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STATE OF FLORIDA


DEPARTMENT OF ENVIRONMENTAL PROTECTION
David B. Struhs, Secretary



DIVISION OF RESOURCE ASSESSMENT AND MANAGEMENT
Edwin J. Conklin, Director



FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief


OPEN FILE REPORT 86

GEOLOGY OF SUWANNEE COUNTY, FLORIDA

By

Frank R. Rupert


FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
2003
ISSN 1058-1391










Geology of Suwannee County, Florida
Frank R. Rupert, PG 149


The following overview of the geology of
Suwannee County was prepared for the
United States Department of Agriculture,
Natural Resources Conservation Service,
for inclusion in their Soil Survey of
Suwannee County, Florida. Included are
sections on: 1) geomorphology, describing
the shape and origin of the land surface, 2)
stratigraphy, describing the underlying
rock strata, 3) ground water, providing an
overview of the aquifer systems in
Suwannee County, and 4) mineral
resources present in the county.

GEOMORPHOLOGY

Suwannee County encompasses por-
tions of two broad geomorphic zones (Figure
1). The western two-thirds of the county
lies within the Gulf Coastal Lowlands geo-
morphic zone (White, 1970). This zone is
characterized as a low, flat, frequently
swampy, westward-sloping plain that
extends from east-central Suwannee
County to the Gulf of Mexico. Land surface
elevations generally range between about
35 and 100 feet above mean sea level (msl).
Most of the lowlands area is ancient marine
terrace terrain. Plio-Pleistocene seas alter-
nately flooded and retreated from this
region, depositing a step-like series of
marine terraces, which generally parallel
the modern Florida coastline. Healy (1975)
recognizes three marine terrace elevation
zones in Suwannee County. The Wicomico
Terrace (70 to 100 feet above msl) corre-
sponds to the Gulf Coastal Lowlands zone,
while the older Sunderland/Okeefenokee
Terrace (100-170 feet above msl) and the
Coharie Terrace (170 to 215 feet above msl)
cover the remainder of the county. Imposed
on these terrace surfaces in the western
part of the county are relict marine features


such as bars, dunes, and beach ridge sys-
tems. Such relict features, composed prin-
cipally of quartz sand, may be observed far
inland from the modern coastline.
Land surface slope in the Gulf Coastal
Lowlands zone ranges between 1 and 4 feet
per mile southwestward. The highly karstic
Oligocene and Eocene carbonates underly-
ing this area are masked by a blanket of
undifferentiated sand. Solution sinkholes
are common features throughout this
region. Scott (in preparation) includes the
local portion of the Gulf Coastal Lowlands
in his Branford Karst Plain zone of the
Ocala Karst District.
The Gulf Coastal Lowlands extend
eastward across the county to approximate-
ly the 100 feet above msl elevation line. At
this elevation a relict marine escarpment
named the Cody Scarp forms a topographic
break between the Gulf Coastal Lowlands
on the west and the elevationally higher
Northern Highlands in the eastern third of
the county. The Cody Scarp is a former
shoreline associated with the Wicomico sea
level highstand of the Pleistocene Epoch.
Erosion and dissolution of the underlying
carbonate rocks have modified the escarp-
ment into a series of coalesced sand hills
snaking northwest-southeast along the
irregular edge of the Northern Highlands
zone.
The Northern Highlands (White, 1970)
are a series of uplands comprising the
northern and eastern edge of the county.
They extend from the Cody Scarp, at eleva-
tion of about 100-125 feet above msl, north-
ward into Hamilton County and eastward
into Columbia County. Miocene and
Pliocene siliciclastic sediments, resting on
carbonate bedrock, form the core of the
uplands. The highlands have been modified
largely by stream-dissection and land sur-










