The geomorphology and geology of Dixie County, Florida ( FGS: Open file report 45 )

Material Information

The geomorphology and geology of Dixie County, Florida ( FGS: Open file report 45 )
Series Title:
( FGS: Open file report 45 )
Rupert, Frank
Florida Geological Survey
Place of Publication:
Florida Geological Survey
Publication Date:
Physical Description:
6 p. : ill. ; 28 cm.


Subjects / Keywords:
Geomorphology -- Florida -- Dixie County ( lcsh )
Geology -- Florida -- Dixie County ( lcsh )
Dixie County ( local )
City of Ocala ( local )
Suwannee River, FL ( local )
City of Vernon ( local )
Levy County ( local )
Limestones ( jstor )
Aquifers ( jstor )
Counties ( jstor )
Lowlands ( jstor )
Valleys ( jstor )
bibliography ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references.
General Note:
Cover title.
Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
Statement of Responsibility:
by Frank R. Rupert.

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:
002301598 ( aleph )
25641780 ( oclc )
ALQ4881 ( notis )


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Tom Gardner, Executive Director

Jeremy A. Craft, Director

Walter Schmidt, State Geologist and Chief







The geomorphology and geology
of Dixie County, Florida

Frank R. Rupert, P.G. 149


Dixie County is situated in Florida's Big Bend
area, along the northern edge of the Central or
Midpeninsular geomorphic zone of White (1970).
This zone extends down the Florida peninsula from
an approximate line connecting the cities of Perry in
Taylor County, Gainesville in Alachua County, and
St. Augustine in St. Johns County, southward to the
Caloosahatchee River. In Dixie County, the Central
Zone is represented by a broad geomorphic subzone
named the Gulf Coastal Lowlands (Figure 1).

Gulf Coastal Lowlands

All of Dixie County lies within an extensive
geomorphic subzone named the Gulf Coastal
Lowlands (White, 1970). This zone is characterized
as a low, flat, frequently swampy and gently seaward
sloping sandy plain. Surface slope ranges between
1 and 4 feet per mile seaward. Limestone, covered
by a thin veneer of unconsolidated sand, forms the
near-surface substrate in most of the county. The
Gulf Coastal Lowlands extend from the modern
shoreline inland to approximately the 100 feet above






SFigure 1: Geomorphic and cross section location map of Dixie County.


mean sea level (MSL) elevation line. In Dixie
County, the maximum elevation attained is about 60
feet above MSL in the northeastern portion of the
county. Most of the 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
the county, including the Silver Bluff Terrace (less
than 10 feet above MSL), the Pamlico Terrace (8 to
25 feet above MSL), and the Talbot Terrace (25 to
42 feet above MSL). Imposed on the terraces 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 stranded far inland from the
modern coastline.
The present Gulf shoreline in this area is
classified as a low-wave energy drowned karst coast,
which is characterized by having 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 or alluvial sand,
are common offshore. Coastal salt marshes are
common at the land-sea interface.
The Gulf Coastal Lowlands zone in Dixie
County is, in turn, subdivided into a series of
geomorphic subzones based on topographic
elevation and terrain type. These subdivisions
include the Coastal Marshes, the Limestone Shelf
and Hammocks, and the River Valley Lowlands
(Figure 1).

Coastal Marshes

Extensive coastal salt marshes are developed
along the seaward edge of Dixie County. These
comprise the Coastal Marsh Zone (White, 1970),
which typically extends from the shore inland to
approximately the five feet MSL contour. Most of
these marshes are comprised of Juncus and Spartina
grasses rooted in shallow organic-rich silts and
sands lying on limestone. In many areas, the
marshes are dissected by small tidal streams and
creeks, some of which drain freshwater seeping out
of the shallow limestones of the Floridan aquifer

Limestone Shelf and Hammocks

Most of Dixie County is comprised of a flat-
lying, highly karstic, erosional limestone plain
overlain by sand dunes, ridges, and coast-parallel
palco-shoreline sand belts associated with several
Pleistocene sea level highstands. This terrain has
been named the Limestone Shelf and Hammocks by
Puri et al. (1967). The irregular, highly karstic

Eocene limestone underlying this area is masked by
a blanket of Pleistocene sands. Near the coast, the
limestone shelf merges seaward into the Coastal
Marshes, and continues offshore onto the
continental shelf. Inland, the limestone rises gently
to an elevation of nearly 60 feet above MSL in the
northeastern corner of Dixie County. Most of the
area is forest or agricultural land. Small artesian
springs flow from the near-surface limestone, and
during periods of heavy rainfall, much of the region
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 marshes.

