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 Geomorphology
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 Mineral resources
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The geology and geomorphology of Gilchrist County, Florida ( FGS: Open file report 18 )
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Title: The geology and geomorphology of Gilchrist County, Florida ( FGS: Open file report 18 )
Series Title: ( FGS: Open file report 18 )
Physical Description: 10, 4 leaves : ill. ; 28 cm.
Language: English
Creator: Rupert, Frank
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee Fla
Publication Date: [1988]
 Subjects
Subjects / Keywords: Geomorphology -- Florida -- Gilchrist County   ( lcsh )
Geology -- Florida -- Gilchrist County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Frank R. Rupert.
Bibliography: Includes bibliographical references.
General Note: Cover title.
General Note: "March, 1988"
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
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Source Institution: University of Florida
Holding Location: University of Florida
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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: aleph - 001545439
oclc - 21188262
notis - AHF8959
System ID: UF00001017:00001

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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Title Page
    Geomorphology
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
    Groundwater
        Page 8
        Page 7
    Mineral resources
        Page 8
        Page 9
    References
        Page 9
        Page 10
    Figures
        Page 11
        Page 12
        Page 13
        Page 14
        Copyright
            Copyright
Full Text










State of Florida
Department of Natural Resources
Tom Gardner, Executive Director




Division of Resource Management
Jeremy Craft, Director




Florida Geological Survey
Walt Schmidt, State Geologist and Chief









Open File Report 18


The Geology and Geomporphology of
Gilchrist County, Florida



by

Frank R. Rupert


Florida Geological Survey
Tallahassee, Florida
1988


















3 1262 04545 4361

ri)o





;S'^r












State of Florida
Department of Natural Resources
Tom Gardner, Executive Director



Division of Resource Management
Jeremy Craft, Director


Florida Geological Survey
Walt Schmidt, State Geologist






Open File Report 18

The Geology and Geomorphology of Gilchrist County, Florida





by
f
Frank R. Rupert .Ie







Florida Geological Survey
Tallahassee, Florida
March, 1988


L~a~J::

~p :b






GILCHRIST COUNTY


GEOMORPHOLOGY

Gilchrist County lies along the northern edge of the Mid-
peninsular Zone of White (1970). This zone spans the Florida
peninsula from the lower edge of the topographically higher
Northern Highlands southward to approximately the Caloosahatchee
River. The Midpeninsular Zone is comprised of a series of
elevationally-differentiated geomorphic subzones. Two subzones
occur within Gilchrist County, the Gulf Coastal Lowlands and the
Central Highlands (White, 1970).


Gulf Coastal Lowlands

The Gulf Coastal Lowlands geomorphic province parallels the
present Gulf Coast of Florida from Ft. Myers northward and
westward to the Alabama line. In the vicinity of Gilchrist
County, the Gulf Coastal Lowlands extend inland from the present
Gulf of Mexico shoreline a distance of some 50 miles, terminating
at the western edge of the Brooksville Ridge and High Springs Gap
(see Figure 1). The Gulf Coastal Lowlands are characterized by
broad flat marine plains, underlain by Eocene limestones, and
blanketed by thin Pleistocene (one million to ten thousand years
before present) sands, which were deposited by the regressing
Gulf of Mexico. Elevations within the province vary from
approximately 20 feet .above mean sea level (MSL) in westernmost
Gilchrist County, to over T1n -feet...MSL in the eastern portion of
the county. Several geomoprhic subdivisions, based on
topography, punctuate the Gulf Coastal Lowlands zone in Gilchrist
County. These include the Wacasassa Flats, the Bell Ridge, the
Chiefland Limestone Plain, and the Santa Fe and Suwannee River
Valley Lowlands (Puri et al., 1967).


