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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 27


The Geology of Hamilton County, Florida

by

Frank R. Rupert


Florida Geological Survey
Tallahassee, Florida
1989













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




a
Open File Report 27

The Geology of Hamilton County, Florida

by

Frank R. Rupert


Florida Geological Survey
Tallahassee, Florida
1989


Florida Geological Survey
Library
903 West Tennessee Street
Tallahassee, Florida 32304







GEOMORPHOLOGY
Hamilton County is situated in the Northern Zone of
White(1970). In Hamilton County, the Northern Zone is divid-
ed into two major geomorp*lc province, the Northern High-
lands and the topographically lower Gulf Coastal Lowlands.
These adjacentprovnces are separated by a persistent topo-
graphic break called the Cody Scuap (see Figure 1). The Cody
Scarp is believed to be a relict marine escarpment, originally
formed by high-standing Pleistocene seas. The surface eleva-
tion of the toe of the Cody Scarp varies between about 75 and
100 feet above MSL (mean sealevel) in Hamilton County. In
some areas, dissolution of the underlying limestone has low-
ered the original escarpment elevation.
The Norther Highlandsprovince spans north Florida from
the astern edge of Bradford County, Florida, westward into
Alabama. The topographically high clayey sand hills compris-
ing this zone ae thought to be dissected remnants of a much
more extensive highland plain which covered much of the Gulf
Coastal Plain (White, 1970). Within Hamilton County the
Northern Highlands occupy most of the eastern and northern
portions of the county. The topography is comprised of gently
rolling hills and large, flat swampy area. Near surface sedi-
ments are predominantly sands and clayy sands. Dissolution
of the underlying limestones has modified theiterran in many
areas of the county, producing numerous depressions and low
. wmpy re called "bays'. Many of the large bays remain
wet during the rainy season. Land surface elevations vary from
approximately 70 feet MSL at the south edge of the county
to about 160 feet MSL at the northern and northwestern edges
of the county.
The Gulf Coastal Lowlands comprise an area of southwest-
em Hamilton County, south of the Cody Scarp (se Figure 1).
These topographic lowlands extend from the too of the Cody
Scarp southward to the Gulf of Mexico. Land surface eleva.
tion range between SO and 100 feet MSL. Much of the gener-


EXPLANATION Ne
-- orowr-
/' E3TOWN
*WELL LOCATION
d CROSS SECTION LOCATION
0 INT~$STATE HIGHWAY
- ----- STATELCOUNTY ROAD
.U.S. HIGHWAY


ally flat, sandy terrain of the lowlands has been modified by
karst depressions.
Hamilton County is bounded on the west by the Withlacoo-
chee River, and on the southern and eastern edges by the
Suwannee River. The Alapaha River bisects western Hamilton
County, flowing southwestward, and forms a tributary to the
Suwannee River. The valleys of these rivers comprise a
geomorphic subzone of the Gulf Coastal Lowlands named the
River Valley Lowlands (Ceryak et al. 1983). These valleys are
typically incised, and are topographically lower than the sur-
rounding terrain. Elevations of the valley floors range from 50
feet MSL in the Suwannee River Valley to nearly 80 feet MSL
along the northern stretches of the Alapaha and Withlacoochee
River valleys. In some portions of these valleys, older geologic
formations crop out along the stream banks. The valley floor
sediments are comprised principally of.Holocene age alluvial
clay and sand.
Large surface water features are rare in Hamilton County.
Lake Octahatchee, situated in the extreme northwestern corer
of Hamilton County, is the county's largest lake. A series of
small lakes, many formed in sinkhole collapse depressions, are
scattered throughout the county.
Hamilton County has several major springs, most situated
adjacent to the large rivers. Morpns Spring, Adams Spring,
Alapaha Rise and Holton Spring are located in the Gulf Coast-
al Lowlands and generally display variable flow rates, depend-
ent upon local precipitation. Bluff Cemetery Spring is situated
on the Alapaha River in northern Hamilton County, and
Louisa Spring, Wesson Iron Spring, and White Springs, once
the site of a sulfur spring health resort, are all located near the
Suwannee River in southeastern Hamilton County. Most of
these springs flow from conduits in the underlying Suwannee
Limestone and Ocala Group sediments.





"~- -- --
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W-786 ,W-70 53







A'_ 0
_653
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GEOMORPHIC ZONES
NORTHERN HIGHLANDS ,

GULF COASTAL LOWLANDS
Figure 1: Geomorphlo and cross section location map.


