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STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Virgina Wetherell, Secretary








DIVISION OF ADMINISTRATIVE AND TECHNICAL SERVICES
Nevin G. Smith, Director







FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief






OPEN FILE REPORT NO. 70

THE GEOMORPHOLOGY AND GEOLOGY OF TAYLOR COUNTY, FLORIDA

BY

FRANK R. RUPERT


FLORIDA GEOLOGICAL SURVEY
Tallahassee
1996




ISSN 1058-1391




UNIVERSITY OF FLORIDA LIBRARIES








The geomorphology and geology of Taylor County, Florida
Frank R. Rupert, P.G. 149


GEOMORPHOLOGY
Taylor County is situated in Florida's Big
Bend area, lying wholly within a broad
geomorphic subdivision named the Gulf Coastal
Lowlands (White, 1970). The Gulf Coastal
Lowlands are characterized as a low, flat,
frequently swampy, seaward-sloping plain with
surface slope ranging between 1 and 5 feet per
mile seaward. The maximum land surface
elevation attained is about 100 feet above mean
sea level (msl) along the Taylor/Madison County
line in the northern portion of the county.
Limestone and dolostone, covered by a veneer
of unconsolidated sand, form the near-surface
bedrock in most of the county. Similar terrain
has been named the Limestone Shelf and
Hammocks in neighboring Dixie County by Puri
et al. (1967), and is called the Woodville Karst
Plain to the west in adjacent Jefferson County
(Yon, 1966).
The irregular, highly karstic Oligocene and
Eocene carbonates underlying this area are
masked by a blanket of undifferentiated
Pleistocene sand. Near the coast, the
undifferentiated sands are thin to absent. West
of Perry, in the San Pedro Bay region, these
sands may attain thicknesses of nearly 80 feet
and contain enough clay to function as local
aquitards to the underlying Floridan aquifer
system. The top of the underlying carbonate
bedrock rises gently from approximately sea
level at the coast to an elevation of
approximately 60 feet above msl in the
northeastern corner of the county (Alison and
Rupert, 1996). Commercial forest and
agricultural lands comprise much of the region.
Near the coast, the karst plain merges seaward
into the coastal marshes, and continues offshore
as a broad, sand-covered, continental shelf.
Small artesian springs flow from the near
surface limestone, and during periods of heavy
rainfall, portions of the karst plain may flood to
form a shallow swamp. Drainage from the
coastal hammocks is sluggish, and occurs
through a number of small creeks and sloughs,
which empty into the coastal swamps.
Most of the Gulf Coastal Lowlands area is
ancient marine terrace terrain. Pleistocene seas
alternately flooded and retreated from this
region, depositing a step-like series of marine
terraces, which generally parallel the modern
coastline. Healy (1975) recognizes three marine


terrace elevation zones in Taylor County,
including the Silver Bluff Terrace (less than 10
feet above msl), the Pamlico Terrace (8 to 25
feet above msl) and the Wicomico Terrace (70
to 100 feet above msl). Superimposed on these
terrace surfaces are numerous relict Pleistocene
marine features such as bars, dunes, and beach
ridge systems. Such relict features, composed
principally of white quartz sand, may be
observed far inland from the modern coastline.
Taylor County's Gulf shoreline is classified
as a low-wave- energy, drowned karst coast. It
is characterized by very low wave activity, a
general lack of sand beaches, and an irregular
outline. A series of small islets, or keys,
comprised of limestone pinnacles, are common
along the southern portion of the coastline.
Extensive coastal salt marshes, with a few small
interspersed sand beaches and numerous
nearshore oyster bars, are developed at the land-
sea interface along the length of the coast.

