FGS Bulletin 68 : Main Report

FLRD WATE MANAGMN DISRIC

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FLOIDA DEARTEN OF ENIRNMNAL PROECIO
FORIDA GOGIAL SUVYBLETNN.6

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FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION
Michael W. Sole, Secretary

LAND AND RECREATION
Bob G. Ballard, Deputy Secretary

OFFICE OF THE FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Director

ADMINISTRATIVE AND GEOLOGICAL DATA MANAGEMENT SECTION
Jacqueline M. Lloyd, Assistant State Geologist

David Arthur, Computer Programmer Analyst
Traci Billingsley, Administrative Assistant
Paulette Bond, Professional Geologist
Doug Calman, Librarian
Brian Clark, Environmental Specialist
Jeff Erb, Systems Programmer
Jessie Hawkins, Custodian

Leslie Knight, Administrative Assistant
Anthony Miller, Environmental Specialist
Sarah Ramdeen, Computer Program Analyst
Ginger Rinkel, Secretary Specialist
Frank Rupert, Professional Geologist
Carolyn Stringer, Management Analyst

GEOLOGICAL INVESTIGATIONS SECTION
Thomas M. Scott, Assistant State Geologist

Ken Campbell, Professional Geologist
Brie Coane, Geologist
Rick Green, Professional Geologist
Eric Harrington, Engineering Technician
Laura Hester, Laboratory Technician
Ron Hoenstine, Professional Geologist Supervisor
Jessie Hurd, Laboratory Technician
Michelle Ladle, Laboratory Technician

Patrick Madden, Laboratory Technician
Harley Means, Professional Geologist
Mike Nash, Laboratory Technician
David Paul, Professional Geologist
Dan Phelps, Professional Geologist
Guy Richardson, Engineering Technician
Wade Stringer, Engineering Specialist
David Wagner, Laboratory Technician
Christopher Williams, Geologist

HYDROGEOLOGY SECTION
Jonathan D. Arthur, Assistant State Geologist (Acting Director)

Rick Copeland, Professional Geologist
Adel Dabous, Environmental Specialist
Rodney DeHan, Senior Research Scientist
Scott Barrett Dyer, Environmental Specialist
Cindy Fischler, Professional Geologist

Lisa Fulton, Environmental Specialist
Tom Greenhalgh, Professional Geologist
Nick John, Geologist
Clint Kromhout, Professional Geologist
Amber Rainsford, Environmental Specialist

STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Michael W. Sole, Secretary

LAND AND RECREATION
Bob G. Ballard, Deputy Secretary

FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist andDirector

BULLETIN NO. 68

HYDROGEOLOGIC FRAMEWORK OF THE SOUTHWEST FLORIDA
WATER MANAGEMENT DISTRICT

By

Jonathan D. Arthur, Cindy Fischler, Clint Kromhout,
James M. Clayton, G. Michael Kelley, Richard A. Lee, Li Li,
Mike O'Sullivan, Richard C. Green, and Christopher L. Werner

Published for the

FLORIDA GEOLOGICAL SURVEY

Tallahassee, Florida

in cooperation with the

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

2008

*4i~~ic

Water Management District

Printed for the
Florida Geological Survey
Tallahassee
2008

ISSN 0271-7832

In memory of the spirited life and geoscience
contributions of Rick Lee (1956 2007)

Lv

PREFACE

A

The Florida Geological Survey/Florida Department of Environmental Protection is publishing
as its Bulletin 68, the Hydrogeologic Framework of the .Sinhi' e\t Florida Water Management
District. The report summarizes a multi-year study of the three-dimensional framework of
southwestern Florida's hydrogeology, with a focus on the subsurface distribution of aquifer
systems and geologic units comprising these systems. As groundwater resources in Florida
experience increased stress due to rapid population growth, an understanding of the aquifer
systems is invaluable to environmental managers, scientists, planners and the public as decisions
are made regarding use, protection and conservation of these vulnerable resources. The FDEP-
FGS is pleased to have had the opportunity to partner with the Southwest Florida Water
Management District to complete this report.

State Geologist and Director
Florida Geological Survey
Florida Department of Environmental Protection

vi

TABLE OF CONTENTS

A abbreviations, acronym s and conversions......................................................................... ....................xi
A ck n ow ledg em ents ..................................................................................... ............................. ............ x ii
In tro d u ctio n .. ...........................................1.... ............ .... ............ .... ............ .... ............ .... ... ........ ....... 1
B background ...................... .......................................... .. ... ........... ..... .... ............... 1
Purpose and scope ..... ................ .. ....... ....... ... .. ............ ..... .................. .. ........... .... ... 1
Stu d y area ....................... ................................................................ ........... ...................... 2
Previous investigations ................................................................ 2
Physical setting ............... ................................................................... 5
Geology ...... ...... ..... ........... ........................... ................. 5
S tru ctu re ........................... .. .................................... .................. .......................... ....... ........... .. 7
G eom orphology ........................................................................... ........................ ........ .. ....... 11
Physiographic provinces and features............................................. ..... ................. .... .................. 11
Sinkholes ................ ........ ............ ..................................................... .... ........... 15
Springs ......................... .................... 15
Hydrogeology .......... .. .............................................................. 17
Methods ....................................... 20
Sam ple description ................ ............................................ ..................................... ...... ..................... 20
D elineation of boundaries .................................. ..................................................................... .......... 2 1
Form ations/M em bers ............................................... ............... ............. .. ............... ..... 21
A quifer system s ............... ..................................................................2 1
Cross-section construction ................................... ..................................................................... ........22
Topography ............... .......... ............................ ......... 22
L ith ology ...................................................................................... ................. ................... . .. ... 24
G am m a-ray logs .......................................................... ... ......... ............................ 24
A quifer sy stem s ..................................................................................................................... 24
M ap develop ent and data m anagem ent .......................................................................... ...................24
Map interpolation and spatial accuracy ................................................... .................... 27
C ontour interval selection ....................................................... .................. ...................... 30
Stratigraphy ............... ........ .......................................... 30
L ith ostratig raphy ................................................................................................................... ........... 30
Introduction ................................................................................................................................... 30
Eocene Series ..................................................................................... ...................................... 30
Oldsm ar Form action ............. .... .......................... ................ ............ ..... ................ 30
A v on P ark F orm action ................................................................................................ ... 3 1
O cala L im stone ................................................... ......................... ................................. 34
Oligocene Series ........................................ 37
Suw annee L im stone ............................................................... 37
O ligocene-Pliocene Series ..................................................................................... .......................40
H aw thorn G group ................................................... .................................................................... 40
A rcadia Form action ................................ ................................................................................ 40
N ocatee M em b er ....................................................................................................................... 4 3
Tam pa M em ber ........................................................................ ............ .......................... 43
"V enice C lay" ..................... ...... ......... ................................. ................................. 45
Peace River Formation .................... ................ ......................................... 45
Bone Valley Member ............................................. .......... ...... .................... 48

TABLE OF CONTENTS (CONTINUED)

H aw thorn G roup (undifferentiated) ........................................................................ ................ 48
Pliocene and younger Series .................................................. .................................. .................... 49
Post-H aw thorn G group sedim ents .......................... ..... ........ .... ...... ................... ... ................49
Tamiami Formation................................. ......... 50
C yp ressh ead F orm action ................................................................................ ......................... 50
C aloosahatchee Form action ......................................................................................................... 50
Fort Thompson Formation ................. ........... ....... .......... .............................. 51
H ydrostratigraphy ............................................... ...................................................... .................... 52
Introduction ....................... ................................................................................ ...................... 52
H ydrogeological properties ...................................................................................... ..... ................ 52
Surficial aquifer system ................. ............. .... ................ 53
Intermediate aquifer system/intermediate confining unit ...................................... ................ 57
F loridan aqu ifer sy stem ....................................................................................................................... 66
M iddle Floridan confining unit........................ ......................... ............................................. 75
Su m m ary ................... ........ .................. ......... ............................................... ......... . ..... 7 9
R eferen ce s ........... .... .... ..... ....................................... ................................ ........... ................. 8 1

FIGURES

Figure 1. Study area. .................................... .. .. .................. ................ ...... .................... ... 4
Figure 2. G eologic m ap of study area ................................................................................................ 6
Figure 3. Structural features within the study area. .......................................... ............................. 8
Figure 4. Environmental geology of the study area ..... ............. ......... ..................... 9
Figure 5. Shaded relief topography of the study area................................. ............... 12
Figure 6. G eom orphology of the study area .......................................................................................... 13
Figure 7. Shaded topographic relief of the southern extent of the Lake Wales Ridge. .......................... 16
Figure 8. Generalized correlation between lithostratigraphic units and the surface of the FAS.............23
Figure 9. Explanation (legend for cross sections).................................... ............................................ 25
Figure 10. Characteristic gam m a-ray log responses. ........................................................... ................. 26
Figure 11. Helicostegina gyralis, a foraminifer common within the Oldsmar Formation. .................... 32
Figure 12. Selected diagnostic fossils common within the Avon Park Formation................................ 33
Figure 13. Selected diagnostic fossils within the Ocala Limestone.................... .................... 35
Figure 14. Selected diagnostic Suwannee Limestone fossils........................................ ................ 38
Figure 15. Diagnostic foraminifera in Hawthorn Group units........ ..................................................41
Figure 16. Assemblage of typical Bone Valley Member fossils ....................... .. ... ... ............. 46
Figure 17. Characteristic Ft. Thompson Formation fossils.................................................................51
Figure 18. Soil perm ability of study area ......................................................... ................. ..................... 56
Figure 19. Statistical summary of SAS transmissivity data................................................................58
Figure 20. Statistical summary of SAS specific yield data................................... .............. 58
Figure 21. Statistical summary of SAS horizontal hydraulic conductivity data................................... 59
Figure 22. Statistical summary of SAS vertical hydraulic conductivity data..................................... 59
Figure 23. Approximate extent of IAS/ICU permeable zones........ ...................................................60
Figure 24. Statistical summary of IAS/ICU transmissivity data......................................................63
Figure 25. Statistical summary of IAS/ICU storativity data.................................................................. 63
Figure 26. Statistical summary of IAS/ICU leakance data........................................... ................ 64

FIGURES (CONTINUED)

Figure 27. Statistical summary of IAS/ICU horizontal hydraulic conductivity data................................ 64
Figure 28. Statistical summary of IAS/ICU vertical hydraulic conductivity data................................ 65
Figure 29. Statistical summary of IAS/ICU total porosity data............................................... 65
Figure 30. Potentiometric surface of the Floridan aquifer system, September, 2005............................... 68
Figure 31. Floridan aquifer system overburden thickness................................................ .....................70
Figure 32. Thickness of the Upper Floridan aquifer (includes non-potable) .......................................... 71
Figure 33. Statistical summary of UFA transmissivity data.................................................................. 72
Figure 34. Statistical summ ary of UFA storativity data........................................................................... 73
Figure 35. Statistical summary of UFA leakance data ................................... ................... 73
Figure 36. Statistical summary of UFA horizontal hydraulic conductivity data.................................. 74
Figure 37. Statistical summary of UFA vertical hydraulic conductivity data .................................. 74
Figure 38. Statistical summary of UFA total porosity data.............. .......................................75
Figure 39. Interpretations of the MFCU in the study area. ..................................................76
Figure 40. Statistical summary of MFCU vertical hydraulic conductivity data........................... .. 78
Figure 41. Statistical summary of MFCU total porosity data..................... .............. .............. 78

TABLES

Table 1. Units mapped in this study. Map types are structure contour (surface) and isopach (thickness) .. 3
Table 2. Generalized correlation chart for units mapped within study area ............................................ 19
Table 3. Summary ofkrige interpolation statistics for each map ......... ..................................................29

APPENDICES

Appendix 1. Commentary on Florida hydrostratigraphic nomenclature.....................................................99
Appendix 2. Explanation of revisions to FDEP-FGS Special Publication 28 aquifer definitions ......... 101

PLATES
1. Cross section locations
2. Wells used in this study
3. Closed topographic depressions in the study area
4. Cross section: A-A' Levy and Marion Counties
5. Cross section: B-B' Levy and Marion Counties
6. Cross section: C-C' Citrus and Sumter Counties
7. Cross section: D-D' Citrus and Sumter Counties
8. Cross section: E-E' Hemando, Sumter, and Lake Counties
9. Cross section: F-F' Hernando, Pasco, Sumter and Lake Counties
10. Cross section: G-G' Pasco, Sumter, and Polk Counties
11. Cross section: H-H' Pasco and Polk Counties
12. Cross section: I-I' Pinellas and Hillsborough Counties
13. Cross section: J-J' Pinellas and Hillsborough Counties
14. Cross section: K-K' Pinellas and Hillsborough Counties

PLATES (CONTINUED)

15. Cross section: L-L' Manatee, Hillsborough, and Polk Counties
16. Cross section: M-M' Manatee County
17. Cross section: N-N' Sarasota and Manatee Counties
18. Cross section: 0-0' Sarasota County
19. Cross section: P-P' Charlotte County
20. Cross section: Q-Q' Polk and Osceola Counties
21. Cross section: R-R' Hillsborough and Polk Counties
22. Cross section: S-S' Hillsborough and Polk Counties
23. Cross section: T-T' Manatee, Hardee, and Highlands Counties
24. Cross section: U-U' Manatee, Hardee, and Highlands Counties
25. Cross section: V-V' Manatee, DeSoto, Hardee, and Highlands Counties
26. Cross section: W-W' Sarasota, DeSoto, and Highlands Counties
27. Cross section: X-X' Sarasota, DeSoto, Highlands, and Glades Counties
28. Cross section: Y-Y' Charlotte and Glades Counties
29. Cross section: Z-Z' Levy, Citrus, Pasco, and Hernando Counties
30. Cross section: AA-AA' Marion, Sumter, Hernando, and Pasco Counties
31. Cross section: BB-BB' Pinellas County
32. Cross section: CC-CC' Hillsborough and Manatee Counties
33. Cross section: DD-DD' Hillsborough and Manatee Counties
34. Cross section: EE-EE' Lake, Polk, Hardee, DeSoto, and Charlotte Counties
35. Cross section: FF-FF' Polk, Highlands, and Glades Counties
36. Cross section: GG-GG' Manatee, Sarasota, and Charlotte Counties
37. Cross section: HH-HH' Manatee, Sarasota, and Charlotte Counties
38. Avon Park Formation surface
39. Ocala Limestone surface
40. Ocala Limestone thickness
41. Suwannee Limestone surface
42. Suwannee Limestone thickness
43. Hawthorn Group surface
44. Hawthorn Group thickness
45. Arcadia Formation surface
46. Arcadia Formation thickness
47. Nocatee Member of the Arcadia Formation surface
48. Nocatee Member of the Arcadia Formation thickness
49. Tampa Member of the Arcadia Formation surface
50. Tampa Member of the Arcadia Formation thickness
51. Peace River Formation surface
52. Peace River Formation thickness
53. Bone Valley Member of the Peace River Formation surface
54. Bone Valley Member of the Peace River Formation thickness
55. Surficial aquifer system thickness
56. Intermediate aquifer system/intermediate confining unit surface
57. Intermediate aquifer system/intermediate confining unit thickness
58. Floridan aquifer system surface
59. Middle Floridan confining unit surface

ASE
BLS
CFHUD II
CTD
DEM
District
FAS
FDCA
FDEP
FGS
IAS/ICU
IDW
IP/FMNH
Kh
Kv
L
LFA
LIDAR
MFCU
MSL
RMS
ROMP
S
SAS
SWFWMD
SY
T
UFA
USGS

Y

ABBREVIATIONS, ACRONYMS AND CONVERSIONS

average standard error
below land surface
Second Ad Hoc Committee on Florida Hydrostratigraphic Unit Definitions
closed topographic depression
digital elevation model
Southwest Florida Water Management District
Floridan aquifer system
Florida Department of Community Affairs
Florida Department of Environmental Protection
Florida Geological Survey
intermediate aquifer system/intermediate confining unit
inverse distance weighted
Invertebrate Paleontology, Florida Museum of Natural History
horizontal hydraulic conductivity
vertical hydraulic conductivity
leakance
Lower Floridan aquifer
light detection and ranging
Middle Floridan confining unit
mean sea level
root mean squared
Regional Observation and Monitor Well Program
storativity
surficial aquifer system
Southwest Florida Water Management District
specific yield
transmissivity
Upper Floridan aquifer
United States Geological Survey
approximately
gamma

Multiply By To obtain
cubic foot (ft3) 0.0283 cubic meter (m3)
foot (ft) 0.305 meter (m)
foot per day (ft/d) 3.53x10-4 centimeter/second (cm/s)
foot squared per day (fl2/d) 0.0929 meter squared per day (m2/d)

gallon (gal) 3.79x10-3 cubic meter (m3)
gallon (gal) 113.79 liter (L)
gallon per minute (gal/min) 6.32x10-5 cubic meter per second (m3/s)
inch (in) 25.4 millimeter (mm)
mile (mi) 1.609 kilometer (km)

ACKNOWLEDGEMENTS

This research was a cooperative effort between the Florida Department of Environmental Protection
(FDEP) Florida Geological Survey (FGS) and the Southwest Florida Water Management District
(SWFWMD). Special thanks are extended to David L. Moore, SWFWMD Executive Director and Dr.
Walter Schmidt, FDEP-FGS Director and State Geologist for administrative and financial support.
Essential geology and hydrogeology data-collection programs in the SWFWMD, FDEP-FGS and the U.S.
Geological Survey (USGS) have made the development of this comprehensive report possible. Numerous
individuals and countless hours of well drilling and logging, aquifer and laboratory testing, database
development and management, lithologic descriptions, formation boundary determinations, surface
modeling, and map/cross section production have contributed to the development of this report.

The authors express their appreciation to the numerous individuals for their insightful review of the
manuscript and plates. From the FDEP-FGS, these individuals include Carol Armstrong, Ken Campbell,
Jackie Lloyd, Frank Rupert, Dr. Walter Schmidt, Dr. Tom Scott; from SWFWMD, Ron Basso, Michael
Beach, Marty Clausen, Michael Gates, Tony Gilboy, Jason LaRoche, John Parker, Robert Peterson and
Donald Thompson. Ken Campbell and Dr. Tom Scott are thanked for their contributions and discussions
regarding the lithostratigraphy and hydrostratigraphy of the study area. Discussions with John J. Hickey,
Rick Spechler, Dr. Tom Scott and Dr. Sam Upchurch helped refine our understanding of the
hydrostratigraphy of the region. Doug Rapphun also contributed to our knowledge of the hydrogeology
in the region.

The authors also gratefully acknowledge those staff of the FDEP-FGS who participated in this project.
Lance Johnson and Paula Polson provided assistance with cross-section development. Surface
interpolations during early phases of the project were completed by Bill Pollock, Amy Graves, John
Marquez and Andrew Rudin. Developers of the database for this project included Mark Groszos, Marco
Cristofari and Rob Stoner. Data management support included the assistance of Jackie Bone, Patricia
Casey, Lance Johnson, Natalie Sudman, and Holly Tulpin. Lithologic descriptions of numerous borehole
samples were completed by Alan Baker, Jim Cichon, Erin Dor, Kris Esterson, Mabry Gaboardi, Diedre
Lloyd, Matt Mayo, Sarah Ramdeen and Holly Williams. Many of the photos and photomicrographs of
fossils presented in this report are provided courtesy of Roger Portell and Sean Roberts (Invertebrate
Paleontology, Florida Museum of Natural History), Dr. Jonathan Bryan (Okaloosa-Walton Community
College) and Frank Rupert. Dr. Rick Copeland was helpful with regard to discussions of quality
assurance of hydrogeologic data and presentation of descriptive statistics.

BULLETIN NO. 68

HYDROGEOLOGIC FRAMEWORK OF THE SOUTHWEST
FLORIDA WATER MANAGEMENT DISTRICT

By Jonathan D. Arthur, (P.G. #1149), Cindy Fischler (P.G. #2512), Clint Kromhout (P.G. #2522),
James M. Clayton, (P.G. #381), G. Michael Kelley (P.G. #249), Richard A. Lee (P.G. #956), Li Li,
Mike O'Sullivan (P.G. #2468), Richard C. Green (P.G. #1776), and Christopher L. Werner (P.G. #2366)

INTRODUCTION

Background

Groundwater comprises approximately 85
percent of the total water-resource supply in the
Southwest Florida Water Management District
(SWFWMD), where existing water demands are
on the order of 435 billion gallons per year
(Southwest Florida Water Management District,
2006a). By 2025, the population of the region is
expected to increase more than 30 percent,
placing further demands on water resources.
Development of alternative water supplies and
continued water-resource management and
conservation are critically important toward the
sustainability of groundwater resources within
the aquifer systems of southwest Florida. These
practices, however, require the accumulation,
management and interpretation of
hydrogeological data.

In the mid-1990's, the SWFWMD and the
Florida Department of Environmental Protection
- Florida Geological Survey (FDEP-FGS)
entered into a cooperative project to develop a
series of geologic and hydrogeologic cross
sections throughout the 16-county SWFWMD
region. The project was designed to characterize
the relation and extent of lithostratigraphic1 and

hydrostratigraphic2 units within the region with
an emphasis on use of hydrogeologic data
collected by the District's Regional Observation
and Monitor-well Program (ROMP). This project
was later expanded to include production of
surface and thickness maps of the units
represented in the cross sections.

To accomplish the goal of the regional cross
section project, the District was divided into four
study areas (three project phases): Phase IA
includes Pinellas and Hillsborough Counties;
Phase IB includes Manatee, Sarasota, Hardee,
DeSoto and Charlotte Counties; Phase II includes
the northern part of the District, from Levy,
Marion and Lake to Pasco Counties; and Phase
III includes the southeastern part of the District,
encompassing all areas not covered in Phases IA,
IB and II. Interim reports were published for
Phase IA and II (Green et al., 1995 and Arthur et
al., 2001a, respectively). Rather than separately
publishing reports for the remaining phases, the
cross sections are incorporated in this report.

Purpose and Scope

The purpose of this study is to refine the
hydrogeological framework of the region to
facilitate science-based decision making with
regard to the protection, conservation and
management of southwest Florida's water

1 Lithostratigraphic units are laterally extensive
sequences of rocks and sediments reflecting unique
lithologic characteristics; each unit was deposited
within a generally similar paleo-environment during
a given period of time in Earth's history.

2 Hydrostratigraphic units include laterally extensive
sequences of rocks and sediments that are related by
hydrogeologic characteristics. Hydrostratigraphic
units may or may not correlate with lithostratigraphic
units.

FLORIDA GEOLOGICAL SURVEY

resources. Thirty-four cross sections have been
produced for this study (Plate 1). Each of the
cross sections illustrates regional
lithostratigraphy of Eocene through Pliocene
formations, lithology, mineralogy, gamma-ray
logs, topographic profiles and hydrostratigraphic
delineations. Although most of the data used to
construct the cross sections was taken from
wells drilled as part of ROMP (Gomberg, 1975),
borehole data (e.g., from cores, cuttings and
geophysical logs) from the FDEP-FGS and the
U.S. Geological Survey (USGS) were utilized to
fill in as many gaps as possible.

The mapping phase of the study facilitated
development of a new geologic and
hydrogeologic database, FGS Wells. Structure
contour (surface elevations) and isopach
(thickness) maps for all regionally extensive
lithostratigraphic and hydrostratigraphic units
within the District were then developed. The
maps include all units between land surface and
the top of the Middle Floridan confining unit
(Table 1).

Data from more than 1050 wells (including
offshore boreholes) serve as control for these
maps (Plate 2). In addition, synthetic wells were
used to provide lateral (edge) control during map
surface interpolation. These wells represent an
artificial stratigraphic record for a given location
based on interpolated elevations from existing
maps or cross sections. The new surface and
thickness maps presented herein were developed
using the ESRI geographic information system
(GIS) program ArcMAP (see Map Development
and Data Management, p. 24) for details on map
production. Each map includes the lateral extent
of each unit and locations of wells within the
study area that were used to interpolate surfaces
and thicknesses.

Study Area

Maps and cross sections produced for this
study cover the entire SWFWMD region (Figure
1). To facilitate present and future hydrologic
modeling and comparison of these maps to
adjacent Water Management Districts, a 10 mi
(16.1 km) wide buffer extending beyond the
District boundary was included in the study area

(Figure 1, Plate 2). Surface interpolation
techniques, such as kriging, can produce non-
representative contours along the margins of
mapped units. To address these undesirable
"edge effects," data from within a second 10 mi
(16.1 km) wide buffer zone was utilized. The
additional data helped stabilize surface
interpolations and contours, and allowed for a
more accurate delineation of the vertical and
lateral extents of certain mapped units. The
project study area, which covers approximately
14,340 mi2 (37,141 km2), does not include
wells within the second (outermost) buffer.

Previous Investigations

Numerous researchers have focused on the
regional geology and hydrogeology of southwest
Florida. Sub-Floridan aquifer system geology,
with an emphasis on pre-Cenozoic basement
geology, is presented in several papers including
Applin (1951), Applin and Applin (1965), Bass
(1969), Barnett (1975), Smith (1982) and
Chowns and Williams (1983). Arthur (1988)
and Heatherington and Mueller (1997) focus on
geochemistry of basement terrains, while Smith
and Lord (1997) summarize the tectonic and
geophysical aspects of the Florida basement.
Gohn (1988) and Randazzo (1997) provide
comprehensive overviews of Mesozoic and
Cenozoic geology of the Atlantic Coastal Plain,
including peninsular Florida. Mesozoic and
Cenozoic paleoceanographic and structural
evolution along the margin of the Florida
peninsula is presented in Hine (1997).

Selected early studies of Cenozoic and
younger formations include Applin and Applin
(1944), Cooke (1945), Puri and Vernon, (1964)
and Chen (1965). More recent stratigraphic
research on units in south and southwest Florida
has been completed by Miller (1986), Scott
(1988), McCarten et al. (1995), Brewster-
Wingard et al. (1997) and Cunningham et al.
(1998). Missimer (2002) focused on Oligocene
through Pliocene stratigraphic relationships in
the southernmost part of the present study area
(Charlotte County), as well as Lee and western
Collier Counties. Pliocene and younger
stratigraphy has been the focus of several studies

BULLETIN NO. 68

Table 1. Units mapped in this study. Map types are structure contour (SC) and isopach (I).

Lithostratigraphic Units Map types Hydrostratigraphic Units Map types

Hawthorn Group SC, I surficial aquifer system I
intermediate aquifer system /c,
Peace River Formation SC, I intermediateSC, I
intermediate confining unit
Bone Valley .
Bone Valley SC, I Floridan aquifer system overburden I
Member
Arcadia Formation SC, I Floridan aquifer system SC

Tampa Member SC, I Upper-Floridan aquifer system I

Nocatee Member SC, I Middle Floridan confining unit SC

Suwannee Limestone SC, I

Ocala Limestone SC, I
Avon Park Formation
SC

(e.g.,Evans and Hine, 1991; Scott,
Missimer, 2001).

Hydrogeologic framework studies that
the southwestern Florida region include

1997;

include
Gilboy

(1985), Johnston and Bush (1988), Miller (1986),
Ryder (1985) and Reese and Richardson (2008).
Maps depicting the thickness and extent of the
Floridan aquifer system (FAS), the "intermediate
aquifer" and intermediate "confining beds" include
Buono and Rutledge (1978), Wolansky et al.
(1979a), Wolansky et al. (1979b), Wolansky and
Garbode (1981), Corral and Wolansky (1984) and
Miller (1986). Allison et al. (1995) present a map
of the top of rock of the FAS in the Suwannee
River region, located along the northeast part of
the SWFWMD study area. Meyer (1989) provides
a comprehensive characterization of the
hydrogeologic framework of southern Florida.
Spechler and Kroening (2007) present a
comprehensive study of Polk County hydrology.
Reese (2000) and Missimer and Martin (2001)
present the hydrogeology and water quality of the
FAS in Lee, Hendry and Collier Counties.

Statewide hydrochemical characterizations of
the upper FAS have focused on aquifer-system
mineralogy and processes that led to observed
native groundwater chemistry (e.g., Plummer,

1977; Sprinkle, 1989), and hydrochemical facies
(Katz, 1992). Upchurch (1992) characterized not
only hydrochemical facies, but also naturally
occurring and anthropogenic constituents in the
FAS. Other studies that focused on regional
aspects of FAS hydrochemistry (i.e., salinity,
solute transport and dolomitization) include Back
and Hanshaw (1970), Cander (1994, 1995),
Hanshaw and Back (1972), Jones et al. (1993),
Maliva et al. (2002), Randazzo and Zachos
(1984), Sacks (1996), Sacks and Tihansky
(1996), Steinkampf (1982), Swancar and
Hutchinson (1995), Trommer (1993), and Wicks
and Herman (1994, 1996). Budd et al. (1993),
Budd (2001, 2002) and Budd and Vacher (2004)
have studied in detail the role of permeability,
compaction and cementation in FAS carbonates
of southwest Florida. An overview of surface-
water and groundwater hydrology is provided by
Wheeler et al. (1998). In contrast to these regional
characterizations, Tihansky (2005) identified the
complex relation between water quality,
groundwater flow patterns and structural
heterogeneity within the FAS in northeastern
Pinellas County by employing diverse
hydrogeological and geophysical analyses.

Hydrochemical studies of the intermediate
aquifer system/intermediate confining unit

FLORIDA GEOLOGICAL SURVEY

Explanation

SStudy Area US Interstate
Cities
Cities FL Turnpike
-- Rivers
Lakes US Highway
- Water Management Districts

Figure 1. Study area.

Study Area
0 5 10 20 30 40
Miles
0 5 10 20 30 40
== == Kilometers
Scale 1 1,750,000
Projection: Custom FDEP Albers

-J LDaytona Beach
i VDavtona Beach

Gulf
of
Mexico

BULLETIN NO. 68

include Joyner and Sutcliff (1976), Upchurch
(1992), Kauffman and Herman (1993), Broska
and Knochenmus (1996) and Torres et al.
(2001). Knochenmus (2006) characterizes the
water quality and hydraulic heterogeneity of the
intermediate aquifer system in the southern part
of the District. The study underscores that
previously defined "permeable zones" of this
aquifer system are hydraulically similar to
"semi-confining units" in the upper Floridan
Aquifer System. A statewide hydrochemical
assessment of the surficial aquifer system was
completed by Upchurch (1992).

Several groundwater flow models of the
SWFWMD region have been published (e.g.,
Ryder, 1985; Barcelo and Basso, 1993; Yobbi,
1996), most of which are discussed in the
comprehensive work of Sepulveda (2002),
wherein he developed a groundwater flow model
for peninsular Florida that includes the
Intermediate and Floridan aquifer systems.
Selected compilations of aquifer parameters on
which many of these models are based are
presented in Hydrogeological Properties, p. 52.

