FLORIDA GEOLOGICAL SURVEY


personal communication, 2004), geophysical
and lithologic evidence indicate that most of the
MFCU surface (Plate 59) correlates with the
middle to lower carbonates of the Avon Park
Formation. In parts of Marion, Osceola and
Pinellas Counties, however, the MFCU occurs in
the upper third of the unit. In the southern
region, a shallower discontinuous MFCU unit
occurs within the middle to upper part of the
formation (Plate 59). The relation between the
Avon Park Formation and the MFCU in east-
central part of the study area (i.e., the vicinity of
southeastern Polk County; Plate 59) requires
further data and research.

 The Avon Park Formation was deposited
within a broad, distally steepened carbonate
platform (Budd, 2002). The deposition is
characterized by peritidal carbonate sediments
that may be significantly dolomitized. Highly
cyclical deposits in supratidal to shallow
subtidal environments are represented in the
vertical sediment sequence (Randazzo et al.,
1990; Budd, 2002). The sediments reflect
repeated short-term changes in relative sea level
throughout Middle Eocene deposition
documenting transgressive, regressive and open
marine to shoreline cycles (Randazzo et al.,
1990). Some researchers propose that
dolomitization within the Avon Park Formation
took place during or proximal in time to
deposition (e.g., Randazzo and Hickey, 1978;
Cander, 1994). Miller (1986) suggests that thin
evaporite beds deposited during the Middle
Eocene may have been formed in a tidal flat or
sabkha environment.

 Ocala Limestone

 The Upper Eocene Ocala Limestone was first
named by Dall and Harris (1892). Puri (1953)
later proposed three separate formations: the
Inglis, Williston and Crystal River Formations,
which were based upon distinct faunal
assemblages. In 1953, Puri elevated the
sequence to Group status. Miller (1986) noted
that these formations were neither easily
recognizable nor mappable and therefore applied
the name Ocala Limestone; however, he
acknowledged that a two-fold division (upper


and lower Ocala Limestone) proposed by Applin
and Applin (1944) was still in use. Recognizing
the biostratigraphic basis of the division on
which the Ocala Group was based, Scott (1991)
identified the Ocala Limestone as a formation in
accordance with the North American
Stratigraphic Code. Despite this rather complex
history in nomenclature leading to recognition of
the unit as a single formation, upper and lower
Ocala Limestone lithologies are generally
recognized.

 The lower Ocala Limestone varies from
white to light gray and is variably indurated,
ranging from a packstone to a grainstone.
Where present, dolomite content increases with
depth in the Ocala Limestone, especially in the
southwestern part of the study area where the
base of the unit is often dolomitized (see Avon
Park Formation, p. 31, for more details).
Gaswirth (2004) also noted this pattern and
documented textural end-members within these
dolostones: 1) friable, light to medium brown,
sucrosic and 2) indurated, dark gray to dark
brown, dense, crystalline. The upper part of the
Ocala Limestone varies from white to light
orange and tends to be more mud-supported
(i.e., mudstone to wackestone) and chalky.

 Mineralogy of the Ocala Limestone unit is
predominantly calcite, and to a lesser extent,
dolomite. Siliciclastics are rare; however, chert
occurs throughout the formation and is generally
more common where the unit occurs at or near
land surface. Trace amounts of organic and
clay (Green et al., 1995) likely represent post-
depositional infilling. Pyrite is also present as a
trace mineral, but to a lesser extent than the
overlying Suwannee Limestone or underlying
Avon Park Formation. Sedimentary structures
in the Ocala Limestone include cross bedding,
fine laminations and bioturbation. The latter is
dominant at the base of the unit in the form of
burrows (Loizeaux, 1995). The Ocala
Limestone has a diverse fossil assemblage
(Figure 13), including Lepidocyclina sp.,
Nummulites (Operculinoides) sp., milliolids,
bryozoans, gastropods, mollusks, pelecypods,
echinoids (e.g., Eupatagus antillarum) and
Rotularia (Spirolina) vernoni.