Geohydrologic model of the Floridan aquifer in the southwest Florida water management district

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Geohydrologic model of the Floridan aquifer in the southwest Florida water management district
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Florida Water Resources Research Center Publication Number 46
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Randazzo, Anthony F.
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University of Florida
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Notes

Abstract:
Nineteen cores from the northern portion of the Southwest Florida Water Management District and three counties adjacent to it were analyzed by megascopic, microscopic, xray diffraction, and atomic absorption spectrometry techniques for the determination of lithofacies, paleontology, mineralogy, and geochemistry. These wells penetrate biozones representative of the "Tampa", Suwannee, Ocala, Avon Park, and Lake City Formations. The Avon Park and Lake City Formations are characterized by interbedded massive, fossiliferous carbonate (limestone and dolomite) rocks (wackestone to grainstone) and thinly bedded peloidal and carbonaceous rocks (mudstone and wackestone). These represent subtidal (open marine and lagoonal), intertidal, and supratidal deposition. The Ocala Limestone is characterized by thickly bedded, fossiliferous limestone (mostly packstone and grainstone), representing subtidal and some intertidal depositional environments. The Suwannee Limestone consists of interbedded fossiliferous, partly dolomitized carbonate rocks (mudstone to grainstone) and an algal boundstone facies. These Suwannee deposits represent subtidal, intertidal and supratidal sedimentation. The "Tampa" Formation represents deposition in shallower marine waters and contains substantial quantities of clay and quartz and phosphatic sand, interbedded with carbonate rocks (mudstone to packstone). Numerous depositional cycles were recognized by cyclic occurrences of rock types and depositional environments. A wide range of diagenetic fabrics from early to late stages of development occur. Fabrics are classified descriptively as equigranular (uni-modal) or inequigranular (multi-modal). Fabrics composed of crystals <0.002mm in diameter (unresolvable) are termed aphanotopic. Equigranular fabrics include sutured mosaic and sieve mosaic fabrics, and a somewhat problematic peloidal fabric. Inequigranular fabrics include porphyrotopic, poikilotopic, fogged mosaic and spotted mosaic fabrics. Two processes of dolomitization are suggested: homogeneous dolomitization resulting in single-stage development of microtextured (groundmass crystals <0.016mm in diameter) aphanotopic, peloidal and mosaic fabrics; and heterogeneous dolomitization resulting in multi-stage development of porphyrotopic and some mosaic fabrics. The pattern of crystallization fabric distribution appears to be related to sedimentologically defined depositional cycles. Undolomitized rocks generally have high visible porosity, consisting mostly of interparticle and intraparticle pores. Dolomites have variable amounts of visible porosity, consisting mostly of moldic and vug pores, and the type of porosity can be related to the type of crystallization fabric. Greatest total porosity is found in cavernous zones associated with formational contacts. The distribution of Na+ and Sr2+ ions and mole-percent-MgCO3 in carbonate rocks of the Floridan Aquifer supports a mixing zone model of diagenetic dolomitization. The inland phreatic zone consists of brackish solutions in the Floridan Aquifer. A coastal mixing zone exists at the salt/fresh water interface, but the flow patterns of the Floridan Aquifer can modify the three dimensional shape of this interface. Areas of locally high discharge, such as artesian springs, move the interface seaward. Variations in sea level and fluctuations of the phreatic zone related to climatic and tectonic changes could cause the dolomitizing solutions to contact large volumes of rock through time, resulting in the thick sequences of dolomite in the Floridan Aquifer. The Na+ content of carbonate rocks is an approximate indicator of the salinity of the latest diagenetic solution. Sodium concentrations of the calcites are 37-970 ppm, indicating a slightly saline diagenetic fluid. Dolomite has 281-1963 ppm Na+ and was formed in a slightly more saline solution. Strontium concentrations of carbonate rocks reflect the salinity of the latest diagenetic fluid and the diagenetic mineralogy. The Sr2+ concentration range of the calcites is 89-968 ppm, demonstrating diagenesis in a slightly saline solution, probably in an open system. The average Sr2+ content of the dolomites is approximately 59% of that in the calcites, indicating a more saline diagenetic environment for dolomite than calcite. The more nearly stoichiometric dolomite generally has a narrower range of Sr2+ concentrations than non-stoichiometric dolomite indicating a more saline diagenetic environment for the non-stoichiometric dolomite where a greater number of competing ions inhibit dolomite ordering. The formation of dolomite and its influence on rock texture and porosity are directly related to past and present hydrologic regimes interacting with aquifer limestones.

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Publication No. 46


GEOHYDROLOGIC MODEL OF THE FLORIDAN AQUIFER IN THE
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT


By


Anthony F. Randazzo
(Principal Investigator)


Department of Geology
University of Florida
Gainesville


- ., '-
* .-,. .. .


d~ *











GEOHYDROLOGIC IODEL OF THE FLORIDAN AQUIFER IN THE
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT


By




Anthony F. Randazzo


Publication No. 46



FLORIDA WATER RESOURCES RESEARCH CENTER




RESEARCH PROJECT TECHNICAL COMPLETION REPORT


CWRT Project Number B-032-FLA




Matching Grant Agreement Number



14-34-0001-7148




Report Submitted: January 7, 1980





The work upon which this report is based was supported in part
by funds provided by the United States Department of the
Interior, Office of Water Research and Technology
as authorized under the Water Resources
Research Act of 1964 as amended








TABLE OF CONTENTS

Abstract .............................................. iv

Introduction .......................................... 1

Methods of Study.................................... 1

Previous Work .................................... 3

Manatee Springs and Homosassa Springs................... 4

Stratigraphy ..................................... 4

Sedimentology-Lithofacies ........................ 4

Cyclic Sedimentation ........................ 10
Depositional Environments.................... 10

Diagenesis ....................................... 12

Crystallization Texture and Fabric
Classification............................... 12
Porosity..................................... 16
Fabric Selectivity of Dolomitization........ 24
Summary.......... ............................ 32

Romp Cores ............................................ 33

Avon Park Formation .............................. 33

Cyclicity.................................... 33
Recognition of Depositional Environments
in Avon Park Strata ......................... 37
General Lithology ........................... 38
Depositional Facies ......................... 43

Ocala Limestone................................... 44

Lower Ocala Limestone ....................... 44
Upper Ocala Limestone ....................... 45

Ballast Point, Brandon, and Duette Cores .............. 47

Stratigraphy ..................................... 48

Stratigraphic Interpretation ................ 48

Diagenesis ....................................... 52

Geochemistry .......................................... 58

Importance of Sodium.............................60

Sodium in Calcite. ........................... 62
Sodium in Dolomite........................... 62

ii










Importance of Strontium ........................... 66

Strontium in Calcite ......................... 66
Strontium in Dolomite ........................ 67

Strontium and Sodium in Relation to
Mole-Percent-MgCO3................................. 67

Calcite ...................................... 68
Dolomite ..................................... 69

Summary ................................................70

References Cited ....................................... 74












































iii








ABSTRACT


Nineteen cores from the northern portion of the South-
west Florida Water Management District and three counties
adjacent to it were analyzed by megascopic, microscopic, X-
ray diffraction, and atomic absorption spectrometry techniques
for the determination of lithofacies, paleontology, mineralogy,
and geochemistry. These wells penetrate biozones representative
of the "Tampa", Suwannee, Ocala, Avon Park, and Lake City
Formations. The Avon Park and Lake City Formations are
characterized by interbedded massive, fossiliferous carbonate
(limestone and dolomite) rocks (wackestone to grainstone)
and thinly bedded peloidal and carbonaceous rocks (mudstone
and wackestone). These represent subtidal (open marine and
lagoonal), intertidal, and supratidal deposition. The Ocala
Limestone is characterized by thickly bedded, fossiliferous
limestone (mostly packstone and grainstone), representing
subtidal and some intertidal depositional environments. The
Suwannee Limestone consists of interbedded fossiliferous,
partly dolomitized carbonate rocks (mudstone to grainstone)
and an algal boundstone facies. These Suwannee deposits
represent subtidal, intertidal and supratidal sedimentation.
The "Tampa" Formation represents deposition in shallower
marine waters and contains substantial quantities of clay
and quartz and phosphatic sand, interbedded with carbonate
rocks (mudstone to packstone). Numerous depositional cycles
were recognized by cyclic occurrences of rock types and
depositional environments.

A wide range of diagenetic fabrics from early to late
stages of development occur. Fabrics are classified descriptively
as equigranular (uni-modal) or inequigranular (multi-modal).
Fabrics composed of crystals <0.002mm in diameter (unresolvable)
are termed aphanotopic. Equigranular fabrics include sutured
mosaic and sieve mosaic fabrics, and a somewhat problematic
peloidal fabric. Inequigranular fabrics include porphyrotopic,
poikilotopic, fogged mosaic and spotted mosaic fabrics. Two
processes of dolomitization are suggested: homogeneous dolo-
mitization resulting in single-stage development of micro-
textured (groundmass crystals <0.016mm in diameter) aphanotopic,
peloidal and mosaic fabrics; and heterogeneous dolomitization
resulting in multi-stage development of porphyrotopic and some
mosaic fabrics. The pattern of crystallization fabric distri-
bution appears to be related to sedimentologically defined
depositional cycles.

Undolomitized rocks generally have high visible porosity,
consisting mostly of interparticle and intraparticle pores.
Dolomites have variable amounts of visible porosity, consisting
mostly of moldic and vug pores, and the type of porosity can be
related to the type of crystallization fabric. Greatest total
porosity is found in cavernous zones associated with formational
contacts.








The distribution of Na+ and Sr2+ ions and mole-percent-
MgCO3 in carbonate rocks of the Floridan Aquifer supports a
mixing zone model of diagenetic dolomitization. The inland
phreatic zone consists of brackish solutions in the Floridan
Aquifer. A coastal mixing zone exists at the salt/fresh
water interface, but the flow patterns of the Floridan Aquifer
can modify the three dimensional shape of this interface. Areas
of locally high discharge, such as artesian springs, move the
interface seaward. Variations in sea level and fluctuations
of the phreatic zone related to climatic and tectonic changes
could cause the dolomitizing solutions to contact large volumes
of rock through time, resulting in the thick sequences of
dolomite in the Floridan Aquifer.

The Na+ content of carbonate rocks is an approximate
indicator of the salinity of the latest diagenetic solution.
Sodium concentrations of the calcites are 37-970 ppm, indicating
a slightly saline diagenetic fluid. Dolomite has 281-1963 ppm
Na+ and was formed in a slightly more saline solution.

Strontium concentrations of carbonate rocks reflect the
salinity of the latest diagenetic fluid and the diagenetic
mineralogy. The Sr2+ concentration range of the calcites is
89-968 ppm, demonstrating diagenesis in a slightly saline
solution, probably in an open system. The average Sr2+ content
of the dolomites is approximately 59% of that in the calcites,
indicating a more saline diagenetic environment for dolomite
than calcite.

The more nearly stoichiometric dolomite generally has a
narrower range of Sr2+ concentrations than non-stoichiometric
dolomite indicating a more saline diagenetic environment for
the non-stoichiometric dolomite where a greater number of
competing ions inhibit dolomite ordering.

The formation of dolomite and its influence on rock texture
and porosity are directly related to past and present hydrologic
regimes interacting with aquifer limestones.








INTRODUCTION


The Floridan Aquifer represents one of the world's
finest aquifer systems and is relied upon as Florida's
principal supply of fresh water. Detailed geologic knowledge
of the Tertiary limestones comprising the aquifer is only
now beginning to be compiled. Identification of the type
and distribution of minerals, the arrangement, character and
quantity of lithologic constituents,and the correlation of
stratigraphic horizons would aid greatly our understanding
of groundwater flow systems. The inaccuracies and uncertainties
of our geologic knowledge of the Floridan Aquifer could be
resolved by establishing a petrogrphic and geohydrologic
model. Such a model would demonstrate the lithologic evolution
of the aquifer and would be of fundamental importance in
water management practices.

