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State of Florida
Department of Environmental Protection
David B. Struhs, Secretary

Division of Resource Assessment & Management
Edwin Conklin, Director

Florida Geological Survey
Walter Schmidt, State Geologist and Chief

Florida Geological Survey
Special Publication No. 44

Geological Assessment: The Foundation of Understanding the
"Bucket" That Contains Our Precious Water Resources

by

Walter Schmidt, P.G. #1 and Thomas M. Scott, P.G. #99

Published for the
Florida Geological Survey
Tallahassee, Florida
1999

Printed for the
Florida Geological Survey

Tallahassee, Florida
1999

ISSM 0085-0640

(cover artwork by Paulette Bond)

ii

LETTER OF TRANSMITTAL

Florida Geological Survey
Tallahassee

Governor Jeb Bush
Florida Department of Environmental Protection
Tallahassee, FL 32399

Dear Governor Bush:

The Florida Geological Survey, Division of Resource Assessment &
Management, Department of Environmental Protection is publishing the following paper
as Special Publication No. 44, "Geological Assessment: The Foundation of
Understanding The "Bucket" That Contains Our Precious Water Resources". This
report summarizes the lithologic character of our aquifer units, and as such, provides
the basis for understanding our ambient surface and groundwater chemistry, water
transport dynamics for water resource conservation, and the foundation of our various
ecosystems.

Respectfully yours,

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

WS/cac

CONTENTS
PAGE

Introduction 1
Hydrogeologic 1
Earth Systems 3
Geologic Framework 3

Geologic Structure 4

Geomorphology 5

Lithostratigraphy and Hydrostratigraphy 6
Lithostratigraphy 6
Cenozoic Erathem, Tertiary System 7
Paleocene Series 7
Cedar Keys Formation 7
Eocene Series 8
Claiborne Group 8
Oldsmar Formation 8
Avon Park Formation 8
Ocala Limestone 9
Oligocene Series 10
Suwannee Limestone 10
Marianna Limestone 11
Bucatunna Clay Member of the Bryam Formation 11
Chickasawhay Formation 11
Miocene Series 11
Chattahoochee Formation 12
St. Marks Formation 13
Hawthron Group 13
Bruce Creek Limestone 14
Alum Bluff Group 14
Pensacola Clay 15
Intracoastal Formation 15
Pliocene-Pleistocene Series 15
"Coarse Clastics" 16
Tamiami Formation 16
Citronelle Formation 17
Miccosukee Formation 17
Cypresshead Formation 18
Nashua Formation 18
Caloosahatchee Formation 18
Fort Thompson Formation 19
Key Largo Formation 19
Miami Limestone 19
Anastasia Formation 20

PAGE

Undifferentiated Pleistocene-Holocene Sediments 20

Hydrostratigraphy 21

Geologic Structure in Relation to Hydrostratigraphy 21

Aquifer Systems and Confining Units 22
Surficial Aquifer System 22
Northwest Florida Water Management District 23
Suwannee River Water Management District 23
St. Johns River Water Management District 24
Southwest Florida Water Management District 25
South Florida Water Management District 25
Intermediate Aquifer System and Intermediate Confining Unit 26
Northwest Florida Water Management District 27
Suwannee River Water Management District 28
St. Johns River Water Management District 28
Southwest Florida Water Management District 29
South Florida Water Management District 30
Floridan Aquifer System 31
Northwest Florida Water Management District 32
Suwannee River Water Management District 34
St. Johns River Water Management District 34
Southwest Florida Water Management District 35
South Florida Water Management District 36

References 37

SPECIAL PUBLICATION NO. 44

GEOLOGICAL ASSESSMENT: THE FOUNDATION OF
UNDERSTANDING THE "BUCKET" THAT CONTAINS OUR
PRECIOUS WATER RESOURCES

Walter Schmidt, P.G. #1, and Thomas M. Scott, P.G. #99

INTRODUCTION

Hydrogeologic Framework

Water supply and protection concerns are not isolated issues only
involving the study and planning for surface and ground water resources. To
fully understand and protect our precious, life sustaining water resources,
knowledge of the medium, which the water flows through, and over must also be
considered. The geologic framework serves as the "bucket" that contains the
water, and it contributes dissolved minerals and elements, which characterizes
the ambient water chemistry. Without a basic understanding of the local and
regional geology which must include information on rock and sediment lithology,
stratigraphy, mineralogy, and several hydrogeologic parameters including
porosity and permeability interpretations (not just measurements) among other
geologic concerns, no real water resource planning or protection plan can be
successful. This includes most of the issues identified in the FLORIDA WATER
PLAN, 1995, including: links between land and water planning, watershed basin
protection, source sustainable yields, availability of water supply, quantity and
location concerns, contamination threats, potential property damage from flood
disasters, threatened ecosystems from water related problems, and the
cumulative impacts of population growth including land-use changes, increased
ground water withdrawals, and aquifer minimum flows and the levels of our
surface watercourses.

EARTH SYSTEMS

To begin to relate the geologic component of our hydrogeologic
framework to the overall picture of land and water use and planning practices,
first we must understand how the physical "earth systems" are the building
blocks of our environment. Much has been written in recent years on ecosystem
management as a way of managing and providing for best resource planning
practices. Ecosystem management as an expression of holistic environmental
awareness has in recent years become the principal focus of federal and state
agencies charged with the conservation and protection of the environment. A
truly complete or "holistic" understanding of our environment, however, cannot
be realized unless the natural systems which comprise our dynamic earth are
the focus of our efforts.

FLORIDA GEOLOGICAL SURVEY

The floral and faunal communities that make up classically defined
ecosystems are the complex result of the interaction of water and our enveloping
atmosphere with the solid earth itself. Water, if it is available, acts as a
mechanical agent as it sculpts the landscape by erosion. At the same time water
is active as a chemical agent, breaking down rocks and sediments to form soils
or dissolving rocks in such a way that subterranean aquifers are created,
enhanced, or clogged up. Upland ecosystems, wetland and aquatic
ecosystems, and coastal ecosystems are differentiated by availability of water
and local geology. This differing availability of water is a direct result of the
interaction of the earth's moisture-laden atmosphere with its infinitely complex
crust. These inter-related Earth Systems can be divided into four component
systems. The Geosystem (the solid earth), Hydrosystems (terrestrial
components of the hydrologic cycle), Atmosystems (meteorological and climate
cycles), and the Ecosystems (the inter-relationships of biologic communities
with their associated environment). All environments on earth exist in their
present form because of the composite and historical cumulative interaction of
these four earth systems.

Our expanding human population has had a profound effect on fragile
ecosystems that coexist with us. Likewise, our relentless growth has seriously
affected the earth systems, which ultimately yield water, food, and all other
natural resources required for sustainable life. Any program of environmental
management philosophy that ignores the role of the solid earth is seriously
shortsighted and destined to fall short of its goal. Diverse floral and faunal
populations (including the human population) are unique aspects of life on earth.
Truly "holistic" ecosystem management, environmental regulations, and land-use
planning must recognize that life on earth can never be realistically separated
from the geology of the solid earth that sustains life.

Recognition of geological assessment as the foundation of environmental
management is especially germane to Florida. While the layman may ask why is
geology important in Florida because we don't have volcanoes or earthquakes,
and we don't have mountains, the informed can respond with the benefit from a
complete understanding of our dynamic earth. The Florida platform itself is a
result of long standing sedimentary and geochemical processes continuing
today. Some of these recognizable "uplands" natural hazards include such
things as, coastal erosion and or accretion, coastal and fluvial flooding, sinkhole
collapse, building foundation or roads cracking from "pipe clays", ground water
contamination problems (from septic tanks, landfills, injection wells, surface run-
off, and many other sources), ground water source or flow impacts (including
development dewatering, recharge area alterations, etc.), fresh water springs
degradation, perceived radon health risks, mercury environmental and health
concerns, and many others. While these issues clearly demonstrate the
fundamental nature that the solid earth geologic framework plays in

SPECIAL PUBLICATION NO. 44

environmental solutions, these geologic hazards solutions are not the main
thrust of our discussion here.

Florida is a low relief platform, jutting out between the Gulf of Mexico and
the Atlantic Ocean. On the north it is connected to the southeast coastal plain,
where a transition between the clastics (sands, gravels and clays) from the
Appalachian Mountains, and the carbonates (limestones, dolostones, and
evaporates) of the Florida Platform occurs. The low relief physiography, high
water tables, and humid mild climate, results in an abundant and diverse
integrated environment. This has resulted in many unique and rare ecosystems,
often pressured by our societies changes to the local physical earth systems. As
our society continues to grow we continue to consume more energy, and fresh
water, and demand more construction materials for the building of homes and
community infrastructure. Generally, resource regulations focus on either human
health and safety or esthetics and recreation. A complete understanding of the
entire earth systems involved and the consequences of our actions, must
become a routine part of our decision making process if we are to be successful
in developing "sustainable" environmental conservation and land management
practices.

GEOLOGIC FRAMEWORK

The State of Florida lies principally on the Florida Platform. The western
panhandle of Florida occurs in the Gulf Coastal Plain to the northwest of the Florida
Platform. This subdivision is recognized on the basis of sediment type and
depositional history. The Florida Platform extends into the northeastern Gulf of
Mexico from the southern edge of the North American continent. The platform
extends nearly four hundred miles north to south and nearly four hundred miles in its
broadest width west to east as measured between the three hundred-foot isobaths.
More than one-half of the Florida Platform lies under water leaving a narrow
peninsula of land, we know as the State of Florida, extending to the south from the
North American mainland.

A thick sequence of primarily carbonate rocks capped by a thin, siliciclastic
sediment-rich sequence forms the Florida Platform. These sediments range in age
from mid-Mesozoic (200 million years ago [mya]) to Recent. Florida's aquifer
systems are developed in the Cenozoic sediments ranging from latest Paleocene
(55 mya) to Late Pleistocene (<100,000 years ago) in age (Figure 1). The
deposition of these sediments was strongly influenced by fluctuations of sea level
and subsequent subaerial exposure. Carbonate sediment deposition dominated the
Florida Platform until the end of the Oligocene Epoch (24 mya). The resulting
Cenozoic carbonate sediment accumulation ranges from nearly two thousand feet
thick in northern Florida to more than five thousand feet in the southern part of the
state. These carbonate sediments form the Floridan aquifer system; one of the
world's most prolific aquifer systems, regional intra-aquifer confining units and the

FLORIDA GEOLOGICAL SURVEY

sub-Floridan confining unit. The sediments suprajacent to the Floridan aquifer
system include quartz sands, silts, and clays (siliciclastics) with varying admixtures
of carbonates as discrete beds and sediment matrix. Deposition of these sediments
occurred from the Miocene (24 mya) to the Recent. The Neogene (24 mya to 1.6
mya) and Quatemary (1.6 mya to the present) sediments form the intermediate
aquifer system and/or confining unit and the surficial aquifer system (Figure 1).

Geologic Structure

The oldest geologic structures recognized as affecting the deposition of
sediments of the Florida Platform are expressed on the pre-Middle Jurassic
erosional surface (Arthur, 1988). These include the Peninsular Arch, South Florida
Basin, Southeast Georgia Embayment, Suwannee Straits and the Southwest
Georgia Embayment or Apalachicola Embayment. These structures affected the
deposition of the Mesozoic sediments and the Early Cenozoic (Paleogene)
sediments. The structures recognized on the top of the Paleogene section are
somewhat different than the older features. The younger features, which variously
affected the deposition of the Neogene and Quatemary sediments, include the
Ocala Platform, Sanford High, Chattahoochee Anticline, Apalachicola Embayment,
Gulf Trough, Jacksonville Basin (part of the Southeast Georgia Embayment),
Osceola Low and the Okeechobee Basin (Figure 2). For more specific information
on these structures and their origins refer to Chen (1965), Miller (1986) and Scott
(1988a).

