used to construct the pri-
mary stratigraphic sections was chosen
based on the quantity and quality of data
available. Nearly every one of these wells
was drilled as part of a hydrogeologic inves-
tigation, which required the acquisition of
detailed geologic data. Most of the wells
were drilled using the reverse-air rotary
technique, which allows the cuttings to be
rapidly vacuumed from the borehole with-
out contamination with drilling mud or cut-
tings falling into the borehole at locations
above the bit. Geophysical logs were exam-
ined from each well and at a minimum,
electric logs and a natural gamma ray log
were available. These wells allowed the
regional correlation of major stratigraphic
units to be made between the cores. A list-
ing of the site elevations and core depths is
given in Table 1.

Chronostratigraphy

One of the primary problems in analyz-
ing stratigraphy and sedimentation on the
Florida Platform is the lack of accurate
time control. Past definitions of many for-
mations occurring on the Florida Platform
were assigned ages based on incomplete or
inaccurate paleontological data. Time
stratigraphic data in this investigation was
obtained using ages determined from stron-
tium-isotope stratigraphy, magnetostratig-
raphy, and calcareous nannofossils (unpub-
lished work of J. Mitchner Covington).
Data from previous paleontological studies
conducted on the same stratigraphic units
were incorporated into the evaluation of the

BULLETIN NO. 65

Table 1. Well and Core Information.

Altitude Total Depth
Number' Location
T. R. S.
ft. m. ft. m.

Section A-A'

W-16889 21 6.40 2712 826.6 T.42S, R.23E, S.25

LM-3509 15 4.57 1585 483.1 T.43S, R.24E, S.31

LM-1629 4 1.22 1200 365.8 T.45S, R.24E, S.17

LM-1841 14 4.27 1400 426.7 T.45S, R.25, S. 33

W-16523 11 3.35 822 250.5 T.46S, R.25E, S. 33

LM-1980 14 4.27 1306 398.1 T.47S, R.25E, S.17

CO-2317 14 4.27 3400 1036.3 T.48S, R.26E, S.35

CO-2081 10 3.05 1616 492.6 T.49S, R.26E, S.35

CO-2080 5 1.52 1608 490.1 T.51S, R.26E, S.10

W-17115 5 1.52 1040 317.0 T.52S, R.26E, S.8

CO-2271 5 1.52 3354 1022.3 T.52S, R.26E, S.8

Section B-B'

W-16242 2 0.61 760 231.6 T.45S, R.21E, S.26

LM-3368 4 1.22 762 232.3 T.44S, R.22E, S.34

W-15487 4 1.22 662 201.8 T.45S, R.23E, S.4

LM-3484 13 3.96 760 231.6 T.44S, R.23E, S.1

LM-3509 15 4.57 1585 483.1 T.43S, R.24E, S.31

W-10761 29 8.84 450 137.2 T.41S, R.26E, S.33

Section C-C'

W-16242 2 0.61 760 231.6 T.45S, R.21E, S.26

W-16523 11 3.35 822 250.5 T.46S, R.25E, S.33

W-17115 5 1.52 1040 317.0 T.52S, R.26E, S.8

SExplanation of numbers. "W' is an FGS core number. "LM" and "CO" are numbers used by the consultant who drilled the wells.

chronostratigraphy.
Perhaps the most important age dating
method used was the time dependent vari-
ation of strontium isotopes in unaltered
marine organisms. Most stratigraphic
intervals in the cores contained some unal-
tered calcitic barnacles and marine mol-
lusks, particularly oysters, and pectens. A

total of 62 strontium-isotope age determi-
nations were made on material collected
from the three cores. A majority of the age
determinations (34) were made on the
South Seas Plantation core (W-16242),
because of the abundance of datable mate-
rial and the detailed stratigraphic and
lithologic analyses made on this core. The

FLORIDA GEOLOGICAL SURVEY

Legend
-- CROSS RAMP SECTION
------- PRIMARYSECTION
-.-.-.-.- EXISTING SEISMIC LINES
WELLS AND CORES
PRIMARY CORES STUDIED

SCALE .
25 MILES a

40 KILOMETERS .

Figure 2. Map of South Florida showing the location of all cores and wells used in the
investigation. The geologic section lines are shown along with high-resolution, shallow
seismic reflection lines. The investigation is limited to the western part of South Florida
at the approximate axis of the platform.

BULLETIN NO. 65

strontium isotope ages were determined
using both the Hodell et al. (1991) and the
Ostlick et al. (1994) models. Because the
strontium isotope ratios were measured at
the University of Florida, the Hodell et al.
(1991) regression equations could be used
directly with the appropriate correction.
However, there is a difference in the NBS-
987 number between the University of
Florida and Rutgers University, where the
Ostlick et al. (1994) samples were analyzed.
Before the Ostlick et al. (1994) model was
used for age determination, the measured
7Sr/6Sr ratios were normalized. All age
data were then converted to the time scale
of Berggren et al. (1995b).
Detailed magnetostratigraphic data
were collected from the South Seas
Plantation core (W-16242). Oriented rock
samples were collected from 291 intervals.
Since the core was collected using a drilling
rig, the only orientation of the samples that
could be determined was the stratigraphic
up direction. Core orientation was checked
by locating geopetals in the rocks to be sure
that the cores were properly oriented in the
boxes. Therefore, only inclination data
could be used to determine the polarity of
the earth's magnetic field at the time of
deposition. Magnetic measurements were
made on each sample using a supercon-
ducting magnetometer. Magnetic suscepti-
bility of each sample was measured prior to
and after demagnetization. Both alternat-
ing field and thermal demagnetization
methods were used to demagnetize the
samples. Rock magnetization data were
collected on 12 samples from the same core.
All magnetic susceptibility and magnetic
inclination data were collected at the
Paleomagnetics Laboratory at the
University of Miami (RSMAS). The rock
magnetism data were collected at the
Paleomagnetics Laboratory, California
Institute of Technology by Dr. Donald
McNeill. Magnetostratigraphic correla-
tions were made by comparing the pattern
of polarity reversals determined from the
core measurements to the geomagnetic

polarity timescale (GPTS) using available
biostratigraphy and Sr-isotope age tie-
points.

Paleontological Age Determinations

A study of the calcareous nannoplank-
ton was made previously on the South Seas
Plantation core (W-16242) and the
Koreshan core (W-16523) by J. Michner
Covington of the Florida Geological Survey
(Covington, 1992). Approximate strati-
graphic ages were determined by compar-
ing the overlapping ranges of several iden-
tified species in the cores to the known
stratigraphic ranges of these species in the
world ocean. The original age ranges for
the significant species were determined
from numerous radiometric dates tied to
the stratigraphic occurrence of the calcare-
ous nannofossil species.
A series of previous investigations
were made on the age of many of the strati-
graphic units of interest (Peck, 1976; Peck,
Missimer, and Wise, 1976; Peck et al.,
1977; Slater, 1978; Peck et al., 1979a; Peck
et al., 1979b; Peacock, 1981; Klinzing, 1980,
1987). Most of these investigations utilized
planktonic and benthic foraminifera to
determine stratigraphic ages. Klinzing
(1980, 1987) utilized diatoms and some cal-
careous nannofossils were used by Peck
(1976) and Slater (1978). The data con-
tained in these investigations were re-eval-
uated and incorporated into the overall
effort to determine the ages of various
stratigraphic units.

Seismic and Sequence Stratigraphy

About 125 km of new, high-resolution
seismic reflection data were collected paral-
lel to the major north-south stratigraphic
section from Marco Island north to Sanibel
Island, from the eastern tip of Sanibel
Island west and north to Captiva Island
immediately adjacent to core W-16242, and
in the Caloosahatchee River Estuary from
the Sanibel Causeway Bridge to Fort Myers

FLORIDA GEOLOGICAL SURVEY

(see Figure 2 for seismic line locations).
Also, about 160 km of existing high-resolu-
tion seismic reflection lines were reviewed.
These lines were run by the U.S. Geological
Survey as part of several water resources
investigations (Missimer and Gardner,
1976).
The seismic data were collected using a
variety of sources including a boomer sys-
tem, a multi-element sparker, a single ele-
ment sparker, and a water gun with vari-
able pressure inputs. All of the seismic
reflection data collected for this investiga-
tion were obtained using equipment on the
Rice University vessel, the R/V Lonestar.
The sediment velocities were estimated
using well logs directly adjacent to the seis-
mic lines and density logs from an injection
well located immediately adjacent to the
Macro Island core (W-17115). It was not
possible to obtain velocity logs.
The sequence stratigraphy was studied
using the core data, the well logs, a review
of the seismic reflection data, and the cor-
related stratigraphic sections. The seismic
record showed the overall geometry of the
bedding and the major relationships of the
stratigraphic units. Detailed analyses of
sediment sequences in the cores allowed
more detailed analysis of stacking patterns
of shoaling-upward sequences separated by
discontinuity surfaces.

MIXED SILICICLASTIC AND
CARBONATE SEDIMENTS OF THE
HAWTHORN GROUP,
SOUTH FLORIDA PLATFORM

INTRODUCTION

Mixed carbonate and siliciclastic
sequences can provide considerable insight
into the record of eustatic sea-level
changes, particularly when the sediments
were deposited on a relative tectonically
stable platform. Considerable interest has
arisen over the past decade with regard to
carbonate/siliciclastic mixtures and the
replacement of regionally significant car-

bonate sequences with siliciclastic
sediments or vice-versa in time and/or
space (Byers and Dott, 1981; Doyle and
Roberts, 1988; Budd and Harris, 1990;
Harris and Lomando, 1991). Many mixed
carbonate/siliciclastic sequences are cyclic
or repetitive to some degree in ancient
rocks, making them important in the study
of sequence stratigraphy (Wilson, 1967;
Picard and High, 1968; Meissner, 1972;
McIlreath and Ginsburg, 1982; Brett and
Baird, 1985; Mack and James, 1986; Sarg,
1988; and Shew, 1991).
It was suggested by Mount (1984) that
the stratigraphic contacts between major
siliciclastic and carbonate lithofacies are
quite abrupt and so few examples of grada-
tional contacts occur on shallow shelves
because "(1) faces changes may have taken
place through a fundamental alteration in
depositional conditions on the shelf, involv-
ing either rapid migration of environments
or erosion, and/or (2) the lateral transition
between coexisting carbonate and siliciclas-
tic environments was very abrupt and thus
not likely to be preserved as a mixed sedi-
ment." The suggestion that "most" contacts
between carbonate and siliciclastic sedi-
ment sequences are abrupt seems to con-
flict with Walther's Law, which suggests
that within a vertical succession containing
mixed carbonate and siliciclastic
sediments, records of gradational transi-
tions between carbonate and siliciclastic
faces should commonly occur.
The Oligocene-Miocene stratigraphic
record on the South Florida Platform pro-
vides an opportunity to view a relatively
detailed example of a carbonate-siliciclastic
transition compared to other regions of
eastern North America, where sediments of
this age are not as well preserved. The
South Florida carbonate-siliciclastic transi-
tion is somewhat unique in that it is at the
"end of the pipeline," or isolated from any
other sources of siliciclastic sediment
allowing the opportunity to assess subtle
changes in depositional environments. It is
the purpose of this investigation to assess

BULLETIN NO. 65

the type of carbonate-siliciclastic transi-
tion, whether it is abrupt or fully mixed, by
the study of the sediment composition and
faces types. Also, the hypothesis of Mount
(1984) regarding the tendency of transi-
tions to be abrupt will be tested.
Prior to Miocene time the southern
portion of the Florida Platform was a car-
bonate platform or ramp, believed to be iso-
lated from sources of siliciclastic sediment
to the north by a deep channel known as
the Gulf Trough (commonly referred to as
the Suwannee Straits or the Apalachicola
Embayment) (Applin and Applin, 1944;
Cooke, 1945; Hull, 1962; Purl and Vernon,
1964; Schmidt, 1984; Popenoe et al., 1987;
Huddlestun, 1993). Previous investiga-
tions suggested that the transition of the
Florida Platform from carbonate sedimen-
tation to siliciclastic sedimentation was
quite rapid (Schmidt, 1984; Scott, 1988).
Because the Florida Platform is assumed to
have been tectonically stable during the
time period when the transition occurred
(Oligocene/Miocene?) and there was
between 150 and 250 m of sediment deposi-
tion in this part of the stratigraphic section,
it should be a prime location for the
detailed study of a major transition. Past
investigations suggest that the transition
occurs within the regional stratigraphic
unit known as the Hawthorn Group (Puri
and Vernon, 1964; Scott, 1988).

METHODS

Stratigraphic investigations were con-
ducted by examination of three cores
drilled by the Florida Geological Survey
and eleven wells drilled between these
cores. The locations of the cores and wells
are given in Figure 2. Two stratigraphic
sections were constructed, section A-A'
being a dip section and section B-B' being
constructed perpendicular to the platform
dip. These sections were chosen in order to
carefully evaluate the tops and bottoms of
the major stratigraphic units and to allow
the dip section to closely parallel a continu-

ous seismic reflection profile. Detailed
studies of the cores and well log data were
made to establish both characteristic litho-
facies types and the stratigraphic sequence
patterns for each major unit.
The three cores studied all penetrated
the full thickness of the Hawthorn Group,
which is the stratigraphic unit of primary
concern. These cores were drilled using a
hydraulic rotary rig equipped with a wire-
line coring device, which allowed a high
percentage of core recovery. Geophysical
logs were obtained on the borehole of each
core. Single point resistivity and natural
gamma ray logs were obtained for cores W-
16242 and W-16523. These types of geo-
physical logs were obtained from the Marco
Island core (W-17115) along with a neutron
log and a 16/64 lateral resistivity log. Each
core was studied by cutting a large portion
of the core in half using a rock saw and
then carefully describing the observed
lithology, sedimentary structures, fauna
and flora, and composition using a stereo-
scopic microscope. The lithologies were
described and classified according to the
system of Dunham (1962) with descriptive
language added for the siliciclastic compo-
nents. The lithology changes were routine-
ly compared to the geophysical logs to
assess the correct position of lithologies in
relation to depth and the location of discon-
tinuities.
The mineralogy of each core interval
was determined not only by visual observa-
tion, but also was verified by applying
dilute hydrochloric acid and/or alizarin red
solution to the rock to distinguish calcite
from dolomite. After some experimenta-
tion, it was determined that a 10% solution
of hydrochloric acid was most effective for
differentiating carbonate lithology changes.
Because of the very high percentage of
recovery in core W-16242 and the wide
variety of lithologies found in this core, it
was chosen for very detailed examination.
Samples were collected from the core at 210
different depths and thin sections were
made to assess detailed mircofacies charac-

FLORIDA GEOLOGICAL SURVEY

teristics assessing both faunal and compo-
sitional changes. In addition, 671 samples
were collected and crushed into a fine pow-
der to determine the percentage of carbon-
ate, and for x-ray diffraction study of
selected fine-grained intervals in order to
determine composition. The 671 samples
were analyzed for total carbonate using the
"carbonate bomb" method (Muller and
Gastner, 1971; Jones and Kaiteris, 1983).
The method had to be modified slightly
because the normal digestion time of 20
minutes for calcite and aragonite was
insufficient to allow for the total dissolution
of dolomite and francolite (carbonate fluo-
rapatite). After experimentation, the con-
tact time for dissolution was increased to
two hours. A duplicate sample was run for
every 12 samples analyzed. Based on the
analyses of the duplicates, the precision
error of the measurements averaged less
than one percent. The estimated average
accuracy of the measurements is about +\-
2 percent based on measurements per-
formed on standards known to be pure cal-
cite and pure dolomite and various experi-
ments performed by Muller and Gastner
(1971). It must be noted that this method
is most accurate for calcite and aragonite,
but in the case of dolomite, the amount of
carbon dioxide produced is greater than for
calcite and aragonite. Therefore, for pure
dolomite, the method yielded some carbon-
ate percentages over 100%. However, the
method still reproduced the respective car-
bonate percentage of the standards within
a few percent. The very detailed analysis of
this core allowed the development of type
lithofacies to be distinguished for applica-
tion to the remaining cores. All of the
observed characteristics for each strati-
graphic interval, including composition,
sedimentary structures, fauna and flora,
and rock classification, were incorporated
into a series of master data matrices.
These rock characteristic matrices were
then used to distinguish the major and
minor lithofacies.
Each well used to construct the pri-

mary stratigraphic sections was chosen
based on the quantity and quality of data
available and its geographic position.
Nearly every one of these wells was drilled
as part of a hydrogeologic investigation,
which required the acquisition of detailed
geologic information. Most of the wells were
drilled using the reverse-air rotary method,
which allowed the cuttings to be rapidly
vacuumed from the borehole without con-
tamination with drilling mud or uphole
debris. Geophysical logs were used with at
least a set of electric logs and a natural
gamma ray log available from each well.
The information obtained from these wells
allowed regional correlation of major strati-
graphic units between the more detailed
core data.
Formation age data from the cores and
continuous seismic reflection data were
used to constrain the amount of time miss-
ing across unconformities and to establish
the major sequence geometries. This infor-
mation is described in more detail in later
sections of the report.

PREVIOUS INVESTIGATIONS

The primary geographic area of inves-
tigation is the south-central part of the
Florida Platform lying generally south of
Lake Okeechobee to the Florida Straits
(Figure 1). This area occurs in what was
formerly termed the "South Florida Basin"
(Pressler, 1947; Purl and Vernon, 1964;
Maher, 1971) and currently is known as the
Okeechobee Basin (Riggs, 1979b; Scott,
1988). The cores and wells studied in detail
lie in the middle of the platform along the
southwest coast of Florida, where both the
Peace River and Arcadia Formations thick-
en significantly into the basin (Figure 3).
Stratigraphic and general geologic
investigations of the Hawthorn Group
began in the early part of this century
because of the economic occurrence of phos-
phate deposits. Most detailed investiga-
tions of the stratigraphy of the Hawthorn
Group were limited to the northern part of

BULLETIN NO. 65

FORMATION

QUARTZ SAND, SHELL LIMESTONE

Figure 3. A general stratigraphic section for the study area based on the previous work of Scott
(1988). This investigation was conducted primarily on the Hawthorn Group. The stratigraphic ter-
minology and ages shown are based on Scott (1988) and previous investigators.

AGE

LITHOLOGY

100

LU
w
I--
w

150 z
3f
I-
a

I-

0

200 n

250

FLORIDA GEOLOGICAL SURVEY

the Florida Platform, where the sediments
lying above the major phosphorite ore
deposits are thin. Dall and Harris (1892)
were the first investigators to formally
name the "Hawthorne beds" for the phos-
phatic sediments exposed near Hawthorne,
Florida. When Matson and Sanford (1913)
compiled the first comprehensive descrip-
tion of Florida stratigraphy, they dropped
the "e" from the formation name and the
Florida Geological Survey currently recog-
nizes the formal name as "Hawthorn." A
very detailed history of the evolution of the
Hawthorn Group definition is given in
Scott (1988). Based on the occurrence of a
major regional disconformity and a change
in sediment type across the disconformity,
Scott (1988) elevated the Hawthorn
Formation to the Hawthorn Group and, in
southern Florida, subdivided it into the
Arcadia Formation at the base of the sec-
tion and the Peace River Formation at the
top of the group (Figure 3). Since the area
of investigation is located in South Florida,
no further discussion of the investigations
in north Florida or the evolution of the
nomenclature is appropriate.
Work on the Oligocene and Miocene
geology of South Florida has been limited
mostly to general stratigraphic studies and
studies of the regional oceanic events which
caused the deposition of the massive phos-
phorite deposits. General stratigraphic
studies of what was believed to be the
Miocene in South Florida were conducted
by Scott (1988) and Scott and Knapp
(1987). These studies were limited to the
definition and correlation of regionally
mappable lithostratigraphic units.
Investigations on the Suwannee Limestone
and part of the Hawthorn Group were
made by Cooke (1939), MacNeil (1944),
Armstrong (1980), Peacock (1981),
Hammes (1992), and Brewster-Wingard et
al. (1997). The work by Cooke (1939) and
MacNeil (1944) were regional stratigraphic
studies. Armstrong (1980) and Peacock
(1981) studied the biostratigraphy and

Hammes (1992) analyzed microfacies and
sea level implications. These investiga-
tions were quite limited in scope and less
than 50 wells and ten cores were used to
define the overall stratigraphy.
A number of previous geologic investi-
gations were conducted in the immediate
vicinity of this research area. Missimer
and Banks (1982) studied the stratigraphy
of the Miocene and Oligocene beneath
Sanibel Island and determined the deposi-
tional pattern in the Hawthorn Group to be
cyclic. Hammes (1992) completed a
detailed investigation of the Suwannee
Limestone with work on core W-16242.
Hammes (1992) investigation of the
Suwannee Limestone defined a series of
shallow ramp subfacies, many of which
occur in the Hawthorn Group.
Investigation of the Neogene seismic and
sequence stratigraphy of southwest Florida
was performed by Evans et al. (1989), and
Evans and Hine (1991). A seismic reflec-
tion study of the upper part of the
Hawthorn Group and overlying sediments
was made by Missimer and Gardner (1976).
This investigation lead to the interpreta-
tion that the Arcadia Formation was fault-
ed and folded and that the upper part of the
Peace River Formation was deltaic.
Although very few geologic and strati-
graphic investigations of the South Florida
Platform have been made to resolve large
scale regional problems, a number of small-
er scale studies have been made solely on
the paleontology of a stratigraphic time
interval or unit of interest or on the age of
a unit. These investigations include the
works of Gardner (1926), Cole (1934, 1941),
Mansfield (1937, 1938), Applin and Jordan
(1945), Akers and Drooger (1957), Gibson
(1962, 1983), Shannon (1967), Hunter
(1968), Akers (1972, 1974), Glawe (1974),
Abbott (1978), Klinzing (1980), Hoenstine
(1988), MacFadden et al. (1991), Brewster-
Wingard et al. (1997).
Investigations of the regional develop-

BULLETIN NO. 65

ment of phosphatic sediments in the
Hawthorn Group have related global ocean-
ic events and the change in current pat-
terns to the Miocene evolution of the
Florida Platform. These investigations
include Compton et al. (1993), Riggs
(1979a, 1979b, 1980, 1984), and Synder et
al. (1988). Specific hypotheses have been
presented with regard to the origin of the
dolomite within the Hawthorn Group
(Prasad, 1985; Compton et al., 1994).
Most previous work on the Florida
Platform has been on carbonate deposition-
al patterns and sedimentation. A recent
investigation of mixed siliciclastic/carbon-
ate sedimentation shows part of the region-
al sedimentation pattern developed in this
research (Warzeski et al., 1996;
Cunningham et al. 1998).