W-14313 VA


-N-



C SUWANNEE +
ELLAVILLE RIVER +
STATE PARK +
+ +
FALMOUTH + +
0
o+
SLIVE)W-

/ if IVJE


0 1 2 3 4MILES
o 1 2 3 4 5 6 KILOMETERS
SCALE


PINEMOUNT


McALPIN


S++ + + +
4* S. + + + + +1
+ + + + +++
+++++ +
+ + + ++
EXPLANATION + +. +. + +
Geomorphic Zones + +

I- I NNorthern Highlands

Gulf Coastal Lowlands A

Town /Community o *, W-3311 BRANFORDR 27
> Interstate Highway oo 9
d- Federal Highway "- o
SState / County Road
0 Well location
-0 Geologic cross section line
R Mine location


Figure 1. Geomorphic and geologic cross section location map.


,1









face lowering due to dissolution of the
underlying bedrock. Scott (in preparation)
has applied the name Alachua-Lake City
Karst Hills to this local portion of the
Northern Highlands. Land surface eleva-
tions are mostly less than 150 feet above
msl. The maximum elevation attained is
about 200 feet above msl, on a hilltop about
a mile north of McAlpin in southeastern
Suwannee County.

River Valley Lowlands

The Suwannee River is the largest river
in Suwannee County, and forms the north-
ern and western county boundaries. It
flows southwestward from Georgia to the
Gulf of Mexico in a dissolutional valley,
carved in the underlying Oligocene and
Eocene carbonates. The topographic low-
lands immediately adjacent to the river,
generally characterized by thin Pleistocene-
Holocene sands and clayey sands lying on
limestone, comprise the Suwannee River
Valley Lowlands. River valley floor eleva-
tions range from about 100 feet above msl
in northeastern Suwannee County to about
35 feet above msl at the southern tip of the
county. For most of its course, the valley is
less than one mile wide.
The Santa Fe River arises in the
swampy hammocks to the east in Bradford
County, and flows westward in a narrow,
incised valley generally lying about 35 feet
or less above msl. It forms the southern
county boundary between Suwannee and
Gilchrist Counties. The Santa Fe flows in a
channel cut in Eocene carbonates, which
commonly crop out along the lower portion
of the river. Pleistocene and Holocene sili-
ciclastics form a sediment veneer over the
carbonates in the river bed and along the
banks.
The Ichetucknee River comprises the
southeastern-most boundary of Suwannee
County. The stream arises in a series of


fresh water springs within Ichetucknee
Springs State Park and flows about five
miles southwestward to a confluence with
the Santa Fe River. The Ichetucknee is a
clear, pristine stream flowing in a sand-bot-
tom channel carved in the underlying
Eocene carbonate bedrock. A narrow river
valley lowlands zone, about one-half mile
wide, borders the stream along its upper
reaches. The valley coalesces with the
wider lowlands of the Santa Fe River near
the confluence of the two rivers.

STRATIGRAPHY

The oldest rock commonly penetrated
by water wells in Suwannee County is
marine limestone of the Middle Eocene
Avon Park Formation. Undifferentiated
Pleistocene and Holocene surficial sands,
clayey sands, and alluvium are the
youngest sediments present. Figures 2 and
3 illustrate the shallow stratigraphy of the
county. The Avon Park Formation and the
younger overlying carbonates are important
freshwater aquifers, and the following dis-
cussion of the geology of Suwannee County
is confined to these Eocene and younger
sediments.

Eocene Series
Avon Park Formation
The Avon Park Formation (Applin and
Applin, 1944; Miller, 1986) is a lithological-
ly variable Middle Eocene (about 47 to 43.5
million years ago [mya]) carbonate unit
underlying all of Suwannee County. It is
typically a yellowish-gray to grayish-orange
to dark yellowish brown dolostone,
interbedded with grayish-white to yellow-
ish-gray limestones and dolomitic lime-
stones. The unit commonly contains vary-
ing amounts of peat, lignite, and plant
remains (Florida Geological Survey in-
house well logs). Mollusks, echinoids, and
foraminifera, where preserved, are the prin-















W W
LL J c-

200--


-200 -I- -60


-300-


- -80


- -100


-400--- -120


- -140


- -160


- -180


--200


S1 2 3 MILES
01 2 3456 KILOMETERS
SCALE


VERTICAL EXAGGERATION IS APPROXIMATELY 300 TIMES TRUE SCALE


Figure 2. Geologic cross section A A'.


