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

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Title:
The geomorphology and geology of Dixie County, Florida ( FGS: Open file report 45 )
Series Title:
( FGS: Open file report 45 )
Creator:
Rupert, Frank
Florida Geological Survey
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Tallahassee
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Florida Geological Survey
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English
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6 p. : ill. ; 28 cm.

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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 )
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bibliography ( marcgt )
non-fiction ( marcgt )

Notes

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

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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:
027837252 ( aleph )
25641780 ( oclc )
ALQ4881 ( 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 and Chief







OPEN FILE REPORT NO. 45

'HE GEOMORPHOLOGY AND GEOLOGY OF DIXIE COUNTY, FLORIDA

BY

FRANK R. RUPERT


FLORIDA GEOLOGICAL SURVEY
Tallahassee
1991






















SCIL xCE
LIBRARY










The geomorphology and geology
of Dixie County, Florida

Frank R. Rupert, P.G. 149


GEOMORPHOLOGY

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


EXPLANATION

TOWN
SU.S. HIGHWAY
-- STATE/COUNTY ROAD
* WELL LOCATION
S CROSS SECTION LOCATION
GEOMORPHIC ZONES
IMODIPIED APTlR PURI IT L... It? AND WHITE 1670)
GULF COASTAL LOWLANDS
S- LIMESTONE SHELF
AND HAMMOCKS
E SUWANNEE RIVER VALLEY
LOWLANDS
SSTEINHATCHEE RIVER
VALLEY LOWLANDS

D COASTAL MARSHES

MILIS

KILOMETERS


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


UNIVERSITY O FLORIDA LI 41JRS









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
system.

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.

STRATIGRAPHY

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.



















UNDIFFERENTIATED
SANDS


AVON


SIN


PARK


FORMATION

MILES
0 1 2 3 4 S
o0 8,
0 2 A 6 I
KILOMETERS
T.D.-4,7T0 FT.


T.D.-.Lts FT.
EIRTICAL EXAgIRATION IS 350 TIMES TRUE SCAL.





Figure 2: Geologic cross section A-A'.


11
i3 -


pJOt4 P h0ty


MILES
0 M1 E4 S

0 2 4 8
KILOMETERS


L -S11
VERTICAL XAGGOORATION IS 3S0 TIMES TRUE SCALE.


Figure 3: Geologic cross section B-B'.


I0I


08
I










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

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.

MINERAL RESOURCES

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.

Limestone

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
county.

Dolomite

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.

Sand

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

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.

Phosphate

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

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.

REFERENCES

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
p.

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
P.

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.




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 and Chief OPEN FILE REPORT NO. 45 'HE GEOMORPHOLOGY AND GEOLOGY OF DIXIE COUNTY, FLORIDA BY FRANK R. RUPERT FLORIDA GEOLOGICAL SURVEY Tallahassee 1991

PAGE 2

9I~c SCIL xCE LIIRARY

PAGE 3

The geomorphology and geology of Dixie County. Florida Frank R. Rupert, P.G. 149 GEOMORPHOLOGY Gulf Coastal Lowlands Dixie County is situated in Florida's Big Bend All of Dixie County lies within an extensive area, along the northern edge of the Central or geomorphic subzone named the Gulf Coastal Midpeninsular geomorphic zone of White (1970). Lowlands (White, 1970). This zone is characterized This zone extends down the Florida peninsula from as a low, flat, frequently swampy and gently seaward an approximate line connecting the cities of Perry in sloping sandy plain. Surface slope ranges between Taylor County, Gainesville in Alachua County, and 1 and 4 feet per mile seaward. Limestone, covered St. Augustine in St. Johns County, southward to the by a thin veneer of unconsolidated sand, forms the Caloosahatchee River. In Dixie County, the Central near-surface substrate in most of the county. The Zone is represenfed by a broad geomorphic subzone Gulf Coastal Lowlands extend from the modern named the Gulf Coastal Lowlands (Figure 1). shoreline inland to approximately the 100 feet above A W-1570 LAFAYETTE COUNTY -EXPLANATION .TOWN ' |U.S. HIGHWAY -DSTATE/COUNTY ROAD W-004 WELL LOCATION 0 C I CROSS SECTION LOCATION \ w"1 -GEOMORPHIC ZONES 8 .IMODIPD i APTIR PUR I IT AL.. In? AND WHITE t r70) owe W-8218 Tw -GULF COASTAL LOWLANDS m -LIMESTONE SHELF w-e36 AND HAMMOCKS E SUWANNEE RIVER VALLEY l LOWLANDS I STEINHATCHEE RIVER 0osý ·os N VALLEY LOWLANDS A' N COASTAL MARSHES S,0 0 2 4 8 8 KILOMITERS 0 / Figure 1: Geomorphic and cross section location map of Dixie County. UNIVERSITY O FLORIDA LI4ARIE S