The occurrence and condition of the aquifer systems are directly related to
their position with respect to these subsurface geologic structural features. The
Floridan aquifer system lies at or near the surface under poorly confined to
unconfined conditions on the positive features such as the Ocala Platform, Sanford
High and the Chattahoochee Anticline. Within the negative areas, (the Apalachicola
Embayment, Jacksonville Basin, Osceola Basin and the Okeechobee Basin) the
Floridan aquifer system is generally well confined. The intermediate aquifer system
is generally absent from the positive structures and best developed in the negative
areas. The surficial aquifer system may occur anywhere in relation to these
structures where the proper conditions exist.

The occurrence and development of the beds confining the Floridan aquifer
system also relate to the subsurface structures. On some of the positive areas
(Ocala Platform and Chattahoochee Anticline) the confining beds of the intermediate
confining unit are absent due to erosion and possibly nondeposition. In those areas
where the confining units are breached, dissolution of the carbonate sediments
developed a karstic terrain. Dissolution of the limestones enhanced the porosity and
permeability of the Floridan aquifer system including the development of some
cavernous flow systems.

SPECIAL PUBLICATION NO. 44

Geomorphology

Florida's land surface is relatively flat and has very low relief. The surface
features of Florida are the result of the complex interaction of depositional and
erosional processes, which included fluvial, marine and subaerial systems. As sea
level fluctuated during the later Cenozoic, the Florida Platform has repeatedly been
inundated by marine waters resulting in marine depositional processes dominating
the development of Florida's geomorphology. The relict shoreline features found
throughout most of the state are most easily identified at lower elevations, nearer the
present coastline. Inland and at higher elevations, these features have been
subjected to more extensive erosion and subsequent modification by wind and
water. In those areas of the state where carbonate rocks and shell-bearing
sediments are subjected to dissolution, the geomorphic features may be modified by
development of karst features. The extent of the modification ranges from minor
sagging due to the slow dissolution of carbonate or shell to the development of large
collapse sinkholes. The changes that result may make identification of the original
features difficult.

White (1970) subdivided the State into three major geomorphic divisions, the
northern or proximal zone, the central or mid-peninsular zone and the southern or
distal zone. The northern zone encompasses the Northwest Florida Water
Management District and the northern portions of the Suwannee River and St. Johns
River Water Management Districts. The central zone includes the southern portions
of the Suwannee River and St. Johns River Water Management Districts, the
Southwest Florida Water Management District and the northern part of the South
Florida Water Management District. The southern zone comprises the remainder of
the South Florida Water Management District.

In a broad general sense, the geomorphology of Florida consists of the
Northern Highlands, the Central Highlands and the Coastal Lowlands (White,
Vernon and Puri in Puri and Vernon, 1964). White (1970) further subdivided these
features as shown in Figures 3 through 7. In general, the highlands are well drained
while the lowlands often are swampy, poorly drained areas. The highland areas as
delimited by White, Vernon and Puri in Puri and Vernon (1964) often coincide with
the areas of "high recharge" as recognized by Stewart (1980). Only a few, limited
areas of "high recharge" occur in the Coastal Lowlands.

Many of the highland areas in the peninsula to the central panhandle exhibit
variably developed karst features. These range from shallow, broad sinkholes that
develop slowly to those that are large and deep and develop rapidly (Sinclair and
Stewart, 1985). The development of the karst features and basins has a direct
impact on the recharge in the region. The karst features allow the rapid infiltration of
surface water into the aquifer systems and offer direct access to the aquifers by
pollutants.

FLORIDA GEOLOGICAL SURVEY

Lithostratigraphy and Hydrostratigraphy

The aquifer systems in Florida are composed of sedimentary rock units of
varying composition and induration which are subdivided into geologic formations
based on the lithologic characteristics (rock composition and physical
characteristics). Lithostratigraphy is the formal recognition of the defined geologic
formations based on the North American Stratigraphic Code (North American
Commission on Stratigraphic Nomenclature, 1983). Many units are related by the
similarities of the sediments while others may be defined on the sediment
heterogeneity. An aquifer is a body of sediment or rock that is sufficiently permeable
to conduct ground water and to yield economically significant quantities of water to
wells and springs (Bates and Jackson, 1987). Florida's primary aquifers are referred
to as aquifer systems due to the complex nature of the water-producing zones they
contain. The aquifer systems are identified independently from lithostratigraphic
units and may include more than one formation or be limited to only a portion of a
formation. The succession of hydrostratigraphic units forms the framework used to
discuss the ground-water system in Florida (Figure 1) (Southeastern Geological
Society Ad Hoc Committee on Florida Hydrostratigraphic Unit Definition, 1986).

The lithostratigraphic and hydrostratigraphic framework of Florida shows
significant variability from north to south and west to east in the peninsula and the
panhandle. The formational units discussed are only those Cenozoic sediments that
relate to the Floridan aquifer system, the intermediate aquifer system/confining unit
and the surficial aquifer system.

Lithostratigraphy

The lithostratigraphic units that comprise the aquifer systems in Florida occur
primarily as subsurface units with very limited surface exposures. As a result of the
generally low relief of the state, most of the lithostratigraphic descriptions are from
well cuttings and cores used to study the sediments. Various geophysical surveys
and logs also have proven useful in studying the sediments and in attempting
regional and local correlations (Chen, 1965; Miller, 1986; Scott, 1988a; Johnson,
1984; Schmidt, 1984).

The following description of the lithologic parameters of the various units
associated with the aquifer systems is brief and generalized. More complete
information concerning these groups and formations can be obtained by referring to
Florida Geological Survey and U. S. Geological Survey publications relating to
specific areas and/or specific aquifers. Statewide data concerning the thickness and
tops of sediments of Paleocene (67-55 mya) and Eocene (55-38 mya) age
(chronostratigraphic units) can be found in Chen (1965) and Miller (1986). Miller
(1986) provides this data for Oligocene (38-25 mya) and Miocene (25-5.3 mya)
sediments. Scott (1988a) provides detailed information on the Miocene strata in the
eastern panhandle and peninsular areas. Schmidt (1984) provides stratigraphic

SPECIAL PUBLICATION NO. 44

descriptions and interpretations on Neogene strata from the central and western
panhandle. The Plio-Pleistocene (5.3-.01 mya) and the Holocene (.01 mya -
Present) sediments which make up the surficial aquifer system, are discussed in a
number of references which are cited in the appropriate section of this paper.
Figure 1 shows the lithostratigraphic nomenclature utilized in this text.

Cenozoic Erathem
Tertiary System
Paleocene Series

In general, most of the Paleocene sediments in the Florida peninsula form
the sub-Floridan confining unit and only a limited portion of these rocks is part of the
Floridan aquifer system. Siliciclastic sediments predominate in the Paleocene
section in much of the panhandle (Chen, 1965; Miller, 1986). The siliciclastic
sediments are composed of low permeability marine clays, fine sands and impure
limestone (Miller,1986) which lie below the base of the Floridan aquifer system.
Following Miller (1986), the siliciclastic sediments are referred to as
"Undifferentiated Paleocene Rocks (Sediments)" and are not discussed further.

The siliciclastic sediments grade laterally into carbonate sediments across
the Gulf Trough in the eastern panhandle (Chen, 1965). Carbonate sediments,
mostly dolostone, occur interbedded with evaporite minerals throughout the
Paleocene section in the peninsula (Chen, 1965). These sediments are included in
the Cedar Keys Formation and occur throughout the peninsular area and into the
eastern panhandle.

Cedar Keys Formation

The Cedar Keys Formation consists primarily of dolostone and evaporites
(gypsum and anhydrite) with a minor percentage of limestone (Chen, 1965). The
upper portion of the Cedar Keys consists of coarsely crystalline, porous dolostone.
The lower portion of the Cedar Keys Formation contains more finely crystalline
dolostone, which is interbedded with anhydrite. The Cedar Keys Formation grades
into the Undifferentiated Paleocene Sediments in the eastern panhandle (Miller,
1986) which equate with the Wilcox Group (Braunstein et al., 1988).

The configuration of the Paleocene sediments in peninsular Florida reflect
depositional controls inherited from the pre-existing Mesozoic structures, including
the Peninsular Arch, Southeast Georgia Embayment, and the South Florida Basin
(Miller, 1986). The Cedar Keys Formation forms the base of the Floridan aquifer
system throughout the peninsula except in the northwestern-most peninsular area
where the Oldsmar Formation forms the base (Miller, 1986). The upper, porous
dolostone comprises the lowest beds of the Floridan aquifer system. The lower
Cedar Keys Formation is significantly less porous, contains evaporites and forms
the sub-Floridan confining unit.

FLORIDA GEOLOGICAL SURVEY

Eocene Series

The sediments of the Eocene Series that form portions of the Floridan aquifer
system are carbonates. During the Early Eocene, deposition followed a distribution
pattern similar to the Paleocene carbonate sediments. However, through the
Eocene, carbonate-forming environments slowly encroached further north and west
over what had been siliciclastic depositional environments during the Paleocene.
The Eocene carbonate sediments are placed in the Oldsmar Formation, Avon Park
Formation and the Ocala Group. The Eocene carbonate sediments comprise a
large part of the Floridan aquifer system.

Claibome Group

The Lower to Middle Eocene Claibome Group unconformably (?) overlies the
undifferentiated Lower Eocene and Paleocene sediments. The Claibome Group
consists of the Tallahatta and Lisbon Formations, which are lithologically nearly
identical and are not separated. The group is composed of glauconitic, often clayey
sand grading into fine-grained limestone to the south (Allen, 1987). The Claibome
Group ranges from 250 to 400 feet below NGVD and is up to 350 feet thick (Allen,
1987). It is unconformably overlain by the Ocala Limestone.

Oldsmar Formation

The Oldsmar Formation consists predominantly of limestone interbedded
with vuggy dolostone. Dolomitization is usually more extensive in the lower portion
of the section. Pore-filling gypsum and thin beds of anhydrite occur in some places,
often forming the base of the Floridan aquifer system (Miller, 1986).

The Oldsmar Formation is recognized throughout the Florida peninsula. It
grades laterally in the eastern panhandle into Undifferentiated Lower to Middle
Eocene sediments equivalent to the Claibome Group. The undifferentiated
sediments are marine shales, siltstones, fine sandstones and impure limestones
(Miller, 1986).

Avon Park Formation

The Middle Eocene sediments of peninsular Florida as originally described
by Applin and Applin (1944) were subdivided, in ascending order, into the Lake City
Limestone and the Avon Park Limestone. Miller (1986) recommended the inclusion
of the Lake City in the Avon Park based on the very similar nature of the sediments.
Miller also changed the term limestone to formation due to the presence of
significant quantities of dolostone within the expanded Avon Park Formation.

SPECIAL PUBLICATION NO. 44

The Avon Park Formation is primarily composed of fossiliferous limestone
interbedded with vuggy dolostone. In a few, limited areas of west central Florida,
evaporites are present as vug fillings in dolostone.

The Avon Park Formation occurs throughout the Florida peninsula and the
eastern panhandle in a pattern very similar to the underlying Oldsmar Formation.
The oldest rocks exposed on the surface in Florida belong to the Avon Park
Formation. These sediments are locally exposed on the crest of the Ocala Platform
in west central peninsular Florida.

The carbonate sediments of the Avon Park Formation form part of the
Floridan aquifer system and serve to subdivide it into an upper and lower Floridan in
many areas. Miller (1986) recognized that portions of the Avon Park Formation are
fine-grained and have low permeability, often acting as a confining bed in the middle
of the Floridan aquifer system. In Brevard County, for example, these low
permeability beds are relied upon to keep less desirable water injected into the
lower Floridan from migrating into the potable water of the upper Floridan.