Physical Setting
Geology

Development of the Florida carbonate
platform primarily occurred during the Late
Cretaceous through middle Cenozoic and was
generally free of intermixed sands and clays.
Strong currents across northern Florida in a
feature broadly referred to as the Georgia
Channel System (Huddlestun, 1993) effectively
precluded transport and deposition of these
siliciclastics to the platform. During this period,
deposition of the Cedar Keys Formation,
Oldsmar Formation, Avon Park Formation,
Ocala Limestone, and the Suwannee Limestone
occurred. Huddleston (1993) proposed the
Georgia Channel System recognizing spatially
and temporally overlapping features (e.g.,
Suwannee Strait and Gulf Trough) proposed in
the literature that described paleotopography
(paleobathymetry) and associated paleocurrents.
Randazzo (1997) provides an overview of this

dynamic system and feature names.

During the Oligocene, the southern
Appalachians experienced uplift and erosion
(Scott, 1988). Southward transport and
deposition of ensuing siliciclastic sediments
began to fill the channel system, which allowed
ocean currents to transport sediments southward
across the well-developed carbonate platform.
As a result, some of the first siliciclastic
sediments in southern Florida carbonates appear
as sand lenses in the Lower Oligocene
Suwannee Limestone south of Charlotte County
(Missimer, 2002). The influx of siliciclastic
sediments, mixing with locally-formed
carbonates led to Late Oligocene through the
Early Pliocene deposition of the Hawthorn
Group (Scott, 1988; Missimer et al., 1994)
throughout most of Florida. In much of
peninsular Florida phosphate deposition
occurred yielding many economic phosphorite
deposits. This period of phosphogenesis is
described by Riggs (1979a, 1979b) and
Compton et al. (1993); [see Bone Valley
Member, p. 48, for more detail]. During the
Late Pliocene to Recent, sediment deposition
became even more siliciclastic dominant. Shell
beds were deposited along coastal areas and
migrated in response to sea-level fluctuations.
The geology and depositional environment of
lithostratigraphic units in the region are the
subject of numerous studies in southwestern
Florida; results of which are presented in the
lii~ai,,,,,i, ,,llihy section, p. 30, of this report.
From deposition of the Cedar Keys Formation
through Pliocene-Pleistocene shell beds, a
dynamic transition from carbonate to
siliciclastic-dominated depositional environments
is reflected.

The surface distribution of lithostratigraphic
units (Figure 2) in the study area is a function of
post-depositional influences ranging from
tectonic activity, platform stability, sea-level
changes and karst processes. For example, the
Avon Park Formation is the oldest exposed
lithostratigraphic unit in the study area (Figure
2). This Eocene unit gently dips southward
toward Charlotte County to depths exceeding
1500 ft (457.2 m) below land surface (BLS). In

FLORIDA GEOLOGICAL SURVEY

Geologic Map
0 5 10 20 30 40
i i Miles
0 5 10 20 30 Kilometers

Scale 1:1,750,000
Projection: Custom FDEP Albers

,i TQd,
Tod

I ''
* t1 '" ".*.^ s

Explanation u iQ.Q'-
D Study Area 6
- Water Management Districts I "
Stratigraphic Units r
Qbd Beach Ridge and Dune ,
Qh Holocene Sediments
SQu Undifferentiated Sediments\ .Ts,
STQd Dunes u "Q "
STQsu Shelly Pio-Pleistocene Sediments
TQu Undifferentiated Sediments
STQuc Reworked Cypresshead Sediments Qh
STap Avon Park Formation
STc Cypresshead Formation
STh Hawthorn Group (undifferentiated)
Tha Hawthorn Group, Arcadia Formation
Ti I Hawthorn Group, Arcadia Formation, Tampa Member Qh
The Hawthorn Group, Coosawhatchie Formation
Thp Hawthorn Group, Peace River Formation
SThpb Hawthorn Group, Peace River Formation, Bone Valley Member
STo Ocala Limestone
Ts Suwannee Limestone
STt Tamlaml Formation

Tc
Thpb'.-

Qu

Qu

':-Qu~~;

Gulf
of
Mexico

II
xx hi

Figure 2. Geologic map of study area (from Scott et al., 2001) depicting the uppermost mappable
units within 20 ft (6.1 m) of land surface.

BULLETIN NO. 68

general, the younger formations follow this
pattern, however, many are not observed
throughout the full extent of the study area (i.e.,
absence of the Peace River Formation
[Hawthorn Group] in the northern third of the
District). In the sections that follow, details of
the features and processes affecting the overall
geologic framework are discussed.

Structure

Numerous structural features affect the
thickness and extent of geologic units in the
study area (Figure 3). The oldest known
"basement" feature in the region is the Bahamas
Fracture Zone (Klitgord et al., 1983), which is
also referred to as the Jay Fault (Pindell, 1985).
This zone bisects the Florida peninsula basement
from Tampa Bay southeast to the Lake Worth
area on the east coast. Lithologic and
geophysical data suggest that this basement
feature represents an Early Mesozoic transform
fault that was important to the development of
the Gulf of Mexico. Christenson (1990),
however, suggests that based on assessment of
more recently acquired borehole geology and
magnetic anomaly data, the feature represents a
Triassic-Jurassic extensional rift margin with
little to no lateral offset. He proposes the name
"Florida Lineament" to describe this feature,
which coincides with the Jay Fault and the
Bahamas Fracture Zone across peninsular
Florida (Christenson, 1990; see feature "A" in
Figure 3).

The South Florida Basin (Applin and Applin,
1965; Winston, 1971) is a stratigraphic basin
that contributed to southward thickening of
Mesozoic and Early Cenozoic lithostratigraphic
units in the southern Florida peninsula (Figure
3). A possible successor basin, the younger
Okeechobee Basin (Riggs, 1979a) may have
contributed to south southeastward dipping of
Oligocene and older lithostratigraphic units
along the eastern margin of the study area
(Highlands and Glades Counties).

The influence of "basement" structures on
Cenozoic and younger stratigraphic units is
poorly understood. For example, an apparent
southeast plunging syncline ("B" in Figure 3)

trends from Sarasota to Hendry Counties in the
"sub-Zuni" (i.e., pre-Middle Jurassic) map
presented in Barnett (1975). Shallower
northwest-striking faults reported by Winston
(1996) occur in the same region. Maps of the
structural surface of Eocene rocks (Miller, 1986)
indicate a generally south-plunging trough
extending from central Charlotte County.
Deepening and thickening of units in the
Charlotte County region are observed in the
present study (see I l thiti,,,, Ii,,l'y, p. 30). The
Early Cretaceous "Broward Syncline" (Applin
and Appin, 1965; "C" in Figure 3) is located
approximately 20 mi (32 km) to the east of
feature "B" and has a generally parallel strike.
These inferred faults and basement relationships
warrant further study, especially given their
potential role in water quality and distribution of
permeable zones. Knowledge of the distribution
of low-permeability sediments beneath the FAS
is also important as potential sites for CO2
sequestration are explored.

The Ocala Platform ("D" in Figure 3) is the
most dominant feature in the central peninsular
region. Evidence of this platform is apparent in
the geologic map (Figure 2) where the Eocene
Avon Park Formation (Tap) and Ocala
Limestone (To) are exposed at or near land
surface. This feature is also evident in the
Environmental Geology composite map (Figure
4), which reflects lithologic and sediment types
within 10 ft (3.1 m) of land surface. Shallow or
exposed carbonate rocks in Levy, Marion, Citrus
and Sumter Counties reflect the influence of the
platform. This structure is not thought to be an
uplift (Winston, 1976) but rather a tectonically
stable area on which disconformable marine
sedimentation and differential subsidence has
occurred (Scott, 2001). It is also a major
controlling factor in the thickness and extent of
lithostratigraphic units in central and
southwestern Florida. As a result, this feature
also has a very significant effect on the
distribution of regional aquifer systems.

Remaining structural features are discussed
in this section from north to south. Several
northwest-trending faults, as well as orthogonal
fracture traces (or lineaments), have been
proposed within the Levy and Citrus County
area by Vernon (1951). It is possible that some

FLORIDA GEOLOGICAL SURVEY

Structural Features
0 5 10 20 30 40
0 5 10 20 30 40
Kilometers
r 1,. 1 FDEP Albers
Pr.:1..-:I,:.r, Cu~Ii:.m FDEP Albers

Gulf
of
Mexico

E

Explanation

I Study Area FG-2
SFault Groups

Plunging anticline *

SPlunging syncline "

Proposed Faults I \
--- Present Study (inferred) I
Sproul etal., 1972
Winston, 1996
Hutchinson, 1991 B Okeechobee
===. Christenson, 1990 Basin
Miller, 1986
Pride et al., 1966
Carr and Alverson, 1959
Vernon, 1951 C

Figure 3. Structural features within the study area. A Florida Lineament; B pre-middle
Jurassic plunging syncline inferred from Barnett's (1975) "sub-Zuni" map; C "Broward
Syncline;" D Ocala Platform; E Kissimmee Faulted Flexure; FG-1 fault group along strike
with fault inferred in present study; FG-2 group of reported faults possibly affecting subcrop
extent of the Ocala Limestone. U/D upthrown/downthrown block.

BULLETIN NO. 68

Gulf
of
Mexico

Explanation

I IStucl -,-
- Wat- I I,,5,.,,,,,r n,, -

Environmental Geology
Rock/Sediment Type
Clayey Sand
Dolostone
' Limestone
Limestone/Dolostone
::Med Fine Sand and Silt
Peat
Sandy Clay and Clay
Shelly Sand and Clay
Lake Okeechobee

I
iI'

S Environmental

Geology
0 5 10 2) j0 40
".,. iMiles

..:". ". 1':0 -10

CL.,."n Fu :.EP i. -,.,

)I
;:J

Figure 4. Environmental Geology of the study area (after Knapp, 1978; Scott, 1978; Scott, 1979;
Lane, 1980; Lane et al., 1980; Knapp, 1980; Deuerling, 1981). Lithotypes depicted in this map are

reported to occur less than or equal to 10 ft (3.0 m) from land surface.

~
:~:

~ ':~'=:

:.it

~~::: : ':'
:... ~"'::.': :1.--;

-I"''
-.. i'f
:.:.
r

~: .:

..: ':I?'"'':
':'
:
a .......
a
:. :
9\ _r; I... ;r.

:

~.~ .~~. i'

:

:
~: ::::.~
'

.:: ; 3-

'''

; :

ci ..
(; i
.i
;

~j..~,

: :.:~
;. .:.
:: .:::
::I

.:i ':':::j ::::i::
i :.)~:i' ~ ~

FLORIDA GEOLOGICAL SURVEY

of the inferred "offsets" in his study are due to
wells having encountered buried karst pinnacles
and paleo-sinks. Carr and Alverson (1959),
Pride et al. (1966), and Vernon (1951) report a
northwest trending normal fault(s) in
northwestern Polk County (fault group "FG-1",
Figure 3). Pride et al. (1966) suggest that the
fault affects not only the Avon Park Formation,
but also juxtaposes the Suwannee Limestone and
Ocala Limestone. Carr and Alverson (1959)
indicate that the fault penetrates Hawthorn
Group sediments as well. Both studies report
the northeast block of the inferred fault as the
upthrown side. In the present study, evidence
supports two possible northwest-trending faults
along the northeastern extent of the Suwannee
Limestone (Figure 3; see also Suwannee
Limestone, p. 37). Both faults are similar in
strike and offset direction (polarity) to fault
group "FG-1" in Figure 3. One of the offsets
proposed herein is a northwestern extension of a
fault proposed by Carr and Alverson (1959).

Faults affecting Middle and Upper Eocene
(e.g., Avon Park Formation and Ocala
Limestone) strata are proposed along the Polk-
Osceola County boundary (Pride et al., 1966;
Miller, 1986). The Kissimmee Faulted Flexure
(Vernon, 1951; "E" in Figure 3) occurs in the
same area and was originally considered a
wedge-shaped, fault-bounded block that had
been tilted and rotated, with beds containing
small folds and structural irregularities. Wells
that penetrate the feature contain variably thick
Pliocene-Miocene sediments that overly the
Avon Park Formation. Scott (1988) and Davis
et al., (2001) consider the Kissimmee Faulted
Flexure to be an Avon Park Formation
stratigraphic high with the Ocala Limestone and
Hawthorn Group sediments locally absent due to
erosion. Additional faults ("FG-2" in Figure 3)
affecting the subcrop extent of the Ocala
Limestone along the western margin of the
Flexure have also been proposed. Data
presented in this study support the
interpretations of Scott (1988) and Davis et al.,
(2001).

Further to the south in the vicinity of
Charlotte Harbor, a west-northwest trending
reverse fault penetrating a dolostone layer in the
Suwannee Limestone is proposed (Hutchinson,

1991). Maps presented herein do not lend
support to the inferred reverse fault. In the same
area, a series of northeast-trending lineaments
along the northern margin of Charlotte Harbor
(Michael Fies, personal communication, 2007)
coincide with anomalously high groundwater
temperatures in the upper FAS (Smith and
Griffin, 1977) suggesting a potential line of
further investigation (E. Richardson, written
communication, May, 2006). The "North Port
Fault" (Winston, 1996) strikes nearly coast-
parallel (northwest) across North Port and Punta
Gorda. Winston (1996) suggests that the
downthrown side may occur on the southwest
block, which more or less coincides with
thickening and deepening of several units
mapped in the present study (see
Ilig, ip,,,,b,,,!hy, p. 30, for further discussion).
South of the study area, west-northwest trending
normal and reverse faults offsetting Miocene
Hawthorn Group sediments on the order of 50 to
100 ft (15 to 30.5 m; vertical) are reported
(Sproul et al., 1972).

Evidence of some degree of vertical offset is
present within cores in the study area; however,
there is insufficient proximal well control to
delineate faulting. Core from W-16913 (ROMP
5), for example, contains abundant high-angle
fractures and slickensides that make some
lithostratigraphic unit surfaces obscure.
Regarding hydrostratigraphic units, brecciated
and fractured zones in core from W-17392
(ROMP 13) contribute to difficulties correlating
the Middle Floridan confining unit. These are
only two of many examples of fractured
intervals encountered during data collection that
warrant further structural study.

Small irregular surfaces in Miocene and older
lithostratigraphic units in the southern part of the
study area raise many questions regarding the
prevalence of structural deformation within
Florida's relatively young carbonate platform.
Missimer and Maliva (2004) suggest that
observed disturbances in lithostratigraphic
surfaces throughout Florida are due to
"differential subsidence by tensional basement
displacement." Their conclusions are based on
seismic surveys and borehole data attained from
areas of variable formation depths. Charlotte
and Lee Counties are among the most widely

BULLETIN NO. 68

studied of these areas. Seismic surveys reveal
variations in depth to formations (i.e., relief of
unit surface) between -130 to -230 ft (39.6 m to
70.1 m) (Missimer and Gardner, 1976). Other
seismic profiles in the region also suggest
deformation (Evans and Hine, 1991; Lewelling
et al., 1998). Missimer and Maliva (2004)
propose that these deformed surfaces, some of
which extend more than a mile across, are
tectonically induced folds. On the other hand,
Wolansky et al. (1983), Evans and Hine (1991),
Lewelling et al. (1998) and Cunningham et al.
(2001) prefer the hypothesis that observed
perturbations in seismic reflectors are the result
of karstic processes rather than structurally or
tectonically related deformation.

Geomorphology

The topography (Figure 5) and
geomorphology (Figure 6) of Florida have been
influenced by interactions of sea-level changes,
karst processes and subtle tectonic forces
(Rupert and Arthur, 1990; Schmidt, 1997). The
rate of Florida's carbonate platform deposition
was controlled by sea-level cycles and stand
durations, which produced different
physiographic features (e.g., Healy, 1975;
Randazzo, 1997).

Prominent ridges formed in shallow-water
marine environments during sea-level high
stands. Paleo- water bodies, embayments,
swales, relict coastal features and streams
control where many present-day streams and
lakes are located (White, 1970, Randazzo.,
1997). Orthogonal patterns in modem drainage
systems within the southern part of the study
area may have been influenced by fractures
(Lewelling et al., 1998) formed in response to
peripheral Miocene-Pliocene stress fields
associated with Caribbean tectonics (Missimer
and Maliva, 2004).

Physiographic Provinces and Features

Aerially extensive and distinctive
physiographic provinces in the study area are
summarized in this section, starting with the
coastal zone and working inland (Figure 6). The

coastline along the SWFWMD has been
classified into two zones (Tanner, 1960a,
1960b): 1) north of Pasco County the coastal
zone is dominated by swamps, salt marshes,
oyster reefs and drowned karst topography and
2) south of Pasco County, depositional marine
environments contributed to the formation of
barrier beaches, barrier islands, barrier spits and
over-wash fans.

The Gulf Coastal Lowlands (White, 1970)
include the western extent of the SWFWMD,
ranging in width from less than 2 mi to
approximately 45 mi (3.2 km to -72 km).
Elevations range from sea-level to
approximately 100 ft (30.5 m) above mean sea
level (MSL). Diverse ecosystems are present
within the Gulf Coastal Lowlands including pine
flatwoods, dry prairies and to a lesser extent,
swamps, scrub and high pine and salt marshes
(Crumpacker, 1992). The Gulf Coastal
Lowlands do not coincide with any mappable
marine terrace and are generally characterized
by wide, flat marine karstic plains, including
paleo-dunes (White, 1970). Significant updates
and revisions to Florida's geomorphic
nomenclature are ongoing, with an emphasis on
geologic processes and framework geology
(Scott, 2004). Re-classification of the Gulf
Coastal Lowlands into the Chiefland Karst Plain,
Crystal River Karst Plain, and the Land O'
Lakes Karst Plain is proposed (Scott, 2004).

The Brooksville Ridge is a prominent upland
east of the Gulf Coastal Lowlands, striking
north-northwest discontinuously from Pasco to
Levy Counties. The total length is
approximately 110 mi (177 km) including the
inter-ridge Dunellon Gap (Figure 6). The Ridge
varies in width from approximately 4 to 10 mi
(6.4 to 16.1 km) (White, 1970). Elevations
along this upland range from approximately 70
to -300 ft (21.3 to 91.4 m) above MSL. Fine-
grained, low-permeability sediments within the
Brooksville Ridge, particularly Hawthorn Group
clays, reduce relative infiltration rates and
provide a chemical buffer that inhibits carbonate
dissolution. Areas without thick clay-rich
siliciclastic deposits, through geologic time, are
more vulnerable to a reduction in land surface
elevation. This process, known as topographic

FLORIDA GEOLOGICAL SURVEY

Topography

0 -, III 0 I, 4ii

c al i 7 *. 1 1:11:11:1
Pro:cliio: n CuLIoni F)DEP -I.. rE
"-

Gulf
of
Mexico

Explanation

| 1 | ,S uI, -re,3
- VV.?Itr rM.an.a.gement Distri:ts

Elevation
310 ft

S155 t

Oft

Figure 5. Shaded relief topography of the study area based on 15 m (49 ft) resolution digital
elevation model DEM (digital elevation model) (Arthur et al., in review).

BULLETIN NO. 68

Geomorphology
0 5 10 20 30 40
31 I Miles
0 5 10 20 30 40
Kilometers
Scale 1 1,750,000
Projection: Custom FDEP Albers

Silver Glen

0
g Alexander

Y A
^ .

0

r
oS
S0
0.

- C-

Zep C
Zephyrhill3 Gap

0
'8

0Polk Upland

Polk Upland 1|.

S Volusia Blue

SM i

Mount Dora Ridge

*1
I
I

I

II

IJ

I

0

0

Explanation

I I Study Area \
- Water Management Districts

Springs (1st Magnitude)

o Springs

W Geomorphology

Desoto Plain

d

Caloosahatchee Inch

C -aIooslatchee V
- Caoosa~atchee Valle

: '.

Figure 6. Geomorphology of the study area (from White, 1970 and Puri and Vernon 1964). Spring
locations from Scott et al. (2004).

O O0
~' O

Gulf
of
Mexico

FLORIDA GEOLOGICAL SURVEY

inversion, is thought to have been an important
factor in the origin of the Brooksville Ridge
(White, 1970; Knapp, 1977). Karst features are
abundant along the axis of the Brooksville
Ridge. These features are generally internally
drained and locally breach the low-permeability
sediments in the subsurface and serve as focal
points of aquifer recharge. Ecosystems present
within the Brooksville Ridge area include scrub
and high pine, temperate hardwood forests (with
less extensive swamps), pine flatwoods, and dry
prairies (Crumpacker, 1992).

The Western Valley is located east of the
Brooksville Ridge and Tsala Apopka Plain and
west of the Sumter and Lake Uplands (Figure 6).
It is also bound to the north by the Northern
Highlands and the Polk Upland to the south. The
Western Valley is approximately 140 mi (225
km) long and between 5 and 15 mi (8.0 to 24.1
km) wide; elevations average approximately 40
ft (12.2 m) MSL and range up to 100 ft (30.5 m)
MSL. Ecosystems present in the Western
Valley include temperate hardwood forest (to
the north), scrub and high pine, minor swamps,
pine flatwoods and dry prairies (Crumpacker,
1992). The Western Valley is characterized by
its gently rolling limestone karst plains
containing a veneer of Pleistocene sediments
overlying Eocene carbonates (Rupert and
Arthur, 1990). The Tsala Apopka Plain is
believed to be a relict feature of a larger paleo-
lake (White, 1970). Scott (2004) proposes
reclassification of the Western Valley into the
Williston Karst Plain and Green Swamp Karst
Plain.

The Polk and Lake Uplands, located between
the Gulf Coastal Lowlands and the Lake Wales
Ridge are approximately 100 mi (161 km) in
length and range in elevation from 80 ft (24.4 m)
MSL to 130 ft (39.6 m) MSL. Pine flatwoods
and dry prairies with lesser amounts of
temperate hardwood forest, scrub and high pine
comprise the ecosystems in these uplands
(Crumpacker, 1992). A scarp with relief of
approximately 25 ft (7.6 m) separates the Polk
and Lake Uplands from the Gulf Coastal
Lowlands and Western Valley (Arthur and
Rupert, 1989). These two uplands contain three
minor ridges: the Winter Haven Ridge, the Lake
Henry Ridge and the Lakeland Ridge (White,

1970). The land surface is comprised mostly of
mild to gently rolling hills gradually increasing
in elevation eastward. Miocene-Pliocene clays in
this region overlying older carbonates create a
hydrogeologic environment conducive to the
rapid formation of large cover-collapse
sinkholes. Scott (2004) proposes to rename the
Polk Uplands in combination with the DeSoto
Plain: the Polk-DeSoto Plain. The part of the
Lake Upland in the present study area is
proposed to be renamed the Green Swamp Karst
Plain (Scott, 2004).

The DeSoto Plain is a broad, gently sloping
area south of the Polk Upland, east of the Gulf
Coastal Lowlands and west of the Lake Wales
Ridge. Elevations vary between 30 and 100 ft
(9.1 to 30.5 m) MSL (Wilson, 1977). The
DeSoto Plain varies from 10 to 40 mi (16.1 to
64.4 km) in length from north to south and 10 to
50 mi (16.1 to 80.5 km) in width from west to
east. Ecosystems present within the area include
pine flatwoods and dry prairie with minor
swamp, scrub and high pine (Crumpacker,
1992). The lithology consists of thick sandy
clays over Pliocene and Miocene limestones of
poor induration.

The most prominent geomorphic feature in
the study area is the Lake Wales Ridge. This
large elongate upland extends from Lake County
south to Highlands County, where it is flanked
by paleodune fields on the eastern margin (Scott
et al., 2001). Ecosystems on the Ridge include
freshwater marsh, pine flatwoods and dry
prairies (Crumpacker, 1992). A belt of lakes
dominate the Intraridge Valley in the southern
part of the Lake Wales Ridge. Geophysical
investigations of lakes within the Intraridge
Valley confirm a karst-related origin: irregular,
discontinuous seismic reflectors underneath
some lakes reveal breaches through confining
beds overlying the FAS (Evans et al., 1994;
Tihansky et al., 1996), thus indicating that the
large collapse features occurred prior to or
during Pliocene siliciclastic deposition (Arthur
et al., 1995).

Elevations on the Lake Wales Ridge range
from approximately 70 to 312 ft (21 to 95.1 m)
MSL, the latter forming a hilltop feature known
as Sugarloaf Mountain in Lake County. Unlike
the geology of the Brooksville Ridge, the Lake

BULLETIN NO. 68

Wales Ridge contains a very thick sequence of
permeable Pliocene-Pleistocene sediments (as
much as 350 ft [107 m]; see also Surficial
aquifer system, p. 53) overlying variably thick
clays of the Peace River Formation. In the
southern part of the Ridge, depth to carbonate
rocks exceeds 325 ft (99.1 m) BLS.

Morphology of the eastern flank of the Lake
Wales Ridge was likely controlled by high-
energy shoreline currents throughout the
Pleistocene (and perhaps the late Pliocene) as
indicated by the sharp topographic relief on the
eastern side of the Ridge. The presence of
discoid quartz pebbles in these sediments
(Cypresshead Formation) also indicates a high
energy depositional environment (Tom Scott,
personal communication, 2004). In contrast, the
western side of the southern part of the Ridge is
flanked by less pronounced topographic relief on
the Polk Upland and DeSoto Plain.

The general topographic relief of the
southern part of the Lake Wales Ridge mimics
that of the emergent part of the Florida Platform
with a steep shelf slope along the east and a
broad gentle slope to the west. Along the
southern margin of the Ridge (Figure 7), subtle
topographic ridges that trend toward the west
bear remarkable resemblance to the southern
Florida peninsula and the Florida Keys
suggesting that paleo-longshore and ocean
currents (e.g., loop current) that existed during
the Plio-Pleistocene are similar to those of
present day. Petuch (1994) referred to this area
as the Caloosahatchee Strait.

Sinkholes

In addition to paleo-sea levels and ocean
currents, karst processes have sculpted the
landscape of southwest Florida. Sinclair et al.
(1985) mapped four types of sinkholes in the
SWFWMD: 1) limestone dissolution: slow-
developing, funnel-shaped with a growth rate
similar to the rate at which the carbonate rocks
dissolve, overburden is thin; 2) limestone
collapse: forms abruptly and overburden is thin
3) cover- subsidence sinkholes: gradual
formation and generally small diameter, where
overlying sands infill limestone dissolution
cavities, overburden is greater than 30 ft (9.1 m)
thick; and 4) cover-collapse sinkholes: sudden
formation and relatively large in diameter,

forming upon a breach of clayey material
overlying a cavity, overburden is greater than 30
ft (9.1 m) thick. These sinkholes significantly
contribute to interaction between surface and
groundwater, intra-aquifer and inter-aquifer
communication (e.g., Tihansky, 1999) and the
vulnerability of aquifers to surface sources of
contamination (Arthur et al., 2007).

Plate 3 reflects the distribution of closed
topographic depressions (CTD) throughout the
SWFWMD region. This map is based on a 15 m
(49.2 ft) resolution digital elevation model
(DEM) produced by the FDEP-FGS in
cooperation with other FDEP programs and
Florida's water management districts. While not
all CTDs reflect karst features (i.e., paleodunes,
etc. may also be included), this depression
coverage provides a good approximation of
sinkhole distribution patterns within the study
area. The coverage, however, does not reflect
the tens of thousands (if not more) of buried
sinkholes detectable by means of surface
geophysical surveys (e.g., Wilson and Beck,
1988; Moore and Stewart, 1983), nor does it
include small karst features detectable by
LIDAR or sinkholes that formed since the USGS
topographic maps were last updated.

Springs

Springs predominantly occur in the northern
two-thirds of the study area (Figure 6).
Submarine springs occur offshore of Lee County
and between Pinellas County and Citrus County
(Ryder, 1985; DeWitt, 2003). Five of Florida's
thirty-three first magnitude springs (>100 ft3/sec;
>2.83 m3/sec) occur within the study area: Kings
Bay Springs Group, Homosassa Springs Group,
Chassahowitzka Springs Group (all in Citrus
County), Weeki Wachee Springs Group
(Hernando County) and the Rainbow Springs
Group (Marion County) (Champion and Starks,
2001). The Coastal Springs Groundwater Basin
(Knochenmus and Yobbi, 2001) encompasses
parts of Citrus, Hernando and Pasco Counties
and includes three of the five first magnitude
springs. The Coastal Springs Groundwater
Basin is made up of four sub-basins: Aripeka,
Weeki Wachee, Chassahowitzka and Homosassa
Springs. These groundwater sub-basins
comprise part of the total recharge area for these
springs. Surface water basins comprise the other
component. As defined and described in DeHan

FLORIDA GEOLOGICAL SURVEY

Topography
of South-Central
Florida
0 o10 M lOI-

o0 10 K .-:.-eer,

Prleir: t:bn Cu i ;:n-, FDE P -lbjer

Explanation

I Counties
Lake Wales Ridge
310ft
155 ft
Oft

Area
of -
Interest

Figure 7. Shaded topographic relief of the southern extent of the Lake Wales Ridge.

T.L i

BULLETIN NO. 68

(2004), "those parts of surface-water and
groundwater basins that contribute to the flow of
a spring" are called springsheds. Given the
proximity and hydraulic interrelationships
among the springsheds of the Coastal Springs
Groundwater Basin, the term "Springshed
Group," (analogous to a "Group" in
lithostratigraphic nomenclature) is herein
introduced to characterize this and similar
regions of coalescing springsheds (e.g., Coastal
Springs Springshed Group). Copeland (2003a)
compiled a Florida springs classification system
and glossary to facilitate standardized use of
springs-related nomenclature among Florida's
various technical (i.e. cave divers), scientific and
regulatory/planning communities.

The Coastal Springs Springshed Group and
the many other springs and springsheds in the
study area support unique ecosystems that
harbor diverse flora and fauna (Scott et al.,
2004; Champion and Starks, 2001). When water
quality and quantity decline, these ecosystems
are adversely affected. The magnitude and
nature of the threats varies within each
springshed based on land use and geology
(Hartnett, 2000; Florida Department of
Community Affairs and Florida Department of
Environmental Protection, 2002). It is
noteworthy that springshed boundaries are time-
dependent; they migrate in response to
anthropogenic activity (e.g.,
pumping/withdrawal) and seasonal/climatic
effects on the potentiometric surface (DeHan,
2004; Greenhalgh, 2004; Scott et al., 2004).

Since the 1970's scientists have documented
a decline in water quality in most of Florida's
springs especially with regard to nutrients (Jones
et al., 1998; Hartnett, 2000; Copeland, 2003b).
Nitrate is of particular concern as high amounts
may lead to excessive growth and eventual
eutrophication of surface water bodies. Nuisance
and exotic plants can cause reduction of water
flow, reduction of dissolved oxygen and habitat
changes (Hartnett, 2000). Nitrate has been a
concern in SWFWMD for many years as
increased levels of nitrates are being detected at
many springs (Jones et al., 1997). Natural
background concentration of nitrates in the FAS
is less than 0.01 mg/L (Champion and Starks,

2001). Florida government agencies have
recently proposed best management practices
(BMPs) to protect and conserve Florida's
springs (Florida Department of Community
Affairs and Florida Department of
Environmental Protection, 2002).

