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FLRD GEOLOSk ( IC SUfRiW
[year of publication as printed] Florida Geological Survey [source text]
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State of Florida
Department of Natural Resources
Elton J. Gissendanner, Executive Director
Division of Resource Management
Art Wilde, Director
Florida Geological Survey
Walter Schmidt, Chief
Open File Report 13
Geology of Polk County, Florida
Kenneth M. Campbell
Florida Geological Survey
3 1262 04543 6390
Geology of Polk County, -Florida
Kenneth M. Campbell
Florida Geological Survey
Although, several authors have discussed the physiography of the
Florida peninsula, for the purposes of this report, "White's (1970) classi-
fication will be utilized. Polk County lies within the Central Highlands
physiographic province. The vast majority of the county lies within the
Polk and Lake uplands. Several ridges rise above the Polk Upland surface.
The most prominent ridge is the Lake Wales Ridge which forms the eastern
boundary of the Polk Upland (White, 1970). That portion of the county
lying east of the Lake Wales Ridge is part of the Osceola Plain. A small
portion of north-western Polk County lies within the southern end of the
Western Valley (White, 1970).
Elevations within the county range from 50 to 305 feet above Mean Sea
Level (MSL). The lowest elevations are found along the eastern county
boundary (Kissimmee River Valley). The highest elevations are found along
the crest of the Lake Wales Ridge in the vicinity of Lake Wales and Babson
Park (Stewart, 1966).
Polk and Lake Uplands
The majority of Polk County lies within the Polk and Lake uplands.
Elevations within the Polk Upland range generally between 100 and 130 feet
above MSL (White, 1970). In the northern portion of the county the Polk
Upland merges with the Lake Upland. There is not a distinct topographic
distinction between the' two uplands, therefore the dividing line is drawn
arbitrarily (White, 1970).
The Polk Upland is bounded by the Gulf Coastal Lowlands and the
Western Valley on the west and north, by the DeSoto Plain on the south and
by the higher ground of the Lake Wales Ridge on the east. The Lakeland,
Winter Haven and Lake Henry ridges rise from the surface of the upland.
White (1970) states that these ridges appear to be renmants of a previous
widespread upland. With the exception of the ridges, the surface eleva-
tions of the Polk Upland range from 100 to 130 feet above MSL (White, 1970).
Lake Wales Ridge
The Lake Wales Ridge is the most prominent topographic feature in
peninsular Florida. The ridge is the distal remnant of a much longer ridge
which may have, at one time, included the Trail Ridge in northeastern
Florida. Elevations of the ridge crest range from 150 to 305 feet above
MSL, and are highest at Lake Wales and Babson Park (Stewart, 1966).
The ridge is a highland composed primarily of coarse plastic material
which has been dissected by streams and karst activity and "straightened on
its flanks by coastal erosion to produce its present western bounding scarp
and a probable buried former eastern bounding scarp" (White, 1970). The
preservation of the Lake Wales Ridge as a present day highland is thought
to be due to the presence of the clayey, gravelly, coarse quartz sand which
has limited, but not completely prevented, dissolution of the underlying
That portion of Polk County east of the Lake Wales Ridge lies within
the western portion of the Osceola Plain. The Osceola Plain is bounded on
the west by the Lake Wales Ridge and to the east by lower lying marine
scarps. Thus it is properly a marine terrace (White, 1970). Local relief
is generally small, elevations of the plain typically lie between 60 and 70
feet above MSL '(White, 1970), although it is somewhat lower along the Kis-
.smmeeRiver chain. I-n the'-soltheastern corner of the county, the Bombing
Range Ridge rises above the level of the plain. The Bombing Range Ridge is
21 miles long and 3-4 miles wide and reaches elevations of 125 to 145 feet
above MSL. White (1970) states that it has all the attributes of a large
marine sand bar.
A small portion of northeastern Polk County lies on the eastern flank
of the southern part of the Western Valley. The Western Valley is a low
irregular valley produced by differential reduction of unprotected soluble
material adjacent to the Brooksville Ridge and Polk Upland. That portion
of Polk County which lies within the Western Valley has elevations which
range from 75-100 feet above MSL.