'lot:----








GEOLOGY

Hamilton County is underlain by hundreds of feet of marine
sands clay, limestones and dolomites (Ceryak et al., 1983).
The oldest rock penetrated by water wells is limestone of the
Middle Eocene ap (42 to 49 million years before present)
Avon Park Formation. Undifferentiated surficial sands and
days of Pleistoene to Holocene age (1.8 million years old and
younger) are the youngest sediments present. The Avon Park
Pormation and the younger overlying limestone units ar
impotent freshwater aquifer, and the discussion of the geolo-
g of Hamilton County will be confined to these Eocene age
and younger sediments. Figure shows the geologic cross
section locations, and figure 2 and 3 are cross sections illus-
tring the strtigrapy of Hamilton County.
Beees Serse
tArn a-Im
Avew Park Fonmatioe

The Avon Park Formation (Miller, 1986) is typically a
deme, tan to dark brown, porous dolomite, frequently inter-
bedded with uan, ray, or emam-colored limestone and dolom-
itic limestone of varying hardness (Ceryak et at., 1983).
Poraminife ae the dominant foeal present, although dolom-
itiation has destroyed or altered many of the contained fossils.
The Avon Park Formation is a component of the Ploridan
aqulhr sysam and undertis Hamilton County at depth rnoa
ig from 400 to 450 feet below land surface (Florida eologcal
Survey In-houe well data).
Orab Group

Upper Eoene (38-42 million years old) marine limestone
of the Ocala Group (Purl. 1957) unconformably overlie the
Avon Park Formation under all of Hamilton County (Ceryak et
aL, 1983). The Ocla Group is comprised of three formntioln;
in ceding order, thee an the Inglis Formation, the Wills-
ton Pomation, and the Crytal River Formation. These form-
tions are differentiated on the bais of Ilthology and fossil
content. Typically, the llthology of the Ocala Group rades
upward from alternatig soft and hard, white to tan foslifer-
ou limestone and dolomitic limestone of the Inglia and lower
Williston Formations into white to pale orange, abundantly
fosillferous limestone of the upper Williston and Crystal
River Formations. Foraminlfera, mollusks, bryozoans, and
achinoids an the dominant foil types occurring in the Ocala
Group sediments. Thickness of the Ocala Group sediments
under Hamilton County average about 200 to 300 feet Depth
to the top of the Ocal Group is variable, ranging from about
100 feet to nearly 70 feet. The porous and cavernous nature
of the Ocala Group limestones make them important fresh-
vwter-bearing units of the Floridan aquifer system. Many
drinking water wall in Hamilton County withdraw water from
the Crystal River and Williston Fomations.

eeSum Srok
Sewmasa Lbau

The Suwannee Umeston (Cooke and Manield,1936) is a
Lower Oligocene (33 to 38 million years old) pale ornnp to
white calcrenitic marine limestone overlyng the Ocals Group
in most of Hamilton County. It typically contains abundant
fossils, including foraminifern, mollusks, and echinoids, and
nMy conair interbedded chert and dolomite beds. Depth to
the Suwanne Limestone ranges from about 20 feet to nearly
200 feet below land surface in Hamilton County. Thickness
varies rom about 10 feet to 130 feet. It generally thins to the
east and southeast, ultimately pinching out in Columbia and
Baker Counties to the east. Except where the overlying St.
Mark Formation is present, the Suwannee Umetone is the
uppermost unit of ite Ploridan aquifer system in Hamilton
County.


Miocene Series
SL Marks Formation

Scattered erosional remnants of the Lower Miocene (20 to
25 million years old) St. Marks Formation overlie the Suwan-
nee limestone in western Hamilton County. The St. Marks is
a pale orange to white, sandy, silty, calcilutitic marine lime.
stone, occasionally containing mollusks and forminifera. It is
known from only a few wells in and west of Jasper and along
portions of the Alapaha River in Hamilton County. It generally
occurs In discontinuous units leu than 40 feet thick. Where
present, the St. Marks Formation is the uppermost unit of the
Floridan aquifer system.