_- o
LU U
LU200


100-




0-




-100 -


-200 -- -60
AVON PARK FORMATION

-80 0 1 2 3 4 MILES
S1 234 56 KILOMETERS
-300 SCALE
--100
VERTICAL EXAGGERATION IS APPROXIMATELY 300 TIMES TRUE SCALE

Figure 3. Geologic cross section B B'.


4


A'









cipal fossils present. The top of the Avon
Park Formation varies in depth from
approximately 300 feet below land surface
(bls) in northwestern Suwannee County to
about 100 feet bls in the southernmost part
of the county. Deep oil test well data indi-
cate that the Avon Park Formation ranges
from approximately 650 to 800 feet thick
under Suwannee County (FGS in-house
well logs).

Ocala Limestone
Marine limestones of the Upper Eocene
(39.5 38 mya) Ocala Limestone (Puri,
1957; Scott, 1991) unconformibly overlie the
Avon Park Formation under all of
Suwannee County. It is divided into upper
and lower units based on lithology. The
lithology of the Ocala Limestone grades
upward from alternating hard and soft,
white to tan to gray fossiliferous limestone
and dolomitic limestone of the lower unit
into white to very light gray to light yellow-
ish-orange, abundantly fossiliferous, chalky
limestones of the upper unit (FGS in-house
well files). Foraminifera, mollusks, bry-
ozoans, and echinoids are the most abun-
dant fossils occurring in this unit.
Thickness of the Ocala Limestone under
Suwannee County ranges between about 80
and 220 feet thick. It generally thins
against the structurally high Avon Park
Formation toward the crest of the Ocala
Platform in the western portion of the coun-
ty. The Ocala Platform is a structurally
positive feature centered under the Big
Bend area of the western peninsula. This
feature brings Eocene carbonates close to
the surface over its crest, and younger units
lap onto the flanks of the feature.
Suwannee County lies just east of the axis
of the platform Depth to the irregular and
highly-karstic top of the Ocala Limestone
ranges from exposure at land surface in
eastern and southern Suwannee County to
about 270 feet below land surface in the
eastern part of the county. The Ocala


Limestone commonly crops out along the
banks of the major rivers bordering central
and southern Suwannee County.
The highly permeable and cavernous
natures of the Ocala Limestone make it an
important freshwater bearing unit of the
Floridan aquifer system. Many drinking
water wells in Suwannee County withdraw
water from this limestone.

Oligocene Series
Suwannee Limestone
The Suwannee Limestone (Cooke and
Mansfield, 1936) is an Oligocene (37.5 28
mya) marine limestone and dolostone
underlying the northern half of Suwannee
County. It pinches out against the underly-
ing Ocala Limestone just north of an
approximate west-east line connecting the
towns of Dowling Park and Wellborn. It is
typically a white to yellowish-gray to gray-
ish-brown, skeletal to micritic, fossiliferous
limestone, altered in some areas to variably
recrystallized dolostone. Mollusks,
foraminifera, echinoids, bryozoans, and
ostacods, in various degrees of preservation,
comprise the dominant fossil assemblage
present in this unit. The Suwannee
Limestone forms the near-surface carbon-
ate bedrock in northern Suwannee County.
Its top typically ranges in depth from as
much as 150 feet below land surface to sur-
face exposures in sinks, streambeds, and
along the Suwannee River north of Dowling
Park. Although variable, its thickness
ranges between about 45-180 feet.
The Suwannee Limestone locally com-
prises the uppermost unit of the Floridan
aquifer system. Some shallow rural domes-
tic and agricultural wells draw water from
this unit.

