OPEN FILE REPORT NO. 80


except that the Tampa Member contains noticeably less phosphate (Scott, 1988). The limestone
in the Tampa is white to yellowish gray, fossiliferous and variably sandy and clayey mudstone,
wackestone and packstone with minor to no phosphate grains. Sand and clay beds are like those
in the undifferentiated Arcadia Formation. Mollusks and corals are common in the Tampa
Member as molds and casts, silicified pseudomorphs and original shell material. The Tampa
Member and the lower part of the Arcadia Formation form the upper part of the Floridan aquifer
system (FAS) in parts of southern Florida (Miller, 1986; Scott, 1991).

PANHANDLE

 Upper Oligocene sediments are not known to crop out in the Florida panhandle. The
Chickasawhay Formation of Alabama has been traced in the subsurface into the central
panhandle but is not exposed on the Chattahoochee Anticline (Miller, 1986).

 Miocene Series
 Lower Miocene to Upper Miocene Aquitanian to Messinian Stage

 Sediments of the Miocene Series have been the focus of numerous investigations due to
their complex nature and widespread occurrence in Florida (see Schmidt and Clark [1980],
Huddlestun [1988] and Scott [1988] for a review of previous investigations). The Miocene
sediments consist of siliciclastics, carbonates and mixed siliciclastic-carbonate lithologies with
numerous lateral and vertical facies changes. Exposures are limited and most investigations
dealt with these sediments in the subsurface.
 Miocene sediments crop out or occur in the shallow subsurface on the northwestern flank
of the Ocala Platform in the eastern panhandle to the flanks of the Chattahoochee "Anticline" in
the central panhandle then into the western panhandle to Okaloosa County. In the peninsula, the
Miocene sediments crop out or are in the shallow subsurface from the northern flank of the
Ocala Platform in Hamilton, Columbia and Baker Counties southward to Charlotte County.
Some of the most beautiful landscapes in the State occur where the Miocene sediments are
exposed, eroded and often affected by karstification of underlying Paleogene carbonates.
 The importance of the Miocene sediments in Florida is twofold first, these sediments
contain valuable mineral resources, primarily phosphate and adsorptive clays; and, second, the
Miocene sediments comprise the intermediate confining unit and aquifer system. Whereas the
principle geological hazard associated with Paleogene carbonates is karst development, the
hazards associated with the Miocene sediments are radon gas and swelling clays.
 Significant changes in age determinations or interpretations have occurred for the
sediments traditionally considered as Miocene in the peninsula. Puri and Vernon (1964)
recognized a simple three-fold subdivision of the Miocene in peninsular Florida. Their
subdivision of the Miocene was that all Lower Miocene sediments were St. Marks Formation
(Tampa [Note that they used Tampa as a stage name so all sediments that had been called Tampa
were placed in the St. Marks Formation statewide]), Middle Miocene sediments were Hawthorn
Formation and Upper Miocene sediments were Tamiami Formation. Poag (1972) placed the
lower portion of the Chattahochee Formation in the Upper Oligocene. Currently, geologists
recognize that the Hawthorn Group spans from the mid-Oligocene to Early Pliocene (Brewster-