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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Tom Gardner, Executive Director




DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director




FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist





OPEN FILE REPORT 32
THE GEOMORPHOLOGY AND GEOLOGY OF CALHOUN COUNTY, FLORIDA

BY

Frank R. Rupert


FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
1990









Q f




SCIENCE
LIBRARY








The geomorphology and geology of Calhoun County, Florida


Frank R. Rupert, P.G. No. 149


GEOMORPHOLOGY

Calhoun County is situated in the Northern
Zone geomorphic province of White (1970). In this
portion of the east-central Florida panhandle, the
Northern Zone is divided into four geomorphic
subzones based largely on topographic elevations.
These include the Gulf Coastal Lowlands, Fountain
Slope, New Hope Ridge, and Grand Ridge.

The Gulf Coastal Lowlands (Figure 1) comprise
much of the lower half of Calhoun County. This
subzone is characterized by a generally flat and
often swampy, seaward sloping, sandy plain. Most
of the lowlands area is ancient marine terrace,
shaped by high-standing Pleistocene seas. Eleva-
tions in the Gulf Coastal Lowlands of Calhoun
County range from between 25 and 65 feet above
mean sea level (MSL) at the southern edge of the
county to approximately 100 feet above MSL where
the lowlands meet the higher ridges to the north in
mid-Calhoun County.


Three topographically-higher subzones are
present in northern Calhoun County: the Fountain
Slope, the New Hope Ridge, and the Grand Ridge.
Fountain Slope was the name given by White et al.
(1964) to a ramp-like, northward-rising topographic
slope separating the Gulf Coastal Lowlands and the
New Hope Ridge (Figure 1). The elevations of this
feature range from approximately 100 feet above
MSL at its southern edge, adjacent to the coastal
lowlands, to about 180 feet above MSL to the north
where it meets the New Hope Ridge.

The New Hope Ridge (White et al., 1964)
occupies northwestern Calhoun County, west of the
Chipola River. It is separated from the elevational-
ly-similar Grand Ridge (White et al., 1964) in
eastern Calhoun County by the Chipola River
valley. Both ridges are believed to be stream-in-
cised remnants of a once continuous highland
spanning north Florida from the Alabama line
eastward to Putnam County. The New Hope and
Grand Ridges are topographically high, with eleva-
tions generally varying between 150 and 250 feet


COUNTY


EXPLANATION

STATEICOUNTY ROAD
* WELL
4 CROSS SECTION LOCATION

DNEW HOPE RIDGE
GRAND RIDGE
FOUNTAIN SLOPE
GULF COASTAL
LOWLANDS

0 1 3 4 5


FIGURE 1. Calhoun County location map.


UNIVERSITY Of FLORIDA LIl.ARIES














IWIC



40-

10



-O -200 I J 3
-so



R 2 -G o eoo
-2: .** o200 ro

-ILES
-10 0 2 4 5

--so
SKILOM4TA
VERTICAL MIIOUaMATION APPROMMATILY Ia TIMIS TIRU SCALE



FIGURE 2. Geologic cross section A-A'.




B





n 4 t I I 0






CHA.TTAHOOCHE
to MATIO
-000

-40 -200 SUWA-SNE

--so A MLIMEST
-100
-400 1 2ILE 4 EAR
-140 0 a 4 a a
KILOMETERS
VERTICAL AXAMotATItoN* APPRCxIMATELY I11 TIMES TRUST SCALE


FIGURE 3. Geologic cross section B-B'.


1W B'





~JACKbON
BLF
X w


>NE


IAlNNA LIHeSEtj







above MSL. Both are comprised of resistant cla-
yey-sands overlying limestone. Several collapse
depressions and sinkhole lakes present on the New
Hope Ridge belie the karstic nature of the underly-
ing limestone.

The Apalachicola and Chipola Rivers are the
major streams flowing in Calhoun County. The
Apalachicola River forms the eastern Calhoun
County boundary with adjacent Liberty County. In
northeast Calhoun County, the broad Apalachicola
Valley averages about 50 feet MSL in elevation. It
forms a divide between the bluffs of the Tallahas-
see Hills to the east in Liberty County and the
topographically lower, gently-rolling hills of the
Grand Ridge. The river, meanders southwestward
through a three-mile wide valley, which descends to
an elevation of about 25 feet above MSL at the
southern edge of Calhoun County.