Wacasassa Flats

Vernon (1951) proposed the name Wacasassa Flats for the low,
swampy area about five miles wide and 25 miles long, trending
southward through central Gilchrist County. This province
originates at the south bank of the Santa Fe River and extends
southward, then southeastward into Levy County. Land surface
elevations over most of the "Flats" average about 60 feet MSL,
although isolated sand hills, possibly associated with the Bell
and Brooksville Ridges, reach 90 to 100 feet MSL elevation. A
structural low, filled with Miocene (5 to 25 million years B.P.)
and Pleistocene siliciclastics underlies the area occupied by
Wacasassa Flats. ATth;i~urthere-is-no apparent relationship
between the low,. and the origin of the Flats, siliciclastics
filling the depression may retard downward percolation of
groundwater, resulting in the generally swampy conditions
throughout this province (Puri et al., 1967). The origin of the
flats iis uncertain. Vernon (1951:) believed that the Wacasassa
Flats :are either a remnant stream valley, possibly of the






ancestral Suwannee River, or are of erosional marine origin. Due
to the predominance of relict marine features throughout the area
of the Flats, Puri et al., (1967) consider this feature to be-
marine in origin.


The Bell Ridge

Bordering the eastern edge of the Chiefland Limestone. Plain are a_
20 mile-long series of irregularily-shaped sand ridges named the
Bell Ridge (Puri and Vernon, 1984). The crests of these ridges
range from 80 to 100 feet MSL, and while their origin is
uncertain, they are most likely part of a relict Wicomico Sea
(Pleistocene) barrier island system (Puri et al., 1967). .White
(1970) believes the Bell Ridge is an outlier of the Brooksville
Ridge, to which it is roughly parallel. The sand hills
comprising the Bell Ridge directly overlie karstic Eocene age (37
to 54 million years B.P.) limestone, and the former extent of the
contiguous ridge system may be obscured by solution and collapse
in the underlying limestone (Puri et al., 1967).


The Chiefland Limestone Plain

The western one-third of Gilchrist County is comprised of a flat,
sandy terrain lying on eroded and highly karstic Eocene limestone
called d the Chiefland Limestone Plain (Vernon, 1951; Puri et al.,
L967). This province is bordered on the west by the Suwannee
River Valley Lowlands, and on the east by the Bell Ridge and
Wacasassa Flats provinces. The land surface is generally flat to
gently rolling, with elevations ranging from 25 to approximately
55 feet MSL. Surficial sediments are primarily well-drained
Pleistocene sands, which average less than 20 feet thick.


The River Valley Lowlands

The valleys of the Santa Fe and Suwannee Rivers have been
designated as geomorphic subzones of the Gulf Coastal Lowlands in
Gilchrist County by Puri et al., (1967). These topographically
low, broad valleys are floored with a thin veneer of Holocene
age (10,000 years B.P. to present) siliciclastics over limestone.

The Santa Fe River flows westward from its source in Alachua
County, and forms the northern boundary of Gilchrist County. In
northeastern Gilchrist County, the river is partially entrenched
Ln a limestone channel, and meanders through a one-half mile wide
valley. Elevations in the valley vary between 20 and 30 feet
MSL. Along thls portion -of its course, the Santa Fe is fed by
several sluggish creeks flowing out of the surrounding highly
solutioned terrain, and by the runs of numerous springs.
Northwestward from Cow Creek, as the river enters the Chiefland
Limestone Plain, the valley narrows considerably and assumes a
more tenuous course. Cow Creek, flowing northward out of
GilchrLst County, and numerous smaller creeks draining the






Chiefland Limestone Plain are the primary tributaries.
Elevations within the valley decrease to between 10 and 20 feet
MSL, and much of the valley is swampy. The Ichtucknee River,
flowing southward out of Suwannee County, joins the Santa Fe at
the northern tip of Gilchrist County. From the Ichetucknee River
westward to its confluence with the Suwannee River, the Santa Fe
River flows in a quarter-mile-wide, swampy valley varying in
elevation from 8 to 20 feet MSL.

The Suwannee River forms the western boundary of Gilchrist
County. Its broadly meandering valley varies from less than one
quarter mile wide to nearly one and a half miles wide.
Throughout its course along western Gilchrist County, the valley
floor elevations average 15 feet MSL. In northwestern Gilchrist
County, the 20 feet MSL elevation contour deliniates the extent
of the River Valley Lowlands. Southwestward, near the town of
Suwannee River, the 10 foot contour deliniates the valley. The
Suwannee River flows southward, entrenched in a limestone
channel. Valley floor sediments are predominantly reworked
Pleistocene and Holocene alluvial sands and muds, punctuated
occasionally by outcrops of the Eocene age Ocala Group limestone.