River Valley Lowlands

The Suwannee and Steinhatchee Rivers are the
two major streams flowing in Dixie County. The
Suwannee River forms the eastern county boundary
between Dixie and adjacent Levy and Gilchrist
Counties. It flows in a dissolutional valley, formed
in the near-surface Eocene limestones. The
lowlands immediately adjacent to the river, covered
by a thin veneer of Holocene sediments over
limestone, comprise the Suwannee River Valley
Lowlands geomorphic subzone (Vernon, 1951). The
broadly-meandering valley is less than one mile wide
over most of its course, broadening to about two
and a half miles wide as it approaches the Gulf
coast. Valley floor elevations average about five
feet MSL. Along its lower stretch, the river valley
is drowned and obscured by the coastal marshes.
The Steinhatchee River forms the northwestern
county boundary with Taylor County. It is a deeply
incised stream flowing in a narrow solution valley.
Lowlands associated with the Steinhatchee River are
generally less than one-half mile wide. A one-mile
stretch of the river flows through an underground
cavern near U.S. Highway 19, and then reemerges
west of the highway.


The oldest rock commonly penetrated by water
wells in Dixie County is marine limestone of the
Eocene age Avon Park Formation.
Undifferentiated Pleistocene to Holocene age
surficial sands, clayey sands, and alluvium are the
youngest sediments present. Figures 2 and 3
illustrate the shallow stratigraphy of the county.
The Avon Park Formation and the younger
overlying limestone units are important freshwater
aquifers, and the following discussion of the geology
of Dixie County is confined to these Eocene and
younger sediments.






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Figure 2: Geologic cross section A-A'.

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Figure 3: Geologic cross section B-B'.



Eocene Series
Avon Park Formation

The Avon Park Formation (Miller, 1986) is a
lithologically variable Middle Eocene carbonate unit
underlying all of Dixie County. It is typically a tan
to buff to brown dolomite, commonly interbedded
with white to light cream to yellowish gray
limestones and dolomitic limestones, and containing
varying amounts of peat, lignite, and plant remains
(Florida Geological Survey in-house well files).
Mollusks, echinoids, and foraminifera, where
preserved, are the principal fossils present. The top
of the Avon Park Formation varies in depth from
approximately 50 feet below land surface (bls) in
southern Dixie County to about 150 feet bls in the
northern portion of the county. Surface exposures
of Avon Park occur to the south in Levy County,
over the crest of the Ocala Platform. Deep oil test
well data indicate that the Avon Park Formation
ranges from approximately 800 to 1200 feet thick
under Dixie County (Florida Geological Survey in-
house well files).

Ocala Group

Marine limestones of the Ocala Group (Puri,
1957) unconformibly overlie the Avon Park
Formation under all of Dixie County. The Ocala
Group is comprised of three formations; in
ascending order they are the Inglis Formation,
Williston Formation, and the Crystal River
Formation. These formations are differentiated on
the basis of lithology and fossil content. Typically,
the lithology of the Ocala Group grades upward
from alternating hard and soft, white to tan to gray
fossiliferous limestone and dolomitic limestone of
the Inglis and lower Williston Formations into white
to cream colored, abundantly fossiliferous, chalky
limestones of the upper Williston and Crystal River
Formations (Crane, 1986). Foraminifera, mollusks,
bryozoans, and echinoids are the most abundant
fossils occurring in this unit. Thickness of the Ocala
Group sediments under Dixie County averages
about 100 feet. 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 Group
is generally less than 50 feet. It commonly crops
out in the limestone shelf and hammocks and
coastal marsh zones. In western Dixie County and
offshore of the modern coastline, a thin blanket of
quartz sand covers the Ocala Group limestone and
exposures in the form of limestone boulders and
pinnacles are common.
The highly permeable and cavernous nature of

the Ocala Group limestones make them important
freshwater bearing units of the Floridan aquifer
system. Many drinking water wells in Dixie County
withdraw water from the upper units of this group.

