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The geology and geomorphology of Florida's coastal marshes ( FGS: Open file report 34 )

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Title:
The geology and geomorphology of Florida's coastal marshes ( FGS: Open file report 34 )
Series Title:
( FGS: Open file report 34 )
Creator:
Rupert, Frank
Arthur, Jonathan D
Florida Geological Survey
Place of Publication:
Tallahassee Fla
Publisher:
Florida Geological Survey
Publication Date:
Language:
English
Physical Description:
13 p. : ill., map ; 28 cm.

Subjects

Subjects / Keywords:
Coasts -- Florida ( lcsh )
Geomorphology -- Florida ( lcsh )
Marshes -- Florida ( lcsh )
Geology -- Florida ( lcsh )
City of Ocala ( local )
Gulf of Mexico ( local )
Town of Suwannee ( local )
City of Apalachicola ( local )
City of St. Marks ( local )
City of Vernon ( local )
Limestones ( jstor )
Gulfs ( jstor )
Coasts ( jstor )
Sand ( jstor )
Terraces ( jstor )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (p. 12-13).
General Note:
Title from cover.
General Note:
At head of title: State of Florida, Department of Natural Resources, Division of Resource Management, Florida Geological Survey.
Funding:
Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
Statement of Responsibility:
by Frank R. Rupert and Jonathan D. Arthur.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
001754180 ( aleph )
26724850 ( oclc )
AJG7169 ( notis )

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





DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director




FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist








OPEN FILE REPORT 34





THE GEOLOGY AND GEOMORPHOLOGY OF FLORIDA'S COASTAL MARSHES

By

Frank R. Rupert and Jonathan D. Arthur


FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
1990
















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The geology and geomorphology of Florida's Gulf coastal marshes
by
Frank R. Rupert, P.G. No. 149, and Jonathan D. Arthur, P.G. No. 1149.


GEOLOGY

Florida Is situated in the eastern Gulf of
Mexico sedimentary basin, a broad region of
sediment accumulation comprised of southern
Alabama, southern Georgia, Florida, Cuba, and
the Bahamas (Puri and Vernon, 1964). The
geologic framework of the state includes
thousands of meters of Mesozoic (250 to 67
million years ago) and Cenozoic (67 million years
ago to the present) marine limestones, dolomites,
sands, and clays. These sedimentary rocks in
turn rest on Precambrian (600 million years ago
and older), and Paleozoic (600 to 250 million
years ago) basement rocks, which lie at depths
In excess of about 1200 m (4000 ft) below land
surface.
The emergent portion of Florida and the
offshore continental shelf and slope areas are
comprised principally of Cenozoic marine
sedimentary rocks. Most of these rocks were
deposited in the shallow seas which covered the
Floridlan Platform sporadically during the last 66
million years. Over the millennia, younger rock
layers, or formations, were successively deposited
on top of the older layers. The result is that
Florida's rock units are stacked "layer cake" style
in the subsurface. Many of the layered formations
vary locally In thickness, however, or have been
tilted, downwarped, or modified by erosion since
the time they were originally deposited. This has
resulted In a somewhat complex geologic
structure underlying Florida's west coast. Figure
1 Is a generalized geologic cross section of the
west coast from Pensacola to St. Petersburg. It
illustrates the stratigraphy of the near surface
formations underlying the coastal marshes, and
will serve as a reference in the following
discussion of the geology of Florida's Gulf coast.
Data used in the construction of the cross section
were obtained from lithologic logs of well cores
and samples on file at the Florida Geological
Survey (FGS). The "W-" numbers shown on the
cross section represent FGS well accession
numbers.
The oldest rocks underlying Florida are known
only from samples brought to the surface during


the drilling of deep oil test wells. These
basement rocks typically range in age from Late
Precambrian (about 700 million years ago) to
Middle Mesozoic (about 150 million years ago).
In the eastern Florida panhandle and northern
peninsula, the basement rocks are igneous and
sedimentary in nature, and lie below 1200 m
(4000 ft) in depth; In southern Florida, the
basement rocks are generally more than 4500 m
(15,000 ft) deep, and are comprised primarily of
Middle Mesozoic Igneous rocks (Arthur, 1988).
Overlying the basement rocks are a series of
Mesozoic sedimentary rocks, including sands,
shales and limestones. Most are marine in
origin. Florida's two oil regions, the Jay trend in
northwestern Florida, and the Sunniland trend in
south Florida, produce oil from horizons within
these Mesozoic rocks.
A sequence of Cenozoic (predominantly
marine) sediments in turn overlie the Mesozoic
rocks. These rocks contain Florida's drinking
water aquifers and Industrial mineral deposits, and
comprise the visible portions of the state today.
Figure 2 is a generalized stratigraphic chart
summarizing the Eocene and younger Cenozoic
formations present under west coastal Florida.
The Paleocene rocks are marine limestones and
dolomites. These older rocks are not important
fresh water aquifers, and lie deeper than the
depths attained by most water wells. For the
purposes of this report, the discussion of the
stratigraphy will be limited to Middle Eocene and
younger sediments. Many of these sediments
crop out at the surface, and most directly affect
the geology and hydrology of Florida's Gulf
coastal marsh region. Data on the lithology,
depth, thickness, and occurrence of the
formations is derived from well logs on file at the
Florida Geological Survey.

Middle Eocene Series
Avon Park Formation

The Avon Park Formation (Applin and Applin,
1944; Miller, 1986) is typically a cream to brown
to tan, fossiliferous, marine dolomite. It
commonly contains pasty limestone beds and


































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peat flecks and seams. The Avon Park
Formation was deposited in a shallow sea which
covered the area of present-day Florida about 54
million years ago. Numerous shallow-water
fossils are found in Avon Park Formation
sediments, Including heart urchins, sand dollars,
mollusks, foraminifera, and a "tutle grass-like"
marine plant, very similar to the species living off
the Big Bend coastline today.
The Avon Park Formation is the oldest rock
exposed at the surface In Florida. It occurs In
west-central Florida along the crest of a gentle,
northwest-southeast trending anticlinal feature
variously called the Ocala Uplift, Ocala Arch,
Ocala High, or Ocala Platform (Purl and Vemon,
1964; Scott, 1988), the origin of which is uncertain.
Eocene and younger rocks have been removed
by erosion over the structure.
The Avon Park Formation is exposed only in
small areas of central and southern Levy County
and northernmost Citrus County, corresponding
to the crest of the Ocala Platform (see Figure 1).
It dips westward, where it interfingers with the age
equivalent Usbon Formation under the western
Florida panhandle. Thickness of the unit In
west-central Florida is variable, but generally
ranges from 0 to 240 m (0 to 800 ft) statewide
(Chen, 1965).
Dolomite from the Avon Park Is quarried In
Citrus and Levy Counties for use in construction
materials. The Avon Park is also a unit of the
Floridan aquifer system, one of Florida's primary
drinking water aquifers. It is unconformably
overlain by marine limestone of the Upper
Eocene Ocala Group.

Upper Eocene Series
Ocala Group

The Late Eocene (38 to 41 million years ago)
Ocala Group (Puri, 1957) is composed of three
marine limestone formations. In ascending order,
these are the Inglis, Williston, and Crystal River
Formations, all named for towns in the respective
local outcrop areas of each formation. The
formations have traditionally been differentiated
on the basis of fossil content, and to a lesser
extent, lithology. For the purposes of this report,
these three units will be referred to collectively as
the Ocala Group.
The Ocala Group was deposited In a shallow,
Late Eocene sea. It is typically a white to cream,
abundantly fossiliferous, chalky to coqulnold


limestone. Microfossils are generally the most
common fossil forms present, especially the large
species of foraminifera Lepldocyclina,
Nummulites, and Heterostegina. Mollusks,
bryozoans, and echinoids are also common in
these sediments. As shown on Figure 1, the
Ocala Group also crops out in west central
Florida, along the crest of the Ocala Platform. It
dips generally westward and southwestward from
its outcrop area. The thickness of the Ocala
Group in west-central Florida averages about 60
m (200 ft), but Is locally variable, and generally
thins over the crest of the Ocala Platform.
Limestone of the Ocala Group is exposed
sporadically or is blanketed only by a thin veneer
of Pleistocene and Holocene sands in all of Dixie
County and portions of Lafayette, Gilchrist, Levy,
Citrus, Marion, and Hernando Counties.
Throughout this area it Is quarried as construction
material and road base.
The exposed surface of the Ocala Group
limestone forms a relatively flat-lying, gently
seaward-sloping, solution depression and
sinkhole-pocked plain over most of its outcrop
area. This plain continues offshore onto the
broad western Florida continental shelf.
Boulders, pinnacles, and small islands of Ocala
Group limestone are common along the Gulf
coastline of Dixie, Levy, and Citrus Counties
(Vemon, 1951). Many of the coastal marshes in
this area are developed in the thin calcitic muds,
silt, organs, and relict marine sands deposited in
solution depressions in the underlying limestone
(see Figure 3). The Ocala Group is an important
unit of the Floridan aquifer system. Along much
of the central west coast and within many of the
coastal marsh areas, the potentiometric surface of
the Floridan aquifer system is at or above land
surface. As a result, numerous seeps and small
springs feed freshwater into the marshes. Fow
from some of these springs is sufficient to form
small tidal creeks and tributaries through the
otherwise dense marsh grasses (Nettles, 1976).