The Central Highlands

The Central Highlands geomorphic province includes a series
localized highlands and ridges as well as intervening lowland
valleys, which trend generally coast-parallel down the central
peninsula. The Brooksville Ridge and the High Springs Gap,
situated at the eastern edge of Gilchrist County, are two
subdivisions of the Central Highlands Zone.


The Brooksville Ridge

The northern terminus of the Brooksville Ridge geomorphic
province is situated along the eastern edge of Gilchrist County
(Puri et al., 1967). This ridge is a topographic highland and
extends a total distance of 110 miles southeastward into Pasco
County. In Gilchrist County, the ridge sediments rest on karstic
Eocene limestone. The core of the ridge is largely comprised of
Pleistocene siliciclastics, and is capped by a depression-pocked,
rolling plain of Pleistocene marine terrace sand. Bordering the
western edge of the ridge is a well-defined marine escarpment at
70 to 75 feet MSL, which is'probably associated with the Wicomico
(Pleistocene) sea level stand (Puri et al., 1967). Surface
elevations attain 100 feet MSL in crests along the eastern edge
of Gilchrist County.


High Springs Gap

The High Springs Gap (Puri and Vernon, 1964) is a geomoprhic
S lowland situated in northeastern Gilchrist County at the northern






terminus of the Brookaville Ridge. This lowland provides a
drainage egress, via the Santa Fe River, between the
northernmost limit of the Western Valley geomorphic zone of the
central peninsula and the Gulf Coastal Lowlands zone to the west.


STRATIGRAPHY

The oldest rock penetrated by water wells in Gilchrist County is
limestone of the Eocene age Avon Park Formation,
Undifferentiated surficial sands and clayey sands of Pleistocene
to Holocene age are the youngest sediments present. The Avon
Park Formation and the younger overlying limestone units are
important freshwater aquifers, and this discussion of the geology
of Gilchrist County will be confined to these Eocene age 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 Gilchrist
County. It is typically a tan to buff to brown dolomite,
frequently interbedded with white to light cream to yellowish
gray limestones and dolomitic limestones of varying hardness
(Puri et al.. 1967 and Florida Geological Survey in-house
lithologic files). Mollusks and foraminifera, where preserved,
are the principle fossils present. The Avon Park Formation is a
component of the Floridan aquifer system, and the top of this
unit occurs at depths ranging from 115 to 145 feet below land
surface (Florida Geological Survey in-house well data). The Sun
Oil Company #1 Alto Adams test well, (Permit 5, W-1003) located
four miles southeast of Bell, was the only well to penetrate the
entire Avon Park Formation section. Core data from this well
indicates the Avon Park is 850 feet thick under this part of the
county.


Ocala Group

Marine limestones of the Ocala Group (Puri, 1957) unconformibly
overlie the Avon Park Formation under all of Gilchrist County
(Puri et al., 1967). The Ocala Group is comprised of three
formations; in ascending order, these are the Inglis Formation,
the 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,
abundantly fossiliferous, chalky limestones of the upper
Williston and Crystal River Formations. Foraminifera, mollusks,
bryozoans, and echinoids are the most abundant fossil types






occurring in the Ocala Group. Thickness of the Ocala Group
sediments under Gilchrist County averages about 100 feet. The
irregular, karstic surface of the unit varies from five feet
below land surface in the Chiefland Limestone Plain province of
western Gilchrist County to over 80 feet below land surface in
the structural low under the Wacasassa Flats (Florida Geological
Survey in-house lithologic files). Erosion has removed the
Crystal River Formation in portions of Gilchrist County,
resulting in the Williston Formation being the uppermost Ocala
Group unit encountered 'in some wells. In addition, a series of
faults postulated in western Gilchrist County, and what is
possibly a large graben trending north-south under the Wacasassa
Flats may have further modified the karstic Ocala Group. surface
(Puri et al., 1967).

The permeable and cavernous nature of the Ocala Group limestone
make them important freshwater-bearing units of the Floridan
aquifer system. Many drinking water wells in Gilchrist County
withdraw water from the upper units of this group.


