FLORIDA GEOLOGICAL SURVEY


undifferentiated Lower Oligocene sediments. The Lower Oligocene carbonates form important
parts of the upper FAS (Miller, 1986).

 Tro Residuum on Oligocene sediments The undifferentiated Oligocene residuum,
mapped on parts of the Chattahoochee "Anticline", characteristically consists of reddish brown,
variably sandy clay with inclusions of variably fossiliferous, silicified limestone (Huddlestun,
1993). The residuum includes Lower and Upper Oligocene weathered sediments (Huddlestun,
1993).

 Oligocene Miocene Series
 Upper Oligocene Middle Miocene Chattian Serravalian Stage

PENINSULA

Lower Hawthorn Group
 Recent investigations into the Oligocene of southern Florida documented the existence of
a thick (>330 feet [100 meters]) Upper Oligocene section previously considered Miocene (Scott
et al., 1994; Missimer and Scott, 1995; Brewster-Wingard et al., 1997). The Arcadia Formation,
Hawthorn Group, previously thought to be predominantly Early Miocene (Scott, 1988), is now
known to be late Early Oligocene to Middle Miocene (Brewster-Wingard et al., 1997; Missimer,
1997). The Tampa Limestone (or Formation of previous usage [Puri and Vernon, 1964]) is a
member of the Arcadia Formation, Hawthorn Group (Scott, 1988). The Tampa Member's
previous age assignment was latest Oligocene to Early Miocene (Scott, 1988). Brewster-
Wingard et al. (1997) recognized the Tampa Member as being Late Oligocene to Early Miocene.

 Tha Hawthorn Group, Arcadia Formation The undifferentiated Arcadia Formation
and the Tampa Member crop out on the southwestern flank of the Ocala Platform from Pasco
County southward to Sarasota County. Although ages of the outcropping sediments have not
been accurately determined, stratigraphic position suggests that the Upper Oligocene parts of the
Arcadia Formation and Tampa Member are exposed in this region, particularly from
Hillsborough County northward to Pasco County.
 The Arcadia Formation, named by Scott (1988), is predominantly a carbonate unit with a
variable siliciclastic component, including thin beds of siliciclastics. Within the outcrop area,
the Arcadia Formation, with the exception of the Tampa Member, is composed of yellowish gray
to light olive gray to light brown, micro to finely crystalline, variably sandy, clayey, and
phosphatic, fossiliferous limestones and dolostones. Thin beds of sand and clay are common.
The sands are yellowish gray, very fine to medium grained, poorly to moderately indurated,
clayey, dolomitic and phosphatic. The clays are yellowish gray to light olive gray, poorly to
moderately indurated, sandy, silty, phosphatic and dolomitic. Molds and casts of mollusks are
common in the dolostones. Silicified carbonates and opalized claystone are found in the Arcadia
Formation.

 That Arcadia Formation, Tampa Member The Tampa Member consists predominantly
of limestone with subordinate dolostone, sand and clay (Scott, 1988). The lithology of the
Tampa Member is very similar to that of the subsurface limestone part of the Arcadia Formation