This research effort was concentrated in the northern
portion of the Southwest Florida Water Management District
where drill-cored materials were most available for study
(Figure 1). The principal stratigraphic formations studied
were the Lake City, Avon Park, Ocala, Suwannee, and "Tampa"
units. Rocks from this area were compared with those studied
in an earlier investigation (Randazzo, 1976b).

The petrologic characteristics of the Floridan Aquifer
in the current study area have been described. The original
depositional environments of the rocks were deduced and the
effects of diagenesis have been recognized. Results have
been applied to the clarification of stratigraphic problems.
Geochemical analyses of the rocks have revealed the history
of water/rock interactions. A better understanding of how
porosity evolved has been achieved. Petrologic and geochemical
parameters which control the functioning of hydrologic
systems have been evaluated and may be useful in the prediction
or deduction of future aquifer changes.

Methods of Study

In this study nineteen cored sections were examined
from the northern portion of the Southwest Florida Water
Management District and three counties adjacent to it (Figure
1). Numerous samples were also taken from quarries in the
area. More than 1,000 thin sections were prepared and
analyzed to determine the constituents of the rocks and the
diagenetic changes that have occurred. The composition of
the rocks was determined by point counting with approximately
250-300 point counts made on each thin section.

Mineralogy was determined by X-ray diffraction analysis.
Where calcite and dolomite were present in the same sample,
a thin section of that sample was stained (Friedman, 1959)
to determine which constituents of that rock were of calcite














*MS


LEVY


*GH


MARION
*CP


PINELLAS


GH REPRESENTS 8
CLOSELY SPACED CORES


0 25 50 km

SCALE


Figure 1. Index map of the study area showing core locations (B = Bell,
MS= Manatee Springs, GH = Gulf Hammock, LE = Levy County-ROMP #124,
RS = Rainbow Springs, CP = Cotton Plant, HS= Homosassa Springs,
H = Hernando County-ROMP #107, LA = Lake County-ROMP #101, BP = Ballast
Point, BR = Brandon, D = Duette).








and which were dolomite. Alazarin red-S in a solution of
NaOH was used to distinguish dolomite from calcite. The
scanning electron microscope was also employed for minute
textural studies and the determination of Mg/Ca ratios of
selected allochemical constituents. Atomic absorption
spectrometry was used for strontium and sodium detection
and quantification. Mole-percent MgCO3 of calcite and dolomite
were calculated from data obtained by X-ray diffraction and
atomic absorption spectrometry. The rock classification
used herein is that proposed by Folk (1962). Grain-supported
and matrix-supported distinctions have been made and the
classification scheme of Dunham (1962) is used where appro-
priate.

Previous Work

The petrology and depositional environments of the
carbonate units comprising the Floridan Aquifer have only
recently been investigated. The broadly defined works of
Vernon (1951) and Chen (1965) have been utilized in an
attempt to relate modern carbonate shoreline processes to
the sedimentologic environment represented (Randazzo and
Saroop, 1976; Randazzo et al., 1977). Several studies have
been concerned with the nature and diagenetic alteration of
carbonate rocks (Bricker, 1971; Purser, 1973; Folk, 1974;
Folk and Land, 1975; Veizer et al., 1977). The geochemical
history and characteristics of these rocks and their re-
lationship to hydrologic conditions have been addressed by
Randazzo (1976b) and Randazzo and Hickey (1978).

The oldest exposed rocks in Florida are Late Middle
Eocene (Avon Park Formation). These rocks crop out on the
crest of the Ocala Arch and are surrounded by rocks of Late
Eocene age (Ocala Limestone) which occur on the flanks of
the arch. These formations are the principal units composing
the Floridan Aquifer. The Suwannee Limestone of Oligocene
age, often exposed at the surface, is an important part of the
aquifer in certain areas of Florida. The Lake City Formation
of Middle Eocene age occurs only in the subsurface but is also
a significant component of the Floridan Aquifer.

This investigation involved a number of graduate students
who made noteworthy contributions to the total research effort.
The reader is directed to the works of Saroop (1974), Stone (1975),
Hickey (1976), Liu (1978), Zachos (1978), and Fenk (1979) for
elaborate details on the lithologic and paleontologic charac-
teristics of the various lithofacies recognized. Hickey (1976),
Sarver (1978), Zachos (1978), and Metrin (1979) discussed the
diagenetic and geochemical aspects of the important carbonate
rock-forming minerals, calcite and dolomite. Our combined
efforts have resulted in the verification of a model of dolomiti-
zation by groundwater in the peninsula of Florida as postulated
by Hanshaw et al.,(1971). Some of the results of our studies
are summarized in a number of recent publications (Randazzo and
Saroop, 1976; Randazzo, 1976a; and Randazzo and Hickey, 1978).
References to other important contributions regarding strati-
graphy, petrology, geochemistry and hydrology are presented in
later sections of this report.









MANATEE SPRINGS AND HOMOSASSA SPRINGS


Stratigraphy

Rock cores were drilled at Manatee Springs (MS) and
Homosassa Springs (HS) by the Florida Bureau of Geology.
The oldest of the three formations penetrated in these wells
is the Lake City Formation which is recognized by the following
combination of features: presence of highly carbonaceous
beds; clay beds; common quartz; glauconite and gypsum; and
by poikilotopic fabric seen in thin section. Fabularia
matleyi, Archaias columbiensis, and Dictyoconus americanus
occur together 14.68m above the top of the Lake City in the
MS core, and F. matleyi and A. columbiensis occur together
22.56m below the top in the HS core. Dictyoconus americanus
has not been positively identified in the HS well. Two
distinct depositional cycles are recognized in the Lake City
Formation in the study material.

The Avon Park Formation overlies the Lake City For-
mation in both wells. The top of the Avon Park is deter-
mined by the first occurrence downward of a mudrock litho-
facies which corresponds with the first occurrence of
dolomite. The top is also marked by cavernous porosity;
increased amounts of quartz, gypsum, and metallic sulfides;
by poikilotopic fabric seen in thin section; and by the
first occurrence of Dictyoconus cookei in both cores. Five
distinct depositional cycles are differentiated in the Avon
Park represented by the study material.

The Avon Park Formation is overlain by the Ocala Lime-
stone. The Ocala Limestone has been biostratigraphically
zoned by many authors using many different taxonomic groups
and types of zones. A comparison of various zonations is
shown in Table 1.

Both wells enter the Ocala Limestone at an erosional
unconformity with overlying Pleistocene or Holocene sands
and do not represent the entire formation. Problems concerning
recognition of the top of the entire unit will not be considered
here (see Hunter, 1976). The Ocala Limestone is represented
by one depositional cycle.

Sedimentology- Lithofacies

Rocks of the MS and HS cores can be divided into four
major lithofacies (Table 2). Mudrocks [represented by mudstone
(Dunham, 1962)] have grain contents of less than 10%, and for
the most part contain less than 5% grains. Rocks with 10% or
more grains [represented by wackestone, packstone and grainstone
(Dunham, 1962)] are divided here on the basis of grain type.
Skeletal grains (Leighton and Pendexter, 1962) and peloids
(McKee and Gutschick, 1969) make up the most significant grains
volumetrically (Figure 2) and the variation in their ratios can
be used to differentiate most of the rocks. A few samples contain









Table 1. Ocala biofacies.


McCullough (1969)
Puri (1957) Cheetham (1963) Nicol & Shaak (1973) Zachos & Shaak (1978)
Williams et al. (1977)
Lepidocyclina chaperi Spondylus dumosus
faunizone faunizone


Asterocyclina-Spirulaea
vernoni faunizone

Nummulites vanderstoki
(=Camerina willcoxi)-
Hemicythere faunizone

Lepidocyclina-Pseudophragmina
faunizone

Spiroloculina newberryensis
faunizone

Operculinoides moodybranchensis
(=Camerina willcoxi)
faunizone

Operculinoides jacksonensis
(=Camerina willcoxi)
faunizone


4


Periarchus lyelli floridanus-
Plectofrondicularia?
inglisiana faunizone


Floridina antique
faunizone


Tubucellaria nodifera
faunizone


Periarchus lyelli
fauni zone


Spirulaea vernoni
biozone

Amusium ocalanum
biozone


Exputens ocalensis
biozone


01igovgjys wetherbyi
biozone

Concurrent range zone


Oligopygus haldemani
biozone


Concurrent range zone

01igopygus phelani
biozone































Table 2. Lithofacies terminology.


Dunham Mudstone Wackestone, Packstone, Grainstone
(1962)

<10% Grains 10% Grains


75% Other Grains >75% Other Grains


0-
^ Skeletal/Peloidal Grain Ratio
<1 >1


Lithofacies Mudrock Peloidal Rock Skeletal Rock Characterized yt
Term ocMajor Constituent










% Other Grains


25


75


0


Peloidal
Rocks


75


50


Skeletal
Rocks


25


100-
100


Figure 2. Distribution of grain types in the MS and HS cores.


% Peloidal 100
Grains 0


% Skeletal
Graihs






















LEGEND


Peloidal Rock

Skeletal Rock

Mudrock

Clay 8 Quartz Sand


Figure 3. Skeletal/Peloidal grain ratios and lithofacies
distribution in the MS and HS cores.














00










0 150












05








010













ISO-








greater than 75% grains other than skeletal or peloidal, and
these are referred to minor lithofacies named according to the
major constituent. Skeletal grains include all recognizable
remains of hard parts secreted by organisms. They can generally
be divided into fragmental and non-fragmental grains, but the
distinction is difficult to determine from thin section. Peloids
are allochems composed of non-structured, micro-or crypto-
crystalline material. They may represent wholly micritized
skeletal grains, mud aggregates, pellets, and, in diagenetically
altered rocks, the problematic clotted fabric or structured
grumeleuse of Cayeaux (1935) (see especially Bathurst, 1975,
p. 511-513). The term is very useful in that no genetic origin
is assumed in its usage. Peloidal rocks are characterized by
skeletal/peloidal grain ratios less than 1; skeletal rocks by
ratios of 1 or greater. The distribution of lithofacies in the
two cores is shown in Figure 3.

Cyclic Sedimentation

The variation in the skeletal/peloidal grain ratios are
shown diagrammatically in Figure 3. Plotted values are restricted
to samples containing 10% or more grains. Values were measured
from point-counts of thin sections, and sample only certain
portions of the cores (i.e., the diagrammed variation is only
a sample of the real variation in the cores). The similarity
in trends is, nevertheless, close. Corresponding variations in
the sense if not the actual magnitude of the ratios is used as
a basis of correlation. The mudrock lithofacies may or may not
be correlatable, which is in part caused by the diagenesis of
otherwise recognizable skeletal or peloidal rocks which results
in fabrics lacking original grains. Correlation of the study
cores on this basis makes possible the recognition of repeated
cycles of generally peloidal to skeletal sedimentation. Closer
examination of these grossly defined cycles and consideration
for finer grain-type distinctions, assessory minerals, and sedi-
mentary structures suggests that these may in face represent
actual cycles or carbonate sedimentation, with more than local
significance.

Depositional Environments

Four major depositional environments can be recognized by
a combination of criteria, including grain size and type, miner-
alogy, and sedimentary structures.

Open Marine: This is the normal marine environment, repre-
sented by waters of average salinity, temperature, and composition,
and with a bottom environment characterized by slightly oxidizing
conditions. Sediments deposited in this environment are charac-
terized by a lack of thin stratification or lamination, visible
organic material, gypsum, or significant amounts of clay minerals.
Large echinoids, mobile pelecypods, bryozoans, and abundant benthic
foraminifera are diagnostic. The extensive dolomitization of these
rocks makes it difficult to distinguish low and high energy deposits








(i.e., deep and shallow subtidal), but corals and coralline
algae, when present, indicate fairly shallow, agitated
waters (Purdy, 1963). Skeletal packstones and grainstones
are dominant, with some wackestones.