MIOCENE SERIES

Alachua Formation

The Alachua Formation is a complex and little understood unit.
Originally defined to include only the sand and clay infillings
in older karst depressions or stream channels (Dall and Harris,
1892), the Alachua Formation was later considered to be a mixture
of discontinuous interbedded clay, sand, and sandy -lay,
including commercially important phosphatic sand and gravel
deposits (Vernon, 1951; Puri and Vernon, 1964). In Gilchrist
County, the Alachua Formation sediments are highly variable in
lithology. Typically, this unit is comprised of gray, poorly
indurated fine quartz sands in a matrix of .phosphatic clay;
interbedded with or underlying these sands are pebbles of water-
worn flint, erratic limestone boulders, silicified limestone and
chert, light blue and green, waxy montmorillonite clay lenses,
pebbles and boulders of phosphate rock conglomerate, colloidal
phosphate, and occasional concentrations of vertebrate fossils
(Puri et al., 1967).

The phosphate rock is a minor constituent of the Alachua
Formation, but was economically feasible to mine for many years.
Its mode of occurrence in the formation is highly variable,
ranging from clay to boulder-size clasts as well as in the form
of replacements of limestone and laminated-phosphate (platerock).
Since the Alachua Formation was deposited on the eroded, highly
- -karstic, possibly faulted surface of the Ocala Group limestones,
its thickness varies considerably over relatively short
distances. With the exception of occasional deep sinkhole fill
deposits, the Alachua Formation is absent in westernmost
Gilchrist County. A thick sequence (approximately 80 to 100
feet) of Alachua Formation sediments is present in the structural
low in central Gilchrist County, and to the east, a discontinuous




series of 10 to 20 foot thick occurrences underlie the High
Springs Gap and Brooksville Ridge provinces.

Both the origin and age of the Alachua Formation are uncertain.
Cooke (1945) considered it an in situ accumulation of weathered
Hawthorn Group (Miocene) sediments. Puri and Vernon (1964)
believed it originated as a largely terrestrial deposit, with
lacustrine and fluviatile components, and Brooks (1966) suggested
that is was deposited in an estuarine environment. More
recently, Scott (1988, in press) considers the Alachua Formation
t. be weathered and possibly reworked Hawthorn Group sediments,
although he does not consider it part of the Hawthorn Group.

An age range of Miocene to Pleistocene, based primarily .on
contained vertebrate fossils, has been postulated for the Alachua
Formation. This wide age range tends to support the concept of
the Alachua Formation being composed of time-transgressive,
reworked sediments, with each successive depositional event
incorporating a younger vertebrate fauna into the sediments.


PLEISTOCENE SERIES

Much of the core of the Brooksville Ridge in Gilchrist County is
comprised of reddish, clayey coarse sands, lithologically
similar to the Citronelle Formation of the panhandle, and the
Cypresshead Formation of peninsular Florida, both considered to
be lower Pleistocene in age. For the purposes of this report,
these variably-colored red, orange, and pink siliciclastics, some
containing fossil burrows, are placed in the category of
undifferentiated Pleistocene sediments.

undifferentiated Pleistocene marine quartz sands and clayey sands
form a thin surface veneer over all of Gilchrist County. In the
western part of the county, these sands are generally less than
20 feet thick, and overlie the Ocala Group limestone directly; in
central and eastern Gilchrist County, they cap the reddish coarse
clastics and where present, the Alachua Formation. Many of the
larger and higher sand bodies in the county are relict dunes,
bars, and barrier islands associated with various Pleistocene sea
level stands. The higher crests on the Brooksville Ridge, above
100 feet MSL, are associated with the Sunderland/Okefenokee
terraces (Healy, 1975). With the exception of the Suwannee River
Valley Lowlands, which is part of the Pamlico Terrace, the
surficial siliciclastic sediments occurring over the remainder
of Gilchrist County are Wicomico terrace deposits (Healy, 1975).



HOLOCENE SERIES

Unnamed Freshwater Marl

A white to gray, fossiliferous freshwater marl commonly occurs
along the banks and in the valleys of the Santa Fe and Suwannee





rivers. This marl generally contains an abundant Holocene
freshwater mollusk fauna, and may attain three to four feet in
thickness (Puri et al., 1967).


GROUNDWATER

Groundwate-r is water that fills the pore spaces in subsurface
rocks and sediments. This water is derived principally from
precipitation within Gilchrist and adjoining counties. The bulk
of Gilchrist County's consumptive water is withdrawn from
groundwater aquifers. Two main aquifer systems are present under
Gilchrist County, the surficial aquifer system and the underlying
Floridan aquifer system (Southeastern Geological Society Ad Hoc
Committee on Florida Hydrostratigraphic Unit Definition, 1986,.