Surface and near surface sediments in Polk County consist of quartz
sand, clay, phosphorite, limestone and dolomite. These sediments range in
age from Late Eocene to Holocene (40 million years ago to present).
The Eocene Series in Polk County consists of the Oldsmar, Avon Park
and Ocala Group limestones. Only the uppermost unit, the Ocala Group of
Late Eocene age, will be discussed here.
The Ocala Group consists three formations, which in ascending order
are, the Inglis, Williston and Crystal River formations. Essentially all
of Polk County is underlain by limestone of the Ocala Group.
In Polk County, the Inglis consists of white to cream to dark brown,
granular, fossiliferous, well indurated limestone and dolomite (Stewart,
1966). The Inglis ranges from approximately 35 feet thick in the.north-
western portion of the county, to as much as 95 feet thick in southeastern
Polk County (Stewart, 1966). The Inglis is the uppermost limestone present
in extreme northeastern Polk County (vicinity of Haines City) due to ero-
sion of overlying units (Stewart, 1966).
The Williston is a white to cream or brown limestone consisting of a
coquina of foraminifera set in a pasty calcilutite matrix. The formation
is generally poorly indurated and may be dolomitized (Stewart, 1966). The
formation is missing in extreme northeastern Polk County, but underlies the
remainder of the county with thicknesses which range from 10-90 feet
Crystal River Formation
The Crystal River is a white, cream, gray, or tan very pure limestone.
The formation is generally poorly indurated and consists of a coquina of
large foraminifera in a chalky calcilutite matrix (Stewart, 1966). The
Crystal River is at or near the ground surface over a large area of
northern Polk County. Thicknesses in this area range from 30-60 feet and
thicken southward to approximately 150 feet (Stewart, 1966). The forma-
tion is siliclfied throughout much of the surface exposure area of northern
Polk County (Stewart, 1966).
The Suwannee Limestone is present throughout the western portion of
Polk County, but is missing in the north and.eastern portion of the county
due to erosion on the flanks of the Ocala Uplift (NW-SE trend). The
.Suwanne.e Limestone., in Polk County is white, cream or tan, variably tex-
tured (calcarenite to calcilutite), fossiliferous, poorly to well indurated
and variably recrystallized. The formation locally contains dolomitized or
silicified zones (Stewart, 1966). Common fossils include benthic foramini-
fera, bryozoans, molluscs and echinoids.
The top of the Suwannee is found at 70-80 feet above MSL in the area
north of Lakeland and west of Polk City and dips gently to the south and
south-southwest. Along the western half of the southern county boundary
the Suwannee is found at approximately 250-300 feet below MSL (Wilson,
The thinnest portion of the Suwannee is along the eastern edge of the
formation's extent along the trend of the Ocala Uplift, where the formation
thins to zero. The thickest portion ranges from 100-150 feet in that por-
tion of western Polk County south of Lakeland and Bartow (MacGill, 1976,
unpublished Bureau of Geology map).
Scott (1986) has raised the Hawthorn from formation status to group
status. The Hawthorn Group will include those sediments which in the past
have been included in the Tampa, Hawthorn and Bone Valley formations. In
1986). The Tampa Member is a white to tan-colored, quartz sandy limestone
with a carbonate mud matrix. Varying amounts of clay are usually dissemi-
nated throughout the rock (King and Wright, 1979; Scott, 1986). Some beds
within the Tampa Member contain more than 50 percent quartz sand. Dolomite
is relatively uncommon within the Tampa Member (King and Wright, 1979;
The Tampa Member is present only in the southwestern corner of Polk
County, becoming indistinct due to a faces change at its eastern extent.
The top of the Tampa is encountered at elevations which range from slightly
greater than 50 feet above MSL to approximately 150 feet below MSL in the
extreme southwestern corner of Polk County (Scott, 1986). The thickness of
the member in Polk County is less than 50 feet (Scott, 1986).
The upper (unnamed) member of the Arcadia Formation includes those
sediments which in the past have been referred to as the "Hawthorn car- ,
bonate unit" (Scott, 1986). Lithologically, these sediments consist of
white to yellowish gray, quartz sandy, phosphatic and sometimes clayey,
dolomites and limestones (uncommon). Occasional beds of carbonate rich
quartz sand and thin clay beds are present.