Coastal Swamps
A zone of low, flat, frequently flooded
hammocks and pine flatwoods, rimmed on their
seaward edge by salt marshes, occurs along the
low-energy Gulf coastline of Taylor County. This
subdivision of the Gulf Coastal Lowlands was
named the Coastal Swamps by White, (1970).
It typically extends from the shore inland to
approximately the 10 feet msl contour line,
which is situated a distance ranging from about
one to four miles inland (Figure 1). Due to lack
of sand input and the low wave energy
conditions along the Big Bend coastline, sand
beaches are poorly developed or absent.
Numerous small surface streams, most of
which arise in the swampy hammocks and bays
in western Taylor County, flow generally
southwestward and empty into the Gulf of
Mexico. Most are sluggish, tannic water
streams, flowing in narrow channels and
draining the interior swamps. Some of these
creeks are fed along their courses by small
springs seeping freshwater from the carbonate
rocks of the underlying Floridan aquifer system.
Extensive salt marshes, comprised of Juncus
and Spartina grasses rooted in shallow, organic-
rich silts and sands lying on limestone, border
the land-sea interface along most of the coast.
The marshes are dissected by small, seaward
flowing tidal streams and creeks, which may









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EXPLANATION o,

GEOMORPHIC ZONES 0
THE FOLLOWING ZONES ARE SUBDIVISIONS OF THE
GULF COASTAL LOWLANDS GEOMORPHIC ZONE OF
WHITE (1970), WHICH COMPRISES ALL OF TAYLOR COUNTY:

M COASTAL SWAMPS


RIVER VALLEY


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Figure 1. Geomorphic and Cross Section Location Map.


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also be fed by freshwater seeping out of the
shallow limestone of the Floridan aquifer
system.

River Valley Lowlands
The Aucilla and Steinhatchee Rivers are the
largest surface streams in the county, forming
portions of Taylor County's boundaries with
adjacent counties. The Aucilla River forms the
county boundary between Taylor and
neighboring Jefferson County to the northwest.
It flows southwestward from Georgia to the
Gulf of Mexico in a variable-width dissolutional
valley, carved in the underlying Oligocene
carbonates. The topographic lowlands
immediately adjacent to the river, generally
characterized by thin Holocene sands and clayey
sands lying on limestone, comprise the Aucilla
River Valley Lowlands (Yon, 1966). River valley
floor elevations range from about 35 feet above
msl in northwestern Taylor County to sea level
where it enters the Coastal Swamps. For most
of its course, the valley is less than one mile
wide. Along portions of the stream, rapids flow
over exposed, silicified limestone. The Aucilla
River is captured by subterranean drainage four
and a half miles north of Highway 98, and
approximately two miles of its underground
course are defined by closely-spaced sinks; the
river emerges two and a half miles above
Highway 98, flowing approximately one and a
half miles as a surface stream before flowing
underground once again into a sink. The Aucilla
reemerges at the community of Nutall Rise, in
western Taylor County, for its final course to the
Gulf. The river broadens as it merges into the
coastal swamps near the coast.
The Steinhatchee River arises in the
swampy hammocks of adjacent Lafayette
County, and flows southwestward in a narrow,
incised valley generally lying ten feet or less
above msl. It forms the southern county
boundary between Taylor and Dixie Counties.
The Steinhatchee flows in a narrow channel cut
in Eocene carbonates, which commonly crop out
along the lower portion of the river. The river
flows underground for a one-mile stretch near
the community of Tennile and emerges about
0.3 miles west of Highway 19. The
underground portion of the river's route is
mirrored at the surface by a topographic valley
containing only intermittent flow. The
Steinhatchee River is a sluggish, generally tannic
stream, widening near the coast as it enters the


coastal salt marshes. The lowlands adjacent to
the river are typically very narrow, widening
significantly in only one small area northeast of
Steinhatchee. Pleistocene and Holocene
siliciclastics form a sediment veneer over the
carbonates in the river bed and along the banks.

GEOLOGY
The oldest rock commonly penetrated by
water wells in Taylor County is marine limestone
of the Eocene Avon Park Formation.
Undifferentiated Pleistocene and Holocene
surficial sands, clayey sands, and alluvium are
the youngest sediments present. Figure 2
illustrates the shallow stratigraphy of the
county. The Avon Park Formation and the
younger overlying carbonates are important
freshwater aquifers, and the following
discussion of the geology of Dixie County is
confined to these Eocene and younger
sediments.