Spring-water quantity is another issue
associated with development and population
growth. Under redevelopment conditions
springs accounted for about 84 percent of water
discharged from the FAS (Ryder, 1985). As
development increases and more well fields are
used, the potentiometric surface of the FAS is
lowered. This results in lower spring discharge,
which can then result in changes in water quality
(Lee, 1998). Spring flows become dramatically
reduced or eliminated by over-pumping water
from the aquifer. Near coastal zones, changes in
aquifer conditions can also affect the location of
the transition zone between fresh and salt water
(Scott et al., 2004). As spring discharge rates
decrease, calcium and magnesium have been
observed to increase possibly owing to upcoming
or the removal of water from intergranular
storage (Rick Copeland, personal
communication, 2006). Although not fully
established at the current time, preliminary
evidence suggests that the upcoming of sulfates
and other constituents (i.e., micronutrients) may
be contributing to algal development in springs
(Sam Upchurch, personal communication,
2006). Corresponding increases in chlorides
may also be observed in the spring water as
discharge rates decrease. These conditions also
allow migration of saltwater further inland (Lee,
1998).

Hydrogeology

Three major hydrostratigraphic units occur in
west-central Florida: the surficial aquifer system
(SAS), the intermediate aquifer
system/intermediate confining unit (IAS/ICU)
and the Floridan aquifer system (FAS). Miller
(1986) divides the FAS into two zones of higher
permeability: the Upper Floridan aquifer (UFA)
and the Lower Floridan aquifer (LFA), which
are separated by one or more regional confining
units (Middle Floridan confining unit; MFCU).

FLORIDA GEOLOGICAL SURVEY

In this report, nomenclature and definitions
of units are primarily based on that proposed by
the "Ad Hoc Committee on Florida
Hydrostratigraphic Unit Definitions"
Southeastern Geological Society, 1986). A 2nd
Ad Hoc Committee on Florida
Hydrostratigraphic Unit Definitions (CFHUD II)
is presently convened to address identified
concerns regarding existing nomenclature and
definitions (Copeland et al., in review). The
CFHUD II is comprised of representatives from
the FDEP-FGS, USGS, water management
districts and consulting firms. Appendix 1
includes a commentary on nomenclatural issues
with regard to Florida's hydrostratigraphy.

The present study adopts the following
aquifer-system names and definitions, which are
minor revisions of the widely accepted, yet
dated Southeastern Geological Society (1986)
proposal. These definitions are revised in the
context of statewide application, and not limited
to the study area. Appendix 2 provides
explanation of changes from original
Southeastern Geological Society (1986)
definitions.

surficial aquifer system the permeable
hydrogeologic unit contiguous with land
surface that is comprised principally of
unconsolidated to poorly indurated
siliciclastic deposits. It also includes
carbonate rocks and sediments, other than
those of the FAS where the Floridan is at
or near land surface. Rocks and sediments
making up the SAS belong to all or part of
the Miocene to Holocene Series. The SAS
contains the water table and water within it
is under mainly unconfined conditions;
however, beds of low permeability may
cause semi-confined or locally confined
conditions to prevail in its deeper parts.
Locally perched water-table conditions
occur as well. The lower limit of the SAS
coincides with the top of laterally
extensive and vertically persistent beds of
much lower permeability.

intermediate aquifer system/
intermediate confining unit includes all
rocks that lie between and collectively
retard the exchange of water between the

overlying SAS (or land surface) and the
underlying FAS. These rocks in general
consist of coarse-to-fine-grained
siliciclastic deposits interlayered with
carbonate strata belonging to parts of the
Oligocene and younger series. The
aquifers within this system contain water
under semi-confined to confined
conditions. The top of the IAS/ICU
coincides with the base of the SAS and on
a local scale with land surface. The base
of the IAS/ICU is hydraulically separated
to a significant degree from the top of the
FAS.

Floridan aquifer system a thick,
predominantly carbonate sequence that
includes all or part of the Paleocene to
Lower Miocene Series and functions
regionally as a water-yielding hydraulic
unit. Where overlain by the IAS/ICU, the
FAS contains water under confined
conditions. When overlain directly by the
SAS, the FAS may or may not contain
water under confined conditions
depending on the extent of low
permeability material within the base of
the SAS. Where the carbonate rocks crop
out or are covered by a veneer of
permeable siliciclastics, the FAS generally
contains water under unconfined
conditions near the top of the aquifer
system, but because of vertical variations
in permeability, deeper zones may contain
water under confined conditions. The
FAS is present throughout the State and is
the deepest part of the active groundwater
flow system on mainland Florida. The top
of the FAS generally coincides with the
absence of significant thicknesses of
siliciclastics from the section and with the
top of the vertically persistent permeable
carbonate section.

Generalized correlations between
hydrostratigraphic units and lithostratigraphic
units mapped in this study are presented in Table
2. The HilJiiu,,, ,,g,,' section, p. 52, of this
report provides a more detailed discussion of
these aquifer systems. Delineation of aquifer-
system boundaries is described in Methods, p.
20.

Table 2. Generalized correlation chart for units mapped within study area (ages compiled from Covington, 1993, Missimer et al., 1994,
Scott et al., 1994, and Wingard et al., 1994). Numbers are million years before present. Ages are included for reference only and are not

scaled to correlate with all columns in the table. MFCU is Middle Floridan confining unit;
and Caloosahatchee Formations.

- ~ S II

Holocene
P- .01 -
Pleistocene
1.8

Pliocene

- 5.3

Miocene

--- 23.03-

Oligocene

-- 33.9 -

Eocene

Undifferentiated
sand, shell, and clay
(UDSC)

Bone
Valley Mbr.
3 Peace River Fm.
0
S Arcadia
Formation

r Tampa
c Member
Nocatee
Member

ISuwannee Limestone

Ocala Limestone

Avon Park
Formation

Hydrostratigraphic
unit

Quat-
ernary

0J

z
Zr

UDSC includes the Tamiami, Ft. Thompson

Erathem ISystem

Series

Lithostratigraphic
unit

Generalized lithology

Highly variable lithology ranging from
unconsolidated sands to clay beds with trace
amounts of shell fragments
Peace River Formation contains interbedded
sands, clays and carbonates with siliciclastic
component being dominant;variable
phosphate sand content

Arcadia Formation is a fine-grained carbonate
with low to moderate phosphate and quartz
sand, variably dolomitic

Suwannee Limestone is a fine-to medium-
grained packstone to grainstone with trace
organic and variable dolomite and clay
content
Ocala Limestone is a chalky, very fine-to
fine-grained wackestone/packstone varying
with depth to a biogenic medium- to
coarse-grained packstone grainstone; trace
amounts of organic material, clay and
variable amounts of dolomite

Avon Park is a fine-grained packstone with
variable amounts of organic-rich laminations
near top; limestone with dolostone interbeds
typical in upper part, deeper beds are
continuous dolostone with gypsum near base

surficial aquifer
system (SAS)

intermediate
aquifer
system or
intermediate
confining unit
(IAS/ICU)

71

E Upper
Floridan
S aquifer
S(UFA)

Cr
0I

M UMFCU

_ __

--

FLORIDA GEOLOGICAL SURVEY

Sediments comprising the SAS are
predominately post-Hawthorn in age and
generally consist of some combination of sands
shells and clays. In parts of the northern District
where the IAS/ICU is not laterally extensive,
discontinuous clay lenses serve as basal SAS
confinement, locally separating the SAS from
the FAS. Some of these basal clays may be
erosional remnants of (and correlative with)
lithostratigraphic units comprising the IAS/ICU.
In areas where Pliocene clayey sediments (see
clayeyy sand," Figure 4) are exposed at or near
land surface, such as west-central Polk County,
the SAS or water-table aquifer may not be
present; instead, the setting reflects IAS/ICU
overlying the FAS. Where hydraulic continuity
exists between uppermost Hawthorn Group
sands and younger sediments, the SAS includes
those sands, which are generally less than 20 ft
(6.1 meters) thick. In the southernmost part of
the study area, the Ft. Thompson and
Caloosahatchee Formations and upper
permeable sediments of the Tamiami Formation
comprise the SAS. Although mapping of these
complex "post-Hawthorn" units is beyond the
scope of this study, research did focus on the
depth and extent of clays within the Pliocene
Tamiami Formation, which are significant as
they comprise the base of the SAS in the region
(e.g., Reese, 2000; Weinberg and Cowart, 2001).

The IAS/ICU occurs throughout most of
Florida (Scott, 1992a) and correlates with
aquifer systems in parts of Georgia and
Alabama. In the study area, it is comprised of
mid- to upper Oligocene Pliocene sediments
and is generally continuous south of Pasco
County. As this hydrostratigraphic unit thickens
southward, interlayered permeable carbonates
become important water-producing zones,
especially south of Manatee County where the
FAS water becomes less potable. In this area,
three permeable zones are present; however,
correlation and mapping of these zones is
difficult, even with the use of hydrochemical
parameters (Knochenmus and Bowman, 1998;
Torres et al., 2001; Knochenmus, 2006). North
of Hillsborough County, the IAS/ICU
predominantly occurs within the uplands and
ridges, where it functions hydrologically as a
semi-confining to confining unit.

The FAS is one of the most productive
aquifers in the world. It underlies all of Florida,
southern Georgia and small parts of Alabama
and South Carolina for a total area of about
100,000 mi2 (-259,000 km2) (Johnston and
Bush, 1988). In parts of southwest Florida,
south from Sarasota, Charlotte, Glades and Lee
Counties, the FAS contains mineralized, non-
potable water. As a result, relatively permeable
zones within the IAS/ICU comprise the main
source of water supply (Miller, 1986; Torres et
al., 2001) in this region. The FAS is confined
except in parts of the northern third of the study
area where it occurs at or just below land surface
(Ryder, 1985). Throughout the study area, the
FAS predominately consists of carbonate rocks
(Southeastern Geological Society, 1986) ranging
in age from Paleocene to Miocene.

METHODS

Sample Description

More than 250 detailed lithologic de-
scriptions of borehole cores and cuttings were
completed for this study. These descriptions
record standard rock, mineral, fossil and textural
features. Selected parameters include color,
induration, grain size and range, sorting,
roundness, mineral percentages and special
descriptive, depositional or sedimentary
features. Descriptions of carbonate material
were based on the Dunham (1962) classification
system, which focuses on depositional texture
and whether the rock is mud-supported or grain-
supported: 1) mudstone muddy carbonate rock
containing less than 10 percent grains, 2)
wackestone mud supported rock containing
more than 10 percent grains, 3) packstone grain
supported muddy carbonate, 4) grainstone -
mud-free carbonate rock which is grain
supported and 5) boundstone carbonate rock
showing signs of being bound (e.g. cementation)
during deposition and reflecting original position
of growth. It should be noted that the Dunham
(1962) classification considers a "grain" as
having a diameter greater than 20 microns, while
"mud" is less than 20 microns. As a result, a
very fine grained grainstone may appear as a
mudstone even under a low-power binocular
microscope (David Budd, 2004, personal

BULLETIN NO. 68

communication). It is likely that this factor has
biased identification of mudstones in lithologic
descriptions that may technically be fine-grained
grainstones.

During archiving of borehole cuttings,
samples are gently washed in a 63 micron sieve
to remove any drilling mud (e.g., silt and clay-
sized material). When describing lithologic
characteristics of borehole cuttings, care was
taken to inspect the washed and unwashed
archival fractions of the samples. In many
cases, especially for older wells, the washed
sample fraction may under-represent the clay
fraction of the sample. For example, cuttings
representing the sandy clayey Nocatee Member
(Arcadia Formation) may have been washed to
the degree that only sand remains in the archived
sample. In such cases, the unwashed sets of
samples provide a better representation of the
original clay-rich lithology.

The descriptions are coded within the
aforementioned Microsoft AccessT" database -
FGS Wells. This database is undergoing
continued enhancements including migration to
a more robust enterprise-level platform. These
and other lithologic descriptions are available
from the Florida Geological Survey web site:
http://www.dep.statefl.us/geology/.

Delineation of Boundaries

Formations/Members

Formation and member boundaries were
determined for all described samples and for
cores, cuttings and geophysical logs from an
additional -600 wells. Florida Geological
Survey published and unpublished data (e.g.,
Stewart, 1966; Hickey, 1982, 1990; Johnson,
1986; Miller, 1988; Scott, 1988; Campbell,
1989; DeWitt, 1990; Campbell et al., 1993,
1995; Clayton, 1994, 1999; Green et al., 1995,
1999; Sacks, 1996; Arthur et al., 2001a; Gates,
2001; Missimer, 2002; and O'Reilly et al., 2002)
provided lithostratigraphic and hydrostratigraphic
boundary information on an additional -200
wells. Gamma-ray logs and fossil assemblages
are used only to supplement the lithologic data

in the determination of the boundaries. Where
uncertainty exists regarding the exact position of
the formation boundary, or where the boundary
is inferred within an interval of poor or no
sample recovery, a dashed rather than solid line
is shown on the cross sections. Dashed contacts
are also drawn where only a gamma-ray log was
used and no samples were available for
inspection. In cases where sample quality is
poor, as is often true with cuttings, the gamma-
ray logs become more important in the
determination of formation boundaries.

Uncertainties in lithostratigraphic unit
boundaries were recorded in a database of
elevations and thicknesses. These uncertainties
exist for several reasons. In the case of
inspecting cores, it is not uncommon for two
experienced geologists to disagree on a
formation boundary, especially when it is subtle
or gradational. Moreover, the core may have
poor recovery, resulting in missing intervals.
Regarding cuttings, samples often contain
borehole cavings, whereby the sampled interval
contains sediment or rock fragments from
overlying units. For example, in an extreme
case, dolostone cuttings from the Avon Park
Formation may contain phosphatic sands from
the upper Hawthorn Group. As a result, it is not
uncommon for a formation boundary estimation
based on cuttings to include an uncertainty range
on the order of 20 ft (6.1 m) based solely on
sample quality. Other uncertainties with respect
to mapped unit elevations also exist (see Map
Development and Data Management, p. 24).

Table 2 summarizes the lithostratigraphic
units shown on the maps. The same units are
also shown on the cross sections. For the
purposes of this study, post-Hawthorn units are
depicted as Pliocene-Pleistocene sediments
(undifferentiated) and Pleistocene Holocene
undifferentiated sand and shell or sand and clay
(UDSS or UDSC, respectively).

Aquifer Systems

Delineations of hydrostratigraphic units in
this report are based on the following: 1)
available hydrogeologic data collected during
drilling, 2) borehole geophysical logs,

FLORIDA GEOLOGICAL SURVEY

3) hydrogeologic characteristics of the samples
(e.g., estimated porosity and permeability,
hydraulic continuity between lithostratigraphic
units), 4) potentiometric data from nested
monitor wells, and 5) in the absence of other
data, correlation to lithostratigraphic units.
Application of the first four methods is highly
preferred; the majority of this data originates
from ROMP wells.

Contacts between aquifer systems can be
very subtle or abrupt depending on the
hydrogeologic properties of the rocks and
sediments. When only lithologic material from
a borehole is available on which to base an
aquifer-system boundary, further complications
arise. Preferential removal of clay-sized
particles, either during drilling or sample
archiving (e.g., sorting during material transfer
or washing of cuttings), tend to bias toward
interpretations of higher sample permeability.

Delineation of the basal contact of the SAS is
perhaps the most susceptible to the
aforementioned bias. If the contact is based
solely on estimates of hydrogeologic properties
of lithologic data, misrepresentation of clay
content, especially in borehole cuttings may
result in the interpretation of a preferentially
deep base of the SAS. This issue may become a
factor where the SAS may include sediments as
old as the upper Hawthorn Group. On the other
hand, permeable sands along the top of the upper
Peace River Formation in Manatee County (Tom
Scott, personal communication, 2006) comprise
the lower part of the SAS. If there is reason to
believe that the two units (Hawthorn and post-
Hawthorn Group sediments) are hydraulically
connected, both would be considered part of the
SAS. Alternatively, sandy clays overlying clay-
rich Hawthorn Group sediments would be
considered part of the IAS/ICU (assuming
sufficient lateral extent). Further south, the
Tamiami Formation is included within both the
SAS and IAS/ICU.

Noting the above exceptions, the lateral
extent of the IAS/ICU broadly corresponds to
the extent of Hawthorn Group sediments, except
where those sediments are part of the FAS (e.g.,
the Tampa Member [Arcadia Formation] along
the upper reaches of the Hillsborough River).
For consistency, in areas where the IAS/ICU is

mapped owing to sufficient lateral continuity,
the SAS is mapped over the same extent. In
areas where the SAS and IAS/ICU are
discontinuous, the FAS is generally
characterized as unconfined to semi-confined
(see Hy ,,,I,,i g ph y', p. 52, for more detail).

Figure 8 represents a compilation of
hydrogeological data to provide correlation
between hydrostratigraphic units and
lithostratigraphic units. In most areas, the
correlation is readily apparent, such as the
relation between the top of the Suwannee
Limestone in Sarasota County with the top of the
FAS. In another example, the Tampa Member
(Arcadia Formation) is hydraulically connected to
the FAS in Pinellas County and therefore
comprises the uppermost part of the FAS. The
correlations, however, are not always
straightforward, such as the area denoted as
"variable" (Suwannee Limestone and Nocatee
Member, Arcadia Formation) in DeSoto County
(Figure 8).
Cross-Section Construction

Detailed lithologic descriptions, gamma-ray
logs and hydrologic data comprise the bulk of the
information used to develop the cross sections.
The dominant sources of information for cross-
section control are SWFWMD ROMP wells;
FDEP-FGS wells were included to fill out
appropriate data-point coverage for the cross
sections. Where no lithologic data was available,
borehole geophysical logs were used. Of these
geophysical logs, gamma-ray logs were the most
readily available and generally useful for
correlative purposes within the study area.
Gamma-ray logs were included in the cross
sections to allow comparison of the gamma-ray
signatures relative to each stratigraphic unit. The
following discussion outlines the methods used
for construction of the cross sections for this
study.

Topography

Topographic profiles were included on each
cross section to facilitate comparison of surface
morphologies with subsurface stratigraphy. Data
used to construct these profiles was taken from U.S.
Geological Survey 1:24,000 (7.5 minute) quadrangle
maps. The profiles include selected anthropogenic
features, cultural boundaries and landforms.

BULLETIN NO. 68

Generalized Correlation
Between Lithostratigraphy and
Top of Ihe Floridan aquifer system
.. :. ,.. ,.1 40
SMiles
I ,. ,..ters
S.Pr:o 1 1 l.i: m FC11 1' EAl
Pr,:lec:i:,n Cusl.,m FDEP Albers

Gulf
of
Mexico

Explanation
I Study Area
Contours (75N inler all
Correlated FAS Units
Avon Park Formall:on
Ocala Limestone
Ocala Ls. & Avon Park Fm.
Suwannee Limestone
Suwannee Ls. & Tampa Mbr.
Tampa Member
~ Variable

Figure 8. Generalized correlation between lithostratigraphic units and the surface of the FAS. The
area labeled "Variable" includes parts of the Nocatee Member (Arcadia Formation, Hawthorn
Group) and the Suwannee Limestone.

FLORIDA GEOLOGICAL SURVEY

Lithology

For each well in a cross section, a
stratigraphic column was developed to represent
borehole lithology. The columns were based on
either existing descriptions or new descriptions
generated for this report. Hatch patterns depict
primary lithologies in the columns, with
accessory minerals shown on the right of the
columns as text codes. Where space is
available, the cross sections contain an
explanatory legend that defines mineralogic and
lithologic codes and patterns. For those cross-
sections without sufficient space to include the
"Explanation," it is also provided for reference
in Figure 9. Accessory-mineral codes are
generally the same as those used in the FDEP-
FGS lithologic database (FGS Wells). If the
volume of reported accessory sand-sized
minerals exceeds 5 percent, the content is
represented by a stippled sand pattern. If the
amount of accessory sand-sized minerals is less
than 5 percent, or if the amount is not known
based on existing descriptions, the accessories
are listed in the text codes. The mineral text
codes are listed in decreasing order of
abundance if the relative mineral abundance has
been reported.

The degree of detail within each lithologic
column generally reflects the type of material
available for description as well as the degree of
detail in the description. In most cases, more
detailed lithology exists for the cores. The
minimum bed thickness represented on the
stratigraphic columns is 5 ft (1.5 m) due to
graphical constraints. There are several
examples where lithologies and accessory
minerals have been averaged over a 5 to 10 foot
(1.5 to 3.0 m) interval to accommodate this
graphical limitation.

Gamma-ray Logs

Selected gamma-ray logs are plotted to the
right of stratigraphic columns on the cross
sections. These logs are used as a supplement to
delineate formation boundaries and allow
comparison of gamma-ray activity between the
various lithostratigraphic and hydrostratigraphic
units (e.g. Gilboy, 1983; Green et al., 1995;

Scott, 1988 and Davis et al., 2001). Gamma-ray
intensity units, when known, are shown on the
logs (horizontal axis) in counts per second (CPS)
or in American Petroleum Institute (API) units.
Inconsistencies between logs exist due to
different log settings (e.g., time constant, range)
and borehole characteristics (e.g., depth of
casing and lack of caliper logs to determine
sediment wash-out or cavities), making
quantitative comparison difficult. To allow
assessment of the high degree of variability in
the logs and to represent their natural response,
the intensity scales have not been normalized.
The logs are very useful in the identification of
correlative "packages" of gamma-ray peaks and
for comparison of the overall gamma-ray
signature within formational units. Relatively
high gamma-ray activity is generally correlative
with phosphate, organic materials, heavy
minerals and high-potassium clays. More subtle
changes may reflect dolomite and accessory
mineral content. Figure 10 summarizes general
relationships between gamma-ray activity and
mineralogy, the details of which are included in
the discussion of each lithostratigraphic unit (see
I i,ih, i, ogi,, O h', p. 30).

Aquifer Systems

Aquifer systems on the cross sections appear
as hachured brackets on the left of each
lithologic column. Patterns used in the
hydrostratigraphic columns identify the three
major aquifer systems present in the study area,
as well as the MFCU.

Map Development and Data
Management

For wells used in this study, elevations of
lithostratigraphic and hydrostratigraphic units
were recorded in a database that also included
the corresponding FDEP-FGS well accession
number (W-number), well name, comments
about the well, the geologist(s) who made the
determinations and well location (elevation,
latitude and longitude). The unit elevations on
which the maps are based are recorded in feet
BLS; a separate column calculates the elevation

BULLETIN NO. 68

CROSS SECTIONS EXPLANATION

HATCH PATTERNS
LIMESTONE-

FINE MEDIUM COARSE

t --DOLOSTONE

FINE MEDIUM COARSE

INTERBEDDED
LIMESTONE & DOLOSTONE

FINE MEDIUM COARSE
FINE MEDIUM COARSE

CLAY

SURFICIAL
AQUIFER
SYSTEM

INTERMEDIATE
AQUIFER SYSTEM /
CONFINING UNIT

FLORIDAN
AQUIFER
SYSTEM

MID-FLORIDAN
CONFINING UNIT

AAAAAAAAAAA
hA LA AAA A A
IAA A LAAAA haAl
AAAAAAAAAAI
AAAAAAAAAAA
CHERT

COMMENTS

M MICRITE
S SAND
P PHOSPHATE GRAVEL
D PHOSPHATE SAND

O ORGANIC
R SPAR
I IRON STAIN
Q QUARTZ
A ANHYDRITE
Ch CHERT

T SILT
C CLAY
Sh SHELL
D DOLOSTONE

L HEAVY MINERALS
No Spl NO SAMPLE
G GYPSUM
Py PYRITE

THIN MANTLE OF IAS/ICU SEDIMENTS
' SEMI-CONFINED TO UNCONFINED
FLORIDAN AQUIFER SYSTEM
* CUTTINGS EXAMINED IN THIS INTERVAL
INDICATE FORMATION PICKS SHOWN

Figure 9. Explanation (legend for cross sections).

GRAVEL

SAND

SHELLED GYPSUM

t

FLORIDA GEOLOGICAL SURVEY

u Quanz
A Anhydrite
Ch Chert

IP
Py

Gypsum
Pyrite

ROMP 17
W-15303

S -- IJDSC

i0;T ? .. Pf.ACE I.ER
FORMATION

ARCADIA
55 FORMATION

it -

ROMP 31
W-13514

i L UDSC

PEACE RIVER
.._ ... FORMATION
IO

.. -- R Typical higher count rate
S RCADIA* fortheArcadia Formation
--- FORMATION due tohigherphosphate
: and dolostone content

N!Co .-" TAMPAMEMBERssociated
-iL7 / -raypeaksassociated
i "----- with variable amounts of
S. .-... NOCATEE MEMBER phosphate.

,. /The Tampa and Nocaee
Members have higher
count rates than hat
of the underlying .
S IESUWANNEE (Suwannee Limestone.

- -- - -

l-- OCALA Ocala Limestone response
LIMESTONE with a very low /-ray activity
with few peaks.

r

/-ray peaks due to
-" o-- r ganics commonly found
at or near the top of the r
"- :: \ Avon Park Formation.
i-2'1 \ AVON PARK
,- FORMATION

.I: .0-_- -B"S ,.a..

Comments
Micrite T Silt
Sand C Clay suritcial aquifer system
Phosphate Gravel Sh Shell
Phosphate Sand D Dolostonea a
Organics L Umestone nt meial 'el n o ng uniT"
Spar H Heavy Minerals
Iron Stain NO SPL No Sample

k Flondan aquifer system

Phosphatic lag observed at the
base of the Peace River
Formation with associated 7-ray
peak. The lag may also occur at
the top of the formation.

___ -ray peaks associated
' TAMP.--E--- withe variable amounts
-- TMP, MEMBER of phosphate.

/ The Tampa and Nocatee
SMembers exhibit lower

O CATEE MEMBER \. Arcadia Formation.
S- -__ Peak due to clay beds
.-.. commonly found in the
SNocatee Member.

I.

1.-S

-,

'1,

I.

/-ray response for the
Suwannee Limestone may
exhibit a low count rate for
SLrWANNEE the upper half, and a higher
LIMESTONE for the lower half. The higher
count rate is generally
associated with dolostone
where present (not shown).

OCALA Ocala Limestone response
LIMESTONE with a very low 7-ray activity
with few peaks.

The Avon Park Fm. generally
AVON PARK exhibits a higher background
FORMATION count rate with more
variability than that of the
Ocala Limestone.

Figure 10. Characteristic gamma-ray (y) log responses.

M
S
P
p
0
R
I

F- P

1 -

entateu

BULLETIN NO. 68

relative to MSL. The database also records
uncertainty in the unit elevations. Synthetic
wells were added to the database to serve as
contour control along the margins of the study
area in order to facilitate a more accurate
interpolated surface. Quality assurance of all
well-head elevations was accomplished by
comparing the reported elevation with a 15 m
(49 ft) DEM. The data on which the maps and
cross sections are based is available from
http://ww.uflib.ufl.edu/ufdc/?b UF00087428&
v=00001

Map Interpolation and
Spatial Accuracy

As the GIS database was developed,
preliminary contour maps were generated to
allow identification of anomalous elevations and
data gaps. ArcView with the Spatial Analyst
extension was used to generate the initial
contour maps. For each map, a grid surface
model was calculated using a surface
interpolation method. Contours were then
generated from the surface model. The inverse
distance weighted (IDW) interpolator was found
to provide a very useful surface model for
identifying problem areas and outliers that
required additional research. As these issues
were identified, borehole cuttings were retrieved
from the FDEP-FGS core repository and re-
evaluated in context of: 1) proximal stratigraphy,
2) sample quality, and 3) stratigraphic boundary
uncertainty. This process of generating and
reviewing maps and re-examining samples was
repeated numerous times through the course of
this study. Arthur and Pollock (1998) suggested
that the IDW interpolation method is not suitable
for geologic mapping of stratigraphic data. The
IDW method was used only as an iterative
review tool. Interim maps for the initial phases
of this project were generated using the spline
interpolator. Arthur and Pollock (1998) found
the spline-tension method preferable to IDW
because spline yielded surface models that were
more accurate and geologically characteristic.

Upon review of subsequent interim maps
generated for this project, several shortcomings
in application of the spline interpolator were
recognized. These include false highs and lows

in the model surface that do not reflect any well
control and loss of contour accuracy along the
margins of the maps. Moreover, as the
interpolator was adjusted to yield smoother
contours, the interpolated surface became less
accurate. With the exception of accuracy at a
given well location, it was also difficult to assess
the error associated with the maps in data-poor
areas. Due to the "overshooting contour" effect
(e.g., false topographic highs), shallow map
units may exceed land surface elevations in
certain areas, especially along areas of high
topographic relief.

Prior to generation of the final maps, a re-
assessment of interpolation methods was
completed. Through an iterative process,
kriging was identified as the most robust and
accurate surface interpolator. The GIS project
was then migrated to ESRI ArcMap 8.3. The
map-unit elevation database was imported into
ArcMap and projected in the FDEP standard
projection (custom Albers equal-area conic
projection). Individual surfaces were then
interpolated using the ordinary kriging function
within the ESRI Geostatistical Analyst.
Iterations of krige data models were produced
for each map unit to minimize the map error.
Prediction errors and other descriptive statistics
for each map were recorded and used to identify
appropriate contour intervals (see Contour
interval selection, p. 30). When evaluating krige
statistics, the variability of the prediction (as
standard deviation) is overestimated when the
root mean squared prediction error (RMS) is less
than the average standard error (ASE) of the
prediction error (Table 3; Johnston et al., 2001).

The krige error automatically reported by the
software is based on the error within a
rectangular area defined by the distribution of
the data (i.e., wells). For nearly all of the maps
in this report, these results are misleading
because the datasets have an irregular spatial
distribution. As a result, for each kriged surface,
a prediction standard error map was also created
and masked to the spatial extent of the unit being
mapped. The average standard error of this
prediction standard error map was then
calculated and recorded (Table 3).

FLORIDA GEOLOGICAL SURVEY

As an extra measure to assess map accuracy,
a script was written to allow comparison of the
observed map-unit elevations (i.e., top of the
Suwannee Limestone in a given well) with the
value of the final interpolated grid cell in which
the well is located. On Table 3, this data is
summarized in the "Grid to Point" column,
where the "mean" represents the average of the
difference between grid cells and map unit
elevations for each well located within its
respective grid cell. In every case, the mean
"Grid to Point" value is less than +3 ft, (0.9 m)
for all maps, and the standard deviation (s) is
less than 20 ft (6.1 m) for 18 of the 22 maps and
less than or equal to 30 ft (9.1 m) for the
remaining 4 maps (Table 3). Qualitative
evaluation of these errors suggests they are
normally distributed.