The Chipola River flows southward through
east-central Calhoun County, and forms Dead Lake
near the southern county boundary. In places the
river is well incised, and in northern Calhoun
County, exposes Miocene limestones and Pliocene
shell beds along its course. Several smaller surface
streams contribute to the Chipola River. Tenmile
Creek, Fourmile Creek, and Juniper Creek form a
southward succession of well-incised, northwest-
southeast trending tributaries entering the Chipola
from the west. These creeks may define a parallel
series of relict beach ridge systems. In southern
Calhoun County, Cypress Creek drains several low,
swampy areas and ultimately empties into Dead
Lake.

GEOLOGY

Calhoun County is underlain by hundreds of
feet of marine limestones, dolomites, sands, and
clays. The oldest rocks recovered by well drilling in
the county were Mesozoic Erathem, Cretaceous
System (140 to 65 million years old) marine sedi-
mentary rocks, at depths of approximately 2,800 to
5,000 feet below land surface (bIs) (Florida Geo-
logical Survey unpublished well logs). Petroleum
test wells in nearby Gulf County, however, reveal
the presence of older Paleozoic Erathem (500 to
250 million years old) basement rocks lying at
depths in excess of 12,000 feet bls; similar rocks
probably occur beneath Calhoun County as well.
The youngest sediments present in the county are
Pleistocene and Holocene (1.8 million years old to
recent) alluvium and marine terrace sands and


clays.
The Mesozoic Erathem rocks and early Cenozo-
ic Erathem (Paleocene and Eocene Series, 65 to 38
million years old) rocks underlying Calhoun County
are largely marine carbonates lying at depths
penetrated only by deep oil test wells. Most water
wells in Calhoun County draw from Oligocene and
Miocene (38 to 5 million years old) strata at depths
of 500 feet or less bis. These rocks function as the
important freshwater aquifers for the region. For
the purposes of this report, the discussion of the
stratigraphy of Calhoun County will be limited to
these Oligocene and younger sediments. Figure 1
shows the geologic cross-section locations, and
Figures 2 and 3 illustrate the shallow stratigraphy
of Calhoun County. Most of the geologic data
cited in this study is taken from Schmidt (1984),
Puri and Vernon (1964), and from Florida Geolog-
ical Survey well log files.

Oligocene Series
Marianna Limestone

The Marianna Limestone (Matson and Clapp,
1909) is the oldest unit penetrated by the cores
used in this report. It consists of a gray to cream,
chalky, fossiliferous marine limestone frequently
containing large, coin-shaped Lepidocvclina fora-
minfera fossils. The Marianna Limestone is con-
sidered to be Lower Oligocene (38 to 33 million
years old). This unit was penetrated in only one
core used in this study (W-6901, Liberty County -
see Figure 3), and the extent of its occurrence
under Calhoun County is uncertain due to a gener-
al lack of well coverage. It probably underlies
eastern and northern Calhoun County at depths of
400 to 500 feet bis. The Marianna Limestone is
overlain by sediments of the Upper Oligocene
Suwannee Limestone.

Suwannee Limestone

The Suwannee Limestone (Cooke and Mans-
field, 1936) is an Upper Oligocene (33 to 25 million
years old) light gray to yellowish-gray, well-indurat-
ed, often dolomitized, marine limestone. It typical-
ly contains abundant fossils including foraminifera,
mollusks, and echinoids. Depth to the Suwannee
Limestone ranges between 350 and 460 feet bls in
Calhoun County. Thickness of the unit is variable,
and usually exceeds 100 feet. It generally dips and
thickens to the southeast into the trough of the
Apalachicola Embayment. The Suwannee Lime-
stone is a component of the Florida aquifer system,







and this unit supplies deep municipal water wells in
the county. It unconformibly overlies the Oligo-
cene Marianna Limestone or Eocene Ocala Group
carbonates. In much of central and northern
Calhoun County, it is overlain by Miocene sedi-
ments of the Chattahoochee Formation. The
overlying Chattahoochee Formation grades lateral-
ly into the Bruce Creek Limestone near the south-
ern edge of the county.

