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Geology of Hillsborough County, Florida ( FGS: Open file report 6 )
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 Material Information
Title: Geology of Hillsborough County, Florida ( FGS: Open file report 6 )
Series Title: ( FGS: Open file report 6 )
Physical Description: 17 p. : ill., map ; 28 cm.
Language: English
Creator: Campbell, Kenneth M ( Kenneth Mark ), 1949-
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee Fla
Publication Date: 1984
 Subjects
Subjects / Keywords: Geology -- Florida -- Hillsborough County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Kenneth M. Campbell.
Bibliography: Includes bibliographical references (p. 16-17).
General Note: Cover title.
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: 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: aleph - 001545493
oclc - 22438767
notis - AHF9013
System ID: UF00001005:00001

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Table of Contents
    Main
        Copyright
    Title Page
        Title Page 1
        Title Page 2
    Physiography and Drainage
        Page 1
        Page 2
        Page 3
        Page 4
    Stratigraphy
        Page 5
        Page 6
        Page 4
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Industrial minerals
        Page 12
        Page 13
        Page 14
        Page 15
        Page 11
    References
        Page 16
        Page 17
    Maps and charts
        Page 18
        Page 19
        Page 20
Full Text






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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 Survey
Steve R. Windham, Chief









Open File Report 6

Geology of Hillsborough County, Florida

by

Kenneth M. Campbell


Florida Geological Survey
Tallahassee, Florida
1984






















3 1282 04690 4230













SCIENCE
LIBRARY




OPE4 FILE REPORT 6


GEOLOGY OF HILLSBOROUGH COUNTY

By:
Kenneth M. Campbell
Florida Geological Survey




Physiography and Drainage

The terrain of western Hillsborough County is flat and low

lying. The eastern part of the county is gently rolling

and higher in elevation. The notable physiographic features of

the area are related to ancient stands of the seas which once

covered the region. Relict shorelines are evidenced by subtle

linear escarpments, which in much of the area, have not been

significantly altered by fluvial (river) processes. Four ancient

shorelines are preserved in Hillsborough County. The Pamlico,

Talbot, Penholoway and Wicomico shorelines stand at or near 25,

42, 70 and 100 feet above present mean sea level respectively.

Hillsborough County is divided in, ;o several physiographic

features. These physiography ., Ises are the Polk Upland,

Desoto Plain, Gulf Coasta s L. <.a and the Western Valley_

(White, 1970) (See physio;, ,.e map).



Polk Upland

The Polk Upland occupies much of the eastern part of the

county at elevations which range from 100-160 feet. The terrain

is gently rolling. The Bone Valley Member of the Peace River

Formation underlies most of the upland (White, 1970). Due to the




1
Florida Bureau of Geology Library
903 W. Tennessee St.
Talahassee. FL 32304





presence of clayey material in the Bone Valley, karat features

are not characteristic of the Polk Upland, although there is a

scattering of sinkholes in the Brandon area. Within Hillsborough

County, the Upland is drained by the Alafia and Little Manatee

rivers and their tributaries. The Upland is bounded on the west

by a western facing scarp (the Wicomico shoreline) which slopes

downward to the Desoto Plain and the Gulf Coastal Lowlands in

central Hillsborough County and to the Hillsborough River Valley

in the northern part of the county.



Desoto Plain

The Desoto Plain forms part of the southern and western

boundaries of the Polk Upland. Only a small portion of a north-

ward extending arm of the Desoto Plain is present in Hillsborough

County. The inconspicuous scarp which separates the plairr-from.

the Polk Upland has elevations of 75-80 feet at the toe (White,

1970). The Desoto Plain is similar to the Polk Upland but is

lower in elevation, has less relief and is more poorly drained.