Eocene Series
Avon Park Formation
The Avon Park Formation (Miller, 1986)
is a lithologically variable Middle Eocene
carbonate unit underlying all of Taylor County. It
is typically a yellowish-gray to grayish-orange to
dark yellowish brown dolostone, commonly
interbedded with grayish-white to yellowish-gray
limestones and dolomitic limestones. The unit
may contain varying amounts of peat, lignite,
and plant remains (Florida Geological Survey in-
house well logs). Mollusks, echinoids, and
foraminifera, where preserved, are the principal
fossils present. The top of the Avon Park
Formation varies in depth from approximately
300 feet below land surface (bls) in
northwestern Taylor County to about 90 feet bls
in the southern part of the county. Surface
exposures of Avon Park are absent in this
county, but do occur to the south in Levy
County, over the crest of a positive subsurface
structural feature named the Ocala Platform.
Deep oil test well data indicate that the Avon
Park Formation ranges from approximately 800
to 1400 feet thick under Taylor County (FGS in-
house well logs).

Ocala Limestone
Marine limestones of the Ocala Limestone
(Puri, 1957; Scott, 1991) unconformibly overlie
the Avon Park Formation under all of Taylor
County. It is divided into upper and lower units









NORTH

A

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100 .


-50










-2D00

-250

-300

-350
*-350


SOUTH

A'


UNDIFFERENTIATED SAND AND CLAY
I I


UNDIFFERENTIATED SAND AND CLAY


OCALA,


LIMESTONE


FORMATION


VERTICAL EXAGGERATION = APPROXIMATELY 570 TIMES TRUE SCALE.


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--150

-200

-250

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UNDIFFERENTIATED

UNDIFFERENTIATED


WEST

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MILES
012345
02468
KILOMETERS







FGS 120296


Figure 2. North-South and East-West Cross Sections in Taylor County.

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based on lithology. The lithology of the Ocala
Limestone grades upward from alternating hard
and soft, white to tan to gray fossiliferous
limestone and dolomitic limestone of the lower
unit into white to very light gray to light
yellowish-orange, abundantly fossiliferous,
chalky limestones of the upper unit (FGS in-
house well files). Foraminifera, mollusks,
bryozoans, and echinoids are the most abundant
fossils occurring in this unit. Thickness of the
Ocala Limestone sediments under Taylor County
ranges between 80 and 220 feet thick. It
generally thins against the structurally high Avon
Park Formation toward the crest of the Ocala
Platform in the southern and eastern portions of
the county. Depth to the irregular and highly-
karstic top of the Ocala Limestone is generally
between 10 and 100 feet. The overlying
Suwannee Limestone pinches out against the
Ocala Limestone along an approximate contact
extending northeast-southwest from near the
town of Salem to Little Bear Creek, on the Gulf
coast (Figure 1). North of this contact line the
Suwannee Limestone is the uppermost
carbonate unit; to the south, the Suwannee is
absent and the Ocala Limestone forms the upper
carbonate (Campbell, 1993). The Ocala
Limestone commonly crops out in the
hammocks and coastal marshes of
southernmost Taylor County. Offshore of the
modern coastline, a thin blanket of quartz sand
covers the Ocala Limestone, and exposures in
the form of limestone boulders and pinnacles are
common. Dolomitized exposures of the unit
occur in the vicinity of the town of
Steinhatchee, along the Steinhatchee River in
southernmost Taylor County.
The highly permeable and cavernous nature
of the Ocala Limestone make it an important
freshwater bearing unit of the Floridan aquifer
system. Many drinking water wells in southern
Taylor County withdraw water from this
limestone.

Oligocene Series
Suwannee Limestone
The Suwannee Limestone (Cooke and
Mansfield, 1936) is an Oligocene age marine
limestone and dolostone underlying the northern
two-thirds of Taylor County. It is typically a
white to yellowish-gray to grayish-brown,
skeletal to micritic limestone, altered in some
areas to variably recrystallized dolostone.
Mollusks, foraminifera, echinoids, bryozoans,


and ostracods, in various degrees of
preservation, comprise the dominant fossil
assemblage present in this unit. It's top
typically ranges in depth from as much as 50
feet below land surface in northwestern Taylor
County to some surface exposures in the west
central part of the county and along the Gulf
coastline. The unit climbs and thins to the
southeast. It decreases from about 50 feet
thick in the northeastern part of the county to
zero at its pinchout against the Ocala Limestone
in southern Taylor County. The Suwannee
Limestone locally comprises the uppermost unit
of the Floridan aquifer system. Shallow
domestic and agricultural wells draw water from
this unit.