Oligocene Series
Suwannee Limestone

The Oligocene (33 to 25 million years old)
Suwannee Limestone (Cooke and Mansfield,
1936) is a white to tan, fossiliferous, commonly
dolomitic marine limestone, named after
exposures along the Suwannee River in northern
Florida. As with the preceding Eocene










formations, the Suwannee was probably
deposited in a shallow temperate sea. It contains
abundant microfossils, mollusks, echinolds,
bryozoans, and rare corals. Early Indians of the
region used the abundant chert occurring in both
the Ocala Group and Suwannee Umestone to
fashion tools and weapons. The Suwannee
Umestone has been truncated against the flanks
of the Ocala Platform (Figure 1), and is exposed
at the surface at the northern and southem ends
of this feature. It occurs as the surflcial unit in
eastern Jefferson County, most of Taylor County,
western Hemando County, and northem Pasco
County. In these areas, the Suwannee Umestone
forms a flat-lying, karstic plain which extends
seaward onto the continental shelf. Boulders and
pinnacles of Suwannee Umestone are common
along the low energy coasts of Jefferson and
Taylor Counties. The Suwannee Umestone is the
upper unit of the Floridan aquifer system in its
outcrop area. Small fresh water springs and
seeps commonly occur In the marshes of
southern Jefferson and Taylor Counties, some
forming creeks or contributing to the flow of rivers
such as the Aucila and Econfina.

Miocene Series

The Miocene Epoch marked a significant
change in the depositional regime of the Florida
peninsula. Previously a shallow carbonate bank,
Florida experienced an influx of continental
silclciastic sediments during the Miocene from
the continental mainland to the north. This was
due In large part to the closing of a feature called
the Suwannee Straits or Gulf Trough, which
trended southwestward across the eastern Florida
panhandle (Figure 1). The Gulf Trough was
thought possibly to have been an ancient
channel or seaway, existing from the Cretaceous
Era through the end of the Oligocene Epoch (Dall
and Harris, 1892; Chen, 1965). It probably
connected two major depositional basins, the
Southeast Georgia Embayment and the
Apalachicola Embayment. Currents within this
paleo-strait may have functioned as both a
zoological and a sedlmentologlcal barrier between
the carbonate banks and Islands of peninsular
Florida and the continental mainland.
Phosphogenesis also occurred on a large
scale beginning In the Miocene. Many Miocene
formations contain phosphate grains, ranging
from silt to pebble size. Florida's economic


phosphate deposits are concentrated In the
Miocene Hawthorn Group sediments in the
Central Florida Phosphate District of Polk and
surrounding counties and in the North Florida
Phosphate District in Hamilton County.
The Miocene formations in Florida are
primarily marine In origin. In contrast to the.
nearly pure calcium carbonate limestones of the
Eocene, the Miocene and younger sediments,
Including the carbonates, typically contain
terrigenous quartz and heavy mineral sands and
days and phosphate. Starting In the Lower
Miocene, a massive influx of river-borne
continental sediments poured into the seas
covering present day peninsular Florida (Scott,
1988). The Miocene seas reworked and
deposited these sediments in a broad blanket
over the carbonates of earlier epochs. In the
western panhandle, a series of marine limestones
and shelly sands were laid down. The Miocene
seas supported a rich marine fauna, as shown by
the numerous fossils found in these sediments.
Based on fossils, paleoenvironments ranged from
shallow nearshore and lagoon to deepwater
continental shelf. Many of Florida's commercial
mineral deposits, including phosphate and fuller's
earth, were formed In these ancient sea floor
sediments,

Lower Miocene Series
St. Marks Formation

The St. Marks Formation (Purl and Vernon,
1964) is exposed along the northern Big Bend
coastline in Wakulla County. It Is the only
Miocene carbonate unit exposed in the coastal
marsh zone. This formation Is a white to very
pale orange to light gray, quartz sandy,
fossiliferous marine limestone. Foraminifera and
mollusks are the dominant fossil forms, generally
present as molds. Along the coast the St. Marks
Formation contains abundant chert, which
probably supplied the paleoindlans of the region
with tool and spear point material. The St. Marks
Formation occurs near or at the surface in most
of south central and south eastern Wakulla
County. Here it forms a slightly seaward-slop-
Ing, karstic plain called the Woodville Karst Plain.
Thickness varies from 0 m at the
Wakulla-Jefferson County line to over 30m (100
ft) along the eastern flank of the Apalachlcola
Embayment. Extensive salt marshes, developed
in the thin sand and mud veneer overlying the St.










Marks Formation limestone, border the southern
edge of Wakulla County.
The St. Marks Formation is the uppermost unit
of the Floridan aquifer system in the eastern
panhandle. In southern Wakulla County, the
potentiometric surface of this aquifer is at or
above the land surface elevation. Many small
fresh water springs are scattered through the
coastal marshes, and several submarine springs
are situated on the offshore extension of the karst
plain. The St. Marks pinches out against the
underlying Suwannee Limestone to the east in
Jefferson County (Figure 1), and dips generally to
the west-southwest. To the west under Franklin
and Gulf Counties it becomes indistinguishable
from the Bruce Creek Limestone. It interfingers to
the north and possibly under the western
panhandle with the age-equivalent Chattahoochee
Formation.

Hawthorn Group
Arcadia Formation

The Lower Miocene Arcadia Formation of the
Hawthom Group (Scott, 1988) underlies the
west-central Gulf coast from approximately New
Port Richey to Sarasota (Figure 1). This unit is
comprised primarily of white to yellowish-gray to
light olive-gray limestone and dolomite containing
variable amounts of quartz sand, clay, and
phosphate grains. It unconformably overlies the
Suwannee Umestone, and Is overlain by
undifferentiated Pleistocene quartz sands.
Hawthorn Group sediments are absent along the
panhandle coast.
Hawthorn Group sediments serve as an
Intermediate confining unit to the underlying
Floridan aquifer system. Locally, carbonates
within the Hawthorn Group may also function as
an intermediate freshwater aquifer system, or in
some areas, are in hydrologic continuity with the
underlying Floridan aquifer system and
considered part of the Floridan aquifer.
The Hawthorn Group does not crop out in the
vicinity of the coastal marshes. It is probably
eroding offshore however, as pebbles and
cobbles of Hawthorn Group carbonate are often
found washed up on Pinellas County beaches.


Middle Miocene
West of Wakulla County in the panhandle, the
Miocene units dip and thicken southwestward


into the Apalachicola Embayment (Figure 1).
Both the Lower Miocene St. Marks Formation and
the overlying Middle Miocene Bruce Creek
Limestone dip into the trough of the embayment,
reaching a maximum local depth and thickness
under the axis of the basin. These units shallow
again on the western side of the embayment,
and attain a depth and thickness similar to that
on the eastern edge of the embayment.

Bruce Creek Limestone

Bruce Creek Limestone was the name given
by Huddlestun (1976) to a white to light
yellowish-gray, Middle Miocene marine limestone
underlying part of panhandle Florida. It extends
from the eastern edge of the Apalachicola
Embayment westward, with generally southwest
dip. The Bruce Creek Limestone is commonly
quartz sandy, phosphoritic, and both micro- and
macro-fossiliferous. Fossils are generally
preserved as molds. This formation is primarily a
subsurface unit, and does not crop out in the
vicinity of the coastal marshes. The Bruce Creek
Limestone thickens to over 60 m (200 ft) in the
Apalachicola Embayment. Down-dip, it is
indistinguishable from the underlying St. Marks
Formation. In the central and western panhandle,
the Bruce Creek Limestone comprises the
uppermost unit of the Floridan aquifer system.

Middle Miocene Through Pliocene Series
Intracoastal Formation

Huddlestun (1976) applied the name
Intracoastal Formation to a soft, yellowish-gray to
olive green, sandy, highly microfossiliferous,
argillaceous marine limestone underlying the
coastal area of west Florida. This formation
extends from easternmost Franklin County
westward, and continues to approximately the
Santa Rosa County line (Schmidt, 1984). The
Intracoastal Formation is predominantly a
subsurface unit, dipping and thickening to the
west-southwest into the Apalachicola Embayment.
It approaches 100 m (300 ft) in thickness in the
trough of the Apalachicola Embayment. The unit
shallows and thins west of the embayment, then
thickens and dips westward towards the
Pensacola area. Analysis of the microfossils
present indicate an age range for the Intracoastal
Formation of Middle Miocene (down dip) to Late
Pliocene (in the up-dip portions), with a hiatus










separating the age extremes. Locally it occurs
close to the surface in the central panhandle, but
does not crop out In the coastal marsh region.

Pensacola Clay

The Pensacola Clay (Marsh, 1966) Is a pale,
yellowish-brown to olive-gray, dense, silty,
commonly quartz-rich sandy clay. This unit Is
restricted to the subsurface, occurring under the
panhandle from approximately Okaloosa County
westward into Alabama. It thickens rapidly to the
south and west (see Figure 1), reaching a
maximum thickness of about 150 m (500 ft) under
Pensacola Bay (Clark and Schmidt, 1982). The
Pensacola Clay is considered Late Miocene in
age, overlying the Bruce Creek Limestone, and is
interflngered locally with the Intracoastal
Formation or the Miocene Coarse Clastics (Clark
and Schmidt, 1982).