Ocala Limestone

Dall and Harris (1892) referred to the limestones exposed in central
peninsular Florida near the city of Ocala in Marion County as the Ocala Limestone.
Puri (1957) raised the Ocala to group and recognized formations based on the
incorporated foraminiferal faunas. As a result of the biostratigraphic nature of these
subdivisions, formational recognition is often difficult. In keeping with the intent of
the Code of Stratigraphic Nomenclature, the Florida Geological Survey has returned
to the use of the Ocala Limestone terminology.

The lower and upper subdivisions of the Ocala Limestone are based on
distinct lithologic differences. The lower subdivision consists of a more granular
limestone (grainstone to packstone). The lower faces is not present everywhere
and may be partially to completely dolomitized in some regions (Miller, 1986). The
upper unit is composed of variably muddy (carbonate), granular limestone
(packstone to wackestone with very limited grainstone). Often this unit is very soft
and friable with numerous large foraminifera. In southern Florida, virtually the entire
Ocala Limestone consists of a muddy (carbonate) to finely pelletal limestone
(Miller,1986). Chert is a common component of the upper portion of the Ocala
Limestone. The Bumpnose "Formation", a very early Oligocene fossiliferous
limestone, is lithologically very similar to the Ocala Limestone. It is included in the
Ocala Limestone.

The sediments of the Ocala Limestone form one of the most permeable
zones within the Floridan aquifer system. The Ocala Limestone comprises much of
the Floridan aquifer system in the central and western panhandle. The extensive
development of secondary porosity by dissolution has greatly enhanced the

FLORIDA GEOLOGICAL SURVEY

permeability, especially in those areas where the confining beds are breached or
absent. The Ocala Limestone forms the lower portion of the Floridan in the western
panhandle (Schmidt and Coe, 1978, Wagner, 1982). In much of the peninsular
area, it comprises all or part of the upper Floridan.

By Late Eocene, carbonate sediments were deposited significantly further to
the north and west than had previously occurred during the earlier parts of the
Cenozoic. The Ocala Limestone is present throughout much of the State except
where the unit has been erosionally removed. This occurs in outcrop on the crest of
the Ocala Platform and in the subsurface on the Sanford High, a limited area in
central Florida and a relatively large area in southernmost Florida (Miller, 1986).
Chen (1965) suggests that the Ocala Limestone is also absent in a portion of Palm
Beach County in eastern southern Florida. The surface and thickness of the Ocala
Limestone are highly irregular due to dissolution of the limestones as karst
topography developed.

Oligocene Series

The carbonate sediments of the Oligocene Series form much of the upper
portion of the Floridan aquifer system in Florida. The depositional pattern of the
Oligocene sediments shows that carbonate sediments were deposited well updip to
the north of the Florida Platform (Miller, 1986). In the central panhandle and to the
west, siliciclastic sediments began to be mixed with the carbonates.

The Oligocene sediments in peninsular Florida and part of the panhandle are
characteristically assigned to the Suwannee Limestone. The Oligocene sediments
in the central and western panhandle are placed in the Marianna, Bucatunna and
Chickasawhay Formations (Miller, 1986). In the westernmost panhandle, the lower
carbonates of the Suwannee Limestone grade into the siliciclastic Byram Formation
(Braunstein et al., 1988).

Suwannee Limestone

The Suwannee Limestone consists primarily of variably vuggy and muddy
(carbonate) limestone (grainstone to packstone). The occurrence of a vuggy,
porous dolostone is recognized in the type area, the eastern to central panhandle
(Schmidt and Coe, 1978) and in southwest Florida. The dolostone often occurs
interbedded between limestone beds.

The Suwannee Limestone is absent throughout a large area of the northern
and central peninsula probably due to erosion. Scattered outliers of Suwannee
Limestone are present within this area. Where it is present, the Suwannee
Limestone forms much of the upper portion of the Floridan aquifer system. The
reader is referred to Miller (1986) for a map of the occurrence of the Suwannee
Limestone in the peninsula.

SPECIAL PUBLICATION NO. 44

Marianna Limestone

The Marianna Limestone is a fossiliferous, variably argillaceous limestone
(packstone to wackestone) that occurs in the central panhandle (Schmidt and Coe,
1978). It is laterally equivalent to the lower portion of the Suwannee Limestone.
The Marianna Limestone forms a portion of the uppermost Floridan aquifer system
in the central panhandle region.

Bucatunna Clay Member of the Byram Formation

The Bucatunna Clay Member is silty to finely sandy clay. Fossils are
generally scarce in the Bucatunna (Marsh, 1966). The sand content of the
Bucatunna ranges from very minor percentages too as much as 40 percent (Marsh,
1966).

The Bucatunna Clay Member has a limited distribution in the western
panhandle. It occurs from the western end of the state eastward to approximately
the Okaloosa-Walton County line where it pinches out (Marsh, 1966, Clark and
Schmidt, 1982). The Bucatunna Clay Member provides an effective intra-aquifer-
confining unit in the middle of the Floridan aquifer system in the western panhandle.

Chickasawhay Formation

Marsh (1966) describes the Chickasawhay Formation as being composed of
highly porous limestone and dolomitic limestone. This is often interbedded with
porous to compact dolomitic limestone to dolostone. The Chickasawhay Formation
grades into the upper Suwannee Limestone eastward. Due to difficulty in separating
the Chickasawhay from the Lower Miocene limestones in the western panhandle,
both Marsh (1966) and Miller (1986) included thin beds of possible Lower Miocene
carbonate in the upper portion of the Chickasawhay Formation. The permeable
sediments of the Chickasawhay Formation form part of the upper Floridan in the
western panhandle (Wagner, 1982).

Miocene Series

The Miocene Epoch was a time of significant change in the depositional
sequence on the Florida Platform and the adjacent Gulf and Atlantic Coastal Plains.
During the early part of the Miocene, carbonate sediments continued to be
deposited over most of the State. Intermixed with the carbonates were increasing
percentages of siliciclastic sediments. By the end of the Early Miocene, the
deposition of carbonate sediments was occurring only in southern peninsular
Florida. Siliciclastic deposition dominated the Middle Miocene statewide with this
trend continuing into the Late Miocene.

FLORIDA GEOLOGICAL SURVEY

The basal Miocene carbonate sediments often form the uppermost portion of
the Floridan aquifer system. The remainder of the Miocene sediments form much of
the intermediate aquifer system and intermediate confining system. In some
instances, these sediments may also be included in the surficial aquifer system.

Unusual depositional conditions existed during the Miocene as is evident
from the occurrence of abundant phosphate, palygorskite, opaline cherts and other
uncommon minerals plus an abundance of dolomite within the Hawthorn Group
(Scott, 1988a). The presence of these minerals may influence ground-water quality
in areas where the Miocene sediments are being weathered. Ground-water quality
may also be affected where these sediments form the upper portion of the Floridan
aquifer system or portions of the intermediate aquifer system.

Current geologic thought holds that in the peninsula the Miocene section is
composed of the Hawthorn Group. The Tampa Formation is included as a member
in the basal Hawthorn Group. In the panhandle, the Lower Miocene remains the
Chattahoochee and St. Marks Formations, the Middle Miocene Alum Bluff Group
and the Upper Miocene Choctawhatchee Formation and equivalents. Formations
previously mentioned in the literature as being Miocene in age include the Tamiami,
which is Pliocene in age, and the Miccosukee Formation which is now recognized as
being Late Pliocene to possibly early Pleistocene in age.

The Miocene sediments are absent from the Ocala Platform and the Sanford
High (Scott, 1988a). These sediments are as much as 800 feet thick in southwest
Florida (Miller, 1986; Scott, 1988a), 500 feet thick in the northeastern peninsula
(Scott, 1988a) and 900 to 1000 feet thick in the westernmost panhandle (Miller,
1986).

Chattahoochee Formation

The Chattahoochee Formation is predominantly a fine-grained, often
fossiliferous, silty to sandy dolostone which is variable to a limestone (Huddlestun,
1988). Fine-grained sand and silt may also form beds with various admixtures of
dolomite and clay minerals. Clay beds may also be common in some areas (Puri
and Vernon, 1964).

The Chattahoochee Formation occurs in a limited area of the central
panhandle from the axis of the Gulf Trough westward. It appears that the
Chattahoochee grades to the west into a carbonate unit alternately referred to as
Tampa Limestone (Marsh, 1966; Miller, 1986) or St. Marks (Puri and Vernon, 1964).
Northward into Georgia, this unit grades into the basal Hawthorn Group
(Huddlestun, 1988). To the east of the axis of the Gulf Trough, the Chattahoochee
Formation grades into the St. Marks Formation (Puri and Vernon, 1964; Scott,
1986). The gradational change between the Chattahoochee and St. Marks
Formations occurs over a broad area of Leon and Gadsden Counties (Scott, 1986).

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The sediments of the Chattahoochee Formation comprise the upper zone of the
Floridan aquifer system in the central panhandle.

St. Marks Formation

The St. Marks Formation is a fossiliferous limestone (packstone to
wackestone). Sand grains occur scattered in an often very moldic limestone. The
lithology of the St. Marks and associated units in the Apalachicola Embayment to the
west are often difficult to separate (Schmidt, 1984). The St. Marks Formation
lithology can be traced in cores grading into the Chattahoochee Formation (Scott,
1986). This formation forms the upper part of the Floridan aquifer system in portions
of the eastern and central panhandle.

Hawthorn Group

The Hawthorn Group is a complex series of the phosphate-bearing Miocene
sediments in peninsular and eastern panhandle Florida. The carbonate sediments
of the Hawthorn Group are primarily fine-grained and contain varying admixtures of
clay, silt, sand and phosphate. Dolostone is the dominant carbonate sediment type
in the northern two-thirds of the peninsula while limestone predominates in the
southern peninsula and in the eastern panhandle area.

The siliciclastic sediment component consists of fine- to coarse-grained
quartz sand, quartz silt and clay minerals in widely varying proportions. The clay
minerals present include palygorskite, smectite and illite with kaolinite occurring in
the weathered sediments.

The top of the Hawthorn Group is a highly irregular erosional and karstic
surface. This unconformable surface can exhibit dramatic local relief especially in
outcrop along the flanks of the Ocala Platform.

In the peninsula, the Hawthorn Group can be broken into a northern section
and a southern section. The northern section consists of interbedded phosphatic
carbonates and siliciclastics with a trend of increasing siliciclastics in the younger
sediments. In ascending order, the formations in northern Florida are the Penney
Farms, Marks Head and Coosawhatchie and its lateral equivalent Statenville (Scott,
1988a). The sediments comprising these formations characteristically have low
permeabilities and form an effective aquiclude, the intermediate-confining unit. In a
few areas, permeabilities within the Hawthorn sediments are locally high enough to
allow the limited development of an intermediate aquifer system.

The southern section consists of a lower dominantly phosphatic carbonate
section and an upper phosphatic siliciclastic section. In the southern area, in
addition to increasing siliciclastics upsection, there is also a trend of increasing
siliciclastics from west to east in the lower carbonate section. The Hawthorn Group

FLORIDA GEOLOGICAL SURVEY

in southern Florida has been subdivided into, in ascending order, the Arcadia
Formation with the former Tampa Formation as a basal member, and the Peace
River Formation (Scott, 1988a). Throughout much of south Florida, these sediments
have limited or low permeabilities and form an effective intermediate-confining unit.
However, where the Tampa Member is present and permeable enough, it may form
the upper portion of the Floridan aquifer system. In portions of southwestern
Florida, the Hawthorn sediments are permeable enough to form several important
producing zones in the intermediate aquifer system (Knapp et al., 1986; Smith and
Adams, 1988).