The upper member of the Arcadia is present throughout Polk County with
the exception of the northernmost portion of the county. In those areas
where the Tampa and Nocatee Members are not recognized, the entire for-
mation remains undifferentiated. The top of the formation ranges from 112
feet above MSL in the vicinity of Lakeland, to approximately 125 feet below
MSL in the southeastern corner of the county (Scott, 1986). The thickness
of the Arcadia ranges from zero at its northern extent, to approximately
300 feet in the southwest corner of the county. In general the formation
dips to the south and southeast (Scott, 1986).
Polk County, the Hawthorn Group consists of, in ascending order, the
Arcadia Formation and the Peace River Formation.
The Arcadia Formation contains, in ascending order, the Nocatee and
Tampa members and an unnamed member. The Nocatee Member is composed of the
sediments which were previously described as the "sand and clay unit" of
the Tampa Limestone (Wilson,. 1977).g. The Tampa Member includes the sedi-
ments of the type Tampa Formation of King and Wright (1979). The unnamed
(upper)-member includes those sediments which in the past have been
referred to as the "Hawthorn carbonate unit" (Scott, 1986).
The Nocatee Member consists of a complexly interbedded sequence of
variably phosphatic quartz sands, clays and'carbonates (Scott, 1986). The
Nocatee is predominantly a plastic (sand and clay) unit. Quartz sands are
typically fine to coarse grained, sometimes silty, clayey, calcareous or
dolomitic and variably phosphatic (Scott, 1986). Clay beds are common.
The clays are variably quartz sandy and silty, phosphatic and calcareous to
dolomitic. Carbonate beds are subordinate within the Nocatee (Scott,
The Nocatee within Polk County is present only in the southwestern
corner of the county. The top of the formation is encountered at eleva-
tions which range from 81 to 150 feet below MSL (Scott, 1986). Thickness
of the Nocatee ranges from less than 50 to slightly more than 100 feet.
The upper surface dips generally to the south and southeast. The limits of
the formation are primarily by faces change (Scott, 1986).
The Tampa Member of the Arcadia Formation is lithologically similar to
the type Tampa Formation of King and Wright (1979), but has a slightly
greater phosphate content-(1-3 percent) and greater area extent (Scott,
Peace River Formation
The Peace River Formation includes two members: a downdip, unnamed
member and the updip Bone Valley Member [formerly the Bone Valley
Formation (Matson and Clapp, 1909)] (Scott, 1986). Lithologically, the
unnamed member consists of yellowish'gray to light olive-green interbedded
sands, clays and dolomite with variable phosphate content which, in the
past, have been described as "upper Hawthorn clastics" (Scott, 1986).
Scott (1986) defines the BOre Valley Member as "all the phosphorite pebble
or gravel bearing beds with sand-sized phosphorite in a sandy to clayey
The Peace River Formation is present throughout Polk County with the
exception of the northernmost part of the county. The Bone Valley Member
is present only in the western part of the county and thins in all direc-
tions from a center of deposition located in the Bartow-Mulberry area
(Bernardi and Hall, 1980; Scott, 1986). Throughout much o the area
underlain by the Bone Valley Member the Bone Valley comprises the entire
Peace River section, with the Bone Valley directly overlying the Arcadia
(Scott, 1986). In southernmost Polk County the Bone Valley interfingers
laterally and vertically with the undifferentiated Peace River. In the
eastern part of the county, only the undifferentiated Peace River is pre-
sent (Scott, 1986).
The Bone Valley Member of the Peace River is found at elevations as
high as 175 feet above MSL in southwestern Polk County. The top of the
Bone Valley throughout much of its extent-occurs above 100 feet MSL (Scott,
1986). In Polk County the top of the Peace River dips to the east and is
found at depths slightly greater than 50 feet below MSL. The thickness of
the Peace River is generally less than 50 feet in Polk County (Scott,
1986). The Bone Valley Member has a maximum thickness of approximately 50
Undifferentiated surficial sands, clayey sands and clays blanket essen-
..tially al.l of Polk County. These sediments range in age from Pliocene (T.