GEOLOGIC AND
STRATIGRAPHIC SETTING

Stratigraphy

The Hawthorn Group occurs regionally
beneath most of the Florida Platform with
the exception of areas located in and
around the Ocala High in west central
Florida (Puri and Vernon, 1964). In south-
ern Florida the Group is subdivided into
two formations, the Arcadia and the Peace
River Formation, following the nomencla-
ture of Scott (1988). According to the liter-
ature, the Hawthorn Group is underlain by
the Suwannee Limestone and overlain by
the Tamiami Formation (Figure 3).
There has been considerable debate
over the past 40 years with regard to the
formation boundaries and sediment charac-
teristics by which to recognize the forma-
tion boundaries as rock stratigraphic units
in South Florida (Missimer, 1978; Missimer
and Banks, 1982; Scott and Knapp, 1987;
Scott, 1988). Missimer (1978) proposed that
the upper boundary of the Hawthorn

Formation (at that time) be located on a
major regional, disconformity, which sepa-
rates a section of predominantly siliciclas-
tic sediments from an underlying mixed
carbonate/siliciclastic unit. This easily
mapped boundary was chosen because it
represented a major lithology change with
the probability of a considerable amount of
time missing. Missimer and Banks (1982)
utilized the definition of the overlying
Tamiami Formation following the concepts
presented by Hunter and Wise (1980a,
1980b), who removed the Peace River
Formation sediments and restricted the
Tamiami Formation to the originally
described sandy limestone. Wedderburn et
al. (1982) also utilized the restricted defini-
tion of the Tamiami Formation. Because of
the lithologic change across the disconfor-
mity and the restricted stratigraphic posi-
tion of the Tamiami Formation (along with
many other inconsistencies), Scott (1988)
elevated the Hawthorn Formation to Group
status, thereby creating a more consistent
and mappable section throughout Florida.

Formation Boundaries

Suwannee Arcadia

The contact between the Arcadia
Formation and the underlying Suwannee
Limestone is distinctive throughout the
study area. The basal faces of the Arcadia
Formation is generally a sandy, phosphatic,
wackestone and the uppermost faces of the
Suwannee Limestone is a foraminiferal
packstone or grainstone lacking mud
and/or any significant concentration of
phosphorite, and containing distinctly less
quartz sand than above (Plates 1, 2, and 3).
In core W-16523, a thin clay layer marks
the disconformity (Plate 2). A marked
reduction in gamma ray activity across the
formation contact can be distinguished in
natural gamma ray logs in all cores and
wells studied.

FLORIDA GEOLOGICAL SURVEY

Arcadia Peace River

Throughout the study area, the contact
between the Peace River and Arcadia for-
mations within the Hawthorn Group is a
distinct disconformity between a sandy,
highly phosphatic, dolomitic mud and an
underlying sandy, phosphatic wackestone.
In core W-16242 and the wells in northern
Lee County, the uppermost part of the
Arcadia Formation is dolomitic and in the
south it is calcitic. Quartz gravel, phospho-
rite pebbles, and marine vertebrate fossils
commonly occur in the detritus above the
disconformity. This contact is always dis-
tinctive in a gamma ray log, where a peak
is caused by the large accumulation of
phosphorite, which contains relatively
greater concentrations of uranium and
other radioactive trace elements (see Plates
1, 2, and 3).

Peace River Tamiami

The stratigraphic contact between the
Tamiami Formation and the Peace River
Formation (upper part of the Hawthorn
Group) in the northern part of the study
area is clear and mappable. In core W-
16242 (Plate 1) and areas to the west, the
base of the Tamiami Formation is a quartz
sand and shell faces or a sandy, phosphat-
ic, calcitic wackestone (Missimer, 1992b)
and the top of the Peace River Formation is
a dolomitic, clayey quartz silt with a dis-
tinct green color. In the southern part of
the study area, the Tamiami Formation is a
sandy limestone faces and the Peace River
Formation is a quartz sand and shell unit
commonly containing some dolomitic
cement. In the W-17115 core (Plate 3), the
contact is not distinct, but is placed on the
occurrence of a disconformity with an
underlying beach subfacies that has been
dolomitized.

Age of the Hawthorn Group
and Bounding Formations

Within the past 10 years a considerable
amount of new information has been
obtained on the age of the Neogene and
upper Paleogene stratigraphic section
beneath the South Florida Platform. The
ages of most major stratigraphic units were
determined in the past by rather crude
paleontological correlations to stratigraph-
ic units with better age control. A detailed
analysis of the age of the stratigraphic
units of interest is presented later in this
dissertation.
For many years the ages of the strati-
graphic units in south Florida conformed to
those assigned by Parker et al. (1955),
which were as follows: the Suwannee
Limestone was Oligocene, the Hawthorn
Formation was middle Miocene, the
Tamiami Formation was late Miocene, and
the younger units were assigned to the
Pleistocene. Recent stratigraphic investi-
gations by Scott (1988), COSUNA (1988),
Missimer (1992b), Jones et al. (1991),
Hammes (1992), Mallinson and Compton
(1993), Compton et al. (1993), and
Brewster-Wingard et al. (1997) have helped
constrict the major stratigraphic units to
more accurate ranges in age. The age
ranges of the Suwannee Limestone, the
Hawthorn Group, and the Tamiami
Formation will be discussed later in the
report.

VARIATIONS IN COMPOSITION
OF SEDIMENT

Total Carbonate Variation: Results

Many of the fundamental questions
posed with regard to mixed carbonate/silici-
clastic sediment sequences center around
variations in composition of the sediment.
All compositional data are located in a
Florida Geological Survey repository and in
Plates 1, 2, and 3. Samples were collected
from all formations in core W-16242,

BULLETIN NO. 65

despite the primary interest in the
sediments of the Hawthorn Group, in order
to make overall stratigraphic comparisons.
A comparison of the average total carbon-
ate concentration in all formations from
Holocene to early Oligocene is given in
Table 2.
There is a decrease in the percentage of
total carbonate from the Suwannee
Limestone up-section to the lower part of
the Peace River Formation, and a slight
increase in total carbonate in the upper
part of the Peace River Formation. The
trend toward increase in total carbonate
continues through the Tamiami Formation
and peaks in the Caloosahatchee
Formation. The total carbonate decreases
through the Fort Thompson Formation and
into the Holocene (Figure 4).
From the base of the Suwannee
Limestone to the Miocene-Pliocene bound-
ary within the Peace River Formation, the
predominant portion of the non-carbonate
fraction of the sediment is quartz sand.
There are a few minor units containing a

high percentage of clay within the Arcadia
Formation. Also, there is a significant
amount of glauconite and a trace of sulfide
minerals within the Arcadia Formation. It
is very important to note that quartz sand
occurs in virtually every sediment faces
within both the Suwannee Limestone and
the Arcadia Formation. A mix of quartz
sand and silt, along with clay, form the
non-carbonate portion of the upper Peace
River Formation. Quartz sand is the pre-
dominant non-carbonate sediment compo-
nent within the remaining Neogene forma-
tions.
Variation in the total carbonate per-
centage can be used to help define disconti-
nuity surfaces and sequence boundaries
within mixed carbonate/ siliciclastic
sediments (Plates 1, 2, and 3). Starting at
the base of the stratigraphic section in core
W-16242, the variation in the total carbon-
ate percentage has a different interpreta-
tion in different stratigraphic units.
Within the Suwannee Limestone, the

Table 2. Comparison of Total Carbonate Percentages by Formation
in the South Seas Plantation Core (W-16242)

Formation Average High Low No. Standard
Percentage Samples Deviation2
Suwannee Limeston 91.01 98.1 64.9 17 8.18
Arcadia Formation 76.4 100.00 4.7 370 20.71
Miocene Section 29.5 68.4 5.3 15 20.70
Pliocene Section 41.5 82.8 8.0 162 18.36
Peace River Formation 40.5 82.8 5.3 177 18.69
Tamiami Formation 50.2 82.8 13.0 63 18.33
Caloosahatchee Formation 82.4 88.5 75.7 19 5.29
Fort Thompson Formation 51.8 84.8 16.6 7 25.69
Holocene 35.9 97.4 4.5 18 30.96

Likely average would be about 95% if numerous samples collected (Hammes, 1992).
2 Sample standard deviation.

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Holocene
Ft Thompson Fm
Caloosahatchee Fm.

Tamiami Fm.

Peace River Fm.

0

-50

-100

I
I-
LU

-150

-200

-250

i

0 10 20 30 40 50 60 70 80 90 100
CARBONATE PERCENTAGE

Figure 4. Variation of total carbonate percentage with depth in core W-16242 based on
760 measurements. There is an overall trend of decreasing carbonate percentage with
decreasing age going up-section from the Suwannee Limestone to the late Pleistocene for-
mations (with exception of the Caloosahatchee Formation). The extreme changes in car-
bonate percentage mark subfacies boundaries and commonly occur at sequence bound-
aries lying on regional disconformities. Depths are below land surface.

Arcadia Fm.

Suwannee Ls.

BULLETIN NO. 65

lowest total carbonate percentages occur at
discontinuity surfaces (Figure 4). Based on
past literature (Puri and Vernon, 1964),
there is little if any quartz sand or other
non-carbonate sediments in the Suwannee
Limestone, but virtually all sediment inter-
vals in core W-16242 contain some non-car-
bonate sediment (Figure 4). The variation
in carbonate percentage provides assis-
tance in interpreting sequence boundaries,
changes in water depth, changes in subfa-
cies, and shoaling-upward sequences with-
in the Arcadia Formation (Figure 5). Based
on the variations in total carbonate per-
centage measured within the Arcadia
Formation, there is a general overall
upward increase in the siliciclastic compo-
nent with abrupt changes in the upper part
of the Arcadia Formation. The relationship
between the carbonate and non-carbonate
components, within shoaling-upward
sequences, is presented later in this bul-
letin. Total carbonate variation in the
Peace River Formation shows the distinct
boundary between the Miocene sands in
the lower three meters of the formation and
the increase in carbonate at the Miocene-
Pliocene contact located in this core at
about 88.4 m (Figure 6). Within the upper
part of the formation, the total carbonate
decreases with depth in a given bed and
sand lags occur at the top of shoaling-
upward sequences, such as at 74 m (Figure
6). It is quite apparent from the carbonate
data presented that the siliciclastic compo-
nent of the sediment in all carbonate/silici-
clastic units observed is mixed within vir-
tually all types of carbonate depositional
environments and many contacts between
faces are gradational. This conclusion
directly conflicts with the hypothesis of
Mount (1984), who stated that there are
few examples of truly mixed carbonate/sili-
ciclastic sediment sequences in the strati-
graphic record. Beginning at the base of
core W-16242, it is observed that the

Suwannee Limestone contains a minor per-
centage of quartz sand throughout the unit,
which confirms a similar observation made
by Hammes (1992) in several other cores
located to the north. The siliciclastic sedi-
ment component within the Arcadia
Formation is mixed with the carbonate
component throughout the unit, but does
show some abrupt, nearly pure composi-
tional contrasts at many sequence bound-
aries. Siliciclastics and carbonates are
completely mixed within the Peace River
Formation. All of the other Neogene for-
mations within the core also show thorough
mixing of carbonate and siliciclastic
sediments within the units. Of the six
ancient formations studied, and the
Holocene sequence, all of the units contain
carbonate and siliciclastic sediments that
are thoroughly mixed in terms of overall
composition.

Variations in Carbonate Mineralogy

Introduction

The two primary carbonate minerals of
interest in this discussion are calcite and
dolomite. Aragonite commonly occurs in
the upper part of the stratigraphic section
in some Pliocene (Pinecrest Member of the
Tamiami Formation), Pleistocene and
Holocene sediments, but this mineral was
not found within the Hawthorn Group in
any of the three cores studied. Aragonite
has been found recently within the
Hawthorn Group stratigraphic section in a
core drilled at Key West (Cunningham et
al., 1998). Another carbonate mineral,
francolite, commonly occurs in these
sediments, but will be discussed separately
under variations in phosphorite. The vari-
ation of the carbonate mineralogy is quite
important, because significant changes in
the mineralogy commonly mark sequence
boundaries and aid in stratigraphic inter-
pretation (Missimer, 1978; Missimer and
Banks, 1982; Scott, 1988). Determinations

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-80

-100

-120

S-140 _.._
I ARCADIA
FORMATION

1-60

-180 -..

-200

-220
0 10 20 30 40 50 60 70 80 90 100
CARBONATE PERCENTAGE
Figure 5. Variation of total carbonate percentage within the Arcadia Formation in core
W-16242. Total carbonate percentage ranges from less than 5% to 100% in the Arcadia
Formation. In the lower part of the formation, the lower total carbonate percentages
occur at coarse sediment accumulations or at disconformities. In the upper part of the
formation, the lower carbonate percentages occur in clay deposits or sandy deposits
(quartz sand). The graph indicates that the composition of the formation is a mix of both
carbonate and siliciclastic sediments in the entire stratigraphic section. Depths are below
land surface.

BULLETIN NO. 65

-55

0 10 20 30 40 50 60 70 80 90 100
CARBONATE PERCENTAGE

Figure 6. Variation of total carbonate percentage in the Peace River Formation in core W-
16242. The total carbonate is low at the base of the formation and increases to a high at
about 87 meters, then decreases to about 70 meters. In the upper 10 meters, the total car-
bonate varies considerably. The lower three meters of the formation is a quartz sand. The
predominantly silty, angular-bedded sediments lie above the basal sand. Depths are
below land surface.

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PEACE RIVER
FORMATION

Pliocene
Miocene

-75

-80

-85

-90

-95

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of the carbonate mineralogy were made
using X-ray diffraction in the fine-grained
mixed sediments of the Peace River
Formation in core W-16242, staining of thin
sections from the Arcadia Formation in
core W-16242, and by staining and applica-
tion of 10% hydrochloric acid in the other
cores.

Large Scale Variation in
Dolomite Occurrence

Dolomite is the predominant carbonate
mineral within the Hawthorn Group in
North and Central Florida as well as geo-
graphic areas located immediately north of
this study area (Prasad, 1985; Scott, 1988;
Weedman et al., 1993; Compton et al.,
1994; Brewster-Wingard et al., 1997).
However, the percentage of dolomite in the
Hawthorn Group decreases dramatically
from north to south into the basin. Calcite
is the predominant carbonate mineral with-
in the underlying Suwannee Limestone,
but dolomite does occur within specific
stratigraphic intervals, particularly near
the base of the formation in Collier County
(see well log of CO-2318). Calcite is the
predominant mineral in the sediment
occurring stratigraphically above the
Hawthorn Group. The occurrence of
dolomite is quite rare in late Pliocene and
Pleistocene sediments of southern Florida.

Variation in Carbonate Mineralogy
in the Arcadia Formation

A distinctive change in the carbonate
mineralogy of the Arcadia Formation
occurs from the north to south across the
area of investigation. Dolomite is the pre-
dominant carbonate component (64%) of
the stratigraphic section in the South Seas
Plantation core (Plate 1). To the south, the
percentage of dolomite in the stratigraphic
section reduces to only 17% in the
Koreshan core and 32% in the Marco Island
core (Table 3). Calcite is the predominant
carbonate mineral within the Arcadia

Formation in the southern part of the study
area. It occurs as primary mud, a micritic
cement, a sparry cement, and as skeletal
grains.
Five different types of dolomite were
recognized based on textures. These
dolomite types are: 1) microcrystalline
dolomite (non-mimetic); 2) microcrystalline
dolomite (mimetic); 3) sucrosic dolomite; 4)
microsucrosic dolomite; and 5) floating
rhombs. The most common dolomite type is
the microsucrosic dolomite, which is fabric
destructive. Commonly, dolomitization is
selective with calcitic skeletal grains
remaining unaltered in the dolomitized
rock. In certain cases, dolomitic cements
occur within primarily calcitic sediments.
Dolomite rhombs commonly occur within
predominantly calcitic sediments. In a few
cases, hard dolomitic rocks contain borings
infilled with friable calcitic mud. There is a
common association between the occur-
rence of hard, dense, relatively thin
dolomite units and the occurrence of phos-
phorite crusts, pyrite, and glauconite.

Variation of Carbonate Mineralogy in the
Peace River Formation

Although the Peace River Formation
consists largely of siliciclastic sediments
with variable proportions of quartz and
clay minerals, there is a significant carbon-
ate component (Figure 6). The predomi-
nant carbonate mineral is calcite. The per-
centage of total carbonate ranges from 5.3
to 82.8% and averages 40.5% (Table 2). In
core W-16242, dolomite is the predominant
carbonate mineral at the top of the section
and calcite is predominant in most of the
lower section (Figures 7 and 8). The high-
est percentages of dolomite occur in the
deltaic faces (subfacies 14) between 57.5
and 62.5 m below surface (see description of
subfacies 14). The dolomite distributed
throughout subfacies 14 consists mostly of
silt-sized rhombs, which "float" in the
mixed sediment. Based on the stratigraph-
ic pattern of occurrence in relation to the

BULLETIN NO. 65

Table 3. Comparison of the calcite and dolomite occurence in the Arcadia
Formation in cores W-16242, W-16523 and W-17115 (north to south).

Thickness of Section Percentape Percentage
Core Number Calcite Dolomite1
(feet) (meters)
W-16242 374 114 36 64
W-16523 608.2 185.4 83 17
W-17155 518 157.9 68 32

1 Percentage of predominant calcite and dolomite in stratigraphic section. Measurements or determinations
were made by staining, direct observation, or x-ray diffraction on the entire length of each core.

graded beds in the upper part of the sec-
tion, the dolomite appears to be hydrauli-
cally sorted. The percentage of calcite
increases dramatically below the 74 m
depth, which lies at a probable sequence
boundary. Also, the abundance of benthic
foraminifera and ostracods increases at
this depth. In the lower three to four m of
the section, within the Miocene siliciclastic
sequence, the dolomite percentage is high
in comparison to the calcite percentage. At
the base of the Peace River Formation, the
accuracy of the dolomite/calcite percent-
ages is not as great because of the high per-
centage of francolite occurring near the dis-
conformity with the underlying Arcadia
Formation.
The occurrence of dolomite in the
Miocene siliciclastic section is more com-
mon in the Marco Island core (W-17115) to
the south, in which the lower part of the
Peace River Formation is greatly expanded
in thickness. In this core, several of the
packstone and grainstone subfacies are
selectively dolomitized (Plate 3). Since the
principal carbonate grains within the pre-
dominantly siliciclastic sediments are
skeletal grains, being mostly mollusk shells
and foraminifera, much of the calcite occurs
as skeletal grains with some calcitic mud.

Variation in Francolite
(Phosphorite) Occurrence

Francolite is the carbonate phosphorite
mineral which commonly occurs through-
out the stratigraphic column above the
Suwannee Limestone. Some minor occur-
rences of blackened discontinuity surfaces,
which may contain some francolite, do
occur within the Suwannee Limestone.
However, the occurrence of major phospho-
rite deposits begins in the Hawthorn Group
on the South Florida Platform.
There are two types of francolite
deposits observed in the cores. The most
common francolite occurrence is in nodular
form with peloids, some coated grains, fecal
pellets, intraclasts, and skeletal grains
being phosphatized. The second type of
phosphorite occurrence is in the form of a
crust, which commonly formed on disconti-
nuity surfaces and on marine hardgrounds.
The formation of francolite in the
Hawthorn Group is described in detail by
Riggs (1979a; 1979b; 1980; 1984), Compton
et al. (1990), and Compton et al. (1993).
The percentage of phosphorite on the
southern part of the Florida Platform is
generally lower compared to the northern
part of the platform. Detailed work by
Compton et al. (1993) on core W-10761 (see
section A-A'), showed phosphorite concen-
trations ranging between 0 and 100% with
an average concentration within the
Arcadia Formation of about 20%. It is also
important to note that very little phospho-
rite was found in the upper part of the

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-55

-60

-65

-70

-75

-80

-85

-90

-95

J

PEACE RIVER
FORMATION

\ ^ ^ ^___

0 10 20 30 40 50 60 70 80 90 100
CALCITE PERCENTAGE
Figure 7. Calcite percentage with depth in the Peace River Formation in core W-16242.
The sharply lower calcite percentages within individual beds, from about 75 meters to the
base of the formation, correspond to high concentrations of quartz sand. Within the upper
part of the Peace River Formation (all but lower three meters), the percentage of calcite
increases with depth. The calcite is mostly silt-sized material, some mud, and some skele-
tal grains, mostly foraminifera and ostracods. The calcite percentage was measured using
x-ray diffraction (see methods). Depths are below land surface.

L-
W
0J

BULLETIN NO. 65

PEACE RIVER
FORMATION

20 30 40 50 60 70 80 90 100
DOLOMITE PERCENTAGE

Figure 8. Dolomite percentage with depth in the Peace River Formation in core W-16242.
The dolomite grains are detrital rock fragments in the lower subfacies in the lowermost
three meters of the formation and exclusively silt-sized rhombs in the upper subfacies.
The percentage of dolomite decreases throughout the upper part of the Peace River
Formation. The dolomite percentage was measured using X-ray diffraction (see methods).
Depths are below land surface.