Oligocene to Pliocene Series
Hawthorn Group Undifferentiated
Sediments of the Hawthorn Group
(Scott, 1988) unconformably overlie the
Ocala and Suwannee Limestones in north-









central and eastern Suwannee County.
Statewide, the age of Hawthorn Group
sediments range from about 25.5 4.8 mya.
The Hawthorn Group is a heteroge-
neous mixture of siliclastic and carbonate
sediments. Tan, brown, gray, and white
sandy, phosphatic dolostone commonly
occurs in the lower part of the Hawthorn
Group in Suwannee County. The upper
portion is typically comprised of olive-green,
blue and or brown, phosphatic clay, quartz
sand and dolosilt, with carbonate interbeds.
Fossils include mollusks and foraminifera.
The predominant unifying character of both
upper and lower portions of the Hawthorn
Group is the presence of black, brown, or
amber, very fine sand to pebble sized phos-
phate grains. Phosphate content ranges
from trace amounts to in excess of 20 per-
cent.
The Hawthorn Group ranges in depth
from surface exposure down to about 75 feet
below land surface. It reaches a maximum
thickness of about 70 feet in northeastern
Suwannee County.

Pliocene, Pleistocene
and Holocene Series
Undifferentiated Pliocene Holocene
marine and alluvial, fine to coarse quartz
sands and clayey sands form a thin veneer
over most of Suwannee County. They are
generally less than about 50 feet thick coun-
ty-wide, but some buried sinkholes may
contain up to 270 feet of undifferentiated
sediments. They directly overlie the karstic
limestones of the Suwannee and Ocala
Limestones. Many of the larger and higher
sand bodies west of the Cody Scarp in
southern Suwannee County are relict
dunes, bars, and barrier islands associated
with various Pleistocene sea level high
stands.


GROUNDWATER

Groundwater is water that fills the
pore spaces in subsurface rocks and
sediments. This water is derived principal-
ly from precipitation within Suwannee and
adjoining counties. The bulk of Suwannee
County's potable water is withdrawn from
groundwater aquifers. Three aquifer sys-
tems are present under Suwannee County,
the surficial aquifer system, the intermedi-
ate aquifer system and confining unit, and
the Floridan aquifer system.

Surficial aquifer system
The surficial aquifer system is the
uppermost freshwater aquifer in Suwannee
County. This non-artesian aquifer is pres-
ent only within the thicker portions of the
Pliocene-Holocene undifferentiated sands
and clays. It is thin or absent in much of
Suwannee County, but may occur sporadi-
cally in the northeastern portion of the
county, east of Live Oak, and in the central
portion of the county (Barineau et al, in
preparation). The surficial aquifer system,
where present, is unconfined and its upper
surface is the water table. In general, the
water table elevation fluctuates with pre-
cipitation and conforms to the topography of
the land surface. Recharge to the surficial
aquifer system is largely through rainfall
percolating downward through the uncon-
solidated surficial sediments, and to a less-
er extent, by upward seepage from the
underlying Floridan aquifer system. Water
naturally discharges from the aquifer by
evaporation, evapotranspiration, spring
seeps and downward seepage into the
Floridan aquifer system. The surficial
aquifer system is not used as a source of
consumptive water in Suwannee County.









Intermediate aquifer system and con-
fining unit
A discontinuous intermediate aquifer
system and confining unit is present within
the Hawthorn Group sediments in
Suwannee County. Clay and clayey sand
beds in the Hawthorn Group, perforated by
sinks, provide a region of semi-confinement
to the underlying Floridan aquifer system
in the eastern and northeastern portions of
the county (Scott et al., 1991). Laterally
discontinuous carbonate beds in the
Hawthorn Group may also function as an
intermediate aquifer system. Wells in the
vicinity of Wellborn, in northeastern
Suwannee County, penetrate this aquifer
system (Ron Ceryak, SRWMD, personal
communication). The intermediate aquifer
system is not used extensively as a source of
water within the county.