Miocene and Pliocene Series
Chattahoochee Formation

The Lower Miocene (25 to 20 million years old)
Chattahoochee Formation (Dall and Stanley-
Brown, 1894) overlies the Suwannee Limestone in
Calhoun County. The Chattahoochee Formation is
generally a very pale orange to white or light gray,
often quartz sandy, phosphoritic, dolomitic marine
limestone. In some cases, post-depositional ground
water alteration of the carbonates in portions of the
central and western panhandle has made differen-
tiation of the Chattahoochee Formation from the
underlying Suwannee Limestone and overlying
Bruce Creek Limestone difficult or impossible.
Where defineable in Calhoun County however, the
top of the Chattahoochee Formation varies from
about 100 feet to 420 feet bls. Thickness ranges
from approximately 185 feet in the central portion
of the county to less than 50 feet in western and
southern Calhoun County. As with the underlying
Suwannee Limestone, the Chattahoochee dips to
the east-southeast, grading into or interfingering
with the Bruce Creek Limestone along the south-
ern edge of Calhoun County. The Chattahoochee
Formation is a unit of the Floridan aquifer system,
and rural Calhoun County wells draw from this
formation. Along the southern edge of the county,
the Bruce Creek Limestone grades into the Chat-
tahoochee Formation (Figure 2). In northern
Calhoun County, the Bruce Creek Limestone is
absent, and the Chattahoochee Formation is over-
lain by sediments of the Middle Miocene Chipola
Formation.

Bruce Creek Limestone

The Middle Miocene (17 to 10 million years
old) Bruce Creek Limestone (Huddlestun, 1984) is
a white to yellowish-gray, fossiliferous, calcarenitic,
marine limestone underlying the southern half of
Calhoun County. It is often highly microfossilifer-
ous, molluscan moldic, and in some areas, dolomit-
ic. From mid-Calhoun County, this unit thickens


and dips rapidly towards the south, into the trough
of the Apalachicola Embayment (Figure 2). The
Bruce Creek Limestone varies in depth from
approximately 100 feet bls at its northern limit in
central Calhoun County to over 400 feet bls in the
southern portion of the county. Its thickness in-
creases rapidly from zero in the central part of the
county southward to nearly 200 feet near the
Calhoun-Gulf county line. The Bruce Creek
Limestone comprises the uppermost unit of the
Floridan aquifer system in Calhoun County.
Where present, it is overlain by the Middle Mio-
cene Intracoastal Formation.

Intracoastal Formation

The Intracoastal Formation (Huddlestun, 1984;
Schmidt and Clark, 1980) is comprised of a yellow-
ish-gray, abundantly microfossiliferous, sandy,
poorly-indurated, marine limestone. It spans an
age range of Middle Miocene to Upper Pliocene
(17 to 2 million years old). Like the underlying
Bruce Creek Limestone, the updip limit of the
Intracoastal Formation occurs along a west-to-east
line across central Calhoun County. The formation
is absent north of Blountstown. It thickens and
dips to the south-southeast, approaching 60 feet in
thickness at the southern edge of the county.
Depth to the top of the unit in Calhoun County is
highly variable, generally averaging about 100 to
150 feet bls. Throughout its extent in Calhoun
County, the Intracoastal Formation is overlain by
the Chipola Formation.

Chipola Formation

The Chipola Formation (Burns, 1889) is a
Middle Miocene carbonate unit underlying most of
Calhoun County. It is typically comprised of a
yellowish-gray to light gray, moderately-to-well
induarated, quartz sandy, marine limestone or
marl. The Chipola Formation approaches the
surface in central and northern Calhoun County,
where it is, in places, covered only by a thin veneer
of Jackson Bluff Formation or undifferentiated
surficial sediments. It is locally exposed along the
banks of Tenmile Creek and along portions of the
Chipola River, the type area for the formation.
Here it commonly contains abundant fossil mol-
lusks. In western and southern Calhoun County,
the top of the Chipola Formation dips to nearly 100
feet bis. The Chipola Formation is overlain by
sediments of the Upper Pliocene Jackson Bluff
Formation:







above MSL. Both are comprised of resistant cla-
yey-sands overlying limestone. Several collapse
depressions and sinkhole lakes present on the New
Hope Ridge belie the karstic nature of the underly-
ing limestone.

The Apalachicola and Chipola Rivers are the
major streams flowing in Calhoun County. The
Apalachicola River forms the eastern Calhoun
County boundary with adjacent Liberty County. In
northeast Calhoun County, the broad Apalachicola
Valley averages about 50 feet MSL in elevation. It
forms a divide between the bluffs of the Tallahas-
see Hills to the east in Liberty County and the
topographically lower, gently-rolling hills of the
Grand Ridge. The river, meanders southwestward
through a three-mile wide valley, which descends to
an elevation of about 25 feet above MSL at the
southern edge of Calhoun County.