The standard deviations for the "Grid to
Point" calculations (Table 3) are well within
acceptable limits, especially when considering:
1) geologic processes that can create
perturbations in a mapped surface (e.g., faults,
paleo-karst, paleo-environmental features [e.g.,
wave-cut scarps, river valleys]), 2) well location
error or uncertainty, 3) sample quality (e.g.,
cuttings interval and borehole cavings) and 4)
formation pick uncertainty (i.e., gradational
contacts, differences in professional opinion,
etc.).

Once the kriged surfaces were optimized for
each map unit, the shallow surfaces (i.e., top of
the Peace River Formation) were compared to
land surface elevations. To accomplish this, the
kriged surface was converted to a raster file
(grid) using a 400 m2 (4305.6 ft2) cell size,
which was then subtracted from the FDEP-FGS
15 m (49.2 ft.) resolution DEM to remove
interpolated elevations that exceeded land
surface. The grid was clipped (i.e., masked) to
the lateral extent of its respective map unit. For
most of the mapped units, contours generated
from the kriged and the DEM-trimmed surfaces
were generally irregular or jagged. This
characteristic is not only atypical for maps
depicting subsurface elevations and thicknesses,

but it also overemphasizes the level of resolution
represented by the maps. To remove these
localized and misrepresentative contour
anomalies, the grids were smoothed using the
neighborhood statistics function in Spatial
Analyst. Color shading, contour lines and labels
were then added.

It is noteworthy that substantial effort was
devoted to surface interpolations that would
allow weighting of data from cores
preferentially over that of cuttings and
geophysical logs. Combinations of grid
averages, weights, and point buffering applied
within various interpolators were evaluated
during extensive sensitivity analyses and
validation. In the final assessment, too many
negative attributes were associated with what
was considered the optimal core-weighting
technique. As a result, the well data from cores,
cuttings and geophysical logs are all considered
equally in the maps.

Unlike hand-drawn contours, the smoothed
contours generated from krige-interpolated
surfaces do not always reflect highly anomalous
elevation data points. While this may be
considered a disadvantage, it is substantially
outweighed by numerous advantages of the
digital products developed during this study: 1)
the interpolated surfaces are supported by
accuracy and precision statistics, 2) the
calculated grids can be used in a variety of
groundwater flow models and 3D applications,
3) GIS compatibility exists, including inherent
scalability and flexibility, and 4) the maps can
be readily updated with new information. As a
result, manual modification (editing) of the
contours to reflect anomalous values would
create discrepancies between the maps and the
grid coverages. In cases where contour
adjustments were deemed necessary to reflect
sharp-relief surface trends (as opposed to single
anomalous well values), synthetic control points
were added to improve map accuracy while
maintaining consistency with the calculated
grids.

Table 3. Summary of krige interpolation statistics for each map; ASE is average standard error of the prediction error; RMS is root mean
square of the prediction error. Gray pattern indicates that the prediction error may be overestimated (i.e., ASE>RMS).

Map Unit Prediction error (1s)J Prediction error (1s; map)4 Map "Grid to Point" Number Model
(s)=surface ASE RMS Mean of the 2 X Mean of Contour Error Calculation of Wells5 Algorithm
(t)=thickness ASE (1s) the ASE (2s) Interval
mean s
Hawthorn Group (s) 23 34 22 44 25 1.64 11 526 Exponential
Hawthorn Group (t) 57 68 56 112 75 -0.25 21 321 Spherical
Peace River (s) 25 35 22 44 25 0.64 9 349 Exponential
Peace River (t) 27 34 37 74 30 0.33 25 324 Exponential
Bone Valley Mbr. (s) 26 35 23 46 40 2.61 10 33 Exponential
Bone Valley Mbr. (t) 7 7 10 20 20 0.26 3 38 Spherical
Arcadia Fm. (s) 29 35 25 50 30 0.7 11 466 Exponential
Arcadia Fm. (t) 67 65 61 122 75 -0.27 19 341 Exponential
Tampa Member (s) 50 39 44 88 50 0.6 11 235 Exponential
Tampa Member (t) 40 40 39 78 50 0.13 30 190 Exponential
Nocatee Member (s) 64 455 110 75 1.11 12 117 Exponential
Nocatee Member (t) 3 3 37 74 50 -0.24 21 105 Exponential
Suwannee Limestone (s) 75 51 68 136 75 0.98 18 414 Exponential
Suwannee Limestone (t) 43 47 37 74 50 0.1 12 265 Exponential
Ocala Limestone (s) 67 47 63 126 75 0.97 14 527 Spherical
Ocala Limestone (t) 34 49 30 60 50 -0.15 10 325 Exponential
Avon Park Fm. (s) 84 53 79 158 100 0.77 13 391 Circular
SAS (t) 25 29 25 50 25 0.41 18 703 Exponential
IA.S/ICU I (s 4 'A 91 4A r5, -1 27 1 4ARR Fvxnnnntial

IAS/ICU (t)
FAS (s)
MFCU (s)

54 108 75 0.02 18 334 Spherical
64 128 75 0.87 16 655 Exponential
167 334 150 0.83 12 101 Spherical

3 krige statistics based on rectangular fit around distribution of wells
4 krige statistics based on irregular extent of mapped unit, which more accurately represents error within the study area
5 total number of wells used to produce each map, including wells (not shown on plates) within the outer 10 mile buffer zone

.'

"`""""""'

FLORIDA GEOLOGICAL SURVEY

Contour Interval Selection

Contour intervals for each map were selected
based on the mean of the ASE for each
respective krige model trimmed to the map unit
extents (Table 3 Footnote 2). If one assumes
normality, the ASE of the prediction error is
essentially the standard deviation (s) of the
interpolated surface and represents a 68 percent
level of significance. If one were to double the
error (i.e., 2s), a 95 percent level of significance
is achieved. To avoid inflating implied accuracy
of the krige surfaces, the contour interval for all
but two maps was selected between Is and 2s.
In other words, the selected contour interval is
always greater than or equal to the mean of the
ASE prediction error, except for the IAS/ICU
thickness map and the MFCU surface map. Per
Table 3, the error for these maps is over-
predicted. For every contour map in this study,
the standard deviation for the "Grid to Point"
calculation described above (Table 3) is less
than the contour interval.

STRATIGRAPHY

The stratigraphic framework of the west-
central Florida peninsula, encompassing the
SWFWMD region, is presented from north to
south in the following geographic subdivisions:
northern region (eastern Levy, western Marion,
Citrus, Sumter, western Lake, Hernando and
Pasco Counties), central region (including
Pinellas, Hillsborough, western Polk, Manatee
and Hardee Counties), southern region
(Sarasota, DeSoto and Charlotte Counties) and
the eastern region (e.g., the Lake Wales Ridge,
including eastern Polk and Highlands Counties).
The framework discussion is subdivided into
lithostratigraphy and hydrostratigraphy, and is
characterized through a series of cross sections
and maps (surfaces and thicknesses). East-west
trending cross sections presented in this report
(see Plate 1 for locations) are ordered from the
north to south (i.e., the northern to southern
regions; Plates 4-19), then north to south within
the eastern region (Plates 20-28). Cross sections
trending north-south are ordered from west to
east as follows: Plates 29 and 30 in the northern
region, Plates 31-35 in the central/eastern
regions and Plates 36 and 37 in the southern

region. Maps of lithostratigraphic units are
presented from oldest to youngest (Plates 38 -
54) and hydrostratigraphic units are presented
from shallow to deep (Plates 55 59).

Lithostratigraphy

Introduction

Structure contour (surface) and isopach maps
(thickness) in this report include Lower Eocene
through Lower Pliocene lithostratigraphic units,
which are described in detail in this section.
Characterization of the mapped units includes
age, lithology, mineralogy, porosity, significant
fossils, distribution, nature of vertical and lateral
contacts, distinguishing gamma-ray activity
responses, relation to hydrostratigraphic units
and environment of deposition. Superjacent and
subjacent lithostratigraphic units (i.e., the
Oldsmar Formation) are also presented.

Eocene Series

Oldsmar Formation

The Lower Eocene Oldsmar Formation
("Oldsmar Limestone" of Applin and Applin,
1944) underlies the entire Florida peninsula.
Miller (1986) describes the Oldsmar Formation
as a white to gray limestone with variably thick
interbeds of gray to light brown, crystalline
dolostone that increases in abundance with
depth. Thin beds of chert and evaporites,
including pore-filling gypsum occur within the
unit (Miller, 1986). Reese and Richardson
(2008) report a glauconite marker horizon that
occurs intermittently within upper -200 ft (- 61
m) of the Oldsmar Formation in the study area.
Porosity types include intergranular,
intragranular and fracture (e.g., "Boulder
Zone"). Braunstein et al. (1988) indicate that
the unit may have an unconformable contact
with the subjacent Cedar Keys Formation;
however, the contact with the overlying Avon
Park Formation is possibly conformable.

In the study area, the Oldsmar Formation
limestones vary from packstone to wackestone.

BULLETIN NO. 68

Dolostone is common as well. The microfossil
Helicostegina gyralis (Figure 11) is common but
not unique to the unit (Miller, 1986). In the
southeastern Florida peninsula, this microfossil
is common within a glauconitic bed that serves
as an excellent geophysical marker (Duncan et
al., 1994). Within the study area, the uppermost
Oldsmar Formation contains gypsum as nodules,
laminations and as pore-filling material. Stewart
(1966) reports "selenite impregnation" in the
unit and proposes that the gypsum is altered
from anhydrite. In some areas, these
gypsiferous, low-permeability carbonates
comprise the upper part of the MFCU, whereas
deeper in the section, the carbonates comprise
the upper part of the LFA. Cander (1994)
suggests that the Oldsmar Formation represents
a shallow subtidal to supratidal carbonate paleo-
environment.

Avon Park Formation

The Middle Eocene Avon Park Formation
(Miller, 1986) occurs in the subsurface
throughout the study area and is the oldest
lithostratigraphic unit exposed in Florida (Scott
et al., 2001). This unit was originally described
by Applin and Applin (1944) as two units, the
Lake City Limestone and the Avon Park
Limestone. Due to the inability (except locally)
to distinguish these two formations based on
lithology or fauna, Miller (1986) proposed that
the term Lake City Limestone be abandoned and
formalized the Avon Park Formation to include
the two units of Applin and Applin (1944).

Lithology of the Avon Park Formation varies
between limestone and dolostone. The
limestone is generally cream to light brown,
poorly to well indurated, variably fossiliferous,
skeletal/peloidal wackestone to grainstone with
minor mudstone. The limestone can be
interbedded with dark brown to tan very-fine to
coarse-grained, vuggy, fossiliferous dolostones.
Incomplete to complete dolomitization of
limestone is also observed. Dolostone textures
range from very fine-grained to coarsely
recrystalized (sucrosic). Minor clay beds and
organic-rich laminations may occur, especially
at or near the top of the unit. Although not
common, sedimentary structures include cross-

beds and burrows. The burrows (Callianassa
sp.) generally occur in the uppermost thinly
bedded updip part of the formation (e.g., crops
out in Levy County). Accessory minerals
include chert, pyrite, celestine, gypsum and
quartz (some as doubly-terminated euhedral
crystals "floating" in vugs). Gypsum tends to be
more abundant with depth. Reese and
Richardson (2008) report a glauconite marker
horizon that occurs intermittently within lower
-200 ft (- 61 m) of the Avon Park Formation.

Porosity in the Avon Park Formation is
generally intergranular in the limestone section.
Fracture porosity occurs in the more densely
recrystallized dolostone and intercrystalline
porosity is characteristic of sucrosic textures.
Pinpoint vugs and fossil molds are present to a
lesser extent. Total porosity measured for 16
Avon Park Formation samples averages 31.7
percent (median = 30.0 percent) and ranges from
22.3 percent to 42.0 percent.

Diagnostic fossils include the foraminifera
Cushmania americana (Dictyoconus
americanus) and Fallotella (Coskinolina)
floridana and the echinoid Neolaganum
(Peronella) dalli (Figure 12). The foraminfer
Fallotella (Dictyoconus) cookei occurs in the
Avon Park Formation as well as the Suwannee
Limestone; however, presence of Cushmania
americana is unique to the Avon Park
Formation. Other fossils include algae,
mollusks and carbonized plant remains (e.g.,
Thalassodendron sp.) (Scott, 2001).

Miller (1986) reports the top of Lower
Eocene rocks (the approximate base of Avon
Park Formation) at depths ranging from -1,000 ft
to -2,400 ft (-304.8 to -731.5 m) MSL within the
study area. The Avon Park Formation varies in
thickness across the study area, from 1,000 ft to
1,600 ft (304.8 to 487.7 m), with the thickest
area occurring along northeastern Polk County
(Miller, 1986). Maximum observed elevations
exceed 50 ft (15.2 m) MSL in northern Polk
County (Plate 20). In the southernmost extent of
the study area, the unit is encountered at depths
exceeding -1500 ft (-457.2 m) MSL (Plate 38).
The area, which is centered along eastern
Charlotte Harbor, may be related to structural
deformation (Winston, 1996).

FLORIDA GEOLOGICAL SURVEY

Figure 11. Helicostegina gyralis, a foraminifer common within the Oldsmar Formation (bar = 1 mm).

The contact relations between the Oldsmar
and Avon Park Formations are generally subtle
and difficult to identify within the study area,
which supports the interpretation that the contact
is possibly conformable (Braunstein et al.,
1988). In general, the contact grades from a
dolostone to a chalky white limestone. In many
cases, however, these characteristics are not
present. A useful faunal indicator of the
transition into the Oldsmar Formation is the
appearance of abundant Helicostegina gyralis
(Figure 12; Miller, 1986). Although this
foraminifer does not exclusively occur in the
Oldsmar Formation, it generally appears in
lowermost Avon Park Formation and increases
in abundance in the Oldsmar Formation
carbonates.

The Ocala Limestone unconformably
overlies the Avon Park Formation throughout
nearly the entire study area; exceptions include
parts of Levy and Citrus Counties (Avon Park
Formation exposures) or where the Ocala
Limestone is absent in the subsurface
(northwestern Osceola County). The contact
between these two units is readily apparent in
many up-dip locations and difficult to determine
down dip. The more obvious contact relations
occur where: 1) lithology of the Avon Park
Formation is tan to brown dolostone, overlain by
white to cream limestone of the Ocala
Limestone (e.g., W-16456 [ROMP 49], Plates

14 and 33; W-9059, Plates 23 and 34) and 2) in
the case where both units are limestone, the
uppermost Avon Park Formation is grain-
supported and contains disseminated organic or
thin (less than 2 inches; 5 cm) beds of peat (in
some cases varying toward lignite), whereas the
lowermost Ocala Limestone is finer grained and
skeletal (e.g., W-720, Plates 6 and 29; W-12943
Plates 12 and 21). Although the Avon Park
Formation is not defined based on bio-
assemblages, additional contact indicators
include the appearance of diagnostic
foraminifera and echinoids listed above, as well
as abundance of coralline algae.

Throughout most of the southwestern part of
the study area, including nearly all of Manatee
and Sarasota Counties, the contact between the
Avon Park Formation and the Ocala Limestone
is dolomitized (e.g., Plate 18) and as a result,
formation boundary delineation is difficult. In
this situation, subtle characteristics can be used
to delineate the two units. Dolomitization of the
limestones with slightly varying textures may
yield differences in dolostone textures and
dolomite grain sizes. Fossil molds are another
useful indicator, because fossil molds of
diagnostic fossils may help narrow the
uncertainty. For example, narrow, discoid vugs
may represent prior Lepidocyclina sp. whereas
smaller cone-shaped vugs may represent where
Cushmania or Fallotella sp. were present prior

BULLETIN NO. 68

Figure 12. Selected diagnostic fossils common within the Avon Park Formation. From left to right:
Cushmania americana (Dictyoconus americanus) (bar = 0.5 mm; Rupert, 1989), Fallotella
(Coskinolina) floridana (bar = 1 mm; photo courtesy of Jonathan Bryan) and Neolaganum
(Peronella) dalli (bar = 15 mm; photo courtesy of Invertebrate Paleontology, Florida Museum of
Natural History [IP/FMNH]).

to dolomitization/leaching (e.g., Plate 27; W-
17056 [ROMP 9]). In rare instances, selective
dolomitization occurs where the original
limestone matrix is dolomitized, however, the
faunal assemblage foraminiferaa and echinoids)
remain as calcite.

Gamma-ray response in the Avon Park
Formation is generally due to variable dolomite
and organic content. In many wells, high
gamma-ray activity at or near the top of the
Avon Park Formation corresponds to thin layers
of organic material (e.g., Plate 16; W-16303
[ROMP TR 7-4]; Figure 10). Similar
observations have been made east of the study
area (Davis et al., 2001). In cases where the top
of the Avon Park Formation has been
dolomitized or recrystallized, this organic-
associated gamma-ray peak tends to be a
broadened, more subdued signal. The degree to
which the signal remains is likely a function of
the extent of recrystallization and amount of
organic impurities remaining in the carbonate.
Relative to the overlying Ocala Limestone, the
Avon Park Formation gamma-ray signature has
higher background count rates and is more
variable throughout the unit. In general, a
relatively higher gamma-ray peak is observed at
the top of the Avon Park Formation throughout
the study area, except for the west-central

region, including northern Hillsborough and
Pinellas Counties as well as eastern Polk and
northern Manatee Counties. Several gamma-ray
logs from wells in the study area also exhibit a
peak at depths greater than 350 ft (106.7 m)
below the top of the unit. Preliminary analysis
attributes this peak to organic content.

All major parts of the FAS (the UFA, MFCU
and LFA) can include the Avon Park Formation.
The "Avon Park permeable zone" (Reese and
Richardson, 2008) generally occurs 200 to 400 ft
(60.9 m to 121.9 m) beneath the top of the Avon
Park Formation in the study area, and is
analogous to the "Avon Park highly permeable
zone" reported by Hutchinson (1992) for
southwestern Florida. Reese and Richardson
(2008) map this permeable zone throughout
most of the southern half of peninsular Florida,
describing it as a thick dolostone unit with
interbedded limestone and dominated by fracture
porosity that may occur in either the UFA or the
LFA.

With increasing depth in the Avon Park
Formation, interbedded and intergranular
evaporites (gypsum/selenite and anhydrite)
reduce formation porosity and permeability
throughout much of the region. Water-quality
data, (Sacks and Tihansky, 1996; Jack Hickey,

FLORIDA GEOLOGICAL SURVEY

personal communication, 2004), geophysical
and lithologic evidence indicate that most of the
MFCU surface (Plate 59) correlates with the
middle to lower carbonates of the Avon Park
Formation. In parts of Marion, Osceola and
Pinellas Counties, however, the MFCU occurs in
the upper third of the unit. In the southern
region, a shallower discontinuous MFCU unit
occurs within the middle to upper part of the
formation (Plate 59). The relation between the
Avon Park Formation and the MFCU in east-
central part of the study area (i.e., the vicinity of
southeastern Polk County; Plate 59) requires
further data and research.

The Avon Park Formation was deposited
within a broad, distally steepened carbonate
platform (Budd, 2002). The deposition is
characterized by peritidal carbonate sediments
that may be significantly dolomitized. Highly
cyclical deposits in supratidal to shallow
subtidal environments are represented in the
vertical sediment sequence (Randazzo et al.,
1990; Budd, 2002). The sediments reflect
repeated short-term changes in relative sea level
throughout Middle Eocene deposition
documenting transgressive, regressive and open
marine to shoreline cycles (Randazzo et al.,
1990). Some researchers propose that
dolomitization within the Avon Park Formation
took place during or proximal in time to
deposition (e.g., Randazzo and Hickey, 1978;
Cander, 1994). Miller (1986) suggests that thin
evaporite beds deposited during the Middle
Eocene may have been formed in a tidal flat or
sabkha environment.

Ocala Limestone

The Upper Eocene Ocala Limestone was first
named by Dall and Harris (1892). Puri (1953)
later proposed three separate formations: the
Inglis, Williston and Crystal River Formations,
which were based upon distinct faunal
assemblages. In 1953, Puri elevated the
sequence to Group status. Miller (1986) noted
that these formations were neither easily
recognizable nor mappable and therefore applied
the name Ocala Limestone; however, he
acknowledged that a two-fold division (upper

and lower Ocala Limestone) proposed by Applin
and Applin (1944) was still in use. Recognizing
the biostratigraphic basis of the division on
which the Ocala Group was based, Scott (1991)
identified the Ocala Limestone as a formation in
accordance with the North American
Stratigraphic Code. Despite this rather complex
history in nomenclature leading to recognition of
the unit as a single formation, upper and lower
Ocala Limestone lithologies are generally
recognized.

The lower Ocala Limestone varies from
white to light gray and is variably indurated,
ranging from a packstone to a grainstone.
Where present, dolomite content increases with
depth in the Ocala Limestone, especially in the
southwestern part of the study area where the
base of the unit is often dolomitized (see Avon
Park Formation, p. 31, for more details).
Gaswirth (2004) also noted this pattern and
documented textural end-members within these
dolostones: 1) friable, light to medium brown,
sucrosic and 2) indurated, dark gray to dark
brown, dense, crystalline. The upper part of the
Ocala Limestone varies from white to light
orange and tends to be more mud-supported
(i.e., mudstone to wackestone) and chalky.

Mineralogy of the Ocala Limestone unit is
predominantly calcite, and to a lesser extent,
dolomite. Siliciclastics are rare; however, chert
occurs throughout the formation and is generally
more common where the unit occurs at or near
land surface. Trace amounts of organic and
clay (Green et al., 1995) likely represent post-
depositional infilling. Pyrite is also present as a
trace mineral, but to a lesser extent than the
overlying Suwannee Limestone or underlying
Avon Park Formation. Sedimentary structures
in the Ocala Limestone include cross bedding,
fine laminations and bioturbation. The latter is
dominant at the base of the unit in the form of
burrows (Loizeaux, 1995). The Ocala
Limestone has a diverse fossil assemblage
(Figure 13), including Lepidocyclina sp.,
Nummulites (Operculinoides) sp., milliolids,
bryozoans, gastropods, mollusks, pelecypods,
echinoids (e.g., Eupatagus antillarum) and
Rotularia (Spirolina) vernoni.

BULLETIN NO. 68

Figure 13. Selected diagnostic fossils within the Ocala Limestone. Top photo: Eupatagus
antillarum (bar = 2.5 cm; photo courtesy of IP/FMNH). Middle row, left: Nummulites
(Operculinoides) sp. (bar = 1mm; photo courtesy of Jonathan Bryan), right: Rotularia (Spirolina)
vernoni (bar = 1 cm, photo courtesy of IP/FMNH). Bottom: Lepidocyclina ocalana, (bar = 3 mm);
(A) from Cushman (1920), (B) from Rupert (1989).

FLORIDA GEOLOGICAL SURVEY

Grainstones of the Ocala Limestone comprise
the most permeable zones in the UFA. Porosity
within the unit is generally moldic and
intergranular with occasional macrofossil molds.
Secondary porosity owing to carbonate
dissolution is extensive and has greatly
enhanced permeability, especially where
confining beds are breached or absent (Berndt et
al., 1998). Based on analyses of 70 samples,
total porosity of the Ocala Limestone averages
39.8 percent (median = 41.0 percent) and ranges
from 17.6 percent to 53.5 percent. Of the end-
member dolostone lithologies reported by
Gaswirth (2004), porosity of the induratedd"
type averages 24 percent (n=30) and the
"sucrosic" type averages 35 percent (n=28),
(Gaswirth et al., 2006).

The Ocala Limestone occurs throughout the
study area except where locally removed by
erosion on the Ocala Platform in the
southeastern part of Levy County and
southwestern part of Marion County. In
southwestern Orange County and northwestern
Osceola County, the Ocala Limestone is also
absent possibly due to structural offset and
erosion. Miller (1986) proposes a graben-like
fault system striking along the Polk-Osceola
County boundary; however, data presented
herein does not confirm its presence. An area of
"locally absent" Ocala Limestone (Plate 39)
does, however, approximately coincide with
Miller's (1986) fault-bound area. The top of the
Ocala Limestone occurs at or near land surface
in the northern region (Figure 2) and deepens to
approximately -1275 ft (-388.6 m) MSL in the
southern region (Plate 39). The thickness of the
unit exceeds 400 ft (121.9 m) in Charlotte and
Highlands Counties (Plate 40). This
lithostratigraphic unit is generally thought to be
bound by unconformities (Braunstein et al.,
1988; Loizeaux, 1995).

Two proposed structural features are
significant with regard to the Ocala Limestone.
A fault striking northwest in northwestern Polk
County is proposed by Carr and Alverson
(1959). Vernon (1951) and Stewart (1966)
present contour maps of the "Inglis" (i.e., basal
Ocala Limestone) suggesting local offset in the
same area with the shallower "Inglis" sediments
toward the northeast. This offset is consistent

with Carr and Alverson's (1959) proposed fault.
Although local thickness variations of the Ocala
Limestone in this area are generally consistent
with the proposed fault, the present study does
not have sufficient well control to confirm the
hypothesis. A fault proposed by Winston (1996)
that trends northwest across Charlotte Harbor
may be related to the deepening and thickening
of the Ocala Limestone in this area.

Contact relationships between the Ocala
Limestone and Avon Park Formation are
discussed under Avon Park Formation, p. 31. In
the northern and central regions, the boundary
between the Ocala Limestone and the overlying
Suwannee Limestone is usually not difficult to
distinguish. Not only is the gamma-ray
character different (Figure 10), but the
uppermost Ocala Limestone is generally
"cleaner" (i.e., significantly less non-calcitic
material) finer-grained and more skeletal than
the overlying unit. In some cases, Ocala
Limestone lithoclasts are found at the base of the
Suwannee Limestone (Loizeaux, 1995).
Moreover, the fossil assemblage differs
significantly, with the disappearance of
Lepidocyclina ocalana and the appearance of
Fallotella sp. (Suwannee Limestone) shallower
in the section. There are, however, areas where
the two units are difficult to distinguish. The
transition from Ocala Limestone to Suwannee
Limestone can be gradational toward the south,
showing some evidence of interbedding and thus
a possible conformable contact. Moreover,
some areas contain basal Suwannee carbonates
that range from fine-grained grainstones to
mudstones, which can be difficult to distinguish
from the underlying, sometimes altered, chalky
mudstones and wackestones of the upper Ocala
Limestone. Torres et al. (2001) and Brewster-
Wingard et al. (1997) have also noted that the
boundary is often difficult to pinpoint and
suggest that foraminifera are often useful to
distinguish the units.

Gamma-ray logs for the Ocala Limestone
consistently exhibit very low gamma-ray activity
(low, background-level count rates) and
relatively fewer peaks than the overlying and
underlying formations (Figure 10). In cases
where the Ocala Limestone is dolomitized, the

BULLETIN NO. 68

gamma-ray logs may exhibit a slightly higher
and more sporadic signature (Arthur et al.,
2001a). Many peaks in the gamma-ray logs for
this unit correlate with the presence of trace
organic or pyrite (e.g., W-12640 [ROMP 59];
Plate 21 and 32).

In peninsular Florida, Ocala Limestone
deposition is interpreted to have occurred on a
homoclinal distally steepened carbonate ramp in
shallow (probably less than 10 m [32.8 ft])
subtidal to intertidal, somewhat high-energy,
open marine environment (Randazzo et al.,
1990; Cander, 1994; and Loizeaux, 1995). The
Ocala Limestone represents a more constant and
stable depositional environment than the
underlying Avon Park Formation (Randazzo et
al., 1990). Specifically, deposition of the Ocala
Limestone occurred during a long-term eustatic
high stand representing an overall transgressive
sequence of sedimentation with shoreline
progradation (Randazzo et al., 1990; Loizeaux,
1995). The lower Ocala Limestone represents a
deepening upward sequence with the sediments
becoming muddier through time and then
shoaling in the uppermost Ocala (Randazzo et
al., 1990). This appears to coincide with the
post-middle Eocene marine transgressions
followed by a fall in eustatic sea level at the end
of late Eocene (Loizeaux, 1995).

Oligocene Series

Suwannee Limestone

The Lower Oligocene Suwannee Limestone
was first identified by Cooke and Mansfield
(1936). This formation ranges from light-gray
to white, variably moldic packstones and
grainstones. Carbonate grains are generally
miliolids and peloids. Small amounts of sand (<
3 percent) and clay generally occur within the
uppermost part of the unit when overlain by
Hawthorn Group sediments. South of the study
area, however, Missimer (2002) reports local
sand beds in the Suwannee Limestone. Trace
amounts of pyrite and organic (finely
disseminated and as laminations) also occur
throughout this formation (Arthur et al., 2001b;
Price, 2003). The Suwannee Limestone is also
variably dolomitized. For example, Green et al.,

(1995) noted a relatively consistent dolostone or
dolomitic limestone bed (10-20 ft thick [-3-6
m]) occurring within the lower third of the unit
in the central part of the study area. Chert is
present throughout the unit, especially within the
updip part of the unit. In Hernando County, for
example, partial silicification of the limestone is
observed, leaving echinoids in their original
calcite form. Sedimentary structures include
cross bedding and bioturbation (Budd, 2002).
Porosity types include moldic and intergranular.
Measured total porosity, based on analysis of 29
samples, averages 36.3 percent (median = 37.1
percent) and ranges from 2.3 percent to 55.8
percent. Fossils within the Suwannee
Limestone include mollusks, gastropods,
echinoids (most commonly the index fossil
Rhyncholampus gouldii), abundant miliolids and
other benthic foraminifera including Fallotella
(Dictyoconus) cookei, Discorinopsis gunteri
(Figure 14) and Fallotella (Coskinolina)
floridana (Figure 12).

For the most part, the Suwannee Limestone
unconformably overlies the Ocala Limestone
and is unconformably overlain by Hawthorn
Group sediments; however, there exists some
question regarding the lateral extent of both
unconformities. The contact between the
subjacent Ocala Limestone and the Suwannee
Limestone can be locally gradational, showing
some evidence of interbedding. In some areas,
the lower Suwannee Limestone increases in
carbonate mud content, which can be difficult to
distinguish from the sometimes chemically
weathered, chalky upper Ocala Limestone.
Torres et al. (2001) and Brewster-Wingard et al.
(1997) have also noted that the boundary is often
difficult to pinpoint. These researchers, as well
as the authors of this report, suggest that
foraminifera are often useful to distinguish the
units.