Floridan aquifer system
In Suwannee County the Floridan
aquifer system is comprised of hundreds of
feet of Eocene and Oligocene marine lime-
stones, including the Avon Park Formation,
Ocala Limestone, and Suwannee
Limestone. It is the principle source of
drinking water in the county. The Floridan
aquifer system exists as an unconfined,
non-artesian aquifer in the Gulf Coastal
Lowlands adjacent to the Suwannee, Santa
Fe and Ichetucknee Rivers, where porous
quartz sand directly overlies the limestone.
In much of the rest of Suwannee County,
the Floridan is semi-confined by clayey beds
in the overlying Hawthorn Group. In the
highlands near the town of Wellborn it is
confined. Depth to the top of the Floridan
aquifer system generally corresponds to the
depth of limestone, and varies from surface
exposure in the Suwannee, Santa Fe, and
Ichetucknee River valley lowlands and the
karst plain areas of western Suwannee
County, to nearly 50 feet under the higher
hills in the eastern part of the county.


Recharge to the Floridan aquifer sys-
tem in Suwannee County is obtained from
lateral inflow from the north and, to a less-
er extent, from local rainfall percolating
downward through the permeable surficial
sands. The highest recharge by percolation
occurs in the highly karstic limestone plain
in western Suwannee County (Stewart,
1980).
Water leaves the Floridan aquifer sys-
tem through well pumping and natural
movement down-gradient and subsequent
discharge through numerous springs and
seeps. Numerous springs occur in and
along the major streams bordering
Suwannee County.

MINERAL RESOURCES

Suwannee County contains deposits of
several economic mineral commodities. The
most important of these is limestone. Other
commodities of lesser potential include
sand, clay, phosphate and peat.
Information for this section is compiled
from Hoenstine et al. (1993) and recent
mining data from the Florida Geological
Survey Mine Database. Mine status may
change frequently.

Limestone
Two commercial grade carbonate rock
units occur in Suwannee County. The
Suwannee Limestone occurs near the sur-
face under the northern half of Suwannee
County, and the higher-purity Ocala
Limestone is the shallow unit in the south-
ern half of the county. The economic grade
may vary considerably from one area to
another. Several inactive mines are located
in Suwannee County. These include Live
Oak, five mines at locations both east and
south of Dowling Park, three west of Pine
Mount, two north and two east of Branford,
and an old mine off county road 247 near
the Suwannee-Columbia county line.









High purity, road base quality rock is
currently mined in the Branford area in
southern Suwannee County. The rock at
this location is too soft and friable for aggre-
gate use. Mining in the Branford area
occurs to depths of 40 feet below water sur-
face, and the total mineable thickness
approaches 60 feet. Extraction is by
dragline, and explosives may be used to
fracture the rock for removal. The rock is
typically dried and crushed before shipment
to market by truck.
Aggregate and secondary road base
grade limestones occur over much of the
rest of the county. Large pits near Live Oak
were worked up until 1975 and the materi-
al was utilized as fine and coarse aggregate
as well as road base. Although overburden
thickness may reach 50 feet in this area,
and the rock is commonly soft with numer-
ous clay seams, the Live Oak area still con-
tains economic reserves.
The primary uses for limestone from
Suwannee County are road base, agricul-
tural soil conditioners, and asphalt screen-
ings. The county has sufficient reserves of
limestone to last many years, and the eco-
nomics of future extraction will depend
largely on market demand.

Sand
Impure quartz sand, commonly con-
taining varying percentages of clay, heavy
minerals and organic, is a principal com-
ponent of surficial and shallow sediments
throughout Suwannee County. Due to the
impurities it has limited industrial poten-
tial. A number of shallow private pits in
Suwannee County are worked for local fill
sand. The potential for commercial mining
is low at this time.