Lagoonal: This environment is characterized by salinities,
temperatures, and bottom Eh different from the open marine
environment, from which it is isolated by actual barriers or
by restriction of circulation by shallowness. It is analogous
to the shelf lagoon environment described by Purdy (1963)
and includes the adjacent subtidal environment discussed by
Shinn et al. (1969). Salinities generally are higher than
open marine, temperatures may rise infrequently as high as
400C (Glynn, 1968), and bottom conditions may be slightly
oxidizing or reducing. Sediments consist mainly of pellets
or mud aggregates (Shinn et al., 1969; Purdy, 1963), combined
here under the term peloids. Water is quiet and non-agitated,
since, as Purdy (1963) notes: "...the preservation as well
as the formation of pellets is dependent upon minimal
bottom agitation" (p. 484). Visible organic matter may be
present, and its decomposition may have induced strong
reducing conditions in the sediment, and thus restriction of
infauna. Lamination and stratification are not common, but
may be present in deeper and quieter parts of the shelf or
lagoon. Generally the faunas will show less diversity;
mudstone, wackestone, and pellet grainstone predominate, and
the rocks are mostly peloidal.

Intertidal: This environment is characterized by an
abundance of preserved sedimentary structures. Evans (1965)
in a detailed study of a tidal flat deposit, delineated six
major zones parallel to coastal strike. In a vertical
sequence, coarsest beds are at the bottom, well-sorted sands
are in the middle, and fine silts and muds at the top. The
deposits are characterized by laminated sands, silts, and
muds. Well-developed burrows may be present and some portions
of the deposits may be completely bioturbated (Shinn et al.,
1969). Park (1976) in studies along the Persian Gulf,
stated that "...optimum conditions for stromatolite development
in the Trucial Coast are restricted to the mid and upper
intertidal areas" (p. 382). Thin beds of organic debris may
be present. The lowest portion of the tidal flat may be
characterized by abundant rock and metazoan fragments (Evans,
1965). Tidal creeks cross the flats and have distinctive
sedimentary characteristics analogous to those described for
fluvial (point bar) deposits, though on a much smaller
scale. According to Evans (1965): "The meandering of the
creeks gives rise to cross-stratification on a scale not
seen in the other sub-environments (of the tidal flat).
Erosion of the concave outer bank is accompanied by the
deposition of inclined strata with dips up to 200 on the
convex inner bank. The meandering creek produces a planar
surface of erosion, commonly covered by a layer of shells
and mud pellets, derived from the banks, which is buried








beneath the cross-stratified deposit of the prograding bank"
(p. 226). Shinn et al. (1969) include the tidal creeks in
the subtidal zone, but they are obviously characteristic of
the tidal flat environment, and their deposits are intimately
associated with intertidal deposits.

Supratidal: This environment may include salt marshes,
beaches and beach ridges, and sabkhas. Salt marsh deposits
are typically well-laminated, fine-grained, and very carbonaceous
(Evans, 1965; Shinn et al., 1969). They may be marked by
root casts, fenestral porosity (Shinn, 1968a; Shinn et al.,
1969), algal stromatolites, and laminate crusts (Multer and
Hoffmeister, 1968). Supratidal ponds may result in deposits
of fine clays and evaporite minerals. Creeks in the supratidal
marsh, according to Evans (1965), may differ from creeks in
the intertidal zone, with the base of the cross-stratification
"...marked by a bed of jumbled angular blocks of marsh sedi-
ments, produced by undercutting of the creek walls. The
overlying set of strata is again wedge-shaped and individual
laminae may show dips of up to 800" (p. 226). Beach ridges
are generally characterized by graded laminae and cross-beds,
and the deposits are very well-sorted, though ranging from
fine to coarse in grain size. Sabkha-type deposits are
evaporitic in character, and contain gypsum and halite or
crystal molds, and are generally laminated by algal stromatolites.

Diagenesis

Crystallization Texture and Fabric Classification

The basic terminology described and defined by Friedman
(1965) is used here. His terms for crystallization textures
are retained. The definitions of euhedral, subhedral, and
anhedral are those of general usage by North American geologists
and do not require explanation. The terms are defined by
Friedman (1965), following Cross et al. (1906). There are
three major groups of crystallization fabrics (Table 3): equi-
granular and inequigranular, distinguished by uni-modal and
multi-modal crystal size distributions, respectively; and
aphanotopic, composed of crystals smaller than 0.002mm in
diameter (unresolvable). The first two groups are further
divided into idiotopic (mostly euhedral textures), hypidio-
topic(mostly subhedral textures), and xenotopic (mostly anhedral
textures).

The Friedman classification of fabrics is expanded here
by finer distinction of types, particularly inequigranular
types (Table 3). Equigranular fabrics are divided into mosaic
and peloidal fabrics, inequigranular into porphyrotopic,
poikilotopic, and mosaic fabrics. Aphanotopic fabrics can
not be further subdivided by use of the optical microscope.
Porphyrotopic fabrics are further divided into floating-rhomb
(Figure 4a) and contact-rhomb (Figure 4b). Floating-rhomb
and contact-rhomb fabrics are characterized by isolated or
loosely aggregated euhedral or subhedral crystals, respectively,























Table 3. Crystallization fabric terminology (modified after Friedman, 1965).


Equigranular Inequigranular Aphanotopic

Peloidal Mosaic Mosaic Porphyrotopic Poikilotopic Aphanotopic

Peloidal Sutured Sieve Spotted Fogged Contact- Floating- Polkilotopic Aphanotopic
Mosaic Mosaic Mosaic Mosaic Rhomb Rhomb


Size classes
0.256mm 0.016mm diameter
0.016mm 0.002mm diameter
<0.002mm diameter


Term

Micro-crystals
Aphanotopic crystals













Figure 4. a) HS 62, 28.65mbt (meters below top). Plane
light. Peloidal lithofacies, partially
dolomitized. Inequigranular, idiotopic
floating-rhomb porphyrotopic.
Small, euhedral dolomite rhombohedra in
aphanotopic calcite groundmass. Large
foraminifer is Dictyoconus cookei.

b) MS 299, 145.85mbt. Plane light. Skeletal
lithofacies, partially dolomitized.
Inequigranular, hypidiotopic contact-rhomb
porphyrotopic.
Pockets of aphanotopic calcite surrounded
by coarse, subhedral dolomite crystals.

c) MS 106, 52.65mbt. Plane light. Mudrock
lithofacies, dolomitized. Inequigranular,
xenotopic fogged mosaic.

d) MS 60, 35.66mbt. Plane light. Skeletal
lithofacies, dolomitized. Inequigranular,
xenotopic spotted mosaic. Spots are micritized
foraminifera.

e) MS 266, 130.00mbt. Crossed polars. Mudrock
lithofacies, partially dolomitized. In-
equigranular, xenotopic poikilotopic. Small,
anhedral to subhedral dolomite crystals
embedded in coarse calcite groundmass.

f) MS 266, 130.00mbt. Crossed polars. Same
as above, slide rotated to extinction of
calcite.





























i ',

b.^.








contained in a fine-grained matrix. Mosaic fabrics are
divided into fogged (Figure 4c) and spotted (Figure 4d) mosaic
fabrics. Fogged mosaic fabric is characterized by irregular
or diffuse areas of very fine crystals contained in a coarse
mosaic groundmass. Isolated and well-defined peloids ("spots"
or blebss") of fine to very fine crystals in a coarse mosaic
groundmass are characteristic of spotted mosaic fabric. Poikilo-
topic fabric (Friedman, 1965, p. 651) is relatively rare in the
study material, but is distinctive when it occurs. Wholerock
poikilotopic fabric is characterized by fine dolomite crystals
contained in large sparry calcite crystals (Figures 4e, f).
The term can also be used to describe the small-scale fabric of
calcitic micrite contained in sparry calcite overgrowths on
skeletal grains (Figure 5a).

Equigranular mosaic fabrics can be further divided into
sutured (Figure 5b) and sieve (Figure 5c) mosaic fabrics. Tightly
packed anhedral crystals, generally with little or no inter-
crystal porosity, are characteristic of sutured mosaic fabric.
Sieve mosaic fabric, on the other hand, is characterized by
loosely packed anhedral to euhedral crystals and high moldic
and intercrystal porosity. It is in part analogous to the
sucrosic or "sugary" texture of many authors. Peloidal fabric
is distinctive but problematic, and characterized by distinct
to indistinct "clotting" of crystals of essentially uni-modal
size distribution (Figure 5d).

A combined texture and fabric nomenclature is used to
describe any crystallized rock sample, e.g., idiotopic floating-
rhomb fabric; or xenotopic sutured mosaic fabric.

The size scales recommended by Friedman (1965, p. 653)
are arbitrary and do not conform to natural size breaks in the
study material. Crystals in this material fall into three
major size classes (according to length of major diameter):
(1) 0.256mm to 0.016mm, (2) 0.016mm to 0.002mm, and (3) less
than 0.002mm. No term is used to describe the first size class;
the second size class is indicated by the prefix micro- added
to the fabric term, and crystals in the third size class are
termed aphanotopic. For example, the term microxenotopic
fogged mosaic indicates that the crystals in the groundmass
are anhedral and fall in the size range 0.016mm to 0.002mm.
Crystals in the aphanotopic size range can not be resolved well
enough for textural classification.

Porosity

Classification

The Choquette and Pray (1970) classification of porosity
is followed, with the following exceptions. No distinction is
made between intraparticle porosity and growth-framework porosity
of solitary corals or bryozoa or shelter porosity inside echinoids.
No distinction is made between channel or cavern porosity. Root
moldic porosity is considered to be simple moldic.







The process of grinding thin sections alters the amount
of intercrystal porosity, the actual amount varying according
to the original grain size, texture, and fabric of the rock.
A significant amount of intercrystal porosity may also be
submicroscopic, particularly in rocks with a large percentage
of aphanotopic grains. Errors in estimation are not known,
but may range over 100%; for this reason only visible porosity
is reported here.
Distribution
Excluding cavernous porosity, total visible porosity in
the MS and HS cores appears to vary randomly (Figure 6),
although the amount of porosity is generally low at depositional
cycle boundaries. Cavernous porosity, on the other hand, is
clearly associated with the formational contacts as selected
in this study. Difference in the dissolution characteristics
of calcite and dolomite probably accounts for caverns at the
Avon Park-Ocala formational contact (see Goodell and Garman,
1969), and suggests its formation during the telogenetic
stage (Choquette and Pray, 1970) of diagenesis. Enhanced
solution beneath the clay beds marking the top of the Lake
City Formation in the HS core may account for cavernous
porosity here.