The upper contact of the Suwannee
Limestone is locally gradational with the
overlying Tampa Member (Arcadia Formation)
in northeastern Hillsborough and Pinellas
Counties. Researchers faced with the difficulty
of making formation picks in this area have
come to informally refer to this transitional zone
as "SuwTampaHaw" (Tom Scott, personal
communication, 2004). The Suwannee
Limestone is also locally overlain by green clays

FLORIDA GEOLOGICAL SURVEY

Figure 14. Selected diagnostic Suwannee Limestone fossils. Top row left: Fallotella (Dictyoconus)
cookei (bar = 1 mm; from Rupert, 1989), right: Rhyncholampus gouldii (bar = 2.5 cm, photo
courtesy of Sean Roberts). Bottom row left: Discorinopsis gunteri (bar = 2 mm; Cooke, 1945),
right: milliolid (bar = 1 mm; photo courtesy Jonathan Bryan).

comprising the base of the Tampa Member
(Arcadia Formation) in parts of northern and
central Pinellas County, south-central
Hillsborough County and eastern Polk County.
In other areas, lack of phosphate sand in the
Suwannee Limestone distinguishes it from
overlying phosphatic (i.e., non-Tampa Member)
Hawthorn Group sediments. South of the study
area, however, Suwannee Limestone carbonates
include minor occurrences of blackened
(possibly francolite) discontinuity surfaces
(Missimer, 2002).

The northern extent of the Suwannee
Limestone occurs in Citrus County based on
isolated outcrops and discontinuous borehole
data. The approximate northern limit of laterally
continuous Suwannee Limestone, however,
occurs in southernmost Citrus County (Plates 41

and 42). In the eastern region, the subcrop limit
occurs beneath the Lake Wales Ridge. In
Highlands County, the eastern extent of the unit
is uncertain and denoted with a dashed line
(Plates 41 and 42). Two wells east of the line
contain limited thicknesses of the Suwannee
Limestone; however, nearby wells deep enough
to have encountered the unit do not contain it.
This suggests the two wells represent outliers.
Maximum elevation of the unit exceeds 75 ft
(22.9 m) MSL in parts of Hillsborough and Polk
Counties as well as along the Brooksville Ridge,
while in the southern region, depths exceed -825
ft (-251.5 m) MSL (Plate 41). Maximum
thickness of the Suwannee Limestone in the
study area exceeds 450 ft (137.2 m) in south-
central Charlotte County (Plate 42).

Evidence supporting previously identified

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BULLETIN NO. 68

faults in the Suwannee Limestone exists to some
degree within two areas. The feature most
supported by the data presented herein is an
inferred northwest-striking fault in northwestern
Polk County (Figure 3). The Suwannee
Limestone thickness map (Plate 42) indicates an
abrupt change in thickness; wells reflecting
more than 100 ft (30.5 m) of the unit are
proximal to wells that contain no Suwannee
Limestone even though the wells are deep
enough to have encountered the unit (assuming
similar regional dip). The strike and polarity of
this particular feature, indicated as an inferred
fault on Plate 41 and 42, roughly agrees with a
fault proposed by Pride et al. (1966). Northeast
of the fault, the Suwannee Limestone is reported
to occur as exposed remnant boulders in Sumter
County (Campbell, 1989).

A second inferred fault may occur along the
updip limit of the Suwannee Limestone in
northeastern Hernando County (Figure 3).
Vernon (1951) reports a fault intersecting the
"Inglis Member" in the area, with the upthrown
side to the northeast. Data represented in Plates
41 and 42 support the location and polarity of
Vernon's (1951) fault for the Suwannee
Limestone. Thicknesses greater than 50 ft (15.2
m) terminate along the northeastern subcrop
limit of the unit (Plate 41 and 42). In the
Charlotte Harbor area, the "North Port" fault
(Winston, 1996) may have affected the
Suwannee Limestone surface and thickness,
similar to that of the Ocala Limestone and Avon
Park Formation. Other faults and lineaments are
reported in this area (Hutchinson, 1991;
Winston, 1996; Michael Fies, personal
communication, 2007) suggesting a complex
geologic setting.

The Suwannee Limestone is characterized by
a gamma-ray log response (i.e., activity) that is
generally more variable within the lower half of
the unit (e.g., Plate 11 and 12; Figure 10).
Relative to the Ocala Limestone, it has an
overall higher background rate and exhibits
much more variability. This variability is likely
due to higher amounts of dolomite, organic
material and other non-calcitic constituents in
the Suwannee Limestone relative to the Ocala
Limestone. Although the gamma-ray log is
generally useful for providing corroborative

evidence for the lithostratigraphic boundary
between the Eocene Oligocene carbonates, use
of the logs for determination of the upper
boundary of the Suwannee Limestone is not
always as straightforward. For example, where
the Tampa Member (Arcadia Formation) is in
contact with the Suwannee Limestone, gamma-
ray signatures for the two units are quite similar,
both in their background count rates and
distribution of peaks (e.g., Plate 31, W-15204
[TR14-2] and Plate 33, W-16740 [ROMP 39]).

A generally consistent pattern in the
Suwannee Limestone gamma-ray logs,
especially for wells in Gulf-coastal counties, is
the presence of a 50- to 100-ft (15.2 to 30.5 m)
thick interval of high gamma-ray activity within
the central to lower parts of the Suwannee
Limestone. This interval varies in thickness and
depth and apparently does not correlate with a
given stratigraphic horizon. Inspection of
lithologic logs suggests that this high gamma-
ray activity zone is associated with dolomite
and/or minor organic content.

The Suwannee Limestone, where present,
comprises most of the FAS surface; exceptions
being where hydraulic continuity exists between
the Tampa Member (Arcadia Formation) and
Suwannee Limestone in Pasco, Pinellas, most of
Hillsborough and northern Manatee Counties
(Figure 8). Along the updip limit of the Tampa
Member in Pasco County, the top of the FAS
includes the Tampa Member (where present)
and the Suwannee Limestone (Figure 8).
Grainstones within the Suwannee Limestone are
among the most permeable zones in the UFA.

Suwannee Limestone deposition occurred in
shallow open marine to peritidal environments
on the Florida Platform (Cander, 1994) until the
Late Oligocene sea-level low stand (Hammes,
1992). During deposition of the unit in the study
area, the Georgia Channel System (Huddlestun,
1993) acted as a barrier to a southward influx of
plastic sediments from the Appalachian
Mountains. Deposition of the predominantly
skeletal lithologies was cyclic and controlled by
the pre-existing topography as well as
fluctuating sea level. Restricted marine facies
and skeletal shoal facies developed on previous
highs and deeper subtidal facies occurred in the
lows. Hammes (1992) describes the Suwannee

FLORIDA GEOLOGICAL SURVEY

Limestone as three megacycles each composed
of several shallowing upward cycles: 1) the
outer ramp characterized by skeletal-rich, grain
supported to muddy, open-marine, shallow and
deep-ramp facies, 2) shallow ramp facies -
composed of wave dominated skeletal banks and
shoal complexes and shallow and deep subtidal
lagoonal deposits, and 3) restricted marine -
deposition in a restricted marine, brackish
lagoon and mud-rich tidal flat environment.

Oligocene-Pliocene Series

Hawthorn Group

Hawthorn Group sediments range in age
from mid-Oligocene (Brewster-Wingard et al.,
1997) to Early Pliocene (Scott, 1988; Covington,
1993; Missimer et al., 1994) and generally
consist of phosphatic siliciclastics (sands, silts
and clays) and carbonates. Trace amounts of
pyrite occur throughout the Hawthorn Group
section in southwestern Florida (Lazareva and
Pichler, 2007). In the study area, the Hawthorn
Group consists of the Arcadia Formation, the
Peace River Formation and undifferentiated
sediments, all of which generally lie
unconformably above the Suwannee Limestone
and unconformably beneath undifferentiated
Pliocene and younger sands, shells and clays.
Benthic foraminifera characteristic of the
Hawthorn Group include Archaias sp., Sorites
sp., Amphistegina lesson and Cassigerinella
(Cassidulina) chipolonsis (Figure 15).
Predominant formational members of the
Hawthorn Group present in the study area
include the Tampa and Nocatee Members
(Arcadia Formation) and the Bone Valley
Member (Peace River Formation). The extent of
all Hawthorn Group sediments (Plate 43)
generally includes those areas where
undifferentiated confining beds of the IAS/ICU
(Plate 56) are present beyond the mapped extent
of the Arcadia and Peace River Formations
(Plates 45 and 51, respectively) such as Marion
County, Pinellas County and central Pasco
County. The maximum observed thickness of
the Hawthorn Group exceeds 825 ft (251.5 m) in
south-central Charlotte County (Plate 44).

The Hawthorn Group was deposited in a
shallow marine to nonmarine fluvial and deltaic
environment that prograded over the older

carbonate platform (Scott, 1988; Ward et al.,
2003). Similar to other units mapped in this
study, the top of the Hawthorn Group can
demonstrate variable local relief, as exhibited by
its irregular erosional and karstic surface (Berndt
et al., 1998). Based on mineralogy of Hawthorn
Group sediments, incipient stages of
phosphogenesis occurred during the Late
Oligocene during deposition of the lower
Arcadia Formation (Brewster-Wingard et al.,
1997). Sea-level fluctuations strongly
influenced deposition and exerted a major
control on phosphogenesis and sedimentation
(Riggs, 1979a, 1984; Compton et al, 1993).
During sea-level transgressions a large part of
the Florida platform was submerged.
Meandering of the Gulf Stream resulted in
upwelling over the platform, which increased
organic productivity and enhanced
phosphogenesis in the shallow waters of the
shelf (Compton et al, 1993). Maximum
phosphorite precipitation is thought to have
occurred in shallow-water coastal and nearshore
shelf platforms or other submarine topographic
highs (Riggs, 1979a). Sea-level fluctuations and
ocean currents facilitated transport, deposition
and concentration of phosphate grains (Scott,
1988, 1992b). Primary depositional features
such as graded bedding and cross beds provide
evidence of this high-energy depositional
environment (Scott, 1988). The height of
phosphate deposition and reworking was
synchronous with Peace River Formation
deposition (Middle to Early Pliocene).

Arcadia Formation

The Upper Oligocene (Brewster-Wingard et
al., 1997) to Middle Miocene Arcadia Formation
is comprised of a yellowish gray to white,
variably sandy (quartz and phosphorite)
carbonate with interbeds of siliciclastic-
dominant sediments. Although limestone is
present, dolostones are most common, ranging
in grain size from microcrystalline to medium
sand, with the more coarse material being
sucrosic. Minor clays and chert beds (some
comprised of silicified clay) also occur
(Upchurch et al., 1982; Scott, 1988). Porosity
types include intergranular and moldic.

BULLETIN NO. 68

Figure 15. Diagnostic foraminifera in Hawthorn
right bar = 1 mm; bottom row, bar = 0.5 mm.

Measured total porosity of 25 Arcadia
Formation samples averages 34.1 percent, with a
median value of 32.4 percent and a range from
12.4 percent to 54.5 percent.

The updip limit of the unit occurs in northern
Pasco and Polk Counties where maximum
elevations exceed 90 ft (27.4 m) MSL (Plate 34
and 45). The top of the Arcadia Formation
occurs at depths exceeding -270 ft (-82.3 m)
MSL beneath the Lake Wales Ridge in the
southeastern part of the study area. The unit
ranges in thickness to greater than 750 ft (229
m) in south-central Charlotte County (Plate 46).
Sporadically throughout much of the central and
southern regions, the Arcadia Formation

Group units. Upper left bar = 0.1 mm; upper

(undifferentiated) is observed below the Tampa
and Nocatee Members. In several wells, the
contacts between the Tampa and Nocatee
Members and the underlying Arcadia Formation
(undifferentiated) are gradational. The Arcadia
Formation is unconformably overlain by the
Peace River Formation (where present);
however, apparent gradational contacts between
these two units are locally observed.

In general, the Arcadia Formation comprises
the most permeable parts of the IAS/ICU in the
study area (see IAS/ICU, p. 57, for more details).
In addition, the uppermost part of the FAS is
comprised of the Tampa Member where it is in
hydraulic connection with the subjacent

FLORIDA GEOLOGICAL SURVEY

Suwannee Limestone (Figure 8).

Gamma-ray activity in the Arcadia
Formation is distinctive, with strong gamma-ray
peaks characterizing the upper undifferentiated
part of the unit (e.g., W-16784 [ROMP 33],
Plates 16 and 37; Figure 10). Lithostratigraphic
members within and below the formation are
characterized by significantly weaker gamma-
ray responses. For example, where the
undifferentiated Arcadia Formation overlies the
Suwannee Limestone, the gamma-ray response
for the older unit is often contrastingly low in
gamma-ray activity (e.g., W-15683 [TR 3-3],
Plate 19 and W-15333 [TR 2-1], Plates 19, 28
and 37). Although the high gamma-ray activity
sequence in the Arcadia Formation is distinctive,
it is not always useful as a diagnostic tool for
identifying the upper formational boundary.
Phosphate lag deposits locally comprising the
base of the Peace River Formation have gamma-
ray peaks as high as that of the Arcadia
Formation.

Deposition of the Arcadia Formation is
somewhat unique owing to its composition of
mixed carbonate and siliciclastic sediments. In
most depositional environments, an influx of
siliciclastic sediments usually inhibits the
production of carbonates. During the Oligocene,
siliciclastics began to deposit along the Florida
Platform (Hammes, 1992; Missimer, 2002).
This influx of siliciclastics, during low sea-level
stands, began to slowly bypass the Georgia
Channel System (Huddlestun, 1993) as it filled.
By Late Oligocene the lower part of the Arcadia
Formation was being deposited and a more
continuous influx of quartz sand was occurring
(Missimer and Ginsburg, 1998). These
siliciclastics were transported south several
hundred kilometers to the southern part of the
Florida carbonate platform by longshore currents
(Scott, 1988; Missimer and Ginsburg, 1998).
The rate of siliciclastic transport was initially
episodic and sufficiently low to minimize
interruption of the production of carbonates.
Differences in shoreline positions caused by
fluctuating sea levels allowed siliciclastics to
mix over a broad area. Mixing of the carbonates
and siliciclastics was achieved by tidal transport,
storms, longshore currents, bioturbation and
aeolian processes (Scott, 1988; Missimer and

Ginsburg, 1998; Missimer, 2002). Missimer and
Ginsburg (1998) list three important factors that
allowed the homogenized, co-deposition of
Arcadia Formation carbonates and siliciclastics
to occur: 1) a relatively slow rate of siliciclastic
sediment influx, 2) the lack of mud or clay, and
3) marine transport without river or stream
transport. Freshwater input would have caused
an increase in finer-grained siliciclastics (e.g.,
silts and clays), increased turbidity and
decreased salinity, all of which would have
diminished carbonate production.

Noteworthy topographic features occur along
the surface of the Arcadia Formation. In the
Tampa Bay area, interpreted seismic data
indicate subsurface relief of up to -197 ft (60 m;
Hine et al., in press). These features are
attributed to "spatially restricted, semi-enclosed,
siliciclastic-filled karst" that may coalesce into
larger collapse systems (Hine et al., in press). A
karst basin identified in their study due south of
the Pinellas County peninsula in Tampa Bay
correlates well with a trough extending
northward into the peninsula (Plate 45; see also
Tampa Member surface map, Plate 49).

Along the southern part of the Lake Wales
Ridge, the Arcadia Formation deepens sharply
(Plate 45). This elongate depression (or trough)
also occurs in the overlying Peace River
Formation (Plate 51). Although topographic
relief of the troughs are similar (-175 to -200 ft;
-53 to -61 m), the Arcadia Formation exhibits
little evidence of thinning, unlike the Peace
River Formation (Plate 52). Periods of erosion
(scouring?) or non-deposition owing to sea-level
fluctuations and paleo-ocean currents are likely
factors contributing to the origin of this trough.
Miocene-Pliocene structural control of the
feature is not indicated by the thickness of either
formation. The thickness of post-Hawthorn
Group sediments (see Plate 55 for
approximation) suggests that the trough may
have become a depoaxis for Pliocene-
Pleistocene siliciclastics.

A third significant topographic feature occurs
in south-central Charlotte County, where the
surface of the Arcadia Formation deepens to
more than 200 ft (60.9 m) MSL and notably
thickens to more than 700 ft (213 m; Plates 45

BULLETIN NO. 68

and 46). Locations of depocenters within
subjacent lithostratigraphic units occur in
roughly the same locale: the Ocala Limestone,
Suwannee Limestone and Hawthorn Group
deepen in this area (Plates 39, 41 and 43,
respectively), and the units thicken as well
(Plates 40, 42 and 44, respectively). This basin
is also observed in the surface of the Avon Park
Formation (Plate 38); however, due to lack of
well control, Miller's (1986) Middle Eocene
maps do not reflect this feature. These
observations suggest that the area experienced
continued subsidence and infilling from Middle
Eocene through at least Late Miocene.
Alternatively, the apparent depocenters may
have structural control owing to the proximity of
the "North Port" fault (Winston, 1996).

Nocatee Member

The Upper Oligocene (Brewster-Wingard et
al., 1997) Nocatee Member of the Arcadia
Formation is an interbedded sequence of quartz
sands, clays and carbonates all containing
variable amounts of phosphate (Scott, 1988) that
generally average five percent but locally can
reach ten percent or more. The unit is
predominately siliciclastic and generally
interbedded with lower percentages of
carbonate. Original macrofossil material is not
common in this unit; however, fossil molds of
mollusks, algae and corals are observed.
Diatoms are commonly found within the clay
units. Porosity of the Nocatee Member is
generally intergranular, with highly variable
permeability. Total porosity of five core
samples from the Nocatee Member average 27.5
percent (median =24.7 percent) and range from
20.4 percent to 35.4 percent.

The subcrop extent of the Nocatee Member
includes west-central Polk County south to
Charlotte and Glades Counties and extends as
far west as central Sarasota County. The
northeastern limits of the unit are generally well
defined and comprise a stratigraphic pinchout
(e.g., Polk and Highlands Counties); however,
the southwest extent is more subjective as the
unit grades laterally into the undifferentiated
Arcadia Formation, or locally into the Tampa
Member. In an area extending south from

southwestern Polk County, the Nocatee Member
is conformably overlain by the Tampa Member
of the Arcadia Formation. Elsewhere in the
study area, the upper and lower limits of the
Nocatee Member are gradational into the
undifferentiated Arcadia Formation.

The top of the Nocatee Member ranges in
elevation from greater than 50 ft (15.2 m) MSL
in west-central Polk County to depths exceeding
-600 ft (-183 m) MSL in the southeastern part of
the study area (Plate 47). Although the Nocatee
Member ranges in thickness to more than 240 ft
(73.2 m), it averages approximately 75 ft (22.9
m) thick (Plate 48).

Gamma-ray activity within the Nocatee
Member is generally less than or equal to that of
the overlying Hawthorn Group units (i.e., Tampa
Member and Arcadia Formation; e.g., Figure 10
and Plate 26). Where the Nocatee Member is
underlain by (and generally grades into) the
undifferentiated Arcadia Formation, gamma-ray
logs are not as useful in distinguishing between
the two units. On the other hand, where the
Nocatee Member overlies the Suwannee
Limestone, the gamma-ray activity can be very
useful for distinguishing the two units.

Although most of the Nocatee Member
correlates with the IAS/ICU, this
lithostratigraphic unit is hydraulically connected
to the UFA within part of DeSoto County
(Figure 8) and thus locally comprises the
uppermost UFA in those areas.

The Nocatee Member was deposited on the
southeast edge of the carbonate bank prior to
and during deposition of the Tampa Member.
The Nocatee represents a higher energy, more
open near-shore environment and grades
westward into a very sandy facies of the
undifferentiated Arcadia Formation and
northwestward into the carbonate facies of the
Tampa Member (Scott, 1988).

Tampa Member

The Upper Oligocene to Lower Miocene
(Brewster-Wingard et al., 1997) Tampa Member
of the Arcadia Formation is white to yellowish
gray in color and ranges from a wackestone to

FLORIDA GEOLOGICAL SURVEY

packstone with varying amounts of quartz sand
and clay (Scott, 1988). Minor phosphate (less
than 3 to 5 percent), dolomite and chert
(siliceous limestone, silicified corals; see also
Upchurch et al., 1982) are also observed. Fossil
molds of foraminifera, mollusks, gastropods and
algae are all common within the Tampa Member
(Scott, 1988). Pinkish gray to light olive gray
dolostones also occur with a similar accessory
mineral assemblage and fossil assemblage as the
limestones. Thin sand and clay beds can be
found sporadically within the unit (Scott, 1988).
Porosity of the Tampa Member is generally
intergranular and moldic, with measured total
porosity values (17 samples) ranging from 10.4
percent to 49.6 percent, averaging 32.3 percent
(median value =33.6 percent).

The subcrop limit of the Tampa Member
extends from Pasco County to the northernmost
part of Charlotte County and eastward into the
western half of Polk, DeSoto and Hardee
Counties (Plate 49 and 50). The top of the
Tampa Member ranges from more than 100 ft
(30.5 m) MSL in Pasco County to deeper than -
350 ft (-107 m) MSL in Sarasota County (Plate
49) and exhibits variable thickness. The
maximum observed thickness of the Tampa
Member is 292 ft (89.0 m) (Plate 17; W-14882
[TR 6-1]); however, some would propose that
the lower Tampa Member in this well is more
characteristic of the undifferentiated Arcadia
Formation.

In the northern third of its extent, the Tampa
Member overlies the Suwannee Limestone and
the contact appears to be locally conformable.
In Pinellas and northwest Hillsborough
Counties, for example, samples have been
informally referred to as "SuwTampaHaw" due
to the subtle transition between the units. In the
central and southern regions, this unit overlies
the Arcadia Formation (undifferentiated), or the
Nocatee Member of the Arcadia Formation. In
many wells, the transition between the Tampa
Member and the underlying Arcadia Formation
is gradational, with phosphorite content
increasing with depth. The Tampa Member is
conformably overlain by the Arcadia Formation
(undifferentiated) in many areas (e.g., Plate 14);
however numerous exceptions exist. In parts of

Pasco and northern Hillsborough Counties, the
unit is unconformably overlain by UDSC or
undifferentiated clay-rich Hawthorn Group
sediments. East of this area, the Tampa Member
is unconformably overlain by the Peace River
Formation. Toward the east and south, the
Tampa Member facies grades laterally into the
Arcadia Formation. In Sarasota County, the unit
appears to grade laterally into the Nocatee
Member as it becomes increasingly more sandy.
Scott (1988) also reports this lateral facies
change in northern Hardee County.

The Tampa Member generally exhibits
variable gamma-ray activity (Figure 10; Arthur
et al., 2001a) that limits the value of this log to
discern unit boundaries. For example, when
underlain by the Arcadia Formation
(undifferentiated), the Nocatee Member or the
Suwannee Limestone, it is difficult to
distinguish these units from the Tampa Member
based on gamma-ray activity. On the other
hand, where the Tampa Member is overlain by
the Arcadia Formation, the two units are usually
readily distinguishable due to higher gamma-ray
activity in the undifferentiated Arcadia
Formation.

Along the updip erosional pinchout of the
Tampa Member, where it forms an irregular
subcrop contact with the Suwannee Limestone
(Plate 49), the top of the FAS generally
coincides with the uppermost carbonate unit
occurrence (Figure 8). In the west-central part
of the study area, the Tampa Member is the
uppermost lithostratigraphic unit within the FAS
(Figure 8); however, based on lithologic and
hydrologic data from wells in south-central
Hillsborough County, the Tampa Member is
locally hydraulically separated from the
Suwannee Limestone and is therefore considered
part of the IAS/ICU (Figure 8). This latter
hydrogeologic setting occurs locally in northern
Pinellas County as well.

The depositional environment of the Tampa
Member was that of a quiet water lagoon, much
like present day Florida Bay (King, 1979). An
influx of siliciclastics nearly devoid of
phosphorite distinguishes Tampa Member
deposition from older and younger Hawthorn
Group units in the stratigraphic section.

BULLETIN NO. 68

"Venice Clay"

The Venice Clay is an informal unit
originally considered part of the lower Tamiami
Formation (Pliocene); however, microfossil data
suggest an age of Early to Middle Miocene
(Scott, 1993). Scott (1992b) suggests informal
placement of the Venice Clay in the upper half
of the Arcadia Formation based on subjacent and
suprajacent lithologies and preliminary fossil
evidence. The Venice Clay is gray-green
magnesium-rich clay, variably dolomitic with
minor amounts of quartz sand and silt. The unit
rarely contains phosphorite and becomes
increasingly silty toward its upper and lower
contacts (Campbell et al., 1993).

The subcrop extent of the Venice Clay
includes Sarasota County and adjacent parts of
Manatee, DeSoto and Charlotte Counties; the
unit may also extend offshore (Barr, 1996).
Based on data collected in the present study, the
top of the unit generally occurs between -10 ft
MSL and -100 ft MSL (-3.1 to -30.5 m). Barr
(1996) reports that thickness of the unit ranges
up to approximately 30 ft (9.1 m). Gamma-ray
activity is diagnostically very low for this unit,
(note clay beds near top of the Arcadia
Formation in W-15683 [TR 3-3]; Plate 19),
suggesting the mineral assemblage does not
include abundant potassium-rich illite-group
clays. The Venice Clay was likely deposited in
a quiet shallow water marine environment -
possibly an estuary (Tom Scott, personal
communication, 2004).

The Venice Clay acts as a confining unit in
the upper part of the IAS/ICU. Specifically,
Barr (1996) suggests that it comprises the
confining unit below "permeable zone 1."
Owing to its limited thickness and aerial extent,
as well as recent mapping by Barr (1996), the
Venice Clay is not mapped in the present study.

Peace River Formation

The Middle Miocene to Lower Pliocene
(Scott, 1988; Covington, 1993) Peace River
Formation is comprised of yellowish gray to
olive gray, interbedded sands, clays and
carbonates with the siliciclastic component

being dominant (Scott, 1988). The relative
abundance of carbonate beds generally increases
toward the south, especially near the base of the
unit. Variable amounts of phosphate sand and
gravel are interspersed throughout the unit;
however, they are most common within the
uppermost beds. The Peace River Formation
contains a diverse fossil assemblage of marine
and terrestrial fauna (e.g., shark teeth and
vertebrae, ray spines, horse teeth, dugong and
whale ribs, etc.), especially within the Bone
Valley Member (Figure 16). Porosity types in
the formation are generally intergranular, except
in the carbonate-rich zones, where moldic
porosity is also present. Only two total porosity
analyses of Peace River Formation samples have
been measured in this study. The results, 34.4
percent and 39.4 percent, should not be taken as
representative of the unit given its diverse
lithology.

Lithologic characteristics of the Peace River
Formation are generally consistent; however, the
carbonate component becomes more prevalent
from north to south as the unit thickens.
Throughout most of its extent, the Peace River
Formation does not contain shell material, with
possible exception of southeast DeSoto County,
where barnacles are present within the unit
(Green et al., 1999). These barnacle-rich
sediments may be the equivalent of "unit 11"
from Petuch (1982). Missimer (2001) reports
shell material in the Peace River Formation
south of Charlotte County. In the same region,
calcareous nannofossils occur in the unit
(Covington, 1993).

The Peace River Formation generally has an
unconformable contact with the underlying
Arcadia Formation. In an isolated area in north-
east-central Hillsborough County, the Peace
River Formation directly overlies the Tampa
Member (Plates 13 and 33). The Peace River
Formation also has an unconformable contact
with the underlying Ocala Limestone in northern
Polk County (Plates 11 and 34; W-14389
[ROMP 76]). In this area, reworked Peace River
Formation sediments may occur unconformably
above the Avon Park Formation where the Ocala

FLORIDA GEOLOGICAL SURVEY

Figure 16. Assemblage of typical Bone Valley Member fossils. Clockwise from upper left: ray
spines, shark vertebra, shark teeth, horse teeth, alligator tooth in matrix, (nickel for scale) dugong
rib, mammoth tooth and bone fragment. Background is a slab of Avon Park Formation dolostone
with Thalassodendron sp. carbonized impressions. (Photo credit: Jon Arthur, FDEP-FGS).

Limestone is locally absent (Plate 39).

Delineation of the Peace River Arcadia
Formation contact is problematic in some
localities. In many cores, the two units appear to
be conformable, with phosphate-rich
siliciclastics grading with depth to more
siliciclastic-interbedded carbonates containing
generally finer-grained and less abundant
phosphorite. Thickness of this transition zone
may exceed tens of feet. With increasing depth,
Arcadia Formation lithologies become more
dominant. In such cases, the lower contact of
the Peace River Formation is estimated based on
sedimentary structures as well as a best
approximation of where the overall lithologic
sequence becomes more carbonate dominant. In
contrast to the locally gradational contacts, other
areas provide strong evidence of an
unconformity, where a phosphatic rubble zone
occurs at the base of the Peace River Formation
(Scott, 1988).

Post-Pliocene/Miocene sediments disconformably
overlying the Peace River Formation in the
study area are comprised of fossiliferous sands,
clays and shell beds with variable amounts of
limestone and reworked phosphorite (e.g., Plate
11, W-14389 [ROMP 76] and Plate 13, W-
16576 [ROMP DV-1]). The contact of these
sediments with the Peace River Formation can
be difficult to determine because of lithologic
similarities (e.g., clays and phosphorite),
especially where the uppermost beds of the
Peace River Formation have been leached by
groundwater, giving the sediments an
appearance similar to that of some post-
Hawthorn Group lithologies. In addition, it can
be very difficult to distinguish Peace River
Formation sediments from those of reworked
Peace River sediments (e.g., post-Hawthorn
Group undifferentiated sands and clays) when
studying cores (the distinction is extremely
difficult to impossible when evaluating
cuttings).

BULLETIN NO. 68

Similar to basal Peace River Formation lag
deposits, reworked Miocene-Pliocene sediments
may also yield a phosphate lag deposit at the
base of overlying (e.g., post-Hawthorn Group)
sediments. Units superjacent to the Peace River
Formation include the Tamiami, Ft. Thompson
and Caloosahatchee Formations. In most cases,
the Peace River Formation is readily
distinguished from these overlying
sand/shell/carbonate lithofacies.

Lateral facies transitions of the Peace River
Formation are most evident along the
northwestern extent of the unit in Hillsborough
and Polk Counties (Plate 51). In this area,
sediments characteristic of the Peace River
Formation grade into clay-rich and phosphate-
poor sediments of the undifferentiated Hawthorn
Group (e.g., Plate 13).

Maximum elevations of the Peace River
Formation occur in the vicinity of the Polk
Upland and Lakeland Ridge, where the unit
exceeds 125 ft (38.1 m) MSL (Plate 51). The
maximum observed depth of the Peace River
Formation exceeds -200 ft (-60.9 m) MSL along
the Lake Wales Ridge. Thicknesses range to
over 120 ft (36.6 m) along the southeastern third
of the unit's mapped extent (Plate 52).