Hawthor Group

The Hawthorn Group (Scott, 1988) is comprised of a series
of Lower and Middle Miocene (10 to 25 million years old)
pnerally phosphate clays, sands, limestone and dolomites.
These sediments unconformably overlie the St. Marks Forna-
tion, where present, the Suwannee Limestone, or the Ocala
Group. Scott (1988) recognized four formations of the Haw-
thorn Group in Hamilton County. In ascending order, these
ar the Penny Parms Pormation, the Marks Head Formation,
the Coouwatchee Formation, and the Statenville Formation.
The predominant lithologies in the different formations are
light gay to olive gray to yellowish gay interbedded sands,
days, and dolostones, containing varying quantities of phos-
phate grains. For the purposes of the present report, these
formations are collectively included in the Hawthorn Group
sediments, as shown on Figures 2 and 3. Hawthorn Group
sediments are exposed along the banks of the larger streams
and rivers bounding the county, particularly the Suwannee
River. Throughout the county, the top of the Hawthorn Group
is usually les than 50 feet below land surface. Thickness of the
Hawthorn Group varks locally between approximately 30 feet
south of the Cody Scarp and 150 feet in the northern and
eastern portions of the county.
The clay of the Hawthorn Group comprise an intermediate
confining unit which overlies the Floridan aquifer system. At
the same time, the carbonate units within the Hawthor Group
may seem locally u an intermediate aquifer system.

lelstoene and Holoene Series

Overlying the Hawthorn Group sediments are a series of
Pleistocene and Hotocene age (1.8 million years old and young-
er) undifferentiated quartz sands and clayey quartz sands.
Most of these deposits represent relict Pleistocene marine
sands and Hoocene eolian and alluvial deposits. These undif-
ferentated sands are generally less than 50 feet thick in Hamil.
ton County..

GROUND WATER

Ground water is water that fills the pore space in subsur-
face rocks and sediments. This water is derived principally
from precipitation within Hamilton County and adjoining
counties. The bulk of Hamilton County's consumptive water is
withdrawn from ground water aquifers. Three main aquifers
are present under Hamilton County; in order of increasing
depth, these are the surfcial aquifer system, the intermediate
aquifer system, and the Floridan aquifer system.

The srfkical aquifer system

The surficial aquifer system is the uppermost freshwater
aquifer in Hamilton County. This non-artesian aquifer is
contained within the undifferentiated Pleistocene and Holo-
cene snds In eastern and northwestern Hamilton County. The
aal extent of the surfiial aquifer system approximately core
spends to the occurrence of relict Okeeenokee Terrace sands,







generally situated between 100 and 170 feet MSL (Ceoyak et al.,
1963). The surfcial 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 topogra.
phy of the land surface, Recharge to this aquifer is largely
through rainfall percolating through the loose surficial sedi-
ments, and to a lesser extent, by upward seepage from the


underlying intermediate aquifer system. Water naturally dis-
charges from the aquifer by evaporation, transpiration, spring
flow, lateral discharge along the Cody Scarp and into topo-
graphically low areas, and by downward seepage into the
intermediate aquifer system (Ceryak et al., 1983).


Figure 2: Cross section A A'


A

5-0 4


1 4HAWT



-SO
Mean,


-as a


-so- MILBS


-7S -2s1 KILOMnTERS


OCALA


-200
- .oo --se

t-,so AVC
VUSTIAL IXAO0GATION I*o TIME TUa KsCAL
WSLL NUMBERS ARI FLORIOA OsLCAI UVY s ACCSSVO ON HUMERUS.


UNDIFFERENTIATED
SAND AND CLAY -


)N PARK FORMATION
T. .,,as


0oQ O0*7O1


Figure 3: Cross section B B'


B

I -
t: F I

9==4RA


*" I1


-0O 1'
meaner


L-,00
VaRTIGA.L INAOOEATIO 1*0 TIMes TR* sALS
ILL. NUMsaEI AI rOAIInOn OIOOLOIOAL. suNVV alssION NUMseIIII.


MILES
012345
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KILOMUTIts
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Thle iesmedlte aquifer system

The intermediate aquifer system underlies the surficial
aquifer system in Hamilton County, and is largely contained
within the sand and carbonate units of the Miocene age
Hawthorn Group sediments. Permeable beds within the in-
termediate aquifer system vry considerably In thickness over
the real extet of the aquifer. When clayey confining beds are
abeant in the upper Hawthorn Group sediments, the interme-
diate aqifer system may be recharged by downward seepage
from the surficial aquifer system. Likewi, if clay beds or the
typical dolomitized limestone beds in the lower Hawthorn
Group sediment section ae absent, the intermediate aquifer
system may be in hydrologic continuity with the underlying
Florld aquifer system. Lateral diacharp from the intnnerdk
te aquifer sytem may occur along the Cody Scarp or t arma
where sreams have cut down into the sediments comprising
the unit.
in pnral, the thickness of the intermediate aquifer system
corresponds to the thickness of the Hawthorn Group sedi-
meats, ranging from approximately 30 to 150 feet. The in-
termediate aquifer system is no used extensively for consump-
ive water in Hamilton County. Most wells draw from the
deeper Suwannee Limestone sad Ocala Group sediments of
the Ploridan aquifer system (Ceyak et al., 1963).