Porosity is dominantly fabric selective (Table 4), a
conclusion arrived at also by Textoris et al. (1972) and
Randazzo et al. (1977).Interparticle porosity is greatest in
rocks in which the original depositional fabric is preserved,
whether dolomitized or not, but intraparticle porosity is
greatest in those not dolomitized. Moldic porosity varies
greatly, since it is dependent on original skeletal content,
but is found predominantly in crystallized fabrics and is
greatest in equigranular sieve mosaic fabric. Fenestral
porosity is rare in the study material, and is restricted to
equigranular fabrics only. Non-fabric selective vug porosity
is restricted to crystallized fabrics, but is distributed
among them and shows no apparent fabric selectivity other
than occurrence in dolomite. The fabric selectivity of the
porosity suggests that interpretable distribution of porosity
can be seen in the cores.
Manatee Springs Core
Distribution of porosity types in the MS core (Figure
7) correlates closely with fabric distribution and also with
the depositional cycles described. Cycles I and VIII, both
represented by significant amounts of calcite, are characterized
by interparticle porosity [primary (Choquette and Pray,
1970)], somewhat modified by pore filling and cementation
[mesogenetic (Choquette and Pray,)1970)]. Crystallized
fabrics are for the most part characterized by moldic porosity
[eogenetic or mesogenetic (Choquette and Pray, 1970)],
although vug development may be important. Moldic porosity
is generally greatest in the upper portions of the depositional
cycles, directly related to the distribution of the skeletal
rock lithofacies (see Figure 3). Sieve mosaic fabrics often
have a significant amount of moldic porosity, and, coupled
with their inherent high intercrystal porosity, are often
soft and may form zones of high transmissivity. Moldic
porosity in inequigranular mosaic fabrics may not lead to
















Figure 5. a) HS 35, 20.73mbt. Crossed polars.
Skeletal lithofacies, undolomitized.
Aphanotopic calcite embedded in sparry
calcite overgrowth on echinoid grain
(between arrows).

b) MS 284, 140.21mbt. Plane light.
Mudrock lithofacies, dolomitized.
Equigranular, hypidiotopic sutured
mosaic.

c) MS 263, 128.40mbt. Plane light.
Mudrock lithofacies, dolomitized.
Equigranular, xenotopic sieve mosaic.
Dolomite crystals, some of which are
hollow (arrows), contain dark nuclei.

d) MS 262, 127.86mbt. Plane light.
Peloidal lithofacies, dolomitized.
Equigranular, microxenotopic peloidal.

e) MS 279, 137.46 mbt. Plane light.
Mudrock lithofacies, dolomitized.
Equigranular microxenotopic sutured
mosaic.

f) MS 151-B, 71.63mbt. Plane light.
Skeletal lithofacies, dolomitized.
Inequigranular, hypidiotopic spotted
mosaic. Spot is transverse section of
micritized foraminifer.
















































* d.
















Table 4. Fabric selectivity of porosity.


S.- .- .*- .-







Sutured Mosaic 0 0 4.8 0.1 0.9 5.8

Sieve Mosaic 0 0.03 13.3 0.3 1.2 14.8


Spotted Mosaic 0 0 5.0 0 3.0 8.0

Fogged Mosaic 0 0 7.3 0 2.2 9.5

Contact-Rhomb 0 0.6 3.3 0 1.5 5.4
Porphyrotopic

Floating-Rhomb 3.4 2.2 0.4 0 0.6 6.7
Porphyrotopic

Uncrystallized 9.4 1.9 3.0 0 0 14.4
Fabrics

All values in area percent of total rock.









MS


% Porosity _
20 40 60 80 100 X
, I I 1 OQ
/ F'


Caverns


HS


% Porosity
20 40 60 80 100
I i I I I


0











50
Sol




0




0


0.


Figure 6. Distribution of total visible porosity in the MS and HS cores.
21


0
O
!


Caverns





















Caverns










LEGEND


Type of Porosity.


Interparticle
Intrapcrticle
Moldic
Fenestral
Vug


Crystallization Fabric

Equigranular
Sutured Mosaic
Sieve Mosaic
Peloidal
Inequigranuiar
Floating-Rhomb
Porphyrotopic
Contact-Rhomb
Porphyrotopic
Fogged Mosaic
Spotted Mosaic
Poikilotopic
Aphanotopic
Original Fabric
Preserved


Figure 7. Distribution of porosity types (excluding cavernous) in
the Manatee Springs core and comparison with distribution of
crystallization fabrics.


000


--- -






C


i-a
-- U- % Porosity

0 -,_ 0 10 20




S> -<
..** ***.*.. ..
...... .. ..... ...*********.


: ~-_



50











100 .



Soo* .--



--* .






150
23


*








better permeability since the pores are often not interconnected.
Vug porosity is probably necessary for high permeability in these
fabrics.

Highest permeabilities are suggested at the base of Cycle I
(vug development in mosaic fabric) and in the center of Cycle I
(interparticle porosity in the calcitic fabrics); in the upper
part of Cycle IV and Cycle V (moldic and vug porosity in sieve
mosaic fabric); and in the parts of Cycle VIII with high inter-
particle porosity (Figure 7).

Homosassa Core

Distribution of porosity types in the HS core (Figure 8)
also correlates closely with the depositional cycles, although
it differs from the distribution found in the MS core (Figure 7).
Cycle VIII, represented entirely by calcite, is characterized by
interparticle porosity. Crystallized fabrics are for the most
part characterized by moldic porosity, but vug development is
more significant in this core than in the MS core.

Highest permeabilities are suggested in Cycle III, the
upper part of Cycle IV, and in Cycle V (moldic porosity in sieve
mosaic and aphanotopic fabrics); the lower part of Cycle IV and
lower part of Cycle VI (vug porosity in peloidal and inequigranular
mosaic fabrics); and in Cycle VIII (interparticle porosity) (Figure
8).

Fabric Selectivity of Dolomitization

The sequence and association of crystallization fabrics
and porosity evidenced in the HS and MS cores reveal much about
their mode of origin and their genetic relationships.

Heterogeneous Dolomitization

A continuous spectrum of dolomite fabrics ranging from early
stage floating-rhomb porphyrotopic (Figure 4a) to later stage
contact-rhomb porphyrotopic (Figure 4b) fabrics is clearly revealed
in the study rocks. These fabrics often grade into mosaic fabrics
(Figures 4c,d), which appear to represent the completion stage
of dolomitization in the rock (Figure 9). This process of dolo-
mitization is multistage, and a full range of fabrics is present
in the study rocks. Dolomite porphyrotopes are almost invariably
restricted to aphanotopic (mud) calcite matrix, and therefore the
appearance of the final fabric is dependent upon the occurrence and
distribution of mud matrix in the original fabric (Figure 10).
Because of this restriction, the process is here termed heterogeneous
dolomitization. This process is initiated by nucleation of isolated
dolomite crystals in an aphanotopic matrix consisting of calcite
(or possibly aragonite). The preservation of a full range of
fabrics indicates the process takes place during a geologically
significant period of time (probably on the order of a thousand
years or more). Heterogeneous dolomitization of mudstone leads to
the formation of sutured mosaic fabric (Figure 10). Heterogenous









dolomitization of wackestone leads to spotted mosaic fabric
if the allochems are also dolomitized, or to sutured or sieve
mosaic fabrics if they are dissolved (Figure 10). The large
number of allochems present in a packstone causes the dolomite
porphyrotopes to penetrate the grains and destroy original
outlines, resulting in diffuse patches of finer-grained crystals
and fogged mosaic fabric, or to sutured or sieve mosaic fabrics
if the allochems are dissolved (Figure 10). No true grain-
stones were observed that had more than 1% porphyrotopic dolomite;
presumably grainstones can not be dolomitized by heterogeneous
dolomitization since they contain no mud matrix.

Homogeneous Dolomitization

The process of heterogeneous dolomitization can not explain
the origin of aphanotopic or peloidal fabric, or of dolomitized
grainstones. The excellent preservation of original grainstone
fabric in some dolomite samples is not possible if dolomitization
proceeded by porphyrotopic growth, and heterogeneous dolomiti-
zation of a mudstone or peloidal grainstone would lead to sutured
mosaic fabric. These particular fabrics are always composed of
fine or very fine dolomite crystals, generally with mean diameters
less than 0.016mm, and they are here referred to as micro-textured
fabrics. Some mosaic fabrics are also composed of crystals in
this size range, and these are also referred to as micro-textured.
Dolomitization of micro-textured fabrics is not dependent upon
the occurrence of mud matrix and the process is termed homo-
geneous dolomitization. Micro-textured fabrics are always composed
of 99+% dolomite and no full range of fabrics is preserved as for
heterogeneous fabrics. The process is, therefore, single-stage
and nucleation of dolomite crystals occurs at a large number of
sites throughout the rock and growth is completed in a geologically
insignificant period of time. Destruction of allochems is probably
minimized, and original fabrics often preserved. Fogged and
spotted micro-textured mosaics are uncommon. Homogeneous dolo-
mitization of mudstone leads to micro-textured sutured mosaic
fabric, or, if the rate of nucleation is very high (essentially
spontaneous throughout the rock), it can lead to aphanotopic
fabric (Figure 11). Wackestone and packstone are generally dolo-
mitized to micro-textured sieve mosaic fabric, although fogged
or spotted mosaic fabrics might be developed (Figure 11). Homo-
geneous dolomitization preserves the original fabric of peloidal
grainstone to a large degree (Figure 11).

Poikilotopic Fabric

The origin of poikilotopic fabric is problematic. This
type of fabric is rare in the study rocks and its isolated occur-
rences provide little evidence of mode of origin. The character
of the mixed mineralogy and the association with unconformities
or zones of weathering suggest that it might originate by de-
dolomitization of crystallized fabrics (see Friedman, 1965,
p. 651).









LEGEND


Type of Porosity.


Interparticle
Intraparticle
Moldic
Fenestral
Vug


Crystallization Fabric

Equigranular
Sutured Mosaic
Sieve Mosaic
Peloidal
Inequigranular
Floating-Rhomb
Porphyrotopic
Contact-Rhomb
Porphyrotopic
Fogged Mosaic
Spotted Mosaic
Poikilotopic
Aphanotopic
Original Fabric
Preserved


Figure 8. Distribution of porosity types (excluding cavernous) in
the HS core and comparison with distribution of crystallization
fabrics.


000
**





































0
50














100


0.
10


O
0
N

o %LL.













oo



















o00
000
00

ooo
no

o**

***

0**
*5*


















coo
***



-@**
000


0
@ .- o0
o ^U




39


40


% Porosity


20







LEGEND


Lithofacies
Peloidal Rock
Skeletal Rock
Mudrock
Clay & Quartz
Sand


El.


%Dolomite=


Dolomite
Dolomite *-Calcite


x 100


Crystallization Fabric
Equigranular
Sutured Mosaic
Sieve Mosaic
Peloidal
Inequigranular
Floating-Rhomb
Porphyrotopic
Contact Rhomb
Porphyrotopic
Fogged Mosaic
Spotted Mosaic
Poikilotopic
Aphanotopic
Original Fabric
Preserved


Figure 9. Distribution of crystallization fabrics in the MS and
and HS cores and comparison with lithofacies distribution and
variation in carbonate mineralogy.


jMoo


777










Depth 5 In Meters Below Top Of a Well
0 0


(I)


100


Lithofacies

Crystallization
Fabric


Depth o In Meters


Below Top Of


Well


I I I A
0


Crystallization
Fabric

Lithofacies


CO-
U)


100










Wackestone


Original
Fabric


Floating -Rhomb
Stage







Contact-Rhomb
Stage


Completion
Stage


Spotted Mosaic


Sieve Mosaic
Figure 10. Genesis of crystallization fabrics by heterogeneous dolomitization.













Packatone,
Waokestone


Peloidal
Grainstone


Original Fabric







Nucleation






Completion


Micro-textured
Sutured Mosaic


Micro-textured
Sieve Mosaic


Figure 11. Genesis of crystallization fabrics derived by homogeneous dolomitization.


Mudstone


Peloldal










Summary

There is a descriptive basis for the classification of
crystallization fabrics (primarily dolomites). Categori-
zation of the rock fabrics found in the two study cores
reveals patterns similar to those of the depositional cycles
deduced from sedimentologic considerations. Type and distri-
bution of porosity also occur in patterns that can be associated
with the depositional cycles. The various crystallization
fabrics caused by dolomitization can be placed into a genetic
framework and there is a fabric dependency upon both the
process of dolomitization and the original fabric. Unless
the rock has undergone repeated neomorphism of dolomitized
fabrics, it is generally possible to deduce the original
depositional fabric (and thus the lithofacies) from even
highly crystallized fabrics. Only in the case of sutured
mosaic fabric is the original fabric in great doubt, primarily
because repeated neomorphism will lead to this fabric.