Gamma-ray activity in the Peace River
Formation is highly variable. In some areas, due
to the high-phosphorite content in the sediments,
strong gamma-ray peaks are readily observed in
contrast to lower gamma-ray activity of the
Arcadia Formation (e.g., W-16576 [ROMP DV-
1], Plate 33). The opposite occurs as well,
where gamma-ray activity in the Peace River
Formation is lower than that of the Arcadia
Formation (Figure 10). Where the Peace River
Formation lies above Eocene carbonates, the
difference is also pronounced, with the younger
unit exhibiting a stronger gamma-ray signal
(Plate 20). In many wells, a lack of gamma-ray
contrast between the Peace River Formation and
the Arcadia Formation is observed (W-16740
[ROMP 39], Plate 33). In wells where the base
of Peace River Formation contains a reworked
phosphate lag deposit, a characteristically strong
gamma-ray peak is observed (e.g., W-15938,

Plate 22). The unit may also be overlain by a
similar lag deposit within undifferentiated post-
Hawthorn Group sediments.

The Peace River Formation is a regional
confining to semi-confining lithostratigraphic
unit within the upper part of the IAS/ICU.
North of central Hillsborough and Polk
Counties, the Peace River Formation and
undifferentiated Hawthorn Group sediments
comprise a low-permeability confining to semi-
confining facies of the IAS/ICU. South of this
region, permeable, water-producing zones exist
within interlayered carbonate lenses (e.g., Ryder,
1985, Torres et al., 2001). In some areas, the
uppermost sediments of the Peace River
Formation are in hydraulic connection with
overlying sands due to a low-to-absent clay
content (e.g., Plate 17, W-14382 [ROMP 23]).
As a result, the Peace River Formation may
comprise the lower part of the SAS. Clay-poor
sediments occur within the uppermost Peace
River Formation in eastern Sarasota County and
western Manatee County (Tom Scott, personal
communication, 2006).

The Middle Miocene Lower Pliocene Peace
River Formation sediments characterize a
complex depositional environment strongly
influenced by sea-level fluctuations (Missimer et
al., 1994). The northern extent of the unit was
deposited in a shallow marine, deltaic to
brackish water environment while further south
open marine conditions prevailed (Scott, 1988).
Carbonate deposition in the unit was
periodically restricted by a flood of siliciclastics
from the north and a rise in sea level (Scott,
1988). Missimer (2001) suggests that the Peace
River Formation immediately south of the study
area was deposited in a variety of depositional
environments ranging from inner ramp to deltaic
to beach and can be explained by shoaling
upward or lateral accretion of sediment. Sea-
level transgressions or highstands appear to
favor phosphogenesis, while reworking of the
sediments during sea-level regressions or
lowstands concentrate the phosphorite (Compton
et al., 1993). Phosphorite concentrations are
considered economic ore deposits in the central
region and are locally mined.

FLORIDA GEOLOGICAL SURVEY

Bone Valley Member

The Middle Miocene to Lower Pliocene
(Webb and Crissinger, 1983) Bone Valley
Member of the Peace River Formation has a
limited areal extent, centered in southwestern
Polk County (Plate 53). It occurs in the Central
Florida Phosphate District which is among the
world's largest economic phosphorite deposits
(Freas and Riggs, 1968). Due to mining, most
of the Bone Valley Member sediments have
been removed. Although similar in lithology to
the Peace River Formation, the Bone Valley
Member contains greater amounts of
phosphorite (more than 30 percent by volume)
that is coarser-grained, ranging up to gravel-size
nodules. Phosphorite occurs as carbonate-
fluorapatite (francolite) nodules, peloids, fecal
pellets, intraclasts and grain coatings. Some
pebble-sized grains show evidence of reworking,
boring structures and multiple stages of
phosphatization. The non-phosphorite
component of the Bone Valley Member is
comprised of quartz sand with clay (e.g.,
palygorskite and sepiolite; Scott, 1988)
generally exceeding 20 percent by volume.
Carbonate beds are not present; however
limestone and dolostone cobbles and larger
fragments are observed (Tom Scott, personal
communication, 2005).

An extremely diverse fossil assemblage
exists within the unit (Webb and Crissinger,
1983) ranging from dugong and whale ribs,
shark teeth and turtle scutes to petrified wood
and teeth from horses and alligators (Figure 16).
Thicknesses of the Bone Valley Member exceed
40 ft (15.2 m) (Plate 54). In terms of hydrologic
function, the unit is a localized, yet efficient
confining unit within the IAS/ICU. On the other
hand, due to the significant economic value of
phosphorite deposits, the unit has been
extensively mined thereby reducing or
eliminating local confinement.

Owing to the high phosphorite content,
gamma-ray log intensities for Bone Valley
Member sediments are very high. For example,
the truncated, high-intensity gamma-ray peak at
the top of the Peace River Formation for W-

14385 (ROMP 45; Plate 22) represents Bone
Valley Member sediments.

Many questions exist regarding the genesis
of phosphate in Florida. Given the diverse fossil
assemblage, it reflects near-shore marine
conditions and is unlike other large phosphate
deposits of the world. Parts of the Bone Valley
Member were deposited in a high-energy
nearshore environment (topographic highs)
while other parts were deposited in a shallow
marine environment such as an embayment or
lagoon (Scott, 1988). The stratigraphy of the
unit is complicated by rapid facies changes and
post-depositional erosion, redeposition and
weathering (Freas and Riggs, 1968; Webb and
Crissenger, 1983).

Hawthorn Group (Undifferentiated)

Undifferentiated Hawthorn Group sediments
lie unconformably above Eocene and Oligocene
carbonates and unconformably below
undifferentiated Pliocene and younger sands and
clays along the upland geomorphic provinces
within the northern region, as well as in parts of
Pinellas, Hillsborough and Polk Counties. In
Marion, Sumter and Lake Counties, sediments
mapped as undifferentiated Hawthorn Group
may be comprised of one or more of the
following lithostratigraphic units (from oldest to
youngest): the Penney Farms Formation, the
Marks Head Formation and the Coosawhatchie
Formation (Scott, 1988). These formations are
not delineated owing to their limited extent and
stratigraphic pinch-out along the northeastern
part of the study area. Moreover, Scott (1988)
reported on the difficulty of distinguishing the
uppermost Coosawhatchie Formation from
undifferentiated Hawthorn Group sediments in
central Florida. In the north-central part of the
study area, undifferentiated Hawthorn Group
sediments occur along the Brooksville Ridge
(e.g., W-6903, Plate 5 and W-15933, Plate 9) as
well as within karst features and isolated lenses
flanking the ridge. Vernon (1951) describes
"Miocene Hawthorn formation" sediments along
the Brooksville Ridge in Citrus County as
greenish-gray montmorillonitic clays. The
distribution of these sediments, as well as the

BULLETIN NO. 68

occurrence of hard-rock phosphate in the region
lend support to the proposal by Scott (1988) that
Hawthorn Group sediments once covered the
entire Florida peninsula. Upchurch (1992) also
suggests that Hawthorn sedimentation occurred
on the crest of the Ocala Platform.

Undifferentiated Hawthorn Group sediments
are generally comprised of clay beds with
variable amounts of carbonate, quartz sand and
silt, phosphorite, organic material and minor
shell fragments. Maximum elevations of
undifferentiated Hawthorn Group sediments
exceed 100 ft (30.5 m) MSL along inland
uplands and ridges north of Pasco County. In
Pinellas County, these sediments generally occur
deeper than -25 ft (-7.6 m) MSL.
Undifferentiated Hawthorn Group sediments
occurring in Hillsborough, Pinellas and Pasco
Counties grade laterally southeastward into the
Peace River Formation. In central Pinellas
County undifferentiated Hawthorn Group
sediments exceed 100 ft (30.5 m) thick and
grade southward into the Arcadia Formation
(Plate 31).

Gamma-ray response of the undifferentiated
Hawthorn Group sediments varies from low-
background counts where the unit is dominated
by clays, to broad and diffused patterns where
phosphorite is more abundant. Gamma-ray logs
are generally not very useful as a tool to
determine the contact with underlying and
overlying units.

In the northern region, undifferentiated
siliciclastic sediments of the Hawthorn Group
comprise discontinuous semi-confinement
between the SAS and FAS. The lateral extent
and effectiveness of this lower-permeability
layer is difficult to define due to factors such as:
1) variable lithology (e.g., percent clay) and
thickness, 2) desiccation cracking of thin clay-
rich beds during long-term low-water table
conditions and 3) breaches due to fractures and
sinkholes. As a result, many areas in this region
are denoted on Plate 55 as "discontinuous basal
confinement of SAS." These same areas are
likewise labeled "discontinuous" on Plates 56 and 57.

Pliocene and younger Series

Post-Hawthorn Group Sediments

Sediments overlying Hawthorn Group and
older units in the study area are generally
comprised of varying percentages of
undifferentiated sand, shell and clay. Within the
eastern half of the study area, the Cypresshead
Formation dominates most uplands (Figure 2)
and is well exposed along the Lake Wales
Ridge. In the southern region, three Pliocene-
Pleistocene formations are recognized: the
Tamiami Formation, the Caloosahatchee
Formation and the Fort Thompson Formation.
The latter two formations are faunally rather
than lithologically based. As a result, Scott
(1992c) provides a conceptual framework to
include Caloosahatchee and Fort Thompson
sediments as part of the Okeechobee formation
(informal). The framework also includes
informal "Bermont formation" sediments.

Although mapping post-Hawthorn Group
sediments is beyond the scope of this study,
general descriptions of the units are provided
herein. These undifferentiated surficial
sediments and formations generally comprise
the SAS. In the southern region, the lower
Tamiami Formation is considered part of the
IAS/ICU. In the cross sections (Plates 4-37),
undifferentiated sediments are broadly
classified as sand and clay (UDSC) or sand
and shell (UDSS). Existing lithologic
descriptions may identify "Pliocene -
Pleistocene" sediments (often referred to as
"PCPC"); however in the present study, these
sediments are labeled "UDSC" due to
difficulty in distinguishing the two
undifferentiated types as well as inconsistent
usage of PCPC. Gamma-ray activity in post-
Hawthorn Group sediments is highly variable
(Plates 4-37; Davis et al., 2001). In some
areas, however, a consistent peak at the base
of these sediments represents a phosphate lag
deposit reworked from Hawthorn Group
sediments (Scott, 1988; Green et al., 1995;
see also W-16303 [TR 7-4] and W-17057
[TR 7-2], Plate 16).

FLORIDA GEOLOGICAL SURVEY

Tamiami Formation

Lithology of the Lower- to mid Pliocene
(Missimer, 2002) Tamiami Formation
(Mansfield, 1939) is difficult to characterize due
to the large number of sediment facies it
contains. These facies occur over a large region
of southern Florida and represent a complex set
of depositional environments (Berndt et al.,
1998). The Tamiami Formation consists of a
wide range of mixed carbonate/siliciclastics
(sandy limestone, sand and clay with varying
percentages of phosphate grains) and shell beds
that are subdivided as members (e.g., Ochopee
Limestone Member) south of the study area
(Missimer, 1993). The Tamiami Formation is
unconformably overlain by the Caloosahatchee
Formation and overlies the Peace River
Formation either conformably or
unconformably.

Where present in the study area, the Tamiami
Formation is part of the IAS/ICU and SAS
(Bemdt et al., 1998). A semi-regionally
extensive clay layer within the Tamiami
Formation comprises the top of the IAS/ICU,
whereas the uppermost higher permeability
sediments are hydraulically connected with the
SAS.

Sands and finer-grained facies probably
represent deposition in a regressing Tamiami sea
in the brackish water of a lagoon or bay (DuBar,
1962). Deposition of the shell beds are most
likely the result of storms and processes
occurring in shallow coastal waters (Missimer,
2001). Phosphatic quartz sand facies containing
giant barnacles and echinoids exposed along
Alligator Creek and in pits near Acline
(Charlotte County) are thought to represent
deposition in a shallow water, nearshore
environment (DuBar, 1962).

Cypresshead Formation

The Upper Pliocene Cypresshead Formation
(Huddlestun, 1988) is composed entirely of
siliciclastics, predominantly quartz and clay
minerals (Scott, 1992b; Berndt et al., 1998). It
consists of characteristically mottled reddish

brown to reddish orange, unconsolidated to
poorly consolidated, fine to very coarse grained,
clean to clayey sands (Scott, 2001), some of
which are cross bedded. Discoid quartz pebbles
and mica are also often present. Clay beds are
generally thin and discontinuous. Overall, the
clay content varies from trace amounts to more
than 50 percent, averaging 10-20 percent (Scott,
1992b). Due to weathering, the clays are often
altered to kaolinite. Davis et al. (2001) describe
three lithozones within the unit, which are based
on color, sedimentary structures and varying
proportions of siliciclastics. Original fossil
material is not present in the sediment but poorly
preserved casts and molds of mollusks and
burrow structures are occasionally present
(Scott, 2001).

The Cypresshead Formation occurs in the
central uplands of the Florida peninsula south
into Highlands County (Arthur, 1993; Scott et
al., 2001). Exposure of the formation generally
occurs above 100 ft. (30.4 m) MSL (Scott,
1992b, 2001). In the northern half of the study
area, the unit lies unconformably on Eocene
carbonates, whereas in the southern half it
unconformably overlies Hawthorn Group
sediments. The Cypresshead Formation can be
readily distinguished from the Hawthorn Group
because the younger unit is non-phosphatic,
contains prominent horizontal bedding and cross
bedding, is largely nonfossiliferous and contains
burrow and bioturbation structures (Huddlestun,
1988). Along the Lake Wales Ridge, the SAS is
comprised of sediments from the Cypresshead
Formation and undifferentiated sediments (Scott,
1992b). Huddlestun (1988) suggests that the
depositional environment was coastal marine
(see also discussion of Figure 7 on p. 15).

Caloosahatchee Formation

The Caloosahatchee Formation was first
recognized by Heilprin (1887) as a Pliocene
formation he called the "Floridan Beds." Dall
(1887) also considered the deposits Pliocene and
described many of the fossils; he referred to
them as the Caloosahatchee Beds or Marls.
Scott (1992c) includes sediments informally
referred to as the Bermont formation within the

BULLETIN NO. 68

Caloosahatchee Formation and reports a Late
Pliocene to Early Pleistocene age. The
Caloosahatchee Formation consists of marls
composed primarily of quartz sand, silt and
shells with varying amounts of carbonate in the
matrix. It varies from poorly indurated to well
indurated and the fauna is varied and often well
preserved. Usually moderately to abundantly
fossiliferous, some sands are almost or
completely barren of fossils (DuBar, 1958).
Freshwater limestones are commonly present.

The extent of the Caloosahatchee Formation
is shown on previous geologic maps by Cooke
(1945) and Vernon and Puri (1964). The contact
between the subjacent Tamiami Formation and
the Caloosahatchee Formation is generally
unconformable. The Tamiami Formation was
subjected to significant subaerial erosion and the
deposition of the Caloosahatchee Formation
gradually filled in old "Tamiami valleys"
(DuBar, 1958). The Caloosahatchee Formation
comprises part of the SAS. In most
hydrogeological investigations, the
Caloosahatchee Formation is not differentiated
from the Fort Thompson Formation (Scott,
1992a). The depositional environment was
subtropical with predominantly carbonate
deposition and a coastal influx of quartz sand.
Tropical and subtropical mollusks and corals
abundant in the unit reflect an environment
similar to the present area between Cape Sable
and Florida Bay (Missimer, 2001).

Fort Thompson Formation

Sellards (1919) proposed the name Fort
Thompson Beds, which were informally
designated a formation by Cooke and Mossom
(1929). DuBar (1958) recognized the unit as
upper Pleistocene. The Fort Thompson
Formation is a sandy limestone deposited under
freshwater and marine conditions. The sand is
fine to medium grained and is interlayered with
shell beds and limestones. The shell beds are
slightly indurated to unconsolidated and variably
sandy (Scott, 1992b; Berndt et al., 1998). A
characteristic Fort Thompson marine fossil is
Chione elevata and Helisoma scalare (Figure
17) is typical of freshwater beds in the unit
(DuBar, 1958).

The Fort Thompson Formation is thin, does
not exceed 30 ft (9.1 m) in thickness, and has an
unconformable relationship to the variable units
above and below. It is most commonly
underlain by the Caloosahatchee Formation or
the Tamiami Formation (DuBar, 1958). The
Fort Thompson Formation is part of the
undifferentiated sediments in southern Florida
(Scott, 1992b) and comprises part of the SAS.
The extent of the Fort Thompson Formation is
shown on geologic maps by Cooke (1945) and
Vernon and Puri (1964). On the most recently
published geologic map of Florida (Scott et al.,
2001), the Ft. Thompson and Caloosahatchee
Formations are mapped as undifferentiated
Tertiary Quaternary shell-bearing sands
(TQsu; Figure 2).

Figure 17. Characteristic Ft. Thompson Formation fossils Chione elevata (left) and Helisoma
scalare (right; photos courtesy of IP/FMNH); bar = 12 mm.

FLORIDA GEOLOGICAL SURVEY

Hydrostratigraphy

Introduction

The hydrostratigraphic setting of the study
area varies from a locally exposed single aquifer
system in the north, to three aquifer systems in
the central and southern parts of the study area.
In the northern region, the FAS ranges from
variably confined to unconfined; clayey
sediments of the IAS/ICU or basal SAS are
locally present; IAS/ICU confining sediments
are present especially within the uplands and
ridges. The SAS, where present, is intersected
by numerous karst features (Trommer, 1987; see
also Plate 3) which may act as direct hydraulic
connection between the SAS and the FAS.
Increased permeability of the IAS/ICU occurs
where the Hawthorn Group sediments thicken
southward from central Hillsborough and Polk
Counties. In the central and southern regions,
the IAS/ICU collectively forms a thick confining
unit with intervening permeable zones that
separate the FAS from the SAS. As noted
earlier, the nomenclature applied herein is based
on aquifer system nomenclature as modified
from Florida Geological Survey Special
Publication 28 (see Hydrogeology, p. 17;
Appendix 2).

Hydrogeological properties

Numerous studies provide details on
hydrogeologic properties of aquifer systems in
the study area. For detailed information on
aquifer transmissivity, storativity, leakance
coefficients, etc., the reader is referred to USGS
publications (e.g., Ryder, 1985; Wolansky and
Corral, 1985; Metz, 1995; Yobbi, 1996;
Knochenmus, 2006), numerous SWFWMD
ROMP technical reports (e.g., Clayton, 1994,
1999; Gates, 2001; LaRoche, 2004); SWFWMD
hydrogeological studies (e.g., Barcelo and
Basso, 1993; Hancock and Basso, 1993; Basso,
2002, 2003) and especially the Southwest Florida
Water Management District (2006b) compilation:
"Aquifer Characteristics within the Southwest Florida
Water Management District, July 2005."

To provide a general characterization of these

hydrogeologic parameters, two datasets are
statistically and graphically summarized in the
discussion of each aquifer system: 1) data in
Southwest Florida Water Management District
(2006b) that meet certain quality
assurance/quality control (QA/QC) standards6
and 2) results of more than 200 hydraulic
conductivity and total porosity analyses
measured at the FDEP-FGS on cores from
within the study area. Both datasets are
presented to represent laboratory and field-scale
conditions. The Southwest Florida Water
Management District (2006b) compilation
represents properties measured during aquifer
pumping and performance tests, while the
FDEP-FGS dataset represents matrix
permeability (vertical) and porosity of core
samples. In Florida's dual-porosity (e.g,
intergranular and conduit flow) heterogeneous
carbonate terrain, it is widely recognized that
permeability calculated from field-scale aquifer-
test data (e.g., Basso, 2002) may differ by orders
of magnitude from that of laboratory
measurements. These data summaries are
presented herein to characterize expected ranges
of these parameters for use in hydrologic models
and to provide a frame of reference for those
collecting hydrological data in the field or lab.
For further details on matrix permeability, as
well as discussion of its significance and
limitations, the reader is referred to Budd (2001,
2002) and Budd and Vacher (2004).

In the descriptive statistics for each aquifer
system, standard parameters are summarized,
including mean, median, range, quartile values,
and number of analyses. Also included are
distribution descriptors: skewness, kurtosis and

6 QA/QC screening guidelines: 1) used data with
"acceptable" and "good" test-reliability scores as
defined and assigned in Southwest Florida Water
Management District (2006b); 2) avoided aquifer
tests where partial penetration was noted and no
corrections applied; 3) avoided tests where aquifer
penetration thicknesses were inconsistent with casing
and total depth data; 4) avoided use of well pairs in
which the observation well open interval differed
from the open interval in the test well by more than
15 percent; 5) avoided short-duration tests; and 6)
evaluated comments with respect to quality of test
data.

BULLETIN NO. 68

the Anderson-Darling test for normality. In the
Anderson-Darling test, the A2 value is the test
statistic for normality; if the probability (P-
value) is greater than 0.05, the data are normally
distributed. Graphical summaries of the
hydrogeological data include histograms, box
plots and 95 percent confidence interval range
charts. The histograms include a log-normal
curve fit for all parameters except for the
porosity data and SAS vertical hydraulic
conductivity. The vertical (y) axis on the
histograms reflects the total number of analyses
(N), which are listed in each statistical summary.
Units for each parameter are listed in the figure
header. The horizontal (x) axis of the box plots
corresponds to the histogram x-axis. Asterisks
in the box plots denote statistical outliers.

Surficial aquifer system

The surficial aquifer system (SAS) is
predominately comprised of Late Pliocene to
Holocene sediments and is contiguous with land
surface. This hydrostratigraphic unit occurs
throughout the study area, with the exception of
two hydrogeologic settings: 1) where an
unobstructed vertical hydraulic connection exists
between surficial sediments and the FAS (e.g.,
unconfined FAS) and 2) where the very low-
permeability sediments of the Hawthorn Group
(e.g., Peace River Formation) locally occur at or
near land surface (e.g., SAS absent and FAS is
confined). This latter setting occurs in the
central and southern Polk Upland physiographic
province (Figure 6). The extents of either of
these settings are too localized or disturbed by
mining to delineate accurately within the scale
and scope of this project. The SAS generally
consists of unconsolidated quartz sand with
variable amounts of shell, clay, phosphate and
organic material. Shell content in the SAS
increases significantly toward the southern part
of the study area (Vacher et al., 1993; see also
"UDSS" comprising the SAS in the
southernmost cross sections [e.g., Plates 18,
19]). Excluding the ridges, thickness of the SAS
averages -30 ft (-9 m). Along the Lake Wales
Ridge in the southeastern part of the study area,
SAS thicknesses range to more than 300 ft (99.4
m) (Plates 26 and 55). In the southern region,
the areas with relatively thick SAS generally

correspond to localities where the permeable
upper Tamiami Formation sediments are
included within the SAS.

The SAS is delineated in areas where
laterally extensive, sufficiently confining clayey
sediments of the IAS/ICU occur beneath
unconsolidated surficial sediments. In parts of
the northern region, the SAS locally may
directly overly the FAS. Iron-cemented zones
("hardpan") and intermittent basal clays may
result in a "perched" water table or local SAS-
like unit. On the other hand, basal confinement
breached by sinkholes or fractures precludes
characterizing much of the northern region as a
laterally extensive and functional SAS due to
lack of regional hydraulic continuity. In this
hydrogeologic setting, delineation of the SAS
becomes subjective. To account for such areas,
a hachured pattern is included on Plate 55 to
reflect "discontinuous basal confinement of the
SAS." It is noteworthy that this subjective
delineation could also be applied to the northern,
significantly karstified part of the Brooksville
Ridge; however, in recognition of available data
and to maintain consistency with the IAS/ICU,
the SAS is delineated in this area.

Groundwater w ithdrawals from the SAS are
minimal compared to that of the IAS/ICU or
FAS. Based on data from Marella (2004), the
SAS yielded between 1 percent and 5 percent of
total groundwater withdia\\als in Charlotte,
Citrus, Levy, Marion, and Sumter Counties
during 2000. In Lee County, the SAS comprised
more than 55 percent of total w ithdia\\al
(Marella, 2004). Each of the remaining counties
in the study area withdrew less than 1 percent
groundwater from the SAS (Marella, 2004).

Throughout the study area, the local water
table mimics topography (Sepulveda, 2002;
Arthur et al., in review). Elevation of the water
table varies widely throughout the study area,
ranging to more than 175 ft (53.3 m) MSL
(Arthur et al., in review). Along much of the
Lake Wales Ridge, such as in the Intraridge
Valley (Figure 6) the water table is often less
than 10 ft (3.0 m) below land surface. The water
table in other parts of the Lake Wales Ridge, as
well as other upland areas, can exceed 50 ft
(15.2 m) below land surface. Movement of SAS

FLORIDA GEOLOGICAL SURVEY

groundwater is dynamic, due to complex
interactions between recharge, discharge
(including pumping and mining operations),
runoff, infiltration, evapotranspiration and
seepage to and from underlying aquifers
(Lewelling et al., 1998). Evidence from paired
monitor wells confirms local semi-permeable
hydrologic connection between the SAS and
FAS in parts of the Lake Wales Ridge due in
part to interaquifer connectivity through sinks or
paleosinks (Tihansky et al., 1996). Depending
on hydraulic conditions, karst density, and the
leakance of basal SAS clays (or IAS/ICU clays),
the SAS may locally recharge the FAS in parts
of the northern study area. Local pumping,
rainfall events, seasonal and climatic variations
add to the complex dynamics of this
relationship.

Surface-water/groundwater interactions are
evident throughout the study area, such as
coastal springs and base flow in rivers and
streams. An outstanding example of these
dynamic interactions occurs within the Peace
River basin. Along the upper part of the basin,
maximum river-flow losses exceed 11 million
gallons per day (4.2x107 liters per day), locally
recharging underlying aquifers due to a
downward head gradient, riverbed sinkholes and
inferred buried subsidence structures (Lewelling
et al., 1998). Further downstream in the lower
part of the basin, the river receives intergranular
(rather than karst-related) seepage from the SAS
and possibly the IAS/ICU (Lewelling et al.,
1998). Understanding such surface-
water/groundwater interactions is essential
toward the establishment of effective minimum
flows and levels (MFL) and total maximum
daily loads (TMDL). Some karst-related
features, however, do not affect these
interactions. For example, the closed
topographic depressions in eastern Sarasota
County (Plate 3) are likely "sags" formed due to
the dissolution of carbonate shell material (Sam
Upchurch, personal communication, 2004).
These sags likely do not function as preferential
recharge pathl an s from the SAS to underlying
aquifer systems.
Correlation of the SAS with lithostratigraphic
units in the study area generally places the
system within post-Hawthorn Group sediments.
In the northern region, these Pliocene and

younger sands and clays are undifferentiated
(UDSC). Along the eastern region, the
sediments correlate with the Cypresshead
Formation. Further south, the Ft. Thompson,
Caloosahatchee and Tamiami Formations
comprise most of the SAS. Basal SAS clays
may represent low-permeability undifferentiated
Hawthorn Group sediments, or re-worked
Hawthorn Group sediments in the northern and
central region. In the central and eastern
regions, the base of the SAS generally coincides
with the top of the Peace River Formation
(Hawthorn Group); however, relatively clean
sands of the Peace River Formation comprise
part of the SAS in localized areas (e.g., W-
14382 [ROMP 23], Plate 17). In the southern
region, the base of the SAS not only overlies the
Peace River Formation, but also the fine-grained
dolostones of the Arcadia Formation (parts of
western/coastal Manatee and Sarasota Counties)
and middle-Tamiami clays (e.g., southeastern
Charlotte and Lee Counties; Reese, 2000;
Weinberg and Cowart, 2001). Note however,
that Missimer and Martin (2001) report two
aquifers within the SAS in Lee County, the
lowermost being the "Lower Tamiami Aquifer;"
whereas researchers such as Knochenmus and
Bowman (1998) and Torres et al. (2001) place
the entire Tamiami Formation within the
IAS/ICU. The relation between the Tamiami
Formation and hydrostratigraphic units from Lee
County north to Sarasota County warrants
further investigation.

Vadose-zone hydrogeologic characteristics of
the SAS can be approximately inferred from a
comparison of environmental geology and soil
permeability maps (Figures 4 and 18,
respectively). Patterns in both of these maps
roughly correlate with major geomorphic
provinces (Figure 6). The most permeable soils
and shallow sand-dominated sediments or
carbonate lithologies are located in the Coastal
Swamps, Gulf Coastal Lowlands, the Lake
Wales Ridge, whereas some of the least
permeable soils occur along the southern extent
of the Brooksville Ridge and parts of the
Western Valley.

In the northern region, surficial deposits may
be missing, having been eroded away and
exposing limestone at the surface (e.g.,

BULLETIN NO. 68

unconfined FAS; see Plates 29 and 30). In
contrast, these same deposits may locally exceed
100 ft (30.5 m) thick where they infill karst
features (including paleo-sinks represented by
W-15075 and W-10829; Plates 5, 6 and 29).
Depending on the permeability of infilling
sediments, the karst features may provide
hydraulic connection between the SAS and the
FAS.

Topographic inversion (i.e., differential
carbonate dissolution due to chemical buffering
and confinement) also contributes to the highly
variable thickness of the SAS in the northern
region. Along the axis of the Brooksville Ridge,
for example, more than 50 ft (15.2 m) of SAS is
locally observed. Much of the Ridge, however,
is perforated by sinkholes (Plate 3), making
delineation of the SAS problematic. Although
lithologic data from wells support presence of
the SAS along the Brooksville Ridge, extent of
the unit is even more subjective in the
surrounding region. Assessment of regional
mapping (geology [Figure 2], environmental
geology [Figure 4], and soil permeability [Figure
18]) warrants the dashed (i.e., approximate)
extent of the SAS in the region (Plate 55).
These hachured areas are considered semi-
confined to unconfined FAS.

In addition to lithologic evidence, hydraulic
data support local delineation of the SAS in
parts of the northern region. Well W-15647
(ROMP 90; Plate 10) provides a classic example
of confinement between the SAS and the FAS in
this region. Water levels measured during
drilling rose 3 ft (0.9 m) when the clays
underlying the SAS were fully penetrated and
artesian conditions of the FAS became evident.
The IAS/ICU in this well is too thin to depict
graphically in Plate 10. Moreover, given the
proximity of the well to the IAS/ICU extent,
whether the clays are basal SAS or IAS/ICU is
subjective. Confined and semi-confined areas of
Citrus County have been identified (Lee, 1998).