Miocene-Pliocene Coarse Clastics

Marsh (1966) proposed the name Miocene
Coarse Clastics for a series of sands, gravel,
days, and shell beds underlying the western
panhandle. These sediments are largely
comprised of light-gray to pale-yellowish-brown
quartz sand and gravel, with minor clay and
marine mollusk shells. The Miocene-Pliocene
Coarse Clastics occur from western Okaloosa
County westward through Santa Rosa and
Escambia Counties. Thickness of this unit
reaches nearly 150 m (500 ft) under Santa Rosa
County. The coarse clastics overlie the
Pensacola clay and Intracoastal Formations, and
locally may be contemporaneous (Late Miocene
to Early Pliocene In age) with portions of both
formations; they are overlaln by undifferentiated
Pleistocene sand (Clark and Schmidt, 1982).

Chlpola Formation

The Chipola Formation (Puri and Vemon,
1964) is present at depth under the coastal
marshes in the vicinity of Gulf County, along the
axis of the Apalachlcola Embayment.
Lithologlcally, it is comprised of a yellowish-gray
to light-gray, quartz sandy marine limestone.
Foraminifera and mollusks are typically the most
abundant fossils. Thickness of this unit reaches
about 15 m (50 ft) In the central Apalachlcola
Embayment, thinning and pinching out to the


west and east of the embayment. In the down-
dip coastal and offshore areas, the Chipola
Formation overiles the Intracoastal Formation and
is considered to be late Pliocene In age (Schmidt,
1984). It Is unconformably overlain by the
Jackson Bluff Formation.

Jackson Bluff Formation

The Late Pliocene Jackson Bluff Formation
(Purl and Vemon, 1964) consists of tan to
oranglsh-brown to grayish green sandy, clayey
shell beds. It Is restricted in occurrence to the
central Apalachlcola Embayment, where the unit
reaches about 30 m (100 ft) in thickness. The
Jackson Bluff Formation overlies the Chipola and
Intracoastal Formations, and Is in turn overlain by
undifferentiated Pleistocene and Holocene sands.
The Jackson Bluff Formation does not crop out in
the coastal marshes.

Pleistocene and Holocene Series

A series of undifferentiated Pleistocene (1.8
million to 10,000 years old) and Holocene (10,000
years and younger) quartz sands, clayey sands,
and sandy clays blanket the older formations
along much of Florida's west coast. These
sediments are composed largely of reworked
relict Pleistocene marine sands and Holocene
alluvium, calcitic muds, and organic.
The Pleistocene Epoch, or "Ice Age", was
characterized by four great glacial periods.
During this epoch, global temperatures cooled,
and huge Ice sheets grew southward from
Canada. Large quantities of seawater were
consumed to build the glaciers, and sea level
dropped as much as 130 m (400 ft). Each glacial
period was punctuated by warmer Interglacial
periods during which the sea level rose, at times
to over 30 m (100 ft) above modem level. As the
Pleistocene seas transgressed Inland, wave and
current activity eroded, reworked, and
redeposited the sands of earlier formations. At
the same time, rivers and an active southward-
moving littoral drift system brought new plastic
sediments into Florida. The Big Bend Area was a
drowned karst coastline during the Pleistocene
sea-level highstands. Planing by wave action and
in-filling of the karst features with sand resulted in
the flat, seaward-sloping plain characterizing this
region today. Figure 3 illustrates a typical near-
surface cross-section in the coastal marsh zone


_~_Ul___l~_ I____ ___~___I__











































S 100 METERS

0 300 FEET


VERTICAL EXAGERATION APPROXIMATELY 110 TIMES TRIE SCALE







Figure 3. Generalized near-surface cross section
in the coastal marshes, west-central Florida
(modified from Hine and Belknap, 1986).


EOCENE/OLIGOCENE LIMESTONE
Ir . . I . . . .
.........................
...........

. . . .
. . . I . .




ii










scarps and terraces do exist in the Gulf Coast
region; however, further study is required in order
to more accurately define their occurrence and
extent.
Pliocene-Pleistocene sea-level fluctuations are
the primary reason for the presence of these
terraces (Winker and Howard, 1977a, 1977b).
During the Pleistocene "Ice Age" when the
fluctuations became more prevalent, four major
glacial cycles occurred due to major climatic
changes. As glaciers spread over the continents,
sea-level dropped. During periods of melting or
interglacial periods, sea-level rose. Healy (1975)
and MacNell (1950) suggested that during
subsequent (younger) interglacial periods, the
seas stood at levels below that of the prior event,
thus preserving the earlier formed terraces and
scarps. Several authors have recognized that
glacial melting alone cannot account for the
present-day anomalously high elevations of the
older marine terraces. Tanner (1968, 1985) and
Winker and Howard (1977a, 1977b) document
evidence for regional uplift during this time.
In a study entitled "The Geomorphology of the
Florida Peninsula," White (1970) subdivided the
region Into a series of uplands and lowlands.
Most of the present study area lies within a
single, major physiographic province: the Gulf
Coastal Lowlands (Figure 4). This province
stretches from the western Florida panhandle to
southern peninsular Florida and averages 40
kilometers (25 miles) in width. Various highlands,
ridges or scarps constitute the Inland limits of the
Gulf Coastal Lowlands, whereas the present-day
shoreline marks the seaward boundary. Unlike
eastern coastal areas of Florida, this geomorphic
province does not correspond to any specific
marine terrace delineated by Healy (1975). The
Gulf Coastal Lowlands contain various erosional
and depositional landforms that occurred in
response to Pliocene-Pleistocene sea-level.
fluctuations. Several relict bars, spits and
terraces are superimposed on the modem
topography of the region. Subdivisions within the
Gulf Coast Lowlands include Gulf Barrier Chains,
Coastal Swamps, Coastal Lagoons and Estuaries.
Using White's (1970) terminology, the Gulf
Coastal Swamps include areas where a
deficiency exists In the sand budget for building
beaches. These low-lying areas correspond to
areas on topographic maps where the swamps
are immediately adjacent to the coast. No
distinction is made between salt marshes and
fresh water swamps. Where Isolated patches of


swamp are separated from the coast by dry land,
the term "coastal lagoons" is applied (White,
1970). This generalized terminology is being
revised based on vegetation, soil type and
topography in concurrent investigations (C.L.
Coultas, personal communication, 1990).
White (1970) presented a two-fold classification
for the Gulf Coast of peninsular Florida. Within
the study area, this includes a coastal salient that
extends from Tampa Bay north to the southern
part of Pasco County, and a coastal reentrant
spanning from this point north toward Apalachee
Bay. The salient is characterized by a relatively
steep offshore profile which allows wave energy
to transport, deposit and erode sand along the
shoreline. This coastal area contains many relict
barrier bars, beach ridges and lagoons. In
contrast, the reentrant offshore profiles have
gentle slopes and are floored by limestone. White
(1970) suggested that these broad shallow
profiles sufficiently dissipate wave energies to
account for the sand-starved marshy coasts. The
sand deficiency Is also due to a lack of sediment
transported by the Suwannee River. The very
low-energy reentrant coast Is virtually free of
relict shoreline features.
Along the Florida panhandle coastline, White's
(1970) generalization concerning the peninsula's
offshore profiles Is also applicable. Westward
from the west end of Apalachee Bay, the profile
is either as steep as or steeper than in the Tampa
Bay area. The entire panhandle coastline
consists of spits, lagoons, beach ridges and
offshore barrier islands. An even steeper offshore
slope (ramp) in the central panhandle region has
precluded barrier island formation offshore of
Walton and the west half of Bay counties (Tanner,
1960). Puri and Vernon's (1964) geomorphic
map of the region, which uses White's criteria for
landform definition, shows no coastal swamps.
Tanner (1960) presented data which quantify
energy levels within the study area. Rather than
focussing on shelf slope, he reported average
annual breaker heights to estimate wave energy.
Energy levels of Tanner (1960) are shown on
Figure 4. The "zero energy" coast corresponds to
the coastal swamps and marshes in the Big Bend
area. The lack of both wave energy and thus
sediment transport and deposition are the two
most significant factors that have allowed
swamp/marsh development in the region.
In addition to the regional geomorphic
characteristics of the study area, two localized
features are noteworthy, both of which pertain to










along the west-central Florida coast. The larstic,
irregular surface of the underlying limestone is
infilled with Pleistocene and Holocene sediments,
with a few limestone pinnacles exposed at the
surface. The younger sands, muds, and silts form
a substrate for many of the coastal marshes in
this area.
Relict dunes, bars, and barrier Island sand
bodies, left by retreating Pleistocene seas, also
are common features today along much of
Florida's central and northem Gulf coasts. In the
central panhandle, the ancestral Apalachicola
River meandered over a large area of Bay and
Gulf Counties during the Pleistocene and
Holocene, leaving In its wake relict levee deposits
and alluvium. Much of the surficial and near-
surface sediments in the central and western
panhandle coastal areas are a mixture of marine
and alluvial sands and clays.
The Pleistocene deposits are thinnest in the
Big Bend area, where limestone Is near or at the
surface. West of Wakulla County, these
Pleistocene sediments thicken to nearly 60 m (200
ft) near the Alabama state line.
Holocene sand deposition continues today.
Accumulation of these deposits Is primarily
concentrated along the banks, bottoms, and
mouths of the major Gulf coast rivers, such as the
Apalachicola, Ochlockonee, Aucilla, Suwannee,
and Withlacoochee. In portions of the central
west coast and Big Bend areas, a Holocene
Intertidal calcitic mud often overiles the
Pleistocene sand (Nettles, 1976). Organics
derived from decaying marsh grasses are
Intermixed with sandy typically forms the surface
layer In the coastal marshes (Hine and Belknap,
1986).