ROMP CORES


Three cores were extracted by the Southwest Florida
Water Management District from locations in north central
and northwestern peninsular Florida as part of its Regional
Observation and Monitor-Well Program (ROMP). The location
of these cores (#101, #107, #124) are shown in Figure 1. At
the writing of this report some ten additional ROMP cores
are in various stages of investigation. The major stratigraphic
units encountered are the Avon Park and Ocala Formations
(Figure 12).

Avon Park Formation

The Avon Park Formation exhibits many features which
are strikingly similar to carbonate sediments produced in
modern tidal-flat environments. These features include:
flat, millimeter-thick laminations; undulating stromato-
lites; vertical burrows; desiccation cracks; "birdseye"
structures; root casts and molds, flat pebbles; sediment
mottling; evaporite mineral molds; and thin, micritic beds.
These features have been described as being products of
tidal-flat accretion over adjacent shallow marine deposits.

Petrographic examination has revealed the presence of
eleven commonly occurring subfacies representative of the
supratidal, intertidal and subtidal zones. The repetitive
vertical arrangement of these rock types has enabled the
recognition of cyclic sedimentation patterns in Avon Park
strata.

Cyclicity

The vertical sequence of interbedded lithologies found
in the Avon Park Formation depict a complex model of sediment
accumulation in which the recognition of cyclic depositional
patterns proves to be, "... the single most illuminating
factor in making sense of the seemingly bewildering vertical
parade of subfacies" (Reinhardt and Hardie, 1976). The
vertical organization of lithologies represents a repetition
of sedimentation cycles in which the basic Avon Park depositional
cycle is represented by an offlapping or progradational
facies sequence (Figure 13). Subtidal facies represents the
lowest unit in most depositional cycles. This is often in
sharp contact with a bed which represents the top of the
underlying cycle. Periods of submergence to subtidal levels
were followed by shoaling and progradation of intertidal and
supratidal deposits over subtidal sediments. Interruptions
in these progradational trends are indicated by numerous in-
complete cycles marked by minor unconformable contacts found
along cyclic boundaries.











LEGEND


THINLY BEDDED AND LAMINATED MUDSTONE


FLATLY LAMINATED, PELLETED MUDSTONE TO PACKSTONE

ALGAL BIOLITHITE

ROOTED AND MOTTLED FORAMINIFERAL WACKESTONE


PELLETED WACKESTONE TO PACKSTONE

ROOTED AND BURROWED MUDSTONE

BIOCLASTIC WACKESTONE TO MUDSTONE


FCRAMINIFERAL-ECHINOID WACKESTONE TO PACKSTONE

FORAMINIFERAL PACXSTONE TO GRAINSTONE


DICTYOCONID WACKESTONE TO PACKSTONE

MILIOLID PACKSTONE

PELOID-MILIOLID PACKSTONE


COMPOSITE GRAIN-MIXED SKELETAL GRAINSTONE TO PACKSTCNE

FRAGMENTAL GRAINSTONE TO PACKSTONE


FRAGMENTAL PACKSTONE TO WACKESTONE

LARGE FORAMINIFERAL WACKESTONE TO PACKSTONE


NUMMULITID WACKESTONE TO PACKSTONE


LIMESTONE


DOLOMITE


LITHOLOGIC BOUNDARY

FAUNIZONE BOUNDARY -------...


DOLOMITIC LIMESTONE

CALCITIC DOLOMITE


DEPTH IN METERS BELOW TOP OF WELL


Figure 12. Columnar sections showing the relationship of assemblage
zones to lithologic units in the ROMP cores, corrected to datum at
the top of the Avon Park Formation.


-- --:*:* ..:''.






*- .KT _.' .t..l"




g^,-." .,._
- .. -- .


^m 1

















L.1
0L
0L








z



0m
a-


Hernando County
Well 107





Nummulites
6 '/coxi Zone







5 5s olens --
is AmpiSitegnac
pmarensks cosdai





1 -- ------



Sfounizoneda ,
0 %F fdonofl J









T I30 3
> 85ii,,P^-tj 0cycw
"^*'y i^ fwia is
^f 7:,0 to~a c~


Levy County
Well 124


Spiro/ocuilna
Ssminbolsnes-
S0 Amplitegma
pinarensis casden
Zone
,ft .
--u 20 rupizone ,,
ooliteraled ,.,
by d,,olo- s
n ion -










630
I Oictyocous
f oridanus,
Dcoockei Zcne


i50







75--5-
5


Well 101



:;' ==

zo



Z5

40

45











0 -5





_ so
10^ 5 -T}


0O




n
7-
0
U-





O
zr
0


Lake County











SEDIMENTARY
FEATURES


DEPOSITIONAL
ENVIRONMENT


0
*0. '1
.* .~
* 4 *
9 ~ 0.
~*t0e8 ,.,


cj~








0~


C
C


Shallow

/ EROSIONAL CONTACT Lagoon
LITHOLOGY: Algal biolithites;
thinly bedded and laminated
mudszones to wackestones.
STRUCTURES: Thin algal and Supratidal
sedimentary laminations, des- Mudf at
iccation cracks, fenestral
cavities, rare burrows.
FOSSILS: Sparse to absent
LITHOLCOGY: Skeletal and pel-
letal mudstones, wackestones
and packstones.
STRUCTURES: Vertical burrows, lInerftJcI
root casts and molds, sediment
mottling, thin micritic beds. Mudflat
FOSSILS: Low faunal diversity
(small forms, ostracods and
fewer gastropods).
LITHOLOGY: Skeletal wacke-
stones to grainst.)nes.
STRUCTURES: Micrites show a
general lack of sedimentary
fabric because of intensive
reworking by burrowing organ-
isms; sparites may show faint ShlCHOW
current-produced laminations. LI oon
FOSSILS: Moderate faunal di-
versity containing a variety
of species of foraminifera,
dasyclad algae, echinoids,
bryozoans, solitary corals
and molluscs.


0 .






0)00

00 4

0 00
0 o g
*~~ 0


Figure 13. Schematic drawing showing the essential aspects of an Avon Park
depositional cycle. The vertical sequence of sedimentary textures and
structures is produced by the progradation of supratidal and intertidal
mudflat deposits over shallow lagoonal sediments.


CORE


Incomplete cycles are marked by minor
unconformities found along cyclic
boundaries,









Recognition of Depositional Environments in
Avon Park Strata

Although each of the ROMP cores used in this study
displayed its own unique set of interpretive problems,
similarities were found to exist which enabled the recogni-
tion of the supratidal, intertidal and subtidal zones within
the Avon Park strata.

The most characteristic feature of supratidal deposits
in the Avon Park is thin, algal and sedimentary laminations.
Crinkled and flat laminar morphologies similar to those
described by Hardie and Ginsburg (1977) are abundantly
represented in supratidal facies. Many beds consist of
laminated fine and medium crystalline dolomites which pre-
sumably have replaced original, finely bedded or laminated,
muddy sediments. Supratidal rocks are largely mud-supported.
Invertebrate skeletal remains are sparse and pellets usually
represent the dominant allochemical constituent. Burrow
structures are rare and, where they do occur, they stand out
in vivid contrast against the well-preserved, laminated
matrix of the rock. Desiccation structures are found in
supratidal beds and include laminoid fenestral cavities
("birdseye" vugs), algal mat deformation structures, flat
pebbles and vertically oriented cracks disrupting algal
laminations and thin micritic beds. No evidence of evaporite
minerals were found in the ROMP cores although small amounts
of gypsum and the presence of evaporite mineral molds have
been previously reported from supratidal facies within the
Avon Park (Saroop, 1974; Hickey, 1976).

The boundary between rocks representing the supratidal
and the underlying intertidal zones is typically gradational
(Figure 13). Changes in the nature of preserved sedimentary
structures and a relatively greater abundance and diversity
of fossils serve to distinguish these tidal deposits.
Intertidal rocks are characterized by a predominance of
micrite, indicative of the low tidal and wave energies which
prevailed in the depositional environment. Fossils consist
of a sparse number of individuals and relatively few species
(mostly foraminifera and ostracods with fewer gastropods).
These beds are further distinguished by the presence of
preserved sedimentary structures including vertical burrows,
open root tubules and a churned-to-wispy-sediment mottling.
These features are of debatable value as primary indicators
of a particular subenvironment within a shallow nearshore
regime of sediments. They do, however, provide clues to the
role of organisms in the paleoenvironment which may have
exerted some control over sediment disrupting processes and
allowing for the preservation of these structures.

Recognizable transition in fossil communities, as seen
in vertical sequence, was the most useful criteria enabling
the differentiation between subtidal and intertidal facies.









The fauna of subtidal rocks is represented by a larger
number of individuals and wider diversity of fossils than
associated intertidal and supratidal deposits. A general
lack of stratification in subtidal rocks may be an indi-
cation of early bioturbative processes; the activities of
burrowing and sediment-ingesting organisms result in the
destruction of primary sedimentary structures and in the
homogenization of the ambient sediment body (Shinn, 1968b;
Heckel, 1972). Locally, wave and current energy was strong
enough to winnow interstitial muds and reorganize the sedi-
ments into flat to low angle, current laminations.

General Lithology

The general distribution of Avon Park lithologies in
the ROMP cores is shown in Figures 14, 15 and 16. The lower
part of the Avon Park in these cores (unit A) shows a
dominance of supratidal-intertidal ("tidal-flat") sedimentation
over accompanying subtidal phases. Vernon (1951, p. 96) had
described this lithology as a "...tan to brown, thin-bedded
and laminated very finely crystalline dolomite...." Well-
preserved, thinly laminated deposits, interpreted as algal
stromatolites, are abundantly represented in this lowermost
unit. These distinctly laminar rocks were originally described
by Vernon as varve-like features with the implication that
they represented slowly-settled organic and plant residues
in a relatively deep body of water. Dolomitization is more
extensive in this unit than in overlying strata, often to a
degree such that the original microfabric of the rock is
largely obscured and sometimes obliterated. Desiccation
features in algal bedding structures are generally more
abundant than in overlying lithologies.

The central portion (unit B ) of the formation is
similar in many aspects (particularly in the ROMP core #124
to the Avon Park unit designated by Randazzo and Saroop
(1976) as Lithofacies I. Vernon's (1951, p. 96) description
of this lithology is repeated below:

Cream to brown, pasty and fragmental, peat
flecked and seamed, very fossiliferous marine
limestone. This bed is extremely rich in
well-preserved bryozoa, foraminifers and
ostracods, and the fauna is concentrated and
somewhat deformed along thin beds that are
interbedded with peat and more barren pasty
limestone seems to give the rock a laminated
and mottled appearance, to which the term
'molasses and butter' has been applied by
some geologists.

The interbedding of rock types observed by Vernon may be
expressed in terms of cyclic depositional patterns. Sub-
tidal beds, characterized by their abundant and distinct
microfauna, are interlayered with sparsely fossiliferous
carbonate rocks of tidal-flat origin. The lack of a conspicuous












LEGEND

THINLY BEDDED AND LAMINATED MUDSTONE


FLATLY LAMINATED, PELLETED MUOSTONE TO PACKSTONE


ALGAL BIOLITHITE


ROOTED AND MOTTLED FORAMINIFERAL WACKESTONE


PELLETED WACKESTONE TO PACKSTONE


ROOTED AND BURROWED MUDSTONE


BIOCLAST1C WACKESTONE TO MUDSTONE


FORAMINIFERAL-ECHINOID WACKESTONE TO PACKSTONE


FORAMINIFERAL PACKSTONE TO GRAINSTONE


DICTYOCONID WACKESTONE TO PACKSTONE


MILIOLiD PACKSTONE


PELOID-MILIOLID PACKSTONE


COMPOSITE GRAIN-MIXED SKELETAL GRAINSTONE TO PACKSTONE


FRAGMENTAL GRAINSTONE TO PACKSTONE


FRAGMENTAL PACKSTONE TO WACKESTONE


LARGE FORAMINIFERAL WACKESTONE TO PACKSTONE


NUMMULITID WACKESTONE TO PACKSTONE


LIMESTONE

DOLOMITE


CHERT


Symbolic patterns for Figures 14, 15, and 16.