F119r a9 ue" suSys!

The Floridan aquifer system is comprised of hundreds of
feet of Boen through Miocene a marine limestone. includ-
ig the Avon Park Formation, the Ocala Group, the Suwannee
iUmetone, and when ptmest, the St Marks Formation. It is
the principal source of drinking water in Hamilton County.
The Floridan aquifer system occurs u an artesian aquifer in
the portion of Hamilton County corresponding to the Northern
Highlands gomorphie zone. In the Gulf Coastal Lowlands,
whee the Hawthorn Group sdiments are absent or less than
about 50 feet thick, the Florida is generally under non-arte-
san conditions (Ceyak at al, 193). Stwart(1960) showed the
Gulf Coasul Lowlands to be a zcharp area for the Florida
aquifer system. Depth to the Floridan aquifer system in
Hamilton County nmaa from about 20 feet in southern Hamil-
ton County to about 250 feet below land surface in the north-
era penrt of the county. Total thickness of the potable water
within the Floridan aquifer system is estimated to be about
1000 feew (Cerya at 1963).
The Floridan aquifer system is recharged in part from
sepap from the oring intermediate aquifer system, locally
though slan and limestone exposes along rive and largely
fmon hyarmogi continuity withthe principal aquifer system to
the north in Geoga Water leaves the Florida aquifer system
through natural movement dow-gradient and subsequent
discharge from springs and through seeps along the River
Valley Lowlands.
MINIMAL RESOURCES

The principal mineral commodities occurring in Hamilton
County ae sand, day, imestone, and phosphate. The follow-
iag discumion summaries the current mining status and poten-
tial for each commodity in the county.

Sod

A number of shallow private pits in Hamilton County are
worked for local fill send and aggregate. Pleistocene send
deposits occur as thin venees over Hawthorn Group sediments
in much of the region. Since thee is insufficient local demand
for sand products, the potential for commercial mining is low at
present.


Localized deposits of clay and sandy clay are associated with
the Pleistocene and Holocene marine terrace deposits and
alluvium and in the Hawthorn Group sediments. Most of these
deposits are contained in and interbedded with other sedi-
ments, and as a result are relatively impure. Reserve estimates
of the clay deposits in Hamilton County have not been made,
and future exploitation will depend largely on more extensive
exploration and testing as well as market demand.

Limestoe

Limestone deposits occur at or near the surface in south-
western Hamilton County in the Gulf Coastal Lowlands and
adjacent to the Suwannee River. Most near surface limestone
is associated with the Suwannee Limestone and Ocala Group.
These deposits are not mined, and are largely untested as to
purity and commercial potential. Future exploitation will be
largely dependent upon local demand for limestone products
such as medbase.

Phosphate

Phosphate is currently mined in southeastern Hamilton
County. Occidental Chemical Corporation operates in two
mining areas in Hamilton County, the Swift Creek Mine north-
west of White Springs and the Suwannee River Mine, northeast
of White Springs.
The phosphate oe is contained in the Miocene age Haw-
thorn Group sediments, and is extracted with the sand and
clayey sand matrix by large draglines. Beneficiation of the
phosphate is accomplished through a flotation process, which
separates the quart matrix sands and clays from the phosphate
ore. The uses for phosphate are primarily as agricultural ferti-
lizers
Potential for this resource remains high in southeastern
Hamilton County. Continued mining of phosphate will be
dependent on market demand worldwide.

REFERENCES

Ceryak, I, Knapp, M., and Burnson, T., 1983, The geolovy and
watresources of the uer Suwannee Rive basin.
Florida:gFlorida Bureau of Geology Report of Investigation
o. 97,166p

Cook C., and Mansfield, W, 1936, Suwannee Limestone of
fida (abstract): Geological Society of America Proceed
inp, 1935, p. 71-72.

Miller, J., 196, Hvdronolori framework of the Floridan
auifaer stem In Florida and In arts of Georsia. Alabama.
nSouth Cmrlin: U.S. Geological Survey Professional
Paper 1403-B, p. 25- 27.
Purl, H, 1957, Stratimaohv and donation of the Ocala
Gm:Flosrida Geological Survey Bulletin no. 38, 248 p.

Scott, T., 1968, The lithostratianhv of the Hawthorn Group
(Miocenel of Florida Florida Geological Survey Bulletin
no. 59, 148 p.

Stewart, J., 1960, Areas of natural recharge to the Ploridan
auifer in Florida: Florida Bureau of Geology Map Series
96.