GEOMORPHOLOGY

The geomorphology of Florida's Gulf Coast
has been shaped primarily by coastal processes
and sea-level changes during the past five million
years. These sea-level changes have caused
shifts In ground water levels which in turn have
enhanced the development of karst landforms
during this time. The karst features have thus
altered some of the original shoreline erosional
and depositional features within the Gulf Coast
region. Discussion of these two Interrelated
geomorphic features is limited to an Inland
distance of 16 kilometers (10 miles), spanning the
study area from Pensacola to St. Petersburg. In


that the focus herein Is on the recent geologic
past, modern offshore landforms such as spits,
barrier Islands and bars are not discussed.
Up to six marine terraces are reported to occur
within the region of Interest (Cooke, 1945; Healy,
1975). As defined by Garner (1974), a marine
terrace Is a surface of erosion or deposition
formed along a coast by wave action. These
terraces represent the floors of ancient shallow
seas and are situated in a step-like manner,
roughly parallel to the present-day coast. Each
"step" Is a topographic break ranging from a
gentle slope to a sharp Incline. Where sharp,
these changes In topography which separate two
terraces are well preserved seaward-facing wave
cut scarps, some of which are regional in extent
and contain up to 15 meters (50 feet) of relief
(e.g. the Cody Scarp, Purl and Vernon, 1964,
p.11). Although there are few of this magnitude
proximal to the Gulf Coast, coastal terraces and
scarps appear to control surface drainage In
localized areas. For example, Healy's (1975)
Silver Bluff terrace generally coincides with the
location of several Gulf coastal swamps.
Early marine terrace studies have applied
physiographic and geomorphic evidence (White,
1970), aerial photography (Vernon, 1951),
sedimentology/stratigraphy (Altschuler and
Young, 1960; Pirkle and others, 1970), field
mapping (Parker and others, 1955) and fossil
evidence (Alt and Brooks, 1965). Although
conclusions drawn for localized areas are well
constrained by these data, studies based on
elevation correlations over large areas (e.g.
MacNeil, 1950; Healy, 1975) should be considered
with reservation. Given the possibility of
regional Pllocene-Pleistocene warping (Winker
and Howard, 1977a, 1977b), the predominance of
karst development in the region (White, 1970) as
well as other erosional processes, some of these
long-distance correlations may not be valid. For
example, a present day low-lying area may
appear to correlate with a certain low elevation
terrace, whereas in fact it may have been an
upland or higher elevation terrace which was
subsequently lowered by subsurface limestone
dissolution. On the other hand, a "young", low
elevation terrace may have undergone
epelrogenic uplift and now topographically
correlates with a higher elevation, older terrace.
Thus, the correlation between
swamps/marshlands and the Silver Bluff terrace
may be an artifact of the manner in which some
terraces have been delineated. Ancient marine


































o00Ck494


0.


N EXPLANATION
RH IHIOHLAND
o: -n COASTAL
SCALE


S

SWAMPS LOW


Figure 4. Geomorphic features along study area
modified from White (1970) and Purl and Vernon
(1964). Wave energy zones are from Tanner
(1960).


11










karstiflcation. The first of these can be seen on
Tanner's (1960) map which classifies a shoreline
region of Citrus County as "drowned karst"
(Figure 4). This area, discussed in detail by Hine
and Belknap (1986) is called the Ozello Marsh
Archipelago and consists of several limestone
cored marsh Islands. The outer islands are
separated either by creeks or salt marsh
vegetation whereas the interior is pocked with
circular ponds. Various karstification processes
have controlled the shape and orientation of
these water bodies (Hine and Belknap, 1986).
Figure 3 illustrates the undulatory nature of
bedrock limestone in this area due to dissolution.
The Woodville Karst Plain (Hendry and Sproul,
1966) is a subdivision of the Gulf Coastal
Lowlands and is located north of the coastal
swamp belt in Wakulla County. Portions of the
Woodville Karst Plain extend into Jefferson and
Leon Counties where it is bounded to the north
by the Northern Highlands (Purl and Vernon,
1964). Permeable sands form a veneer over a
shallow, southward dipping limestone bedrock.
Dissolution of the underlying bedrock, which has
probably been occurring ever since the area has
been above sea level, has caused subsidence.
This somewhat localized depression, and its
prevalence of shallow sand filled sinkholes
characterizes the Woodville Karst Plain. Although
surrounding areas are also underlain by
limestone, dissolution has not been prevalent
because the overlying sediments contain clays
which both buffer the acidic rainwater and
reduce the amount of percolation. Geologic
variables such as those characterizing the
Woodville Karst Plain bedrock type, sediment
composition, and sea level history are significant
in the development of Florida's Gulf Coast
geomorphology.

ACKNOWLEDGEMENTS

The authors would like to thank Ken
Campbell, Dr. Walt Schmidt and Dr. Thomas Scott
of the Florida Geological Survey, and Dr. William
F. Tanner of Florida State University for critically
reviewing the manuscript of this report.

REFERENCES

Alt, D. and Brooks, H. K. 1965. Age of the Florida
marine terraces: Journal of Geology
73:406-411.


Altschuler, Z. S. and Young, E. J. 1960. Residual
origin of the "Pleistocene" sand mantle in
central Florida uplands and its bearing on
marine terraces and Cenozoic uplift: U.S.
Geological Survey Professional Paper
400-B:202-207.
Applin, P. L, and Applin, E. R., 1944, Regional
subsurface stratigraphy and structure of
Florida and southern Georgia: American
Association of Petroleum Geologist
Bulletin, 28:1673-1753.
Arthur, J. D., 1988, Petrogenesis of Early
Mesozoic tholelite in the Florida basement
and an overview of Florida basement
geology: Florida Geological Survey
Report of Investigation 97.
Chen, C. S., 1965, The regional lithostratlgraphic
analysis of Paleocene and Eocene rocks
of Florida: Florida Geological Survey
Bulletin 45.
Clark, M., and Schmidt, W., 1982, Shallow
stratigraphy of Okaloosa County and
vicinity, Florida: Florida Bureau of
Geology Report of Investigation 92.
Cooke, C. W., 1945,. Geology of Florida: Florida
Geological Survey Bulletin 29.
and Mansfield, W. C., 1936,
Suwannee Umestone of Florida [abs.]:
Geological Society of America
Proceedings for 1935.
Dall, W. H., and Harris, G. D., 1892, Correlation
papers Neocene: U. S. Geological
Survey Bulletin 84.
Garner, H. F. 1974. The origin of landscapes.
Oxford University Press. New York.
Healy, H. G. 1975. Terraces and shorelines of
Florida: Florida Geological Survey Map
Series 71.
Hendry, C. W. and Sproul, C. 1966. Geology and
ground-water resources of Leon County,
Florida: Florida Geological Survey
Bulletin 47.
Hine, A. C., and Belknap, D. F., 1986, Recent
geological history and modern
sedimentary processes of the Pasco,
Hernando, and Citrus County coastline:
west central Florida: Florida Sea Grant
College Report No. 79.
Huddlestun, P. F., 1976, The Neogene
stratigraphy of the central Florida
panhandle. [Ph.D. dissert.]: Tallahassee,
Florida, Florida State University.
MacNeil, F. S. 1950. Pleistocene terraces and
shorelines in Florida: U.S. Geological









Survey Professional Paper 221-F.
Marsh. O. T., 1966, Geology of Escambla and
Santa Rosa Counties, western Florida
panhandle: Florida Geological Survey
Bulletin 46.
Miller, J. A., 1986, Hydrogeologic framework of
the Floridan aquifer system In Florida and
in parts of Georgia, Alabama, and South
Carolina: U. S. Geological Survey
Professional Paper 1403B8.

Nettles. S., 1976. Intertidal calcitic muds along the
west coast of Florida (thesis], Department
of Geology, University of Florida,
Galneevlle, Florida.
Parker, G. G., Ferguson, G. E. and Love, S. K.
1965. Water resources of southeastern
Florida with special reference to
the geology and ground water of the
MIamarea. U.S. Geological Survey
Water-Supply Paper 1255.
Pirlde, E. C., Yoho, W. H. and Hendry, C. W.
1970. Ancient sea level stands in Florida:
Florida Bureau of-Geology Bulletin 52.
Puri, H. S., 1967, Stratigraphy and zonation of the
Ocala Group: Florida Geological Survey
Bulletin 38.
and Vemon, R. 0., 1964, Geology
of Florida and a guidebook to the classic
exposures: Florida Geological Survey
Special Publication 5 (revised).
Schmldt, W., and Clark, M., 1980, Geology of Bay
County, Florida: Florida Bureau of
Geology Bulletin 57.
1964, Neogene stratigraphy and
geologic history of the Apalachicola
embayment, Florida: Florida Geological
Survey Bulletin 58.
Scott, T. M., 1986, The lithostratlgraphy of the
Hawthorn Group (Miocene) of Florida:
Florida Geological Survey Bulletin 59.
Tanner, W.F., 1900, Florida coastal classification:
Transactions Gulf Coast Association
of Geological Societies 10:259-266.
1968, Tertiary sea level
symposium Introduction:
Paleogeography, Paleocllmatology,
Paleoecology 5:7-14.
1965, Late Cenozocl sea level
history In the Southeastem United States:
Institute for Tertiary-Quatemary Studies -
TER-QUA Symposium Series 1:3-8.
Vemon, R. 0., 1961, Geology of Citrus and Levy
Counties Florida: Florida Geological


Survey Bulletin 33.
White, W. A. 1970. The geomorphology of the
Florida Peninsula: Florida Bureau of
Geology Bulletin 51.
Winker, C. D. and Howard, J. D., 1977a,
Correlation of tectonically deformed
shorelines on the southem Atlantic
coastal Plain: Geology 5:123-127.
1977b,
Pllo-Plelstocene paleogeography of the
Florida Gulf Coast interpreted from relict
shorelines: Transactions Gulf Coast
Association of Geological Societies
27:409-420.