-55

-60

-65

-70

-75

-80

-85

-90

-95

0 10

z
4_

L

c
i
i

L

FLORIDA GEOLOGICAL SURVEY

Peace River Formation in core W-10761.
Compton et al. (1993) also found a direct
correlation between natural gamma ray
activity and the percentage of phosphorite.
The percentage of phosphorite in cores W-
16242, W-16523, and W-17115 was esti-
mated under the microscope using visual
comparison charts. A direct estimation
using the gamma ray logs was not used
because of recent data generated by Green
(1994) who found a considerable quantity of
uranium and other radioactive isotopes are
contained within the bulk carbonate rock in
the Hawthorn Group along with the
radioactive isotopes contained within the
phosphorite nodules. Therefore, direct use
of the gamma ray logs for estimation pur-
poses will tend to yield francolite percent-
ages higher than actual occurrence.
The francolite percentage in core W-
16242 ranged from 0 to 100% with an aver-
age of less than 1% in the Peace River
Formation and about 10% in the Arcadia
Formation (see Plate 1). The highest per-
centages in all cores are associated with lag
deposits in the lower part of the Peace
River Formation near the disconformity
with the underlying Arcadia Formation
and in lag deposits and primary phospho-
rite deposition zones within the Arcadia
Formation. (Note: Primary phosphorite
deposits were "crusts" within the
sediments, whereas nodular phosphorite
can be either primary or transported.) The
francolite percentage in core W-16523
ranged from 0 to 100% with an average of
about 5% in the Peace River Formation
(mostly lower section) and about 7.5% in
the Arcadia Formation (see Plate 2). The
francolite percentage in core W-17115
ranged from 0 to 100% with an average of
one to two percent (only lower section of for-
mation) and less than 5% in the Arcadia
Formation (see Plate 3). Based on the
observed francolite percentages in the
cores, the trend for reduced phosphorite
deposition moving from north to south on
the platform continues through the area
investigated.

There is a definite tendency for phos-
phorite lag deposits to form at discontinuity
surfaces, particularly in the open marine,
inner and outer ramp subfacies. Although
the significant accumulations of francolite
commonly mark sequence boundaries, they
also occur within sequences as primary
deposits and as storm lags. Therefore, the
occurrence of accumulations of francolite at
any stratigraphic interval must be evaluat-
ed in terms of the overall characteristics of
the sediment sequence.
Although francolite formed during dep-
osition of the Hawthorn Group, the nodules
are quite resistant to weathering and the
francolite nodules are reworked upward
through the entire Neogene stratigraphic
section. Accumulations of phosphorite nod-
ules can also be used to help locate
sequence boundaries within the younger
formations, such as the Tamiami and
Caloosahatchee Formations.

Non-carbonate Sediment
Composition Variation

Introduction

There are three principal components
of the non-carbonate portion of the
Hawthorn Group sediments. These compo-
nents are quartz, clay minerals, and a
series of trace minerals with pyrite and
glauconite being of most significance. The
larger scale occurrence of the siliciclastic
minerals within the predominantly carbon-
ate Arcadia Formation is not random, but
is directly related to changes in the deposi-
tional environment caused by sea-level
changes. Bed-scale variations in quartz
sand occurrence may be related to lag
deposits or minor stratigraphic discontinu-
ities.
There is a distinctive increase in the
siliciclastic sediment percentage in the
stratigraphic section moving from the
Suwannee Limestone upward into the
Arcadia Formation (contact at about 206 m

BULLETIN NO. 65

Holocene
Ft Thompson
Caloosahatchee

Tamiami

Peace River

0

-50

-100

I
I-
0-
U.l

-150

-200

-250

5
Z

5
_

-----
~-- --

,---

i

0 10 20 30 40 50 60 70 80 90 100
NON-CARBONATE PERCENTAGE

Figure 9. Non-carbonate sediment percentage with depth in core W-16242 based on 760
analyses. The age of the sediments ranges from Oligocene to the Holocene. There is a gen-
eral increase in non-carbonate or siliciclastic sediment from the bottom to the top of the
core. The siliciclastic component of the Caloosahatchee Formation is lower and does not
follow the general trend. The non-carbonate sediment percentage was determined by sub-
traction of the carbonate percentage from the total. Figure 9 is the inverse of Figure 4.
Depths are below land surface.

Arcadia

Suwannee

FLORIDA GEOLOGICAL SURVEY

in Figure 9), with a substantial increase in
the upper Arcadia. After deposition of the
Suwannee Limestone, all sediments
deposited on the South Florida Platform
had a significant percentage of non-carbon-
ate sediment, which is thoroughly mixed
with the carbonate component.
The non-carbonate part of the sedi-
ment in the Suwannee Limestone in core
W-16242 shows a rather irregular varia-
tion, which may be a function of the small
number of samples collected for analysis or
may be a function of diagenesis (Figure 9).
The non-carbonate portion of the sediment
contains mostly very fine quartz sand with
a minor quantity of terrigenous clay and
another component consisting of siliceous
replacement of echinoid grains.
The non-carbonate component of the
sediment in the Arcadia Formation shows
an increasing percentage going up-section
in core W-16242 (Figure 10). Nearly 50% of
the sediment in the upper 30 m of core W-
16242 is non-carbonate sediment. This
trend in up-section increased siliciclastic
sediment deposition occurs in each of the
Arcadia Formation cores.
Within the Peace River Formation, sili-
ciclastic sediment becomes the predomi-
nant component of the stratigraphic section
(Figure 11). The lower Peace River
Formation sediments, below 88.5 m in
Figure 11, are mostly siliciclastic deposits
with compositions being nearly 100% non-
carbonate in many stratigraphic intervals.
In the upper part of the Peace River
Formation, the siliciclastic component of
the sediment ranges mostly between 70
and 80% and decreases to between 30 and
40% in the lower part of this sequence.
There is a change in the overall pattern of
sedimentation within the Peace River
Formation from north to south with the
upper subfacies becoming less significant.
The fine-grained, upper subfacies thins sig-
nificantly between Captiva Island and
Koreshan and does not exist in the Marco

Island core. The subfacies terminates at
about the Lee-Collier county line.

Variation in Quartz Sand Occurrence

Quartz sand is the primary component
of the non-carbonate portion of the sedi-
ment throughout the Late Paleogene and
Neogene section on the South Florida
Platform. Terrigeneous clays occur as thin,
laminated deposits in the upper Arcadia
Formation, as a minor component of the
muddy carbonate deposits, and in the
Peace River Formation. The percentage of
quartz sand was determined for nearly
every stratigraphic interval in the three
cores intensely studied (see Plates 1, 2, and
3). A more detailed analysis of the quartz
silt percentage of the fine-grained sediment
within the Peace River Formation in core
W-16242 was attempted using X-ray dif-
fraction techniques. This analysis method
was unsuccessful because the clay fraction
of the sediment tended to greatly and
inconsistently interfere with the intensity
of the quartz peak and a calibration equa-
tion could not be developed. The quartz
percentages were estimated using visual
comparison charts and microscopic exami-
nation along with the total carbonate
measurements (core W-16242). It is quite
important to note that quartz sand and the
carbonate sediment component are thor-
oughly mixed in each formation and within
each and every depositional environment in
the entire Neogene section.
The percentage of quartz sand in the
Arcadia Formation generally increases in
each core from the base to the top of the for-
mation (Plates 1, 2, and 3). There is a dis-
tinctive reduction in the overall content of
quartz sand within the formation from
north to south moving away from sources to
the north. In core W-16242, the percentage
of quartz sand averages between 10 and
20% in the lower part of the formation and
over 50% in the uppermost part of the for-
mation (Plate 1). There is at least 5%
quartz sand in nearly every type of deposi-

BULLETIN NO. 65

-80

-100

-120

r -140

I
S-160
0-
u -160

-180

-200

-220

0 10 20 30 40 50 60 70 80 90 100
NON-CARBONATE PERCENTAGE

Figure 10. Non-carbonate sediment percentage with depth in the Arcadia Formation in
core W-16242. In this mixed carbonate/siliciclastic unit, there is some non-carbonate sed-
iment in virtually all depositional environments found in the section. There is a general
increase in non-carbonate sediment percentage from the bottom to the top of the forma-
tion. The spikes of high non-carbonate sediment percentage in the lower part of the for-
mation commonly correspond to disconformities and sequence boundaries. The overall
percentage of non-carbonate sediment increases abruptly in the upper Arcadia Formation
at about 117 meters. Depths are below land surface.

ARCADIA
FORMATION

i
5

--
1

FLORIDA GEOLOGICAL SURVEY

-55

-60

-65

-70

-75

-80

-85

-90

-95

PEACE RIVER
FORMATION

__ ~ ~~~~ ^/

^ ^ ^ = ^/

0 10 20 30 40 50 60 70 80 90 100
NON-CARBONATE PERCENTAGE
Figure 11. Non-carbonate sediment percentage with depth in the Peace River Formation
in core W-16242. Note that the base of the formation has a high non-carbonate sediment
percentage associated with the quartz sand section in the lowermost three meters of the
core. There is a general upward increase in the non-carbonate sediment percentage with-
in the upper subfacies. Relatively thin intervals with high non-carbonate sediment per-
centages are commonly quartz sand beds, for example between 73 and 74 meters. The bot-
tom of the formation is at 91.74 meters and the top is at 57.91 meters. The non-carbonate
portion of the sediment was determined by subtraction of the total carbonate measured
from unity. Depths are below land surface.

BULLETIN NO. 65

tional environment. The percentage of
quartz sand is significantly lower in core
W-16523 (Plate 2). In the lower part of the
formation, the percentage of quartz sand
averages less than 10% and there are many
stratigraphic intervals, where there is only
a trace of quartz sand. The overall average
percentage of quartz sand is less than 20%
in the upper part of the section. The per-
centage of quartz sand is significantly
lower throughout the formation (Plate 3).
In core W-17115, through the lower part of
the formation, there are many stratigraph-
ic intervals wherein only a trace of quartz
sand was observed in the formation. In the
upper part of the formation the overall per-
centage of quartz sand averages less than
5% with a few intervals having up to 25%.
The quartz-rich part of the Peace River
Formation consists of a number of subfa-
cies. The lower Peace River Formation in
core W-16242 is predominantly quartz
sand. In core W-16523 to the south, the
lower part of the Peace River is also pre-
dominantly quartz sand with some terrige-
nous mud. Most of the sand deposits con-
tain medium-to-fine grained, well-sorted
quartz sand, occurring as laminated or bio-
turbated deposits. The lower Peace River
Formation section in core W-17115 is also
predominantly quartz sand. However,
some of the deposits contain quartz gravel
and discoid quartz pebbles.
Variation in quartz content with depth
in the Peace River Formation is quite com-
plex. Approximate percentages of quartz
sand with depth in cores W-16242, W-
16523, and W-17115 are shown in Plates 1,
2, and 3. The upper section contains a sig-
nificant percentage of quartz, which is silt-
sized along with sand-sized quartz. The
highest percentage of quartz silt occurs
near the top of the stratigraphic section in
cores W-16242 and W-16523. Quartz sand
occurs in the lower part of the beds
throughout the upper part of the sequence
and as lag deposits.
The percentage of quartz sand in the
Tamiami, Caloosahatchee, Fort Thompson,

and Holocene formations in core W-16242
was approximated by subtraction of the
total carbonate measurements from unity
(Figure 9). Quartz sand percentage ranges
from about 5% to about 95%. The average
quartz sand percent-age is over 50% in the
Holocene, Fort Thompson, and Tamiami
Formation sediments and is only about 20%
in the Caloosahatchee Formation.

Variation in Clay Occurrence

Deposition of terrigenous clay is limit-
ed to the upper part of the Arcadia
Formation, the angular-bedded subfacies in
the upper part of the Peace River
Formation and to a laminated subfacies
occurring within the lower part of the Peace
River Formation. A trace of clay was found
in the outer shelf faces. The exact per-
centage of clay minerals within the
sediments was not measured, although an
attempt to quantify the relative percent-
ages of carbonate minerals, quartz and clay
was made using X-ray diffraction tech-
niques. This method did not yield reliable
data because the clay minerals interfered
with the intensity of the quartz peak in an
irregular manner.
The composition of clay minerals with-
in the Hawthorn Group has been studied in
considerable detail by Weaver and Beck
(1977; 1982). Some work on the clay min-
eralogy of the subfacies showed the clays to
be mostly palygorskite (attapulgite) and
montmorillonite (smectite). The clay min-
eralogy of the sediment sequence in the
upper part of the Peace River Formation is
more complex with a greater variety of clay
minerals, including palygorskite, sepiolite,
and montmorillonite (smectite) (Green,
1994). The mineralogy of the clays was
studied by the Florida Geological Survey
(X-ray diffractograms), Scott (1988), Green
(1994), Peck et al. (1979b), and other inves-
tigators. A trace of feldspar was also pres-
ent, but is not considered significant

FLORIDA GEOLOGICAL SURVEY

because only a few grains were noted in two
thin sections.

Variation in Glauconite Occurrence

Glauconite occurs within the Arcadia
Formation primarily as sand-sized, well-
rounded grains. It also occurs as thin lens-
es of material that are up to 10 mm in
length and about two to five mm in thick-
ness associated with other sediment parti-
cles. The glauconite grains are light green
in color and are commonly magnetic. The
well-rounded grains are interpreted to be
fecal pellets that have undergone verdisse-
ment, while the "lenses" may be primary
glauconite or clay that has been altered.
Although glauconite grains occur in a num-
ber of different depositional environments
within the Arcadia Formation, the greatest
abundance of grains occurs within muddy,
bioturbated subfacies (Tables 4 and 5). The
lenses of what may be primary glauconite
occur only in the inner and outer ramp sub-
facies primarily in relatively deep water
(see inner and outer shelf subfacies descrip-
tion). Using the classification of Odin and
Fullager (1988), the most common grains
occur in the granular habit as "1.2 Fecal
grains" with some occurrences of the film
habit in association with "2.2 Hardground"
or "2.3 Diffuse habit." All occurrences of
glauconite grains observed in the thin sec-
tions of core W-16242 are listed in Table 4.
Based on the research of Odin and
Fullager (1988), the presence of glauconite
commonly indicates deeper, cooler water,
but with a wide distribution of latitudinal
occurrences. There is some agreement with
a slightly cooler water temperature when
the occurrence of "primary" glauconite is
compared to the oxygen isotope curve for
core W-16242 (see section 3). However, the
overall climate is still interpreted to be sub-
tropical based on the flora and fauna pres-
ent in the sediments. The most abundant
occurrence of glauconite does correspond

closely to the maximum flooding of the
South Florida Platform, which occurred in
the Burdigalian and Langhian (Miocene).
COMPOSITION INFLUENCE ON
INTERPRETATION OF SEDIMENT
FACIES

Introduction

Hawthorn Group sediments vary
greatly in composition within all scales of
stratigraphic units ranging from lamina-
tion-scale to bed-scale to subfacies-scale to
sequence-scale. Siliciclastic particles are
completely mixed with carbonate particles
in virtually each depositional environment.
Therefore, the occurrence of particle types
cannot be used for interpretation of deposi-
tional environment without the addition of
primary sedimentary structures and the
occurrences of faunal effects on the
sediments, such as bioturbation. This dis-
cussion relates to depositional environ-
ments in a mixed siliciclastic/carbonate
ramp model, which is the most probable
geometry for the South Florida Platform
(see Suwannee Limestone ramp model from
Hammes, 1992).

Siliciclastic Components

Quartz

There are some general concepts that
were used to interpret depositional rela-
tionships of the sediment types based on
composition. Quartz sand is pervasive
throughout all of the depositional environ-
ments, but the processes of transport are
limited and cause specific concentrations
and grain-size distributions that constrain
depositional environment interpretations.
Within the Hawthorn Group, quartz occurs
as bedded or disseminated silt-sized parti-
cles, as bedded or disseminated sand-sized
particles, and as bedded or disseminated
gravel or pebbles.
Most occurrences of quartz pebbles
found in the cores studied were in either

BULLETIN NO. 65

Table 4. Occurrence of glauconite in core W-16242
(Note: R = Rare, A = Abundant)

Depth (ft) Depth (m) Description of Glauconite Abundance Subfacies

301-304.5 91.74-92.81 Rounded size-sized grains R 8

304.5-305.7 92.81-93.18 Rounded size-sized grains R 4,3,1

307.5-312.3 93.73-95.19 Rounded size-sized grains R 3

313.5-321.5 95.55-97.99 Rounded size-sized grains R 7

326.5-327(?) 99.52-99.67 Rounded size-sized grains R 8

349.9-362.6(?) 106.65-110.52 Rounded size-sized grains R 8

427.5-432 130.30-131.67 Rounded size-sized grains R 6

476-484 145.08-147.52 Rounded size-sized grains R 10

498-503 151.79-153.31 Rounded size-sized grains R,A1 10

505.8-520.5 154.17-158.65 Rounded size-sized grains R,A1 10

520.5-523.5 158.65-159.56 Rounded size-sized grains R,A1 8,9

523.5-533 159.56-162.46 Rounded size-sized grains R 9

533-536.5 162.46-163.53 Rounded size-sized grains R 9

537-540.8 163.68-164.83 Rounded size-sized grains R 9

540.8-546 164.83-166.42 Grains & lenses (primary) A 9,10

546.5-553.5 166.57-168.71 Grains & lenses (primary) A 9,10

553.5-554 168.71-168.86 Rounded sand-sized grains R 3,1

564-568 171.91-173.13 Rounded sand-sized grains R 11

574-574.4 174.96-175.08 Coarse sand-sized grains A 1,4

574.4-575.2 175.08-175.32 Rounded sand-sized grains R 9

578-580 176.17-176.78 Grains & lenses (primary) A 3

588-588.4 179.22-179.34 Rounded sand-sized grains R 3,1

590-591.3 179.83-180.23 Rounded sand-sized grains R 9

602.15-608.2 183.54-185.38 Rounded sand-sized grains R 9

643.2-656 196.05-199.95 Rounded sand-sized grains R 3,7

657.2-660.2 200.31-201.23 Rounded sand-sized grains R 7,3

Abundant grains are concentrated in thin intervals.

FLORIDA GEOLOGICAL SURVEY

bedded units containing shell fragments,
interpreted as beach deposits, near the
more-prominent disconformities, interpret-
ed as erosional concentrations, or in bur-
rows occurring within muddy sediments,
interpreted as storm transport lag deposits
(similar to the skeletal deposits in burrows
of Florida Bay described by Tedesco and
Wanless, 1991). When gravel or pebble-
sized quartz occurs in bedded sediment, the
processes required to transport are limited
to either stream flow or wave-generated
movement on beaches. Erratic quartz peb-
ble occurrence can occur via floating trees
in tropical environments or can be the
result of storm-transport into lower energy
environments, such as removal from beach-
es into tidal flats (filling burrows).
The occurrence of concentrated quartz
sand also provides some limitation on envi-
ronmental interpretation. Bedded quartz
sands that are reasonably well sorted occur
almost excessively in beach or dune envi-
ronments. The occurrence of quartz sand
in the absence of primary bedding and with
a mud component, whether clay or carbon-
ate, also limits environmental interpreta-
tion based on the relative concentration of
mud in the sediment. However, if the sand
concentration is very high then the deposi-
tional environment interpretation is limit-
ed to either shallow shelf, or well-flushed
intertidal. The interpretation of sand and
mud deposits being in river channels or
deltas must also be considered. In all
cases, the depositional environment must
be interpreted using a combination of sedi-
ment composition, sedimentary structures,
and biological indicators (for example the
occurrence of oysters that live exclusively
in a lagoon). The definition of a subfacies
cannot be based solely on the physical com-
positions of the sediment.
Disseminated quartz sand occurs
throughout nearly every rock type in the
Hawthorn Group. The occurrence of quartz
sand in relatively low concentrations bears
little significance to the environmental
interpretation, because it is an inert parti-

cle within a carbonate environment, and
natural processes can cause transport into
a very wide variety of depositional environ-
ments.
The occurrence of quartz silt presents a
wide variety of interpretations that could
involve several different transport mecha-
nisms. The large-scale structure of bedding
patterns and the compositional variations,
in both the horizontal and vertical dimen-
sions, bear significance in interpretation,
as well as the occurrence of fauna within
the sediment.

Clay

The occurrence of clay in a primarily
carbonate environment is relatively rare
and has distinctive implications concerning
deposition environment. Continuously tur-
bid water with suspended clay particles
commonly precludes carbonate deposition,
particularly in reefal settings. Bedded or
laminated clay deposits can only occur
where the clay particles have sufficient
time to settle from the water column and
are undisturbed by currents, storm activi-
ty, or bioturbation.
If the clay is mixed with carbonate sed-
iment in thick beds without bioturbation,
there is an implication that sedimentation
was relatively rapid and the source of sedi-
ment was relatively close. Some typical
environmental interpretations include a
tropical estuarine system with considerable
stream-transport of the terrigeneous sedi-
ment component or an open-shelf deposit
related to some type of delta. If sedimenta-
tion was not rapid, the bedding features
would not be preserved because of biotur-
bation. The proximity to the source stream
can be determined by the fossil types in the
sediment, whether they are predominantly
open marine or brackish-water species.
Nearly compositionally pure clay
deposits occur within a mixed
siliciclastic/carbonate ramp setting only in
a few depositional environments.
Laminated or thinly-laminated clay

BULLETIN NO. 65

deposits can be deposited and preserved
only in environments such as deep lagoons
and certain tidal flats. Deep, lagoonal lam-
inated-clay deposits, in order to be pre-
served without substantial bioturbation,
would have to either be relatively thin with
preservation caused by early covering by
storm deposits or be relatively anoxic, deep-
water deposits containing organic matter,
an environment non-conducive to benthic
infauna. Tidal flat deposits containing
laminated clays may or may not be biotur-
bated to a large degree with primary bed-
ding destroyed based on the rate of deposi-
tion and specific environmental conditions.
Special circumstances could allow bedding
preservation when rapid burial occurs.
Disseminated clay does not usually
occur in shallow water carbonate deposits,
because of the problem of carbonate-organ-
ism productivity loss caused by water clari-
ty reduction. The occurrence of dissemi-
nated clay in a mixed environment implies
relatively calm water with sediment mix-
ing, such as intertidal and shallow lagoonal
environments with pervasive bioturbation.
The very occurrence of clay deposits in
a mixed system places constraints on the
environmental interpretation. Utilizing
information from primary sedimentary
structures (bedding types and form) and
the fauna, depositional environments con-
taining clay can be interpreted with rea-
sonable certainty.