Western Valley

The Hillsborough River flows in a southwesterly direction

through the north-central part of the county and occupies the

southern end of the,Western Valley (White, 1970). The

Withlacoochee River occupies the Western Valley north of the dif-

ference of the Withlacoochee and Hillsborough rivers from-their..

common headwaters (the upper Withlacoochee River). Occasionally,







the Withlacoochee overflows into the Hillsborough through a

topographic low (White, 1958). White (1958) believed there is

evidence that the Western Valley originally contained a single

stream which flowed into Hillsborough and Tampa bays. Deep sands

cover much of the Western Valley, with the result that these

areas are well-drained. Portions of the Hillsborough River

Valley are swampy; however, there are relatively few lakes pre-

sent.



Gulf Coastal Lowlands

The Gulf Coastal Lowlands encompass northwestern

Hillsborough County, the interbay peninsula and extend several

miles inland from the present coast in the southern part of the

county (White, 1970). The Pleistocene age (10,000 1.6 million

years ago) terraces are located within the coastal lowlands.

Dune fields are often associated with the terrace deposits. The

terrace deposits were developed on sediments of the Peace River

Formation in southern Hillsborough County, while in the northern

part of the county, the terraces were developed on a clayey resi-

duum of the Hawthorn Group or locally directly on limestone of

the Tampa Member of the Arcadia Formation.

The coastal lowlands, in southern Hillsborough County are

fairly well-drained by the Alafia and Little Manatee rivers and

their tributaries. Numerous lakes and swamps are present in the

less well-drained central-western portion of the county. A large

portion of northwestern Hillsborough County is riddled with






sinkholes due to the absence or thinning of the clayey residuum

of the Hawthorn Group. This area is low, poorly drained and

swampy. Many of the sinkhole lakes are in direct hydrologic con-

tact with the Tampa Limestone, with the consequence that water

levels fluctuate in response to the potentiometric surface of the

Floridan Aquifer.



Stratigraphy

Oligocene Series

Suwannee Limestone

The Suwannee Limestone occurs in the subsurface throughout

Hillsborough County and is the oldest geologic formation which

is exposed at the surface in the county. The Suwannee is found

near the ground surface in the northeastern part of the county

and is exposed in the Hillsborough River bed. In all other parts

of the county, the Suwannee is overlain by the Tampa Member of

the Arcadia Formation.

Lithologically, the Suwannee Limestone can be divided into

three units in Hillsborough County. The lowermost unit is a

yellowish-grey microcrystalline (less than 1/16mm) limestone

which contains minor amounts of peat, pyrite and clay. The

limestone is chalky and has low intergranular porosity.

Microfossils and macrofossil fragments are fairly common (Wright

and MacGill, 1974).

The middle unit is a cream to yellow, skeletal limestone,

composed almost entirely of medium (1/4 1/2mm) to coarse (1/2 -






1.0 mm) sized skeletal fragments. This unit is highly

recrystallized and exhibits good intergranular and vugular poro-

sity. Foraminifera and mollusc fragments are the primary fossils

(Wright and MacGill, 1974).

The uppermost unit of the Suwannee Limestone, as described

by Wright and MacGill (1974) is a pale yellow, finely crystalline

limestone which contains minor amounts of fine (1/8 1/4mm)

quartz sand. The carbonate grains range from fine (1/8 1/4mm)

to coarse (1/2 Imm) in size and consist primarily of foramini-

fera and mollusc fragments. Portions of the upper unit are

recrystallized, but more commonly the unit is chalky and has low

to moderate intergranular and moldic porosity.

The Suwannee dips to the south and southwest and thickens to

the southwest. The thickness of the Suwannee, in the county,

ranges from just under~100 feert-to-more than 300 feet. The top

of the Suwannee Limestone is encountered at about 50 feet above

mean sea level in northeastern Hillsborough County and dips to

about 300 feet below mean sea level at the southern border.



Miocene Series

Hawthorn Group

Scott (1984, personal communication, manuscript in

preparation) intends to raise the Hawthorn from Formation status

to Group status. The Hawthorn Group will include those sediments

which in the past have been -ineluded-in- the Tampa, Hawthorn and

Bone Valley formations.





Arcadia Formation

The Arcadia Formation (Scott, 1984, personal communication)

consists of, in ascending order, the Nocatee Member," the Tampa

Member and an unnamed upper member.

