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OPEN FILE MAP SERIES NO. 12


FLORIDA GEOLOGICAL SURVEY
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GEOLOGIC MAP OF

SLACHUA COUNTY
FLORIDA


T. Scott, P.G.# 99
Preliminary field mapping by
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1992


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CARTOMMPH BY JIM JONES & TED KMPR


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Scott. T.M., 1988b, The Cypresshead Formation In northern
peninsular Florida: in Pirkle, F.L, and Reynolds, J.G.,
(eds.) Southeastern Geological Society Annual Field Trip
Guidebook, February 19-29, 1988, pp. 70-72.


























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GEOLOGIC MAP OF ALACHUA COUNTY, FLORIDA:.
by
T. Scott, P.G.# 99 and Kenneth M. Campbell, P.G.: 192 i

The geologic map of Alachua County. Florida was developed as
a generalized base map to be utilized in predicting radon potential
hazards. Funding for this effort was provided by the U. S.
Environmental Protection Agency (EPA) and the Florida Department 6f
Community Affairs. The geology of the county was mapped utilizing
well cuttings, cores, natural and man-made exposures and
topographic maps. Geologic units identified include formal
lithostratigraphic units and informal units. Both types of units
were included in order to provide a more accurate picture of the
geology despite an often sparse data base. As a general rule, if
the undifferentiated sediments were less than 20 feet thick, the
underlying recognizable formation was mapped.
The oldest stratigraphic unit mapped in Alachua County is the
Upper Eocene Ocala Umestone (To). The Ocala Limestone consists of-
very pure, highly fossiliferous grainstones and packstones.
Predominant fossils Include large and small foraminifera, mollusks,
echinoids and bryozoans. It is mapped in the western portion of
the county. Characteristically, the Ocala Umestone is highly
karstified. often exhibiting dramatic local relief. It is exposed
In springs and quarries. The Ocala is overlain unconformably by
the Miocene Hawthorn Group sediments.
The Miocene Hawthorn Group (Th) marine sediments are mapped, in
the central and eastern portions of the county. Two fo~les of the;. .
Hawthorn Group can be seen In Alachua County. Near the western '
limits of the Hawthom's occurrence, the group is dominated by.
clays and clayey sands with only minor carbonate and phosphate. To'--,
the east of this faces the sediments consist sediments cont*ang
more sand, less clay, and more carbonate and phosphate (Seott,
1988a). It is often exposed in sinkholes and scattered road cut8.
Highly weathered Hawthorn Group sediments (Thw) occur on the
Brooksville Ridge in the southwestern corner of the county. Thl'
Hawthorn Group unconformably overiles the Eocene Ocala Umestoe. ,
and is overlain unconformably by the Cypresshead Formation (To} or '
undifferentiated sediments (Q ).
The late TertiaVy. Late Pliocene Cypresehead Formation (Tc)
(Scott, 1988b) consists of quartz sands ranging from fine to very
coarse, moderately to well sorted with common occurrences of quartz
gravel. Clay Is commonly present in very minor amounts and aI
generally kaolinite. Mica often occurs in minor percentages. I ,
particularly in the finer grained sediments. Colors range from ,.
reddish-orange in exposed sections to olive gray in the sub*u "'
Huddlestun (1988) suggests that the Cypresshead Formation, gades
laterally down dip into the Nashua Formation, a variably shelly.
clayey sand. The Cypresshead was deposited in a shallow,
nearshore, marine setting and unconformably overlies the Hawthorn''-
Group. It is unconformably(?) overlain by the undifferentiated
sediments (QTu). .. .
The undifferentiated imen (OTu) are mapped In the eastern
portion of the county. These sediments consist of sands with :: .
variable amounts of silt, clay and organic matter. This unit may
lie unconformably on the Ocala Uimestone. Hawthorn Group or ()
Cypresshead Formation.
REFERENCES
Huddlestun, P.F., 1988, A revision of the llthostratigraphic units
of the Coastal Plain of Georgia: Miocene through Holocene: .
Georgia Geologic Survey Bulletin 104, 162p.
Scott, T.M., 1988a, The lithostratigraphy of the Hawthorn Group '
(Miocene) of Florida: Florida Geological Survey Bulletin 59,'
148p.


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