PAGE 4

mean sea level (MSL) elevation line. In Dixie Eocene limestone underlying this area is masked by County, the maximum elevation attained is about 60 a blanket of Pleistocene sands. Near the coast, the feet above MSL in the northeastern portion of the limestone shelf merges seaward into the Coastal county. Most of the lowlands area is ancient marine Marshes, and continues offshore onto the terrace terrain. Pleistocene seas alternately flooded continental shelf. Inland, the limestone rises gently and retreated from this region, depositing a stepto an elevation of nearly 60 feet above MSL in the like series of marine terraces, which generally northeastern corner of Dixie County. Most of the parallel the moder coastline. Healy (1975) area is forest or agricultural land. Small artesian recognizes three marine terrace elevation zones in springs flow from the near-surface limestone, and the county, including the Silver Bluff Terrace (less during periods of heavy rainfall, much of the region than 10 feet above MSL), the Pamlico Terrace (8 to may flood toorm a shallow swamp. Drainage from 25 feet above MSL), and the Talbot Terrace (25 to may flood to form a shallow swamp. Drainage from 25 feet above MSL), and the Talbo Terrace(25 to the coastal hammocks is sluggish, and occurs 42 feet above MSL). Imposed on the terraces are to n e s numerous relict Pleistocene marine features such as through a number of small creeks and sloughs, bars, dunes, and beach ridge systems. Such relict which empty into the coastal marshes. features, composed principally of white quartz sand, may be observed stranded far inland from the River Valley Lowlands modern coastline. The present Gulf shoreline in this area is The Suwannee and Steinhatchee Rivers are the classified as a low-wave energy drowned karst coast, two major streams flowing in Dixie County. The which is characterized by having very low wave Suwannee River forms the eastern county boundary activity, a general lack of sand beaches and an between Dixie and adjacent Levy and Gilchrist irregular outline. A series of small islets, or keys, Counties. It flows in a dissolutional valley, formed comprised of limestone pinnacles or alluvial sand, in the near-surface Eocene limestones. The are common offshore. Coastal salt marshes are lowlands immediately adjacent to the river, covered common at the land-sea interface, by a thin veneer of Holocene sediments over The Gulf Coastal Lowlands zone in Dixie limestone, comprise the Suwannee River Valley County is, in turn, subdivided into a series of Lowlands geomorphic subzone (Vernon, 1951). The geomorphic subzones based on topographic broadly-meandering valley is less than one mile wide elevation and terrain type. These subdivisions over most of its course, broadening to about two include the Coastal Marshes, the Limestone Shelf and a half miles wide as it approaches the Gulf and Hammocks, and the River Valley Lowlands coast. Valley floor elevations average about five (Figure 1). feet MSL. Along its lower stretch, the river valley Coastal Marshes is drowned and obscured by the coastal marshes. The Steinhatchee River forms the northwestern Extensive coastal salt marshes are developed county boundary with Taylor County. It is a deeply along the seaward edge of Dixie County. These incised stream flowing in a narrow solution valley. comprise the Coastal Marsh Zone (White, 1970), Lowlands associated with the Steinhatchee River are which typically extends from the shore inland to generally less than one-half mile wide. A one-mile approximately the five feet MSL contour. Most of stretch of the river flows through an underground these marshes are comprised of Juncus and Spartina cavern near U.S. Highway 19, and then reemerges grasses rooted in shallow organic-rich silts and west of the highway. sands lying on limestone. In many areas, the marshes are dissected by small tidal streams and STRATIGRAPHY creeks, some of which drain freshwater seeping out of the shallow limestones of the Floridan aquifer The oldest rock commonly penetrated by water system. wells in Dixie County is marine limestone of the Eocene age Avon Park Formation. Limestone Shelf and Hammocks Undifferentiated Pleistocene to Holocene age surficial sands, clayey sands, and alluvium are the Most of Dixie County is comprised of a flatyoungest sediments present. Figures 2 and 3 lying, highly karstic, erosional limestone plain illustrate the shallow stratigraphy of the county. overlain by sand dunes, ridges, and coast-parallel The Avon Park Formation and the younger palco-shoreline sand belts associated with several overlying limestone units are important freshwater Pleistocene sea level highstands. This terrain has aquifers, and the following discussion of the geology been named the Limestone Shelf and Hammocks by of Dixie County is confined to these Eocene and Purl et al. (1967). The irregular, highly karstic younger sediments. 2