Other Non-Carbonate Components

There are a number of other non-car-
bonate grain types that occur within the
Hawthorn Group that produce some, but
less significant, implications concerning
depositional environment. These sediment
types include: glauconite, pyrite, iron
oxide, and potassium feldspar.
Glauconite occurrence was discussed
earlier in the text and yields some implica-
tions for environmental setting. There are
two types of glauconite grains found in
sediments of the Arcadia Formation, which

are sand-sized, rounded grains of "second-
ary" glauconite. These grains occur
throughout a variety of sediment types and
are transported like quartz sand and phos-
phorite grains of similar size. But unlike
quartz and phosphorite, they can only be
transported short distances because they
are easily abraded. The other glauconite
type is lenticular "lenses" of altered clay or
"primary" glauconite. The sand-sized glau-
conite occurs in predominantly muddy
environments within a wide range of depo-
sitional settings. The lenticular glauconite
occurs primarily in wackestones containing
open-shelf mollusk assemblages.
Pyrite occurs in some of the sediments
containing both carbonate mud and clay
and in the predominantly carbonate wacke-
stones. The occurrence of pyrite in the
sediments implies a reducing environment,
which may be related to primary phosphate
deposition (Compton et al., 1990). There is
no specific depositional environment impli-
cation other than anoxic condition in the
sediment.
Iron oxide occurrence is rare in
Hawthorn Group sediments. There are
several laminated crust deposits that con-
tain some iron oxide staining of carbonate
grains. The iron oxide occurrence implies
some atmospheric exposure.
Within the siliciclastic sediment com-
ponent, some potassium feldspar grains
were identified. These grains are quite
rare and only imply that a terrigeneous
sediment source was present. Since potas-
sium feldspar is relatively resistant to
weathering, the occurrence of a few grains
bears no significance in terms of transport
duration or depositional environment.
Potassium feldspar has been found in
northeast Florida beach sands (Martens,
1935).

Carbonate Components

Introduction

Carbonate sediment composition on a

FLORIDA GEOLOGICAL SURVEY

shallow ramp is controlled by hydrodynam-
ic factors, such as currents, wave activity,
and overall energy level of the environ-
ment. The principal carbonate sediment
components found on the southern Florida
Platform are skeletal, mud, and non-skele-
tal particles, such as intraclasts, phospho-
rite nodules, lumps, and peloids. In terms
of the hydrodynamic properties of the
sediments, the size and shape of the parti-
cles is affected by processes similar to the
siliciclastic sediment components. The
sand-sized skeletal and non-skeletal
sediments occupy the same depositional
environments as quartz sand. Larger
skeletal particles concentrate where there
is sufficient current or winnowing process-
es to allow transport or concentration. An
exception is larger non-skeletal fragments,
which can be trapped in low energy envi-
ronments and may not be transported far
from the point of origin. Carbonate muds
are deposited in areas where there is
enough time to allow sediment to settle
from the water column. Some of the depo-
sitional environments for the muds are
similar to clays. In terms of sediment
transport, carbonate sediments differ from
siliciclastic sediments in that most silici-
clastic sediment components are transport-
ed onto the platform, while carbonate sedi-
ment are produced locally with a relatively
short component of transport.
The mixed sediments of the Hawthorn
Group are described using the classification
of (Dunham, 1962). Siliciclastic sediment
components are used as modifiers of the
primary carbonate rock type. An example
would be a sandy skeletal packstone, which
is a skeletal packstone with a quartz sand
component. Various descriptive schemes
have been used to describe these sediment
types, but all suffer from flaws in implied
interpretation. The descriptive terms used
herein to identify these mixed sediments
are solely descriptive, without interpreta-
tive implications. The four principal class-

es of carbonate sediments: grainstones,
packstones, wackestones, and mudstones,
all are deposited within specific deposition-
al environments. The carbonate sediment
type does bear on the interpretation of
depositional environment in the Hawthorn
Group.

Grainstone

Grainstones do not contain any mud
and therefore are thoroughly winnowed or
had no mud at the production/accumulation
site. Based on the detailed description of
the sediments of the Hawthorn Group,
there are few examples of predominantly
carbonate grainstones, while there are
numerous nearly pure quartz sand
deposits. Grainstones can occur on beach-
es, in offshore bars within a strong current
regime, in dunes, in storm lag deposits, in
some lagoons, and on continental slopes.
Differentiation between these types of envi-
ronments was accomplished by assessing
the sedimentary structures within the sed-
iment in combination with the composition,
grain size, and sorting of the sediment. A
thinly laminated or bedded grainstone can
be interpreted as a beach deposit, a dune or
an offshore bar. If the sediment is thinly
laminated, nearly all sand-sized, is well-
sorted, and does not contain large sediment
particles, it is interpreted as a dune
deposit. If the grainstone contains larger
skeletal particles, some pebbles, is laminat-
ed, and well sorted, it is interpreted as a
beach deposit. If the grainstone is laminat-
ed, well-sorted, predominantly sand-sized,
and contains some evidence for bioturba-
tion, it is interpreted as a bar deposit. If
the grainstone is thickly-bedded, contains a
variety of sand-sized and larger particles
(particularly skeletal particles and phos-
phate nodules), and is bioturbated, it is
interpreted as a shelf deposit. The inter-
pretation is strengthened by the occurrence
of siliciclastic components. For example, if
a grainstone is bedded, contains principally
skeletal grains, and discoid quartz pebbles,

BULLETIN NO. 65

the deposit is interpreted as a beach
deposit, because it is the environment with
sufficient energy to remove any mud and to
transport both the skeletal sands and
quartz pebbles. The identification of depo-
sitional environments in which grainstones
is deposited are subject to some variation in
interpretation, but the limited number of
depositional environments allows greater
certainty in interpretation.

Packstone

Packstones are grain-supported and
contain some mud. There are a number of
deposition environments on a shallow ramp
that can produce packstones. These envi-
ronments include: intertidal flat areas
adjacent to tidal inlets (reasonably well-
washed), offshore bars, nearshore seaward
of beach deposits, and various types of lag
deposits, including emergent storm ridge
deposits within restricted water bodies and
in submergent settings over broad areas of
the shelf. There are also some primarily
biogenic deposits that form packstones,
such as certain oyster bars, Sabellarid
"reef' deposits, and the Hyotissa deposits in
the deep shelf area (Meeder, 1987). The
interpretation of the depositional environ-
ments of packstones must include analyses
of both sedimentary structure and the bio-
genic composition of the sediment.

Wackestone

Wackestones are deposited in a variety
of different environments on a shallow
ramp setting. The lithology is only nega-
tive evidence concerning what the deposi-
tional environment cannot be rather than
what it was. Mud-supported carbonate
sediments are deposited where there is suf-
ficient time to allow mud to settle out of the
water column and where the sediment is
not winnowed by wave action or strong cur-
rents. Wackestones may occur from
supratidal to intertidal to lagoonal to shal-
low or deep open-shelf environments. In

order to interpret the depositional environ-
ment of a wackestone, it is necessary to
assess both the sedimentary structures
contained within the sediment and the
composition of the faunal assemblage.
Few of the wackestones found in the
Hawthorn Group retain bedding features.
Wackestones that are laminated, fine-
grained, and contain some other features,
such as intraclasts, are interpreted to be
supratidal deposits. Wackestones having
thick beds, partially bioturbated, with some
quartz sand and a shallow water restricted
faunal assemblage are interpreted to be
intertidal deposits. Many wackestones con-
tain oysters and interbedded terrigeneous
material, which is further evidence for
intertidal deposition. Wackestones con-
taining dark-colored organic material,
heavy bioturbation with no distinguishable
1Id.liin., and a restricted assemblage of
mollusks or other fauna and/or some grass
root structures are interpreted to be
lagoonal. Wackestone deposited on the
open-shelf rarely contain any primary bed-
ding features, because they are heavily bio-
turbated. Thicker wackestone deposits,
those over one meter, that contain some
packstone lag deposits must be deposited in
the inner shelf where storm wave drag on
the bottom sediments is a significant
process. The most diagnostic feature sepa-
rating inner and outer shelf wackestones is
the faunal assemblage. The models used to
interpret the faunal assemblage with
regard to water depth are discussed later in
the text.
In the mixed carbonate/siliciclastic
sediments of the Hawthorn Group, the rel-
ative quantity of quartz sand can be used to
simplify the interpretation between inner
and outer shelf depositional environments.
High percentages of quartz sand in a
wackestone containing an open-shelf fau-
nal assemblage are interpreted to be an
inner shelf deposit, because the sand is not
likely to be transported in the deeper shelf
environment. Interbedded wackestone and
quartz sand deposits with an open-shelf

FLORIDA GEOLOGICAL SURVEY

faunal assemblage are interpreted to be
inner shelf deposits. The occurrence of
quartz sand and phosphorite lag deposits is
most common in inner shelf deposits. Lag
deposits are also observed in wackestones
that are interpreted as outer shelf deposits.
These deposits may represent shoaling of
water during some minor sea-level change
or may be the result of strong hurricane
drag in deeper water. Because of the very
heavy bioturbation of shelf wackestones,
the bulk composition of the sediments is
not a reliable indicator of depositional
environment, because shallow shelf sands
fill deep burrows in outer shelf deposits.
Interpretation of depositional environ-
ments of wackestone deposits is most diffi-
cult and must be based on composition, sed-
imentary structures, and the faunal assem-
blages found in the sediments. Upon com-
pletion of the interpretations of these envi-
ronments, the overall stratigraphic
sequence was assessed to check for obvious
interpretation errors.

Mudstone

Mudstones occur within a very limited
number of depositional environments in a
shallow ramp setting. Nearly pure clays
and mudstones accumulate where there is
a minimum effect of currents and wave
activity that tend to keep the fine sediment
in suspension. Mudstones are deposited in
lagoons, intertidal flat areas at distance
from tidal inlets, or in supratidal environ-
ments. Differentiation between these depo-
sitional environments is accomplished by
assessing the sedimentary structures and
faunal assemblage within the sediments.
All of these environments, however, share
the characteristic of occurring in restricted
waters.
Mudstone deposits commonly retain
bedding in the form of thin laminations or
thin beds. Within the Hawthorn Group,
the carbonate mudstones are commonly
associated with laminated clay deposits.
Where the mudstones are associated with

dark-colored clays containing thin lamina-
tions, they are interpreted to be lagoonal
deposits. Mudstones containing some pre-
served l-.dl.inM., some bioturbation, and a
variety of very shallow water fauna are
interpreted to be intertidal deposits.
Mudstones containing some preserved bed-
ding, fenestral pore features, some small to
medium-sized intraclasts, and a paucity of
infauna are interpreted to be supratidal
deposits.
Mudstones are also deposited in the lee
of emergent land masses occurring on car-
bonate platforms. An example of this shelf
occurrence is the mud deposits of Andros
Islands in the Bahamas (Hardie, 1977).
Many of these mud deposits are quite bio-
turbated, mixed with infauna and flora.
Although some of the mudstones found
within the Hawthorn Group could be inter-
preted to be similar to the leeward mud
accumulations, the characteristics of the
sediments show greater evidence of lagoon-
al, intertidal, or supratidal deposition.

FAUNAL OCCURRENCE AND
INTERPRETATION OF WATER DEPTH

Introduction

The faunal characteristics of mixed
carbonate and siliciclastic sediment deposi-
tional patterns in Tertiary shelf deposits
are not well documented. Most descrip-
tions of faunal occurrence with water depth
in a shelf setting are for predominantly car-
bonate environments, such as those found
in the Mediterranean (Frost, 1981; Buxton
and Pedley, 1989), the Arabian Gulf
(Purser, 1973), and the Florida Platform
(Hammes, 1992). The carbonate/siliciclas-
tic deposits of the Holocene on the west
Florida shelf are one of the few mixed sedi-
ment sequences documented (Doyle, 1979;
Doyle and Sparks, 1980).

Faunal Characteristics and Water Depth

Biological characteristics of relatively

BULLETIN NO. 65

shallow water are not consistent through-
out the world, because of climatic, current,
and natural faunal variations. Therefore,
in order to draw some comparisons between
the variations in biota found within the
Hawthorn Group and water depth, these
characteristics must be compared to other
documented faunal assemblages within the
general range of climatic conditions
believed to have occurred at the time these
sediments were deposited.
Some of the most significant faunal
assemblages that are used for comparison,
include: 1) restricted-water species, 2)
shallow shelf assemblages, including coral,
algal, and mollusks, 3) known deep shelf
species, such as some deep-water oysters,
and 4) depth tolerant species, such as some
families of bryozoans and mollusks. The
relative abundance of various types of
organisms within a sediment subfacies is
also significant.

DESCRIPTION OF THE
HAWTHORN GROUP SUBFACIES

Introduction

Examination of the three cores
revealed a large number of microfacies
based on lithic, faunal, floral composition,
and sedimentary structures. The microfa-
cies were grouped into 92 categories, but
the extreme compositional variation could
have allowed more than 200 categories to
be described. The microfacies were then
grouped into 14 primary subfacies with
each subfacies being interpreted to repre-
sent a specific depositional environment
based on water depth, salinity, and water
movement, as controlled by wave energy
and current velocities (Table 5).

Subfacies Descriptions

Introduction

Each of the 14 subfacies exhibit specif-
ic characteristics that allow them to be

interpreted to have been deposited in a spe-
cific depositional environment. A summary
of the characteristics of each subfacies is
given in Table 5. For each subfacies, there
is a list of microfacies faces types found
within the subfacies with the most abun-
dant lithic type listed first and the least
abundant type listed last.
All grain types found within the subfa-
cies are listed in order from greatest to
least abundant. The matrix material is
described for each subfacies in order of
abundance. All sedimentary structures
found within the subfacies are also listed in
order of common occurrence. The subfacies
are described in terms of where in the
Hawthorn Group they occur and how com-
mon they are in terms of the overall strati-
graphic section. In order to define some
scale for the grain size of the components
and the range in thickness of the unit,
ranges are listed for each of these charac-
teristics. A brief description of the charac-
teristics of each subfacies is given to reveal
the most diagnostic features. The diagnos-
tic features considered to be most impor-
tant are highlighted with bold type on the
table.

Subfacies 1

Subfacies 1 consists of a series of
microfacies that are either laminated, brec-
ciated, or contain coarse grains with poor
sorting. The occurrence of this subfacies is
most common at stratigraphic breaks, com-
monly correlating with abrupt increases in
the percentage of siliciclastic grain types.
Occurrences of this subfacies are character-
istically thin with a range from 15 to 60 cm.
The most common grain type is quartz sand
followed by mollusks, intraclasts, peloids,
phosphate nodules, and quartz gravel. In
the predominantly carbonate portions of
the Arcadia Formation (near the base), sub-
facies 1 commonly occurs as a laminated
crust and is often selectively dolomitized
(Figure 12). Within parts of the upper
Arcadia Formation, subfacies 1 is charac-

FLORIDA GEOLOGICAL SURVEY

terized by the occurrence of coarse pebble-
sized phosphate nodules at boundaries
between distinct changes in lithology.
Subfacies 1 is one of the only subfacies
types to have preserved bedding in the form
of thin laminations and laminations.
Although this subfacies occurs commonly
throughout the stratigraphic section of the
Hawthorn Group, it constitutes only a
small portion of the section.

Subfacies 2

Subfacies 2 is characterized by the

overall lack of mud, the occurrence of
quartz sand, gravel, and skeletal carbon-
ates with a relatively large grain-size aver-
age diameter compared to other sediment
subfacies, and the preservation of bedding
with thin laminations, laminations, and
cross beds. Virtually all carbonate and sili-
ciclastic grain types occur in subfacies 2
with all grains being at least sand-sized.
The most common grain types are quartz
sand and mollusks. In most cases, the
quartz sand component is well-sorted
(Figure 13). The overall size of grains
ranges up to 2.5 cm, which is the size of

Table 5. Subfacies Type Descriptions and Microfacies Grouped
within each Subfacies (Bold indicates primary features).

Subfacies No. Subfacies 1. Subfacies 2.

Subfacies Properties: Brecciated and laminated Laminated sands and sandy packstones
packstones

Microfacies Types: a. Sandy packstone (sandstone) a. Medium to fine-grained quartz sand
b. Sandy brecciated packstone b. Quartz gravel and sand
(In order of abundance) c. Intraclast packstone c. Quartz sand and skeletal grains
d. Brecciated packstone d. Sandy molluscan grainstone
e. Sandy interclast packstone e. Sandy molluscan packstone
f. Quartz pebbles and sand
g. Molluscan grainstone
h. Molluscan packstone

Grain Types: Quartz sand Quartz sand
Mollusks Mollusks
(in order of abundance) Intraclasts Phosphorite nodules (peloids, intraclasts)
Peloids Quartz gravel
Phosporite Nodules Lithoclasts
Quartz gravel Quartz pebbles
Corals
Red algae
Bryozoans
Vertebrates

Matrix: Micrite, microspar None, micrite, sparite, microsucrosic dolomite
Microsucrosic dolomite

Size of Grains: 0.1 to 2.5cm 0.1 to 2.5cm

Sedimentary Structures: Laminations Laminations
Thin laminations Interbedding (skeletal grains and quartz)
(in order of abundance) Brecciation Well sorted (no mud)
Poor sorting Thin laminations
Sand and shell lenses Cross-stratification

Occurrence: Lower Peace River Formation, Lower Peace River Formation
Arcadia Formation (most common in
lower)

Thickness of Strata: 15 to 60cm 3 to 10m

BULLETIN NO. 65

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 3. Subfacies 4.

Subfacies Properties: Laminated sandy mudstone/ Quartz sand/sandy molluscan
wackestone grainstone/packstone/
wackestone

Microfacies Types: a. Sandy dolomite mudstone a. Medium to fine-grained
b. Sandy dolomite wackestone quartz sand
(In order of abundance) c. Sandy dolomitic, red algae wackestone b. Quartz sand and
d. Sandy microsucrosic mollusk shell grainstone
dolomitic, molluscan, c. Quartz sand, mollusks, and
red algae wackestone intraclast grainstone
e. Sandy intraclast, dolomitic mudstone d. Sandy molluscan grainstone
f. Sandy intraclast, dolomitic wackestone e. Sandy molluscan packstone
g. Sandy calcitic, clayey f. Sandy molluscan wackestone
molluscan wackestone
h. Sandy calcitic red algae
mudstone (floating
dolomitic rhombs)
i. Sandy calcitic, molluscan,
ostracod wackestone
(floating dolomite
rhombs)
j. Sandy calcitic, molluscan,
red algae wackestone
k. Sandy calcitic, molluscan,
mudstone
I. Sandy calcitic, molluscan,
organic wackestone
(floating dolomite
rhombs)
m. Sandy calcitic, intraclasts, phosphorite
molluscan wackestone

Grain Types: Quartz sand (medium to very fine) Quartz sand
Phosphorite Phosphorite
(in order of abundance) Organics Mollusks, bivalves and
Mollusks Gastropods
Intraclasts of mud Intraclasts
Red Algae Peloids
Red algae (rare)

Matrix: Micrite None, micrite, microsucrosic
Microcrystalline dolomite dolomite
Microsucrosic dolomite Carbonate mud
Carbonate mud Clay

Size of Grains: 0.04mm to 5mm 0.1 to 10mm

FLORIDA GEOLOGICAL SURVEY

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 3. Subfacies 4.

Sedimentary Structures: Laminations Burrows (mud or sand infilled)
Thin laminations (algal) Root molds
(In order of abundance) Intraclasts Thick beds
Lithoclasts/brecciation Isolated quartz sand and shell
Mud cracks deposits
Burrows Shell beds
Fenestral pores Laminations (rare)

Occurrence: Peace River Formation, Peace River Formation
Lower part of Arcadia
Formation

Thickness of Strata: 20cm to 3m 1 to 10m

Subfacies No. Subfacies 5. Subfacies 6.

Subfacies Properties: Laminated clay Laminated microsucrosic dolomitic
mudstone/wackestone

Microfacies Types: a. Thinly laminated clay a. Microsucrosic dolomitic
b. Laminated dolomitic clay mudstone
(In order of abundance) c. Sandy, laminated dolomitic b. Sandy microsucrosic
clay dolomite mudstone
c. Sandy microsucrosic
dolomitic wackestone
d. Sandy microsucrosic
dolomitic skeletal
wackestone

Grain Types: Quartz silt Microsucrosic dolomite
Dolomite (floating rhombs) Quartz silt
(in order of abundance) Very fine quartz sand Very fine quartz sand
Phosphorite (very fine Very fine phosphorite sand
sand-sized) Red algae (sand sized grains)
Organic material Mollusks (sand sized grains)

Matrix: None, microsucrosic dolomite Microsucrosic dolomite cement
Clay Clay

Size of Components: 0.02 to 0.5mm 0.02 to 0.5mm

Sedimentary Structures: Thin laminations Laminations
Laminations Burrows
(in order of abundance) Burrows (minor)
Root structures (minor)

Occurrence: Upper Arcadia Formation Arcadia Formation always above
subfacies 5

Thickness of Strata: 1 to 2m 1 to 3m

BULLETIN NO. 65

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 7. Subfacies 8.