The Hawthorn Group, Torreya Formation sediments in the eastern
panhandle are predominantly siliciclastics with limited amounts of carbonates (Scott,
1988a). In this area, carbonates become increasingly important in the Gulf Trough
where the basal Hawthorn sediments are fine-grained carbonates. The siliciclastic
sediments are very clayey and form an effective intermediate confining unit. The
carbonate sediments may locally be permeable enough to form the upper portion of
the Floridan aquifer system.

Bruce Creek Limestone

Huddlestun (1976) applied the name Bruce Creek Limestone to a late Middle
Miocene limestone occurring in the Apalachicola Embayment and coastal areas of
the central and western panhandle. The Bruce Creek Limestone is a fossiliferous,
variably sandy limestone (Schmidt, 1984). This lithology becomes indistinguishable,
to the east, from lithologies found in the St. Marks Formation (Schmidt, 1984). The
Bruce Creek Limestone is laterally equivalent to and grades into the lower portion of
the Alum Bluff Group (Schmidt, 1984). The Bruce Creek Limestone forms part of the
upper Floridan aquifer system in the central and western panhandle.

Alum Bluff Group

The Alum Bluff Group, present in the panhandle includes the Chipola
Formation, Oak Grove Sand, Shoal River Formation and the Choctawhatchee
Formation (Schmidt and Clark, 1980, Braunstein et al., 1988). The formations
included in this group are generally defined on the basis of their molluskan faunas
(Schmidt, 1984) and are of variable area extents. These sediments can be
distinguished as a lithologic entity at the group level and will be referred to as such
in this text.

The Alum Bluff Group consists of clays, sands and shell beds which may vary
from a fossiliferous, sandy clay to a pure sand or clay and occasional carbonate
beds or lenses. The Jackson Bluff Formation is currently thought to be Late Pliocene
in age (Schmidt, 1984) and, even though Huddlestun (1976) included it in the Alum
Bluff Group, it was not included in the Alum Bluff Group on the latest correlation

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charts (Braunstein et al., 1988). Sediments comprising the Jackson Bluff Formation
are very similar to those making up the Alum Bluff Group.

The sediments comprising the Alum Bluff Group are generally impermeable
due to the abundance of clay-sized particles. These sediments form an important
part of the intermediate confining unit in the central panhandle.

Pensacola Clay

The Pensacola Clay consists of three members: lower and upper clay
members and a middle sand member, the Escambia Sand (Marsh, 1966).
Lithologically, the clay members consist of silty, sandy clays with carbonized plant
remains (Marsh, 1966). The sand member is fine to coarse, quartz sand. Marine
fossils are rarely present in the Pensacola Clay with the exception of a fossiliferous
layer near the base (Clark and Schmidt, 1982). The Pensacola Clay grades laterally
into the lower portion of the "Miocene Coarse Clastics" to the north and the Alum
Bluff Group and the lower Intracoastal Formation to the east (Clark and Schmidt,
1982).

The Pensacola Clay forms the intermediate confining unit for the Floridan in
the western panhandle. It lies immediately suprajacent to the limestones of the
upper Floridan aquifer system.

Intracoastal Formation

Schmidt (1984) describes the Intracoastal Formation as a "very sandy, highly
microfossiliferous, poorly consolidated, argillaceous, calcarenitic limestone."
Phosphate is generally present in amounts greater than one percent. This unit is
laterally gradational with the Pensacola Clay and Mio-Pliocene "Coarse Clastics"
(Schmidt, 1984). The lower Intracoastal Formation is Middle Miocene while the
upper portion is Late Pliocene reflecting an intraformational hiatus. Wagner (1982)
indicates that the Intracoastal Formation forms part of the intermediate confining unit
in the central to western panhandle.

Pliocene-Pleistocene Series

The sediments of the Pliocene-Pleistocene Series occur over most of the
State. These sediments range from nonfossiliferous, clean sands to very
fossiliferous, sandy clays and carbonates. Lithologic units comprising this series
include the "Coarse Clastics", Tamiami Formation, Citronelle Formation,
Miccosukee Formation, Cypresshead Formation, Nashua Formation,
Caloosahatchee Formation, Fort Thompson Formation, Key Largo Limestone, Miami
Limestone, Anastasia Formation and Undifferentiated Pleistocene-Holocene
sediments. The upper portion of the Intracoastal Formation is Pliocene and is
discussed with the lower Intracoastal Formation under the Miocene Series. For a

FLORIDA GEOLOGICAL SURVEY

further discussion of the Plio-Pleistocene sediments in southern Florida, see Scott
and Allmon (1992).

"Coarse Clastics"

The name "Coarse Clastics" has been applied to sequences of quartz sands
and gravels in a number of areas around Florida. These sediments are often
referred to in the literature as "Miocene Coarse Clastics" (for example, Puri and
Vernon, 1964).

In northern Florida, these sediments are referred to as the Cypresshead
Formation of Late Pliocene to Early Pleistocene age (Scott, 1988b). In southern
Florida, Knapp et al. (1986) referred to these sediments as the "Miocene Coarse
Clastics" and placed them in the Hawthorn Group. In the panhandle, Marsh (1966)
mentions the "Miocene Coarse Clastics" as sands and gravel with some clay, which
underlie the Citronelle Formation.

In the panhandle, the "Coarse Clastics" are variably clayey sands with gravel
and some shell material (Clark and Schmidt, 1982). These siliciclastics occur in
Escambia, Santa Rosa and western Okaloosa Counties in the western panhandle.
They equate in part to the upper part of the Pensacola Clay, part of the Intracoastal
Formation and part of the Alum Bluff Group.

In southern peninsular Florida, the coarse siliciclastics are fine to very coarse
quartz sands with quartz gravel and variable amounts of clay, carbonate and
phosphate. These sediments may equate with the Cypresshead Formation
sediments in central and northern Florida.

These siliciclastic sediments form important aquifer systems in portions of
southern and panhandle Florida. In the western panhandle, the "Coarse Clastics"
form a portion of the Sand-and-Gravel aquifer, part of the surficial aquifer system.
These sediments also comprise a portion of the surficial aquifer system in the
peninsular area, especially in southern Florida.

Tamiami Formation

The Tamiami Formation consists of the Pinecrest Sand Member, the
Ochopee Limestone Member, and the Buckingham Limestone Member (Hunter,
1968). The various faces of the Tamiami occur over a wide area of southern
Florida. The relationships of the faces are not well known due to first, the
complexes set of depositional environments that were involved in the formation of
the sediments and second, the Tamiami Formation most often occurs as a shallow
subsurface unit throughout much of its extent. Many of the faces are important from
a hydrogeologic perspective in an area of ground-water problems.

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The limestone in the Tamiami Formation occurs as two types: 1- a
moderately to well-indurated, slightly phosphatic, variably sandy, fossiliferous
limestone (Ochopee) and 2- a poorly indurated to unindurated, slightly phosphatic,
variably sandy, fossiliferous limestone (Buckingham). The sand faces is often
composed of a variably phosphatic and sandy, fossiliferous, calcareous, quartz sand
often containing abundant, well-preserved mollusk shells (Pinecrest). The sand
varies from a well-sorted, clean sand with abundant well-preserved shells and traces
of silt-sized phosphate in the type Pinecrest Sand Member (Hunter, 1968) to a
clayey sand with sand-sized phosphate, clay-sized carbonate in the matrix and
abundant, well preserved mollusk shells. Siliciclastic sediments (undifferentiated) of
this age appear to occur along the eastern side of the peninsula but have not been
assigned to the Tamiami Formation.

Sediments of the Tamiami Formation exhibit variable permeabilities and form
the lower Tamiami aquifer and Tamiami confining beds of the surficial aquifer
system (Knapp et al., 1986). Smith and Adams (1988) indicate that the upper
Tamiami sediments form the basal portion of the "water table aquifer" overlying the
Tamiami confining beds.

Citronelle Formation

The Citronelle Formation is composed of fine to very coarse siliciclastics.
The name was extended to include the siliciclastics comprising the central ridge
system in the Florida peninsula by Cooke (1945). As it is currently recognized in
Florida, the Citronelle Formation occurs only in the panhandle. The unit is
recognized from central Gadsden County on the east to the western boundary of the
State. The Citronelle Formation is composed of very fine to very coarse, poorly
sorted, angular to subangular quartz sand. The unit contains significant amounts of
clay, silt and gravel, which may occur as beds, lenses or stringers and may vary
rapidly over short distances. Limonite nodules and limonitic cemented zones are
common.

The Citronelle Formation extends over much of the central and western
panhandle. Previous investigators encountered problems in the separation of the
Citronelle and the overlying terrace deposits and generally considered the thickness
of the Citronelle including these younger sediments (Marsh, 1966; Coe, 1979). The
Citronelle Formation grades laterally into the Miccosukee Formation through a broad
transition zone in Gadsden County. The Citronelle Formation forms an important
part of the Sand-and-Gravel aquifer in the western panhandle and produces up to
2,000 gallons of water per minute (Wagner, 1982).

Miccosukee Formation

Hendry and Yon (1967) describe the Miccosukee Formation as consisting of
interbedded and cross-bedded clay, silt, sand and gravel of varying coarseness and

FLORIDA GEOLOGICAL SURVEY

admixtures. Limonite pebbles are common in the unit. The Miccosukee Formation
occurs in the eastern panhandle from central Gadsden County on the west to
eastern Madison County on the east. Due to its clayey nature, the Miccosukee
Formation does not produce significant amounts of water. It is, however, generally
considered to be part of the surficial aquifer system (Southeastern Geological
Society, 1986).

Cypresshead Formation

The name Cypresshead Formation was first used by Huddlestun (1988). It
was extended into Florida by Scott (1988b). The Cypresshead Formation is
composed entirely of siliciclastics; predominantly quartz and clay minerals. The unit
is characteristically a mottled, fine- to coarse-grained, often gravelly, variably clayey
quartz sand. As a result of weathering, the clay component of these sediments has
characteristically been altered to kaolinite. Clay serves as a binding matrix for the
sands and gravels. Clay content may vary from absent to more than fifty percent in
sandy clay lithologies although the average clay content is 10 to 20 percent. These
sediments are often thinly bedded with zones of cross bedding. The Cypresshead
Formation appears to occur in the Central Highlands of the peninsula south to
northern Highlands County, although the extent of the Cypresshead Formation has
not been accurately mapped in this area. This unit may locally comprise the surficial
aquifer system where clay content is low.

Nashua Formation

The Nashua is a fossiliferous, variably calcareous, sometimes clayey, quartz
sand. The fossil content is variable from a shelly sand to a shell hash. The
dominant fossils are mollusks. The extent of the Nashua in northern Florida is not
currently known. It extends some distance into Georgia and appears to grade
laterally into the Cypresshead Formation (Huddlestun, 1988). The Nashua
Formation may produce limited amounts of water in localized areas where it forms
part of the surficial aquifer system.

Caloosahatchee Formation

The Caloosahatchee Formation consists of fossiliferous quartz sand with
variable amounts of carbonate matrix interbedded with variably sandy, shelly
limestones. The sediments vary from nonindurated to well indurated. The fauna
associated with these sediments are varied and often well preserved. Fresh water
limestones are commonly present within this unit.

Sediments identified as part of the Caloosahatchee Formation by various
investigators occur from north of Tampa on the west coast south to Lee County,
eastward to the East Coast then northward into northern Florida (DuBar, 1974). The

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Caloosahatchee Formation as used here includes those sediments informally
referred to as the Bermont formation (Dubar, 1974).