PAGE 5

A' '-E-o n ° UNDIFFERENTIATED 1 0 20 SANDS -50 o o MIL OCALA GROUp -20 -100 -40 -so AVON PARK FORMATION MILES 0 1 2 3 4 S -0 -200 II ' 0 2 A 6 a KILOMETERS T.D.-4,7T0 FT. T.D.-.Ltl PT. VIRTICAL EIXXAATIOH IS 380 TIMES TRUE SCALE. Figure 2: Geologic cross section A-A'. B' B 8 S,* 0. .0 MB OC L.. GROUp WES " 4m -60 so SANDL -t00 p904 Pg FORMATION ILES MILES -400 1 2 -150 0 2 4 6 8 VERTICAL EXOAGERATION IS 3S0 TIMIS TRUE SCALE. KILOMETERS Figure 3: Geologic cross section B-B'.

PAGE 6

the Ocala Group limestones make them important Eocene Series freshwater bearing units of the Floridan aquifer Avon Park Formation system. Many drinking water wells in Dixie County withdraw water from the upper units of this group. The Avon Park Formation (Miller, 1986) is a lithologically variable Middle Eocene carbonate unit Pleistocene-Holocene Series underlying all of Dixie County. It is typically a tan to buff to brown dolomite, commonly interbedded Undifferentiated Pleistocene marine quartz with white to light cream to yellowish gray sands and clayey sands form a thin veneer over all limestones and dolomitic limestones, and containing of Dixie County. They are generally less than about varying amounts of peat, lignite, and plant remains 40 feet thick county-wide, and thin to less than 20 (Florida Geological Survey in-house well Files). feet thick near the coast. They directly overlie the Mollusks, echinoids, and forammifera, where Mollusks, echinoids, and foraminifera, where karstic limestones of the Ocala Group. Many of the preserved, are the principal fossils present. The top ar n er san oes n e on of the Avon Park Formation varies in depth from larger and higher sand bodies in Dixie County are approximately 50 feet below land surface (bls) in relict dunes, bars, and barrier islands associated southern Dixie County to about 150 feet bls in the with various Pleistocene sea level high stands. northern portion of the county. Surface exposures A white to gray, fossiliferous freshwater marl of Avon Park occur to the south in Levy County, commonly occurs along the banks and in the valley over the crest of the Ocala Platform. Deep oil test of the Suwannee River. This marl contains an well data indicate that the Avon Park Formation abundant Holocene freshwater mollusk fauna, and ranges from approximately 800 to 1200 feet thick may attain a thickness of three to four feet (Vernon, under Dixie County (Florida Geological Survey in1951; Puri et al., 1967). house well files). Ocala Group GROUND WATER Marine limestones of the Ocala Group (Puri, 1957) unconformibly overlie the Avon Park Ground water is water that fills the pore spaces Formation under all of Dixie County. The Ocala in subsurface rocks and sediments. This water is Group is comprised of three formations; in derived principally from precipitation within Dixie ascending order they are the Inglis Formation, and adjoining counties. The bulk of Dixie County's Williston Formation, and the Crystal River consumptive water is withdrawn from ground water Formation. These formations are differentiated on aquifers. Two aquifer systems are present under the basis of lithology and fossil content. Typically, Dixie County, the surficial aquifer system and the the lithology of the Ocala Group grades upward Floridan aquifer system. from alternating hard and soft, white to tan to gray fossiliferous limestone and dolomitic limestone of al a the Inglis and lower Williston Formations into white Surfiial aquifer system to cream colored, abundantly fossiliferous, chalky limestones of the upper Williston and Crystal River The surficial aquifer system is the uppermost Formations (Crane, 1986). Foraminifera, mollusks, freshwater aquifer in Dixie County. This nonbryozoans, and echinoids are the most abundant artesian aquifer is present only within the thicker fossils occurring in this unit. Thickness of the Ocala portions of the Pleistocene undifferentiated sands Group sediments under Dixie County averages and clays. It is thin or absent in much of Dixie about 100 feet. It generally thins against the County, but may occur sporadically in the northern structurally high Avon Park Formation toward the portion of the county. The surficial aquifer system, crest of the Ocala Platform in the southern and where present, is unconfined and its upper surface eastern portions of the county. Depth to the is the water table. In general, the water table irregular and highly-karstic top of the Ocala Group elevation fluctuates with precipitation and conforms is generally less than 50 feet. It commonly crops to the topography of the land surface. Recharge to out in the limestone shelf and hammocks and the surficial aquifer system is largely through rainfall coastal marsh zones. In western Dixie County and percolating downward through the unconsolidated offshore of the modern coastline, a thin blanket of surficial sediments, and to a lesser extent, by quartz sand covers the Ocala Group limestone and upward seepage from the underlying Floridan exposures in the form of limestone boulders and aquifer system. Water naturally discharges from the pinnacles are common. aquifer by evaporation and downward seepage into The highly permeable and cavernous nature of the Floridan aquifer system. The surficial aquifer 4