Full Text

PAGE 1

STATE OF FLORIDA DEPARTMENT OF NATURAL RESOURCES Tom Gardner, Executive Director DIVISION OF RESOURCE MANAGEMENT Jeremy A. Craft, Director FLORIDA GEOLOGICAL SURVEY Walter Schmidt, State Geologist OPEN FILE REPORT 34 THE GEOLOGY AND GEOMORPHOLOGY OF FLORIDA'S COASTAL MARSHES By Frank R. Rupert and Jonathan D. Arthur FLORIDA GEOLOGICAL SURVEY Tallahassee, Florida 1990

PAGE 2

i 1/ * /r~ /Lt / 2'4'

PAGE 3

The geology and geomorphology of Florida's Gulf coastal marshes by Frank R. Rupert, P.G. No. 149, and Jonathan D. Arthur, P.G. No. 1149. GEOLOGY the drilling of deep oil test wells. These basement rocks typically range in age from Late Florida Is situated in the eastern Gulf of Precambrian (about 700 million years ago) to Mexico sedimentary basin, a broad region of Middle Mesozolc (about 150 million years ago). sediment accumulation comprised of southern In the eastern Florida panhandle and northern Alabama, southern Georgia, Florida, Cuba, and peninsula, the basement rocks are igneous and the Bahamas (Purl and Vernon, 1964). The sedimentary in nature, and lie below 1200 m geologic framework of the state includes (4000 ft) in depth; In southern Florida, the thousands of meters of Mesozoic (250 to 67 basement rocks are generally more than 4500 m million years ago) and Cenozoic (67 million years (15,000 ft) deep, and are comprised primarily of ago to the present) marine limestones, dolomites, Middle Mesozoic Igneous rocks (Arthur, 1988). sands, and clays. These sedimentary rocks In Overlying the basement rocks are a series of turn rest on Precambrian (600 million years ago Mesozoic sedimentary rocks, including sands, and older), and Paleozoic (600 to 250 million shales and limestones. Most are marine in years ago) basement rocks, which lie at depths origin. Florida's two oil regions, the Jay trend in In excess of about 1200 m (4000 ft) below land northwestern Florida, and the Sunnlland trend in surface. south Florida, produce oil from horizons within The emergent portion of Florida and the these Mesozoic rocks. offshore continental shelf and slope areas are A sequence of Cenozoic (predominantly comprised principally of Cenozoic marine marine) sediments in turn overlie the Mesozoic sedimentary rocks. Most of these rocks were rocks. These rocks contain Florida's drinking deposited in the shallow seas which covered the water aquifers and Industrial mineral deposits, and Floridlan Platform sporadically during the last 66 comprise the visible portions of the state today. million years. Over the millennia, younger rock Figure 2 is a generalized stratigraphic chart layers, or formations, were successively deposited summarizing the Eocene and younger Cenozoic on top of the older layers. The result is that formations present under west coastal Florida. Florida's rock units are stacked "layer cake" style The Paleocene rocks are marine limestones and in the subsurface. Many of the layered formations dolomites. These older rocks are not important vary locally In thickness, however, or have been fresh water aquifers, and lie deeper than the tilted, downwarped, or modified by erosion since depths attained by most water wells. For the the time they were originally deposited. This has purposes of this report, the discussion of the resulted In a somewhat complex geologic stratigraphy will be limited to Middle Eocene and structure underlying Florida's west coast. Figure younger sediments. Many of these sediments 1 Is a generalized geologic cross section of the crop out at the surface, and most directly affect west coast from Pensacola to St. Petersburg. It the geology and hydrology of Florida's Gulf illustrates the stratigraphy of the near surface coastal marsh region. Data on the lithology, formations underlying the coastal marshes, and depth, thickness, and occurrence of the will serve as a reference in the following formations is derived from well logs on file at the discussion of the geology of Florida's Gulf coast. Florida Geological Survey. Data used in the construction of the cross section were obtained from lithologic logs of well cores Middle Eocene Series and samples on file at the Florida Geological Avon Park Formation Survey (FGS). The "W-" numbers shown on the cross section represent FGS well accession The Avon Park Formation (Applin and Applin, numbers. 1944; Miller, 1986) is typically a cream to brown The oldest rocks underlying Florida are known to tan, fossiliferous, marine dolomite. It only from samples brought to the surface during commonly contains pasty limestone beds and 1.

PAGE 4

MWUMAT OWa $30uaa. f .sIA 0 m0WIM cMg -ARAIMA r FAI WFPWMMIT90 MmTOCOMOLOORIS WIICI CIA= t RAMFN JACIWON SUPP fam"MAT Sr.WNI OP 001 &HOLA I ;WM *mm MAOCU-PUIOCV~k COAMCLAIM OCALA *F PVOCOLA CLAY MON RW FORMATIONXTRAC MA, * INMA1 Forge 1, GanhraIsd geclogc cIroa section Wong Flaontle wes aowa "Mat(~~lIUCLI*PUWI~IKIID~ COASSTAL 2Y COASTAL COASTAL CENTAL I ~ "m'sPA14HADLE BIG BISND P) CNTRA j HOLOCENE UIPPIrINI1ATUD UND1rU11HN1A1M7U UNCFPEIt4TIA71UO PLAUDOCKGP P1u1RSNTATID 10wIFrR1MTIATIO UNWFWRITIATEo I I JAIYu~ lw 0 0 .%.NU ANEWA L PAL coeeve mmhe I I YOO~ll*WftAr IM& B ~ ~ ~ Cm a, unl D Ir owr CHTTOO" g ARCADIA PM. OUWImp -l SUWANYYI Le. WAN)ll I.. laco P OCALA GROUP I OCALA GROW OCALA OROUP AVON PARK PM.MI(N I ANON POK 10. AVON PARK FM. YOMM ft nmkrlw Wxmdft Flormals ot oou 2 n rne ah dahesa m

PAGE 5

peat flecks and seams. The Avon Park limestone. Microfossils are generally the most Formation was deposited in a shallow sea which common fossil forms present, especially the large covered the area of present-day Florida about 54 species of foraminifera Lepldocyclina, million years ago. Numerous shallow-water Nummulites, and Heterostegina. Mollusks, fossils are found in Avon Park Formation bryozoans, and echinoids are also common in sediments, Including heart urchins, sand dollars, these sediments. As shown on Figure 1, the mollusks, foraminifera, and a "tutle grass-like" Ocala Group also crops out in west central marine plant, very similar to the species living off Florida, along the crest of the Ocala Platform. It the Big Bend coastline today. dips generally westward and southwestward from The Avon Park Formation is the oldest rock its outcrop area. The thickness of the Ocala exposed at the surface In Florida. It occurs In Group in west-central Florida averages about 60 west-central Florida along the crest of a gentle, m (200 ft), but Is locally variable, and generally northwest-southeast trending anticlinal feature thins over the crest of the Ocala Platform. variously called the Ocala Uplift, Ocala Arch, Umestone of the Ocala Group is exposed Ocala High, or Ocala Platform (Purl and Vemon, sporadically or is blanketed only by a thin veneer 1964; Scott, 1988), the origin of which is uncertain, of Pleistocene and Holocene sands in all of Dixie Eocene and younger rocks have been removed County and portions of Lafayette, Gilchrist, Levy, by erosion over the structure. Citrus, Marion, and Hernando Counties. The Avon Park Formation is exposed only in Throughout this area it is quarried as construction small areas of central and southern Levy County material and road base. and northernmost Citrus County, corresponding The exposed surface of the Ocala Group to the crest of the Ocala Platform (see Figure 1). limestone forms a relatively flat-lying, gently It dips westward, where it interfingers with the age seaward-sloping, solution depression and equivalent Usbon Formation under the western sinkhole-pocked plain over most of its outcrop Florida panhandle. Thickness of the unit In area. This plain continues offshore onto the west-central Florida is variable, but generally broad western Florida continental shelf. ranges from 0 to 240 m (0 to 800 ft) statewide Boulders, pinnacles, and small Islands of Ocala (Chen, 1965). Group limestone are common along the Gulf Dolomite from the Avon Park Is quarried In coastline of Dixie, Levy, and Citrus Counties Citrus and Levy Counties for use in construction (Vemon, 1951). Many of the coastal marshes in materials. The Avon Park is also a unit of the this area are developed in the thin calcitic muds, Floridan aquifer system, one of Florida's primary silt, organlqs, and relict marine sands deposited in drinking water aquifers. It is unconformably solution depressions in the underlying limestone overlain by marine limestone of the Upper (see Figure 3). The Ocala Group is an important Eocene Ocala Group. unit of the Floridan aquifer system. Along much of the central west coast and within many of the Upper Eocene Series coastal marsh areas, the potentlometric surface of Ocala Group the Floridan aquifer system is at or above land surface. As a result, numerous seeps and small The Late Eocene (38 to 41 million years ago) springs feed freshwater into the marshes. Fow Ocala Group (Puri, 1957) is composed of three from some of these springs is sufficient to form marine limestone formations. In ascending order, small tidal creeks and tributaries through the these are the Inglis, Williston, and Crystal River otherwise dense marsh grasses (Nettles, 1976). Formations, all named for towns in the respective local outcrop areas of each formation. The Oligocene Series formations have traditionally been differentiated Suwannee Limestone on the basis of fossil content, and to a lesser extent, lithology. For the purposes of this report, The Oligocene (33 to 25 million years old) these three units will be referred to collectively as Suwannee Limestone (Cooke and Mansfield, the Ocala Group. 1936) is a white to tan, fossiliferous, commonly The Ocala Group was deposited In a shallow, dolomitic marine limestone, named after Late Eocene sea. It is typically a white to cream, exposures along the Suwannee River in northern abundantly fossiliferous, chalky to coqulnold Florida. As with the preceding Eocene 3.