Surficial aquifer system

The surficial aquifer system is the uppermost freshwater aquifer
in Gilchrist County. This non-artesian aquifer is contained
within the interbedded sands and clays of the Alachua Formation
and the overlying Pleistocene siliciclastics and marine terrace
sands in central and southeastern Gilchrist County. In western
Gilchrist County, where the Alachua Formation is absent, the
surficial aquifer system may occur "perched" in locally thick
Pleistocene sands immediately overlying the Ocala Grioup
limestone; in these areas, the surficial aquifer system i3
separated from the underlying Floridan aquifer system by zones of
unsaturated limerock (Meyer, 1962). On average, the surfici.-
aquifer system ranges from 10 to 80 feet thick, with the thicker
portions located under the higher geomorphic sand ridges cf
central and eastern Gilchrist County, and in the structural low
under the Wacasassa Flats. The surficial aquifer system is
unconfined, and its upper surface is the water table. In
general, the water table elevation fluctuates with precipitation
rate and conforms to the topography of the land surface.
Recharge to the surficial aquifer system is largely through
rainfall percolating downward through the loose surficial clastic
sediments, and to a lesser extent, by upward seepage from the
underlying Floridan aquifer system. Water naturally discharges
from the aquifer by evaporation, transpiration, spring flow, and
by downward seepage into the Floridan aquifer system. The
surficial aquifer system may yield quantities of water suitable
for consumptive use, but in some areas the concentration of iron
and/or tannic acid impart a poor taste and color to the water
(Meyer, 1962).


Floridan aquifer system

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
Gilchrist County. The Floridan aquifer system exists as an







unconfined, non-artesian aquifer in portions of western,
northern, and northeastern Gilchrist County, where porous
Pleistocene quartz sand directly overlies the limestone. In
areas of central and southeastern Gilchrist County, where clay
beds in the Alachua Formation form low-permeability confining
units, the Floridan may function as an artesian aquifer. Depth
to the top of the Floridan aquifer generally corresponds to the
depth to limestone, and varies from less than five feet in the
Suwannee and Santa Fe river valleys,: to nearly 80 feet under the
Wacasassa Flats. The piezometric gradent is generally west-
southwestward.

Recharge to the Floridan aquifer system in Gilchrist County is
obtained from local rainfall percolating through the permeable
surficial sands in the western and northeastern portions of the
county. The thick sequence of low permeability clastics under
the Wacasassa Flats retards downward percolation, resulting in
only low to moderate recharge in this area (Stewart, 1980).
Water leaves the Floridan aquifer through natural movement
downgradient and subsequent discharge through numerous springs
and seeps along the river valley lowlands.


MINERAL RESOURCES

At present, no mineral commodities are being mined on a
commercial basis in Gilchrist County. However, both hard rock
and colloidal phosphate, as well as high purity limestone have
been mined here in the past. The following discussion of the
major mineral commodities is intended to provide an overview of
the mining potential for each mineral.


Sand

A number of shallow private pits in Gilchrist County are worked
for fill sand. These sand deposits are concentrated in the
unconsolidated Pleistocene surficial sands which cover most of
the county. Since there is insufficient local demand for sand
products, the potential for commercial mining is low at this
time.


Phosphate

The phosphatic sands, clays and limestones of the Alachua
Formation have been mined in eastern Gilchrist County since the
1900's. Hard rock phosphate, a calcium phosphate fluorapatite
mixture, occurs as a replacement of limestone float contained in
basal Alachua Formation sediments and on the top of the Ocala
Group. The clays within the Alachua Formation contain colloidal
phosphate and phosphorite, and comprise what is termed soft rock
phosphate.

No commercial phosphate mines are in operation in Gilchrist





rivers. This marl generally contains an abundant Holocene
freshwater mollusk fauna, and may attain three to four feet in
thickness (Puri et al., 1967).