71\~

















L7A












MINERALOGY L1THCLOGY


25 -

30


FAUNIZONES
(from Hunter, 1976)





Nummu/ites
w/lcoxi Zone


TIDAL
ZONES
sup inter u b














































J


Figure 14. ROMP well #107 (H).
and biozonations.


Mineralogy, lithology, tidal zones


Spirc/ocullna
semmolensis-
Amphistegnea
ponarensmi csdeni
Zone












U.tHnella

Dictyocorus
florkdanuei
D. cooksei Zone


46-


50 -

55 -





zUj

7.
w




as



CL T
LUJ


100

1051


z




QO


6mm


40










MINERALOGY LITHOLOGY


-j


0
C/j


a


0--no---j


TIDAL
ZONES
sup inter sub


FAUJNIZONES
(from Hunter, 1976)


Spiro/lc.,ina
samino0/ensis-
Amphitsfegina
piwrensis condeni
Zone
















Lituone/ao
floridana,
DicOyoconus
floridanus,
0 cookei Zone


Figure 15. ROMP well #101 (LA).
and biozonations.


Mineralogy, lithology, tidal zones,


0)
Lr-
U 55-
60-

LU
CE
0 65-
=
S70-
0 -


- .









TIDAL


MINERALOGY LITHOLOGY


FAUNIZONES
(from Hunter, 1976)



Spiro/ocu/na
semino/ensis-
Amphistegtna
pin7rensis cosdeni
Zone


Lftunei/a
floridana,
Oictyoconus
floridanus,
0. cooked Zone


Figure 16. ROMP well #124 (LE).
biozonations.


Mineralogy, lithology, tidal zones,


20-- "


30-






40-


Z 5-


W5C-


/ ~ ~ V 7lj,*f' *a mb __
--.====== ~ ~ ~ ~ C;^ :"_!m ^_. --







fauna imparts a "barren" appearance to these rocks. Por-
tions of this unit have been partially or completely dolo-
mitized. Dolomitization is more extensive in ROMP core #124.
This portion of the Avon Park records a gradual net change
in sea level. Subtidal facies predominate in the lower
portion of the unit. Cycles become shorter and less regular
in the upper portions of the lithology where tidal-flat
carbonates dominate.

Vernon (1951, p. 96) describes the uppermost lithology
of the Avon Park as a "...cream to brown, highly fossil-
iferous, miliolid rich, marine, fragmental to pasty lime-
stone...." He remarks that this unit sometimes appears as a
coquina of "cones" (i.e., dictyoconid foraminifera) with
locally abundant specimens of the small echinoid, Neolaganum
(=Peronella) dalli. The unit (unit C) is characterized by
wide vertical and lateral variations in character. This
lithology, as it is represented in the ROMP core #124, bears
a close resemblance to the carbonate rocks designated by
Randazzo and Saroop (1976) as Lithofacies II. The unit has
been extensively dolomitized in this locality. Lenses of
peat and carbonaceous plant remains are abundant in the
upper beds of this core. Dolomite represents only a small
portion of this unit in ROMP core #107 and is absent in ROMP
core #101. The preservation of fossils is typically poor in
these beds and often molds or impressions are all that
remain of the original tests. Subtidal deposits in the
lower portion of this unit are characterized by a low diversity
fauna dominated by species of dictyconid and large miliolid
foraminifera. These beds become highly fossiliferous towards
the top of the unit and support a diverse array of fossils.

Depositional Facies

Eleven commonly occurring subfacies representing the
supratidal, intertidal and subtidal zones have been re-
cognized in these cores of the Avon Park Formation. These
include:

I. Supratidal rocks
a. thinly bedded and laminated mudstone
b. flatly laminated, pelleted mudstone-wackstone
c. algal biolithite

II. Intertidal rocks
a. rooted and mottled, foraminiferal wackestone
b. pelleted wackestone to packstone
c. rooted and burrowed mudstone
d. microlaminated, bioclastic wackestone to mudstone

III. Subtidal rocks
a. foraminiferal-echinoid wackestone to packstone
b. foraminiferal packstone-grainstone
c. dictyoconid wackestone to packstone
d. miliolid packstone








All lithologies have been partially to completely
replaced by dolomite. The distribution of facies in the
three cores is shown in Figures 14, 15, and 16. The de-
positional environments and possible water depths of sub-
facies in the Avon Park Formation are described in Table 5.
Figure 17 illustrates the generalized distribution of
depositional environments.

Ocala Limestone

In contrast to the complex cyclic sequences expressed
by the Avon Park strata, the rocks of the Ocala Limestone
are interpreted as products of a more constant and stable
depositional environment. The presence of an abundant and
diverse marine fauna signifies a transition to less-restricted,
more normal, open marine conditions. In general, the change
from the tidal-flat and restricted subtidal deposits of the
Avon Park to the offshore, high and low energy marine deposits
of the Ocala Limestone is indicative of an overall trans-
gressive sequence of sedimentation.

Chen (1965, p. 76) has concluded that the sediments of
the Ocala had been deposited under warm and shallow water
marine conditions on a relatively flat and broad carbonate
shelf or platform similar to the present day Great Bahama
Banks.

The ROMP cores reveal that the Ocala Limestone is
composed of two major lithologies, separating the strata
into distinct upper and lower lithologic units (Figures 3
and 7). Deposits representing shallow-water, moderately
high energy conditions occur in the lower unit where deposition
is interpreted to have taken place relatively close to
shore. These grade into slightly deeper water, lower energy
deposits which characterize the upper unit. Data from the
ROMP cores are most consistent with the interpretation of
Applin and Applin (1944), dividing the Ocala Limestone into
an upper and a lower member.

Lower Ocala Limestone

The Lower Ocala unit occupies the same stratigraphic
interval recognized by the U.S. Geological Survey as the
Lower Ocala, and would include the Williston and (at least
part of) the Inglis designations of Puri (1957). This
portion of the Ocala has been generally described as a light
cream to tan colored miliolid limestone, porous, friable,
microcoquinoid in appearance, often chalky and generally
harder than strata characterizing the upper unit. Petrographic
examination reveals that this lower unit consists predominately
of cleanly washed skeletal packstones to grainstones in
marked contrast to the overlying muddier deposits of the
Upper Ocala. The contact between rocks of the Upper and
Lower Ocala is gradational.








Depositional Facies


Three commonly occurring depositional subfacies have
been identified in the rocks of the Lower Ocala, on the
basis of lithology, textures, constituent grain composition
and grain attributes. These are:

Peloidal/miliolid packstone (subtidal sand flat
facies).
Composite grain/mixed skeletal grainstone-packstone
(detrital shoal facies).
Fragmental grainstone-packstone (intertidal shoal
facies).

These subfacies delineate distinctive depositional
subdivisions of the open shelf environment. The vertical
arrangement of lithologies in Lower Ocala strata is shown in
Figures 14, 15 and 16. The depositional environments and
possible water depths of subfacies in the Lower Ocala Limestone
are described in Table 5. Figure 17 illustrates the generalized
distribution of depositional environments.

Upper Ocala Limestone

The carbonate deposits of the Upper Ocala Limestone
represent a transition into progressively deeper water
environments of sedimentation. A continuation of the general
transgressive sequence is suggested by the presence of a
deeper-water faunal assemblage and the deposition of wackestones
and muddy packestones over the cleanly washed deposits of
the lower unit. Megascopically, the unit is very pale
orange in color. Beds are uniformly textured and range from
sparsely granular to coquinoid in appearance. The rock is
friable and generally softer than the lower unit.

The Upper Ocala is characterized by the presence of
abundant whole and fragmented tests of large foraminifera.
Specimens which have been identified from the ROMP cores
include:

Nummulites willcoxi
Lepidocycline ocalana
Heterostegina ocalana
Spiroloculina newberryensis
Sphaerogypsina globula
Textularia sp.

Whole tests of small, thin-shelled foraminifera, ostracods,
echinoid plates and spines, small gastropids and fragments
of pelecypids and bryozoans are also present. Grain sizes
range from coarse silt-sized (0.04mm) bioclasts to coarse
pebble-sized grains measuring from several millimeters to



















AND I RESTRICTED I '---" ""--- _^-

I INTERTIDAL SANDFLATS I ":'F"HOR:!
I SHOALS OFFSHORE, OPEN
CYCLIC SEDIMENTATION I NEARSHORE SHELF I SHELF
I NEARSHORE SHELF I

Figure 17. Generalized relationship among depositional environments
interpreted for the Avon Park Formation and the Ocala Limestone.

Table 5. Depositional environments and probable water depths of subfacies
in the ROMP cores.


FACES


ENVIRONMENTS OF DEPOSITION
AND PROBABLE WATER DEPTHS


a. THINLY BEDDED AND LAMINATED MUDSTONE
b. FLATLY LAMINATED, PELLETED MUDSTONE
TO PACXSTONE
C. ALGAL BIOLITHITE


(. ROOTED AND MOTTLED FORAMINIFERAL
WACKESTONE
T b. PELLETED WACXESTONE TO PACKSTONE
C. ROOTED AND BURROWED MUDSTONE
d. SIOCLASTIC WACKESTONE TO MUDSTONE


a. FORAMINIFERAL-ECHINOID WACXESTONE
TO PACXSTONE
I b. FORAMINIFERAL PACKSTONE TO GRAINSTONE
C. DICTYOCONID WACKXESTONE TO PACXSTONE
d. MILiOLID PACXSTONE


a. PELOID-ULIOLID PACXSTONE


b. COMPOUND GRAIN-MIXED SKELETAL
GRAINSTONE TO PACXSTONE
C. FRAGMENTAL GRAINSTONE TO PACXSTONE


0. FRAGMENTAL PACXSTONE TO WACXESTONE
b. LARGE, PERFORATE PORAMINIFERAL
WACXESTONE TO PACXSTONE
C. NUMMULITID WACXESTONE TO PACXSTONE


- SUPRATIDAL MUDFLAT





- INTERTIDAL MUDFLAT


PROTECTED, SHALLOW-WATER
LAGOON. WATER DEPTH
LESS THAN 10 METERS.


SHALLOW SUBT!DAL
SANDFLATS. WATER
DEPTH LESS THAN 10 METERS

SHALLOW SUSTIDAL TO
INTERTIDAL SHOALS. WATER
DEPTH 0--O METERS.


OFFSHORE, OPEN SHELF.
WATER DEPTH GREATER
THAN 35 METERS.









a few centimeters or more along their long axis. Some of
the larger tests have been broken and extensively frag-
mented; however, they show little signs of mechanical abra-
sion in that grain boundaries tend to be ragged or angular
in shape. The evidence suggests that most fragments were
derived through biologically controlled processes. Some
large burrow structures are encountered which are probably
of crustacean origin. These are preserved as open tubes
which show a characteristic dense micritic lining. Similar
burrows have been attributed to crustaceans by Shinn (1968b).

The upper unit is characterized by a largely mud-
supported fabric. The matrix is composed of micrite and very
finely crystalline microspar often cluttered by silt-sized
bioclasts. It sometimes displays a clotted fabric although
discrete pellets are rarely observed.

Depositional Facies

The limestone of the Upper Ocala can be subdivided into
its component subfacies. Three primary depositional sub-
facies are recognized. These are:

Bioclastic packstone to wackestone
Large perforate foraminiferal wackestone to packstone
Nummulitid wackestone to packstone

Subdivisions were based primarily upon paleontologic
criteria including the relative abundance and identity of
the various faunal constituents. The vertical arrangement
of lithologies in Upper Ocala strata is shown in Figure 14.
The depositional environments and possible water depths of
subfacies in the Upper Ocala Limestone are described in
Table 5. Figure 17 illustrates the inferred distribution of
depositional environments.