In most hydrogeologic investigations of southern Florida, the Caloosahatchee
Formation is not differentiated from the Fort Thompson Formation and other faunal
units. The undifferentiated sediments form much of the surficial aquifer system.

Fort Thompson Formation

The Fort Thompson Formation consists of interbedded shell beds and
limestones. The shell beds are characteristically variably sandy and slightly
indurated to unindurated. The sandy limestones present in the Fort Thompson
Formation were deposited under both freshwater and marine conditions. The sand
present in these sediments is fine- to medium-grained. The sediments of Fort
Thompson age in central Florida along the East Coast consist of fine to medium
quartz sand with abundant mollusk shells and a minor but variable clay content.

The Fort Thompson Formation, as the Caloosahatchee Formation, is part of
the undifferentiated sediments in southern Florida. It forms a portion of the surficial
aquifer system.

Key Largo Limestone

The Key Largo Limestone is a coralline limestone composed of coral heads
encased in a matrix of calcarenite (Stanley, 1966). Hoffmeister and Multer (1968)
indicate that the Key Largo Limestone occurs in the subsurface from as far north as
S Miami Beach to as far south as the Lower Keys. The fossil reef tract represented by
the Key Largo sediments may be as much as 8 miles wide (DuBar, 1974). Near the
northern and southern limits of the Key Largo Limestone, it is overlain conformably
by the Miami Limestone with which the Key Largo is, in part, laterally equivalent.

The Key Largo Limestone forms a part of the Biscayne aquifer of the surficial
aquifer system. The Biscayne aquifer provides water for areas of Dade, Broward
and Monroe Counties.

Miami Limestone

The Miami Limestone includes an oolitic faces and a bryozoan faces. The
bryozoan faces underlies and extends west of the western boundary of the oolitic
faces. The bryozoan faces consists of calcareous bryozoan colonies imbedded in
a matrix of ooids, pellets and skeletal sand. It generally occurs as a variably sandy,
recrystallized, fossiliferous limestone (Hoffmeister et al., 1967). The oolitic faces
consists of variably sandy limestone composed primarily of oolites with scattered
concentrations of fossils.

FLORIDA GEOLOGICAL SURVEY

Hoffmeister et al. (1967) indicate that the Miami Limestone covers Dade
County, much of Monroe County and the southern part of Broward County. It grades
laterally to the south into the Key Largo Limestone and to the north into the
Anastasia Formation. The oolitic faces underlies the Atlantic Coastal Ridge
southward from southern Palm Beach County to southern Dade County.

The Miami Limestone forms a portion of the Biscayne aquifer of the surficial
aquifer system. It is very porous and permeable due to the dissolution of carbonate
by ground water as it recharges the aquifer system.

Anastasia Formation

The Anastasia Formation consists of interbedded quartz sands and
coquinoid limestones. The sand beds consist of fine to medium-grained, variably
fossiliferous, calcareous, quartz sand. The contained fossils are primarily broken
and abraded mollusk shells. The limestone beds, commonly called coquina, are
composed of shell fragments, scattered whole shells and quartz sand enclosed in a
calcareous matrix, usually sparry calcite cement.

The Anastasia Formation forms the Atlantic Coastal Ridge through most of its
length (White, 1970). Natural exposures of this unit occur scattered along the East
Coast from St. Augustine south to southern Palm Beach County near Boca Raton.
South of this area the Anastasia Formation grades into the Miami Limestone. Cooke
(1945) felt that the Anastasia Formation extended no more than three miles inland
from the Intracoastal Waterway. Field work by this author (Scott) suggests that the
Anastasia may extend as much as 10 miles inland; although, Schroeder (1954)
suggest that this unit may occur more than 20 miles inland.

The Anastasia Formation forms a portion of the surficial aquifer system along
the eastern coast of the State. Ground water is withdrawn from the Anastasia
Formation in many areas along the Atlantic Coastal Ridge where, locally, it may be
the major source of ground water. Near the southern extent of the Anastasia
Formation, it forms a portion of the Biscayne aquifer (Hoffmeister, 1974).

Undifferentiated Pleistocene-Holocene Sediments

The sediments referred to as the "undifferentiated Pleistocene-Holocene
sediments" cover much of Florida effectively hiding most older sediments. Included
in this category are marine "terrace" sediments, eolian sand dunes, fluvial deposits,
fresh water carbonates, peats and a wide variety of sediment mixtures. These
sediments often occur as thin layers overlying older formations and are not definable
as formations. As such, these sediments have been referred to by many different
names including Pliocene to Recent sands, Pleistocene sands, Pleistocene Terrace
Deposits.

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The sediments incorporated in this category are most often quartz sands.
The sands range from fine- to coarse-grained, nonindurated to poorly indurated and
nonclayey to slightly clayey. Gravel may be present in these sediments in the
panhandle area. Other sediments included in this group include peat deposits,
some clay beds, and freshwater carbonates. The freshwater carbonates occur in
many freshwater springs and in large areas of the Everglades.

Locally, these sediments may form a portion of the surficial aquifer system.
The greatest thicknesses of these sediments occurs infilling paleokarst features
where more than 300 feet of undifferentiated Pleistocene-Holocene sediments have
been recorded (Florida Geological Survey, unpublished well data).

Hydrostratigraphy

Florida's ground-water resources occur in a complex lateral and vertical
sequence of Cenozoic sediments comprised of both siliciclastics and carbonates,
which underlie the entire state. Hydrostratigraphically, the section consists of
several major aquifer systems defined on lateral extent, degree of confinement, and
hydrologic parameters of the sediments. The Southeastern Geological Society's ad
hoc Committee on Florida Hydrostratigraphic Unit Definition (Southeastern
Geological Society (SEGS), 1986), in an attempt to alleviate many of the
nomenclatural problems surrounding Florida's hydrostratigraphic units, defined the
framework of the various aquifer systems occurring in the state. Most of the
geologic community have accepted these definitions and are using the suggested
nomenclature. Aquifers of lesser importance have been recognized in some areas
of the state and are discussed in the literature on specific areas. This text will define
S and characterize only the major aquifer systems discussed by the SEGS (1986).
These systems include the surficial aquifer system, the intermediate aquifer system
or intermediate confining unit, and the Floridan aquifer system including the
Claibome aquifer and the sub-Floridan confining unit. Figure 1 indicates which
formations form portions of the various aquifer systems throughout the state. Miller
(1986) provides an excellent, in-depth discussion of the Floridan aquifer system and
the associated shallower strata. It is recommended that the reader review Miller's
volume for a more detailed description of the ground-water system in Florida.

Geologic Structures in Relation to Hydrostratigraphy

The occurrence, thickness and, to some extent, the aquifer characteristics
are directly related to the structural features present in a given area. The major
positive features affecting the various aquifer systems include the Ocala Platform,
Chattahoochee Anticline, Sanford High and the St. Johns and Brevard Platforms
(Figure 2). The major negative features include the Gulf Basin, Apalachicola
Embayment, Gulf Trough, Jacksonville Basin, Osceola Low and the Okeechobee
Basin (Figure 2). These structures affected the deposition and erosion of the later

FLORIDA GEOLOGICAL SURVEY

Cenozoic sediments. Older structures, including the Peninsular Arch and the South
Florida Basin (Figure 2) affected the lower portions of the Cenozoic section.

The surficial aquifer system is thin to absent on the positive features. Its
thickness increases off the positive structures reaching maximum thicknesses in the
Okeechobee, Jacksonville and Gulf Basins and the Apalachicola Embayment.

The intermediate aquifer system and intermediate confining unit also thin
onto the positive features. Sediments forming these units are erosionally absent
from the Chattahoochee Anticline, Ocala Platform and the Sanford High. These
units thicken off the highs, reaching the maximum thicknesses in the basinal areas.
As the sediments of the intermediate aquifer system and confining unit thicken,
permeable beds become more commonly interbedded with the impermeable strata,
resulting in a more fully developed intermediate aquifer system.

Eocene and Oligocene carbonate sediments of the Floridan aquifer system
are exposed to thinly covered on the Ocala Platform and the Chattahoochee
Anticline. These sediments are covered by a thin intermediate-confining unit on the
flanks of the positive features. In these areas, the carbonates have been exposed to
aggressive ground water developing an extensive karstic terrain. In the basinal
areas, the carbonate sediments have not undergone such extensive dissolution due
to the thick protective cover provided by the intermediate aquifer system and
intermediate-confining unit.

Aquifer Systems and Confining Units
Surficial aquifer system

The SEGS (1986) defines the surficial aquifer system as the "permeable
hydrologic unit contiguous with the land surface that is comprised principally of
unconsolidated to poorly indurated, (silici) plastic deposits. It also includes well-
indurated carbonate rocks, other than those of the Floridan aquifer system where
the Floridan is at or near land surface. Rocks making up the surficial aquifer
system belong to all or part of the Upper Miocene to Holocene Series. It contains
the water table, and the water within it is under mainly unconfined conditions; but
beds of low permeability may cause semi-confined or locally confined conditions to
prevail in its deeper parts. The lower limit of the surficial aquifer system coincides
with the top of the laterally extensive and vertically persistent beds of much lower
permeability."

The surficial aquifer system occurs throughout most of the state. In many
areas, it is used for small yield domestic and agricultural water supplies. However,
in the western panhandle the surficial aquifer system, referred to as the Sand and
Gravel Aquifer, supplies important amounts of water for municipal and industrial
supplies. In the southeastern part of the state, the surficial aquifer system is called
the Biscayne Aquifer and provides enormous quantities of water for the coastal

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communities in this area. Elsewhere in the state, the surficial aquifer system is of
limited importance. Throughout the extent of the surficial aquifer system, the
thickness varies significantly from a feather edge to more than 350 feet in
southeastern Florida and 500 feet in the western-most panhandle (Scott et al.,
1991). The top of the surficial aquifer system is the natural land surface. The base
occurs where impermeable beds of the intermediate confining unit and aquifer
system begin or, in those areas where the intermediate is absent, at the top of the
Floridan aquifer system carbonates.

In many areas of the state, the surficial aquifer system lies on a karstified
erosional surface developed on Eocene to Miocene carbonates. Karst processes
have also affected the surficial aquifer system by forming collapse features, which
filled with surficial aquifer system sediments and may be in direct hydrologic contact
with the Floridan aquifer system. Karst features also perforate the surficial aquifer
system developing open sinkholes on the present land surface.

Northwest Florida Water Management District

The surficial aquifer system in the Northwest Florida Water Management
District (NWFWMD) occurs over most of the district. It is absent only in a limited
portion of Wakulla, Leon and Jefferson Counties at the eastern edge of the district
along the western flank of the Ocala Platform. It is thin to absent on part of the
Chattahoochee Anticline in Jackson and Holmes Counties. Where the surficial is
present it ranges in thickness from less than 10 feet in the east to more than 500
feet in the northwestern corer of the area (Scott et al., 1991).

The siliciclastic sediments comprising the surficial aquifer system in the
NWFWMD are part of the Citronelle and Miccosukee Formations, "Coarse Clastics"
and the undifferentiated sediments of Pleistocene-Holocene age (Marsh, 1966;
Scott, 1991). These sediments are primarily quartz sands with varying percentages
of clay. Where the clay content becomes great enough to inhibit the transmission of
ground water, localized impermeable beds may confine water creating artesian
conditions within the surficial aquifer system. The surficial aquifer system yields
greater quantities of water in the western panhandle where the Citronelle contains
less clay and is thicker than in those areas where the clayey Miccosukee occurs.