The Chipola River flows southward through
east-central Calhoun County, and forms Dead Lake
near the southern county boundary. In places the
river is well incised, and in northern Calhoun
County, exposes Miocene limestones and Pliocene
shell beds along its course. Several smaller surface
streams contribute to the Chipola River. Tenmile
Creek, Fourmile Creek, and Juniper Creek form a
southward succession of well-incised, northwest-
southeast trending tributaries entering the Chipola
from the west. These creeks may define a parallel
series of relict beach ridge systems. In southern
Calhoun County, Cypress Creek drains several low,
swampy areas and ultimately empties into Dead
Lake.

GEOLOGY

Calhoun County is underlain by hundreds of
feet of marine limestones, dolomites, sands, and
clays. The oldest rocks recovered by well drilling in
the county were Mesozoic Erathem, Cretaceous
System (140 to 65 million years old) marine sedi-
mentary rocks, at depths of approximately 2,800 to
5,000 feet below land surface (bIs) (Florida Geo-
logical Survey unpublished well logs). Petroleum
test wells in nearby Gulf County, however, reveal
the presence of older Paleozoic Erathem (500 to
250 million years old) basement rocks lying at
depths in excess of 12,000 feet bls; similar rocks
probably occur beneath Calhoun County as well.
The youngest sediments present in the county are
Pleistocene and Holocene (1.8 million years old to
recent) alluvium and marine terrace sands and


clays.
The Mesozoic Erathem rocks and early Cenozo-
ic Erathem (Paleocene and Eocene Series, 65 to 38
million years old) rocks underlying Calhoun County
are largely marine carbonates lying at depths
penetrated only by deep oil test wells. Most water
wells in Calhoun County draw from Oligocene and
Miocene (38 to 5 million years old) strata at depths
of 500 feet or less bis. These rocks function as the
important freshwater aquifers for the region. For
the purposes of this report, the discussion of the
stratigraphy of Calhoun County will be limited to
these Oligocene and younger sediments. Figure 1
shows the geologic cross-section locations, and
Figures 2 and 3 illustrate the shallow stratigraphy
of Calhoun County. Most of the geologic data
cited in this study is taken from Schmidt (1984),
Puri and Vernon (1964), and from Florida Geolog-
ical Survey well log files.

Oligocene Series
Marianna Limestone

The Marianna Limestone (Matson and Clapp,
1909) is the oldest unit penetrated by the cores
used in this report. It consists of a gray to cream,
chalky, fossiliferous marine limestone frequently
containing large, coin-shaped Lepidocvclina fora-
minfera fossils. The Marianna Limestone is con-
sidered to be Lower Oligocene (38 to 33 million
years old). This unit was penetrated in only one
core used in this study (W-6901, Liberty County -
see Figure 3), and the extent of its occurrence
under Calhoun County is uncertain due to a gener-
al lack of well coverage. It probably underlies
eastern and northern Calhoun County at depths of
400 to 500 feet bis. The Marianna Limestone is
overlain by sediments of the Upper Oligocene
Suwannee Limestone.

Suwannee Limestone

The Suwannee Limestone (Cooke and Mans-
field, 1936) is an Upper Oligocene (33 to 25 million
years old) light gray to yellowish-gray, well-indurat-
ed, often dolomitized, marine limestone. It typical-
ly contains abundant fossils including foraminifera,
mollusks, and echinoids. Depth to the Suwannee
Limestone ranges between 350 and 460 feet bls in
Calhoun County. Thickness of the unit is variable,
and usually exceeds 100 feet. It generally dips and
thickens to the southeast into the trough of the
Apalachicola Embayment. The Suwannee Lime-
stone is a component of the Florida aquifer system,








Jackson Bluff Formation

The Upper Pliocene (3 to 1.8 million years old)
Jackson Bluff Formation (Puri and Vernon, 1964)
is predominantly comprised of light gray to olive
gray, poorly-consolidated, clayey quartz sands and
sandy shell beds. It overlies the Chipola Formation
in Calhoun County. In the high bluffs across the
Apalachicola River from northeastern Calhoun
County in Liberty County, the Jackson Bluff
Formation rests on Miocene Hawthorn Group
deposits (Figure 3). The Jackson Bluff Formation
is a thin unit, averaging less than 50 feet thick in
eastern Calhoun County. It dips and thickens to
the south, reaching a maximum thickness of about
50 feet in the southern part of the county. Depth to
the top of the Jackson Bluff is variable throughout
the county. It crops out locally along the Apalachi-
cola and Chipola Rivers, and is closest to the sur-
face in northeastern Calhoun County, where it is
overlain by 20 to 25 feet of Citronelle Formation
sediments. In the western portion of the county, it
approaches a depth of 80 feet bls, and is covered
primarily by undifferentiated sands and clays.
Along the southern edge of Calhoun County, the
Jackson Bluff is overlain by approximately 50 feet
of undifferentiated sands.