Subfacies Properties: Muddy quartz sand and mollusks, Quartz sand and mollusks, muddy
muddy-sandy molluscan wackestone

Microfacies Types: a. Muddy quartz sand, a. Fine to very fine
medium to fine quartz sand
(In order of abundance) b. Muddy quartz sand b. Muddy quartz sand
and mollusks c. Muddy molluscan
(agoonal species, i.e. oysters) quartz sand
c. Muddy-sandy molluscan d. Molluscan quartz
wackestone (lagoonal sand
species) e. Molluscan, red algae
d. Sandy, intraclastic quartz sand
molluscan wackestone f. Red algae quartz
e. Quartz sand sand
f. Quartz sand and shell g. Molluscan, red algae,
g. Molluscan packstone echinoid quartz sand
(oysters, barnacles)

Grain Types: Quartz sand, medium to fine Quartz sand
Clay Quartz silt
(in order of abundance) Dolomitic mud Phosphorite sand and gravel
Mollusks (lagoon and open marine) Mollusks (open-marine species)
Intraclasts Red algae
Phosphorite sand and gravel Echinoids
Red algae (rare) Glauconite (detrital)

Matrix: Micrite, microsucrosic dolomite No cement, some clay
Lime mud

Size of Grains: 0.2 to 5cm 0.04mm to 2cm

Sedimentary Structures: Burrows Burrows
Isolated sand and shell lenses or Interbedding
(in order of abundance) beds Isolated sand and shell beds
Thin beds (rare)

Occurrence: Tamiami Formation, Peace River Lower Peace River Formation, Upper
Formation (lower) Arcadia Formation

Thickness of Strata: 1.5 to 6m 1.5 to 10m

FLORIDA GEOLOGICAL SURVEY

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 9. Subfacies 10.

Subfacies Properties: Sandy molluscan skeletal wackestone Sandy molluscan, echinoid, bryozoan,
wackestone

Microfacies Types: a. Sandy molluscan packstone a. Sandy molluscan,
b. Sandy molluscan wackestone echinoid bryozoan
(In order of abundance) c. Sandy molluscan, packstone
red algae packstone b. Sandy molluscan,
d. Sandy molluscan, echinoid, bryozoan
red algae wackestone wackestone
e. Sandy molluscan, c. Sandy molluscan,
benthic foraminiferal rhodolith, bryozoan
packstone wackestone
f. Sandy molluscan, benthic d. Sandy molluscan,
foraminiferal, echinoid bryozoan wackestone
wackestone e. Sandy molluscan,
g. Sandy molluscan, benthic bryozoan, echinoid,
foraminiferal, red algae, foraminiferal
echinoid wackestone wackestone
h. Sandy molluscan, f. Sandy molluscan,
coralline, packstone bryozoan, echinoid,
i. Sandy molluscan, foraminiferal
coralline, red algae, packstone
wackestone g. Sandy molluscan,
bryozoan, echinoid,
foraminiferal, red
algal wackestone

Grain Types: Mollusks (bivalves and Mollusks
gastropods) Bryozoans
(in order of abundance) Quartz sand (fine to very fine grained) Echinoids
Phosphorite (sand-sized to gravel) Phosphorite
Bryozoans Quartz sand (fine to very fine)
Corals Benthic foraminifera
Benthic foraminifera Ostracods
Red algae Planktonic foraminifera
Ostracods Glauconite (detrital and primary)
Green algae Marine vertebrates
Glauconite (detrital)
Pyrite

Matrix: Micrite, sparite, microcrystalline Micrite, microcrystalline (mimetic)
dolomite, microsucrosic dolomite dolomite, microsucrosic dolomite
Carbonate mud Carbonate mud

Size of Grains: 0.1 to 5cm 0.1 to 25mm

Sedimentary Structures: Burrows Burrows
Boring (into skeletal grains) Marine hardgrounds
(in order of abundance) Isolated sand and shell Lamination
accumlations Thin bedding
Lenses of sand in mud Isolated sand and shell
Thin bedding (rare) accumulations

BULLETIN NO. 65

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 9. Subfacies 10.

Occurrence: Major facies of Arcadia Formation, Arcadia Formation
Caloosahatchee Formation

Thickness of Strata: 10cm to 15m 0.5 to 4m

Subfacies No. Subfacies 11. Subfacies 12.

Subfacies Properties: Hyotissa packstone (wackestone) Molluscan wackestone (no significant
quartz sand)

Microfacies Types: a. Sandy Hyotissa, molluscan a. Molluscan wackestone
wackestone b. Molluscan, echinoid
(In order of abundance) b. Sandy Hyotissa, molluscan, wackestone
bryozoan wackestone c. Molluscan, bryozoan
c. Sandy Hyotissa, molluscan wackestone
packstone d. Molluscan, foraminiferal
wackestone
e. Molluscan, foraminiferal
packstone

Grain Types: Hyotissa Mollusks
Quartz sand (medium to very fine) Echinoids
(in order of abundance) Phosphorite (sand to gravel sized) Bryozoans
Carbonate mud Phosphorite
Mollusks Quartz sand (minor, low percentage)
Bryozoans Foraminifera benthicc and planktonic)
Glauconite

Matrix: Micrite, microsucrosic dolomite Micrite, microsucrosic dolomite
Carbonate mud

Size of Grains: 0.1 to 30cm 0.04mm to 2cm

Sedimentary Structures: Boring Burrows
Laminations (rare)
(In order of abundance)

Occurrence: Arcadia Formation (middle to upper) Arcadia Formation
Tamiami Formation

Thickness of Strata: 0.5 2m 0.5 2m

FLORIDA GEOLOGICAL SURVEY

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 11. Subfacies 12.

Subfacies Properties: Hyotissa packstone (wackestone) Molluscan wackestone (no significant
quartz sand)

Microfacies Types: a. Sandy Hyotissa, molluscan a. Molluscan wackestone
wackestone b. Molluscan, echinoid
(In order of abundance) b. Sandy Hyotissa, molluscan, wackestone
bryozoan wackestone c. Molluscan, bryozoan
c. Sandy Hyotissa, molluscan wackestone
packstone d. Molluscan, foraminiferal
wackestone
e. Molluscan, foraminiferal
packstone

Grain Types: Hyotissa Mollusks
Quartz sand (medium to very fine) Echinoids
(in order of abundance) Phosphorite (sand to gravel sized) Bryozoans
Carbonate mud Phosphorite
Mollusks Quartz sand (minor, low
Bryozoans percentage)
Glauconite Foraminifera benthicc and planktonic)

Matrix: Micrite, microsucrosic dolomite Micrite, microsucrosic dolomite
Carbonate mud

Size of Grains: 0.1 to 30cm 0.04mm to 2cm

Sedimentary Structures: Boring Burrows
Laminations (rare)
(In order of abundance)

Occurrence: Arcadia Formation (middle to upper) Arcadia Formation
Tamiami Formation

Thickness of Strata: 0.5 2m 0.5 2m

BULLETIN NO. 65

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

Subfacies No. Subfacies 13. Subfacies 14.

Subfacies Properties: Bryozoan wackestone (minor quartz Mixed siliciclastic/carbonate
sand) clay, graded bed

Microfacies Types: a. Bryozoan wackestone a. Silty mudstone
b. Bryozoan, molluscan b. Clayey mudstone
(In order of abundance) wackestone c. Sandy, clayey,
c. Clayey bryozoan wackestone
wackestone d. Sandy, clayey,
foraminiferal
wackestone
e. Sandy, clayey,
foraminiferal,
ostracod
wackestone
f. Sandy, clayey,
foraminiferal,
diatom wackestone
g. Clayey, foraminiferal
mudstone
h. Clayey, foraminiferal,
diatom mudstone
i. Silty, clayey,
foraminiferal
wackestone
j. Sandy, molluscan,
clayey, wackestone
k. Silty, clayey,
molluscan, echinoid
wackestone
I. Quartz sand
m. Foraminiferal quartz
sand

Grain Types: Bryozoans Dolosilt
Mollusks Calcite silt
(In order of abundance) Phosphorite (very fine sand sized) Clay
Quartz sand (very fine, rare) Quartz silt
Clay Quartz sand (medium to very fine)
Benthic foraminifera
Mollusks
Phosphorite (fine sand-sized)
Planktonic foraminifera
Diatoms
Echinoids
Glauconite (rare, detrital)

Matrix: Microsucrosic dolomite Microcrystalline dolomite (rare),
Carbonate mud microsucrosic dolomite (rare), mostly
uncemented

Size of Grains: 0.04 to 10mm 0.04mm to 3cm

FLORIDA GEOLOGICAL SURVEY

Table 5. (Cont.) Subfacies Type Descriptions and Microfacies
grouped within each subfacies.

some discoid quartz pebbles and mollusk
shell fragments.
This subfacies commonly occurs in the
lower part of the Peace River Formation,
particularly in core W-17115 (Macro
Island), where it constitutes about 25% of
the section. The thickness of subfacies 2
occurrence ranges from three to 10 m. It
rarely occurs in the Arcadia Formation and
does not constitute a significant part of that
formation.

Subfacies 3

Subfacies 3 is a fine-grained deposit
containing a variety of preserved sedimen-
tary structures, including laminations, thin
laminations with organic material, intra-
clasts, lithoclasts associated with a brec-
ciated texture, mud cracks, burrows, and
some fenestral pores (Figure 14). Extreme
variation in composition cause a very large
number of microfacies types to occur within
relatively thin stratigraphic intervals. The
predominant grain type is carbonate mud
with a variety of minor grain types, includ-
ing quartz sand, intraclasts, phosphorite
nodules, mollusk fragments, and red algae.

This subfacies commonly occurs at, or
immediately below, strati-graphic disconti-
nuities. The subfacies is commonly dolomi-
tized, sometimes selectivity between cal-
citic subfacies. Subfacies 3 occurs in the
Peace River Formation (lower section) and
is quite common in the lower section of the
Arcadia Formation. It constitutes only a
few percent of the lower Peace River
Formation section and about 5% of the
lower Arcadia Formation section.
Thickness of occurrence range from 20 cm
to three meters.

Subfacies 4

Subfacies 4 is a predominantly silici-
clastic deposit containing wide variations
in mud content. Bedding is preserved, and
is relatively thick (10 to 20 cm). All
deposits are burrowed to some degree, even
in locations where bedding is preserved
(Figure 15). In a few locations, laminations
are preserved in lithologies lacking mud.
Root molds and a variety of course-grained
(lag) deposits occur within the subfacies.
Subfacies 4 occurs exclusively in the Peace
River Formation, most commonly in the

Subfacies No. Subfacies 13. Subfacies 14.

Sedimentary Structures: Burrows Angular bed (thick)
Laminations (rare) Graded beds
(in order of abundance) Thin bedding
Laminations
Thin laminations
Isolaged sand and shell
deposits

Occurrence: Arcadia Formation Peace River Formation

Thickness of Strata: 1 to 2m 0.5 to 1.5m

BULLETIN NO. 65

A.

B.

Figure 12. Subfacies 1. Discontinuity deposits within the Hawthorn Group.
A. A duracrust or calcrete deposit in an outcrop of the Late Pleistocene Fort Thompson Formation in Lee
County, Florida. Note the thin laminations and the general conformance of the crust to the underlying micro-
topography. (Scale in centimeters)
B. Laminated crust (arrow) from the Arcadia Formation in core W-17115 at a depth of 257.16 to 257.22 meters
(843.7 to 843.9 ft). Note the thin laminations and the conformance of the crust to the underlying microtopogra-
phy. In this case, the fine-grained crust lies upon a wackestone with a coarser texture. Laminated, dolomitized
crusts ranging between 5 and 10 cm in thickness are particularly common in the lower part of the Arcadia
Formation in core W-17115. (Scale in centimeters).

FLORIDA GEOLOGICAL SURVEY

B.

O 1 mm

Figure 13. Subfacies 2. Quartz sand and shell deposits in the Peace River Formation in
core W-17115
A. Quartz sand and discoid pebbles with skeletal carbonate fragments from core W-17115 at a depth of 59.22
to 59.34 meters (194.3 to 194.7 ft). The sediment is cemented with sparry calcite. There is no carbonate mud in
the rock. Some discoid pebbles are marked with arrows. The scale at the side is in centimeters.

B. Example of an unlithified quartz sand deposit (grain mount) containing discoid quartz pebbles from 73.15
to 74.68 meters (240 to 245 ft) in core W-17115. This sand deposit is devoid of mud and skeletal carbonates. The
core recovery is poor in this interval because the lack of mud gives the sediment little cohesion, allowing the sed-
iment to wash from the core barrel. The sand is well-sorted and medium to fine-grained.

BULLETIN NO. 65

Figure 14. Subfacies 3. Example of brecciated texture in subfacies 3 from core W-17115 at
a depth of 236.77 to 236.86 m (776.8 to 777.1 ft). Brecciated textures are common in the subfa-
cies along with some fenestral pores and mudcracks infilled with sparry calcite and some sediment.
The sediment is predominantly a fine-grained carbonate mud. In this case, the voids between the
brecciated clast are filled with sparry calcite (small arrows). Subrounded clasts (large arrow) are
common near the top of brecciated layers. (Scale in centimeters)

FLORIDA GEOLOGICAL SURVEY

Figure 15. Subfacies 4. Intertidal mixed siliciclastic/carbonate deposits from Estero Bay,
Florida and an example of subfacies 4 from the Peace River Formation.
A. Holocene mixed siliciclastic/carbonate sand deposit from an intertidal flat area located immediately
north of New Pass at Estero Bay on the southwest coast of Florida. Note the thick and thin laminations. Larger-
scale bedding is relatively thick at over 10 cm. The deposit is bioturbated, but primary bedding is still preserved
to some degree. Dark colored laminations occur within the sand and are organic deposits. A variety of thin-
walled mollusks are mixed with the quartz sand. Intraclasts are common in this environment.

B. An example of subfacies 4 from core W-16523 at 36 m (118 ft) below surface in the Peace River
Formation. In core W-16523, subfacies 4 shows some preservation of laminations, but most preserved bedding
is relatively thick and alternates between clean, fine quartz sand and muddy quartz sand. Also, the muddy sand
tends to have few, if any, laminations preserved, because of extensive bioturbation. Some organic staining is
present, but is distorted by either bioturbation or perhaps by the coring process. (Scale in centimeters)

BULLETIN NO. 65

lower section. It constitutes up to 15% of
the section.
Subfacies 5

Subfacies 5 is a laminated clay occur-
ring exclusively in the upper part of the
Arcadia Formation. The predominant
grain type is clay with minor occurrences of
quartz silt and sand, dolosilt, and sand-
sized phosphorite grains. The clay, com-
monly is very darkly colored, nearly black
(Figure 16). It lacks preserved skeletal car-
bonate grains. In some cases, the laminat-
ed clays are burrowed to a minor degree
and some apparent root structures are pre-
served. Subfacies 5 always grades upward
into subfacies 6. It constitutes a minor por-
tion of the upper Arcadia Formation (less
than 2%) in the northern part of the study
area and does not occur in core W-17115.

Subfacies 6

Subfacies 6 is a laminated, microsu-
crosic dolomitic mudstone/wackestone.
Subfacies 6 always occurs associated with
subfacies 5, normally stratigraphically
above it. The transition between subfacies
5 and 6 is usually gradational, but in some
cases the laminated clays of subfacies 5 are
brecciated at the contact (Figure 17). These
dolomitic mudstones and wackestones are
very fine-grained with the predominant
particle type being microsucrosic dolomite.
A variety of other particle types occur as
mostly floating grains that include quartz
silt, very fine sand-sized quartz sand and
phosphorite, and sand-sized red algae and
mollusk shell fragments. Subfacies 6 is
commonly laminated with the laminations
sometimes disturbed by burrows. The
thickness of deposits ranges from one to
three m and this subfacies constitutes only
to 2% of the Arcadia Formation.

Subfacies 7

Subfacies 7 is a muddy quartz sand
and mollusk deposit or a clayey/sandy mol-

luscan wackestone. Variations in composi-
tion are rather extreme, but some sedimen-
tary structures are preserved. Subfacies 7
is similar to subfacies 4 in composition, but
it contains significantly more mud, the pre-
served bedding is thinner, the degree of bio-
turbation is greater, the occurrence of intr-
aclasts is greater, and the mollusk assem-
blage is different. Fine quartz sand is the
predominant particle type with lime mud
and clay being the next most abundant par-
ticle types. A variety of other particle types
occur within the deposit, including mol-
lusks, intraclasts, sand and gravel-sized
phosphorite nodules, and a few red algae
grains. The matrix mud is commonly
dolomitic or a mix of dolomite and clay.
This subfacies occurs in the Tamiami
Formation and in the lower Peace River
Formation. The thickness of occurrences
ranges from 1.5 to six m and constitute up
to 10% of the lower Peace River Formation.

Subfacies 8

Subfacies 8 is an unlithified (in most
cases) muddy quartz sand with mollusks
and other skeletal grains (Figure 18). The
predominant characteristics are the lack of
preserved 1I.-ldinM., very heavy bioturba-
tion, some percentage of mud throughout
the section, and interbedded wackestone
and coarse sand and shell containing no
mud. The predominant biogenic particle
type is mollusks with some red algae and
echinoid fragments. Carbonate mud occurs
in most of the sediment with some clay also
present. Some deposits of coarse shell and
quartz sand also occur within subfacies 8.
These coarse deposits contain no significant
quantity of mud or clay. Detrital grains of
glauconite occur, but represent an insignif-
icant percentage of the sediment composi-
tion.
Subfacies 8 occurs within the lower
Peace River Formation and in the upper
part of the Arcadia Formation. It consti-
tutes a significant part of the lower Peace

FLORIDA GEOLOGICAL SURVEY

A.

CM

0 1 mm-

Figure 16. Subfacies 5. Laminated terrigeneous clay.
A. Core W-16242 between 133.11 and 133.20 m (436.7 to 437 ft). Some burrows infilled with the overlying
carbonate sediment occur at the top of the core. The laminations are 1 and 5 mm in thickness (arrows mark
some laminations). The color of the clay is dark green.
B. Thin section from 133.5 m (438 ft) in core W-16242. Note the lack of skeletal carbonate fragments and
quartz sand or silt. Some of the clay is very dark in color and appears nearly opaque in the thin section. This
dark-colored material is commonly thin and lenticular. It is believed to be organic material or remnant organic
staining. The lighted-colored streaks mark the base of some laminations.

BULLETIN NO. 65

Figure 17. Subfacies 6. Example of subfacies 6 in core W-16242 from a depth of 131 to 133.5
meters. Contact between subfacies 5, a clay deposit, and subfacies 6, a carbonate mud deposit, in
core W-16242 is between 131 and 132.0 meters (429.8 to 433 ft). The actual contact occurs at the
arrow labelled as "C" and clay is mixed into the overlying carbonate sediment. Within this section,
the deposit is laminated. The base of subfacies 6 is burrowed (arrows labelled "A"). Note the very
fine-grained texture of the carbonate. (Scale in centimeters).

FLORIDA GEOLOGICAL SURVEY

CM

Figure 18. Subfacies 8 in the Arcadia Formation.
A. Segment of core between 160.63 and 160.75 meters (527 to 527.4 ft.). Note the mottled texture and the "salt
and pepper" appearance, caused by the mixture of quartz sand and dark-colored phosphorite sand. (Scale in cen-
timeters)

B. Fine to very fine quartz sand and sand-sized phosphate in a matrix of carbonate mud from the Arcadia
Formation from 159.87 to 159.96 meters (524.5 to 524.8 ft). Thin section in plain light from 159.87 m (524.5 ft)
in core W-16242. Note the relatively abundant percentage of quartz sand and sand-sized phosphate nodules.
The large concentration of sand-sized sediment and the relatively large thickness of these deposits (in many
cases over 5 meters) is an indication of nearshore sediment transport. The deposit contains significant quanti-
ties of carbonate mud. Note that there is no grading and the distribution of grains appears to be random, also
an indicator of heavy reworking.

BULLETIN NO. 65

River Formation stratigraphic section, up
to 35%. It is also a significant subfacies in
the upper part of the Arcadia Formation,
particularly in the northern part of the
study area (core W-16242), where it consti-
tutes up to 15% of the section.

Subfacies 9

Subfacies 9 consists of a number of
microfacies types, but the predominant
lithology is sandy molluscan wackestone
(Figure 19). The most significant charac-
teristics of subfacies 9 are the high degree
of bioturbation, the lack of preserved bed-
ding, the large diversity of biogenic grain
types, the presence of quartz sand in signif-
icant abundance, and the presence of car-
bonate mud. The most abundant particle
type is carbonate mud, much of which is
dolomitized. Quartz sand and phosphorite
nodules are dispersed throughout this sub-
facies. Glauconite and pyrite grains are
commonly found in the middle section of
the Arcadia Formation. In the lower part of
the Arcadia Formation, a wide variety of
biogenic components occur, with mollusks
and corals being quite common (Figure 19).
In this part of the section, the predominant
wackestones commonly contain molluscan
and coralline packstones and numerous
other grain types are common. In the mid-
dle and upper part of the Arcadia
Formation, the skeletal grain components
are predominantly mollusks with occur-
rences of many other flora and fauna.
Although subfacies 9 is heavily bioturbat-
ed, there are some rare occurrences of thin
bedding. Burrows are commonly infilled
with coarser sediment and shell, and sand
beds lacking mud are present. Some phos-
phatic crusts occur within subfacies 9, com-
monly at discontinuities. Subfacies 9
occurs throughout the Arcadia Formation
and is the most common subfacies, consti-
tuting up to 45% of the formation at a given

location.

Subfacies 10

Subfacies 10 is a sandy, molluscan,
echinoid, bryozoan wackestone. It contains
a variety of other microfacies types when
viewed on a smaller scale. The subfacies is
heavily bioturbated with bedding rarely
preserved. The predominant grain type
found in the sediment is carbonate mud. In
many ways, subfacies 10 is similar to sub-
facies 9, but there are some significant dif-
ferences, which are: the abundance of
quartz sand is lower, the predominant bio-
genic grain types are mollusks, echnoids,
and bryozoans commonly similar in abun-
dance, the percentage of skeletal grains in
the matrix mud is often lower, the range of
grain sizes of particles is smaller, and no
corals or green algae are found in this sub-
facies (Figure 20). Skeletal grain deposits
lacking mud are not common, but still are
present. Although some bedding is pre-
served, it is rare and is thin or lamination
(less than one cm in thickness) in scale.
Subfacies 10 occurs predominantly in the
upper and middle parts of the Arcadia
Formation, where it constitutes up to 30%
of the section at a given location.