White, W., 1970, The 7 eomornholonv of the Florida
weninful:Plorida Bureau of Geology Bulletin no. 51,164 p.










FLRD GEOLOSk ( IC SUfRiW


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Permanent Link: http://ufdc.ufl.edu/UF00001026/00001
 Material Information
Title: The geology of Hamilton County, Florida ( FGS: Open file report 27 )
Series Title: ( FGS: Open file report 27 )
Physical Description: 4 p. : ill., maps ; 28 cm.
Language: English
Creator: Rupert, Frank
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee Fla
 Subjects
Subjects / Keywords: Geology -- Florida -- Hamilton 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.
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
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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 27

The Geology of Hamilton County, Florida

by

Frank R. Rupert


Florida Geological Survey
Tallahassee, Florida
1989











GEOMORPHOLOGY


Hamilton County is situated in the Northern Zone of
White(1970). In Hamilton County, the Northern Zone is divid-
ed into two major geomorphic provinces, the Northern High-
lands and the topographically lower Gulf Coastal Lowlands.
These adjacent provinces are separated by a persistent topo-
graphic break called the Cody Scarp (see Figure 1). The Cody
Scarp is believed to be a relict marine escarpment, originally
formed by high-standing Pleistocene seas. The surface eleva-
tion of the toe of the Cody Scarp varies between about 75 and
100 feet above MSL (mean sea level) in Hamilton County. In
some areas, dissolution of the underlying limestones has low-
ered the original escarpment elevation.
The Northern Highlands province spans north Florida from
the eastern edge of Bradford County, Florida, westward into
Alabama. The topographically high clayey sand hills compris-
ing this zone are thought to be dissected remnants of a much
more extensive highland plain which covered much of the Gulf
Coastal Plain (White, 1970). Within Hamilton County the
Northern Highlands occupy most of the eastern and northern
portions of the county. The topography is comprised of gently
rolling hills and large, flat swampy areas. Near surface sedi-
ments are predominantly sands and clayey sands. Dissolution
of the underlying limestones has modified the terrain in many
areas of the county, producing numerous depressions and low
swampy areas called "bays". Many of these large bays remain
wet during the rainy season. Land surface elevations vary from
approximately 70 feet MSL at the southern edge of the county
to about 160 feet MSL at the northern and northwestern edges
of the county.
The Gulf Coastal Lowlands comprise an area of southwest-
ern Hamilton County, south of the Cody Scarp (see Figure 1).
These topographic lowlands extend from the toe of the Cody
Scarp southward to the Gulf of Mexico. Land surface eleva-
tions range between 50 and 100 feet MSL. Much of the gener-


ally flat, sandy terrain of the lowlands has been modified by
karst depressions.
Hamilton County is bounded on the west by the Withlacoo-
chee River, and on the southern and eastern edges by the
Suwannee River. The Alapaha River bisects western Hamilton
County, flowing southwestward, and forms a tributary to the
Suwannee River. The valleys of these rivers comprise a
geomorphic subzone of the Gulf Coastal Lowlands named the
River Valley Lowlands (Ceryak et al. 1983). These valleys are
typically incised, and are topographically lower than the sur-
rounding terrain. Elevations of the valley floors range from 50
feet MSL in the Suwannee River Valley to nearly 80 feet MSL
along the northern stretches of the Alapaha and Withlacoochee
River valleys. In some portions of these valleys, older geologic
formations crop out along the stream banks. The valley floor
sediments are comprised principally of Holocene age alluvial
clay and sand.
Large surface water features are rare in Hamilton County.
Lake Octahatchee, situated in the extreme northwestern corner
of Hamilton County, is the county's largest lake. A series of
small lakes, many formed in sinkhole collapse depressions, are
scattered throughout the county.
Hamilton County has several major springs, most situated
adjacent to the large rivers. Morgans Spring, Adams Spring,
Alapaha Rise and Holton Spring are located in the Gulf Coast-
al Lowlands and generally display variable flow rates, depend-
ent upon local precipitation. Bluff Cemetery Spring is situated
on the Alapaha River in northern Hamilton County, and
Louisa Spring, Wesson Iron Spring, and White Springs, once
the site of a sulfur spring health resort, are all located near the
Suwannee River in southeastern Hamilton County. Most of
these springs flow from conduits in the underlying Suwannee
Limestone and Ocala Group sediments.