Citronelle Formation

The reddish, clayey, coarse quartz sands and
gravels of the Upper Pliocene Citronelle Formation
(Matson, 1916) blanket large areas of the northern
half of Calhoun County. Believed to be of fluvial
origin, the characteristic Citronelle Formation
sediments are comprised of cross-bedded sands,
gravels, and clays. Portions of the Calhoun County
surficial deposits may represent reworked and
redeposited Citronelle sediments, transported from
the eroding highlands to the north. Thickness
generally varies between 20 and 80 feet, and the
Citronnelle deposits comprise the surficial sedi-
ments in their area of occurence. Within Calhoun
County, the Citronelle Formation sediments grade
laterally into a series of undifferentiated quartz
sands and clayey sands.

Plio-Pleistocene and Holocene Series
Undifferentiated Sand and Clays

Much of the southern half of Calhoun County is
covered by surficial quartz sands, clays, and clayey
sands. Due to the massive and discontinuous


nature of many of these units, they are lumped
together as undifferentiated deposits. These depos-
its represent a mixture of marine and fluvial clastics
associated with Pleistocene (1.8 million to 10,000
years old) sea level highstands and the prograding
Apalachicola' delta. The modern soil profiles
probably evolved during the Late Pleistocene and
Holocene (10,000 years ago to present). Holocene
alluvium, in the form of river-borne clays and sand,
are deposited along the banks and bars of the
Apalachicola River in eastern Calhoun County.

GROUND WATER

Ground water is water that fills the pore spaces
in subsurface rocks and sediments. This water is
derived principally from precipitation within
Calhoun and adjacent counties. The bulk of
Calhoun County's consumptive water is withdrawn
from ground water aquifers. Three main aquifers
are present under Calhoun County. In order of
increasing depth, these are the surficial aquifer
system, the intermediate aquifer and confining
system, and the Floridan aquifer system. Data on
aquifer extent and thicknesses are taken from Scott
et al., 1990 (in preparation).

Surficial aquifer system

The surficial aquifer system is the uppermost
freshwater aquifer in Calhoun County. This non-
artesian aquifer is largely contained within the
undifferentiated sands and the Citronelle Forma-
tion sediments. It is present in the northeastern
part of Calhoun County, where it reaches thick-
nesses of 55 feet, and trends southward through the
middle of the county, adjacent to the Chipola
River. In.parts of central Calhoun County it is
nearly 70 feet thick. It is absent or sporadic in
occurence in eastern and western portions of the
county. The surficial aquifer system is unconfined,
and its upper surface is the water table. In general,
the water table elevation fluctuates with precipita-
tion rate and conforms to the topography of the
land surface. Recharge to the aquifer is largely
through rainfall percolating through the loose
surficial sediments, and to a lesser extent, by
upward seepage from the underlying intermediate
aquifer system. The surficial aquifer is not used
extensively as a water source in the county.

Intermediate aquifer and confining system

The intermediate.aquifer system underlies the








surficial aquifer system in Calhoun County, and is
largely contained within the Intracoastal, Chipola
and Jackson Bluff Formations. Permeable beds
within the intermediate aquifer system vary consid-
erably in thickness over the areal extent of the
aquifer. In general, the aquifer ranges from 50 to
200 feet in thickness under Calhoun County, corre-
sponding to the variable thicknesses of the geologic
formations containing it. The top of the intermedi-
ate is also highly variable, dipping from a low of
about 20 feet bls in north-central Calhoun County
to over 70 feet bls in the western part of the Coun-
ty. Some rural wells draw from this unit, but the
intermediate aquifer system is not widely used as a
potable water source in this area. Low-permeabili-
ty beds in the basal intermediate aquifer system
may locally function as confining units to the under-
lying Floridan aquifer system.