BALLAST POINT, BRANDON, AND DUETTE CORES

Drill cores, located at Ballast Point and Brandon in
Hillsborough County, and at Duette in Manatee County, were
obtained from the Florida Bureau of Geology. These cores
penetrate the "Tampa Formation" and Suwannee Limestone
(Figure 18).

The Suwannee Limestone is of Oligocene age, and defined
as a biostratigraphic unit rather than a lithostratigraphic
unit. In the area of study, it is lithologically conformable
with the underlying Late Eocene Ocala Limestone. An un-
conformity is present toward the north in Hernando County
(Yon and Hendry, 1972, p. 30) and Citrus County (Vernon,
1951, p. 177). The pelecypod Amusium ocalanum, which is
apparently present at and below the depth of about 116m from
sea level within the Ballast Point core, is utilized herein
as a biostratigraphic marker of the Upper Ocala (McCullough,
1969, p.1).









Because the Suwannee Limestone and Tampa Formation have
been defined on the basis of biostratigraphic evidence,
confident recognition and correlation have been difficult at
best. These traditional formational names are invalid on the
basis of the Code of Stratigraphic Nomenclature (Randazzo,
1976a). King and Wright (1979, p. 1605) have defined the
Tampa Formation from biostratigraphic and geochronologic
criteria. The Tampa Formation is lithologically similar in
places to other "post-Suwannee" units. The Tampa Formation
described in the cores studied may actually be the Hawthorn
Formation. Because of the uncertainty of its identity,
references made to the Tampa Formation in the remaining part
of this report will be offset in quotation marks.

Stratigraphy

The regional stratigraphy of the "Tampa Formation" and
Suwannee Limestone is summarized by Applin and Applin (1944)
and Puri and Vernon (1964).

The Ballast Point, Brandon and Duette drill cores were
used in making a northwest-southeast correlation of the
"Tampa Formation" and Suwannee Limestone (Figure 18). The
correlation was done on the basis of petrographic simi-
larities between cores. As an aid to correlation, vertical
variation diagrams of orthochemical, allochemical, and
terrigenous constituents were constructed and compared with
one another. Although neomorphism and silicification are
locally intensive within the cores, orthochemical components
(micrite, microspar, pseudospar and sparite) and ghosts of
allochemical grains are generally recognizable. Among these
diagrams, the similarities in vertical variation of contents
of fossils, pellets, and micrite (and microspar) among cores
proved most useful in correlation.

From the correlation, a composite vertical sequence
(Figure 19) was constructed to show the changes in lithology
and stratigraphic relationships of the various lithologic
types. There are four lithofacies distinguished from one
another by macroscopic appearance. These lithofacies are
further divided into 19 subfacies on the basis of microscopic
and macroscopic attributes. The distinctions among these
subfacies reflect differences in the energy levels represented
(Figure 19, Table 6).

Stratigraphic Interpretation

Petrographically derived subfacies classifications are
listed in Figure 19 with their inferred depositional environments
(i.e., supratidal, intertidal, shallow subtidal and deep
subtidal).

The sequence is subdivided into four distinct litho-
facies representing different environments of deposition.

Lithofacies I together with lithofacies II makes up the
major sequence of the Suwannee Limestone which has a distinct
















SEA LEVEL BALLAST
S0 1 -1


BRANDON



-^ipN


KEY


Limestone of "Tampa Formation"

W Suwannee Limestone

Crystal River Formation

I Part of core not studied
/VAvv Disconformities


sections and correlations of the "Tampa Formation" and Suwannee Limestone.


DUETTE


0 6 12
L I I
KILOMETERS







N


Figure 18. Stratigraphic
















Depositionol
Environments

4 -
0 J


0
z 472
I94


0,








., ~.




I


II



T
1~


AP"CAIMATE ~IMqCRACSS UJ
SSATION 45 A0kAERS


810O5PARITE TO POORLY WASHE~D -=q
WSP5A1 TEPE
MPIELSP&RITE m
INTRA.CLAST-SEA&R.N4 SiOSPAR- r
POORLY WASHED FGSSZL-t.NO
PELLET-SEARING. INTRASIZARITE
POORLY WASHED SANDY PELZCY_5_
POO SIOSPARUISTE C___
SIOMIqNTE
PEAT-01ARIwa StON4CRtTE
SOPELM4CAI~T

CLAYEY PELECYPOO SIO4MCRUO.
PELECTPOO atOMc9UOITE
A.TRAUWMCTE
SANDY INTRAAMICKIrE
INTqAAM~CRUDITE
iI(;RGSftATE [
SANDY ^CLAYEY M*CROSPARITE
SANDY MiLRM
OC.O"4ITZEO SANDY 1WACRiTE
ALGA.L SIOLITHITE rl-=
OISCONPoowIt y
MCO* OISCONFON*MiTY 7
CRYtSTAL RIVER -ORMATIUM


Figure 19. Generalized columnar section of the "Tampa For-
mation" and Suwannee Limestone, based on data from the
Ballast Point, Brandon, and Duette cores.







Table 6. Characteristics of depositional environments of the "Tampa
Formation" and Suwannee Limestone.


ENV I RONMENTS
SUPRATIDAL INTERTIDAL SHALLOW DEEP
CHARACTERISTICS SUBTIDAL SUBTIDAL

F o s s i l f r a g m e n t s .*_.. ..* 7_---

Intraclasts ........

Pellets ................... .
STerrigenous quartz .............
S& Phosphate sands
Terrigenous
clays
Micrite -------

Spari te E ........* ---- .-

Dolomite -- 4- -
Desiccation .........
cracks & birdseyes I_ __
Horizontal | S
burrows ........... ........ -.... _____
Swirled and ver--
tical burrows ....... .........
Micrite- ... ______
envelopes______ _________________
Peat seams .............-------
Artic.corallines ----
& codiaceans_____________________________
Dasyclad _______
calcispheres j
"ncrustose
Coral lines
Molluscs .........-
Solitary f *__*, **_* _--- -
corals _
Colonial I
2 corals____
Bryozoans ..... -" .---

Ostracodes .. **.......-- -... -.. -.. -
Algal -- ---.
structures ___________________________


- Aburndant


Common
51


... Rare









Late Oligocene fauna. This section can be subdivided into
nine subfacies. Lithofacies III is the top unit of the
Suwannee Limestone and is subdivided into three subfacies.
This lithofacies is interpreted as a shoreline sequence with
oscillations in sea level which cause changes in the type of
deposition from time to time. In all, the Suwannee Limestone
consists of lithofacies I-III which recorded a general
transgressive phase with minor episodes of regression, and
lithofacies III recorded a general regression with a later
transgressive phase.

The boundary between the Suwannee Limestone and the
overlying "Tampa Formation" is represented by a discon-
formity, indicating sub-aerial exposure and erosion. This
may be related to the Ocala Uplift which Vernon (1951) dated
as post-Oligocene in age.

Upon an erosional surface was deposited lithofacies IV
of the "Tampa Formation" which is typical of the Lower
Miocene Series and characterized by a lithology and fossil
assemblage different from that of the underlying beds.
Lithofacies IV, making up the limestone portion of the
"Tampa Formation" studied, is subdivided into seven subfacies
and represents two carbonate cycles of sedimentation.

Diagenesis

The most important processes of diagenesis within the
varied facies of the Ballast Point, Brandon and Duette are
those of calcitization, dissolution, micrite-envelope formation,
micritization, compaction, cementation, neomorphism and
replacement (dolomitization and silicification). All of the
microfacies found within the cores reflect the effects of
several of these processes, acting either simultaneously or
sequentially (Liu, 1978). Table 7 lists the prominent
diagenetic features developed in the Suwannee Limestone and
the "Tampa Formation."

There are only four common porosity types present in
the Ballast Point, Brandon and Duette cored sections, although
nearly all porosity types described by Choquette and Pray
(1970) were encountered. These four basic types are inter-
particle, intraparticle, moldic and non-fabric-selective
vugs. Usually a combination of different pore types is
found in a subfacies (Figure 20). The visible porosity in
different microfacies varies mostly between 3 to 22% (Figure
21). Sizes of pores generally vary from micropores (less
than 0.06mm) in interparticle to intraparticle types to
small megapores (less than 32mm) in vugs, molds and inter-
particle types.

Textoris et al. (1972) felt that dissolution of the
skeletal allochems, especially in sediments with interparticle
pores, would provide for the reprecipitation of low-Mg
calcite nearby as cement and at times invert location of









Table 7.


Prominent diagenetic features displayed within the subfacies
of the Suwannee Limestone and "Tampa Formation."


Subfacies Diagenetic Features

!Vg Extensive recrystallization of micrite to microspar.
Dissolution of fossils.
Two generations of cementation.

IVf Dissolution of fossils and infilling of the resultant
molds with two generations of sparry calcite
cementation.
Fossils commonly coated by micrite envelopes.

IVe In Ballast Point and Duette cores: completely dolo-
mitized with preservation of original texture;
partial coalescive neomorphism of dolomite with
original texture obliterated or destroyed.
In Brandon core: partly dolomitized by coalescive
neomorphism without preservation of original texture.

IVd In the lower portions: extensive recrystallization of
micrite to microspar and pseudospar; partial replace-
ment of detrital quartz grains by sparry cacite.

IVc Micritized allochems coated by micrite envelopes.
Dissolution of fossils.
Partial replacement of sparry calcite cement by silica
(chert).

IVb Dissolution of fossils and infilling of the resultant
molds with sparry calcite cement.
Fossils coated by micrite envelopes.

IVa Allochemical grains coated by micrite envelopes.
Two generations of cemencation.

IIIc Allochems coated by micrite envelopes.
Two generations of cementation.
In Ballast Point core, partial replacement of echinoid
fragments by silica (chert).


I lIb


Dissolution of fossils.
In upper part of subfacies: high degree of silicification.
In middle part of subfacies: extensive recrystallization
of micrite to microspar.
in lower part of subfacies: partial silicification; re-
crystallization of nicrite to microspar.









Table 7. (continued)


Subfacies Diagenetic Features

lila A high degree of micritization completely destroying the
original algal cellular structure (Banner and Wood,
1964).
Cementation of fenestral pores by sparry calcite.

lie Recrystallized fossil grains, especially dasyclad algal
segments.
Dissolution of fossils and infilling of the resultant
molds with sparry calcite cement.
In Brandon core, high degree of silicification.

lid Micritized allochems.
High degree of cementation developed in intergranular
pores.
Compaction and mechanical breakdown of allochems.

lic Dissolution of fossils and infilling of the resultant
molds with sparry calcite cement.
Micritiized allochems.

lib High degree of micritization of allochems.
Dissolution of fossils.
High degree of cementation developed in intergranular pores.

IIa In upper section: micritized allochems coated by micrite
envelopes; high degree of cementation; partly silicified
echinoid fragments; allochems rim-encrusted by calcite
crystals in Ballast Point core.
In lower section: micritized allochems coated by micrite en-
velopes; partly silicified echinoid fragments.

Id Recrystallized fossil grains.
Slight pyritization in the micrite matrix.

Ic Micritized fossil grains.
High degree of cementation developed in inter- and intra-
granular pores.
Slight replacement of allochems by silica (chert).







Table 7. (continued)

Subfacies Diagenetic Features

Ib Micritized allochems.
Very high degree of cementation developed in inter-
and intra-granular pores.

la Micritized allochems.
High degree of cementation.
Partial replacement of echinoid fragments by silica
(chert).