Subfacies 11

Subfacies 11 is a Hyotissa packstone or
wackestone. The predominant feature of
this subfacies is the abundant occurrence of
the genus Hyotissa, which is a large, oyster-
like mollusk. These mollusks are quite
large, ranging up to 30 cm in height and are
commonly found in a matrix of carbonate
mud or quartz sand (Figure 21). Other
molluscan species and byrozoans occur in
the sediments. In many cases, the Hyotissa
shells are found in living position and are
heavily bored by other marine organisms.
This subfacies is common in the Tamiami
Formation and occurs in the upper and

FLORIDA GEOLOGICAL SURVEY

Figure 19. Examples of subfacies 9 in core W-16242.

A. A sandy molluscan wackestone from 191.63 to 191.72 meters showing molds of gastropods and bivalves.
The arrow points to a Turritella sp., which commonly lives in a shallow, open-marine environment. (Scale in cen-
timeters)

B. A sandy molluscan wackestone/packstone from 190.8 to 190.9 meters. The lower arrow points to a shell
fragment from the genus Yoldia sp. and the upper arrow to a mold of a Cyprea sp. Other common mollusks
occurring in subfacies 9 include Chione sp. and various different mollusks believed to occupy the shallow, open-
marine environment. These mollusks commonly occur in 1 to 10 meters of water in an open shelf environment
(Parker, 1956). Arrow at upper edge of core is for up orientation. (Scale in centimeters)

C. Thin section from 186.5 m (611.9 ft.) showing a sandy molluscan packstone/wackestone in plain light. Note
the large number of mollusk grains (selectively dissolved molds remaining). Arrow to dissolved mollusk.

r --

Figure 19. Examples of subfacies 9 in core W-16242.
A. A sandy molluscan wackestone from 191.63 to 191.72 meters showing molds of gastropods and bivalves.
The arrow points to a Turritella sp., which commonly lives in a shallow, open-marine environment. (Scale in cen-
timeters)

B. A sandy molluscan wackestone/packstone from 190.8 to 190.9 meters. The lower arrow points to a shell
fragment from the genus Yoldia sp. and the upper arrow to a mold of a Cyprea sp. Other common mollusks
occurring in subfacies 9 include Chione sp. and various different mollusks believed to occupy the shallow, open-
marine environment. These mollusks commonly occur in 1 to 10 meters of water in an open shelf environment
(Parker, 1956). Arrow at upper edge of core is for up orientation. (Scale in centimeters)

C. Thin section from 186.5 m (611.9 ft.) showing a sandy molluscan packstone/wackestone in plain light. Note
the large number of mollusk grains (selectively dissolved molds remaining). Arrow to dissolved mollusk.

BULLETIN NO. 65

0 0a

-a

B.r

0 1
n

Figure 20. Examples of subfacies 10 from the Arcadia Formation in core W-16242.
A. Thin section from 155.75 meters (511 ft) in polarized light. The lithology is a red algae/bryozoan wacke-
stone. Red algae oncoids occur below a depth of 85 meters or on rocky shoreline (Wilson, 1975). The occurrence
of the red algal oncoids in the fine-grained matrix is distinctive evidence for a deep-water environment.

B. Example of the bryozoan Cyclostomata from the Arcadia Formation in core W-16242. This genera of bry-
ozoan has good tolerance to water depths of over 100 meters. Although it is common in relatively deep water, it
also occurs in some shallow water deposits to near wave base. Therefore, it is not an absolute deep water indi-
cator, but when found in abundance with other features of the sediment, such as no quartz sand and other deep
water tolerant mollusks, it is considered to be an auxiliary depth indicator. From 139.08 meters (456.3 ft) in core
W-16242 in plain light.

FLORIDA GEOLOGICAL SURVEY

A. L_ 9rrfllf ..

-" -4

0 1MM

Figure 21. Subfacies 11. Examples of the relatively deep water mollusk Hyotissa
subfacies from the Arcadia Formation in core W-16242.
A. Hyotissa subfacies example from the Arcadia Formation in core W-16242 between 126.7 and 126 meters
(415.6 and 416 ft). Note that the Hyotissa are in growth position (vertical orientation) in the lower part of the
core sample. The sediment between shells is a quartz-rich carbonate mud. Hyotissa are marked by arrows.
(Scale in centimeters)

B. Thin section from 126.7 meters (415.6 ft) in core W-16242 (field width is 16.20 mm). Note that the Hyotissa
shell can be porous (arrow) and commonly contains sediment incorporated into it, such as sand-sized phospho-
rite grains.

BULLETIN NO. 65

middle part of the Arcadia Formation,
where it constitutes a minor part of the
stratigraphic section (a few percent).
Subfacies 12

Subfacies 12 is a molluscan wackestone
lacking significant concentrations of quartz
sand. It occurs predominantly in the south-
ern part of the study area within only the
Arcadia Formation (core W-17115). The
predominant grain type is carbonate mud
with significant quantities of mollusks and
some echinoids and bryozoans (Figure 22).
Minor quantities of phosphorite, fine
quartz sand, and benthic and planktonic
foraminifera also occur in the sediment.
The sediment is extensively bioturbated,
but some laminations are preserved. The
concentration of skeletal grains is lower
compared to subfacies 9 and the sediment
can be described as moderated to lightly
packed (relatively lower abundance of
skeletal grains) wackestone. Subfacies 12
constitutes only about three to five percent
of the Arcadia Formation section and is
most significant in the middle of the forma-
tion.

Subfacies 13

Subfacies 13 is quite similar to subfa-
cies 12, but the dominant skeletal grain
contained in the sediment is bryozoans
(Figure 22). This subfacies also occurs only
within the Arcadia Formation in the south-
ern part of the study area (core W-17115).
The most significant characteristics of this
subfacies are a lack of preserved bedding
caused by extensive bioturbation, the mod-
erate to slight packing of skeletal grains,
and the relatively low abundance of quartz
sand. Where quartz sand and phosphorite
occur in the sediment, they are fine sand-
sized. Some clay occurs within this subfa-
cies. A few preserved laminations occur,
but are truncated by burrows.

Subfacies 14

Subfacies 14 occurs solely within the
Peace River Formation. This subfacies is
characterized by extremely wide variations
in composition, preserved, thick angular
beds (Figure 23), graded beds (Figure 24),
some preserved thin beds and laminations,
and intermittent coarse sand and shell
beds lacking mud. The unit is rarely bio-
turbated. A large number of grain types
occur within the formation. The predomi-
nant grain types are dolosilt, calcite silt,
clay, and quartz silt and sand. The abun-
dance of these constituents varies within
the unit as a whole and within beds (see
composition section). Within the thick
beds, foraminifera and diatoms are com-
monly abundant with some mollusk and
echinoid fragments occurring at the base of
beds. Sand-sized phosphorite grains are
common throughout the unit and a few
grains of glauconite occur. The unit rarely
contains any significant quantities of
cement. Previous studies showed that the
dolosilt grains had sharp edges and showed
little pitting (Green, 1994). This unit con-
stitutes all of the upper part of the Peace
River Formation in the northern part of the
study area, but it pinches out from north to
south and does not occur in core W-17115.

INTERPRETATION OF SUBFACIES

Introduction

Sediment composition, sedimentary
structures, faunal and floral assemblages
and stratigraphic succession were used to
interpret the sediment subfacies. The
described subfacies are interpreted to be
within five general categories. These gener-
al groups include: 1) emergent or disconti-
nuity deposits, 2) restricted shallow water,
including supratidal, intertidal, and
lagoonal deposits, 3) beach and nearshore
deposits, 4) shallow ramp, including car-
bonate, siliciclastic, and mixed deposits,
and 5) deep ramp, including mixed carbon-
ate and silicilcastic deposits. It is impor-
tant to note that quartz sand occurs in vir-

FLORIDA GEOLOGICAL SURVEY

A.

(bar scales are 1 cm increments).
A. Example of subfacies 12 from core W-17115 between 195.38 and 195.53 meters (641 and 641.5 ft). This mol-
luscan wackestone contains no significant quantity of quartz and the density of biota within the sediment is quite
low. Mollusks are the predominant fauna (marked by arrows). (Scale in centimeters)

B. Example of subfacies 13 from core W-17115 between 197.66 and 197.82 meters (648.5 and 649 ft). The biota
in this subfacies are virtually all bryozoa with a few mollusks. The matrix sediment is carbonate mud with no
quartz sand and a minimal quantity of phosphorite. The arrow marked "A" points to a stem of a tubular bry-
ozoan. The arrow marked "B" points to a flat, platy branching bryozoan, which is another genus. (Scale in cen-
timeters)

BULLETIN NO. 65

1000 METERS

- UNDIFFERENTIATED HOLO(

0
o 20.
Z
O

0 25-

1 -
S30 -

- 35.
LU

LL 40.

I
45
45.

Figure 23. High-resolution seismic reflection profile (modified boomer source) in the
Caloosahatchee River illustrating subfacies 14, labelled as Peace River Formation (delta-
ic facies). Profile modified from Missimer and Gardner (1976). Note the large-scale angu-
lar bedding in the upper Peace River Formation. The bedding is flat-lying in the lower
Peace River Formation and the disconformity between the Arcadia Formation and Peace
River Formation shows some erosion features (truncated reflectors).

3500 FEET

2000
7000

FLORIDA GEOLOGICAL SURVEY

(w) Hld30

w -j-
-J?

o cj)o
zowo
m al

ca X

e-Io

0N

o~
U)V

o l

040
r-q

cq -

(4) Hld3G

i)

BULLETIN NO. 65

tually all depositional environments from
shallow to deep with the exception of the
laminated clay deposits (subfacies 5) and
within sections of a few slightly-packed
wackestone subfacies (subfacies 12 and 13).
The diagnostic features most important in
the interpretation of the subfacies are
shown in bold type within Table 5.

Discontinuity Deposits, Subfacies 1

A number of probable discontinuity
horizons (described as subfacies 1) are pres-
ent in the Arcadia Formation and some
within the Peace River Formation. These
features are noted on Plates 1, 2, and 3 and
in the rock data matrices. There are two
general types of features that are interpret-
ed to be exposure horizons or discontinuity
deposits found within subfacies 1, subfacies
3, and subfacies 6, and one or two addition-
al deposits found in subfacies 9 and 10.
The first type of discontinuity surface
is a laminated to thinly laminated crust
consisting of quartz sand and carbonate
cemented by either micrite or dolomite.
These crusts are relatively thin, ranging in
thickness from two to 10 cm, and occur only
at stratigraphic breaks between two differ-
ent subfacies, usually atop a shallow-water
deposit. The laminated crusts do not have a
uniform thickness and laminated
sediments sometimes infill apparent
karstic features within the underlying sed-
iment. The crusts commonly contain
marine mollusk shell fragments and nodu-
lar, detrital phosphorite. Based on the
characteristics described, these crusts are
interpreted to be calcretes, similar to the
laminated crusts, termed duracrusts by
Goudie (1973), Multer and Hoffmeister
(1968), and Robbin and Stipp (1979). The
calcretes occur within the lower and upper
parts of the Arcadia Formation.
The second discontinuity interpreted to
be an exposure horizon is a nearly pure,
microsucrosic dolomite crust, sometimes
laminated with angular lithic fragments.
The crust is dolomitized along the top of the

discontinuity and sometimes contains fine-
grained mud within burrows. The crust is
usually associated with an underlying, lam-
inated calcitic mud containing few skeletal
grains and sometimes fenestral pores.
Commonly, the underlying calcitic sedi-
ment is brecciated or contains mud cracks.
These dolomite crusts stand out because
they are bounded by calcitic sediments con-
taining no evidence of dolomitization. The
crusts range from five to 20 cm in thick-
ness and are common in the lower part of
the Arcadia Formation (five to 10 occur-
rences in core W-17115). Because of the
selective dolomitization of the crusts, their
irregular geometry, their brecciated
nature, and their stratigraphic position at
the contacts between differing subfacies,
they are interpreted to be selectively
dolomitized levee crests such as those
described in the Holocene of Andros Island
in the Bahamas (Shinn et al., 1965; Shinn,
1983). Some alternative depositional envi-
ronment interpretations may also include
selectively dolomitized crusts occurring in
intertidal settings, such as those in the
Florida Keys (Atwood and Bubb, 1970).
Another discontinuity deposit is a
cemented to uncemented carbonate, con-
taining lithic fragments, gravel and pebble-
sized phosphorite nodules, some quartz
sand and gravel with little mud. These
deposits commonly mark the top of a subfa-
cies and are important markers in the
stratigraphic column. The cements are
either microsucrosic dolomite or phospho-
rite.

Restricted Facies, Subfacies 3, 4, 5, 6 and 7

A number of subfacies are interpreted
to be restricted water depositional environ-
ments. These environments are: laminat-
ed to non-laminated sandy carbonate
deposits (subfacies 3), predominantly silici-
clastic with a minimal quantity of mud
(subfacies 4), laminated terrigenous clays
(subfacies 5), laminated predominantly car-

FLORIDA GEOLOGICAL SURVEY

bonate supratidal deposits containing some
quartz sand (subfacies 6), and mixed
muddy quartz sands and carbonate muds
with lagoonal mollusks (subfacies 7). A
shallow-water restricted environment pro-
duced the laminated sandy mudstone/
wackestone subfacies (3). This subfacies is
separated from subfacies 6, because it has
large variations in amount and composition
of carbonates and siliciclastics, it can be
either dolomitic or calcitic, and it is not
absolutely associated with an underlying
terrigenous clay faces. Subfacies 3 com-
monly occurs near or at the top of shallow
water subfacies at many different locations
within the Arcadia Formation.
Laminations are commonly preserved in
the deposits, but an increase in disturbance
of bedding by bioturbation is noted in the
lower part of some sequences. Many sedi-
mentary structures are preserved in subfa-
cies 3 compared to subfacies 6. Brecciation,
mud cracks, intraclasts, lithoclasts, and
burrows, sometimes containing a higher
concentration of skeletal grains, occur with-
in the laminated sandy mudstone/wacke-
stone subfacies. Based on the sedimentary
structures, it is interpreted to be a peri-
tidal (supratidal and intertidal) deposit
occurring over a wide range of energy con-
ditions from above the mean high tide to
about one to two m below sea level to areas
located adjacent to tidal channels. There is
a corresponding wide range of mixed car-
bonate and siliciclastic compositions con-
tained within subfacies 6.
Subfacies 4 is a predominantly silici-
clastic deposit with a skeletal carbonate
and carbonate intraclast component. It is
laminated in certain cases and it can be
separated from subfacies 2 (beach subfa-
cies) by the occurrence of burrows, root
molds, and some mud. It commonly occurs
with an association to subfacies 7. The bed-
ding is commonly relatively thick at 15 to
20 cm. It is interpreted to be a relatively
high-energy deposit (due to lack of signifi-
cant mud deposition), where mud deposi-
tion is not common, such as adjacent to

tidal channels, in intertidal areas adjacent
to deep water, and in areas adjacent to bar-
rier islands. An alternative interpretation
is a shallow offshore bar or ebb delta near a
tidal inlet or offshore of a sandy beach. The
occurrence of intraclasts does suggest
restricted rather than offshore deposition.
Some Holocene deposits with a similar
structure and composition occur in
Charlotte Harbor, Estero Bay, and in the
Ten Thousand Islands (Huang and Goodell,
1967; Missimer, 1970; Scholl, 1963).
Subfacies 4 is considered to be a minor sub-
facies with limited occurrence in the Peace
River Formation.
A laminated terrigenous clay subfacies
(5) occurs at several intervals, commonly
separating predominantly carbonate com-
position sediments within the Arcadia
Formation. This subfacies is characterized
by the occurrence of thin laminations with
some minor burrows and infilled features
characterized by branching and thinning
with depth verses relatively uniform thick-
ness of burrow diameters which are
believed to be root structures. The clays
are palygorskite (attapulgite), sepiolite and
montmorillonite (smectite), sometimes con-
taining various impurities. Commonly, the
clay contains some microsucrosic dolomite
rhombs and some very fine sand-sized
phosphorite (francolite).
Based on the laminations, the associa-
tion with the overlying supratidal carbon-
ate, the presence of organic material, and
the lack of any open marine microfossils,
such as foraminifera, the laminated clay
subfacies (5) is interpreted to be a lagoonal
deposit in a very restricted water body with
little diversity of bottom-dwelling organ-
isms. The dark color, from dark green to
nearly black, is indicative of a reducing bot-
tom condition, which may indicate a
lagoonal environment with no significant
infauna adapted to the reducing conditions
(may be deep lagoon, because of low oxy-
genation). Also, the clays commonly con-
tain elongate streaks of organic material.
An alternative interpretation of the dark-

BULLETIN NO. 65

colored, laminated clays would be a fresh-
water marsh. However, there are some
traces of marine fossils that suggest marine
deposition is more probable. Dark colored
clays, interpreted as anoxic lagoonal
deposits, are known to occur in predomi-
nantly carbonate sequences within
cyclothems in the Upper Pennsylvanian of
Kansas and in the Illinois Basin (Evans,
1966; James, 1970).
The laminated carbonates of subfacies
6 lie on top of the laminated clays of subfa-
cies 5. The contacts are abrupt (composi-
tion changes in 20 to 30 cm), but some clay
is incorporated into the overlying carbonate
(Figure 17). There is a compositional grad-
ing from nearly no carbonate at the base of
subfacies 5 to nearly pure carbonate at the
top of subfacies 6.
Subfacies 6 contains a series of diag-
nostic features that suggest it was deposit-
ed in an intermittently exposed environ-
ment, such as supratidal or high intertidal.
First, it is a fine-grained deposit that
required minimal wave activity to allow
deposition. Second, laminations and fine
laminations are preserved in many exam-
ples. Third, it is sometimes capped with a
laminated, microsucrosic dolomite crust
(subfacies 1) or a laminated carbonate mud
containing oblate mud clasts with organic
staining. Fourth, the subfacies occurs near
or at the top of sediment sequences at a
stratigraphic break marked by a change to
a different subfacies. The thickness of sub-
facies ranges from one to three m. The
composition and sedimentary structures of
subfacies 6 share the characteristics of the
Holocene supratidal deposits of the
Bahamas and the Persian Gulf (Shinn et
al., 1969; Purser and Evans, 1973; Shinn,
1983; Hardie and Shinn, 1988).
A muddy quartz sand with mollusks
and muddy sandy molluscan wackestone
(subfacies 7) occurs in association with sub-
facies 2 in shoaling-upward sequences. The
mud component of subfacies 7 is a mix of
calcitic mud, dolosilt, and clay. Shallow
water mollusks, particularly restricted oys-

ters, pectens, and barnacles, commonly
occur in this subfacies. There is a rare
occurrence of thin beds, but most of the
deposits are bioturbated. Intraclasts of car-
bonate mud with clay occur within the
sediments as well as concentrations of mol-
lusk shell and phosphorite nodules. There
is a complete mixing of the siliciclastic and
carbonate components within these
sediments. Subfacies 7 is interpreted to be
a shallow lagoonal deposit based on the
presence of restricted water mollusks and
the percentage of mud in the sediment.
This subfacies occurs within the Tamiami
Formation, the lower section of the Peace
River Formation (10 to 15% of section), and
in several parts of the Arcadia Formation
section (two to five percent of section). The
stratigraphic position of the subfacies in
Holocene sediments is well illustrated at
the top of core W-16242 (Plate 1) and was
previously described beneath Sanibel
Island by Missimer (1973a), in upper
Biscayne Bay by Wanless (1969), and in
Charlotte Harbor, Florida by Huang and
Goodell (1967).

Beach Facies: Laminated Sands,
Grainstones and Packstones with
Quartz Sand, Subfacies 2

A series of mud-free quartz sands,
sands and mollusk shells, and quartz sands
with discoid, quartz pebbles and quartz
gravel occurs within the Peace River
Formation. Some of the deposits are lami-
nated with either horizontal or angular ori-
entations (cross-bedded). Many of the
microfacies occurring within this subfacies
are composed solely of quartz sand. Some
of the quartz sands contain discoid quartz
pebbles up to 1.5 cm in diameter (Figure
13). The presence of discoid quartz pebbles
in the stratigraphic section in southern
Florida was previously reported by Peck et
al. (1979a) and recently in Warzeski et al.
(1996). In terms of hydraulic movement,
the quartz pebbles are similar to the larger
mollusk fragments that occur on modern

FLORIDA GEOLOGICAL SURVEY

beaches with the well-sorted, fine quartz
sand. The predominantly skeletal deposits
are similar in structure and composition to
the Holocene deposits of Sanibel Island,
Florida (Missimer, 1973a), which contain
both thick beds of shell alternating with
laminated quartz sands (also in core W-
16242, Holocene section). Although subfa-
cies 2 is best illustrated in the Marco Island
core, it is a major regional faces. These
deposits range in thickness from three to 10
m, which is similar to the thickness of
Holocene sand and shell deposits of the
Florida West Coast barrier islands
(Missimer, 1973). Based on the lamina-
tions and cross-laminations, the sorting of
the sands (hydraulically well sorted in most
cases), the occurrence of discoid quartz peb-
bles, and the lack of mud, subfacies 2 is
interpreted to be a beach deposit or a very
shallow ramp deposit adjacent to the shore-
line. The Peace River Formation section in
core W-17115 contains 15 to 20 percent of
this subfacies.

