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FLRD GEOLOSk ( IC SUfRiW


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State of Florida
Department of Natural Resources
Elton J. Gissendanner, Executive Director




Division of Resource Management
Charles W. Hendry, Jr., Director


Florida Geological
Steve R. Windham,


Survey
Chief


Open File Report 5

Geology of Citrus County, Florida

by

Steven M. Spencer


Florida Geological Survey
Tallahassee, Florida
1984














3 1262 04781 1772


675




e' 2-
SCIEICE
LIBRARY








Geology

Physiography

Several authors have discussed Florida's physiographic

features. For the purpose of this report White's (1970) classi-

fication will be used. The major physiographic features of

Citrus County include the Gulf Coastal Lowlands, the Brooksville

Ridge, and the Tsala Apopka Plain (figure 1).

The western portion of Citrus County is a poorly drained low

relief region. Notable features include extensive swamps,

marshes and terraces formed by ancient sea level stands. The

central portion of the county is characterized by the Brooksville

Ridge. The southern extent of this ridge is both higher and

really larger than that in the north. Eastern Citrus County is

lower, .flatter, and encompasses a substantial wetland area.



Gulf Coastal Lowlands



The Gulf Coastal Lowlands extend the entire length of Citrus

County. The lowlands range in elevation from sea level to 100

feet above sea level. Located within the coastal lowlands

are the coastal swamps and marine terraces of Pleistocene age

(10,000-1.5 million years ago).

The westernmost region delineated on White's (1970)

physiographic map is the Coastal Swamps. Puri and Vernon (1954)

and White (1970) defined this area as including all continuous




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fresh water swamps and salt marshes adjacent to the Gulf of

Mexico. The region is a low energy salt or fresh water environ-

ment with insufficient sand to build beaches. Sediments which

have accumulated upon Eocene limestones have in many places been

conducive to the establishment of vegetation. Elevations in the

swamp area are generally less than 10 feet above mean sea level.

The marine terraces are gently sloping features with seaward

facing escarpments. These features formed when sedimentary

materials were alternately deposited and eroded as sea level rose

and fell. Vernon (1951) distinguished the Pamlico terrace

(approximately 25 foot elevation) and the Wicomico terrace

(approximately 100 foot elevation) as the main terrace features

in Citrus County. Also associated with the coastal lowlands are

ancient dune features. The lowlands are composed of sands and

clayey sands of variable thickness overlying Eocene and Oligocene

limestones and dolomites.



Brooksville Ridge



The Brooksville Ridge trends north to south and occupies the

central part of Citrus County. Elevations along the ridge range

from abouo' 70 to 200 feet. The southern part of the ridge is

wider with higher elevations than the northern part. The ridge

has an irregular surface due to karst activity and elevations may

vary over 100 feet in short distances.








The ridge is composed of a core of limestone overlain by

clayey sands, sandy clays, and clays which in turn are overlain

by Pleistocene sands. The clays and clayey sediments have pro-

tected the underlying limestone from dissolution by limiting

downward percolation of ground water in contrast to the coastal

lowlands to the west and the Tsala Apopka Plain to the east which

have experienced substantial dissolution of limestone resulting

in lower elevations.



Tsala Apopka Plain



The Tsala Apopka Plain which is part of White's (1970)

Western Valley occupies the entire eastern portion of Citrus

County. Bounded on the east by the Withlacoochee River and on

the west by the Brooksville Ridge, this region has a number of

interconnected lakes partially separated by peninsulas and

islands. Alluvial deposits of variable thickness cover the

limestone surface. Elevations of the land surface range from

60-80 feet above mean sea level while water surface elevations

vary from 35 to 45 feet.





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STRATIGRAPHY



Exploratory drilling operations have penetrated sediments to

a maximum depth of 5556 feet in Citrus County, stopping in quart-

zitic sandstones. Deep subsurface sediments consist of shales,

sandstones, dolomites and limestones while surface and near sur-

face deposits consist of unconsolidated sands, clays, limestones

and dolomites. Only the surface and near surface units will be

expanded upon here.



Eocene Series

Avon Park Limestone

The Avon Park Limestone was named by Applin and Applin

(1944) for the upper Middle Eocene (40-45 million years ago)

limestone recognized in a Florida Geological Survey well (W-668)

drilled at the Avon Park Bombing Range in Polk-County, Florida.

It is the oldest stratigraphic unit to crop out in Florida.

Exposures of the Avon Park Limestone in Citrus County are rare

except in the northern part of the county along the Withlacoochee

River and near Red Level.