PAGE 6

formations, the Suwannee was probably phosphate deposits are concentrated in the deposited in a shallow temperate sea. It contains Miocene Hawthorn Group sediments in the abundant microfossils, mollusks, echinolds, Central Florida Phosphate District of Polk and bryozoans, and rare corals. Early Indians of the surrounding counties and in the North Florida region used the abundant chert occurring In both Phosphate District in Hamilton County. the Ocala Group and Suwannee Umestone to The Miocene formations in Florida are fashion tools and weapons. The Suwannee primarily marine In origin. In contrast to the. Limestone has been truncated against the flanks nearly pure calcium carbonate limestones of the of the Ocala Platform (Figure 1), and is exposed Eocene, the Miocene and younger sediments, at the surface at the northem and southem ends Including the carbonates, typically contain of this feature. It occurs as the surflclal unit in terrigenous quartz and heavy mineral sands and eastern Jefferson County, most of Taylor County, days and phosphate. Starting In the Lower western Hemando County, and northern Pasco Miocene, a massive influx of river-borne County. In these areas, the Suwannee Umestone continental sediments poured into the seas forms a flat-lying, karstic plain which extends covering present day peninsular Florida (Scott, seaward onto the continental shelf. Boulders and 1988). The Miocene seas reworked and pinnacles of Suwannee Umestone are common deposited these sediments in a broad blanket along the low energy coasts of Jefferson and over the carbonates of earlier epochs. In the Taylor Counties. The Suwannee Umestone Is the western panhandle, a series of marine limestones upper unit of the Floridan aquifer system in its and shelly sands were laid down. The Miocene outcrop area. Small fresh water springs and seas supported a rich marine fauna, as shown by seeps commonly occur In the marshes of the numerous fossils found in these sediments. southern Jefferson and Taylor Counties, some Based on fossils, paleoenvironments ranged from forming creeks or contributing to the flow of rivers shallow nearshore and lagoon to deepwater such as the Aucila and Econfina. continental shelf. Many of Florida's commercial mineral deposits, including phosphate and fuller's Miocene Series earth, were formed In these ancient sea floor sediments, The Miocene Epoch marked a significant change in the depositional regime of the Florida Lower Miocene Series peninsula. Previously a shallow carbonate bank, St. Marks Formation Florida experienced an influx of cpntinental silciclastic sediments during the Miocene from The St. Marks Formation (Purl and Vernon, the continental mainland to the north. This was 1964) is exposed along the northern Big Bend due In large part to the closing of a feature called coastline in Wakulla County. It Is the only the Suwannee Straits or Gulf Trough, which Miocene carbonate unit exposed in the coastal trended southwestward across the eastern Florida marsh zone. This formation Is a white to very panhandle (Figure 1). The Gulf Trough was pale orange to light gray, quartz sandy, thought possibly to have been an ancient fossilferous marine limestone. Foraminifera and channel or seaway, existing from the Cretaceous mollusks are the dominant fossil forms, generally Era through the end of the Oligocene Epoch (Dall present as molds. Along the coast the St. Marks and Harris, 1882; Chen, 1965). It probably Formation contains abundant chert, which connected two major depositlonal basins, the probably supplied the paleoindians of the region Southeast Georgia Embayment and the with tool and spear point material. The St. Marks Apalachicola Embayment. Currents within this Formation occurs near or at the surface in most paleo-strait may have functioned as both a of south central and south eastern Wakulla zoological and a sedlmentologlcal barrier between County. Here it forms a slightly seaward-slopthe carbonate banks and islands of peninsular Ing, karstic plain called the Woodville Karst Plain. Florida and the continental mainland. Thickness varies from 0 m at the Phosphogenesis also occurred on a large Wakulla-Jefferson County line to over 30m (100 scale beginning In the Miocene. Many Miocene ft) along the eastern flank of the Apalachicola formations contain phosphate grains, ranging Embayment. Extensive salt marshes, developed from silt to pebble size. Florida's economic in the thin sand and mud veneer overlying the St.

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Marks Formation limestone, border the southern into the Apalachicola Embayment (Figure 1). edge of Wakulla County. Both the Lower Miocene St. Marks Formation and The St. Marks Formation is the uppermost unit the overlying Middle Miocene Bruce Creek of the Floridan aquifer system in the eastern Limestone dip into the trough of the embayment, panhandle. In southern Wakulla County, the reaching a maximum local depth and thickness potentiometric surface of this aquifer is at or under the axis of the basin. These units shallow above the land surface elevation. Many small again on the western side of the embayment, fresh water springs are scattered through the and attain a depth and thickness similar to that coastal marshes, and several submarine springs on the eastern edge of the embayment. are situated on the offshore extension of the karst plain. The St. Marks pinches out against the Bruce Creek Limestone underlying Suwannee Limestone to the east in Jefferson County (Figure 1), and dips generally to Bruce Creek Limestone was the name given the west-southwest. To the west under Franklin by Huddlestun (1976) to a white to light and Gulf Counties it becomes indistinguishable yellowish-gray, Middle Miocene marine limestone from the Bruce Creek Limestone. It interfingers to underlying part of panhandle Florida. It extends the north and possibly under the western from the eastern edge of the Apalachicola panhandle with the age-equivalent Chattahoochee Embayment westward, with generally southwest Formation. dip. The Bruce Creek Limestone is commonly quartz sandy, phosphoritic, and both microand Hawthorn Group macro-fossiliferous. Fossils are generally Arcadia Formation preserved as molds. This formation is primarily a subsurface unit, and does not crop out in the The Lower Miocene Arcadia Formation of the vicinity of the coastal marshes. The Bruce Creek Hawthom Group (Scott, 1988) underlies the Limestone thickens to over 60 m (200 ft) in the west-central Gulf coast from approximately New Apalachicola Embayment. Down-dip, it is Port Richey to Sarasota (Figure 1). This unit is indistinguishable from the underlying St. Marks comprised primarily of white to yellowish-gray to Formation. In the central and westem panhandle, light olive-gray limestone and dolomite containing the Bruce Creek Limestone comprises the variable amounts of quartz sand, clay, and uppermost unit of the Floridan aquifer system. phosphate grains. It unconformably overlies the Suwannee Limestone, and Is overlain by Middle Miocene Through Pliocene Series undifferentiated Pleistocene quartz sands. Intracoastal Formation Hawthorn Group sediments are absent along the panhandle coast. Huddlestun (1976) applied the name Hawthorn Group sediments serve as an Intracoastal Formation to a soft, yellowish-gray to Intermediate confining unit to the underlying olive green, sandy, highly microfossiliferous, Floridan aquifer system. Locally, carbonates argillaceous marine limestone underlying the within the Hawthorn Group may also function as coastal area of west Florida. This formation an intermediate freshwater aquifer system, or in extends from easternmost Franklin County some areas, are in hydrologic continuity with the westward, and continues to approximately the underlying Floridan aquifer system and Santa Rosa County line (Schmidt, 1984). The considered part of the Floridan aquifer. Intracoastal Formation is predominantly a The Hawthorn Group does not crop out in the subsurface unit, dipping and thickening to the vicinity of the coastal marshes. It is probably west-southwest into the Apalachicola Embayment. eroding offshore however, as pebbles and It approaches 100 m (300 ft) in thickness in the cobbles of Hawthorn Group carbonate are often trough of the Apalachicola Embayment. The unit found washed up on Pinellas County beaches, shallows and thins west of the embayment, then thickens and dips westward towards the Pensacola area. Analysis of the microfossils Middle Miocene present indicate an age range for the Intracoastal West of Wakulla County in the panhandle, the Formation of Middle Miocene (down dip) to Late Miocene units dip and thicken southwestward Pliocene (in the up-dip portions), with a hiatus