Floridan aquifer system

The Floridan aquifer system is comprised of
hundreds of feet of Eocene through Miocene age
marine limestones, including the Ocala Group, the
Suwannee Limestone, and where present, the
Chattahoochee Formation and Bruce Creek Lime-
stone. It is the principle source of municipal drink-
ing water in Calhoun County. The Floridan aquifer
system occurs as an artesian aquifer under the
entire county. Surface springs tapping this aquifer
are absent in Calhoun County. Most recharge to
the Floridan aquifer system occurs in small, scat-
tered areas in the northern part of the county, at
the up-dip portions of the carbonate units compris-
ing the aquifer. Here, overburden to the Floridan
aquifer system is thinnest, and recharge occurs on a
low to moderate level. Much of the regional re-
charge occurs further to the north in Jackson
County where the Floridan aquifer system strata
crops out at the surface.

MINERAL RESOURCES

The principal mineral resources occurring in
Calhoun County are sand, clay, limestone, and
phosphate. The following discussion summarizes
the current mining potential of each commodity in
the county.

Sand

A number of shallow private pits in Calhoun
County are worked for local fill sand. Pleistocene
marine terrace sands and alluvium and Pliocene


Citronelle Formation sediments contain quartz
sand with varying amounts of clay matrix. These
deposits blanket much of the county. Since there is
insufficient local demand for sand products, the
potential for commercial mining is low at present.

Clay

Localized deposits of clay and sandy clay are
also associated with the undifferentiated Pleisto-
cene and Holocene marine terrace deposits,
Holocene alluvium, and Citronelle Formation
sediments. Most of these clays are contained in
and interbedded with other sediments, and as a
result are relatively impure.

Flood-plain clay deposits along the Apalachi-
cola River have been utilized for brick-making in
Calhoun County. The Guilford Brothers Brick
Company plant, located south of Blountstown,
manufactured common brick in the 1920's which
was used in the construction of the Blountstown
Post Office (Bell, 1924). Bell (1924) cited other
potential uses for this clay, including face brick,
drain tile, flower pots, and hollow blocks. Reserve
estimates of the clay deposits in Calhoun County
have not been made, and future exploitation will be
largely dependent upon local market demand.

Limestone

Impure Miocene limestones occur at depth
under most of Calhoun County. Most of the shal-
lower units contain extensive impurities, including
quartz sand. Due to the presence of these impuri-
ties, the overburden thickness (at least 50 feet in
northern Calhoun County), and the presence of
easily-accessible limestone deposits at the surface
in nearby Jackson County, it is unlikely that lime-
stone will ever be an economical commodity in
Calhoun County.

Phosphate

Many of the Miocene formations underlying
Calhoun County contain variable percentages of
phosphate sand and granules. Most quantities are

well below the ecomonic minimum percentage
however. In addition, most phosphate-bearing
strata occur at depths in excess of 50 feet. These
factors preclude a high mining potential for phos-
phate in Calhoun County.








Jackson Bluff Formation

The Upper Pliocene (3 to 1.8 million years old)
Jackson Bluff Formation (Puri and Vernon, 1964)
is predominantly comprised of light gray to olive
gray, poorly-consolidated, clayey quartz sands and
sandy shell beds. It overlies the Chipola Formation
in Calhoun County. In the high bluffs across the
Apalachicola River from northeastern Calhoun
County in Liberty County, the Jackson Bluff
Formation rests on Miocene Hawthorn Group
deposits (Figure 3). The Jackson Bluff Formation
is a thin unit, averaging less than 50 feet thick in
eastern Calhoun County. It dips and thickens to
the south, reaching a maximum thickness of about
50 feet in the southern part of the county. Depth to
the top of the Jackson Bluff is variable throughout
the county. It crops out locally along the Apalachi-
cola and Chipola Rivers, and is closest to the sur-
face in northeastern Calhoun County, where it is
overlain by 20 to 25 feet of Citronelle Formation
sediments. In the western portion of the county, it
approaches a depth of 80 feet bls, and is covered
primarily by undifferentiated sands and clays.
Along the southern edge of Calhoun County, the
Jackson Bluff is overlain by approximately 50 feet
of undifferentiated sands.

Citronelle Formation

The reddish, clayey, coarse quartz sands and
gravels of the Upper Pliocene Citronelle Formation
(Matson, 1916) blanket large areas of the northern
half of Calhoun County. Believed to be of fluvial
origin, the characteristic Citronelle Formation
sediments are comprised of cross-bedded sands,
gravels, and clays. Portions of the Calhoun County
surficial deposits may represent reworked and
redeposited Citronelle sediments, transported from
the eroding highlands to the north. Thickness
generally varies between 20 and 80 feet, and the
Citronnelle deposits comprise the surficial sedi-
ments in their area of occurence. Within Calhoun
County, the Citronelle Formation sediments grade
laterally into a series of undifferentiated quartz
sands and clayey sands.