Water levels in paired monitor wells also
provide valuable information regarding the
presence of the SAS (i.e., basal confinement) in

the absence of an extensive IAS/ICU. This data,
however, should be interpreted with caution:
similar water levels may reflect "leaky"
confinement and seasonal or local pumping
conditions should be considered. The "Floridan"
water levels in W-14336 (ROMP 93, Plate 10),
are at least 5 ft (1.5 m) lower than SAS water
levels (U.S. Geological Survey, 1990) indicating
a well-defined hydraulic separation between the
two aquifer systems. Hydrologic data from W-
16644 (ROMP LP-6), located approximately 2
mi (3.2 km) north of cross section D-D' (Plate 7)
indicates that FAS water levels are typically
more than one foot (0.3 m) above the surficial
water table. At W-16644, 12 ft (3.7 m) of clay
and clayey sand provide sufficient confinement
between the FAS and SAS.

As noted above, effectiveness of the
hydraulic separation between the SAS and the
subjacent FAS varies locally. Water levels in
the paired wells L11KD and L11KS (northeast
of W-5054, Plate 2), are nearly
indistinguishable, thus indicating leaky to
unconfined conditions between the FAS and
"water table" levels in surficial sediments (U.S.
Geological Survey, 1998). In contrast, water
levels from the monitor-well pair L11MM and
L11MS (southeast of W-5054, Plate 2) confirm
existence of SAS conditions because "water-
table" elevations differ from the FAS
potentiometric surface (U.S. Geological Survey,
1998). Paired monitor wells with inconsistent
trends in water levels suggest that there may be
some degree of confinement of the FAS, either
as low permeability horizons in the base of the
SAS or in the uppermost carbonates of the FAS
(e.g., mudstones/micrites or densely
recrystallized zones).

A SWFWMD Technical Memorandum
(Basso, 2004) provides detail on the
hydrogeologic setting of the Herando-Pasco
County (or "Northern Tampa Bay") region. In
the memorandum, the location of wetlands, soil
properties, lithologic data and hydrographs from
nested wells and lakes are used to delineate three
zones: unconfined UFA, locally perched water
table (generally restricted to the southern

FLORIDA GEOLOGICAL SURVEY

7W7
hUc.

Mexico 1. -f

II'
Gulf
0of

Explanation
T _Ld, 4re3
- -- VV3l-r Mana,.-n-i-nl Dislri.:l;
Soil Permeability
S20 0 n/hr
100 n/hr
0 1 in/hr

Soil Permeability

S '1- Ir I l -, ",.=
PrOleichr, C l-lr.:.nm FDEP -I1.Er.
L

E'00
J Ai
**
i

C,'

Figure 18. Soil permeability of study area (Arthur et al., in review); (data compiled on per county
basis from U.S. Department of Agriculture, Natural Resource Conservation Service, 2002 and the
Florida Geographic Data Library [www.fgdl.org]).

~ "

BULLETIN NO. 68

Brooksville Ridge) and semi-confined UFA.
This localized study provides a refinement of
confining conditions within the northern Tampa
Bay region. Although differences in
nomenclature and scale of study exist, the areas
delineated by Basso (2004) are broadly
consistent with regional representations of the
SAS in Plate 55. Basso suggests, however, that
the locally perched water table aquifer (SAS in
this report) along the southern part of the
Brooksville Ridge terminates northward near the
Hemando-Citrus County boundary. This
conclusion is consistent with an increase in soil
permeability and a relative abundance of closed
topographic depressions within the Brooksville
Ridge in Citrus County (Figure 18 and Plate 3).
Moreover, the potentiometric surface for paired
SWFWMD monitor wells in southern Citrus
County ("Lecanto 1" [deep] and "Lecanto 2"
[shallow]), which have been measured since
1965, track almost perfectly indicating
unconfined FAS. On the other hand, lithologic
data from wells in the Brooksville Ridge, Citrus
County, documents more than 30 ft (9.1 m) of
local confinement. These observations serve as
additional examples of the complex and variable
degrees of confinement in the northern region
and underscore the subjective nature of the SAS
extents shown in Plate 55.

The SAS occurs throughout most of the
central and southern regions, except where
IAS/ICU sediments crop out (e.g., central Polk
County). Several paired monitor wells
document the SAS, for example, discrete
monitor wells constructed in both the SAS and
the FAS at W-12943 (Plates 12 and 31) reveal
head differences between the two aquifer
systems (Coffin and Fletcher, 1992). Other
complementary pairs of monitor wells in the
northern Pinellas and Hillsborough Counties
support the presence of a "water table" that is
distinguishable from FAS potentiometric levels,
suggesting that some degree of laterally
extensive confinement exists between the two
aquifer systems. In the southern region, the SAS
is isolated from the FAS by thick intervening
permeable and less permeable siliciclastics and
carbonates of the IAS/ICU. High-density karst
areas (Plate 3) such as the Lake Wales Ridge increase
the potential for inter-aquifer communication
between the SAS and subjacent aquifers.

Hydraulic properties for the SAS vary widely,
owing to its heterogeneous composition and
thickness. Selected hydrogeologic data from
SWFWMD (2006b; see also p. 52) and Florida
Geological Survey laboratory data are
summarized in Figures 19-22. Surficial aquifer
system parameters include transmissivity,
specific yield and horizontal and vertical
hydraulic conductivity, respectively. Note that
the horizontal hydraulic conductivity (Kh) is
calculated from the unsaturated aquifer thickness
and the transmissivity. In the vertical hydraulic
conductivity (Kv) data, if outliers are excluded,
the range in Kv is similar to that reported by
Vacher et al. (1993). A difference of several
orders of magnitude exists between Kv and Kh
values. One factor influencing this difference
pertains to sampling bias, where many Kv
samples were selected to characterize the degree
of basal confinement of the SAS. Arguably,
some of these sediments may represent the semi-
confining facies of the IAS/ICU.

Intermediate aquifer system/
intermediate confining unit

The IAS/ICU occurs throughout much of
Florida (Scott, 1992a) and is comprised of all
rocks "that lie between and collectively
retard the exchange of water" between the
SAS and the FAS (Southeastern Geological
Society, 1986). In general, this aquifer
system correlates with Oligocene-Pliocene
clays, sands and carbonates of the Hawthorn
Group, and Pliocene clays, sands, limestone
and shell beds of the Tamiami Formation
(e.g., Berndt et al., 1998; Arthur et al., 2001a;
Torres et al., 2001; Ward et al., 2003). In the
study area, the IAS/ICU is broadly characterized
by three hydrogeologic settings: 1) relatively thin,
laterally discontinuous low-permeability
confining to semi-confining sediments that
provide local hydraulic separation between the
SAS and the FAS hachuredd area in Plates 56 and
57), 2) low-permeability confining to semi-
confining sediments hydraulically separating the
SAS from the FAS (non-hachured areas in the
northern region, Plate 56 and 57), and 3)
interlayered sequences of permeable and less-
permeable rocks and sediments separating the
SAS from the FAS (central and southern regions;
Figure 23 and Plates 56-57).

FLORIDA GEOLOGICAL SURVEY

Figure 19. Statistical summary of SAS transmissivity data from Southwest Florida Water
Management District (2006b). The horizontal (x) axis of the box plots corresponds to the histogram
x-axis. Asterisks in the box plot denote statistical outliers.

Figure 20. Statistical summary of SAS specific yield data from Southwest Florida Water
Management District (2006b).

Summary for SAS T (ft^2/day)

0 1500 3000 4500 6000 7500

i I I-- I

95% Confidence Intervals

Mean- I I

Median- I I
500 1000 1500 2000 2500 3000

Anderson-Darling Normality Test
A-Squared 1.50
P-Value < 0.005
Mean 1830.4
StDev 2119.8
Variance 4493649.8
Skewness 1.80288
Kurtosis 2.50311
N 15
Minimum 20.0
1st Quartile 374.0
Median 1260.0
3rd Quartile 2206.0
Maximum 6930.0
95% Confidence Interval for Mean
656.5 3004.3
95% Confidence Interval for Median
459.2 2041.3
95% Confidence Interval for StDev
1552.0 3343.2

Summary for SY

0.00 0.05 0.10 0.15 0.20 0.25

95% Confidence Intervals

Mean I

Median-

0.050 0.075 0.100 0.125 0.150 0.175 0.200

Anderson-Darling Normality Test
A-Squared 0.74
P-Value 0.036
Mean 0.14617
StDev 0.09114
Variance 0.00831
Skew ness -0.59933
Kurtosis -1.35168
N 10
M inim um 0.00510
1st Quartile 0.05625
Median 0.20000
3rd Q uartile 0.20500
Maxim um 0.25660
95% C confidence Interval for Mean
0.08097 0.21137
95% Confidence Interval for Median
0.05117 0.20685
95% C confidence Interval for StDev
0.06269 0.16639

BULLETIN NO. 68

Summary for SAS Kh** (ft/day)

Anderson-Darling Normality Test
A-Squared 0.36
P-Value 0.407
Mean 31.015
StDev 17.940
Variance 321.854
Skewness 0.17215
Kurtosis -1.27803
N 15
Minimum 6.930
1st Quartile 12.000
12 24 36 48 60 Median 32.700
3rd Quartile 50.300
Maximum 59.000
_______ 95% Confidence Interval for Mean
21.080 40.950
95% Confidence Interval for Median
95% Confidence Intervals 14.988 45.706

Mean- I I 95% Confidence Interval for StDev
13.135 28.294
Median- I I
15 20 25 30 35 40 45

Figure 21. Statistical summary of SAS horizontal hydraulic conductivity data from Southwest
Florida Water Management District (2006b). ** calculated from transmissivity and saturated
aquifer thickness.

Figure 22. Statistical summary of SAS vertical hydraulic conductivity data based on falling-head
permeameter analyses of core samples completed at the FDEP-FGS. Due to sampling bias, most
samples represent clay-bearing sediments. Asterisks in the box plot denote statistical outliers.

Summary for SAS Kv (ft/day)

L-

0.1 0.4 0.7 1.0 1.3 1.6 1.9

u-u *

95% Confidence Intervals

Mean I-------*------

Median- 0
-0.05 0.00 0.05 0.10 0.15 0.20 0.25

Anderson-Darling Normality Test
A-Squared 7.75
P-Value < 0.005
Mean 0.09749
StDev 0.36853
Variance 0.13582
Skewness 4.7300
Kurtosis 23.0704
N 26
Minimum 0.00002
st Quartile 0.00004
Median 0.00010
3rd Quartile 0.02215
Maximum 1.85700
95% Confidence Interval for Mean
-0.05137 0.24634
95% Confidence Interval for Median
0.00004 0.00090
95% Confidence Interval for StDev
0.28903 0.50873

FLORIDA GEOLOGICAL SURVEY

OSCEOLA

" POLR

Explanation -
I-] Extent of IAS from Miller (1986)
L I FDEP IAS public supply wells +20km buffer
_ _I Approximate extent of permeable IAS/ICU
(present study)

20 10 0 20
Miles
20 10 0 20
Kilometers

Figure 23. Approximate extent of IAS/ICU permeable zones. The region mapped as IAS/ICU
(Plates 56 and 57) north of this line is dominated by lower permeability hydrogeologic facies.

BULLETIN NO. 68

Up to three relatively more permeable water-
yielding zones exist in the latter regions (Corral
and Wolansky, 1984; Trommer, 1993; Torres et
al., 2001; Knochenmus, 2006), which provide
groundwater to municipalities, industries and
agriculture. During 2000, the IAS/ICU was the
source of approximately 10 percent to 15 percent
of total groundwater withdrawal in DeSoto,
Hardee, and Highlands Counties (Marella 2004).
In Sarasota and Charlotte Counties, the usage
was 32 percent and 75 percent respectively
(Marella, 2004).

Lithology and hydrology of IAS/ICU
permeable zones is heterogeneous and complex.
Where multiple water-producing zones exist,
they are generally laterally discontinuous and
difficult to map, even with the aid of
hydrochemical assessment (Knochenmus and
Bowman, 1998; Knochenmus, 2006).
Moreover, the hydraulic character of the
IAS/ICU is unpredictable due to varying degrees
of vertical and lateral permeability within the
unit. In the northern region, IAS/ICU sediments
generally occur along upland features such as
the Brooksville Ridge, Fairfield Hills and
Sumter and Lake Uplands (Figure 6, Plate 56).
This hydrostratigraphic unit also occurs
throughout the central and southern regions.
Maximum IAS/ICU elevations exceed 125 ft
(38.1 m) MSL along the Brooksville and
Lakeland Ridges. Thickness of the IAS/ICU
ranges to more than 900 ft (274 m) in the
southernmost part of the study area (Plate 57).

Various extents of IAS/ICU water-producing
zones have been proposed within the study area
(Figure 23). In the Florida Aquifer
Vulnerability Assessment (FAVA), (Arthur et
al., in review) the extent includes Miller's
(1986) delineation plus a region defined by the
distribution of FDEP-regulated public water
supply wells that utilize the IAS/ICU (Figure
23). Included among the FDEP supply-well
region is a 12.4 mile (20 km) buffer, which was
added to account for lateral uncertainty (Arthur
et al., in review). In the present study, however,
lithologic data represented in cross sections were
assessed to re-define an approximate northern
limit of IAS/ICU permeable zones (Figure 23).
This redefined extent is comparable to that
proposed by Basso (2003). The region north of

the zone is dominated by variably low-
permeability IAS/ICU sediments, except for
localized relatively permeable sediments within
the Brooksville Ridge (e.g., W-15933; Plate 9).

Within the northeastern part of the study
area, the IAS/ICU is comprised of the
Coosawhatchie Formation (Hawthorn Group)
and possibly other Hawthorn Group units (i.e.,
the Marks Head and Penney Farms Formations)
(W-8883, Plate 5; W-12794, Plate 8). In the
central part of the northern region, the IAS/ICU
occurs along the axis of the Brooksville Ridge
and is comprised of undifferentiated Hawthorn
Group sediments (e.g., W-6903, Plate 5; W-
15933, Plate 9). Scott (1988) suggests that these
sediments at one time likely blanketed the entire
northern region. In the lowlands flanking the
Brooksville Ridge, laterally discontinuous
Hawthorn Group remnants (possibly reworked)
or Pliocene-Pleistocene clayey sediments (e.g.,
W-707, Plate 9) function hydrologically as semi-
confining sediments that promote local FAS
artesian and perched water-table conditions.

As indicated by the hachured areas in Plates
56 and 57, at least half of the northern region is
discontinuous with respect to semi-confining
sediments of the IAS/ICU. This qualitative
delineation is based on inspection of borehole
lithologic data, assessment of the state geologic
map (Scott et al., 2001) and topographic analysis
(i.e., comparing Hawthorn Group distribution
and depth to carbonate rocks with the 15 m (49.2
ft) resolution DEM. In some of these areas, the
IAS/ICU is absent and local aquifer conditions
range from SAS overlying FAS (with varying
degrees of hydraulic separation) to unconfined
FAS. Thickness of the IAS/ICU along the
Brooksville Ridge and the northeastern part of
the study area averages -35 ft (-11 m) and
locally exceeds 100 ft (30.5 m) (W-15933, Plate
9). Highly variable and localized IAS/ICU
thicknesses in these areas are due in part to
infilling ofpaleosinks. Plates 5 and 6 reflect this
scenario, however, due to the localized
occurrence, the IAS/ICU was not delineated.

In the central region, hydrogeologic
properties of the IAS/ICU are highly variable
due to lithologic heterogeneity and complex
interbedding typical of the Hawthorn Group

FLORIDA GEOLOGICAL SURVEY

sediments. The IAS/ICU primarily correlates
with the Hawthorn Group in this region;
however, some post-Hawthorn siliciclastics may
also be included in the uppermost IAS/ICU (e.g.
reworked Hawthorn Group sediments in
southern Pasco and northern Hillsborough
Counties).

Throughout most of Pinellas and
Hillsborough Counties, vertical hydraulic
continuity generally exists between the Tampa
Member (Arcadia Formation) and the Suwannee
Limestone, thereby placing the base of the
IAS/ICU at the top of the Tampa Member
(Broska and Barnette, 1999). In northern
Pinellas County, however, roughly a third of the
wells penetrating the Suwannee Limestone
encounter clay beds at the base of the Tampa
Member. Given the discontinuous nature of
these clays, the base of the IAS/ICU is
considered to correlate with the top of the
Tampa Member although local-scale head
differences may occur between this unit and the
Suwannee Limestone. In southern Hillsborough
County, however, lithologic data from six
adjacent wells indicate that basal Tampa
Member clays are more laterally extensive,
suggesting contiguous hydraulic separation from
the Suwannee Limestone. In this area (Figure
8), the Tampa Member is considered part of the
IAS/ICU (Green et al., 1995; Figure 8; Plates 14,
21 and 20). As additional hydrologic and
lithologic data become available, the base of the
IAS/ICU should be reassessed in these areas.

Mixed siliciclastic-carbonate deposits of the
IAS/ICU thicken southward from -75 ft (22.8
m) in central Polk County to more than 900 ft
(274 m) in Charlotte County (Plate 57) creating
several water-bearing zones (Trommer, 1993).
In most of west central Florida the IAS/ICU is
less permeable than the underlying FAS and
restricts movement of water between the SAS
and FAS (Ryder, 1985).

Where multiple permeable zones exist in the
IAS/ICU in the central and southern regions,
flow regimes are not fully understood. Extents
of these permeable zones need to be better
defined along with groundwater flow patterns in
order to improve management of the IAS/ICU as
a water supply source (Torres et al., 2001). The

hydrologic parameters for these zones have been
well characterized by Basso (2002) for southern
Hillsborough, Manatee and northern Sarasota
Counties. Additional details regarding depths,
thicknesses, extents and hydraulic properties of
these permeable zones are presented in Duerr
and Enos (1991), Barr (1996), Knochenmus and
Bowman, (1998), Torres et al. (2001), Basso
(2003) and Knochenmus (2006).

Distinct differences exist among
potentiometric levels representing IAS/ICU
permeable zones (Duerr, 2001). Regional
IAS/ICU potentiometric maps, however, are
generally constructed from wells open to
multiple permeable zones. As a result, the
potentiometric surface of the IAS/ICU
represents a composite of permeable zones,
which likely contributes to its high variability
across the study area. In May 2001, the
composite head level in the IAS/ICU ranged
from more than 120 ft (36.6 m) MSL in the
"Four Corers" area (northwestern Hardee
County) to approximately 50 ft (15.2 m) MSL in
Highlands County (Duerr, 2001). Within the
study area, IAS/ICU potentiometric elevation
lows occur in southern Hillsborough County and
northern Sarasota County (Duerr, 2001).

Selected hydrogeologic data compiled in
SWFWMD (2006; see also discussion on p.52)
are statistically summarized in Figures 24-27
(transmissivity, storativity, leakance and Kh,
respectively). Laboratory data from the FDEP-
FGS, including falling-head Kv analyses (Figure
28) and total porosity (Figure 29) are also
presented. Basso (2002) presents similar
hydrologic data subdivided based on IAS/ICU
permeable zones. A five order-of-magnitude
difference exists between Kv and Kh mean
values reported herein.

Similar to the SAS data, sampling bias may
account for some of this variation; Kh values
predominately reflect data from IAS/ICU
permeable zones while samples from which Kv
was measured may have been somewhat biased
toward less permeable zones or more indurated
core samples. Moreover, as with all Kv data in
heterogeneous strata, the measured values are
affected by lower-permeability horizons within
the analyzed core segments.

BULLETIN NO. 68

Figure 24. Statistical summary of IAS/ICU transmissivity data from Southwest Florida Water
Management District (2006b).

Figure 25. Statistical summary of IAS/ICU storativity data from Southwest Florida Water
Management District (2006b). Asterisks in the box plot denote statistical outliers.

Summary for IAS T (ft^2/day)

0 2000 4000 6000 8000 10000 12000

-I i i *

95% Confidence Intervals

Mean- I I

Median- I I
1000 2000 3000 4000

Anderson-Darling Normality Test
A-Squared 2.66
P-Value < 0.005
Mean 2916.2
StDev 3679.0
Variance 13534930.9
Skewness 1.59693
Kurtosis 1.82144
N 30
Minim um 3.0
1st Quartile 265.5
Median 1186.6
3rd Quartile 4975.1
Maximum 12967.9
95% Confidence Interval for Mean
1542.4 4290.0
95% Confidence Interval for Median
655.4 2874.0
95% Confidence Interval for StDev
2930.0 4945.7

Summary for IAS S

0.0000 0.0004 0.0008 0.0012 0.0016 0.0020 0.0024

95% Confidence Intervals
Mean I S I

Median- I I
0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 0.0007

Anderson-Darling Normality Test
A-Squared 4.03
P-Value < 0.005
Mean 0.000397
StDev 0.000621
Variance 0.000000
Skewness 2.75235
Kurtosis 7.29439
N 25
Minimum 0.000030
1st Quartile 0.000073
Median 0.000180
3rd Quartile 0.000351
Maximum 0.002530
95% Confidence Interval for Mean
0.000141 0.000653
95% Confidence Interval for Median
0.000100 0.000276
95% Confidence Interval for StDev
0.000485 0.000863

FLORIDA GEOLOGICAL SURVEY

Summary for IAS L (per day)

0.00 0.01 0.02 0.03

95% Confidence Intervals

Mean-

Median-

Figure 26. Statistical summary of IAS/ICU leakance data from Southwest Florida Water
Management District (2006b). Asterisks in the box plot denote statistical outliers.

Summary for IAS Kh** (ft/day)

Anderson-Darling Normality Test
A-Squared 3.07
P-Value < 0.005
Mean 38.481
StDev 53.858
Variance 2900.656
Skewness 2.12027
Kurtosis 4.85107
N 30
Minimum 0.045
1st Quartile 4.988
0 60 120 180 240 Median 13.200
Median 13.200
3rd Quartile 59.125
MI Maximum 232.000
F 95% Confidence Interval for Mean
18.370 58.592
95% Confidence Interval for Median
95% Confidence Intervals 8.684 34.030

Mean- I 'I 95% Confidence Interval for StDev
42.893 72.402
Median- I I
10 20 30 40 50 60

Figure 27. Statistical summary of IAS/ICU horizontal hydraulic conductivity data from Southwest
Florida Water Management District (2006b). Asterisk in the box plot denotes statistical outliers.

** calculated from transmissivity and permeable zone thickness.

Anderson-Darling Normality Test
A-Squared 3.70
P-Value < 0.005
Mean 0.003427
StDev 0.008193
Variance 0.000067
Skewness 3.7045
Kurtosis 14.2198
N 16

Minimum 0.000033
1st Quartile 0.000187
Median 0.000968
3rd Quartile 0.001921
Maximum 0.033425
95% Confidence Interval for Mean
-0.000939 0.007792
95% Confidence Interval for Median
0.000196 0.001759
95% Confidence Interval for StDev
0.006052 0.012680

BULLETIN NO. 68

Figure 28. Statistical summary of IAS/ICU vertical hydraulic conductivity data based on falling-
head permeameter analyses of core samples completed at the FDEP-FGS. Asterisks in the box plot
denote statistical outliers.

Figure 29. Statistical summary of IAS/ICU total porosity data based on core sample volumetric
analyses completed at the FDEP-FGS.

Summary for IAS Kv (ft/day)

0.0035 0.0110 0.0185 0.0260 0.0335

I l- ** *

95% Confidence Intervals

Mean- I I

Median I-I ------I

0.000 0.001 0.002 0.003 0.004 0.005 0.06

Anderson-Darling Normality Test
A-Squared 6.72
P-Value < 0.005

Mean 0.003318
StDev 0.006677
Variance 0.000045
Skewness 2.69316
Kurtosis 7.41148
N 38
Minimum 0.000000
1st Quartile 0.000048
Median 0.000337
3rd Quartile 0.003100
Maximum 0.030300
95% Confidence Interval for Mean
0.001124 0.005513
95% Confidence Interval for Median
0.000102 0.001230
95% Confidence Interval for StDev
0.005443 0.008638

Summary for IAS Total Porosity (% )

A

15.0 22.5 30.0 37.5 45.0 52.5

959

95c
95% Confidence Intervals

Mean- I I 95

Median- I I
30 32 34 36 38 40

nderson-Darling Normality Test
A-Squared 0.34
P-Value 0.447
Mean 34.126
StDev 9.540
Variance 91.010
Skew ness -0.547647
Kurtosis 0.466245
N 19
Minimum 14.130
1st Quartile 28.900
Median 35.370
3rd Quartile 39.400
Maximum 49.550
i% Confidence Interval for Mean
29.528 38.724
o Confidence Interval for Median
29.626 38.225
% Confidence Interval for StDev
7.208 14.108

FLORIDA GEOLOGICAL SURVEY

Floridan aquifer system

The FAS occurs throughout Florida and is
often an artesian aquifer. Artesian conditions
may vary with seasonal rainfall and pumping
conditions. In the study area, springs flow year-
round along parts of coastal Citrus, Pasco and
Hemando Counties (Figure 6; Healy, 1974;
Scott et al., 2004). Other common areas of FAS
discharge include wetlands in the Tsala Apopka
Plain, southern Pasco County, and the Green
Swamp (northwest Polk County). The FAS
discharges into the SAS along the northern part
of the Lake Wales Ridge and also provides
baseflow to surface-water bodies (e.g.,
Hillsborough River). Along the trace of the
Peace River, the FAS discharges into permeable
zones of the IAS/ICU (Sepulveda, 2002).
Similar conditions exist within southern
Sarasota County, southwestern DeSoto County
and most of Charlotte County. Throughout the
remainder of the study area, the FAS is
recharged from overlying aquifer systems.

The top of the FAS does not always coincide
with a specific lithostratigraphic unit. Instead, it
is defined by permeability and hydraulic
connection (Johnston and Bush, 1988).
Moreover, per the Southeastern Geological
Society (1986) definition, the top of the FAS
"generally coincides with the absence of
significant thicknesses of (silici)clastics from the
section and with the top of the vertically
persistent permeable carbonate section." In the
study area, the surface of this hydrostratigraphic
unit may include the following formations in
ascending order: Avon Park Formation, Ocala
Limestone, Suwannee Limestone, and units
within the Hawthorn Group (Trommer, 1993;
Ryder, 1985; Berndt et al., 1998; Corral and
Wolansky, 1984).

Figure 8 summarizes the extent of
lithostratigraphic units that comprise the FAS
surface. The top of the FAS correlates
regionally with the Oligocene Suwannee
Limestone where present; however, in west-
central Florida, the Tampa Member (Arcadia
Formation) of the Hawthorn Group coincides
with the top of the FAS where it is hydraulically
connected to the underlying Suwannee

Limestone (generally Pinellas [e.g., Hickey,
1982; Broska and Barnette, 1999], southern
Pasco, Hillsborough and Manatee Counties
[Green et al., 1995]). In the absence of the
Tampa Member or Suwannee Limestone,
Eocene rocks (Avon Park Formation or Ocala
Limestone) comprise the top of the FAS (Figure
8; Miller, 1986). Based on lithostratigraphic
correlation and the FAS definition applied
herein (see also Appendix 2), the top of the unit
ranges in age from Middle Eocene to Early
Miocene.

In the northern region, the FAS (Plates 4
through 8) includes the Avon Park Formation,
Ocala Limestone and Suwannee Limestone. In
Pasco County (Plate 11), hydrogeologic data
suggest that the Tampa Member is also
hydraulically connected to the FAS. For
example, water levels measured at well W-
16609 (TR 18-2A; Plates 11 and 29) increased
only -1.2 inches (- 3 cm) in elevation while
coring through the Tampa Member into the
Suwannee Limestone (DeWitt, 1990). Overall,
the FAS is unconfined to semi-confined in the
region. Along parts of the northern coastal zone,
laterally extensive confining units are thin to
absent (Plate 56) and hydraulic head differences
allow local recharge to the FAS, which in turn
enhances development of secondary porosity
along fractures and bedding planes in the FAS.
These dissolution-widened channels have a
much higher hydraulic conductivity. For
example, dissolution channels in the Ocala
Limestone are highly developed in Hernando,
Citrus and Marion Counties (Trommer, 1993).
Abundant sinkholes in the region, indicated by
the region's pattern of closed topographic
depressions (Plate 3), locally breach confining
beds.

As indicated by the hydrologic data
presented in the Surficial aquifer system section,
p. 53, local unconfined to semi-confined FAS
conditions exist in the northern region. For
example, water levels in a FAS monitor well and
a surficiall" monitor well at site W-16311
(ROMP LP-4, Plate 7) exhibit nearly identical
elevations, suggesting that confinement is leaky
or absent between surficial sediments and the
carbonates of the FAS. Along the Brooksville
Ridge and parts of the northeastern margin of

BULLETIN NO. 68

the study area, IAS/ICU Hawthorn Group
sediments provide increased confinement of the
FAS. Numerous sinkholes (Plate 3) and paleo-
sinks breach confining clayey sediments that
would otherwise justify delineation of confined
FAS (Plates 6, 7 and 8; Trommer, 1987). As a
result, characterization of certain areas along the
Brooksville Ridge as IAS/ICU and SAS is very
subjective.

In the central, southern and eastern regions,
the zero MSL (sea-level) contour of the FAS
surface (central Hillsborough and Polk Counties;
Plate 58) represents a hinge-line, south of which
the dip of the FAS markedly increases. As
noted in Figure 8, the FAS surface generally
correlates with lithostratigraphic units. The
surfaces of these units have been affected by
depositional, erosional or structural features
(e.g., dissolution, basins, channel scouring,
fracture-controlled drainage systems, possible
faults, etc.). Other variations in the FAS surface
(Plate 58) are due to sub-regional confinement
between lithostratigraphic units. For example,
several wells in central Hillsborough County
indicate that confinement exists between the
Suwannee Limestone and the Tampa Member
(Arcadia Formation), resulting in correlation of
the FAS surface with the Suwannee Limestone.
Uncertainty in the area with regard to vertical
hydraulic connectivity between these two
lithostratigraphic units and lateral/regional
groundwater flow warrant further study.

In the southern region, the FAS surface
generally coincides with the top of the
Oligocene Suwannee Limestone. Along western
DeSoto County, however, the FAS surface
correlates poorly with any specific
lithostratigraphic unit (Figure 8). In some
boreholes, such as W-18117 (ROMP 35,
northwest DeSoto County, Plate 2), the FAS
surface occurs approximately 90 ft (27.4 m)
below the top of the Suwannee Limestone
(LaRoche, 2004). Along the eastern margin of
the study area, the Ocala Limestone comprises
the surface of the FAS, except for a small area in
northeastern Osceola County, where the Ocala
Limestone is absent and the Avon Park
Formation is the uppermost unit (Figure 8;
Gates, 2006). Plate 34 is a representative cross
section of the FAS surface, where it occurs

nearly 100 ft (30.4 m) MSL in well W-15650
(ROMP 88; northern Polk County) and deepens
significantly toward the south where it occurs at
-861 ft (-262 m) MSL in well W-15289.