Scott, 1986, personal communication) to Pleistocene (5.3 million years to
10,000 years ago). The Lake Wales and Winter Haven ridges, are composed of
clayey, micaceous, quartz pebbly sands which in the past have been
described as "Miocene coarse clastics". These sediments are presently
thought to be Pliocene in age (T. Scott, 1986, personal communication) and
are included in the undifferentiated surficial sediments for the purpose of
In general, the surficial sediments are thinnest in the southwest por-
tion of the county and are thicker to the north and east and beneath the
ridges. The thickness of undifferentiated surficial sediments ranges from
less than 10 feet to more than 120 feet.
Deposits of Holocene age (10,000 years ago to present) are primarily
limited to present day stream flood plains, beaches, swamps, marshes and
lakes. These sediments consist of sand, silt, clay and organic materials.
Groundwater in Polk County is obtained from the surficial aquifer
system, the intermediate aquifer system and from the Floridan Aquifer. The
aquifers are separated by confining layers which restrict vertical water
movement between the aquifer systems. The hydrogeological units utilized
here are those presented by the Southeastern Geological Society Ad Hoc
Committee on Florida Hydrostratigraphic Unit Definition (1986).
Surficial Aquifer Systems
The surficial aquifer consists primarily of quartz sand and includes
the undifferentiated surficial sands and clay as well as the uppermost por-
tions of the Peace River Formation. The top of the surficial aquifer is
the ground water table and water within the'surficial aquifer is generally
under unconfined conditions. The base of the surficial aquifer system is
formed by the clayey, less permeable beds of Peace River Formation. The
surficial aquifer system underlies essentially all of Polk County and is
utilized primarily for domestic and low volume irrigation uses where high
flow rates are not required (Stewart, 1966).
Intermediate Aquifer System
The intermediate aquifer system, present over much of western Polk
County south of Polk City, contains water under confined conditions and
consists primarily of the limestones and dolomites of the Arcadia Forma-
tion. The intermediate aquifer corresponds with the "secondary artesian
aquifer" of Stewart (1966). The upper confining layer of the intermediate
aquifer system consists of the clayey sediments of the Peace River Forma-
tion. The lower confining layer consists of the Nocatee Member of the
Arcadia Formation. Locally the intermediate aquifer and the Floridan Aquifer
are in direct contact, or are hydrologically connected where confining beds
are absent or have been breached (Stewart, 1966).
The intermediate aquifer system in Polk County ranges from about 10
to 150 feet thick (Stewart, 1966; Scott, 1986). The principal uses for
this aquifer include domestic; truck farm irrigation and some large volume
citrus irrigation (Stewart, 1966).
The Floridan Aquifer in Polk County consists of the persistent verti-
ca.lly permeable portions of the Avon Park (combined-with the Lake City
Limestone by.Miller, in press), Ocala-Group and Suwannee limestone
(.Stewart, 1966). In the eastern portion of the county where confining beds
. at the base of the Hawthorn Group are thin or missing, the Floridan inclu-
des the permeable portions of the Arcadia Formation which are in hydrologic
contact with the remainder of the aquifer.
The Floridan Aquifer is the principal aquifer in Polk County and is
the source of all major municipal, industrial and irrigation water supplies
(Stewart, 1966). The Floridan is an artesian aquifer throughout much of
the county. In the general area north of Polk City, however, the confining
layers have been removed by erosion and the Floridan is unconfined. *In
this area the top of the Floridan is at about 100 feet above MSL. The top
dips generally to the south, southeast and southwest and is at about 250
feet below MSL in the southeastern and southwestern corners of the county
(Buono and Rutledge, 1978).
Phosphate, byproduct uranium and fluorine, limestone, peat, construc-
tion and industrial sand are presently being produced in Polk County.
Phosphate rock is the mineral commodity of greatest economic impor-
tance in Polk County. The majority of the Central Florida Phosphate Dis-
trict is -located in southwest Polk County. Eight companies are presently
mining phosphate in Polk County. Florida has led the nation in phosphate
production for over 90 years; the bulk of this production is from Polk
County (Boyle and Hendry, 1985).