Pleistocene-Holocene Series
Undifferentiated Pleistocene marine quartz
sands and clayey sands form a thin veneer over
all of Taylor County. They are generally less
than about 50 feet thick county-wide, and thin
to less than 20 feet thick near the coast. They
directly overlie the karstic carbonates of the
Suwannee and Ocala Limestones. Many of the
larger and higher sand bodies in Taylor County
are relict dunes, bars, and barrier islands
associated with various Pleistocene sea level
high stands.
Discontinuous deposits of sparsely-
phosphatic, clayey sands, likely reworked
Hawthorn Group sediments (Tom Scott,
personal communication, 1992) comprise
portions of the undifferentiated sediments in
northern Taylor County. These deposits are
common in karst depressions and may, in part,
represent Plio-Pleistocene paleosinkhole fill.

GROUND WATER
Ground water is water that fills the pore
spaces in subsurface rocks and sediments. This
water is derived principally from precipitation
within Taylor and adjoining counties. The bulk
of Taylor County's consumptive water is
withdrawn from ground water aquifers. Two
aquifer systems are present under Taylor
County, the surficial aquifer system and the
Floridan aquifer system.

Surficial aquifer system
The surficial aquifer system is the uppermost
freshwater aquifer in Taylor County. This non-
artesian aquifer is present only within the
Pleistocene undifferentiated sands and clays of








the San Pedro Bay region of northeastern Taylor
County. In this area, a variably thick clay unit
semi-confines the underlying Floridan aquifer
system and separates it from the surficial aquifer
system. In some areas, the Floridan and surficial
aquifer systems are in hydrologic contact, but
typically, the two contain chemically different
water. The surficial aquifer system, where
present, is unconfined and its upper surface is
the water table. In general, the water table
elevation fluctuates with precipitation and
conforms to the topography of the land surface.
Recharge to the surficial aquifer system is
largely through rainfall percolating downward
through the unconsolidated surficial sediments,
and to a lesser extent, by upward seepage from
the underlying Floridan aquifer system. Water
naturally discharges from the aquifer by
evaporation, outflow from surface seeps, and
downward seepage into the Floridan aquifer
system. The surficial aquifer system is not used
as a source of consumptive water in Taylor
County.

Floridan aquifer system
In Taylor County, the Floridan aquifer system
is comprised of hundreds of feet of Eocene and
Oligocene marine limestones, including the Avon
Park Formation, Ocala Limestone, and
Suwannee Limestone. It is the principle source
of drinking water in the county. The Floridan
aquifer system exists as an unconfined, non-
artesian aquifer in most of Taylor County, where
porous quartz sand directly overlies the
limestone. In the San Pedro Bay area, clay units
may serve to locally confine the aquifer. Depth
to the top of the Floridan aquifer system
generally corresponds to the depth of limestone,
and varies from less than five feet in the coastal
marshes and River Valley Lowlands to more
than 80 feet under the larger relict Pleistocene
sand bodies. The potentiometric gradient is
southwestward.
Recharge to the Floridan aquifer system in
Taylor County is obtained from lateral inflow
from the north and, to a lesser extent, from local
rainfall entering karst features and percolating
downward through the permeable surficial
sands. The highest recharge by percolation
occurs in a narrow, northwest-southeast
trending swath of dune sands overlying karstic
carbonates in southwestern Taylor County
(Stewart, 1980).


Water leaves the Floridan aquifer system
through natural movement down-gradient and
subsequent discharge through numerous springs
and seeps. These springs generally occur in the
River Valley Lowlands and along the coastal
marshes and offshore on the continental slope
where the potentiometric surface of the Floridan
aquifer system is at or above land surface.

MINERAL RESOURCES
Taylor County contains deposits of several
economic mineral commodities. The most
important of these is dolostone. Other minerals
of lesser potential include limestone and sand.
Each commodity and its economic potential and
mining status at the time of publication are
summarized below, with data from Spencer
(1996 in prep.)