Pleistocene-Holocene Series

Undifferentiated Pleistocene marine quartz
sands and clayey sands form a thin veneer over all
of Dixie County. They are generally less than about
40 feet thick county-wide, and thin to less than 20
feet thick near the coast. They directly overlie the
karstic limestones of the Ocala Group. Many of the
larger and higher sand bodies in Dixie County are
relict dunes, bars, and barrier islands associated
with various Pleistocene .sea level high stands.
A white to gray, fossiliferous freshwater marl
commonly occurs along the banks and in the valley
of the Suwannee River. This marl contains an
abundant Holocene freshwater mollusk fauna, and
may attain a thickness of three to four feet (Vernon,
1951; Puri et al., 1967).


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

Surficial aquifer system

The surficial aquifer system is the uppermost
freshwater aquifer in Dixie County. This non-
artesian aquifer is present only within the thicker
portions of the Pleistocene undifferentiated sands
and clays. It is thin or absent in much of Dixie
County, but may occur sporadically in the northern
portion of the county. 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 and downward seepage into
the Floridan aquifer system. The surficial aquifer

system is not used as a source of consumptive water
in Dixie County.

Floridan aquifer system

In Dixie County, the Floridan aquifer system is
comprised of hundreds of feet of Eocene marine
limestones, including the Avon Park Formation and
the Ocala Group. It is the principle source of
drinking water in the county. The Floridan aquifer
system exists as an unconfmed, non-artesian aquifer
in most of Dixie County, where porous quartz sand
directly overlies the limestone. 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 Suwannee River
Valley to nearly 50 feet under the larger relict
Pleistocene sand bodies. The potentiometric
gradient is south-southwestward.
Recharge to the Floridan aquifer system in
Dixie County is obtained from lateral inflow from
the north and, to a lesser extent, from local rainfall
percolating downward through the permeable
surficial sands. The highest recharge by percolation
occurs in the highly karstic limestone plain in
northwestern Dixie 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
Suwannee River Valley Lowlands, portions of the
Limestone Shelf and Hammocks zone, and along
the coastal marshes, where the potentiometric
surface of the Floridan aquifer system is at or above
land surface.


Dixie County contains deposits of several
economic mineral commodities. The most
important of these is limestone. Other commodities
of lesser potential include dolomite, sand, clay,
phosphate and peat. Each commodity and its
economic potential are summarized below.


Limestones of the Ocala Group occur near the
surface under most of Dixie County. The economic
grade may vary considerably from one area to
another. High purity, road base quality rock is
principally concentrated in the Chiefland Limestone
Plain area of eastern Dixie County. Aggregate and
secondary road base grades occur over much of the
rest of the county. Limestone has been mined
extensively in Dixie County in the past, particularly

from quarries along U.S. Highway 19 (Schmidt et
al., 1979). Most was used for road construction, but
at least two quarries produced building stone (Puri
et al., 1967). Although mining potential remains
high, no companies currently mine limestone in the


Near-surface dolomitized Ocala Group
sediments are present in western Dixie County in a
band paralleling the Gulf coast. The dolomite
ranges from about 2 to 10 feet thick, making it
uneconomical for mining as crushed stone (Puri et
al, 1967). Future potential for additional this
commodity is therefore low in Dixie County.


A number of shallow private pits in Dixie
County are worked for fill sand. Pleistocene quartz
sand deposits occur as thin veneers 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 sporadically occurs as a component of the
undifferentiated surficial sediments covering Dixie
County. Due to the impure nature of this clay, it is
not an economic commodity in the county.


Several thin, discontinuous deposits of hard rock
phosphate have been recorded in quarries near the
community of Hines in Dixie County (Puri et al.,
1967). These.deposits are generally developed at
the top of the Ocala Group limestone in isolated
pockets, and are generally less than 5-feet thick.
Due to the limited thickness and discontinuous
nature of the phosphate deposits, they are not
sufficient to maintain an economic mining operation
in the county.


Peat forms in a wet, reducing environment when
accumulation of organic materials exceeds the
decomposition rate of that material. Shallow
wetlands in the limestone shelf and hammocks areas
of Dixie 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; White, WA., 1970, Geomorphology of the Florida
Bond et al., 1986). Therefore, the potential for peat peninsula: Florida Geological Survey
mining in Dixie County is low. Bulletin 51, 164 p.


Bond, PA., 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.

Crane, JJ., 1986, An investigation of the geology,
hydrogeology, and hydrochemistry of the
lower Suwannee River Basin: Florida
Geological Survey Report of Investigation
No. 96, 205 p.

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

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

Miller, JA., 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

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

Vernon, R.O., 1951, Geology of Citrus and Levy
Counties, Florida: Florida Geological
Survey Bulletin 33, 256 p.

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