The Nocatee Member consists of the "lower Tampa" or "Tampa

sand and clay unit" of Wilson (197'7'). The updip limits of the

Nocatee are not well-defined at this time, however, the unit

extends into southern and eastern most Hillsborough County where

it is believed to be present as a thin (several feet) clay layer

often described in the past at the base of the Tampa Limestone

(Scott, 1984, personal communication).

The Tampa Member overlies the Nocatee (where it is present) o

the Suwannee Limestone and is lithologically similar to the type

Tampa Formation of King and Wright (1979) but has a slightly

greater phosphate dorntent.Ll-3 percent) and greater areal limits

(Scott, 1984, personal communication). The Tampa Member is a

white to tan-colored, quartz sandy limestone with a carbonate mud

matrix. Varying amounts of clay are usually disseminated

throughout the rock (King and Wright, 197'97 Scott, 1984, personal

communication). Some beds within the Tampa Member contain more

than 50 percent quartz sand. Dolomite is relatively uncommon

within the Tampa Member, and the upper beds are locally sili-

cified (King and Wright, 197'9 Scott, 1984, personal communication;

The lower boundary of the Tampa Member is gradational with

the top of the under-lyi-ng Suwannee Limestone. King (1979)

arbitrarily set the boundary for the Tampa Formation at the point






sinkholes due to the absence or thinning of the clayey residuum

of the Hawthorn Group. This area is low, poorly drained and

swampy. Many of the sinkhole lakes are in direct hydrologic con-

tact with the Tampa Limestone, with the consequence that water

levels fluctuate in response to the potentiometric surface of the

Floridan Aquifer.



Stratigraphy

Oligocene Series

Suwannee Limestone

The Suwannee Limestone occurs in the subsurface throughout

Hillsborough County and is the oldest geologic formation which

is exposed at the surface in the county. The Suwannee is found

near the ground surface in the northeastern part of the county

and is exposed in the Hillsborough River bed. In all other parts

of the county, the Suwannee is overlain by the Tampa Member of

the Arcadia Formation.

Lithologically, the Suwannee Limestone can be divided into

three units in Hillsborough County. The lowermost unit is a

yellowish-grey microcrystalline (less than 1/16mm) limestone

which contains minor amounts of peat, pyrite and clay. The

limestone is chalky and has low intergranular porosity.

Microfossils and macrofossil fragments are fairly common (Wright

and MacGill, 1974).

The middle unit is a cream to yellow, skeletal limestone,

composed almost entirely of medium (1/4 1/2mm) to coarse (1/2 -






where quartz sand content decreased to less than 5 percent of the

rock volume. 'Scott (1984, personal communication) has maintained

this criteria for the Tampa Member.

The contact at the upper boundary of the Tampa Member is

gradational where the upper member of the Arcadia Formation is

present. The contact is sharp in the most updip areas of the

*Tampa Member where undifferentiated sands immediately overlie the

Tampa (Scott, 1984, personal communication).

The Tampa Member is present in the subsurface over most of

the county and is exposed in many areas, especially within the

Hillsborough River Valley. The Tampa has been removed by erosion

in a band along the eastern part of northernmost Hillsborough

County. In this area, the Suwannee Limestone is the first for-

mation encountered beneath the surficial sands (Wright and

MacGill, 1974).

The Tampa dips generally to the southwest and thickens in

the downdip direction. The top of the Tampa Member is encoun-

tered at just above mean sea level in northern Hillsborough

County to approximately 260 feet below mean sea level in the

southwestern corner of the county (King, 1979).

The uppermost (unnamed) member of the Arcadia Formation

includes those sediments which in the past have been referred to

as the "Hawthorn carbonate unit" (Scott, 1984, personal

communication). Lithologically, these sediments consist of white

to yellowish-grey, quartz sandy, phosphatic, sometimes clayey,

dolomites and limestones (uncommon). Occasional beds of car-





bonate rich quartz sand and thin clay beds are present.