In Citrus County the Avon Park Limestone can be a dolomite,

or limestone with varying degrees of dolomitization. Where the

lithology is that of a dolomite the grain size varies from

microcrystalline (siltsized) to very fine grained. The dolomite

crystals are frequently enhedral and the rock appears sucrosic

and is unconsolidated to well indurated. When the Avon Park is








lithologically a limestone it is white or cream to brown and

gray. The limestone is cryptocrystalline to very fine grained

(up to .125mm), thin bedded or laminated with organic flecks

and seams. The limestone can also be relatively structureless.

The Avon Park can be a recrystallized limestone in which case it

typically is more indurated.

The Avon Park Limestone lies upon the Lake City Limestone.

It unconformally underlies the younger Ocala Group limestones

where the Ocala Group has not been eroded away.

Fossils found in the Avon Park Limestone include echinoids,

foraminifera, mollusks, bryozoa, and corals. These fossil groups

are indicative of a shallow marine environment.



Eocene Series

Ocala Group

The Ocala Group limestones consist of three formations

which in ascending order are: Inglis Formation, Williston

Formation, and the Crystal River Formation. These formations

are, where they have not been eroded away, at or near the land

surface.

Inglis Formation

The lithological characteristics of the Inglis Formation in

Citrus County are that of a limestone (calcarenite or grainstone
to packstone) with varying degrees of dolomitization, poor to

well indurated, white to cream, yellowish brown to tan in color,

with calcite or dolomite cement. In part, the formation is a




-6-


foraminiferal coquina. Dolomitic sections are poor to well

indurated, and composed of euhedral crystals of microcrystalline

(silt sized) to very fine grain sized dolomite. Thickness of the

formation is variable with the average being about 50 feet.

The Inglis Formation lies unconformably upon the Avon Park

Limestone. The Inglis Formation conformably lies below the

Williston Formation where the Williston Formation has not been

eroded away.

Exposures of the Inglis Formation in Citrus County occur at

a quarry near Red Level, along the coastal area on the Pamlico

terrace, and along the Withlacoochee River in northeastern Citrus

County.

Fauna is abundant in the Inglis and is made up of species of

mollusks, echinoids, and foraminifera. Where in abundance the

foraminifera may form a coquina.



Williston Formation

Lithologically, the Williston Formation is a marine

limestone, cream to tan colored foraminiferal coquina of miliolids

(grainstone or calcarenite). This granular to chalky limestone

is Loosely held together by carbonate cement. The average thick-

ness of the Williston Formation is approximately 30 feet.

Comprising the middle unit of the Ocala Group, the Williston

Formation is conformably overlain by the Crystal River Formation

and conformably underlain by the Inglis Formation. The transition

between the Crystal Formation and the Williston Formation is gra-









national and therefore, may be difficult at times to delineate.

Exposures of the Williston Formation in Citrus County occur

in the western regions near the coast as well as in the eastern

areas where it forms the bedrock of the Tsala Apopka Plain.

Other exposures occur in solution features such as sinkholes but

since these are often filled with sediments observing the for-

mation is often difficult. Several exposures can be observed

along the Withlacoochee River in northeastern Citrus County. In

the southeastern areas of the county the Williston Formation is

present in old phosphate quarries but vegetation and slump

material has nearly obscured all of the formation (Vernon, 1951).

Miliolid foraminifera are the most abundant fauna in the

Williston Formation. Other fauna include echinoids, mollusks,

and other species of foraminifera.



Crystal River Formation

The Crystal .River Formation of late Eocene age (35.6 40

million years ago) was named for an exposure in the Crystal River

Rock Quarry in Citrus County (Puri, 1953; Vernon and Puri, 1956).

The lithology of the Crystal River Formation is a white or

cream to buff colored, moderately indurated packstone to

wackestone, variably recrystallized, foraminiferal coquina (large

foraminifera) in part set in a pasty calcite matrix. The

thickness of the Crystal River Formation at the Crystal River

Quarry is 108 feet.

The Crystal River Formation lies conformably upon the


I -- ~ ----st ~c--~b~Bra~ed~P~dl~







Williston Formation. The Crystal River Formation lies uncon-

formably below Recent age sediments to Oligocene age limestones

where present in Citrus County.

Exposures of the Crystal River Formation can be found in the

Crystal River Quarry. Other exposures of this formation occur

along the coastal region on the Pamlico terrace and in south-

central Citrus County in sinkholes.

The common occurrence of the foraminifera genus

Lepidocyclina is frequently used as a guide in identifing this

formation. Other common fossil groups include bryozoa, echi-

noids, and mollusks.



Oligocene Series

Suwannee Limestone

The Suwannee Limestone of Oligocene age (23.7-35.6 million

years ago) was named by Cooke and Mansfield (1936) for exposures

along the Suwannee River near Ellaville, Madison County, Florida.