Clay
Clay sporadically occurs as a compo-
nent of the undifferentiated surficial
sediments covering Suwannee County, in


alluvial deposits in the major stream val-
leys, and in Hawthorn Group sediments.
Clay deposits in the county are typically
stratified with quartz sands and clayey
sands. Due to the impure nature of this
clay, it is not an economic commodity in the
county. Several local pits provide road and
fill material, but there is currently little
potential for commercial use.

Phosphate
Suwannee County lies at the northern
extent of Florida's hard rock phosphate
deposits. These deposits are typically
formed at the top of the Ocala Limestone in
isolated pockets, and are generally less
than 5-feet thick. This commodity was
mined in southeastern Suwannee County
until 1966. The extensive pebble phosphate
deposits of south-central Florida are more
economical to mine, and their availability
aided in the demise of the hard rock indus-
try statewide. Due to the limited thickness
and discontinuous nature of the hard rock
phosphate deposits, it is unlikely that eco-
nomic mining operations will resume in
Suwannee County.

Peat
Peat forms in a wet, reducing environ-
ment when accumulation of organic materi-
als exceeds the decomposition rate of that
material. The U. S. Department of
Agriculture, Soil Conservation Service,
mapped about 90 acres of commercial grade
peat in three isolated areas of northeastern
Suwannee County (USDASCS, 1965). The
peat varies in thickness from 30 to 60 inch-
es and rests on sand. It is comprised large-
ly of the remains of sweetbay, ash, cypress,
pine, and other water tolerant plants. The
lack of a local market keeps the potential
for development of these resources low.









REFERENCES

Applin, P. L., and Applin, E. R., 1944,
Regional subsurface stratigraphy and
structure of Florida and southern
Georgia: American Association of
Petroleum Geologists Bulletin, v. 28, n.
12, p. 1673-1753.

Barineau, C., Ponchak, M., Ceryak, R. and
Rupert, F., (in preparation), Isopach
map of surficial sediments above a
shallow clay layer in the Suwannee
River Water Management District:
Florida Geological Survey Open File
Map Series.

Cooke, C. W., and Mansfield, W. C., 1936,
Suwannee Limestone of Florida [abs.]:
Geological Society of America
Proceedings, p. 71-72.

Healy, H. G., 1975, Terraces and shorelines
of Florida: Florida Bureau of Geology
Map Series n. 71.

Hoenstine, R.W., Spencer, S.M., and Lane,
B.E., 1993, Mineral Resources of
Suwannee County, Florida: Florida
Geological Survey Map Series n. 137.

Miller, J.A., 1986, Hydrogeologic
Framework of the Floridan aquifer sys-
tem in Florida and in parts of Georgia,
Alabama, and South Carolina: U.S.
Geological Survey Professional Paper
1403-B, p. 25-27.

Puri, H.S., 1957, Stratigraphy and Zonation
of the Ocala Group: Florida Geological
Survey Bulletin n. 38, 248 p.

Scott, T.M., (in preparation), Geomorphic
map of the State of Florida: Florida
Geological Survey Map Series.


Scott, T.M., 1988, The Lithostratigraphy of
the Hawthorn Group (Miocene) of
Florida: Florida Geological Survey
Bulletin n. 59, 148 p.

Scott, T.M., Lloyd, J.M., and Maddox, G.,
1991, Florida's Ground Water Quality
Monitoring Program Hydrogeological
Framework: Florida Geological Survey
Special Publication n. 32, 97 p.

Scott, T. M., 1991, in Scott, T. M., Lloyd, J.
M., and Maddox, G., (eds.), Florida's
Ground Water Quality Monitoring
Program Hydrogeological Framework:
Florida Geological Survey Special
Publication n. 32, 97 p.

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

USDASCS, 1965, Soil survey report for
Suwannee County, Florida: U. S.
Department of Agriculture Soil
Conservation Service, in cooperation
with the University of Florida Institute
of Food and Agricultural Services,
Gainesville, 101p.

White, W.A., 1970, Geomorphology of the
Florida Peninsula: Florida Geological
Survey Bulletin n. 51, 164 p.