Suwannee River Water Management District

The surficial aquifer system in the Suwannee River Water Management
District (SRWMD) is present in several areas of the district. According to Ceryak
(SRWMD, personal communication, 1991), the surficial aquifer system is present in
adjoining portions of southern Madison, northeastern Taylor and northwestern
Lafayette Counties, western Hamilton County, eastern Suwannee County, much of
Columbia and Union Counties, along the eastern edge of Bradford County under
Trail Ridge and under Waccassassa Flats in central Gilchrist County. Sediments

FLORIDA GEOLOGICAL SURVEY

equivalent to the surficial aquifer system are present throughout much of the district
but are not utilized for water resources. Thicknesses of the surficial aquifer system
range from 10 to 30 feet but may reach 50 to 60 feet under Trail Ridge. The surficial
aquifer system sediments in SRWMD are part of the undifferentiated sediments.
The upper Hawthorn Group sediments may form the basal part of the system in the
eastern-most portions of the district. These sediments are quartz sands with varying
amounts of clay and carbonate. In localized areas the clay content of the sediments
may form confining beds within the surficial system.

The base of the surficial aquifer system in the SRWMD occurs at the top of
the impermeable sediments of the Hawthorn Group throughout much of the district.
However, in the eastern portion of the district, the base may occur within the
sediments of the upper Hawthorn Group. In other areas, the intermediate confining
unit may be absent and the surficial aquifer system may lie directly on the
carbonates of the Floridan aquifer system.

St. Johns River Water Management District

The surficial aquifer system in the St. Johns River Water Management
District (SJRWMD) is an important source of potable water in Duval and Clay
Counties and portions of Alachua and Putnam Counties. The coastal counties
utilize the surficial to varying degrees with Brevard County being a major user.
Eastern Orange County also utilizes the surficial aquifer system. In other areas of
the district, the surficial aquifer system may be used for limited domestic supplies.
The surficial aquifer system thickness is highly variable, ranging from a few feet to in
excess of 200 feet. The thickest sequence occurs in the Duval County area in the
Jacksonville Basin, where the upper part of the Hawthorn Group (Coosawhatchie
Formation) forms the base of the surficial aquifer system.

Sediments forming the surficial aquifer system in SJRWMD are
lithostratigraphically assigned to the undifferentiated sediments, Cypresshead and
Nashua Formations, Caloosahatchee Formation-equivalent shell beds and the
Coosawhatchie Formation of the Hawthorn Group. The undifferentiated sediments
and the Cypresshead Formation consist of quartz sands with varying percentages of
clay. The Nashua Formation and Caloosahatchee Formation-equivalent beds are
composed of varying admixtures of quartz sand, clay, shells and shell debris.
Quartz sands and varying amounts of clay make up the Coosawhatchie Formation
with limestone becoming prominent in portions of Duval and Nassau Counties.
Locally, the sediments contain sufficient clay to form impermeable beds creating
artesian conditions in the surficial aquifer system.

The base of the surficial aquifer system in the SJRWMD occurs at the top of
the Hawthorn Group when those sediments are relatively impermeable. Where the
Hawthorn (Coosawhatchie Formation) sediments are sufficiently permeable, the
base of the surficial occurs within these sediments. In the area where the Hawthorn

SPECIAL PUBLICATION NO. 44

Group is absent, the surficial aquifer system may extend down to the top of the
Floridan aquifer system, as is the case in much of Volusia County.

Southwest Florida Water Management District

The surficial aquifer system occurs over much of the Southwest Florida
Water Management District (SWFWMD). It is of generally limited value in the
northern portions of the district and increases in importance to the south.
SWFWMD data indicates that the surficial aquifer system is thin over much of the
district (Scott et al., 1991). Thicknesses range from less than 25 feet in much of the
northern part of the district on the Ocala Platform to 25 to 50 feet in the southern
area and more than 250 feet under the Lake Wales Ridge.

Surficial aquifer system sediments in SWFWMD belong to the
undifferentiated sediments in the northern half of the district. In the southern half of
SWFWMD the sediments include the Tamiami, Caloosahatchee and Fort
Thompson Formations. Along the Lake Wales Ridge, the surficial aquifer system is
comprised of sediments belonging to the Cypresshead Formation and the
undifferentiated sediments. In a limited area in central SWFWMD, the Bone Valley
Member of the Peace River Formation, Hawthorn Group forms part of the surficial
aquifer system. The sediments in these units generally consist of quartz sand with
varying percentages of clay and shell except in the Bone Valley Member where
phosphate forms a significant proportion of the sediment. Vacher et al. (1990)
characterizes the sediments as quartz sand with less than 10 percent clay over
much of the district. They also show shell content of the surficial aquifer system
increasing toward the coast and to the south in the southern half of the district.

The base of the surficial aquifer system occurs at the top of the impermeable
sediments overlying the carbonates of the Floridan aquifer system in the northern
part of the district. When impermeable sediments of the Hawthorn Group are
subjacent to the undifferentiated sediments they form the base of the surficial. The
Hawthorn Group lies subjacent to the Cypresshead Formation under the Lake
Wales Ridge and forms the base of the system. The Hawthorn Group sediments
also form the base of the surficial aquifer system in southern SWFWMD where the
Hawthorn underlies the Tamiami, Caloosahatchee and Fort Thompson Formations.

South Florida Water Management District

The surficial aquifer system is widespread in the South Florida Water
Management District (SFWMD) constituting an important water resource. Although
the surficial aquifer system is present over much of the district, it is the most
important source of ground water in the southeastern portion of SFWMD, in Dade,
Broward and Palm Beach Counties. In Lee, Hendry and Collier Counties, the
surficial provides significant quantities of potable water for domestic and agricultural

FLORIDA GEOLOGICAL SURVEY

uses. Throughout the district, the surficial aquifer system varies in thickness from a
few feet to more than 400 feet thick.

The sediments comprising the surficial aquifer system are from several
lithostratigraphic units. In the north central SFWMD area, the surficial occurs in the
undifferentiated sediments, Cypresshead Formation and shell beds of the
Caloosahatachee / Fort Thompson Formations. In the western part of SFWMD,
sediments of the Tamiami, Caloosahatchee and Fort Thompson Formations and the
undifferentiated sediments make up the system. In the eastern area of SFWMD, the
surficial aquifer system, in part referred to as the Biscayne Aquifer, consists of
sediments from the Anastasia Formation, Miami and Key Largo Limestones, Fort
Thompson Formation, and Caloosahatchee and Tamiami-equivalent sediments. In
SFWMD, the base of the surficial system occurs at the first impermeable sediments
in the Hawthorn Group. Occasionally, the upper Hawthorn Group sediments may
form the basal portion of the surficial.

The lithostratigraphic units forming the surficial aquifer system consist of a
complex array of facies. The sediments range from quartz sands to limestones with
varying admixtures of shell and clay. As a result of the variability, the quality of the
surficial aquifer system in SFWMD changes dramatically from place to place.
Numerous investigations of these sediments have discussed the variable nature of
the aquifer characteristics (for example, Causaras, 1985; Wedderburn et al., 1982;
Shaw and Trost, 1984; Knapp et al., 1986; Smith and Adams, 1988).

Intermediate Aquifer System and Intermediate Confining Unit

The SEGS (1986) defines the intermediate aquifer system or intermediate
confining system as including "all rocks that lie between and collectively retard the
exchange of water between the overlying surficial aquifer system and the underlying
Floridan aquifer system. These rocks in general consist of fine grained (silici) plastic
deposits interlayered with carbonate strata belonging to all or parts of the Miocene
and younger Series. In places poorly-yielding to non-water-yielding strata mainly
occur and there the term intermediate confining unit applies. In other places, one or
more low to moderate-yielding aquifers may be interlayered with relatively
impermeable confining beds; there the term intermediate aquifer system applies.
The aquifers within this system contain water under confined conditions." 'The top
of the intermediate aquifer system or intermediate confining unit coincides with the
base of the surficial aquifer system. The base of the intermediate aquifer is at the
top of the vertically persistent permeable carbonate section that comprises the
Floridan aquifer system, or, in other words, that place in the section where (silici)
plastic layers of significant thickness are absent and permeable carbonate rocks are
dominant."

The intermediate aquifer system or intermediate confining unit occurs over
much of the state. It is absent from those areas where it was removed by erosion

SPECIAL PUBLICATION NO. 44

and the surficial aquifer system sediments, if present, lie immediately suprajacent to
the carbonates of the Floridan aquifer system. Springs are a common feature of
these areas. Surrounding the areas where these sediments are missing, the
intermediate aquifer system or intermediate confining unit is often perforated by
karst features. Where this condition exists, the intermediate aquifer system and the
intermediate confining unit allows water to pass through into the Floridan aquifer
system or into the surficial aquifer system.

The regional significance of the intermediate aquifer system is quite limited.
Statewide, this section is referred to as the intermediate-confining unit. It serves to
confine the Floridan aquifer system and forms the base of the surficial aquifer
system. The sediments comprising this section is predominantly siliciclastic (quartz
sand, silt and clay) with varying proportions of carbonates (limestone and dolostone)
present. Much of the intermediate confining unit was deposited during the Miocene
and Early Pliocene. It is interesting to note that in some areas Miller (1986) has
included low permeability Oligocene and Eocene carbonates in contact with the
Miocene sediments as part of the intermediate confining unit.

The top of the intermediate aquifer system or intermediate confining unit
ranges from more than 350 feet below sea level to greater than 225 feet above sea
level. Miller (1986) cites thicknesses of the intermediate confining unit (his upper
confining unit) ranging from very thin or absent too greater than 1000 feet.

Northwest Florida Water Management District

The intermediate confining unit occurs over much of the NWFWMD serving
to effectively confine the Floridan aquifer system. It is thin to absent over the
Chattahoochee Anticline in portions of Jackson and Holmes Counties. The
intermediate confining unit is also thin to absent in eastern Wakulla, southeastern
Leon and southern Jefferson Counties. The intermediate confining unit thickens
dramatically under the western end of NWFWMD in Escambia County and in the
Apalachicola Embayment under Gulf and Franklin Counties (Clark and Schmidt,
1982; Schmidt and Clark, 1980; Schmidt, 1984). Thicknesses range from less than
10 feet too greater than 1000 feet.

The ability of the intermediate confining unit to effectively confine the
subjacent Floridan aquifer system is impaired in those areas where it has been
breached by karst development. These areas include portions of Jackson, Holmes,
Washington, Walton, Leon and Wakulla Counties (Sinclair and Stewart, 1985).

Siliciclastic sediments predominate in the intermediate confining unit in
NWFWMD. Carbonate sediments are present in the sediments of the Apalachicola
Embayment and east of the Apalachicola River. In western NWFWMD, the
confining unit is the Pensacola Clay, which grades eastward into the Alum Bluff
Group. Further east, generally east of the Apalachicola River, the Hawthorn Group

FLORIDA GEOLOGICAL SURVEY

forms the intermediate confining unit. Within the Apalachicola Embayment, portions
of the Intracoastal Formation form the intermediate confining unit.

The intermediate aquifer system is generally not an important water-bearing
unit in NWFWMD. Permeable beds of limited extent are present locally and may
provide limited amounts of water too small, domestic wells. The intermediate aquifer
system/confining unit acts as an aquifer system primarily east of the
Choctawhatchee River (Wagner, 1988). The permeable zones utilized for ground
water are siliciclastic and carbonate beds in the Intracoastal Formation (Barr and
Wagner, 1981), the Alum Bluff Group and, to a very limited extent, the Hawthorn
Group.