-- -- -- -- -

f N

W-7826
W-7053
z
^A'




SW--6836



r,0


EXPLANATION N' ,
[ TOWN
SWELL LOCATION
CROSS SECTION LOCATION
INTERSTATE HIGHWAY
@STATE/COUNTY ROAD
&U.S. HIGHWAY


GEOMORPHIC ZONES

D NORTHERN HIGHLANDS

I] GULF COASTAL LOWLANDS


Figure 1: Geomorphic and cross section location map.


MILES
01234ER
KIOMETERS


FGS 010489











Miocene Series
St. Marks Formation


Hamilton County is underlain by hundreds of feet of marine
sands, clays, limestones and dolomites (Ceryak et al., 1983).
The oldest rock penetrated by water wells is limestone of the
Middle Eocene age (42 to 49 million years before present)
Avon Park Formation. Undifferentiated surficial sands and
clays of Pleistocene to Holocene age (1.8 million years old and
younger) are the youngest sediments present. The Avon Park
Formation and the younger overlying limestone units are
important freshwater aquifers, and the discussion of the geolo-
gy of Hamilton County will be confined to these Eocene age
and younger sediments. Figure 1 shows the geologic cross
section locations, and figures 2 and 3 are cross sections illus-
trating the stratigraphy of Hamilton County.

Eocene Series
Avon Park Formation

The Avon Park Formation (Miller, 1986) is typically a
dense, tan to dark brown, porous dolomite, frequently inter-
bedded with tan, gray, or cream-colored limestones and dolom-
itic limestones of varying hardness (Ceryak et al., 1983).
Foraminifera are the dominant fossils present, although dolom-
itization has destroyed or altered many of the contained fossils.
The Avon Park Formation is a component of the Floridan
aquifer system and underlies Hamilton County at depths rang-
ing from 400 to 450 feet below land surface (Florida Geological
Survey in-house well data).

Ocala Group

Upper Eocene (38-42 million years old) marine limestones
of the Ocala Group (Puri, 1957) unconformably overlie the
Avon Park Formation under all of Hamilton County (Ceryak et
al., 1983). The Ocala Group is comprised of three formations;
in ascending order, these are the Inglis Formation, the Willis-
ton Formation, and the Crystal River Formation. These forma-
tions are differentiated on the basis of lithology and fossil
content. Typically, the lithology of the Ocala Group grades
upward from alternating soft and hard, white to tan fossilifer-
ous limestone and dolomitic limestone of the Inglis and lower
Williston Formations into white to pale orange, abundantly
fossiliferous limestones of the upper Williston and Crystal
River Formations. Foraminifera, mollusks, bryozoans, and
echinoids are the dominant fossil types occurring in the Ocala
Group sediments. Thickness of the Ocala Group sediments
under Hamilton County averages about 200 to 300 feet. Depth
to the top of the Ocala Group is variable, ranging from about
100 feet to nearly 270 feet. The porous and cavernous nature
of the Ocala Group limestones make them important fresh-
water-bearing units of the Floridan aquifer system. Many
drinking water wells in Hamilton County withdraw water from
the Crystal River and Williston Formations.

Oligocene Series
Suwannee Limestone

The Suwannee Limestone (Cooke and Mansield,1936) is a
Lower Oligocene (33 to 38 million years old) pale orange to
white calcarenitic marine limestone overlying the Ocala Group
in most of Hamilton County. It typically contains abundant
fossils, including foraminifera, mollusks, and echinoids, and
may contain interbedded chert and dolomite beds. Depth to
the Suwannee Limestone ranges from about 20 feet to nearly
200 feet below land surface in Hamilton County. Thickness
varies from about 10 feet to 150 feet. It generally thins to the
east and southeast, ultimately pinching out in Columbia and
Baker Counties to the east. Except where the overlying St.
Marks Formation is present, the Suwannee Limestone is the
uppermost unit of the Floridan aquifer system in Hamilton
County.


Scattered erosional remnants of the Lower Miocene (20 to
25 million years old) St. Marks Formation overlie the Suwan-
nee Limestone in western Hamilton County. The St. Marks is
a pale orange to white, sandy, silty, calcilutitic marine lime-
stone, occasionally containing mollusks and foraminifera. It is
known from only a few wells in and west of Jasper and along
portions of the Alapaha River in Hamilton County. It generally
occurs in discontinuous units less than 40 feet thick. Where
present, the St. Marks Formation is the uppermost unit of the
Floridan aquifer system.