Phosphate content averages 7-8 percent but can vary from just.a

trace to 30 percent (Scott, 1984, personal communication).

In portions of northwest Hillsborough County and the

Hillsborough River Valley, limestone of the Tampa Member of the

Arcadia Formation are overlain by irregular thicknesses of sandy

calcareous clays. These clays are presently considered to be

residual sediments derived from weathering of the Hawthorn Group.

In the past, these sediments have been assigned to the Tampa,

Hawthorn, Bone Valley, Alachua and Pleistocene by various

authors.

Lithologically, these residual sediments consist of illltes

or mixed layer clays of illite (predominant) and montmorillonite

which contain variable amounts of quartz sand, organic material

and calcium carbonate. Calcium carbonate generally increases

downward (Wright and MacGill, 1974).



Peace River Formation



The Peace River Formation proposed by Scott (1984, personal

communication) includes two members: a downdip, unnamed member

and the updip Bone Valley Member (formerly the Bone Valley

Formation). Lithologically, the unnamed member consists of

interbedded sands, clays and dolomite with variable phosphate

content which, in the past, have been described as "upper

Hawthorn plastics."






In many parts of Hillsborough County, the Peace River For-

mation is difficult to differentiate from the uppermost Arcadia

due to the gradational nature of the contact and the northward

thinning of the Peace River Formation. Both the upper member of

the Arcadia Formation and the Peace River Formation pinch out in

northern Hillsborough County; however, the Peace River pinches

out farther to the south than the upper member of the Arcadia

Formation.

The Bone Valley Member consists of a series of sands and

clays which contain abundant quantities of phosphorite sand and

gravel. Cathcart (1963) divided the Bone Valley Formation into a

lower phosphorite unit and an upper unit of sandy clay.

The lower unit is a poorly sorted, highly phosphatic, quartz

sand or clayey sand. Both the quartz sand and phosphorite range

__in size from fine to coarse (1/16 mm 1.0 mm) (Gurr, 1977).

Pebble-size phosphate beds are common (Bernardi and Hall, 1980).

Phosphorite particles are generally rounded, well-polished

(except when leached) and of variable color, generally brown,

tan, amber, grey and black (Bernardi and Hall, 1980).

The upper unit consists of clayey sand which is signifi-

cantly less phosphatic and more clayey than the lower unit.

Sediments of the upper Bone Valley are difficult to differentiate

from the surface sands in the area (Wright and MacGill, 1974).

Bone Valley sediments are present only in the eastern part

-..-of.Hillsborough County. Bone Valley deposition was restricted to

the north by the presence of the Hillsborough High and to the





west by the ancestral Valrico Ridge (Bernardi and Hall, 1980).

Bone Valley sediments thin in all directions from a center of

deposition located in the Bartow-Mulberry area of Polk County

(Bernardi and Hall, 1980).



Pleistocene Series

Pleistocene shell deposits are located in the southwestern

portion of the county in the vicinity of the mouth of the Little

Manatee River. The shell deposits are overlain by thin surface

sands (maximum of 5 feet) and are found at elevation less than 25

feet. The lithology of the deposit is quite variable, ranging

from poorly indurated sand, shell and clay beds to lithified

coquina (Knapp, 1980). The thickness of the shelly deposit is

variable but generally increases toward Tampa Bay (Wright and

MacGill, 1974).

Pleistocene terrace sands, deposited during higher sea level

stands, blanket most of Hillsborough County. These sands are

very fine to medium-grained (1/16mm 1/2mm) quartz sands with a

minor amount of heavy minerals. Generally, the sands are clean

and white in color, however, locally they may contain some organic

matter and may be iron stained. Thickness of the terrace sands

ranges from a few inches to more than 50 feet in the Plant City

area (Wright and MacGill, 1974).

The Pleistocene terrace sands overlie the clayey residuum of

the Hawthorn Group in the northern part of the county. In the

southwestern portion of the county, a thin veneer of Pleistocene





sand overlies the Pleistocene shell deposits. In the remainder

of the county, the terrace sands overlie the sediments of the

Peace River Formation.