The FAS potentiometric surface within the
study area (Figure 30) is highly variable and
contains several prominent features. Maximum
elevations (exceeding +130 ft [39.6 m] MSL)
occur in north-central Polk County, near Polk
City and within the Green Swamp. This
maximum is located in the center of a ridge-like
potentiometric high that extends north-northwest
into Marion and Sumter Counties, and south-
southeast along the axis of the Lake Wales
Ridge. Another topographically associated high
occurs along the Brooksville Ridge in Pasco and
Hernando Counties. At least two distinct
potentiometric highs with more than 20 ft (6.1
m) of relief also occur: 1) the Dunellon Gap
(Levy County), and 2) the Big Cypress Swamp
(central Pasco County). Minimum elevations
occur within a few feet below sea level in
southwestern Hillsborough County. Troughs in
the UFA potentiometric surface align with the
Withlacoochee River in Hernando and Pasco
Counties, the Hillsborough and Alafia Rivers
(Hillsborough County), indicating significant
baseflow contributions to these rivers (Figure
30). A less distinct trough is associated with
lakes in eastern Citrus County (i.e., Tsala-
Apopka Lake and Lake Panasofkee). Flow
directions vary considerably in response to these
highs/ridges and lows/troughs; however, in a
very broad sense the groundwater flow in the
UFA for the region west of the Lake Wales
Ridge is generally toward the Gulf coast.

Seasonal perturbations in the potentiometric
surface are generally due to variable recharge
rates and pumping. Regionally, the most notable
difference between the May 2005 (Ortiz and
Blanchard, 2006) and September 2005
potentiometric surface (Ortiz, 2006) is a
broadening of the ridge-like high along the Lake
Wales Ridge in response to the rainy season.
Relative to a predicted "pre-development"
potentiometric surface, Bush and Johnston
(1988) report drawdown exceeding 20 ft (6.1 m)
in a region encompassing roughly one-third of
the District centered on northwest Hardee
County.

FLORIDA GEOLOGICAL SURVEY

Floridan aquifer system
Potentiometric Surface
September, 2005
0 5 10 20 30 40
-Miles
0 5 10 20 30 40
Kilometers
Scale 1:1,750,000
Contour Interval: 10 ft
Projection: Custom FDEP Albers

Explanation --
aMajor Rivers
-- Potentiometric Line (Feet) 7
- Water Management Districts
rI Study Area

Figure 30. Potentiometric surface of the Floridan aquifer system, September, 2005 (from Ortiz,
2006); A Withlacoochee River, B Hillsborough River and C Alafia River. See Figure 1 for
additional river labels.

Gulf
of
Mexico

BULLETIN NO. 68

A meaningful comparison of the IAS/ICU
potentiometric surface (Duerr, 2001) with that of
the FAS is qualitative at best (see discussion
starting on page 62). A more accurate, although
site-specific method for assessing the
recharge/discharge relation between the
IAS/ICU and FAS is to compare water levels in
nested wells, many of which are located at
District ROMP sites. As noted above, Miller
(1986) subdivided the FAS into the Upper
Floridan aquifer (UFA) and the Lower Floridan
aquifer (LFA). The UFA is the principal source
of groundwater throughout the study area except
for Charlotte County, where only 20 percent of
total w ithdra \als originate from the UFA (based
on data from 2000 as compiled by Marella,
2004) due to naturally poor water quality. The
most productive units of the UFA are located
within the Avon Park Formation, Ocala
Limestone and the Suwannee Limestone (Ryder,
1985).

A highly permeable facies of the FAS,
referred to as the "Boulder Zone" (Kohout,
1965), is characterized by cavernous, fractured
dolostones with very high transmissivities (Puri
et al., 1973). Vernon (1970) reported "Boulder
Zone" facies throughout the Florida peninsula.
More recently, however, this hydrogeologic
facies has been recognized as discontinuous and
found to be limited to the southern third of the
Florida peninsula (Miller, 1986). The facies
does not occur within the same lithostratigraphic
unit throughout its extent (Miller, 1986).
Maliva et al. (2001) report occurrences of
"Boulder Zone" facies in the Early Eocene
Oldsmar Formation in Charlotte, Lee and Collier
County injection wells. This facies has been
reported to occur at depths shallower than -1300
ft (-396.2 m) MSL in Charlotte County (Maliva
et al., 2001), which corresponds to Avon Park
Formation carbonates. In the southernmost
peninsula, the facies occurs within the Paleocene
Cedar Keys Formation as well as the Eocene
Avon Park Formation and Ocala Limestone
(Puri and Winston, 1974).

Wolansky et al. (1980) mapped "the highly
permeable dolomite zone" of the Avon Park
Formation throughout the southern two-thirds of
the District. These well-indurated dolostones
are commonly fractured and contain large

dissolution channels. The zone occurs -100 ft
(- 30.5 m) below the top of the Avon Park
Formation in the central part of the study area
and 400 ft (- 122 m) below the Avon Park
Formation surface in the southern region. The
SAS and IAS/ICU generally provide
confinement of the UFA (Berndt et al., 1998)
except for areas in the northern region where the
UFA may be unconfined and where karst and
paleokarst promote inter-aquifer connectivity.
Hydrogeologic conditions vary considerably
between the northern and southern regions
depending on the degree of confinement.

The interpolated surface of the UFA ranges
from greater than 75 ft (22.9 m) MSL along the
Brooksville Ridge to less than -825 ft (-251 m)
MSL in southern Charlotte County (Plate 58).
Locally, maximum elevations exceed 130 ft
(39.6 m) along the Brooksville Ridge (W-14917
[ROMP 109], Plate 7). A map of overburden
thickness provides a different perspective on the
depth to the top of the UFA (Figure 31). This
map, developed by subtracting the UFA surface
from a 15 m (49.2 ft) resolution DEM (Arthur et
al., in review), allows comparison of the aquifer
system to geomorphic features. For example,
note the thin overburden along the Brooksville
Ridge compared to the Lake Wales Ridge, as
well as the maximum overburden thickness of
-900 ft (-274 m) in Charlotte County.

The base of the UFA occurs within the lower
Avon Park Formation, where vertically and
laterally persistent evaporite minerals (gypsum
and anhydrite) are present in the carbonate rocks
(e.g., Ryder, 1985; Hickey, 1990; see Middle
Floridan confining unit [MFCU], p. 75, for more
information). Thickness of the UFA, calculated
as a "grid difference map," ranges from less than
300 ft (91.4 m) to more than 1500 ft (457 m;
Figure 32). Regional subjacent confinement of
the UFA is comprised of the MFCU where
present. Examples of basal UFA confinement
are represented in several cross sections (e.g.,
Plates 7, 9, 21 and 31). Note, however, that
Miller's (1986) delineation of overlapping
MFCU units by default suggests that the base of
the UFA in these areas is a complex
discontinuous surface. This aspect of the UFA
is described in more detail in the next section.

FLORIDA GEOLOGICAL SURVEY

Floridan aquifer system
Overburden Thickness
0 5 10 20 30 40
m mMiles
0 510 20 30 40
Kilometers
Scale 1:1,750,000
Projection: Custom FDEP Albers

I

Explanation
| Study Area
- Water Management Districts
FAS Overburden Thickness
900 ft
450 ft

Figure 31. Floridan aquifer system overburden thickness as predicted from geospatial modeling
(i.e., DEM minus top of FAS). The map is not contoured due to extreme resolution differences in
source grids.

Gulf
of
Mexico

BULLETIN NO. 68

Upper Floridan aquifer
Thickness
0 5 10 20 30 40
Im 3 Miles
0 510 20 30 40
Kilometers
Scale 1:1,750,000
Contour Interval: 150 ft
Projection: Custom FDEP Albers

II
I

'I

Explanation

I Study Area
Contours
- Water Management Csit[r.:ti.
UFA Thickness
S1600 ft
665 ft
265 ft

Figure 32. Thickness of the Upper Floridan aquifer (includes non-potable).

Gulf
of
Mexico

FLORIDA GEOLOGICAL SURVEY

The LFA lies beneath MFCU strata and
consists of the lower part of the Avon Park
Formation, the Oldsmar Formation and the
upper part of the Cedar Keys Formation (Miller,
1997). The Cedar Keys Formation forms the
lower boundary of the LFA and generally
consists of persistently dolomitized carbonates
with widespread bedded and intergranular
gypsum and anhydrite. Except for the
northeastern part of the study area, the LFA is
commonly highly saline and not used as a
potable or an economically treatable water
source. Research on use of the LFA as a
sustainable fresh water resource for the
northeastern part of the District is underway
(Southwest Florida Water Management District,
2006a).

The LFA is the lowermost known and well-
defined aquifer, ranging in elevation from -400
ft (-122 m) MSL in the northeastern part of the
study area to more than -2500 ft (-762.0 m)
MSL in Sarasota and Charlotte counties; LFA
thicknesses exceed 2,400 ft (731.5 m) in the
southeast part of the study area (Miller, 1986).
Per findings of the CFHUD II (Copeland et al.,
in review) the low-transmissivity strata lying at
the base of the FAS (e.g., the "sub-Floridan
confining unit" referenced in Southeastern

Geological Society, 1986) is informally referred
to as "undifferentiated aquifer systems."

Hydraulic properties of the FAS are
summarized in Figures 33-38 for the parameters
transmissivity, storativity, leakance, Kh, and
total porosity, respectively. A large degree of
vertical anisotropy exists in the FAS (e.g., Ryder
et al., 1980; Ryder, 1982) due to variations in
grain size and diagenetic factors affecting
permeability (e.g., Budd, 2002; Budd and
Vacher, 2004). Median horizontal and vertical
hydraulic conductivity values differ by three
orders of magnitude, which is notably less than
the difference between these same parameters in
the SAS and IAS/ICU. This is due in part to a
relative lack of sampling bias in the analyzed
FAS core samples. A greater degree of
anisotropy in the SAS and IAS/ICU relative to
the FAS is another possible contributing factor.
Anomalously high transmissivity values (Figure
33) likely reflect the influence of dual-porosity
(i.e. fracture/conduit flow). It is also noteworthy
that spatial analysis of dolines (e.g., sinkholes)
in the northern and central region indicates a
statistically significant correlation between FAS
hydraulic conductivity and doline-area ratios
(Armstrong et al., 2003).

Summary for UFA T (ft^2/day)

A nderson-D arling Normality Test
A-Squared 18.49
P-Value < 0.005
Mean 88602
StDev 187201
Variance 35044192303
Skewness 4.4198
Kurtosis 21.3092
N 90
Minimum 1300
0 200000 400000 600000 800000 1000000 1200000 1st Quartlle 18650
M edian 38369
3rd Q uartile 69789
-J -- Maximum 1203210
95% Confidence Interval for Mean
49393 127810
95% Confidence Intervals 95% Confidence Interval for Median
29279 48540
Mean- I 95% Confidence Interval for StDev
Median 163279 219401
Median
20000 40000 60000 80000 100000 120000 140000

Figure 33. Statistical summary of UFA transmissivity data from Southwest Florida Water
Management District (2006b). Asterisks in the box plot denote statistical outliers.

BULLETIN NO. 68

Figure 34. Statistical summary of UFA storativity data from Southwest Florida Water
Management District (2006b). Asterisks in the box plot denote statistical outliers.

Figure 35. Statistical summary of UFA leakance data from Southwest Florida Water Management
District (2006b). Asterisks in the box plot denote statistical outliers.

Summary for UFA S

0.000 0.016 0.032 0.048 0.064 0.080 0.096

95% Confidence Intervals

Mean-

Median-

0.000 0.001 0.002 0.003 0.004 0.005

A nderson-Darling Normality Test
A-Squared 24.66
P-Value < 0.005
Mean 0.002660
StDev 0.010812
Variance 0.000117
Skew ness 6.6858
Kurtosis 47.7119
N 81
Minimum 0.000000
1stQuartile 0.000265
Median 0.000640
3rd Q uartile 0.001200
Maximum 0.086000
95% Confidence Interval for Mean
0.000269 0.005050
95% Confidence Interval for Median
0.000404 0.000935
95% Confidence Interval for StDev
0.009365 0.012792

Summary for UFA L (per day)

0.000 0.012 0.024 0.036 0.048 0.060 0.072

** *

95% Confidence Intervals

Mean- II

Median- -

0.000 0.001 0.002 0.003 0.004 0.005 0.006

Anderson-Darling Normality Test
A-Squared 15.47
P-Value < 0.005
Mean 0.003141
StDev 0.010668
Variance 0.000114
Skewness 5.6131
Kurtosis 33.5295
N 59
Minimum 0.000029
1st Quartile 0.000147
Median 0.000300
3rd Q uartile 0.001800
Maximum 0.072380
95% Confidence Interval for Mean
0.000361 0.005921
95% Confidence Interval for Median
0.000241 0.000567
95% Confidence Interval for StDev
0.009031 0.013036

FLORIDA GEOLOGICAL SURVEY

Figure 36. Statistical summary of UFA horizontal hydraulic conductivity data from Southwest
Florida Water Management District (2006b). ** calculated from transmissivity and permeable
zone thickness. Asterisks in the box plot denote statistical outliers.

Summary for UFA Kv* (ft/day)

Anderson-Darling Normality Test
A-Squared 26.02
P-Value < 0.005
Mean 0.10028
StDev 0.22808
Variance 0.05202
Skewness 4.2139
Kurtosis 21.8401
N 137
i-- M minimum 0.00000
0.0 0.3 0.6 0.9 1.2 1.5 1st Q uartile 0.00565
Median 0.01967
3rd Quartile 0.08725
|- I* Maximum 1.72957
95% C confidence Interval for Mean
0.06175 0.13882
95% Confidence Intervals 95% Confidence Interval for Median
M 0.01422 0.02795
Mean 95% Confidence Interval for StDev

Median 0.20389 0.25882
Median I-

0.000 0.025 0.050 0.075 0.100 0.125 0.150

Figure 37. Statistical summary of UFA vertical hydraulic conductivity data based on results of
falling-head permeameter analyses of core samples completed at the FDEP-FGS. Asterisks in the
box plot denote statistical outliers.

Summary for UFA Kh** (ft/day)

0 1000 2000 3000 4000 5000 6000

-I-& 9
9.

95% Confidence Intervals 95

Mean- I

Median- -

100 200 300 400 500

Anderson-Darling Normality Test
A-Squared 21.43
P-Value < 0.005
Mean 276.61
StDev 787.65
Variance 620386.37
Skewness 5.8896
Kurtosis 38.2409
N 86
Minim urn 7.65
1st Quartile 50.50
Median 91.90
3rd Quartile 178.75
Maxim urn 6050.00
5% Confidence Interval for Mean
107.74 445.49
% Confidence Interval for Median
78.51 110.07
5% Confidence Interval for StDev
684.97 926.82

BULLETIN NO. 68

Summary for UFA Total Porosity (% )

Anderson-Darling Normality Test
A-Squared 1.91
P-Value < 0.005
Mean 37.056
StDev 8.601
Variance 73.978
Skewness -1.22649
Kurtosis 2.93402
N 117
SMinimum 2.300
0 10 20 30 40 50 1st Q uartile 31.950
S Median 38.730
3rd Quartile 42.625
IM axim um 53.490
95% Confidence Interval for M ean
35.481 38.631
95% Confidence Intervals 95% Confidence Interval for Median
S37.100 39.950
Mean II 95% Confidence Interval for StDev
7.622 9.870
Median I I
35 36 37 38 39 40

Figure 38. Statistical summary of UFA total porosity data based on results of core sample
volumetric analyses completed at the FDEP-FGS. Asterisks in the box plot denote statistical
outliers.

Middle Floridan confining unit

Miller (1986) recognizes three confining
units within the study area (Units I, II and VI)
that separate the UFA from the LFA; however,
in context of the overall FAS he states: "... the
units act as a single confining unit within the
main body of permeable limestone that
constitutes the aquifer system." In the present
study, we adopt a more descriptive
hydrostratigraphic name for the Miller's (1986)
"middle confining unit" of the FAS: the Middle
Floridan confining unit (MFCU). This name
simply associates the confining units with the
aquifer system in which they reside. This
nomenclature has also been adopted by the
CFHUD II (Copeland, et al., in review).
Complexity of the MFCU within and beyond the
study area is readily apparent given the seven
units mapped by Miller (1986) separating the
UFA from the LFA in Florida. On a more local
scale, delineation of the base of the UFA
becomes challenging where overlapping
confining units of the MFCU occur.

Within the study area, unit I occurs along the

eastern margin and is identified as a leaky
confining unit that is "...not much different from
that of the permeable zones vertically adjacent to
it..." (Miller, 1986). Units II and VI are
identified as carbonates (primarily dolostone)
with intergranular gypsum and comprise a
hydrogeologically significant confining facies
that separates the UFA from the LFA in the
study area.

The MFCU mapped herein includes Miller's
(1986) units II and VI and is principally
identified based on lithology and mineralogy:
borehole samples that contain thin
gypsum/anhydrite beds or intergranular
gypsum/anhydrite > five percent (by volume).
While some may consider five percent too
conservative (e.g., too high), a notable relative
increase in matrix confining properties is the
emphasis herein, recognizing that transition
zones may occur, as well as zones where
variable precipitation and dissolution of these
minerals may have occurred. Geophysical logs
and water-quality data are also used to identify
or infer evidence of the MFCU. In addition to
data generated for this report, data from Miller

FLORIDA GEOLOGICAL SURVEY

(1988), Hickey (1982), Sacks (1996), Stewart
(1966), O'Reilly et al. (2002) and unpublished
SWFWMD ROMP reports are also used to
interpolate the MFCU surface.

Miller's (1986) unit II, which reaches depths
of -1,900 ft (-579.1 m) MSL in Sarasota County
correlates with most of the MFCU surface (Plate
59). Unit VI (Miller, 1986) reaches depths of -
2,100 ft (-640.1 m) MSL in southeastern DeSoto
County and along the southern half of Charlotte
County. According to data from Miller (1988),
the two units overlap in western
Highlands/eastern DeSoto Counties as well as
western Charlotte and Lee Counties. Several
wells investigated by Miller (1986, 1988) and in
the present study indicate that the MFCU may
not be laterally continuous throughout the study
area; however for purposes of regional mapping,
the MFCU is contoured continuously and the
areas in question are annotated (Plate 59).

The initial protocol for mapping the MFCU
was to reflect the uppermost occurrence of the
unit in a borehole using the lithologic criteria
outlined above. This method, however, yielded
anomalous surface patterns and vertical
discontinuities where Miller's (1986) units II
and VI coexist in a well. A MFCU surface map
based on this initial protocol yielded two dome-
like features in the southern region in the
vicinity of these wells. The domes represented
unit II overlying unit VI, separated by high
permeability zones (Miller, 1988) and thus did
not reflect a contiguous mappable surface. The
distribution of well control for unit II (Plate 59)
also brings into question the degree to which
unit II is laterally continuous. Many sufficiently
deep wells within the extent of unit II do not
encounter the unit. It is also noteworthy that
Miller (1986) describes units II and VI as having
nearly indistinguishable lithologic characteristics.

Figure 39. Interpretations of the MFCU in the study area. Upper cross section reflects MFCU units
mapped by Miller (1986); lower cross section reflects alternate interpretation showing continuity
between Miller's units II and VI, with isolated MFCU middle to upper Avon Park confinement
overlying the deeper, more laterally continuous unit. See Plate 59 for cross-section location.

A A'
NORTH 2 a SOUTH
Fee I F M Fw
MSL f MSL
0 0

-500- 500
Miller (1986.1988)
MFCU -1000ooo -1000
Unit II
UnitVI -i SO- 1500
2000 -2 000

-2500- -2500

Present Study o o
MFCU = -500o -s00
Locally
Shallow | ia Olow000 t-
MFCU

BULLETIN NO. 68

Evaluation of the regional slope of the
MFCU, lithologic similarities between the units,
and sparse data for unit II lead to an alternate
interpretation: unit II north of Manatee and
Hardee Counties may correlate with unit VI
south of these counties (Figure 39). In this
interpretation, isolated MFCU facies occur
approximately 400 ft (122 m) above the lower
MFCU unit in southwestern Highlands and
western Charlotte Counties. Plate 59 and Figure
39 (bottom half) reflect this latter interpretation.
Wells that encountered both MFCU facies (II
and VI) are represented by green symbols (Plate
59) and are labeled with the elevation of the
shallower discontinuous MFCU facies, which is
informally referred to as the "middle to upper
Avon Park confining unit." Data in Miller
(1988) indicate a high permeability zone
between the base of the "middle to upper Avon
Park confining unit" and the MFCU as mapped
herein within all wells containing both of
Miller's MFCU facies (II and VI).

Based on comparison of Plate 38 with
Miller's (1986) Middle Eocene isopach, the
MFCU as defined and mapped in this study
generally occurs within the lower half of the
Avon Park Formation. Exceptions to the
generalization include Marion, Osceola and
Pinellas Counties, where the MFCU occurs
within the upper third of the Avon Park
Formation. Several cross sections contain wells
that penetrate the MFCU (e.g., Plates 7, 9, 21,
29, 30 and 34). In the northwestern part of the
study area, the elevation of the MFCU is
generally deeper than -400 ft (-122 m) MSL.
The unit dips southward to depths below -2100
ft (-640.1 m) MSL in Charlotte County. South
of the study area, Reese (2000) mapped the
"dolomite-evaporite unit in the middle confining
unit" of the FAS, recognizing the significance of
dense unfractured dolostones in his study area.
He also notes that this unit may locally be
considered the top of the MFCU, which is
generally supported by the MFCU surface in
Plate 59. It is possible that the few wells with
shallower elevations in Reese's (2000)
"dolomite evaporite unit" map are related to
the discontinuous "middle to upper Avon Park
confining unit" described herein.

Presence of the MFCU is debatable for two
regions within the eastern half of the study area.

Throughout most of Marion County (including
parts of Alachua, Sumter and Lake Counties),
the MFCU is inferred. Borehole cuttings from
multiple wells in the area show no evidence of
gypsum/anhydrite; however, anomalously high
sulfate concentrations (some exceeding 500
mg/L; Sacks, 1996) in FAS groundwater
samples suggest the MFCU may be present. As
such, this area is denoted on Plate 59 as "MFCU
inferred based on water quality data." In eastern
Polk County, Miller (1986) mapped the MFCU;
however, available well control (this study and
Miller, 1988), as well as water quality data for
the area, yields no direct evidence that it is
present. Sprinkle (1989) and Katz (1992) report
relatively low sulfate concentrations (< 50
mg/L) within the UFA in the area. To
emphasize this uncertainty the MFCU in this
area is labeled "MFCU possibly absent: limited
data" (Plate 59).

Hydraulic conductivity analyses of MFCU
rocks were not completed for this study;
however, data exists in SWFWMD and
consultant's reports. For example, Hickey
(1982) reports hydraulic conductivities ranging
from 1.1 ft/day to 6.0x10-7 ft/day (3.8x10-4 to
2. 1xl0-10 cm/sec) based on core representing the
"lower confining bed" (greater than -1000 ft
[-305 m] MSL) in Pinellas County. To provide
characterization of MFCU hydraulic
conductivity and total porosity, data has been
compiled from three injection well sites:
Knight's Trail, Sarasota County, (Law
Environmental, Inc., 1989), Burnt Store
Utilities, Charlotte County, (ViroGroup, Inc.,
1995) and Punta Gorda, Charlotte County, (City
of Punta Gorda, Water Resource Solutions, Inc.,
and Boyle Engineering Corporation, 2001).
Data from Stewart (1966) and Hickey (1982)
and Montgomery Watson Americas (1997) are
also included. Hydraulic conductivity (Kv) for
the 21 MFCU cores analyzed in these studies
range from 1.5x10-' ft/day to 1.0xl0-6 ft/day
(5.3x10-' to 3.53x10-10 cm/sec), with a median
value of 1.84x10-3 ft/day (6.5x10-7 cm/sec;
Figure 40). Total porosity for these samples
average 17.2 percent (median = 19.6 percent)
and range from 5 percent to 30 percent (Figure
41). Basso (2002) reports Kh values ranging
from .002 to .04 ft/day (7.06x10-07 to 1.4x105
cm/sec). Transmissivity data range from 0.08 to
2.9 ft2/day (0.86 to 31.2 m2/day).

FLORIDA GEOLOGICAL SURVEY

Figure 40. Statistical summary of MFCU vertical hydraulic conductivity data based on results of
falling-head permeameter analyses of core samples; compiled from Stewart (1966), Hickey (1982),
Law Environmental (1989), ViroGroup (1995), Montgomery Watson Americas, Inc., (1997), City of
Punta Gorda, et al., (2001). Asterisks in the box plot denote statistical outliers.

Summary for MFCU Total Porosity (%)

Anderson-Darling Normality Test
A-Squared 0.77
P-Value 0.038
Mean 17.147
StDev 6.854
Variance 46.980
Skewness -0.499332
Kurtosis -0.197892
N 19
Minimum 5.000
1st Quartile 13.700
4 8 12 16 20 24 28 32 Median 19.600
3rd Quartile 21.000
M maximum 30.000
95% Confidence Interval for Mean
13.844 20.451
95% Confidence Interval for Median
95% Confidence Intervals 15.169 21.000
Mean I I 95% C confidence Interval for StDev
5.179 10.136
Median- I I
14 16 18 20 22

Figure 41. Statistical summary of MFCU total porosity data based on volumetric analyses of core
samples; compiled from Stewart (1966), Law Environmental (1989), ViroGroup (1995),
Montgomery Watson Americas, Inc. (1997), City of Punta Gorda, et al., (2001).

Summary for MFCU Kv (ft/day)

0.00 0.03 0.06 0.09 0.12 0.15

95% Confidence Intervals
Mean I

Median
-0.005 0.000 0.005 0.010 0.015 0.020 0.025

Anderson-Darling Normality Test
A-Squared 5.50
P-Value < 0.005
Mean 0.010796
StDev 0.032419
Variance 0.001051
Skewness 4.2710
Kurtosis 18.8184
N 21
Minimum 0.000001
1st Quartile 0.000326
Median 0.001840
3rd Quartile 0.007085
Maximum 0.149000
95% Confidence Interval for Mean
-0.003961 0.025553
95% Confidence Interval for Median
0.000426 0.004443
95% Confidence Interval for StDev
0.024803 0.046816

BULLETIN NO. 68

SUMMARY

The hydrogeologic framework of the
Southwest Florida Water Management District
region described in this report is spatially
characterized through a series of 32 maps (plates
and figures) and 34 cross sections. Lithologic,
hydrologic and geophysical data from more than
1050 wells comprise a database of subsurface
elevations and thicknesses for nine
lithostratigraphic and four hydrostratigraphic
units represented in these maps and cross
sections. Elevations of unit boundaries for most
of the wells used in the maps and cross sections
have been confirmed through visual inspection
of cores and cuttings by the authors and those
acknowledged in this report. Additional data on
which the maps and cross sections are based are
incorporated from peer-reviewed reports and
interpreted from geophysical logs and existing
lithologic descriptions. The lithostratigraphic
units are discussed in terms of age, lithology,
mineralogy, common fossils, sedimentary
structures, porosity/permeability, contact
relations with other units, facies changes, spatial
distribution (vertical and lateral), gamma-ray log
responses, hydrostratigraphic unit correlations
and depositional environments.
Hydrostratigraphic units are similarly discussed
in terms of spatial distribution, regional and
local hydraulic characteristics, hydrogeologic
properties and correlation with lithostratigraphic
units.

Among the challenges that exist when
creating subsurface stratigraphic maps based on
well data is the need to balance three factors: 1)
accuracy of the interpolated contours relative to
the data on which each map is based, 2) the
implicit resolution of the map, which is depicted
by the contour interval and the degree of
perturbations in the contours and 3) an accurate
regional characterization of the unit being
mapped. For example, a map that is 100 percent
accurate with respect to elevations or
thicknesses may overemphasize local anomalies
such as karst features. Although a small
percentage of wells represent these anomalous
elevations, the wells also represent an
infinitesimal fraction of the total number of
anomalous features in the mapped surface. In

other words, thousands of paleosink features
may exist in the top of a carbonate unit;
however, less than five percent of the wells in
the database may have encountered one of these
features. Hence, a regional-scale map would be
more representative of the true regional
character of the surface (or thickness) if the local
anomalies had less influence on the interpolated
surface. Moreover, a highly accurate map may
also result in jagged, irregular contours, which
may imply changes in elevation (or thickness) at
a scale that is not justified by the distribution
and density of the well data.

To achieve an appropriate balance of the
aforementioned factors, an iterative process of
data evaluation, sample inspection, data
interpretation, and spatial and statistical analysis
was completed. For the final maps, kriging was
used to interpolate map surfaces, which were
then corrected as needed for consistency with
land surface and other mapped units. The
interpolated surfaces were then smoothed to
reflect the regional character of each mapped
unit. The surface interpolations also provide
GIS coverages that can be applied in
groundwater flow models and 3D applications.

The cross sections focus on data from cores,
with an emphasis on those collected through the
SWFWMD Regional Observation and Monitor-
well Program (ROMP). Data from geophysical
logs as well as cores and cuttings archived in the
Florida Geological Survey sample repository
were used to fill gaps in the cross-section well
coverage. Of the 34 cross sections, nine trend
approximately north-south, averaging
approximately 60 mi (-96 kilometers) in length,
while the remaining sections generally trend
east-west and average approximately 35 mi (-56
km) in length. Graphical representation of
borehole data from 149 wells used in the cross
sections include lithostratigraphic and
hydrostratigraphic boundaries and cross-well
correlations, lithology, mineralogy and gamma-
ray log response. Each section also includes
topographic profiles labeled with selected
anthropogenic features.

The relationship between lithostratigraphic
and hydrostratigraphic units is straightforward in
many parts of the study area; however, the

FLORIDA GEOLOGICAL SURVEY

association can be locally complex and
indistinct. In either case, the relationship
depends on the degree of hydraulic continuity
between and among lithostratigraphic units. The
variable hydrogeologic setting in the northern
region serves as an example: characterization of
the SAS (water-table aquifer) is complicated by
lateral hydraulic discontinuities. Regionally, the
water table may reflect the potentiometric
surface of the unconfined FAS (e.g., west of the
Brooksville Ridge); however, local hydraulic
separation between the SAS and the FAS may
exist. As a result, delineation of a regionally
extensive SAS that is significant as a water-

producing unit is the subject of some debate.

The framework of stratigraphy and
hydrogeology developed during this
investigation serves as a foundation for
numerous applications, ranging from more
refined hydrogeological mapping to mineral
resource assessments, well-field designs and
groundwater models. Regardless of the
application, it is our hope that this study
facilitates science-based decision making
regarding the protection, conservation and
management of the solid-earth and water
resources of southwestern Florida.

BULLETIN NO. 68

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	Front Cover
	Title Page
	Dedication
	Preface
	Table of Contents
	Abbreviations, acronyms and...
	Acknowledgement
	Main
	Summary
	References
	Appendices
	Plates

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