The Suwannee Limestone is present at or near the ground surface

in the south-central region of the Brooksville Ridge in Citrus

County. Exposures may also be found in road cuts, quarries, and

sinkholes.

The general lithology is a cream to tan colored limestone,

which is granular to chalky, moderate to well indurated, variably

recrystallized, partially silicified and very fossiliferous.

Vernon (1951) states that in this region the Suwannee Limestone

may be 120 feet thick. The Suwannee Limestone unconformably






-9-


rests upon the Crystal River Formation and unconformably

underlies Recent to Miocene age sediments.

Fragments of macrofossils and microfossils are found in the

Suwannee Limestone. Common fauna groups found in the limestone

include pelecypods and gastropods along with foraminifera such as

miliolids and Dictyoconus cookei.



Post-Oligocene Series

Undifferentiated Sediments

A veneer of sand, clayey sand and sandy clay overlies most

of Citrus County. These sediments range in age from Miocene to

Recent. Thicknesses vary substantially due to the irregular sur-

face of the underlying limestone.

The Gulf Coastal Lowlands and the Tsala Apopka Plain surface

sediments are composed of light colored, medium to fine grained,

poorly consolidated to unconsolidated quartz sand and silt. The

surface of the Brooksville Ridge is covered by sand which is

underlain by orange to reddish orange clayey sand and sandy clay

which in turn is underlain by the Suwannee Limestone or Ocala

Group limestones. Some of the sediments on the ridge (clays and

quartz sands which are phosphatic and contain organic material)

are considered to be residual material of the Hawthorn Group

(Scott, personal communications, 1984, manuscript in preparation)

which was present in the area prior to being eroded (Scott, et al.,

1980). Cooke (1945) assigned plastic sediments of this type to

the Alachua Formation. He further goes on to say that the




-10-


Brooksville Ridge is underlain by the Alachua Formation.

Vernon (1951) states that marine clays overlying the Suwannee

Limestone in southern Citrus County belong to the Miocene

Hawthorn Formation and that terrestrial clays belong to the

Alachua Formation.

ECONOMIC GEOLOGY

STONE

Limestone is mined predominantly from the Lecanto, Red Level,

northern (south of Inglis) and southeast regions of Citrus County.

Formational units from which mining presently is occurring are

the late Middle Eocene age Avon Park Limestone, the late Eocene

Ocala Group, and the Oligocene Suwannee Limestone (Schmidt, et al.,

1979).

All limestone and dolomite mined in Citrus County is mined

by open pit methods. Generally, overburden must be removed using

bulldozers or draglines. If, after overburden removal, soft rock

conditions are encountered, bulldozers equipped with a claw can rip

the rock loose. When hardness increases, blasting becomes necessary

prior to mining. Where pits are flooded, draglines must be uti-

lized. After mining, the rock is loaded onto trucks for transport

to a processing plant or crushed and stockpiled (Campbell, personal

communication, 1984, manuscript in preparation).

Size reduction and grinding are the common processing proce-

dures. These procedures involve crushing and screening to produce

the desired size material. The beneficiation procedures, those

which upgrade the material by removing impurities and adding






-11-


desirable materials, are washing, screening, drying and blending.

After all processing is completed the material may be utilized as

a road base material, fertilizer and soil conditioners, rip rap,

and as a concrete and asphalt aggregate.

SAND

In Citrus County only the Brooksville Ridge contains sand

deposits of primary importance. The sands of the ridge range in

age from Miocene to Recent. These clastics are predominantly poorly

sorted, fine to medium grain sized quartz sands. Except for sur-

face sand, the sand may contain a clay matrix (Scott, et al., 1980).

Recent dune and alluvial sand deposits exist in Citrus

County but are of variable quality and volume. These deposits

are economically valuable only on a local scale. Sand deposits

of the Pleistocene terraces in the Gulf Coastal Lowlands are con-

sidered too fine grained for construction uses.

Once mined, sand may be graded by size (coarse to fine)

using a series of shaker screens. Sand is almost exclusively

transported by truck. The major uses of construction sand and

gravel are for concrete aggregate, roadbase material, construc-

tion fill, and asphalt mixtures.

PHOSPHATE

Hard rock phosphate was mined in Citrus County for many years

until about 1966 when it became economically unfeasible to continue

operations (Deuerling and MacGill, 1981). The origin of Hard

Rock Phosphate has been discussed for many years. Phosphoric acid

in solution in water can under favorable conditions, replace the







carbonate of limestone thus forming calcium phosphate (i.e., hard

rock phosphate). Sellards (1913) states that the matrix material

ij. the hard rock phosphate deposits is the residue of previously

eroded limestone.