Byproduct Uranium and Fluorine
Uranium and fluorine are byproduct resources which can be recovered
from the phosphoric acid produced by the acidulation of phosphate rock.
The phosphate deposits of the Central Florida Phosphate District contain an
average of 0.015 percent U308 (Sweeney and Windham, 1979) and 3-4 percent
fluorine (Nash and Blake, 1977).
With present technology approximately one pound of U308 is recoverable
from a ton of P205 (Sweeney and Windham, 1979). Under present economic
conditions only those companies with long term contracts are producing by-
product uranium. The uranium produced is utilized primarily by the
electric powdr generation industry. \
When phosphate rock is treated to produce phosphoric acid approxi-
mately 40 percent of the fluorine present in the phosphate rock is vola-
tilized forming silicia-tetrafluoride (SiF4). The fluorine recovered is
utilized to produce compounds for the chemical industry and for water
fluoridation (Boyle and Hendry, 1985). Under current economic conditions,
much of the recoverable fluorine is not recovered.
Limestone resources are limited in Polk County. Although extensive
limestone deposits are present, the impure nature of the limestone, coupled
with excessive overburden thickness, prevent economic utilization through-
out much of the county. The only limestone mining in the county is in the
extreme northwestern corner of the county.
Several peat mining operations are active in Polk County. The majo-
rity of this product is utilized to improve soil conditions, for nursery
uses and for potting soils.
Several companies.are mining construction and industrial sand in Polk
County. The primary areas of development are in the vicinity of Polk City
and along the Lake Wales Ridge in the eastern part of Polk County.
Bernardi, J. P. and R. B. Hall, 1980, Comparative Analysis
Florida Phosphate District to its Southern Extension:
neering, August, 1980, pp. 12b6-1l61.
of the Central
Boyle, J. R. and C. W. Hendry, Jr., 1985, The Mineral Industry of Florida,
1983, in Minerals Yearbook, 1983: U.S. Bureau of Mines, V. 2,
Buono, A. and A. T. Rutledge, 1978, Configuration of the Top of the
Floridan Aquifer, Southwest Florida Water Management District, and
Adjacent areas: U. S. Geol. Survey, Water Resources Investigation
King, K. C. and R. C. Wright, 1979, Revision of the Tampa Formation, West-
Central Florida: Transactions Gulf Coast Association of Geological
Societies, Volume XXIX, pp. 257-262.
Matson, G. C. and F. G. Clapp, 1909, A Preliminary Report
Florida with Special Reference to the Stratigraphy:
Geological Survey, 2nd Annual Report, pp. 25-173.
on the Geology of
Miller, J. A., in press, Hydrogologic Framework of the Floridan Aquifer
System: U. S. Geol. Survey Professional Paper 1403-B.
Nash, B. D. and H. E. Blake, Jr., 1977, Fluorine Recovery from Phosphate
Rock Concentrates: U. S. Bureau of Mines, RI 8205, 16 p.
Scott, T. M., 1986, The Regional Lithostratigraphy of the Hawthorn Group
(Miocene) of Florida: Florida Bureau of Geology, Bull. ff9, in
Southeastern Geologic Society, 1986, Hydrogeologic Units of Florida:
Florida Geological Survey, Special Publication No. 28, 8 p.
Stewart, H. G., Jr., 1966, Ground-Water Resources of Polk County:
Geological Survey Report or investigation NO. 44, /1U p.
Sweeney, J. W. and S. R. Windham, 1979, Florida: the New Uranium Producer:
Florida Bureau of Geology, Special Publication No. 22, 13 p.
White, W. A., 1970, Geomorphology of the Florida peninsula: Florida Bureau
of Geology, Bull. #51, 164 p.
Wilson, W. E.,
1977, Ground Water Resources of DeSoto and Hardee Counties,
Florida Bureau of Geology, Report of Investigation No. 83,
Generalized Physlographic Map of Polk County, after White (1970).
0 3 6 9 12
I I I I I MI.
HILLSBOROUGH CO. POLK CO.
POLK CO. JOSCEOLA CO.
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