Hawthorn Group

The Hawthorn Group (Scott, 1988) is comprised of a series
of Lower and Middle Miocene (10 to 25 million years old)
generally phosphatic clays, sands, limestones and dolomites.
These sediments unconformably overlie the St. Marks Forma-
tion, where present, the Suwannee Limestone, or the Ocala
Group. Scott (1988) recognized four formations of the Haw-
thorn Group in Hamilton County. In ascending order, these
are the Penny Farms Formation, the Marks Head Formation,
the Coosawhatchee Formation, and the Statenville Formation.
The predominant lithologies in the different formations are
light gray to olive gray to yellowish gray interbedded sands,
clays, and dolostones, containing varying quantities of phos-
phate grains. For the purposes of the present report, these
formations are collectively included in the Hawthorn Group
sediments, as shown on Figures 2 and 3. Hawthorn Group
sediments are exposed along the banks of the larger streams
and rivers bounding the county, particularly the Suwannee
River. Throughout the county, the top of the Hawthorn Group
is usually less than 50 feet below land surface. Thickness of the
Hawthorn Group varies locally between approximately 30 feet
south of the Cody Scarp and 150 feet in the northern and
eastern portions of the county.
The clays of the Hawthorn Group comprise an intermediate
confining unit which overlies the Floridan aquifer system. At
the same time, the carbonate units within the Hawthorn Group
may serve locally as an intermediate aquifer system.

Pleistocene and Holocene Series

Overlying the Hawthorn Group sediments are a series of
Pleistocene and Holocene age (1.8 million years old and young-
er) undifferentiated quartz sands and clayey quartz sands.
Most of these deposits represent relict Pleistocene marine
sands and Holocene aeolian and alluvial deposits. These undif-
ferentiated sands are generally less than 50 feet thick in Hamil-
ton County..

GROUND WATER

Ground water is water that fills the pore spaces in subsur-
face rocks and sediments. This water is derived principally
from precipitation within Hamilton County and adjoining
counties. The bulk of Hamilton County's consumptive water is
withdrawn from ground water aquifers. Three main aquifers
are present under Hamilton County; in order of increasing
depth, these are the surficial aquifer system, the intermediate
aquifer system, and the Floridan aquifer system.

The surficial aquifer system

The surficial aquifer system is the uppermost freshwater
aquifer in Hamilton County. This non-artesian aquifer is
contained within the undifferentiated Pleistocene and Holo-
cene sands in eastern and northwestern Hamilton County. The
areal extent of the surficial aquifer system approximately corre-
sponds to the occurrence of relict Okeefenokee Terrace sands,


GEOLOGY













generally situated between 100 and 170 feet MSL (Ceryak et al.,
1983). 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 topogra-
phy of the land surface. Recharge to this aquifer is largely
through rainfall percolating through the loose surficial sedi-
ments, and to a lesser extent, by upward seepage from the


underlying intermediate aquifer system. Water naturally dis-
charges from the aquifer by evaporation, transpiration, spring
flow, lateral discharge along the Cody Scarp and into topo-
graphically low areas, and by downward seepage into the
intermediate aquifer system (Ceryak et al., 1983).


Figure 2: Cross section A A'


* A
!
Iu.
50-
-150

-100
25-

-50
Mean
-0 Sea
Level

-50

-25 --S
-100


--150
-50- MILES
0 1 2 3 4 5
S.-200 I '
0 2 4 6 8
-75- --250 KILOMETERS


-100 -,30


S-e


OCALA


AV(
--400
VERTICAL EXAGGERATION 160 TIMES TRUE SCALE
WELL NUMBERS ARE FLORIDA GEOLOGICAL SURVEY ACCESSION NUMBERS.


UNDIFFERENTIATED
SAND AND CLAY 7


ON PARK FORMATION


FGS 020489


Figure 3: Cross section B B'


-50
Mean
-0 Sea
Level

--50

--100

--150

--200


-75 -250

-300
VERTICAL EXAGGERATION 160 TIMES TRUE SCALE
WELL NUMBERS ARE FLORIDA GEOLOGICAL SURVEY ACCESSION NUMBERS.


FOS 030489











The intermediate aquifer system

The intermediate aquifer system underlies the surficial
aquifer system in Hamilton County, and is largely contained
within the sand and carbonate units of the Miocene age
Hawthorn Group sediments. Permeable beds within the in-
termediate aquifer system vary considerably in thickness over
the areal extent of the aquifer. When clayey confining beds are
absent in the upper Hawthorn Group sediments, the interme-
diate aquifer system may be recharged by downward seepage
from the surficial aquifer system. Likewise, if clay beds or the
typical dolomitized limestone beds in the lower Hawthorn
Group sediment section are absent, the intermediate aquifer
system may be in hydrologic continuity with the underlying
Floridan aquifer system. Lateral discharge from the intermedi-
ate aquifer system may occur along the Cody Scarp or in areas
where streams have cut down into the sediments comprising
the unit.
In general, the thickness of the intermediate aquifer system
corresponds to the thickness of the Hawthorn Group sedi-
ments, ranging from approximately 30 to 150 feet. The in-
termediate aquifer system is not used extensively for consump-
tive water in Hamilton County. Most wells draw from the
deeper Suwannee Limestone and Ocala Group sediments of
the Floridan aquifer system (Ceryak et al., 1983).