GROUNDWATER

Groundwate-r is water that fills the pore spaces in subsurface
rocks and sediments. This water is derived principally from
precipitation within Gilchrist and adjoining counties. The bulk
of Gilchrist County's consumptive water is withdrawn from
groundwater aquifers. Two main aquifer systems are present under
Gilchrist County, the surficial aquifer system and the underlying
Floridan aquifer system (Southeastern Geological Society Ad Hoc
Committee on Florida Hydrostratigraphic Unit Definition, 1986,.


Surficial aquifer system

The surficial aquifer system is the uppermost freshwater aquifer
in Gilchrist County. This non-artesian aquifer is contained
within the interbedded sands and clays of the Alachua Formation
and the overlying Pleistocene siliciclastics and marine terrace
sands in central and southeastern Gilchrist County. In western
Gilchrist County, where the Alachua Formation is absent, the
surficial aquifer system may occur "perched" in locally thick
Pleistocene sands immediately overlying the Ocala Grioup
limestone; in these areas, the surficial aquifer system i3
separated from the underlying Floridan aquifer system by zones of
unsaturated limerock (Meyer, 1962). On average, the surfici.-
aquifer system ranges from 10 to 80 feet thick, with the thicker
portions located under the higher geomorphic sand ridges cf
central and eastern Gilchrist County, and in the structural low
under the Wacasassa Flats. The surficial aquifer system is
unconfined, and its upper surface is the water table. In
general, the water table elevation fluctuates with precipitation
rate and conforms to the topography of the land surface.
Recharge to the surficial aquifer system is largely through
rainfall percolating downward through the loose surficial clastic
sediments, and to a lesser extent, by upward seepage from the
underlying Floridan aquifer system. Water naturally discharges
from the aquifer by evaporation, transpiration, spring flow, and
by downward seepage into the Floridan aquifer system. The
surficial aquifer system may yield quantities of water suitable
for consumptive use, but in some areas the concentration of iron
and/or tannic acid impart a poor taste and color to the water
(Meyer, 1962).


Floridan aquifer system

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
Gilchrist County. The Floridan aquifer system exists as an







unconfined, non-artesian aquifer in portions of western,
northern, and northeastern Gilchrist County, where porous
Pleistocene quartz sand directly overlies the limestone. In
areas of central and southeastern Gilchrist County, where clay
beds in the Alachua Formation form low-permeability confining
units, the Floridan may function as an artesian aquifer. Depth
to the top of the Floridan aquifer generally corresponds to the
depth to limestone, and varies from less than five feet in the
Suwannee and Santa Fe river valleys,: to nearly 80 feet under the
Wacasassa Flats. The piezometric gradent is generally west-
southwestward.

Recharge to the Floridan aquifer system in Gilchrist County is
obtained from local rainfall percolating through the permeable
surficial sands in the western and northeastern portions of the
county. The thick sequence of low permeability clastics under
the Wacasassa Flats retards downward percolation, resulting in
only low to moderate recharge in this area (Stewart, 1980).
Water leaves the Floridan aquifer through natural movement
downgradient and subsequent discharge through numerous springs
and seeps along the river valley lowlands.


MINERAL RESOURCES

At present, no mineral commodities are being mined on a
commercial basis in Gilchrist County. However, both hard rock
and colloidal phosphate, as well as high purity limestone have
been mined here in the past. The following discussion of the
major mineral commodities is intended to provide an overview of
the mining potential for each mineral.


Sand

A number of shallow private pits in Gilchrist County are worked
for fill sand. These sand deposits are concentrated in the
unconsolidated Pleistocene surficial sands which cover most of
the county. Since there is insufficient local demand for sand
products, the potential for commercial mining is low at this
time.


Phosphate

The phosphatic sands, clays and limestones of the Alachua
Formation have been mined in eastern Gilchrist County since the
1900's. Hard rock phosphate, a calcium phosphate fluorapatite
mixture, occurs as a replacement of limestone float contained in
basal Alachua Formation sediments and on the top of the Ocala
Group. The clays within the Alachua Formation contain colloidal
phosphate and phosphorite, and comprise what is termed soft rock
phosphate.

No commercial phosphate mines are in operation in Gilchrist







County today. Loncala Phosphate Company operated soft rock
phosphate mining operations as late as 1973, in an area just
south of Mona. A large area of eastern Gilchrist County, along
the Gilchrist-Alachua County line and corresponding to the
Brooksville Ridge, has commercial mining potential. Future
exploitation of these remaining deposits will depend largely on
phosphate market prices and the economic health of the phosphate
industry.