Inner Ramp Facies, Subfacies 8 and 9

Subfacies 8 and 9 are predominantly
siliciclastic and carbonate units that share
the following diagnostic characteristics: 1)
extremely heavy bioturbation and a gener-
al lack of preserved 1l.lding., 2) diverse
composition with a mix of sediment and
faunal and floral types, 3) the presence of
corals, mollusks, red algae, some green
algal, and other fauna and flora that live in
a shallow, open-shelf environment, 4) the
presence of some mud, either carbonate or
clay, and 5) frequent occurrences of win-
nowed quartz sand and/or shell beds sand-
wiched between wackestones or muddy
sands.
Subfacies 8 is a group of quartz-rich
microfacies. It is a slightly muddy quartz
sand and shell unit containing a nearshore
mollusk assemblage with echinoids, some
bryozoans, and red algae (Figure 18). The
quartz sand ranges from medium to very
fine in grain size and the sand component

is generally well-sorted. The mud compo-
nent is a combination of carbonate silt and
clay with both calcite and dolomite grains
and a small concentration of clay minerals
being mostly montmorillonite and paly-
gorskite. Detrital grains of glauconite
occur in some of the sands. Thin concen-
trations of winnowed sand and shell, com-
monly containing phosphorite sand and
gravel, occur in between muddy sediments.
Subfacies 9 is a series of mixed carbon-
ate/siliciclastic microfacies containing a
diverse composition. The predominant
fauna is mollusks with some echinoids, bry-
ozoans, red algae, green algae, and corals
(lower section of Arcadia Formation)
(Figure 19). Some detrital phosphorite and
glauconite occurs throughout the section
and is concentrated at discontinuities.
Some "primary" glauconite occurs in the
sandy wackestone microfacies in deeper
water where there is less quartz sand.
Concentrations of winnowed sand, shell,
and phosphorite occur frequently within a
wackestone matrix. No evidence for well-
developed reefs was found and the vertical
and horizontal distribution of corals seems
to indicate that the corals are solitary,
growing on hardgrounds.
Based on the characteristics described,
the quartz sand and shell subfacies (subfa-
cies 8) and the sandy molluscan/skeletal
subfacies (subfacies 9) are interpreted to be
inner ramp deposits. The inner ramp is
defined as open marine conditions with
water depths from about 1.5 to 20 m.
Although wave base in the Gulf of Mexico is
considered to be about 10 m, storm wave
base is at about 20 m (Bernard et al., 1959;
Bernard et al., 1962). Evidence for sedi-
ment movement between 10 and 20 m in
the Gulf of Mexico includes the observation
of coarse sediment accumulations on the
bottom, particularly in small depressions.
Some grading of sediment on continental
shelves is reported to a depth of 20 m at
several other locations around the world,
such as the Atlantic Ocean shelf off the
United States and the shelf off the Elbe

BULLETIN NO. 65

Estuary (Swift, 1970; Reineck and Singh,
1980). In the Gulf of Mexico off of Sanibel
Island, from the shoreline to a depth of 20
m, there are storm lag deposits and the
soft, sessile organisms are not present on
the rock ledges. From a depth of 20 m sea-
ward, there is no visible evidence of shifting
sediment.
Subfacies 8 shows similar characteris-
tics to the predominantly siliciclastic
Holocene Southwest Florida ramp, where
the sands contain some mud and mollusk
shell is the predominant skeletal compo-
nent (Doyle, 1979; Holmes, 1988). Another
example of a similar mixed siliciclastic/car-
bonate ramp is the Holocene inner ramp off
Puerto Rico (Pilkey et al., 1988). Subfacies
8 constitutes about 50% of the lower Peace
River Formation in core W-17115, about
20% of the lower Peace River Formation in
core W-16523, all of the lower Peace River
Formation in core W-16242, and about 5%
of the Arcadia Formation in core W-16242.
Some Holocene inner ramp deposits that
share similar characteristics of Subfacies 9
are the Great Pearl Bank in the Arabian
Gulf and the inner ramp off extreme South
Florida (Tucker and Wright, 1990; Wilson
and Jordan, 1983). Storm deposits associat-
ed with this type of environment are
described by Aigner (1985). These deposits
are winnowed sands with variable skeletal
components and generally poor sorting,
commonly isolated within muddy
sediments. Subfacies 9 constitutes about
5% of the lower Peace River Formation in
core W-16523, about 7% of the lower Peace
River Formation in core W-17115, about
40% of the Arcadia Formation in core W-
16242, about 45% of the Arcadia Formation
in core W-16523, and about 40% of the
Arcadia Formation in core W-17115.

Outer Ramp Facies, Subfacies 10, 11,
12 and 13

Four outer ramp subfacies were
defined with one additional subfacies prob-
ably deposited on both the inner and outer

ramp. The outer ramp is defined by water
depth on the open shelf ranging from about
20 to about 120 m or the area between the
approximate storm wave base to just land-
ward of the shelf break. The four primary
outer shelf subfacies are: 1) the mixed
skeletal, sandy molluscan, echinoid, bry-
ozoan packstone/wackestone subfacies
(subfacies 10), 2) the Hyotissa
packstone/wackestone subfacies (subfacies
11), 3) the molluscan wackestone subfacies
(no quartz sand) (subfacies 12), and 4) the
bryozoan wackestone subfacies (subfacies
13).
The sandy molluscan, echinoid, bry-
ozoan packstone/wackestone subfacies
(subfacies 10) is a collection of complex
sandy skeletal assemblages with variable
amounts of mud. The overall percentage of
siliciclastic grains is lower in this subfacies
compared to the sandy molluscan skeletal
subfacies (subfacies 9). Quartz sand occur-
ring in subfacies 10 is fine to very-fine
grained. Nodular phosphorite occurs most-
ly as sand-sized grains with a few thin con-
centrated accumulations. Glauconite is
present as detrital grains and appears as a
primary alteration product in some micro-
facies, in which the glauconite fills pores
and surrounds skeletal and siliciclastic
grains. Although packstones are present,
the predominant rock types are skeletal
wackestones. There are some thin accumu-
lations of skeletal grains along with quartz
sand and phosphorite. This subfacies char-
acteristically has mollusks, echinoids, and
bryozoans present in nearly all stratigraph-
ic intervals (Figure 20). One indicator of
greater water depth is the common occur-
rence of benthic and planktonic
foraminifera and ostracods along with sev-
eral genera of bryozoans and echinoids that
have a deep water depth tolerance. Some
thin bedding (one to 10 cm) occurs in cer-
tain sequences, but most of the sediments
have been bioturbated to a variable degree.
Most of the bryozoans are the flat-branch-
ing and encrusting varieties, along with the
small round genera, which occur in the

FLORIDA GEOLOGICAL SURVEY

order Cyclostomata (Figure 20). Bryozoans
and echinoids occur in a wide range of
water depths and numerous species have
been dredged from up to several hundred
meters of water in the Florida Straits
(Canu and Bassler, 1928). Most of the liv-
ing species of Cyclostomata and other bry-
ozoans have depth tolerance up to well over
100 m (Canu and Bassler, 1928; Osburn,
1914; 1940). The exact water depth of bry-
ozoan occurrence for various genera is
unknown in the Gulf of Mexico. There are
also occurrences of red algal oncoids, which
commonly occur below a depth of 85 m
(Wilson, 1975; Fig. 20). Based on reduced
percentage of quartz sand, the stratigraph-
ic position of this subfacies, the observed
sedimentary structures, and the overall
faunal composition, subfacies 10 is inter-
preted to be the innermost of the outer
ramp deposits, bordering and overlapping
the sandy molluscan skeletal subfacies. A
Holocene example of this subfacies occurs
in the Arabian Gulf (Purser, 1973) and the
infaunal assemblage is similar to that
found on part of the Holocene Southwest
Florida ramp (Doyle, 1979). In models of
carbonate ramps, Irwin (1965) and Heckel
(1974) place some similar microfacies in the
outer ramp. Hammes (1992) also consid-
ered this subfacies type to be an outer ramp
faces in the Oligocene Suwannee
Limestone. Subfacies 10 is common in the
Arcadia Formation where it constitutes 15,
20, and 20% of the section in cores W-
16242, W-16523, and W-17115, respective-
ly.
The Hyotissa packstone/wackestone
subfacies (subfacies 11), has no known
Holocene equivalent. The occurrence of
Hyotissa indicates open marine conditions
with associated water depths ranging from
one to 110 m (Stenzel, 1971). Living rela-
tives of this genus live in the northern
warm temperate and tropical zones
described by Harry (1985; 1986). An
absolute water depth of between 20 and 40
m is considered to be reasonable by Harry
(pI.r',,n.1 communication). An extensive

review of the depositional environment of
Hyotissa was conducted by Meeder (1987),
who concluded that the Hyotissa packstone
environment occurred on the open ramp
more or less straddling the area shallower
and deeper than wave base. In the Pliocene
occurrences of Hyotissa studied by Meeder
(1987), the large gryphaeid commonly
occurred in thick accumulations with some
sand and mud contained in the large inter-
particle openings between shells. Based
strictly on the occurrence of Hyotissa in
growth position, this subfacies is interpret-
ed to be an outer ramp deposit. In the
Arcadia Formation, Hyotissa occurs mostly
in relatively thin accumulations or as soli-
tary organisms in growth position (Figure
21). This subfacies may actually be consid-
ered to be part of the sandy molluscan,
echinoid, bryozoan packstone/wackestone
subfacies. The Hyotissa subfacies occurs in
the Arcadia Formation (maximum of 5% of
section in the cores) and in the Tamiami
Formation.
The molluscan wackestone subfacies
(subfacies 12) differs from the inner ramp
sandy molluscan skeletal subfacies by the
lack of quartz sand and the reduced diver-
sity of species (Figure 22). Among the
microfacies grouped under this subfacies,
echinoids, bryozoans, and both benthic and
planktonic foraminifera are common con-
stituents. The molluscan wackestone sub-
facies commonly is quite bioturbated, con-
tains only a few percent of very fine quartz
sand, and commonly is sparsely packed
(ratio of shell to mud is low). This subfacies
occurs only in the Marco Island core (W-
17115), which lies on the eastern margin of
the Arcadia Formation platform. Based on
the lack of quartz sand, depth tolerant mol-
lusks, and the stratigraphic position, subfa-
cies 12 is interpreted to be an outer ramp
deposit. A Holocene similar in composition
and water depth occurrence lies off the
Trucial Coast in the Arabian Gulf (Purser,
1973).
The bryozoan wackestone subfacies
(13) commonly contains branching, tubular,

BULLETIN NO. 65

and some encrusting bryozoans with a few
mollusks. The wackestone is commonly
sparsely packed with a very minor percent-
age of very-fine quartz sand (Figure 22).
The matrix mud is mostly carbonate with a
minor amount of clay. The matrix is
cemented with microsucrosic dolomite, but
the skeletal grains are commonly calcitic.
Based on the abundance of depth tolerant
bryozoans, the lack of shallow-water fauna,
the high percentage of mud, the absence of
significant quantities of quartz sand, and
stratigraphic position, subfacies 13 is inter-
preted to be an outer ramp deposit.
Hammes (1992) described a similar outer
ramp faces from the Oligocene Suwannee
Formation in Southwest Florida. Her
interpretation was based on a ramp model
and the stratigraphic position of this subfa-
cies at the base of shoaling-upward
sequences. This subfacies occurs only in
core W-17115, similar to the molluscan
wackestone subfacies, where it constitutes
less than two percent of the section.
Subfacies 1 and 13, respectively the mol-
luscan and byrozoan wackestones, could be
grouped within subfacies 10, but the distin-
guishing characteristics are the sparse
packing with skeletal grains and very low
percentage or absence of quartz sand.

Inner and Outer Ramp, Subfacies 14

Subfacies 14 is characterized by a very
diverse composition and graded beds,
which appear as low-sloping, angular fea-
tures on seismic reflection records (Figures
23 and 24). Commonly, the graded beds
have a base of quartz sand with
dolosilt/quartz silt above the sand and are
capped with laminated clay/carbonate clay
(Figure 24). There are a large number of
different grain types with many detrital
grains including quartz sand and silt, phos-
phorite, calcite silt, and dolosilt. There is a
wide diversity of bedding features which
indicates deposition over a wide range of
water depths. There are sand beds with
thicknesses ranging from 0.2 to about one

m, which are indicative of shallow inner
ramp deposition. Some of the sand beds
contain coarse sediment deposits that are
probably storm lags. Some of the mud beds
contain isolated sand deposits and other
sands are associated with the graded beds,
caused by hydraulic separation during dep-
osition. There are relatively thick beds of
fine-grained sediment containing some
internal laminations.
A large percentage of the skeletal
grains occurring within this subfacies are
benthic foraminifera with some planktonic
foraminifera, ostracods, diatoms and mol-
lusks (few). Based on the occurrence of this
assemblage, Peck et al. (1979b) concluded
that this faces was deposited strictly in
shallow water due to the presence of sever-
al species of brackish water ostracods and
benthic foraminifera. However, the type of
bedding shown in the seismic record
(Figure 23), the graded 1,i.,inL. and faunal
assemblage indicate a deltaic type of depo-
sitional environment with a wide variation
in water depths as the deltaic lobes covered
a ramp. Therefore, based on the bedding
structure, the microfossil assemblage and
composition, this subfacies is believed to
range from inner to outer ramp in deposi-
tional environment.
It is quite difficult to find a Holocene
deposit analogous to subfacies 14. The
wide range in composition, with carbonates
and siliciclastics totally mixed, is perhaps
unique to this location because of the input
of eroded carbonate from the pre-existing
platform and the influx of terrigenous sili-
ciclastics from the north into a semi-tropi-
cal environment. Subfacies 14 constitutes
all of the upper Peace River Formation in
cores W-16242 and W-16523.

DISCUSSION

Depositional Model for the Hawthorn
Group on the South Florida Platform

Based on the interpretations of the
depositional environments in which the

FLORIDA GEOLOGICAL SURVEY

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BULLETIN NO. 65

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FLORIDA GEOLOGICAL SURVEY

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BULLETIN NO. 65

microfacies of the Hawthorn Group were
deposited, the entire stratigraphic unit was
deposited on a ramp (Table 6). Homoclinal
ramp deposits are characterized by low,
rather uniform slopes from shallow water
into the basin with a continuous grading of
sediment types from nearshore sands 8
deep-water sands and muds (Reed, 1982).
Distinct geometries occur on ramps with
predominantly carbonate deposition (Ahr,
1972; Wilson, 1975). The mixed siliciclastic
and carbonate sediments of the Hawthorn
Group produce a nearly continuous transi-
tion of sediment faces from shallow to deep
water. The low slope and the deposition of
many subfacies above the storm wave base
caused an extreme variation in sediment
composition, resulting in a large number of
microfacies being deposited within short
geographic distances. A model relating the
subfacies to water depth on the ramp is
given in Figure 25 and a sectional diagram
is given in Figure 26.
Most described ramp deposits occur
where the predominant sediment type is
carbonate. Where siliciclastic sediments
are present on these carbonate ramps, the
siliciclastic sediments are not greatly
mixed with the carbonates, but occur in
belts, such as the Arabian Gulf and the
Holocene beaches of southeastern Florida.
The subfacies and microfacies described
from the Hawthorn Group contain some
rather unique characteristics atypical of
other ramp deposits. Commonly, ramp
deposits contain a rather abrupt boundary
between mud deposits occurring within the
restricted environments and well-washed
grainstones and packstones occurring at
the shoreline and on the inner and outer
ramp.
Many described ramp deposits contain
little or no mud in the open inner or outer
ramp subfacies, such as the eastern Florida
ramp, the present day west Florida ramp,
and other wave-dominated ramps, such as
southern Australia (Boreen and James,
1993; James et al., 1994). Modern ramp
deposits bordering restricted water bodies,

such as the Arabian Gulf, do contain a belt
of muddy open-water inner and outer ramp
deposits. Ancient eperic sea ramp deposits
also produced wackestone and mudstone
deposits in the open shelf area.
During the Early Oligocene, the
Suwannee Limestone was deposited on the
southern Florida Platform as a ramp
(Hammes, 1992). The characteristics of the
Suwannee Limestone ramp deposition dif-
fer significantly from the ramp deposits of
the Hawthorn Group despite the common
geographic setting. The Suwannee
Limestone contains a nearly identical set of
subfacies as the Arcadia Formation, but the
sediments contain significantly less mud
and the predominant lithologies from the
shoreline to the deep shelf are grainstones
and packstones with only a minor section of
wackestone or muddy carbonates (Figure
27).
The Arcadia Formation is character-
ized by an abundance of mud deposition on
the inner and outer ramp. This difference
in deposition on this ramp compared to the
underlying Suwannee Limestone and other
modern or Tertiary ramps is believed to be
the result of deposition in deeper water in a
somewhat restricted setting with the Gulf
of Mexico providing a lower tidal range. A
reasonable comparison is that the Gulf of
Mexico is more similar to the Arabian Gulf
than it is to the Atlantic Ocean in terms of
tidal range. The occurrence of mud deposi-
tion on the inner and outer ramp tends to
occur in "restricted" seas and also occurs in
the Arabian Gulf. Within the uppermost
part of the Arcadia Formation and in the
lower Peace River Formation, the abun-
dance of open ramp wackestone deposits is
diminished, indicating shallower water.
The influx of siliciclastic sediments into the
predominantly carbonate environment also
contributed to a change in the ramp deposi-
tional characteristics.
In conclusion, the Hawthorn Group
was deposited on a homoclinal ramp in

FLORIDA GEOLOGICAL SURVEY

o .
a 0a

0
a,0

------------------------------ .N ,--
o
So a,

w -

a M 00 a a
--O ena
o o -
E -, o c I 1 < .

= c

O 1 0 1 -D -o -

.0 m = a m = x o 09_ "0
o c 02 >O E o "

2 c m -cm .) M0 0
0I m
Sa 0 m0

zu c- z ,..,3
> U o a) a

z E N i|e
-a,

a, o Q

z_ ^ N
--------------------------------------------------- J ^
-0~~ r vE^

BULLETIN NO. 65

Figure 26. South Florida mixed and carbonate/siliciclastic ramp.

A. Cross-section of a mixed carbonate siliciclastic ramp showing the location of subfacies 1 to 14. Note that
subfacies 4 cannot be specifically located on the cross-section.

B. An aerial view of a tidal pass with barrier beaches. Subfacies 4 is believed to occur in intertidal areas adja-
cent to tidal inlets or tidal delta bars or nearshore bars. Also, it may occur in the channel. Subfacies 2 is nor-
mally a beach deposit, but may occur in well-wash channel bars.

INNER OUTER
RAMP 14 RAMP
14

EBB DELTA BARS

FLORIDA GEOLOGICAL SURVEY

RA EXPOSURE SUPRA- INTERTIDAL SUBTIDAL LGOON SKELETALBANK OPENMARINE
PALEOGEOGRAPHIC TIDAL
PROFILE
S-------MHT
MLT

BIOLOGICAL N
AND N
TEXTURAL CRITERIA
:jw T_ "T

water depth cod
SKELETAL GRAINS

FORAMINIFERA
MILIOLIDS
ROTALIDS
MICRO FORAMS
PENEROPLIDS
AGGLUTINATING
PLANKTONICS

OSTRACODS
CHAROPHYTES

PELECYPODS
OYSTERS

GASTROPODS

SERPULIDS

RED ALGAE
ARTICULATE
ENCRUSTING

ECHINOIDS

BRYOZOA
NON-SKELETAL GRAINS

PELOIDS

INTRACLASTS

ONCOIDS
OOIDS

LITHOCLASTS

DETRITAL GRAINS

QUARTZ
DOLOMITE

PEAT

SHALE

DEPOSITIONAL TEXTURES
MUDSTONE

WACKESTONE

PACKSTONE
WELL-WASHED PACKSTONE

GRAINSTONE

DOLOMITE

KARST/CALICHE
DEPOSITIONAL STRUCTURES

CROSS-BEDDING

BIOTURBATION

'e:0 1i 2 I3 4 6 7 4 5 7 8 9 10

- S ----
------------
-------------------

---

--- -- -
-- -- -- -- -

LEGEND:

INTRACLASTS OTHER FORAMW

PE.: ,, PELECYPODS

BRYOZOA GASTROPODS
OSTRACODS ECHINOIDS
RED ALGAE

VERY ABUNDANT (DOMINANT)

ABUNDANT

PRESENT - - -

Figure 27. A profile across the Suwannee Limestone shallow-water carbonate ramp
displaying the dominant occurrences of major grain types, sedimentary structures, and
biological and textural attributes. Each subenvironment is characterized by distinct asso-
ciations of grain types (from Hammes, 1992). The predominant lithologies in the
Suwannee Limestone in southern Florida are packstones and grainstones lacking mud.

BULLETIN NO. 65

relatively deep water compared to other
described ramp deposits. The ramp evolved
over time from deposition of predominantly
shallow water subfacies near the base of
the Arcadia Formation to predominantly
deep ramp subfacies in the middle of the
formation back to predominantly shallow
ramp subfacies in the upper part of the for-
mation. Shallow water ramp deposition
was predominant throughout deposition of
the lower Peace River Formation. The
entire northern part of the ramp was cov-
ered by mixed silicilcastic and carbonate
sediment in the upper Peace River
Formation.