Suwannee River Water Management District

The intermediate confining unit is present in SRWMD under the Northern
Highlands. This includes portions or all of Jefferson, Madison, Taylor, Lafayette,
Hamilton, Suwannee, Columbia, Baker, Bradford, Union and Alachua Counties.
Within this area, the thickness of the intermediate confining unit may exceed 300
feet (Scott, 1988a) and confined to semiconfined conditions exist. It is thin to absent
on the Ocala Platform and thickens on its flanks reaching the greatest thickness in
the Jacksonville Basin. Karst features are common throughout this area except in
the northeastern part of SRWMD (parts of Baker, Bradford and Union Counties).
Outliers and sinkhole fill consisting of the sediments of the intermediate confining
units are common in the areas where the unit is absent.

Siliciclastic sediments dominate the intermediate confining unit in SRWMD.
These sediments most often are part of the Hawthorn Group or materials that are
residual from it ("Alachua Formation").

The intermediate aquifer system is interbedded with the impermeable beds of
the intermediate confining unit. The intermediate aquifer system is developed in the
sands and carbonates of the Hawthorn Group and attains a thickness of at least 234
feet in the northeastern portion of the district (Ceryak et al., 1983).

St. Johns River Water Management District

The intermediate confining unit and intermediate aquifer system occur
throughout the SJRWMD except along the western district boundary in parts of
Marion and Alachua Counties on the Ocala Platform. The combined confining unit
and aquifer system ranges in thickness from less than ten feet to more than 500
feet. It is thickest in the Jacksonville Basin in northeastern SJRWMD. It thins over
the St. Johns Platform, Sanford High and Brevard Platform in the central portion of
the district then thickens into the Osceola Low and the Okeechobee Basin in
southern SJRWMD.

SPECIAL PUBLICATION NO. 44

The intermediate confining unit and intermediate aquifer system consist
primarily of interbedded siliciclastic and carbonate sediments of the Hawthorn
Group. Additionally, Plio-Pleistocene siliciclastic sediments suprajacent to the
Hawthorn Group may act as part or, in the areas where the Hawthorn sediments are
absent, the entire intermediate confining unit. The Hawthorn Group sediments are
absent over much of the Sanford High and limited portions of the St. Johns and
Brevard Platforms in southern Flagler County, much of Volusia County and northern
Brevard County.

Karst conduits breaching the intermediate aquifer system and intermediate-
confining unit are common in much of the SJRWMD. Sinclair and Stewart (1985)
indicate that the karst features are most abundant in parts of Clay, Putnam, Alachua,
St. Johns, Flagler, Marion, Volusia, Lake, Seminole, Orange, Osceola and Polk
Counties. Small karst features are present in portions or all of Volusia, Seminole,
Orange, Brevard, Osceola and Indian River Counties. In Baker, Nassau, Duval and
parts of Clay and St. Johns Counties karst features are very few in number and the
intermediate confining unit is not often breached.

The intermediate aquifer system is utilized for limited domestic and
agricultural supplies. Permeable strata in the Hawthorn Group often exhibits rapid
lateral and vertical variability resulting in a limited areal distribution of the water-
producing units. The intermediate aquifer system is most often utilized in Nassau,
Duval, Baker, St. Johns and Clay Counties where the Hawthorn Group sediments
are thickest, infilling the Jacksonville Basin.

Southwest Florida Water Management District

The intermediate confining unit and intermediate aquifer system are present
throughout most of SWFWMD (Buono et al., 1979). Although the sediments
comprising this section are absent to very thin in the northern half of SWFWMD,
they thicken to more than 650 feet in the southern end of the district (Buono et al.,
1979; Scott, 1988a). In the northern half of the district, the section is generally the
intermediate confining unit and is thin to absent on the southern end of the Ocala
Platform. In the southern half of SWFWMD, approximately from northern Polk and
Hillsborough Counties south, the intermediate confining unit also contains
permeable sediments forming the intermediate aquifer system. In this area, the
sediments thicken to the south into the Okeechobee Basin (Buono et al., 1979;
Scott, 1988a).

Siliciclastic and carbonate sediments of the Hawthorn Group comprise the
majority of the intermediate confining unit and intermediate aquifer system in
SWFWMD. In addition, some post-Hawthorn siliciclastics may form a limited portion
of the intermediate confining unit in the northern half of the district. In the northern
portion of the district, clayey sediments lying on the Floridan aquifer system

FLORIDA GEOLOGICAL SURVEY

carbonates belong in part in the Hawthorn Group and in part may be reworked
Hawthorn sediments along with residuum from dissolution of carbonates.

Breaching of the intermediate confining unit and the intermediate aquifer
system by karst features is common in the northern half of the district and along the
Lake Wales Ridge in Polk County (Sinclair and Stewart, 1985). The southern
portion of SWFWMD has limited karst development (Sinclair and Stewart, 1985) and
few karst conduits penetrate the intermediate confining unit and intermediate aquifer
system.

The intermediate aquifer system is utilized in the southern half of SWFWMD
and becomes most important at the southern end of the district where the Floridan
aquifer system is deeply buried and highly mineralized. The permeable strata of the
Hawthorn Group and portions of the Tamiami Formation form the water-producing
horizons providing variable quantities of ground water (Sutcliffe, 1975).

South Florida Water Management District

The intermediate confining unit and the intermediate aquifer system occur
throughout SFWMD. However, the intermediate aquifer system is utilized in a
limited number of counties along the western edge of the district. This section
ranges in thickness from approximately 500 feet in the northern SFWMD area to
more than 900 feet in the southernmost portion of the district (Scott, 1988a). Much
of the SFWMD area lies in the Okeechobee Basin.

Interbedded siliciclastic and carbonate sediments from the Hawthorn Group
form the intermediate confining unit and intermediate aquifer system in SFWMD.
Previously, some of the sediments currently included in the intermediate confining
unit and intermediate aquifer system along the west coast were placed in the
Tamiami Formation but are now considered part of the Hawthorn Group (Missimer,
1978; Wedderburn et al., 1982; Scott,1988a). In the eastern part of the district,
Tamiami-equivalent sediments may form the top of the intermediate confining unit
(Causaras, 1985).

The importance of the intermediate confining unit and intermediate aquifer
system in the western part of SFWMD has led to a number of studies in Charlotte,
Lee, Hendry and Collier Counties (Sutcliffe, 1975; Wedderburn et al., 1982; Knapp
et al., 1986; Smith and Adams, 1988;). There are three principle producing zones
within the intermediate aquifer system in this area, the "Sandstone aquifer" named
by Boggess and Missimer (1975), the "mid-Hawthor aquifer" of Wedderburn et al.
(1982) and the "lower-Hawthorn aquifer" of Knapp et al. (1984). These producing
zones have been very important to the development of southwestern Florida.

SPECIAL PUBLICATION NO. 44

Floridan Aquifer System

The SEGS (1986) defines the Floridan aquifer system as a "thick carbonate
sequence which includes all or part of the Paleocene to Early [sic] Miocene Series
and functions regionally as a water-yielding hydraulic unit. Where overlain by either
the intermediate aquifer system or the intermediate confining unit, the Floridan
contains water under confined conditions. Where overlain directly by the surficial
aquifer system, the Floridan may or may not contain water under confined
conditions..." 'The top of the aquifer system 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. For the most part, the top of the
aquifer system coincides with the top of the Suwannee Limestone, where present, or
the top of the Ocala Group (Limestone)."

In limited areas the Avon Park Formation forms the top of the aquifer system.
Sediments of the Arcadia Formation (Hawthorn Group), the Bruce Creek Limestone,
the St. Marks Formation or the Tampa Member of the Arcadia Formation may form
the top of the Floridan aquifer system (SEGS, 1986). The base of the aquifer
system in panhandle Florida is at the gradational contact with the fine-grained (silici)
plastic rocks belonging to the Middle Eocene Series. In peninsular Florida, the base
coincides with the appearance of the regionally persistent sequence of anhydrite
beds that lies near the top of the Cedar Keys Limestone (Formation) (SEGS, 1986)."

The Floridan aquifer system exhibits extreme variations in permeability
resulting from a combination of original depositional conditions, diagenesis,
structural features and dissolution of carbonates and evaporites (Miller, 1986). The
system has been extensively altered by karst processes in some areas of the state.
Dissolutional and diagenetic processes have been extremely important in the
development of the Floridan aquifer system from carbonate sediments deposited
during the Paleocene through Early Miocene.

The thickness and lithology of the sediments suprajacent to the Floridan
determine the surficial expression of the karst processes. On the Ocala Platform
from Hillsborough and Polk Counties north to the state line, then westward into Leon
and Wakulla Counties and on the Chattahoochee Anticline in Jackson and
Washington Counties, carbonate sediments of the Floridan aquifer system crop out
or are covered by a thin layer of unconsolidated siliciclastics (Sinclair and Stewart,
1985). In these areas, the carbonates have been exposed to extensive dissolution
by aggressive ground waters percolating downward from land surface. Often the
karst geomorphology has reached a relatively mature stage of development
resulting in numerous surface depressions, which often coalesce. The Floridan
aquifer system exhibits well developed cavernous porosity and conduit flow paths.
Most of Florida's major springs occur in this zone including Wakulla and Silver
Springs.

FLORIDA GEOLOGICAL SURVEY

The carbonates of the Floridan aquifer system lie beneath a variable
thickness of post-Floridan siliciclastics and carbonates of the intermediate confining
unit, intermediate aquifer system and the surficial aquifer system on the flanks of the
Ocala Platform and the Chattahoochee Anticline. Although karst processes have
affected the sediments of the Floridan in these areas, forming dissolutional conduits
and caverns, the karst topography is not as well developed as in the areas of thin
cover. However, in these areas the karst features are often of large diameter and
depth due to overburden thickness (Sinclair and Stewart, 1985).

The Floridan aquifer system lies subjacent to a thick sequence of post-
Floridan sediments in the Okeechobee Basin, Jacksonville Basin, Gulf Trough,
Apalachicola Embayment and the Gulf Basin of the western panhandle. In these
areas, the carbonates of the Floridan have apparently not been subjected to
extensive karstification. However, subsurface investigations of the limestones
indicate some karstic modification of the sediments during subaerial exposure prior
to the deposition of the sediments of the intermediate confining unit and intermediate
aquifer system (U. Hamms and D. Budd, University of Colorado, personal
communication, 1991).

The elevation of the top of the Floridan aquifer system varies significantly
throughout the state. The top occurs at elevations in excess of 100 feet above
National Geodetic Vertical Datum (NGVD) on the Ocala Platform and
Chattahoochee Anticline to depths greater than 1100 feet below NGVD in southern
Florida and 1500 feet below NGVD in the western-most panhandle (Miller, 1986).
The thickness of the Floridan varies from less than 100 feet in the western half of the
panhandle to in excess of 3500 feet in southwestern peninsular Florida (Miller,
1986).

The base of the Floridan aquifer system, the sub-Floridan confining unit,
varies stratigraphically throughout the state. The SEGS (1986) indicates that the
base of the Floridan in the panhandle occurs in the Middle Eocene approximately at
the top of the Claiborne Group. The base of the system in the peninsula generally is
considered to occur within or near the top of the Paleocene Cedar Keys Formation
(SEGS, 1986). Miller (1986) provides a more detailed picture of the variability of the
stratigraphic positioning of the Floridan aquifer system base but indicates the same
general regional trends.

Northwest Florida Water Management District

The Floridan aquifer system in NWFWMD supplies more than 90 percent of
the water demand and is utilized in all the counties in the district except Escambia
and part of Santa Rosa Counties (Wagner, 1988). It underlies the entire district but
is too saline for potable water in the western end of the panhandle. The water
quality over a broad area corresponding to the Apalachicola Embayment and the

SPECIAL PUBLICATION NO. 44

Gulf Trough and the coastal zone may be affected by the upcoming of mineralized
waters (Scott et al., 1991).