Holocene Series


Holocene sediments within the county consist of fluvial,

lacustrine, mangrove and swamp deposits. Lakes are most preva-

lent in northwest Hillsborough County. Lacustrine deposits con-

sist of sand, silt and clay washed into lakes by storm water

runoff, as well as organic material derived from the decay of

aquatic plants within the lakes.

Fluvial deposits consist of sand, silt, clay and organic

material deposited in the stream beds and flood plains of rivers

and streams. The majority of such deposits occur along the

Hillsborough, Alafia and Little Manatee rivers and their tribu-

taries.

Mangroves trap sediment by reducing wave and current energy

to the point where fine-grained sediments suspended in the water

column can settle out. Swamp and bay head sediments consist of

variable amounts of organic matter and sand, silt and clay. If

plastic sediment influx is small, the organic sedimentation may

result in predominantly organic deposits.



Industrial Minerals


Phosphate, uranium, portland cement, peat, shell and

unclassified sand are presently being produced in Hillsborough

County.






Phosphate

Phosphate rock is a mineral commodity of great importance to

Hillsborough County. Phosphatic sediments are common throughout

the county, however, the deposits of economic importance are

located in eastern Hillsborough County where several companies

are engaged in mining. The majority of the present production

from the Central Florida Phosphate District, however, is from

western Polk County. In 1981, Florida produced 83 percent of the

total U. S. 'hosphate production (Stowasser, 1982), essentially

all of which w a shipped through the Port of Tampa either as raw

phosphate rock o as phosphate products. In 1979, this accounted

for 93 percent of 11 exports from the port (Boyle and Hendry,

1981).



Uranium

Uranium is a by-product resource which can be recovered from

the phosphoric acid produced by the acidulation of phosphate

rock. The phosphate deposits in the Central Florida Phosphate

District contain an average of .015 percent U308 (Sweeney and

Windham, 1979). With present technology, approximately one pound

of U308 is recoverable from a ton of P205 from the central

Florida phosphates. The 1980 capacity was projected at more than






2100 short tons, an amount which would provide approximately 15

percent of U.S. requirements (Sweeney and Windham, 1979). A

significant amount of this resource will be recovered from faci-

lities in Hillsborough County.



Portland Cement



Portland cement, although not strictly a mineral, is con-

sidered as a mineral resource. Cement is composed of limestone

or lime, plus minor amounts of silica, alumina and iron. The

final composition is determined by the product specifications but

generally ranges from Ca3Sio5 to Ca4Al2Fe2012 (Lefond, 1975). If

the minor constituents needed are not present in the limestone,

they are added by introducing materials which contain the desired

components. Silica sand, staurolite (iron and alumina) and clay

(silica, alumina and iron) are commonly added. Fly ash and slag

are man-made substances which may be utilized for this purpose.

The limestone and clay needed by the one plant in Hillsborough

County has been obtained in the past from outside the county.



Limestone and Dolomite



Limestone resources are limited in Hillsborough County.

Although extensive limestone deposits are present, the impure

nature of the limestone, coupled with excessive overburden

thickness, prevent economic utilization throughout much of the





county (Wright, 1974). Areas in northeast Hillsborough County

may present viable future mining options (Schmidt, et al, 1979).


Peat



Several peat mining operations are active in the Mango-

Seffner area of Hillsborough County. The majority of this pro-

duct is utilized to improve soil conditions and for nursery and

potting soils.



Shell


Shell is or has been produced from several areas in and

around Tampa Bay. The Pleistocene shell beds provide good road

metal and are extensively used for that purpose (Wright, 1974).



Sand



Sand pits for fill dirt are common throughout Hillsborough

County, however, most area sands are too fine-grained for many

construction purposes. The majority of the high quality

construction sand needed in the county is shipped from the Lake

Wales Ridge area of Polk County.