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separating the age extremes. Locally it occurs west and east of the embayment. In the downclose to the surface In the central panhandle, but dip coastal and offshore areas, the Chipola does not crop out In the coastal marsh region. Formation overles the Intracoastal Formation and is considered to be late Pliocene In age (Schmidt, Pensacola Clay 1984). It Is unconformably overlain by the Jackson Bluff Formation. The Pensacola Clay (Marsh, 1966) is a pale, yellowish-brown to olive-gray, dense, silty, Jackson Bluff Formation commonly quartz-rich sandy clay. This unit Is restricted to the subsurface, occurring under the The Late Pliocene Jackson Bluff Formation panhandle from approximately Okaloosa County (Purl and Vemon, 1964) consists of tan to westward into Alabama. It thickens rapidly to the orangish-brown to grayish green sandy, clayey south and west (see Figure 1), reaching a shell beds. It is restricted in occurrence to the maximum thickness of about 150 m (500 ft) under central Apalachlcola Embayment, where the unit Pensacola Bay (Clark and Schmidt, 1982). The reaches about 30 m (100 ft) in thickness. The Pensacola Clay is considered Late Miocene in Jackson Bluff Formation overiles the Chipola and age, overlying the Bruce Creek Limestone, and is Intracoastal Formations, and Is in turn overlain by interfingered locally with the Intracoastal undifferentiated Pleistocene and Holocene sands. Formation or the Miocene Coarse Clastics (Clark The Jackson Bluff Formation does not crop out in and Schmidt, 1982). the coastal marshes. Miocene-Pliocene Coarse Clastics Pleistocene and Holocene Series Marsh (1966) proposed the name Miocene A series of undifferentiated Pleistocene (1.8 Coarse Clastics for a series of sands, gravel, million to 10,000 years old) and Holocene (10,000 clays, and shell beds underlying the western years and younger) quartz sands, clayey sands, panhandle. These sediments are largely and sandy clays blanket the older formations comprised of light-gray to pale-yellowish-brown along much of Florida's west coast. These quartz sand and gravel, with minor clay and sediments are composed largely of reworked marine mollusk shells. The Miocene-Pllocene relict Pleistocene marine sands and Holocene Coarse Clastics occur from western Okaloosa alluvium, calcitic muds, and organics. County westward through Santa Rosa and The Pleistocene Epoch, or "Ice Age', was Escambla Counties. Thickness of this unit characterized by four great glacial periods. reaches nearly 150 m (500 ft) under Santa Rosa During this epoch, global temperatures cooled, County. The coarse clastics overlie the and huge Ice sheets grew southward from Pensacola clay and Intracoastal Formations, and Canada. Large quantities of seawater were locally may be contemporaneous (Late Miocene consumed to build the glaciers, and sea level to Early Pliocene In age) with portions of both dropped as much as 130 m (400 ft). Each glacial formations; they are overlaln by undifferentiated period was punctuated by warmer Interglacial Pleistocene sand (Clark and Schmidt, 1982). periods during which the sea level rose, at times to over 30 m (100 ft) above modem level. As the Chipola Formation Pleistocene seas transgressed Inland, wave and current activity eroded, reworked, and The Chipola Formation (Puri and Vernon, redeposited the sands of earlier formations. At 1964) is present at depth under the coastal the same time, rivers and an active southwardmarshes in the vicinity of Gulf County, along the moving littoral drift system brought new clastic axis of the Apalachicola Embayment. sediments into Florida. The Big Bend Area was a Lithologically, it is comprised of a yellowish-gray drowned karst coastline during the Pleistocene to light-gray, quartz sandy marine limestone, sea-level highstands. Planing by wave action and Foraminifera and mollusks are typically the most in-filling of the karst features with sand resulted in abundant fossils. Thickness of this unit reaches the flat, seaward-sloping plain characterizing this about 15 m (50 ft) In the central Apalachlcola region today. Figure 3 illustrates a typical nearEmbayment, thinning and pinching out to the surface cross-section In the coastal marsh zone

PAGE 9

DEPITH S I TIDAL LIMESTONETID CHANNEL PINNACLE TIDAL 3 CHANNEL MARSH GRASSES 0. W. PLISTOCENE AND HOLOCENE -I " l EOCENE/OUIGOCENE LMESTONE SVER EXAERAT AM-1LY TIMES DIE S EALE Figure 3. Generalized near-surface cross section in the coastal marshes, west-central Florida (modified from Hine and Belknap, 1986), .00 VERTICAL EXAERAION -AWNO3OTELY 110 1uES TRIM SCALE Figure 3. Generalized near-surface cross section in the coastal marshes, west-central Florida (modified from Hine and Belknap, 1986). Coo

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along the west-central Florida coast. The Iarstic, that the focus herein Is on the recent geologic irregular surface of the underlying limestone is past, modern offshore landforms such as spits, infilled with Pleistocene and Holocene sediments, barrier Islands and bars are not discussed. with a few limestone pinnacles exposed at the Up to six marine terraces are reported to occur surface. The younger sands, muds, and silts form within the region of Interest (Cooke, 1945; Healy, a substrate for many of the coastal marshes in 1975). As defined by Garner (1974), a marine this area. .terrace Is a surface of erosion or deposition Relict dunes, bars, and barrier Island sand formed along a coast by wave action. These bodies, left by retreating Pleistocene seas, also terraces represent the floors of ancient shallow are common features today along much of seas and are situated in a step-like manner, Florida's central and northem Gulf coasts. In the roughly parallel to the present-day coast. Each central panhandle, the ancestral Apalachicola "step" Is a topographic break ranging from a River meandered over a large area of Bay and gentle slope to a sharp Incline. Where sharp, Gulf Counties during the Pleistocene and these changes In topography which separate two Holocene, leaving In its wake relict levee deposits terraces are well preserved seaward-facing wave and alluvium. Much of the surficial and nearcut scarps, some of which are regional In extent surface sediments in the central and western and contain up to 15 meters (50 feet) of relief panhandle coastal areas are a mixture of marine (e.g. the Cody Scarp, Purl and Vernon, 1964, and alluvial sands and clays. p.11). Although there are few of this magnitude The Pleistocene deposits are thinnest in the proximal to the Gulf Coast, coastal terraces and Big Bend area, where limestone Is near or at the scarps appear to control surface drainage in surface. West of Wakulla County, these localized areas. For example, Healy's (1975) Pleistocene sediments thicken to nearly 60 m (200 Silver Bluff terrace generally coincides with the ft) near the Alabama state line. location of several Gulf coastal swamps. Holocene sand deposition continues today. Early marine terrace studies have applied Accumulation of these deposits Is primarily physiographic and geomorphic evidence (White, concentrated along the banks, bottoms, and 1970), aerial photography (Vernon, 1951), mouths of the major Gulf coast rivers, such as the sedimentology/stratigraphy (Altschuler and Apalachicola, Ochlockonee, Aucllla, Suwannee, Young, 1960; Plrkle and others, 1970), field and Withlacoochee. In portions of the central mapping (Parker and others, 1955) and fossil west coast and Big Bend areas, a Holocene evidence (Alt and Brooks, 1965). Although Intertidal calcitic mud often overles the conclusions drawn for localized areas are well Pleistocene sand (Nettles, 1976). Organics constrained by these data, studies based on derived from decaying marsh grasses are elevation correlations over large areas (e.g. Intermixed with sandy typically forms the surface MacNeil, 1950; Healy, 1975) should be considered layer In the coastal marshes (Hine and Belknap, with reservation. Given the possibility of 1986). regional Pliocene-Pleistocene warping (Winker and Howard, 1977a, 1977b), the predominance of GEOMORPHOLOGY karst development in the region (White, 1970) as well as other erosional processes, some of these The geomorphology of Florida's Gulf Coast long-distance correlations may not be valid. For has been shaped primarily by coastal processes example, a present day low-lying area may and sea-level changes during the past five million appear to correlate with a certain low elevation years. These sea-level changes have caused terrace, whereas in fact it may have been an shifts In ground water levels , which in turn have upland or higher elevation terrace which was enhanced the development of karst landforms subsequently lowered by subsurface limestone during this time. The karst features have thus dissolution. On the other hand, a "young", low altered some of the original shoreline erosional elevation terrace may have undergone and depositional features within the Gulf Coast epelrogenic uplift and now topographically region. Discussion of these two Interrelated correlates with a higher elevation, older terrace. geomorphic features is limited to an Inland Thus, the correlation between distance of 16 kilometers (10 miles), spanning the swamps/marshlands and the Silver Bluff terrace study area from Pensacola to St. Petersburg. In may be an artifact of the manner in which some terraces have been delineated. Ancient marine

