FLORIDA GEOLOGICAL SURVEY


Oligocene Series
 Suwannee Limestone

 The Lower Oligocene Suwannee Limestone (Ts), named by Cooke and Mansfield (1936)
for exposures of limestone along the Suwannee River from White Springs to Ellaville,
unconformably overlies the Ocala Limestone throughout the study area. It is exposed in the bed
of the Wacissa River from just below the headwaters of the river to the confluence of the Aucilla
River just above Nutall Rise (Yon, 1966). Numerous additional exposures of the Suwannee
Limestone also occur within the southern one-third of the map area (see OFMS 99-01). The
Suwannee Limestone is primarily a white to cream, poorly- to well-indurated packstone to
grainstone comprised of foraminifera, miliolid tests, pelecypods, gastropods and echinoids. The
echinoid Rhyncholampas gouldii, an index fossil for the Suwannee Limestone, is commonly seen
in outcrops. The lithology is variably recrystallized and may range from poorly-indurated,
friable limestone to well-indurated limestone cemented by calcite spar. Dolomitization of the
Suwannee Limestone is common in the area, particularly in the vicinity of the Aucilla River. The
Suwannee Limestone forms the bottom of the Gulf of Mexico offshore of the study area (Yon,
1966). Silicified residual boulders of the Suwannee Limestone ("float") are commonly found in
the south-central to southeastern portion of the study area, indicating that it was once thicker than
wells indicate (OFMS 99-01).
 The top of the Suwannee Limestone ranges from 84 feet (25.6 meters) above MSL in W-
6925 (cross section B-B' on OFMS 99-02) to 63 feet (19.2 meters) below MSL in W-6906 (cross
section E-E' on OFMS 99-02). The Suwannee Limestone ranges in thickness from
approximately 27 feet (8.2 meters) in W-15930 (cross section G-G' on OFMS 99-02) to 113 feet
(34.4 meters) in W-18841 (cross sections B-B' and G-G' on OFMS 99-02).
 The unit is unconformably overlain by sediments of the Miocene Hawthorn Group,
Torreya Formation (Tht) in the northern portion of the study area, sediments of the St. Marks
Formation (Tsmk) in the west-central portion of the study area, and undifferentiated Quaternary
sediments (Qu) throughout the middle portions of the study area. The Suwannee Limestone
forms part of the FAS (Southeastern Geological Society Ad Hoc Committee on Florida
Hydrostratigraphic Unit Definition, 1986).

Miocene Series

 St. Marks Formation

 The Lower Miocene St. Marks Formation (Tsmk), named by Finch (1823), is exposed
west of the study area in Wakulla, Leon and western Jefferson Counties along the northwestern
flank of the Ocala Platform (Scott, 2001). The St. Marks Formation, which unconformably
overlies the Suwannee Limestone, was only recognized in a few wells within the northwestern
region of the study area (see cross sections A-A', B-B' and E-E' on OFMS 99-02) and no
outcrops of the formation were observed within the study area. The St. Marks Formation is a
white to yellowish-gray, poorly- to moderately-indurated, quartz sandy, fossiliferous limestone
(packstone to wackestone). Mollusk molds and casts are common and may be abundant.
Common foraminifera present in the St. Marks Formation include Sorites sp. and Archaias
floridana.