Timing of the Transition from Pure
Carbonate to Mixed Carbonate-
Siliciclastic Sediment Deposition on
the South Florida Platform

Siliciclastic sediments began to enter
the South Florida Platform during deposi-
tion of the lower part of the Suwannee
Limestone, which has an age of Early
Oligocene or about 33.7 Ma. Significant
accumulations of quartz sand in the
Suwannee Limestone were observed in well
CO-2318 as well as in a number other wells
penetrating this unit in southern Florida.
Also, quartz sand is disseminated through-
out the Suwannee Limestone in Southwest
Florida as observed in thin sections and
drill cuttings both in this investigation and
by Hammes (1992). The maximum thick-
ness of nearly pure quartz sand observed
was about 10 meters. In a few locations,
where a series of closely-spaced (less than
1000 m) wells were oriented approximately
parallel to the strike of the platform, quartz
sand was observed in each well at the same
approximate stratigraphic interval. In
closely-spaced (less than 1000 m) wells pen-
etrating the Suwannee Limestone in an
east-west direction, perpendicular to the
platform strike, the occurrence of quartz
sand is not commonly observed in the same
stratigraphic position. It is concluded that

the quartz sand deposits are narrow belts,
likely deposited as shorelines. It is very
important to note that the influx of silici-
clastic sediment is limited to predominant-
ly quartz sand with little or no terrigenous
clay reaching the South Florida Platform.
The largest influx of quartz sand began
to occur in the Late Oligocene with the
accumulation of the shallow ramp subfacies
in the lower part of the Arcadia Formation.
The rate of siliciclastic sediment influx
increased progressively from the base to
the top of the Arcadia Formation and in
time from about 26.6 to 12.4 Ma. Some sili-
ciclastic muds accompanied the deposition
of the quartz sands. Some of the fine-
grained muds were deposited in shallow
lagoonal deposits on the platform and in
deeper water deposits to the east. It is
probable that the influx of muddy
sediments along the eastern platform mar-
gin was responsible for the partial drown-
ing of that margin (Missimer and Scott,
1995).
After the Middle Miocene sea-level
event, which caused the extensive erosion
of the Arcadia Formation, subsequent sili-
ciclastic sediment influx in the Peace River
Formation, particularly along the eastern
margin of the Arcadia Platform, was nearly
a "river of sand," producing a sequence of
beach deposits. It is probable that some
deep water, mixed siliciclastic/carbonate
deposits were deposited to the east of the
study area (Missimer and Scott, 1995). The
carbonate subfacies produced during this
time period were limited to mostly beach
deposits containing a large percentage of
skeletal grains, but siliciclastic sediment
deposition was predominant.
In the northern part of the study area,
the upper part of the Peace River
Formation is a deltaic deposit consisting of
a variety of mixed carbonate and siliciclas-
tic sediments. This deposit is very muddy
and completely terminated carbonate sedi-
mentation. The deltaic, fine-grained
deposit helped infill the eastern margin of
the platform that was part of the platform

FLORIDA GEOLOGICAL SURVEY

drowned during Arcadia Formation time
(Missimer and Scott, 1995).

Siliciclastic and Carbonate Sediment
Mixes and the Process of
Sediment Mixing

The transition of the South Florida
Platform from primarily carbonate sedi-
mentation to mixed carbonate/siliciclastic
sedimentation occurred gradually, begin-
ning with a series of quartz sand influxes.
Despite the fact that the siliciclastic sedi-
ment influxes were rather rapid pulses,
and that the volume of siliciclastic sedi-
ment increased with time, the sediments
show nearly every composition from nearly
pure carbonate to pure siliciclastic on a bed
scale, but the sediments were thoroughly
mixed throughout the section. Despite the
inferred process of siliciclastic sediment
transport, and siliciclastic sediment belts
along the margins of the platform, the
sediments did mix with interior platform
carbonate sediments
Based on the observed characteristics
of the sediments, the processes of mixing
included: storms, wind, and bioturbation.
Throughout the entire Arcadia Formation,
the sediments are heavily bioturbated, par-
ticularly in all of the inner and outer ramp
deposits. The distribution of siliciclastic
sediments within each of the ramp subfa-
cies is quite irregular with quartz sand
infilling carbonates and fine-grained car-
bonates infilling predominantly siliciclastic
sediments. Many lag deposits occur
throughout the entire Hawthorn Group sec-
tion. In the restricted water deposits with-
in the Arcadia Formation, some very fine to
fine-grained, well-sorted, angular quartz
sands are present. These sands were likely
transported by eolian processes.
The South Florida Platform was a
region of predominantly carbonate sedi-
mentation to the end of Eocene time
(Schmidt, 1984). The Gulf Trough or
Apalachicola Embayment separated
sources of siliciclastic sediments to the

north from the pristine carbonate deposi-
tional environments to the south (Schmidt,
1984). During the deposition of the
Suwannee Limestone in the Early
Oligocene, a significant volume of quartz
sand bypassed the Apalachicola
Embayment, probably during minor low
sea-level stands. The first pulses of quartz
sand reached the South Florida Platform in
the Early Oligocene as prograding belts of
sand forming along the platform margins.
This depositional model is based on the
same pattern observed in the Florida
Holocene, where margin quartz sand
deposits intrude into the carbonates of
Biscayne Bay on the east and the carbonate
sediments of Florida Bay to the west.
During deposition of the Suwannee
Limestone and some of the lower part of the
Arcadia Formation, minor eustatic sea-
level changes and storms tended to trans-
port the quartz sands from the shoreline to
areas near the interior of the platform.
Organisms living in the sediments mixed
the quartz sands by burrowing and rework-
ing the predominantly carbonate
sediments. The mixing of quartz sands
with the carbonates had little initial effect
on carbonate sedimentation, because a sig-
nificant volume of terrigenous mud was not
present. The quartz sand was inert and did
not affect water turbidity or biological pro-
ductivity. As the volume of siliciclastic sed-
iment influx onto the South Florida
Platform increased, the diversity of deposi-
tional environments in the central part of
the platform increased with some terrige-
nous mud being deposited in restricted
environments. Storms, bioturbation and
wind aided in the mixing of siliciclastic
sediments into the carbonate environments
of the central part of the platform.
Carbonate sedimentation was interrupted
over a large area of the eastern part of the
margin by the influx of the siliciclastic sed-
iment and possibly by water clarity
changes caused by the major influx of
nutrients related to the movement of nutri-
ent-laden water from the Gulf of Mexico

BULLETIN NO. 65

over the southern part of the platform (for-
mation of phosphatic limestone in the cen-
tral part of the platform). The reduction in
carbonate sedimentation on the eastern
margin caused this margin to migrate west
from its approximate current position
about 100 km (Missimer and Scott, 1995).
After the Middle Miocene, the central
part of the South Florida Platform ceased
to grow upward with predominantly car-
bonate sediments. In the late Miocene, pre-
dominantly siliciclastic sediments were
added, again as southward prograding
beach deposits. After the Messinian, a
major change in the sedimentation pattern
occurred with a prograding deltaic unit
burying the mixed siliciclastic and carbon-
ate sediments. The deltaic sediments pen-
etrated the southern platform only to a
location near the Lee-Collier county line
(central platform). A large portion of the
drowned part of the eastern platform was
infilled by predominantly mixed muddy
siliciclastic and carbonate sediments dur-
ing the late Miocene and early Pliocene.
In conclusion, the hypothesis of Mount
(1984) that most carbonate/ siliciclastic
sediment mixes show minimal internal
mixing within small scale faces is not sup-
ported by the sediment transition on the
South Florida Platform. Beginning with
the Lower Oligocene Suwannee Limestone
and continuing with all of the Neogene for-
mations lying above it, all of the strati-
graphic section contains mixes of both car-
bonate and siliciclastic sediments. The
extreme variations in sediment composi-
tion and the diversity of associated flora
and fauna within the Hawthorn Group,
show that mixed siliciclastic and carbonate
systems can produce rather continuous sed-
imentation without the siliciclastic sedi-
ment totally eliminating carbonate sedi-
ment production. Carbonate deposition on
a shallow ramp will persist until there is
sufficient siliciclastic mud deposition to ter-

minate carbonate sediment production and
cause either a change in the geometry of
platform growth (migration of eastern plat-
form margin) or complete succession of dep-
osition from carbonate to siliciclastic (delta-
ic burial). Completely mixed carbonate/sili-
ciclastic sediment sequences are probably
quite common in the geologic record based
on observations made on the Hawthorn
Group and younger deposits found on the
Florida Platform.

LATE PALEOGENE AND NEOGENE
CHRONOSTRATIGRAPHY OF THE
CENTRAL PART OF THE SOUTH
FLORIDA PLATFORM

INTRODUCTION

Ages of the upper Paleogene and
Neogene sediments on the South Florida
Platform have been subject to debate for
many years. Previous stratigraphic inves-
tigations have assigned ages to many of the
formations based on paleontological data
correlated to areas outside of the Florida
Platform (Cooke, 1936; Mansfield, 1937,
1938; Cooke, 1939; MacNeil, 1944; Parker
and Cooke, 1944; Cooke, 1945; Parker et
al., 1955; Akers, 1972; Riggs, 1979b; Miller,
1986; COSUNA, 1988; Scott, 1988). The
currently accepted ages of many reference
sections used for correlation to the Florida
Platform have changed, but little effort has
been given to revising the chronostratigra-
phy of the Florida Platform until relatively
recent investigations. Beginning in 1972, a
series of stratigraphic investigations were
conducted that yielded a large quantity of
new age data based on planktonic
foraminifera (Akers, 1972; Peck, 1976; Peck
et al., 1976; Slater, 1978; Peck et al., 1979a;
Peck et al., 1979b; Armstrong, 1980;
Peacock, 1981; Peacock and Wise, 1981,
1982; Jones et al., 1991), calcareous nanno-
plankton (Peck, 1976; Covington, 1992),
diatoms (Klinzing, 1980, 1987), helium-
uranium dating (Bender, 1973), vertebrate

FLORIDA GEOLOGICAL SURVEY

fossil stratigraphy (Jones et al., 1991),
strontium isotope stratigraphy (Jones et
al., 1991; Hammes, 1992; Compton et al.,
1993; Mallinson and Compton, 1993;
Weedman et al., 1993; Brewster-Wingard
et al., 1997), and magnetostratigraphy
(Jones et al., 1991).
It is the purpose of this section to pres-
ent new data refining the age ranges in the
central part of the South Florida Platform
of the Suwannee Limestone, the Arcadia
and Peace River Formations of the
Hawthorn Group, the Tamiami Formation,
and the Caloosahatchee Formation (Figure
3). A series of three continuous core bor-
ings were used in this investigation (Nos.
W-16242, W-16523, and W-17115 in Figure
2). The new data were obtained using
strontium-isotope age dating and magne-
tostratigraphic analyses with a comparison
to and correlation with existing planktonic
foraminifera, calcareous nannoplankton,
and other paleontological data including
diatoms and vertebrates. Stable oxygen
and carbon isotope data were also collected
for comparison to isotopic data in marine
sediment of known age to assess distinctive
changes in isotopic composition related to
global climatic events. All age determina-
tions made in this paper utilize the geolog-
ic time scale of Berggren et al. (1995b).

METHODS

Strontium and Stable Isotope
Sample Preparation

Samples of unaltered calcitic mollusk
shell and a few phosphorite nodules were
collected from cores W-16242, W-16523,
and W-17115 for the purpose of measuring
the strontium-isotope ratios to make age
determinations. A total of 62 samples were
chosen for analysis from all samples col-
lected based on the location of the samples
within the stratigraphic section and the
quality of the shell material. A large per-
centage of the samples were collected and

analyzed from core W-16242 (34 samples),
because of the abundant quantity of unal-
tered shell, the high percentage of core
recovery, and the designation of this core
for magnetostratigraphic analysis. All
samples were carefully washed in distilled
water, then placed in an ultrasonic bath to
remove additional contaminants. Each
sample was further cleaned using dilute
hydrochloric acid. Most samples were then
cut to expose a fresh surface. Powdered
shell was collected by either drilling out the
shell interior with a clean dental drill or a
clean cube of shell was extracted from the
middle of the sample and crushed into a
powder. A sufficient quantity of clean pow-
dered shell was collected to perform both
strontium-isotope analyses and carbon and
oxygen-isotope analyses.
All strontium isotope measurements
were made at the University of Florida. The
analytical procedure used is described in
detail in McKenzie et al. (1988) and Hodell
et al. (1990). The 7Sr/86Sr ratios were
measured in the triple-collector dynamic
mode on a VG354 thermal ionization mass
spectrometer. All strontium ratios were
normalized to 86Sr/"Sr = 0.1194 and to
Standard Reference Material (SRM) 987 =
0.710235. An evaluation of the analytical
precision indicated that the average with-
in-run precision was +/-1 x 10-5 (two stan-
dard error of the mean). When all errors
associated with the analytical procedure
were summed, a range of +/-22 to 24 x 10-6
was determined for the period in which the
data were collected. The strontium isotope
variation with time in the world ocean, as
presented in the model of Hoddell et al.
(1991), was used to estimate ages. The
error in conversion to estimated ages can-
not be determined, because the model used
must be assumed to be correct (P. Mueller,
personal communication). The Hodell ages
were then corrected to the Berggren et al.
(1995b) age model.

BULLETIN NO. 65

All carbon and oxygen isotope data
were analyzed at the stable Isotope
Laboratory, University of Miami. The iso-
topic ratios were measured on a mass spec-
trometer using the standard laboratory
procedures (Swart et al., 1991).

Paleomagnetic Measurements

Detailed paleomagnetic data were col-
lected from core W-16242. Up-down orient-
ed samples were collected from 291 strati-
graphic intervals. Since the core was col-
lected with a drilling rig, the only orienta-
tion of the samples that could be deter-
mined was the stratigraphic up direction.
Core orientation was checked using geopels
wherever observed. Therefore, only incli-
nation data were used to determine the
prevalent polarity during or shortly after
deposition. All magnetic measurements
were made at the University of Miami,
Rosenstiel School of Marine and
Atmospheric Science. The paleomagnetic
measurements were made using a 2G
Enterprises 755 superconducting magne-
tometer contained within a shielded room.
All rock magnetic analyses were conducted
at the California Institute of Technology
using a 2G Enterprises 760 magnetometer.
A combination of alternating field and ther-
mal demagnetization methods were uti-
lized to obtain inclination data and to
determine polarity.

FORAMINIFERA

Introduction

Studies of the foraminifera in the
Neogene and late Paleogene sediments in
Southwest Florida were presented in a
series of theses and resultant publications
(Peck, 1976; Peck et al., 1976; Peck et al.,
1977; Peck et al., 1979a; Peck et al., 1979b;
Slater, 1978; Peacock, 1981; Peacock and
Wise, 1981; Peacock and Wise, 1982). Since
detailed analyses of foraminifera were pre-
viously performed on nearby wells having

very direct and reliable lithostratigraphic
correlation to the cores in this study, pro-
jected planktonic foraminifera ages are
used. The stratigraphic correlation
between the cores studied and the plank-
tonic faunal information collected from
nearby wells was accomplished by tracing
continuous seismic reflection lines between
the wells and core W-16242 on the north
(20 km) and by direct correlation of the
stratigraphic units into core W-16523 on
the south (eight km).
The entire Neogene and Late
Paleogene stratigraphic section was not
studied in the foraminifera research, but
the work was concentrated on the
"Tamiami Formation," which was defined
at that time as all sediments lying between
the disconformity marking the top of the
Arcadia Formation and the disconformity
marking the base of the Caloosahatchee
Formation. Since the definitions of the
stratigraphic units have been changed to
produce a more consistent framework
(Scott, 1988), the foraminiferal investiga-
tions were performed on both the Tamiami
and Peace River Formations. The only age
diagnostic data, however, were obtained
from the Peace River Formation. The work
performed by Peacock (1981) was mostly
limited to the foraminiferal occurrences in
the lower part of the Arcadia Formation.

Age of the Arcadia Formation
Based on Foraminifera

Work on foraminifera near the base of
the Arcadia Formation was conducted by
Peacock (1981). He noted the occurrence of
'i,,. /\7.sin,/ hawkinsi and Archaias flori-
danus in the lower part of the Hawthorn
Group. Cole (1938) believed that all species
of Miogypsina to be restricted to the Late
Oligocene. Cole (1941) used the occurrence
of Archaias floridanus as an indicator of
the Tampa Formation in southern Florida.
Both Archaias and Miogypsina were
observed near the base of the Arcadia
Formation in each of the cores studied. The

FLORIDA GEOLOGICAL SURVEY

implied Late Oligocene age of these
foraminifera matches well with the other
age dating methods for this part of the
stratigraphic section.

Age of the Peace River Formation
Based on Foraminifera

Analysis of the foraminifera occurrence
in a series of six wells in Lee County and
several additional wells in Hendry County
were made by Peck et al. (1979a; 1979b).
They defined a series of stratigraphic units
based on several type wells. Well L-1849
lies adjacent to the Caloosahatchee River
only about one km south of the seismic
reflection line made in the river channel
(Figure 28). Based on the correlations and
the unit terminology given in Peck et al.

(1979a) and Peck et al. (1979b), their unit 2
is equivalent to the upper part of the Peace
River Formation and their units 3 to 8 are
equivalent to the lower Peace River
Formation. The lower Peace River
Formation in core W-16242 from 88.54 to
91.74 m is equivalent to unit 8 in well L-
1849. The upper Peace River Formation
from 57.91 to 88.54 m in core W-16242 is
equivalent to units 2A-B in well L-1849.
Additional planktonic foraminifera data
were obtained from well L-1984 (Figure
29). Well L-1984 lies eight km west of core
W-16523 and is directly correlated to the
core by a published geologic section
(B..--.--; et al., 1981). The correlation of
units 1 to 8 in well L-1984 to core W-16523
are shown in Figure 30.

CALCAREOUS
NANNOFOSSILS

PLANKTONIC
FORAMINIFERA

WELL

L -1849

PLIOCENE & PLEISTOCENE
LOWER TO MIDDLE PLIOCENE
Dyocibicides biserialis
zone

Valvulineria
floridana
UPPER zone
MIOCENE i
Lenticilina
amencana zone

UNIT DEPTH
(Peck, (Feet below
et. al.) surface)

POST
MIOCENE

0 -20

20 35
35 55
2A- B 55-75
75 95

S
S

*cv Q
c Q)

Q)
ZC5Z

cL

Q)

cM
S '0

So

-o
0
c0

-a
o ~-
(jc

Q)
X_

~Q)
m
SQ)

m
^ E

1)
s
Q. M

St~
S

95-115 0* S* ** *
115-135 S S ee e

135-145 0 S SO S

S

Figure 28. Distribution of planktonic foraminifers and calcareous nannofossils in well L-
1849 adjacent to seismic line connecting to core W-16242 (from Peck et al., 1979b). The cur-
rent age ranges for these fossils are given in the summary chronostratigraphy for core W-
16242.

+e

BULLETIN NO. 65

CALCAREOUS
NANNOFOSSILS

PLANKTONIC
FORAMINIFERA

WELL

L -1984

LOWER TO MIDDLE
PLIOCENE
Dyocibicides biserialis
zone

Valvulineria

UPPER
MIOCENE

floridana
zone

Lenticilina
americana
zone

UNIT DEPTH
(Peck, (Feet below
et. al.) surface)

U

2A- B

3A

4

c Q)
0.Z(
-c Q)
cL

co) M
CQ)
S w

Is

co
a,

25 45
45-165 *
165-185 * *
185-206 0 *
206-226 _
226-246 *
246 266 _
266 286
286 306
306-326 *

5 1326-346] 11.1. FF]_1.11

6

8

346 366 ___ *
366-386 * *

386 406

Figure 29. Distribution of planktonic foraminifers and calcareous nannofossils in well L-
1984 near core W-16523. This information was taken from Peck et al. (1979). Well L-1984
is located close to core W-16523 (see Figure 34). The age range of the planktonic
foraminifers and calcareous nannoplankton from this analysis is discussed in the chronol-
ogy of core W-16523.

Based on the occurrence of age diag-
nostic foraminiferal forms including
Spheroidinellopsis subdehiscens subdehis-
cens, S. seminulina seminulina,
Globigerina nepenthes, and G. bulloides
apertura along with the occurrences of the
calcareous nannofossils Discoaster quin-
queramus, D. berggrenii, D. brouweri,
Reticulofenestra pseudoumbilica and other
calcareous nannofossils, Peck et al. (1979a,
b) assigned units 2B to 8 to the Late
Miocene Discoaster quinqueramus Zone of

Gartner (1969). This zone was considered
to be equivalent to planktonic foraminiferal
zones N17 to N18 by Gartner (1969), but
Berggren (1973) correlated it to only the
latest Miocene zone N17. The distribution
of planktonic foraminifera and calcareous
nannofossils for well L-1984 is given in
Figure 28.
The age designation developed using
foraminifera for the Peace River Formation
is generally concordant with the chronolo-
gies developed using the other methods.

-o

-a
o ~-
(jc

Q)
X_

~q)
si
s

0~ M

fs

^ E
| S
Q. M
ms

* *

FLORIDA GEOLOGICAL SURVEY

LEE COUNTY COLLIER COUNTY

+50

0

-50

-100

-150

> -200
z

w -250
LL.
I--
_ -300
Q

EXPLANATION
Sand, Quartz
Sandstone

Sand, Clayey

Mud, Mixed Composition

Marl
Limestone

Dolostone

MILES

I I I

10
KILOMETERS

CORRELATION

Figure 30. Correlation of well L-1984 to core W-16523 along section D-D' from Boggess et
al. (1981). The first clay unit in core W-16523 is equivalent to the combined thickness of
units 2A and 2B in Peck et al. (1979b). Unit 2A is equivalent to sediment package P-7 in
Plate 2. Unit 2B is equivalent to sediment package P-6 in Plate 2.

1 1
LI

0

- -50
a

z
ni,
I--

SI

LU
- -100 0

- -150

SCALE
6 MILES

	Front Cover
	Front Matter
	Table of Contents
	Main

MILLISECOND	CLASS.METHOD	MESSAGE
0	sobekcm_page_globals.constructor
0	sobekcm_page_globals.constructor	Application State validated or built
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.constructor	Navigation Object created from URI query string
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.display_item	Retrieving item or group information
0	sobekcm_page_globals.get_entire_collection_hierarchy	Retrieving hierarchy information
0	sobekcm_assistant.get_entire_collection_hierarchy
0	cached_data_manager.retrieve_item_aggregation
0	cached_data_manager.retrieve_item_aggregation	Found item aggregation on local cache
0	item_aggregation_builder.get_item_aggregation	Found 'all' item aggregation in cache
0	system.web.ui.page.page_load (ufdc.page_load)
0	sobekcm_page_globals.constructor.on_page_load
0	html_echo_mainwriter.add_style_references	Adding style references to HTML
0	html_echo_mainwriter.add_text_to_page	Reading the text from the file and echoing back to the output stream
57	html_echo_mainwriter.add_text_to_page	Finished reading and writing the file