The top of the Floridan aquifer system in NWFWMD varies in elevation from
150 feet above NGVD in Jackson and Holmes Counties to greater than 1500 feet
below NGVD in Escambia County (Schmidt and Coe, 1978; Miller, 1986; Scott et al.,
1991). The thickness of the aquifer system ranges from approximately 100 feet thick
in portions of Jackson and Holmes Counties on the Chattahoochee Anticline to more
than 2800 feet thick in Franklin County in the Apalachicola Embayment (Scott et al.,
1991).

In the western part of the district, the Floridan aquifer system is subdivided
into an upper and lower aquifer separated by a confining unit, the Bucatunna Clay.
The confining unit thins and pinches out towards the east in Okaloosa County,
where the Floridan becomes a single aquifer system (Marsh, 1966; Scott et al.,
1991).

Carbonate sediments dominate the Floridan aquifer system with minor
occurrences of siliciclastics. The siliciclastics generally occur intimately mixed with
the carbonates and are more common in the upper portion of the aquifer system.
Within the district, the Floridan aquifer system is composed of the Ocala, Marianna,
Suwannee, Chickasawhay, and Bruce Creek Limestones and the St. Marks and
Chattahoochee Formations.

Stratigraphically, the base of the Floridan aquifer system varies significantly
throughout NWFWMD. In the Pensacola area, the base occurs within the Upper
S Eocene Ocala Limestone (Miller, 1986). Under the eastern end of the district, the
base falls within the Paleocene Cedar Keys Formation. The depth to the base of the
Floridan varies from -100 NGVD on the Chattahoochee Anticline to
-3100 feet NGVD in the Apalachicola Embayment (Miller, 1986).

The Claibome aquifer has been recognized within the sub-Floridan confining
unit. The total extent of this aquifer is not known and it is not often utilized (Allen,
1987). It is composed of carbonate and siliciclastic sediments of the Claibome
Group.

The effects of karstification are most intense on and surrounding the
Chattahoochee Anticline in Jackson, Holmes and Washington Counties and on the
flank of the Ocala Platform in Leon and Wakulla Counties. In these areas, the
aquifer system has been extensively altered by dissolution and often has many
direct conduits from the surface into the Floridan. An extensive, underwater conduit
mapping project of the Woodville Karst Plain by the Woodville Karst Plain Project
(Parker Turner, Florida State University, personal communication, 1991) has
recently documented the length and complexity of the dissolutional features of the
area.

FLORIDA GEOLOGICAL SURVEY

Suwannee River Water Management District

The Floridan aquifer system occurs throughout the SRWMD providing the
vast majority of the water supplies. The top of the Floridan ranges from greater than
100 feet above NGVD in Jefferson County to more than 300 feet below NGVD in
Bradford County (Scott et al., 1991). The thickness ranges from approximately 1100
feet in northern Jefferson County to 2200 feet in southern Jefferson County (Miller,
1986). The thicknesses of the Floridan aquifer system sediments in SRWMD show
the effects of the Apalachicola Embayment and Gulf Trough in Jefferson County.
These sediments also exhibit the thicker carbonate sequence deposited in the
peninsular area.

Carbonate sediments deposited during the Paleocene through the Early
Miocene comprise the Floridan aquifer system in SRWMD. The base of the system
occurs near the top of the Paleocene Cedar Keys Formation (Miller, 1986).
Carbonates of the Oldsmar and Avon Park Formations, the Ocala and Suwannee
Limestones and the St. Marks Formation comprise the Floridan aquifer system in the
district. The Suwannee Limestone forms a portion of the Floridan in approximately
one half of the district while the St. Marks Formation occurs in limited areas. When
the Suwannee Limestone and the St. Marks Formation are absent, the Ocala
Limestone forms the top of the system. In the southern portion of the district, the
Ocala Limestone is absent due to erosion and the Avon Park Formation forms the
top of the system.

The top of the sub-Floridan confining unit generally occurs within the Cedar
Keys Formation throughout SRWMD (Miller, 1986). The positioning of the
permeability barrier shifts locally within the upper part of the Cedar Keys Formation
from the top of the unit to some distance below the top. The depth to the sub-
Floridan confining unit varies from -1200 feet NGVD on the Ocala Platform to -2100
feet on the flank of the Gulf Trough (Miller, 1986).

The sediments of the Floridan aquifer system throughout SRWMD have been
greatly affected by karstification. Sinkholes are very common in most areas and
numerous springs are scattered across the district. The only area of minor
karstification is in northern- most Columbia and Baker Counties.

St. Johns River Water Management District

The Floridan aquifer system is present throughout the SJRWMD containing
potable water supplies in most areas. Salt water intrusion or upwelling is a concern
in many of the coastal areas and along the St. Johns River Valley (Scott et al.,
1991).

The top of the Floridan aquifer system in SJRWMD occurs at the highest
elevations on the flank of the Ocala Platform in Alachua and Marion Counties. In

SPECIAL PUBLICATION NO. 44

this area, the uppermost Floridan sediments range from 50 to more than 100 feet
above NGVD. The upper surface of the system dips into the Jacksonville Basin, in
the northern part of SJRWMD, where it may be more than -550 feet NGVD. To the
south, the top of the Floridan reaches more than -350 feet NGVD (Scott et al.,
1991). The thickness of the system ranges from approximately 1500 feet in Baker
County (northwestern SJRWMD) to 2900 feet in southern Brevard County (Miller,
1986).

Carbonate sediments dominate the Floridan aquifer system within the district.
Siliciclastic sediments, when present, occur mixed in carbonate lithologies and
predominantly in the uppermost portion of the Floridan. The Ocala Limestone forms
the top of the aquifer system over the majority of the district. In very limited areas of
Volusia and Orange Counties, the Avon Park Formation occurs at the top of the
Floridan. Sediments of Oligocene age occur at the top of the aquifer system along
the east coast in southernmost Brevard County and in Indian River County. Miller
(1986) shows small outliers of Suwannee Limestone at the top of the Floridan in the
northern portion of the district. The majority of the aquifer system is comprised
of the Avon Park and Oldsmar Formations.

The sub-Floridan confining unit occurs within the Cedar Keys Formation
throughout the district. The positioning of the base of the Floridan varies from the
top of the Cedar Keys Formation to within the upper portion of the formation (Miller,
1986). The top of the sub-Floridan confining unit varies from -1600 feet NGVD on
the flank of the Ocala Platform to -3200 feet NGVD in the Jacksonville Basin and the
Okeechobee Basin (Miller, 1986).

Karst processes have significantly altered the carbonates of the Floridan
aquifer system in much of the SJRWMD. Karst features are common in much of the
central and western portions of the district (Sinclair and Stewart, 1985). The
karstification in these areas is related to dissolution of the Ocala Limestone. In the
southern half of the district, dissolution of the carbonate fraction of the Plio-
Pleistocene sediments is responsible for the development of most of the karst
features.

Southwest Florida Water Management District

The Floridan aquifer system underlies the entire SWFWMD area and
contains plentiful, potable water supplies throughout most of the district. Areas of
mineralized water along the coast and in portions of Charlotte and Sarasota
Counties limit the availability of fresh water from the Floridan in these areas (Scott et
al., 1991).

The top of the Floridan aquifer system in the SWFWMD displays two distinct
elevational trends. The northern two thirds of the district (from central Polk and
Hillsborough Counties northward) is relatively flat with elevations varying from sea

FLORIDA GEOLOGICAL SURVEY

level to between 100 and 150 feet above NGVD. The top of the Floridan in the
southern one third of the district dips distinctly to the south dropping from sea level
to more than 750 feet below NGVD along the southern district boundary (Scott et al.,
1991). These trends are related to the positions of the Ocala Platform and the
northern edge of the Okeechobee Basin.

The thickness of the aquifer system also displays distinct trends. The
Floridan is more than 1400 feet thick in the northern- most portion of the district and
thins southward across the northern one third of SWFWMD to approximately 600
feet thick (Wolansky and Garbode, 1981). From the thinnest point of the Floridan
aquifer system, it thickens into the Okeechobee Basin southward, reaching more
than 2400 feet thick in the SWFWMD part of Highlands County (Wolansky and
Garbode, 1981).

As in the rest of the peninsula, carbonate sediments dominate the Floridan
aquifer system in SWFWMD. Siliciclastic-bearing carbonates and siliciclastic units
in the basal Hawthorn Group may form the upper portion of the Floridan in part of
the southern portion of SWFWMD. In much of the district, the Suwannee Limestone
forms the top of the Floridan. In the northern most portion of SWFWMD, the Ocala
Limestone and, in limited areas, the Avon Park Formation comprises the top of the
aquifer system. The Avon Park and Oldsmar Formations form the main body of the
Floridan in the district. The sub-Floridan confining unit occurs in the upper Cedar
Keys Formation and varies from -1900 feet NGVD on the Ocala Platform to -4100
feet NGVD in the Okeechobee Basin (Miller, 1986).

Karstic alteration of the Floridan aquifer system has occurred throughout
much of the district. In the southern portion of SWFWMD, where the Hawthorn
Group thickens in the Okeechobee Basin, karst features are not as abundant
(Sinclair and Stewart, 1985). In the northern two-thirds of the district and along the
Lake Wales Ridge, karst features are quite common. Surficial karst features in
much of southern SWFWMD are the result of dissolution of carbonate sediments
and shell material in the Miocene through Pleistocene units.

South Florida Water Management District

Potable water supplies within the Floridan aquifer system in SFWMD are
limited to the northern part of the district. The sediments of the Floridan occur
throughout the district but in many areas do not contain acceptable quality water.

The top of the Floridan aquifer system occurs at elevations ranging from sea
level in the northern most edge of the district (Orange County) to greater than 1100
feet below NGVD in southwestern SFWMD (Miller, 1986). Most of this area lies in
the Okeechobee Basin. The thickness of the Floridan ranges from less than 2300
feet in Orange County to more than 3400 feet under parts of Palm Beach and Martin
Counties and more than 3500 feet under western Lee County (Miller, 1986).

SPECIAL PUBLICATION NO. 44

A thick sequence of carbonate sediments containing some beds of
siliciclastics and siliciclastic-rich carbonates form the Floridan aquifer system in
SFWMD. The majority of the sediments comprising the Floridan are carbonates
with little to no siliciclastics. However, in southwestern Florida, sand beds have
been noted in the Ocala Limestone (Missimer, personal communication, 1991).
Siliciclastic-bearing carbonates and a few siliciclastic beds from the basal Hawthorn
Group may form the upper beds of the Floridan aquifer system in some areas of the
district. In general, the Suwannee Limestone forms the upper unit of the aquifer
system with the Ocala Limestone and the Avon Park, Oldsmar and upper Cedar
Keys Formations comprising the main mass of the system. The base of the Floridan
aquifer system, the top of the sub-Floridan confining unit, occurs within the upper
portion of the Cedar Keys Formation (Miller, 1986). The top of the sub-Floridan
confining unit ranges from -3000 feet NGVD on the northern edge of the
Okeechobee Basin to -4400 feet NGVD in the deeper portion of the Okeechobee
Basin.

The development of karst features in the sediments of the Floridan aquifer
system in SFWMD has not been extensive. Throughout much of the district, the
Floridan contains saline waters and has not been flushed by fresh water. The
Floridan aquifer system is also buried by as much as 1100 feet of confining beds
and other aquifer systems under much of SFWMD.

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FLORIDA GEOLOGICAL SURVEY

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SPECIAL PUBLICATION NO. 44

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FLORIDA GEOLOGICAL SURVEY

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SPECIAL PUBLICATION NO. 44

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	Front Cover
	Title Page
	Copyright
	Front Matter
	Table of Contents
	Main
	Bibliography

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