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system is not used as a source of consumptive water from quarries along U.S. Highway 19 (Schmidt et in Dixie County. al., 1979). Most was used for road construction, but at least two quarries produced building stone (Puri Floridan aquifer system et al., 1967). Although mining potential remains high, no companies currently mine limestone in the In Dixie County, the Floridan aquifer system is county. comprised of hundreds of feet of Eocene marine limestones, including the Avon Park Formation and Dolomite the Ocala Group. It is the principle source of drinking water in the county. The Floridan aquifer Near-surface dolomitized Ocala Group system exists as an unconfined, non-artesian aquifer sediments are present in western Dixie County in a in most of Dixie County, where porous quartz sand band paralleling the Gulf coast. The dolomite directly overlies the limestone. Depth to the top of ranges from about 2 to 10 feet thick, making it the Floridan aquifer system generally corresponds to uneconomical for mining as crushed stone (Puri et the depth of limestone, and varies from less than al, 1967). Future potential for additional this five feet in the coastal marshes and Suwannee River commodity is therefore low in Dixie County. Valley to nearly 50 feet under the larger relict Pleistocene sand bodies. The potentiometric Sand gradient is south-southwestward. Recharge to the Floridan aquifer system in A number of shallow private pits in Dixie Dixie County is obtained from lateral inflow from County are worked for fill sand. Pleistocene quartz the north and, to a lesser extent, from local rainfall sand deposits occur as thin veneers over most of the percolating downward through the permeable county. Since there is insufficient local demand for surficial sands. The highest recharge by percolation sand products, the potential for commercial mining occurs in the highly karstic limestone plain in is low at this time. northwestern Dixie County (Stewart, 1980). Water leaves the Floridan aquifer system Clay through natural movement down-gradient and subsequent discharge through numerous springs and Clay sporadically occurs as a component of the seeps. These springs generally occur in the undifferentiated surficial sediments covering Dixie Suwannee River Valley Lowlands, portions of the County. Due to the impure nature of this clay, it is Limestone Shelf and Hammocks zone, and along not an economic commodity in the county. the coastal marshes, where the potentiometric surface of the Floridan aquifer system is at or above Phosphate land surface. Several thin, discontinuous deposits of hard rock MINERAL RESOURCES phosphate have been recorded in quarries near the community of Hines in Dixie County (Puri et al., Dixie County contains deposits of several 1967). These.deposits are generally developed at economic mineral commodities. The most the top of the Ocala Group limestone in isolated important of these is limestone. Other commodities pockets, and are generally less than 5-feet thick. of lesser potential include dolomite, sand, clay, Due to the limited thickness and discontinuous phosphate and peat. Each commodity and its nature of the phosphate deposits, they are not economic potential are summarized below, sufficient to maintain an economic mining operation in the county. Limestone Peat Limestones of the Ocala Group occur near the surface under most of Dixie County. The economic Peat forms in a wet, reducing environment when grade may vary considerably from one area to accumulation of organic materials exceeds the another. High purity, road base quality rock is decomposition rate of that material. Shallow principally concentrated in the Chiefland Limestone wetlands in the limestone shelf and hammocks areas Plain area of eastern Dixie County. Aggregate and of Dixie County provide potential peat formation secondary road base grades occur over much of the sites. However, while no peat surveys have been rest of the county. Limestone has been mined conducted within the county, studies in adjacent extensively in Dixie County in the past, particularly counties indicate that the peat formed in such areas 5

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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. REFERENCES 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 p. 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 P. 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. 6

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-FLORIDA-GEOLOGICAL-SURVEY COPYRIGHT NOTICE © [year of publication as printed] Florida Geological Survey [source text] The Florida Geological Survey holds all rights to the source text of this electronic resource on behalf of the State of Florida. The Florida Geological Survey shall be considered the copyright holder for the text of this publication. Under the Statutes of the State of Florida (FS 257.05; 257.105, and 377.075), the Florida Geologic Survey (Tallahassee, FL), publisher of the Florida Geologic Survey, as a division of state government, makes its documents public (i.e., published) and extends to the state's official agencies and libraries, including the University of Florida's Smathers Libraries, rights of reproduction. The Florida Geological Survey has made its publications available to the University of Florida, on behalf of the State University System of Florida, for the purpose of digitization and Internet distribution. The Florida Geological Survey reserves all rights to its publications. All uses, excluding those made under "fair use" provisions of U.S. copyright legislation (U.S. Code, Title 17, Section 107), are restricted. Contact the Florida Geological Survey for additional information and permissions.


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