BULLETIN NO. 68


studied of these areas. Seismic surveys reveal
variations in depth to formations (i.e., relief of
unit surface) between -130 to -230 ft (39.6 m to
70.1 m) (Missimer and Gardner, 1976). Other
seismic profiles in the region also suggest
deformation (Evans and Hine, 1991; Lewelling
et al., 1998). Missimer and Maliva (2004)
propose that these deformed surfaces, some of
which extend more than a mile across, are
tectonically induced folds. On the other hand,
Wolansky et al. (1983), Evans and Hine (1991),
Lewelling et al. (1998) and Cunningham et al.
(2001) prefer the hypothesis that observed
perturbations in seismic reflectors are the result
of karstic processes rather than structurally or
tectonically related deformation.

Geomorphology

 The topography (Figure 5) and
geomorphology (Figure 6) of Florida have been
influenced by interactions of sea-level changes,
karst processes and subtle tectonic forces
(Rupert and Arthur, 1990; Schmidt, 1997). The
rate of Florida's carbonate platform deposition
was controlled by sea-level cycles and stand
durations, which produced different
physiographic features (e.g., Healy, 1975;
Randazzo, 1997).

 Prominent ridges formed in shallow-water
marine environments during sea-level high
stands. Paleo- water bodies, embayments,
swales, relict coastal features and streams
control where many present-day streams and
lakes are located (White, 1970, Randazzo.,
1997). Orthogonal patterns in modem drainage
systems within the southern part of the study
area may have been influenced by fractures
(Lewelling et al., 1998) formed in response to
peripheral Miocene-Pliocene stress fields
associated with Caribbean tectonics (Missimer
and Maliva, 2004).

Physiographic Provinces and Features

 Aerially extensive and distinctive
physiographic provinces in the study area are
summarized in this section, starting with the
coastal zone and working inland (Figure 6). The


coastline along the SWFWMD has been
classified into two zones (Tanner, 1960a,
1960b): 1) north of Pasco County the coastal
zone is dominated by swamps, salt marshes,
oyster reefs and drowned karst topography and
2) south of Pasco County, depositional marine
environments contributed to the formation of
barrier beaches, barrier islands, barrier spits and
over-wash fans.

 The Gulf Coastal Lowlands (White, 1970)
include the western extent of the SWFWMD,
ranging in width from less than 2 mi to
approximately 45 mi (3.2 km to -72 km).
Elevations range from sea-level to
approximately 100 ft (30.5 m) above mean sea
level (MSL). Diverse ecosystems are present
within the Gulf Coastal Lowlands including pine
flatwoods, dry prairies and to a lesser extent,
swamps, scrub and high pine and salt marshes
(Crumpacker, 1992). The Gulf Coastal
Lowlands do not coincide with any mappable
marine terrace and are generally characterized
by wide, flat marine karstic plains, including
paleo-dunes (White, 1970). Significant updates
and revisions to Florida's geomorphic
nomenclature are ongoing, with an emphasis on
geologic processes and framework geology
(Scott, 2004). Re-classification of the Gulf
Coastal Lowlands into the Chiefland Karst Plain,
Crystal River Karst Plain, and the Land 0'
Lakes Karst Plain is proposed (Scott, 2004).

 The Brooksville Ridge is a prominent upland
east of the Gulf Coastal Lowlands, striking
north-northwest discontinuously from Pasco to
Levy Counties. The total length is
approximately 110 mi (177 km) including the
inter-ridge Dunellon Gap (Figure 6). The Ridge
varies in width from approximately 4 to 10 mi
(6.4 to 16.1 km) (White, 1970). Elevations
along this upland range from approximately 70
to -300 ft (21.3 to 91.4 m) above MSL. Fine-
grained, low-permeability sediments within the
Brooksville Ridge, particularly Hawthorn Group
clays, reduce relative infiltration rates and
provide a chemical buffer that inhibits carbonate
dissolution. Areas without thick clay-rich
siliciclastic deposits, through geologic time, are
more vulnerable to a reduction in land surface
elevation. This process, known as topographic