Floridan aquifer system

The Floridan aquifer system is comprised of hundreds of
feet of Eocene through Miocene age marine limestones, includ-
ing the Avon Park Formation the Ocala Group, the Suwannee
Limestone, and where present, the St. Marks Formation. It is
the principal source of drinking water in Hamilton County.
The Floridan aquifer system occurs as an artesian aquifer in
the portion of Hamilton County corresponding to the Northern
Highlands geomorphic zone. In the Gulf Coastal Lowlands,
where the Hawthorn Group sediments are absent or less than
about 50 feet thick, the Floridan is generally under non-arte-
sian conditions (Ceryak et al., 1983). Stewart(1980) showed the
Gulf Coastal Lowlands to be a recharge area for the Floridan
aquifer system. Depth to the Floridan aquifer system in
Hamilton County ranges from about 20 feet in southern Hamil-
ton County to about 250 feet below land surface in the north-
ern part of the county. Total thickness of the potable water
within the Floridan aquifer system is estimated to be about
1000 feet (Ceryak et al., 1983).
The Floridan aquifer system is recharged in part from
seepage from the overlying intermediate aquifer system, locally
through sinks and limestone exposures along rivers, and largely
from hydrologic continuity with the principal aquifer system to
the north in Georgia. Water leaves the Floridan aquifer system
through natural movement down-gradient and subsequent
discharge from springs and through seeps along the River
Valley Lowlands.

MINERAL RESOURCES

The principal mineral commodities occurring in Hamilton
County are sand, clay, limestone, and phosphate. The follow-
ing discussion summarizes the current mining status and poten-
tial for each commodity in the county.

Sand

A number of shallow private pits in Hamilton County are
worked for local fill sand and aggregate. Pleistocene sand
deposits occur as thin veneers over Hawthorn Group sediments
in much of the region. Since there is insufficient local demand
for sand products, the potential for commercial mining is low at
present.


Localized deposits of clay and sandy clay are associated with
the Pleistocene and Holocene marine terrace deposits and
alluvium and in the Hawthorn Group sediments. Most of these
deposits are contained in and interbedded with other sedi-
ments, and as a result are relatively impure. Reserve estimates
of the clay deposits in Hamilton County have not been made,
and future exploitation will depend largely on more extensive
exploration and testing, as well as market demand.

Limestone

Limestone deposits occur at or near the surface in south-
western Hamilton County in the Gulf Coastal Lowlands and
adjacent to the Suwannee River. Most near surface limestone
is associated with the Suwannee Limestone and Ocala Group.
These deposits are not mined, and are largely untested as to
purity and commercial potential. Future exploitation will be
largely dependent upon local demand for limestone products
such as roadbase.

Phosphate

Phosphate is currently mined in southeastern Hamilton
County. Occidental Chemical Corporation operates in two
mining areas in Hamilton County, the Swift Creek Mine north-
west of White Springs and the Suwannee River Mine, northeast
of White Springs.
The phosphate ore is contained in the Miocene age Haw-
thorn Group sediments, and is extracted with the sand and
clayey sand matrix by large draglines. Beneficiation of the
phosphate is accomplished through a flotation process, which
separates the quartz matrix sands and clays from the phosphate
ore. The uses for phosphate are primarily as agricultural ferti-
lizers.
Potential for this resource remains high in southeastern
Hamilton County. Continued mining of phosphate will be
dependent on market demand worldwide.

REFERENCES

Ceryak, R, Knapp, M., and Burnson, T., 1983, The geology and
water resources of the upper Suwannee River basin,
Florida:Florida Bureau of Geology Report of Investigation
no. 97, 166p.

Cooke, C., and Mansfield, W., 1936, Suwannee Limestone of
Florida (abstract): Geological Society of America Proceed
ings, 1935, p. 71-72.

Miller, J., 1986, Hvdrogeologic 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., 1957, Stratigraphy and zonation of the Ocala
Grou:.Florida Geological Survey Bulletin no. 38, 248 p.

Scott, T., 1988, The lithostratigraphv of the Hawthorn Group
(Miocene) of Florida: Florida Geological Survey Bulletin
no. 59, 148 p.

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

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