Limestone

Ocala Group limestones occur near the surface in western
Gilchrist County. These high purity limestones approach 95
percent CaC03, and extensive, commercially mineable deposits are
present. To date, no commercial limestone quarries are in
operation in Gilchrist County. However, the Gilchrist County
Road Department is currently operating an open pit limerock mine
off State Road 49, north of Bell. The rock is mechanically
extracted, crushed, and used as roadbase material by the county.


REFERENCES
Brooks, H., 1966, Geological history of the Suwannee River:
Southeastern Geological Society 12th Annual Field Guidebook, p.
37-45.

Cooke, C. W., 1945, Geology of Florida: Florida Geological
Survey Bulletin no. 29, 339 p.

Dall, W., and Harris, G., 1392, Correlation paper Neocene: U.
S. Geological Survey Bulletin 84, 349 p.

Healy, H., 1975, Terraces and shorelines of Florida: Florida
Bureau of..Geology Map Series no. 71.

Meyer, F., 1962, Reconnaissance of the geology and ground-water
resources of Columbia County, Florida: Florida Geological Survey
Report of Investigations no. 30, 74 p.

Miller, J., 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 donation of the Ocala Group:
Florida Geological Survey Bulletin no. 38, 248 p.


and Vernon, R., 1964, Summary of the geology of
Florida and a guidebook to the classic exposures: Florida
Geological Survey Special Publication 5 (Revised), 312 p.

,Yon, J. W., Jr., and Oglesby, W., 1967, Geology of
Dixie and Gilchrist Counties, Florida: Florida Geological Survey







County today. Loncala Phosphate Company operated soft rock
phosphate mining operations as late as 1973, in an area just
south of Mona. A large area of eastern Gilchrist County, along
the Gilchrist-Alachua County line and corresponding to the
Brooksville Ridge, has commercial mining potential. Future
exploitation of these remaining deposits will depend largely on
phosphate market prices and the economic health of the phosphate
industry.


Limestone

Ocala Group limestones occur near the surface in western
Gilchrist County. These high purity limestones approach 95
percent CaC03, and extensive, commercially mineable deposits are
present. To date, no commercial limestone quarries are in
operation in Gilchrist County. However, the Gilchrist County
Road Department is currently operating an open pit limerock mine
off State Road 49, north of Bell. The rock is mechanically
extracted, crushed, and used as roadbase material by the county.


REFERENCES
Brooks, H., 1966, Geological history of the Suwannee River:
Southeastern Geological Society 12th Annual Field Guidebook, p.
37-45.

Cooke, C. W., 1945, Geology of Florida: Florida Geological
Survey Bulletin no. 29, 339 p.

Dall, W., and Harris, G., 1392, Correlation paper Neocene: U.
S. Geological Survey Bulletin 84, 349 p.

Healy, H., 1975, Terraces and shorelines of Florida: Florida
Bureau of..Geology Map Series no. 71.

Meyer, F., 1962, Reconnaissance of the geology and ground-water
resources of Columbia County, Florida: Florida Geological Survey
Report of Investigations no. 30, 74 p.

Miller, J., 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 donation of the Ocala Group:
Florida Geological Survey Bulletin no. 38, 248 p.


and Vernon, R., 1964, Summary of the geology of
Florida and a guidebook to the classic exposures: Florida
Geological Survey Special Publication 5 (Revised), 312 p.

,Yon, J. W., Jr., and Oglesby, W., 1967, Geology of
Dixie and Gilchrist Counties, Florida: Florida Geological Survey





Bulletin no. 49, 155 p.


Scott. T. M., 1988 (in press), The lithostratigraphy of the
Hawthorn Group (Miocene) of Florida: Florida Geological Survey
Bulletin no. 59.

Southeastern Geological Society Ad Hoc Committee, 1986,
Hydrogeoiogical units of Florida: Florida Geological Survey
Special Publication no. 28, 8 p.

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

Vernon, R. 0., 1951, Geology of. Citrus and Levy Counties,
Florida: Florida Geological Survey Bulletin no. 33, 256 p.

White, W.. 1970, The geomorphology of the Florida peninsula:
Florida Bureau of Geology Bulletin no. 51, 164 p.















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