PAGE 11

scarps and terraces do exist in the Gulf Coast swamp are separated from the coast by dry land, region; however, further study is required in order the term "coastal lagoons" is applied (White, to more accurately define their occurrence and 1970). This generalized terminology is being extent, revised based on vegetation, soil type and Pliocene-Pleistocene sea-level fluctuations are topography in concurrent investigations (C.L. the primary reason for the presence of these Coultas, personal communication, 1990). terraces (Winker and Howard, 1977a, 1977b). White (1970) presented a two-fold classification During the Pleistocene "Ice Age" when the for the Gulf Coast of peninsular Florida. Within fluctuations became more prevalent, four major the study area, this includes a coastal salient that glacial cycles occurred due to major climatic extends from Tampa Bay north to the southern changes. As glaciers spread over the continents, part of Pasco County, and a coastal reentrant sea-level dropped. During periods of melting or spanning from this point north toward Apalachee interglacial periods, sea-level rose. Healy (1975) Bay. The salient is characterized by a relatively and MacNell (1950) suggested that during steep offshore profile which allows wave energy subsequent (younger) interglacial periods, the to transport, deposit and erode sand along the seas stood at levels below that of the prior event, shoreline. This coastal area contains many relict thus preserving the earlier formed terraces and barrier bars, beach ridges and lagoons. In scarps. Several authors have recognized that contrast, the reentrant offshore profiles have glacial melting alone cannot account for the gentle slopes and are floored by limestone. White present-day anomalously high elevations of the (1970) suggested that these broad shallow older marine terraces. Tanner (1968, 1985) and profiles sufficiently dissipate wave energies to Winker and Howard (1977a, 1977b) document account for the sand-starved marshy coasts. The evidence for regional uplift during this time. sand deficiency is also due to a lack of sediment In a study entitled "The Geomorphology of the transported by the Suwannee River. The very Florida Peninsula," White (1970) subdivided the low-energy reentrant coast Is virtually free of region into a series of uplands and lowlands, relict shoreline features. Most of the present study area lies within a Along the Florida panhandle coastline, White's single, major physiographic province: the Gulf (1970) generalization concerning the peninsula's Coastal Lowlands (Figure 4). This province offshore profiles Is also applicable. Westward stretches from the western Florida panhandle to from the west end of Apalachee Bay, the profile southern peninsular Florida and averages 40 is either as steep as or steeper than in the Tampa kilometers (25 miles) in width. Various highlands, Bay area. The entire panhandle coastline ridges or scarps constitute the Inland limits of the consists of spits, lagoons, beach ridges and Gulf Coastal Lowlands, whereas the present-day offshore barrier islands. An even steeper offshore shoreline marks the seaward boundary. Unlike slope (ramp) in the central panhandle region has eastern coastal areas of Florida, this geomorphic precluded barrier island formation offshore of province does not correspond to any specific Walton and the west half of Bay counties (Tanner, marine terrace delineated by Healy (1975). The 1960). Puri and Vernon's (1964) geomorphic Gulf Coastal Lowlands contain various erosional map of the region, which uses White's criteria for and depositional landforms that occurred in landform definition, shows no coastal swamps. response to Pliocene-Pleistocene sea-level Tanner (1960) presented data which quantify fluctuations. Several relict bars, spits and energy levels within the study area. Rather than terraces are superimposed on the modem focussing on shelf slope, he reported average topography of the region. Subdivisions within the annual breaker heights to estimate wave energy. Gulf Coast Lowlands include Gulf Barrier Chains, Energy levels of Tanner (1960) are shown on Coastal Swamps, Coastal Lagoons and Estuaries. Figure 4. The "zero energy" coast corresponds to Using White's (1970) terminology, the Gulf the coastal swamps and marshes in the Big Bend Coastal Swamps include areas where a area. The lack of both wave energy and thus deficiency exists In the sand budget for building sediment transport and deposition are the two beaches. These low-lying areas correspond to most significant factors that have allowed areas on topographic maps where the swamps swamp/marsh development in the region. are immediately adjacent to the coast. No In addition to the regional geomorphic distinction is made between salt marshes and characteristics of the study area, two localized fresh water swamps. Where Isolated patches of features are noteworthy, both of which pertain to 1

PAGE 12

SKNIlS i: COASTAL swMPs LOW SCALE FIgure 4. Geomorphic features along study area modified from White (1970) and Purl and Vernon (1964). Wave energy zones are from Tanner (1960). (1960). ~ UU((I

PAGE 13

karstiflcation. The first of these can be seen on Altschuler, Z. S. and Young, E. J. 1960. Residual Tanner's (1960) map which classifies a shoreline origin of the "Pleistocene" sand mantle in region of Citrus County as "drowned karst" central Florida uplands and its bearing on (Figure 4). This area, discussed in detail by Hine marine terraces and Cenozoic uplift: U.S. and Belknap (1986) is called the Ozello Marsh Geological Survey Professional Paper Archipelago and consists of several limestone 400-B:202-207. cored marsh Islands. The outer islands are Applin, P. L, and Applin, E. R., 1944, Regional separated either by creeks or salt marsh subsurface stratigraphy and structure of vegetation whereas the interior is pocked with Florida and southern Georgia: American circular ponds. Various karstificatlon processes Association of Petroleum Geologist have controlled the shape and orientation of Bulletin, 28:1673-1753. these water bodies (HIne and Belknap, 1986). Arthur, J. D., 1988, Petrogenesis of Early Figure 3 Illustrates the undulatory nature of Mesozoictholelite in the Florida basement bedrock limestone in this area due to dissolution, and an overview of Florida basement The Woodville Karst Plain (Hendry and Sproul, geology: Florida Geological Survey 1966) is a subdivision of the Gulf Coastal Report of Investigation 97. Lowlands and is located north of the coastal Chen, C. S., 1965, The regional lithostratlgraphic swamp belt In Wakulla County. Portions of the analysis of Paleocene and Eocene rocks Woodville Karst Plain extend into Jefferson and of Florida: Florida Geological Survey Leon Counties where it is bounded to the north Bulletin 45. by the Northern Highlands (Purl and Vernon, Clark, M., and Schmidt, W., 1982, Shallow 1964). Permeable sands form a veneer over a stratigraphy of Okaloosa County and shallow, southward dipping limestone bedrock. vicinity, Florida: Florida Bureau of Dissolution of the underlying bedrock, which has Geology Report of Investigation 92. probably been occurring ever since the area has Cooke, C. W., 1945,. Geology of Florida: Florida been above sea level, has caused subsidence. Geological Survey Bulletin 29. This somewhat localized depression, and its , and Mansfield, W. C., 1936, prevalence of shallow sand filled sinkholes Suwannee Umestone of Rorida [abs.]: characterizes the Woodville Karst Plain. Although Geological Society of America surrounding areas are also underlain by Proceedings for 1935. limestone, dissolution has not been prevalent Dall, W. H., and Harris, G. D., 1892, Correlation because the overlying sediments contain clays papers -Neocene: U. S. Geological which both buffer the acidic rainwater and Survey Bulletin 84. reduce the amount of percolation. Geologic Garner, H. F. 1974. The origin of landscapes. variables such as those characterizing the Oxford University Press. New York. Woodville Karst Plain -bedrock type, sediment Healy, H. G. 1975. Terraces and shorelines of composition, and sea level history -are significant Florida: Florida Geological Survey Map in the development of Florida's Gulf Coast Series 71. geomorphology. Hendry, C. W. and Sproul, C. 1966. Geology and ground-water resources of Leon County, ACKNOWLEDGEMENTS Florida: Rorida Geological Survey Bulletin 47. The authors would like to thank Ken Hine, A. C., and Belknap, D. F., 1986, Recent Campbell, Dr. Walt Schmidt and Dr. Thomas Scott geological history and modern of the Florida Geological Survey, and Dr. William sedimentary processes of the Pasco, F. Tanner of Rorida State University for critically Hemando, and Citrus County coastline: reviewing the manuscript of this report, west central Florida: Florida Sea Grant College Report No. 79. REFERENCES Huddlestun, P. F., 1976, The Neogene stratigraphy of the central Forida Alt, D. and Brooks, H. K. 1965. Age of the Florida panhandle. [Ph.D. dissert.]: Tallahassee, marine terraces: Journal of Geology Florida, Florida State University. 73:406-411. MacNeil, F. S. 1950. Pleistocene terraces and shorelines in Florida: U.S. Geological 12

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Survey Professional Paper 221-F. Survey Bulletin 33. Marsh, O. T., 1966, Geology of Escambla and White, W. A. 1970. The geomorphology of the Santa Rosa Counties, western Florida Florida Peninsula: Florida Bureau of panhandle: Florida Geological Survey Geology Bulletin 51. Bulletin 46. Winker, C. D. and Howard, J. D., 1977a, Miller, J. A., 1986, Hydrogeologic framework of Correlation of tectonically deformed the Floridan aquifer system In Florida and shorelines on the southem Atlantic in parts of Georgia, Alabama, and South coastal Plain: Geology 5:123-127. Carolina: U. 8. Geological Survey , 1977b, Profesalonal Paper 1403-B. Pllo-Plelstocene paleogeography of the Florida Gulf Coast interpreted from relict Nettles, S., 1976, Intertidal calcltic muds along the shorelines: Transactions -Gulf Coast west coast of Florida [theess], Department Association of Geological Societies of Geology, University of Florida, 27:409-420. Galneesvle, Florida. Parker, G. G., Ferguson, G. E. and Love, 8. K. 1966. Water resources of southeaster Florida with special reference to the geology and ground water of the Miamiaea. U.S. Geological Survey Water-Supply Paper 1255. Pirlde, E. C., Yoho, W. H. and Hendry, C. W. 1970. Ancient sea level stands in Florida: Florida Bureau of-Geology Bulletin 52. Purl, H. S., 1967, Stratlgraphy and zonation of the Ocala Group: Florida Geological Survey Bulletin 38. , and Vemon, R. 0., 1964, Geology of Florida and a guidebook to the classic exposures: Florida Geological Survey Special Publication 5 (revised). Schmidt, W., and Clark, M., 1980, Geology of Bay County, Florida: Florida Bureau of Geology Bulletin 57. , 1964, Neogene stratigraphy and geologic history of the Apalachicola embayment, Florida: Florida Geological Survey Bulletin 58. Scott, T. M., 1986, The lithostratigraphy of the Hawthorn Group (Miocene) of Florida: Florida Geological Survey Bulletin 59. Tanner, W.F.. 1960, Florida coastal classification: Transactions -Gulf Coast Association of Geological Societies 10:259-266. , 1968, Tertiary sea level symposium -Introduction: Paleogeography, Paleoclimatology, Paleoecology 5:7-14. , 1965, Late Cenozoic sea level history In the Southeastem United States: Institute for Tertiary-Quatemary Studies TER-QUA Symposium Series 1:3-8. Vernon, R. 0., 1961, Geology of Citrus and Levy Countes, Florida: Florida Geological

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