During mining and beneficiation of the hard rock phosphate,

phosphatic clays were slurried and discarded as waste in pre-

viously mined out pits or simply allowed to flow onto the natural

ground surface. This waste material is high in phosphate con-

tent. Today, several companies are processing the waste clays of

former hardrock operations primarily for use as animal feed

ingredient, and as a direct application fertilizer.



CLAYS

Clay of an unclassified nature is being mined by one com-

pany east of the Lecanto area in Citrus County.






-13-


GROUNDWATER

In Citrus County the principal source of.water is the

Floridan Aquifer. The aquifer is composed of the Eocene to

Oligocene age limestones and dolomites of the Lake City Limestone,

Avon Park Limestone, Ocala Group and the Suwannee Limestone where

present. The base of the aquifer is approximately at the point

where evaporites consistently fill limestone and dolomite pore

spaces. Generally, fillings of this nature occur within the

lower Lake City Limestone (Fretwell, 1983). The top of the

aquifer is at sea level or just submerged along the coastline.

Inland, the top of the aquifer is covered by a veneer of sand,

clayey sand or sandy clay. The Floridan Aquifer is described as

unconfined for much of Citrus County due to the absence of well

developed low permeability sediments between the ground surface

and the top of the aquifer. In the Brooksville Ridge area where

the aquifer is overlain by several feet of low permeability

sands, clayey sands, and clays, the aquifer may be defined as

semiconfined. In these areas, the local groundwater table may be

developed in the surficial sands above the clayey sediments.

The Floridan Aquifer is recharged by precipitation and

groundwater flow. Direction of groundwater flow is toward the

Gulf of Mexico. Natural artesian discharge occurs in springs

and marshes. On the basis of discharge, the Homosassa and

Crystal River Springs have been labled first-order magnitude

springs, that is, they discharge water at rate more than 100

cubic feet per second.


-





-14-

In Citrus County the Floridan Aquifer is considered to be a

potable water source. The exception.to this is in the coastal

region where saltwater encroachment has occurred. As demand for

water increases so will the problems associated with water

quality. Citrus County has shown a population increase of 185

percent between the census of 1970 and 1980 (Fernald,

1981). Presently, the major demand on the aquifer comes from the

agricultural and industrial communities as well as the domestic

and rural users.





-15-


Applin, P.L., and Applin, E.R., 1944, Regional Subsurface
Stratigraphy and Structure of Florida and Southern
Georgia: Am. Assoc. Petroleum Geologists Bull., vol.
28, no. 12, p. 1673-1753.

Cooke, C.W., 1945, Geology of Florida: Florida Geological
Survey Bulletin 29, 339 p.

and Mansfield, W.C., 1936, Suwannee Limestone
of Florida (abst). Geol. Soc. of Am. Proc. for 1935,
p. 71-72.

Deuerling, R.J. and MacGill, P.L., 1981, Environmental
Geology Series Tarpon Springs Sheet, Florida Bureau
of Geology Map Series 99.

Fernald, Edward A., 1981, Atlas of Florida,
Florida State University Foundation, Inc., 276 p.

Fretwell, J.D., 1983, Ground-water Resources of Coastal
Citrus, Hernando, and Southwestern Levy Counties,
Florida, U.S. Geological Survey Water-Resources
Investigation Report 83-4079, 87 p.

MacNeil, F.S., 1949, Pleistocene Shorelines in Florida and
Georgia: U.S. Geological Survey Professional Paper
221-F, p. 91-107.

Puri, H.S., 1953, Zonation of the Ocala Group in Peninsular
Florida (abst): Jour. Sed. Pet., vol. 23, p. 130.

and Vernon, Robert 0., 1964, Summary of the
geology of Florida and a Guidebook to the Classic
Exposures: Florida Bureau of Geology, Spec. Publ. No. 5
(revised), 312 p.

Schmidt, Walter, and others, 1979, The Limestone Dolomite
and Coquina Resources of Florida: Florida Bureau of
Geology, Report of Invest. No. 88, 54 p.

Scott, Thomas M., and others, 1980, The Sand and Gravel
Resources of Florida: Florida Bureau of Geology,
Report of Investigation No. 90, 41 p.

Sellards, E.H., 1913, Origin of Hardrock Phosphates of Florida:
Fla. Geol. Survey 5th Annual Rept., p. 23-80.

Vernon, Robert 0., 1951, Geology of Citrus and Levy
Counties, Florida: Florida Bureau of Geology, Bull.
33, 256 p.

and Puri, H.S., 1956, A Summary of the Geology
of Panhandle Florida and a Guidebook to the Surface
Exposures: Fla. Geol. Survey, Southeastern G.S.A. Field
Trip Guidebook, 93 p.

White, William A., 1970, Geomorphology of the Florida
Peninsula: Florida Bureau of Geology, Bull. 51, 164 p.












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