Plio-Pleistocene and Holocene Series
Undifferentiated Sand and Clays

Much of the southern half of Calhoun County is
covered by surficial quartz sands, clays, and clayey
sands. Due to the massive and discontinuous


nature of many of these units, they are lumped
together as undifferentiated deposits. These depos-
its represent a mixture of marine and fluvial clastics
associated with Pleistocene (1.8 million to 10,000
years old) sea level highstands and the prograding
Apalachicola' delta. The modern soil profiles
probably evolved during the Late Pleistocene and
Holocene (10,000 years ago to present). Holocene
alluvium, in the form of river-borne clays and sand,
are deposited along the banks and bars of the
Apalachicola River in eastern Calhoun County.

GROUND WATER

Ground water is water that fills the pore spaces
in subsurface rocks and sediments. This water is
derived principally from precipitation within
Calhoun and adjacent counties. The bulk of
Calhoun County's consumptive water is withdrawn
from ground water aquifers. Three main aquifers
are present under Calhoun County. In order of
increasing depth, these are the surficial aquifer
system, the intermediate aquifer and confining
system, and the Floridan aquifer system. Data on
aquifer extent and thicknesses are taken from Scott
et al., 1990 (in preparation).

Surficial aquifer system

The surficial aquifer system is the uppermost
freshwater aquifer in Calhoun County. This non-
artesian aquifer is largely contained within the
undifferentiated sands and the Citronelle Forma-
tion sediments. It is present in the northeastern
part of Calhoun County, where it reaches thick-
nesses of 55 feet, and trends southward through the
middle of the county, adjacent to the Chipola
River. In.parts of central Calhoun County it is
nearly 70 feet thick. It is absent or sporadic in
occurence in eastern and western portions of the
county. The surficial aquifer system is unconfined,
and its upper surface is the water table. In general,
the water table elevation fluctuates with precipita-
tion rate and conforms to the topography of the
land surface. Recharge to the aquifer is largely
through rainfall percolating through the loose
surficial sediments, and to a lesser extent, by
upward seepage from the underlying intermediate
aquifer system. The surficial aquifer is not used
extensively as a water source in the county.

Intermediate aquifer and confining system

The intermediate.aquifer system underlies the








surficial aquifer system in Calhoun County, and is
largely contained within the Intracoastal, Chipola
and Jackson Bluff Formations. Permeable beds
within the intermediate aquifer system vary consid-
erably in thickness over the areal extent of the
aquifer. In general, the aquifer ranges from 50 to
200 feet in thickness under Calhoun County, corre-
sponding to the variable thicknesses of the geologic
formations containing it. The top of the intermedi-
ate is also highly variable, dipping from a low of
about 20 feet bls in north-central Calhoun County
to over 70 feet bls in the western part of the Coun-
ty. Some rural wells draw from this unit, but the
intermediate aquifer system is not widely used as a
potable water source in this area. Low-permeabili-
ty beds in the basal intermediate aquifer system
may locally function as confining units to the under-
lying Floridan aquifer system.

Floridan aquifer system

The Floridan aquifer system is comprised of
hundreds of feet of Eocene through Miocene age
marine limestones, including the Ocala Group, the
Suwannee Limestone, and where present, the
Chattahoochee Formation and Bruce Creek Lime-
stone. It is the principle source of municipal drink-
ing water in Calhoun County. The Floridan aquifer
system occurs as an artesian aquifer under the
entire county. Surface springs tapping this aquifer
are absent in Calhoun County. Most recharge to
the Floridan aquifer system occurs in small, scat-
tered areas in the northern part of the county, at
the up-dip portions of the carbonate units compris-
ing the aquifer. Here, overburden to the Floridan
aquifer system is thinnest, and recharge occurs on a
low to moderate level. Much of the regional re-
charge occurs further to the north in Jackson
County where the Floridan aquifer system strata
crops out at the surface.

MINERAL RESOURCES

The principal mineral resources occurring in
Calhoun County are sand, clay, limestone, and
phosphate. The following discussion summarizes
the current mining potential of each commodity in
the county.

