BULLETIN NO. 68


include Joyner and Sutcliff (1976), Upchurch
(1992), Kauffman and Herman (1993), Broska
and Knochenmus (1996) and Torres et al.
(2001). Knochenmus (2006) characterizes the
water quality and hydraulic heterogeneity of the
intermediate aquifer system in the southern part
of the District. The study underscores that
previously defined "permeable zones" of this
aquifer system are hydraulically similar to
"semi-confining units" in the upper Floridan
Aquifer System. A statewide hydrochemical
assessment of the surficial aquifer system was
completed by Upchurch (1992).

 Several groundwater flow models of the
SWFWMD region have been published (e.g.,
Ryder, 1985; Barcelo and Basso, 1993; Yobbi,
1996), most of which are discussed in the
comprehensive work of Sepulveda (2002),
wherein he developed a groundwater flow model
for peninsular Florida that includes the
Intermediate and Floridan aquifer systems.
Selected compilations of aquifer parameters on
which many of these models are based are
presented in Hydrogeological Properties, p. 52.


 Physical Setting
Geology

 Development of the Florida carbonate
platform primarily occurred during the Late
Cretaceous through middle Cenozoic and was
generally free of intermixed sands and clays.
Strong currents across northern Florida in a
feature broadly referred to as the Georgia
Channel System (Huddlestun, 1993) effectively
precluded transport and deposition of these
siliciclastics to the platform. During this period,
deposition of the Cedar Keys Formation,
Oldsmar Formation, Avon Park Formation,
Ocala Limestone, and the Suwannee Limestone
occurred. Huddleston (1993) proposed the
Georgia Channel System recognizing spatially
and temporally overlapping features (e.g.,
Suwannee Strait and Gulf Trough) proposed in
the literature that described paleotopography
(paleobathymetry) and associated paleocurrents.
Randazzo (1997) provides an overview of this


dynamic system and feature names.

 During the Oligocene, the southern
Appalachians experienced uplift and erosion
(Scott, 1988). Southward transport and
deposition of ensuing siliciclastic sediments
began to fill the channel system, which allowed
ocean currents to transport sediments southward
across the well-developed carbonate platform.
As a result, some of the first siliciclastic
sediments in southern Florida carbonates appear
as sand lenses in the Lower Oligocene
Suwannee Limestone south of Charlotte County
(Missimer, 2002). The influx of siliciclastic
sediments, mixing with locally-formed
carbonates led to Late Oligocene through the
Early Pliocene deposition of the Hawthorn
Group (Scott, 1988; Missimer et al., 1994)
throughout most of Florida. In much of
peninsular Florida phosphate deposition
occurred yielding many economic phosphorite
deposits. This period of phosphogenesis is
described by Riggs (1979a, 1979b) and
Compton et al. (1993); [see Bone Valley
Member, p. 48, for more detail]. During the
Late Pliocene to Recent, sediment deposition
became even more siliciclastic dominant. Shell
beds were deposited along coastal areas and
migrated in response to sea-level fluctuations.
The geology and depositional environment of
lithostratigraphic units in the region are the
subject of numerous studies in southwestern
Florida; results of which are presented in the
Il, ii~i,,g,,il,!h'y section, p. 30, of this report.
From deposition of the Cedar Keys Formation
through Pliocene-Pleistocene shell beds, a
dynamic transition from carbonate to
siliciclastic-dominated depositional environments
is reflected.

 The surface distribution of lithostratigraphic
units (Figure 2) in the study area is a function of
post-depositional influences ranging from
tectonic activity, platform stability, sea-level
changes and karst processes. For example, the
Avon Park Formation is the oldest exposed
lithostratigraphic unit in the study area (Figure
2). This Eocene unit gently dips southward
toward Charlotte County to depths exceeding
1500 ft (457.2 m) below land surface (BLS). In