OPEN FILE REPORT NO. 80


 GEOLOGIC STRUCTURES
 The geologic structures (Figure 4) that have affected shallow Tertiary and Quaternary
sediments of the Florida Platform have been defined by numerous authors (Puri and Vernon,
1964; Miller, 1986; Scott, 1988; Scott, 1991). The majority of the structures recognized as
influencing the deposition, erosion and alteration of the Cenozoic sediments in Florida do not
appear to have had a significant effect on the surface expression of the lithostratigraphic units.
These geologic structures include the Gulf Basin, Jacksonville Basin, St. Johns Platform,
Sanford High, Brevard Platform, Osceola Low and the Okeechobee Basin (Scott, 1992). Those
structural features that exerted an influence on the surficial or very near surface distribution of
the Cenozoic sediments, or mark areas of significant facies changes, include the Gulf
Trough/Apalachicola Embayment, Chattahoochee "Anticline" and the Ocala Platform. Eocene
sediments crop out on the Chattahoochee Anticline and the Ocala Platform. The Gulf Trough/
Apalachicola Embayment formed an important bathymetric and environmental barrier from the
latest Eocene or earliest Oligocene into the Miocene. As a result, the Oligocene carbonate facies
east and south of the Gulf Trough/Apalachicola Embayment are distinctly different from those
occurring to the west and north (see Schmidt [1984] and Bryan [1991] for discussion).



 LITHOSTRATIGRAPHIC UNITS

 TERTIARY SYSTEM

 Eocene Series
 Middle Eocene Bartonian Stage

 Tap Avon Park Formation Middle Eocene carbonate sediments of peninsular Florida,
as originally described by Applin and Applin (1944), were subdivided, in ascending order, into
the Lake City Limestone and the Avon Park Limestone. Miller (1986) recommended combining
the Lake City Limestone with the Avon Park Limestone and, due to the common occurrence of
dolostone, referred to the unit as the Avon Park Formation. Carbonates of the Avon Park
Formation are the oldest sediments exposed in the state. The Avon Park Formation crops out in
a limited area in west-central peninsular Florida in Levy and Citrus Counties on the crest of the
Ocala Platform.
 The Avon Park Formation consists of cream to light-brown or tan, poorly indurated to
well indurated, variably fossiliferous, limestone (grainstone, packstone and wackestone, with
rare mudstone). These limestones are interbedded with tan to brown, very poorly indurated to
well indurated, very fine to medium crystalline, fossiliferous (molds and casts), vuggy
dolostones. The fossils present include mollusks, foraminifers, echinoids, algae and carbonized
plant remains. Molds and casts of gypsum crystals occur locally.
 The Avon Park Formation is part of the Floridan aquifer system (FAS). Parts of the
Avon Park Formation comprise important, subregional confining units within the FAS (Miller,
1986).