BULLETIN NO. 68


general, the younger formations follow this
pattern, however, many are not observed
throughout the full extent of the study area (i.e.,
absence of the Peace River Formation
[Hawthorn Group] in the northern third of the
District). In the sections that follow, details of
the features and processes affecting the overall
geologic framework are discussed.

Structure

 Numerous structural features affect the
thickness and extent of geologic units in the
study area (Figure 3). The oldest known
"basement" feature in the region is the Bahamas
Fracture Zone (Klitgord et al., 1983), which is
also referred to as the Jay Fault (Pindell, 1985).
This zone bisects the Florida peninsula basement
from Tampa Bay southeast to the Lake Worth
area on the east coast. Lithologic and
geophysical data suggest that this basement
feature represents an Early Mesozoic transform
fault that was important to the development of
the Gulf of Mexico. Christenson (1990),
however, suggests that based on assessment of
more recently acquired borehole geology and
magnetic anomaly data, the feature represents a
Triassic-Jurassic extensional rift margin with
little to no lateral offset. He proposes the name
"Florida Lineament" to describe this feature,
which coincides with the Jay Fault and the
Bahamas Fracture Zone across peninsular
Florida (Christenson, 1990; see feature "A" in
Figure 3).

 The South Florida Basin (Applin and Applin,
1965; Winston, 1971) is a stratigraphic basin
that contributed to southward thickening of
Mesozoic and Early Cenozoic lithostratigraphic
units in the southern Florida peninsula (Figure
3). A possible successor basin, the younger
Okeechobee Basin (Riggs, 1979a) may have
contributed to south southeastward dipping of
Oligocene and older lithostratigraphic units
along the eastern margin of the study area
(Highlands and Glades Counties).

 The influence of "basement" structures on
Cenozoic and younger stratigraphic units is
poorly understood. For example, an apparent
southeast plunging syncline ("B" in Figure 3)


trends from Sarasota to Hendry Counties in the
"sub-Zuni" (i.e., pre-Middle Jurassic) map
presented in Barnett (1975). Shallower
northwest-striking faults reported by Winston
(1996) occur in the same region. Maps of the
structural surface of Eocene rocks (Miller, 1986)
indicate a generally south-plunging trough
extending from central Charlotte County.
Deepening and thickening of units in the
Charlotte County region are observed in the
present study (see Il lthmiting, ,lhy, p. 30). The
Early Cretaceous "Broward Syncline" (Applin
and Appin, 1965; "C" in Figure 3) is located
approximately 20 mi (32 km) to the east of
feature "B" and has a generally parallel strike.
These inferred faults and basement relationships
warrant further study, especially given their
potential role in water quality and distribution of
permeable zones. Knowledge of the distribution
of low-permeability sediments beneath the FAS
is also important as potential sites for CO2
sequestration are explored.

 The Ocala Platform ("D" in Figure 3) is the
most dominant feature in the central peninsular
region. Evidence of this platform is apparent in
the geologic map (Figure 2) where the Eocene
Avon Park Formation (Tap) and Ocala
Limestone (To) are exposed at or near land
surface. This feature is also evident in the
Environmental Geology composite map (Figure
4), which reflects lithologic and sediment types
within 10 ft (3.1 m) of land surface. Shallow or
exposed carbonate rocks in Levy, Marion, Citrus
and Sumter Counties reflect the influence of the
platform. This structure is not thought to be an
uplift (Winston, 1976) but rather a tectonically
stable area on which disconformable marine
sedimentation and differential subsidence has
occurred (Scott, 2001). It is also a major
controlling factor in the thickness and extent of
lithostratigraphic units in central and
southwestern Florida. As a result, this feature
also has a very significant effect on the
distribution of regional aquifer systems.

 Remaining structural features are discussed
in this section from north to south. Several
northwest-trending faults, as well as orthogonal
fracture traces (or lineaments), have been
proposed within the Levy and Citrus County
area by Vernon (1951). It is possible that some