Glass sands (usually 99 percent pure SiO2) were mined from

the Plant City area of Hillsborough County in recent years. This

deposit was of sufficient quality that beneficiation was not







required. Deposits. similar to, the Plant City deposit are present

in the region (Wright, 1974) but further exploration is

necessary.



Clay

Clay deposits and clayey sands are abundant throughout the

county. The majority of these clays, however, are of a noncommer-

cial nature.





sand overlies the Pleistocene shell deposits. In the remainder

of the county, the terrace sands overlie the sediments of the

Peace River Formation.



Holocene Series


Holocene sediments within the county consist of fluvial,

lacustrine, mangrove and swamp deposits. Lakes are most preva-

lent in northwest Hillsborough County. Lacustrine deposits con-

sist of sand, silt and clay washed into lakes by storm water

runoff, as well as organic material derived from the decay of

aquatic plants within the lakes.

Fluvial deposits consist of sand, silt, clay and organic

material deposited in the stream beds and flood plains of rivers

and streams. The majority of such deposits occur along the

Hillsborough, Alafia and Little Manatee rivers and their tribu-

taries.

Mangroves trap sediment by reducing wave and current energy

to the point where fine-grained sediments suspended in the water

column can settle out. Swamp and bay head sediments consist of

variable amounts of organic matter and sand, silt and clay. If

plastic sediment influx is small, the organic sedimentation may

result in predominantly organic deposits.



Industrial Minerals


Phosphate, uranium, portland cement, peat, shell and

unclassified sand are presently being produced in Hillsborough

County.




Bernardi, J. P. and R. B. Hall, 1980, Comparative Analysis of
the Central Florida Phosphate OistriCt tb its Southern
Extension, Mining Engineering, August, 1980, pp. 1256-1261.

Boyle, J. R. and C. W. Hendry, Jr., 1981, The Mineral
Industry of Florida 1977, 1978, 1979, Florida Bureau of
Geology Information Circular 94, p. 2.

Cathcart, J.. B., 1963, Economic Geology of the Plant City
Quadrangle, Florida, U. S. Geological Survey Bulletin 1142D,
P.
Gurr, T. M., 1977, The Structure, Stratigraphy and Economic
Geology of the Central Florida Phosphate District, in
Environment of the Central Florida Phosphate District,
Southeastern Geological Society Publication 19, pp. 36-48.

King, K. C., 1979, Tampa Formation of Peninsular Florida a Formal
Definition, Unpublished M. S. Thesis, Florida State
University, Tallahassee, FL.

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.

Knapp, M. S., 1980, Environmental Geology Series Tampa Sheet,
Florida Bureau of Geology Map Series 97.

Lefond, S. J., 1975, Industrial Minerals and Rocks, 4th ed.,
Copyright by American Institute of Mining, Metellurgical and
Petroleum Engineers, Inc.

Schmidt, W., et al., 1979, The Limestone, Dolomite and Coquina
Resources of Florida, Florida Bureau of Geology Report of
Investigation 88, 64 p.

Stowasser, W. F., 1982, Phosphate Rock in Mineral Commodity
Summaries, 1982, U. S. Bureau of Mines, .pp. 112-113.

Sweeney, J. W., and S. R. Windham, 1979, Florida: The New
Uranium Producer, Florida Bureau of Geology Special
Publication 22, 13 p.

Wilson, W. E., 1977, Groundwater Resources of DeSoto and Hardee
Counties, Florida, Florida Bureau of Geology, Report of
Investigation 83, 102 p.

White, W. A., 1958, Some Geomorphic Features of Central Peninsular
Florida, Florida Geological Survey Bulletin 41, 92 p.

1970, Geomorphology of the Florida Peninsula,
Florida Bureau of Geology Bulletin 51, 164 p.






Wright, A. P., 1974, Environmental Geology and Hydrology Tampa
Area, Florida, Florida Bureau of Geology Special Publication
19- 94 p.

and P. MacGill, 1974, Geology of Hillsborough
County, Florida Bureau of Geology, unpublished manuscript.


17





























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NORTH SOUTH
SOUTH
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