Sand

A number of shallow private pits in Calhoun
County are worked for local fill sand. Pleistocene
marine terrace sands and alluvium and Pliocene


Citronelle Formation sediments contain quartz
sand with varying amounts of clay matrix. These
deposits blanket much of the county. Since there is
insufficient local demand for sand products, the
potential for commercial mining is low at present.

Clay

Localized deposits of clay and sandy clay are
also associated with the undifferentiated Pleisto-
cene and Holocene marine terrace deposits,
Holocene alluvium, and Citronelle Formation
sediments. Most of these clays are contained in
and interbedded with other sediments, and as a
result are relatively impure.

Flood-plain clay deposits along the Apalachi-
cola River have been utilized for brick-making in
Calhoun County. The Guilford Brothers Brick
Company plant, located south of Blountstown,
manufactured common brick in the 1920's which
was used in the construction of the Blountstown
Post Office (Bell, 1924). Bell (1924) cited other
potential uses for this clay, including face brick,
drain tile, flower pots, and hollow blocks. Reserve
estimates of the clay deposits in Calhoun County
have not been made, and future exploitation will be
largely dependent upon local market demand.

Limestone

Impure Miocene limestones occur at depth
under most of Calhoun County. Most of the shal-
lower units contain extensive impurities, including
quartz sand. Due to the presence of these impuri-
ties, the overburden thickness (at least 50 feet in
northern Calhoun County), and the presence of
easily-accessible limestone deposits at the surface
in nearby Jackson County, it is unlikely that lime-
stone will ever be an economical commodity in
Calhoun County.

Phosphate

Many of the Miocene formations underlying
Calhoun County contain variable percentages of
phosphate sand and granules. Most quantities are

well below the ecomonic minimum percentage
however. In addition, most phosphate-bearing
strata occur at depths in excess of 50 feet. These
factors preclude a high mining potential for phos-
phate in Calhoun County.








REFERENCES


Bell, 0., 1924, A preliminary report on the clays of
Florida (exclusive of Fuller'sEarth): in:
Florida Geological Survey 15th Annual
Report, p.25-127.

Burns, Frank, 1889, Unpublished Field Notes, U.S.
Geological Survey (Referenced in Cooke
and Mossom, 1929, Geology of Florida:
Florida Geological Survey 20th Annual
Report, 103 p.)

Cooke, C.W., and Mossom, S., 1929, Geology of
Florida: Florida Geological Survey 20th
AnnualReport, 1927-1928, p. 29-227.

and Mansfield, W., 1936, Suwannee
Limestone of Florida: [abs.] Geological
Society of America Proceedings, 1935,
p.71-72.

Dall, W.H., and Stanley-Brown, J., 1894,
Cenozoic geology along the Apalacicola
River: Bulletin of the Geological Society
of America, v. 5, p. 147-170.

Huddlestun, P.F., 1984, The Neogene stratigraphy
of the central Florida Panhandle: [Ph.D
Dissertation], Florida State University,
Tallahassee, 210 p..

Matson, G., and Clapp, F., 1909, A pre-
liminary report on the geology of Florida
with special reference to the stratigraphy:
Florida Geological Survey 2nd Annual
Report, 1908-1909, p. 25-173.

Matson, G. C., 1916, The Pliocene Citronelle
Formation of the Gulf Coastal Plain: U.S.
Geological Survey Professional Paper 98,
p. 167-192.

Puri, H., and Vernon, R.O., 1964, Summary of the
geology of Florida and a guidebook to the
classic exposures: Florida Geological
Survey Special Publication no. 5 (revised),
312 p.

Schmidt, W., 1984, Neogene stratigraphy and
geologic history of the Apalachicola
Embayment, Florida: Florida Geological
Survey Bulletin 58, 146 p.


_, and Clark, M.W., 1980, Geology
of Bay County, Florida: Florida
Geological Survey Bulletin 57,76 p.

Scott, T.M., Lloyd, J., and Maddox, G., 1990 (in
preparation), Florida's ground water
monitoring network, Volume 1: Introduc-
tion and hydrogeologic framework:
Florida Geological Survey Survey Special
Publication no. 32.

White, W., Puri, H., and Vernon, R., 1964,
Unpublished manuscript cited in: Puri, H.
and Vernon, R., 1964, Summary of the
geology of Florida and a guidebook to the
classic exposures: Florida Geological
Survey Special Publication no. 5 (revised),
312 p.

White, W., 1970, The geomorphology of the Florida
peninsula: Florida Geological Survey
Bulletin 51, 164 p.










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