FLORIDA GEOLOGICAL SURVEY


 Grainstones of the Ocala Limestone comprise
the most permeable zones in the UFA. Porosity
within the unit is generally moldic and
intergranular with occasional macrofossil molds.
Secondary porosity owing to carbonate
dissolution is extensive and has greatly
enhanced permeability, especially where
confining beds are breached or absent (Berndt et
al., 1998). Based on analyses of 70 samples,
total porosity of the Ocala Limestone averages
39.8 percent (median = 41.0 percent) and ranges
from 17.6 percent to 53.5 percent. Of the end-
member dolostone lithologies reported by
Gaswirth (2004), porosity of the induratedd"
type averages 24 percent (n=30) and the
"sucrosic" type averages 35 percent (n=28),
(Gaswirth et al., 2006).

 The Ocala Limestone occurs throughout the
study area except where locally removed by
erosion on the Ocala Platform in the
southeastern part of Levy County and
southwestern part of Marion County. In
southwestern Orange County and northwestern
Osceola County, the Ocala Limestone is also
absent possibly due to structural offset and
erosion. Miller (1986) proposes a graben-like
fault system striking along the Polk-Osceola
County boundary; however, data presented
herein does not confirm its presence. An area of
"locally absent" Ocala Limestone (Plate 39)
does, however, approximately coincide with
Miller's (1986) fault-bound area. The top of the
Ocala Limestone occurs at or near land surface
in the northern region (Figure 2) and deepens to
approximately -1275 ft (-388.6 m) MSL in the
southern region (Plate 39). The thickness of the
unit exceeds 400 ft (121.9 m) in Charlotte and
Highlands Counties (Plate 40). This
lithostratigraphic unit is generally thought to be
bound by unconformities (Braunstein et al.,
1988; Loizeaux, 1995).

 Two proposed structural features are
significant with regard to the Ocala Limestone.
A fault striking northwest in northwestern Polk
County is proposed by Carr and Alverson
(1959). Vernon (1951) and Stewart (1966)
present contour maps of the "Inglis" (i.e., basal
Ocala Limestone) suggesting local offset in the
same area with the shallower "Inglis" sediments
toward the northeast. This offset is consistent


with Carr and Alverson's (1959) proposed fault.
Although local thickness variations of the Ocala
Limestone in this area are generally consistent
with the proposed fault, the present study does
not have sufficient well control to confirm the
hypothesis. A fault proposed by Winston (1996)
that trends northwest across Charlotte Harbor
may be related to the deepening and thickening
of the Ocala Limestone in this area.

 Contact relationships between the Ocala
Limestone and Avon Park Formation are
discussed under Avon Park Formation, p. 31. In
the northern and central regions, the boundary
between the Ocala Limestone and the overlying
Suwannee Limestone is usually not difficult to
distinguish. Not only is the gamma-ray
character different (Figure 10), but the
uppermost Ocala Limestone is generally
"cleaner" (i.e., significantly less non-calcitic
material) finer-grained and more skeletal than
the overlying unit. In some cases, Ocala
Limestone lithoclasts are found at the base of the
Suwannee Limestone (Loizeaux, 1995).
Moreover, the fossil assemblage differs
significantly, with the disappearance of
Lepidocyclina ocalana and the appearance of
Fallotella sp. (Suwannee Limestone) shallower
in the section. There are, however, areas where
the two units are difficult to distinguish. The
transition from Ocala Limestone to Suwannee
Limestone can be gradational toward the south,
showing some evidence of interbedding and thus
a possible conformable contact. Moreover,
some areas contain basal Suwannee carbonates
that range from fine-grained grainstones to
mudstones, which can be difficult to distinguish
from the underlying, sometimes altered, chalky
mudstones and wackestones of the upper Ocala
Limestone. Torres et al. (2001) and Brewster-
Wingard et al. (1997) have also noted that the
boundary is often difficult to pinpoint and
suggest that foraminifera are often useful to
distinguish the units.

 Gamma-ray logs for the Ocala Limestone
consistently exhibit very low gamma-ray activity
(low, background-level count rates) and
relatively fewer peaks than the overlying and
underlying formations (Figure 10). In cases
where the Ocala Limestone is dolomitized, the