Dolomite
Shallow dolomitized Suwannee Limestone
occurs in the Cabbage Grove area (Townships 3
and 4 South, Ranges 4, 5 and 6 East) of
northwestern Taylor County. This area is one of
only about five high-quality dolostone producing
areas in Florida (Schmidt et al., 1979). The
dolostone in Taylor County is mined primarily for
use as road gravel. The rock is extracted by
dragline, crushed on-site, and trucked to
customers. Four companies operating in the
Cabbage grove area at the date of this writing
are E.R. Jahna, Martin Marietta, Proctor and
Gamble, and White Construction.
Elsewhere in the county, private pits
produce dolostone on a sporadic, as-needed
basis. The Florida Department of Transportation
operates a road base pit in Section 4, Township
5 South, Range 5 East and Steinhatchee
Construction maintains a pit southwest of Perry.
Although sufficient dolostone reserves for
continued commercial mining are present in
Taylor County, the lack of more extensive local
markets for the product precludes an extensive
industry in this commodity.

Limestone
Ocala Limestone occurs near the surface
under southernmost Taylor County. The
economic grade may vary considerably from one
area to another. Although mining potential
remains high, no companies commercially mine
limestone in the county. At this writing,
Steinhatchee Construction operates a private pit
in Suwannee Limestone southwest of Perry, and








Proctor and Gamble maintains two private road
base pits in southeastern Taylor County. As
with dolostone, low local demand precludes
extensive mining of this mineral.

Sand
A number of shallow private pits in Taylor
County are worked for fill sand. Pleistocene
quartz sand deposits occur as a variably thick
blanket over most of the county. Since there is
insufficient local demand for sand products, the
potential for commercial mining is low at this
time.

Clay
Clay sporadically occurs as a component of
the undifferentiated surficial sediments covering
Taylor County. Due to the impure nature of this
clay, it is not an economic commodity in the
county.

Peat
Peat forms in a wet, reducing environment
when accumulation of organic materials exceeds
the decomposition rate of that material. Shallow
wetlands in the San Pedro Bay region of
northeastern Taylor County provide potential
peat formation sites. However, while no peat
surveys have been conducted within the county,
studies in adjacent counties indicate that the
peat formed in such areas is too thin to be of
economic interest (Davis, 1946; Bond et al.,
1986). Therefore, the potential for peat mining
in Taylor County is low.

REFERENCES

Alison, D., and Rupert, F.R.,1996, Top of rock
of the Floridan aquifer system in the
Suwannee River Water Management
District: Florida Geological Survey Open File
Map Series 84.

Bond, P.A., Campbell, K.M., and Scott, T.M.,
1986, An overview of peat in Florida and
related issues: Florida Geological Survey
Special Publication No. 27, 151 p.

Campbell, K.M., 1993, Geologic Map of Taylor
County, Florida: Florida Geological Survey
Open File Map Series n. 29.

Cooke, C.W., and Mansfield, W.C., 1936,
Suwannee Limestone of Florida (abs.),


Geological Society of America Proceedings,
1935, p. 71-72.

Davis, J.H. Jr., 1946, The peat deposits of
Florida: their occurrence, development, and
uses: Florida Geological Survey Bulletin 30,
250 p.

Healy, 1975, Terraces and shorelines of Florida:
Florida Bureau of Geology Map Series 71.

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 1403-B, p. 25-27.

Puri, H.S., 1957, Stratigraphy and zonation of
the Ocala Group: Florida Geological
Survey Bulletin 38, 248 p.

Yon, J.W., and Oglesby, W.R.,
1967, Geology of Dixie and Levy Counties,
Florida: Florida Geological Survey Bulletin
49, 155 p.

Schmidt, W., Hoenstine, R.W., Knapp, M.S.,
Lane, B.E., Ogden, G.M., and Scott, T.M.,
1979, The limestone, dolomite and coquina
resources of Florida: Florida Bureau of
Geology Report of Investigation No. 88,
54 p.

Scott, T.M., in: Scott, T.M., Uoyd, J.M., and
Maddox, G., (eds.), 1991, Florida's Ground
Water Monitoring Program Hydrological
Framework: Florida Geological Survey
Special Publication 32, p. 5-14.

Spencer, S.M., 1996 (in preparation), The
Industrial Minerals Directory of Florida:
Florida Geological Survey Information
Circular.

Stewart, J.W., 1980, Areas of natural recharge
to the Floridan aquifer in Florida: Florida
Bureau of Geology Map Series 98.

Yon, J.W., 1966, Geology of Jefferson County,
Florida: Florida Geological Survey Bulletin
48, 119 p.

White, W.A., 1970, Geomorphology of the
Florida peninsula: Florida Geological Survey
Bulletin 51, 164 p.