Suwannee
Biosparite Subfacies
(Subfacies Ic)


96


9e


549
\


Suwannee
Biomicrite Subfacies
(Subfacies IIIc)


30-

45,7

15. i 5
E_ o0


3 7. 5

N


12,5


Suwannee
Biomicrite Subfacies
(Subfacies lie)


48.0


20.0


80
L~J


60-

45 -


24.0

I I 1


Suwannee
Biosparite Subfacies
(Subfacies IIa)


24.6




Inter- Intra-
Particles


0-

100-


50.8



401





Moldic Vug and
Channel


"Tampa" Sandy Clayey Micro-
sparite Subfacies
(Subfacies IVd)


15.4




"Tampa" Pelecv
Biomicrudite I
(Subfacies IV,








6.3

Inter- Intra-
Particles


53. 8

!\


C 1,





es


Moldic Vug and
Channel


TYPES OF PORES

Figure 20. Major types of pores and relative percentages in
selected subfacies of the "Tampa Formation" and Suwannee
Limestone.


60-


I I




; l


so60-

45-

30-



0--


0o-,

45-


30-




0-1










BALLAST POINT


CORE
BRANOON
t I I I-


SEA
LEVEL 0


iO


20


30


i 1 I I I


0 !0 20 30 40 0 10 20 30 40 0
PERCENT POROSITY


10 20 30 40


Figure 21. Variations in visible porosity in the "Tampa Formation"
and Suwannee Limestone.


OUETTE
1 I 1 1 1 1


4C


I










original pore spaces. The moldic porosity type (maximum up
to 17% of a rock unit) is completely controlled by the
abundance of original skeletal allochems which have been
dissolved. This pore type is common in both sparites and
micrites (Figure 20). Skeletons may be completely dissolved
and the resultant voids subsequently solution-enlarged, or
filled with low-Mg sparry calcite to varying degrees.

Interparticle pores are common in sparites. The pore
spaces may reach as high as 21% in volume. Original porosity
was higher and dependent on packing and shapes of allochems.
Interparticle porosity still exists commonly in mollusc-
bearing beds (Figure 20) because of the differences in the
shapes of fossils and packing. The intraparticle pore type
may be found in any skeletal grains which originally had
open chambers foraminiferaa and bryozoans). It is common in
the various rock types of both sparites and micrites, and
may be as much as 5% of the rock volume.

The two rather common, non-fabric-selective vug and
channel pore types are grouped together due to their normally
common genesis. Most vugs are probably solution-enlarged
molds, and some channels are often simply connections between
them. Vug porosity may reach as much as 24% in rock volume.
Many channels are solution-enlarged cracks of various origins,
including fractures. Vugs and channels may be in various
stages of infilling and are more common in the micritic
subfacies.

GEOCHEMISTRY

The Na+ and Sr2+ concentrations and mole-percent-MgCO3
of selected pure calcite or dolomite samples from 16 of the
Eocene carbonate rock cores studies (Figure 1) were measured
and the results were used to evaluate a model of diagenetic
dolomitization. In the process of evaluating this model of
dolomitization, an attempt was made to delineate new, and/or
confirm reported relationships between Sr2+ and Na+ and
mole-percent-MgCO3 and the latest diagenetic solution affecting
the rocks. The geographic position of each core and its Na+
and Sr2+ content were considered in determine the affect, if
any, of groundwater flow patterns of the Floridan Aquifer on
the Na+ and Sr2+ content of diagenetic carbonate minerals
formed within the aquifer. The distribution of Sr2+ was
evaluated to determine if the original mineralogy of the
sediments has any control over the present diagenetic products.

The geochemical significance of Sr2+ and Na+ in calcite
and dolomite stems from their ability to substitute in the
cation layers of the crystal structures of these minerals.
The calcite crystal structure consists of alternating layers
of Ca2+ ions and C032 radicals. The dolomite crystal
structure has alternating layers of Ca2+ and Mg2+ ions with
layers of CO3 radicals in between them. High-Mg calcite








has more than 4 mole-percent-MgCO3 and low-Mg calcite has
less than 4 mole-percent-MgCO3. Dolomite in carbonate rocks
of the Floridan Aquifer has been classified as more nearly
stoichiometric if it contains 44-50 mole-percent-MgCO3 and
non-stoichiometric if it has 39-43 mole-percent-MgCO3.

The geochemical significance of ions such as Sr2+, Na+,
and Mg2+ in the formation and diagenesis of carbonate rocks
has been discussed by a number of authors (Odum, 1957;
Kinsman, 1969; Beherns and Land, 1972; Land and Hoops, 1973;
Viezer and Demovic, 1974; Folk and Land, 1975; Randazzo and
Hickey, 1978; Sarver, 1978, Metrin, 1979).

Odum (1957) reported Sr2+/Ca2+ ratios in ancient rocks
much lower than materials of modern sediments, suggesting
that the sediments had been replaced. Kinsman (1969,
p. 487) stated that "The Sr2+/ Ca2+ ratio of a precipitating
solution plays a dominant role in determining the Sr2+
concentration of precipitated carbonate minerals."

Kinsman (1969, p. 501) also found that calcites pre-
cipitated from a single solution in the down flow areas had
higher Sr2+values than those formed in the up flow areas.
Beherns and Land (1972, p. 159) proposed "... that if the
Ca-planes in dolomite behave like calcite and the Mg-planes
exclude the larger Sr2+ion nearly completely, dolomite
should contain approximately half the amount of strontium as
would a calcite co-existing at equilibrium ."

Land and Hoops (1973, p. 613) indicated that, "The bulk
sodium content of carbonate rocks is a crude but useful
indicator of the salinity of genetic and diagenetic solutions,"
and that Na+ substitutes with equal facility into Ca2+ and
Mg2+ lattice positions in dolomite. Viezer and Demovic
(1974) suggested that the Sr2+ content of carbonate rocks is
facies controlled with the high Sr2+ concentrations inherited
from predominately aragonitic sediments. Folk and Land
(1975) found that lower salinities enabled more stoichiometric
dolomite to form because of the lower concentrations of
other ions competing with Mg2+ and Ca2+ for sites in the
dolomite crystal structure.

In this study, a model of diagenetic dolomitization
involving the mixing of fresh and salt water to produce a
dolomitizing solution as addressed by Hanshaw et al. (1971),
Badiozamani (1973), and Randazzo et al. (1977) was evaluated.
This zone of mixing can occur at the interface between fresh
and saline subsurface waters in a coastal regime and farther
inland in a brackish zone (Hanshaw et al., 1971; Land,
1973). This model has been proposed for a "...later and
continuing stage of dolomitization..." for the Eocene Ocala
and Avon Park rocks of the Floridan Aquifer (Randazzo et
al., 1977).








The sixteen cores analyzed include the Bell (B--
Gilchrist County), Rainbow Springs (RS--Marion County),
Cotton Plant (CP--Marion County), and eight from Gulf Ham-
mock (GH--Levy County) as well as ROMP #101 (LA--Lake
County), #107 (H--Hernando County), #124 (LE--Levy County)
and Homosassa Springs (HS--Citrus County) and Manatee Springs
(MS--Levy County). Detailed geology for these cores is
contained in Stone (1975--GH cores),Hickey (1976--B, RS, CP
cores), Zachos (1978--HS, MS cores), and Fenk (1979--LA, H,
LE cores). Pure calcite and dolomite samples from these
cores were analyzed by X-ray diffraction and atomic ab-
sorption spectrometry.

Samples were ground to a powder, dissolved and diluted
to appropriate volumes. Analysis was done on a Perkin-Elmer
403 Model Atomic Absorption Spectrophotometer. An Amdahl-
470 V62 model computer was used to calculate parts per
million (ppm) of each element analyzed. Magnesium data were
calculated in terms of mole-percent-MgCO3. The data were
plotted to determine significant trends. Methods for quanti-
tative analysis of Sr2+, Na+, Mg2+ and Ca2+ are presented in
Sarver (1978) and Metrin (1979).

Importance of Sodium

The most abundant cation in sea water is Na+ (Land et
al., 1975). The partitioning coefficients of Na+/Mg2+ and
Na+/Ca2+ for natural carbonate has not been defined suffi-
ciently to be employed confidently in the determination of
the paleosalinity at the time of deposition. However, the
overall Na+ content may be a rough indicator of the salinity
of the latest diagenetic fluid (Land and Hoops, 1973; Viezer
et al., 1978). In the model of diagenetic dolomitization
evaluated in this study, dolomitization occurs in the mixing
zone of fresh and saline subsurface waters. In Florida, the
coastal mixing zone is formed at the interface of the fresh
water lense and sea water at the depth based on the Ghyben-
Herzberg relation (Walton, 1970) (Figure 22). Sea water in
the vicinity of Miami Beach has 10,970 ppm of Na+ and fresh
ground water from the interior of the Florida peninsula has
combined Na+ and K+ concentrations ranging from a few parts
per million to about 40 ppm (Stringfield, 1966, p. 155). In
the zone of mixing, the Na+ concentration will be directly
proportional to the degree of mixing (Badiozamani, 1973).
Land and Hoops (1973) pointed out that the trapped and
absorbed Na+ could affect the determination of the Na+ in
the crystal structure of calcite and dolomite. However
flushing of the Floridan Aquifer with fresh ground water
would remove most of the Na+ ions released into solution
during the dissolution and replacement of the original
sediments.


























sc~e


12.5km

1 F n n


Figure 22. The coastal zone of mixing environment of peninsular Florida.
























61


Wafte tlaid
-/


Fre!h water


Satt wat~*r




1.. a

***.~* ..-. .. 7







Sodium in Calcite


Removal of aragonite and high-Mg calcite sediments from
the marine environment where they are stable, can bring
about their replacement by more stable low-Mg calcite and/or
dolomite. Whether the change is to low-Mg calcite or dolomite
is dependent upon the mineralogy of the original sediments,
early-formed diagenetic products and the chemistry of the
diagenetic environment. Pure calcite samples from the cores
in this study have a Na+ content range of 37-970 ppm and an
average of 196 ppm (Table 8). Land and Hoops (1973) reported
Na+ concentrations of 1,010 ppm or more for Holocene marine
carbonate sediments (Table 10). Data from these two studies
show a lower Na+ content for the Eocene carbonates, indicating
that the formation of low-Mg calcite took place in an environment
less saline than sea water. This environment may have been
the inland brackish zone of the Floridan Aquifer or the
coastal salt/fresh water interface.

Sodium in Dolomite

Land and Hoops (1973) suggested that Na+ is able to
substitute into the Ca2+ and Mg2+ positions of the dolomite
structure with equal facility. Therefore, the Na+ concen-
trations of calcite and dolomite may be compared directly.
The replacement of aragonite and high-Mg calcite by dolomite
reflects the environment of diagenesis. The Na+ concentration
of the dolomite studied ranged from 50-1,963 ppm, with an
average of 887 ppm (Table 9). Comparison of this average
with the 196 ppm average Na+ content of the calcites, indicates
that the dolomites were precipitated in a more saline environ-
ment than the calcites. When the Na+ concentrations of the
Eocene dolomites in this study are compared to modern marine
dolomites with Na+ concentrations of 2,000 ppm and more
(Land, 1973; Land and Hoops, 1973), a diagenetic environment
considerably less saline than sea water is indicated.

These low Na+ values for the calcites and dolomites in
this study indicate that even slight mixing of hypersaline
and fresh water can cause dolomitization. A modern dolomite
with 2,000-5,000 ppm Na+ can form by reaction with hypersaline
brines, but, if 5-30% of the brine is mixed with fresh water
to form a more dilute dolomitizing solution, the resulting
dolomite will have only 100-1,500 ppm Na+ Badiozamani
(1973, p. 769) stated that 5-30% sea water is enough to
cause undersaturation of CaCO3 and oversaturation of CaMg(C03)2.
Land (1973) found that as little as 3-4% sea water would
also cause oversaturation of CaMg(C03)2, resulting in dolo-
mitization.

Vertical variation diagrams of Na+ concentrations are
presented by Sarver (1978) and Metrin (1979). They show
higher Na+ concentrations in the lower portion of the LA, H,
HS, B, CP, RS and several of the GH cores. LE and MS cores
show higher Na+ values in the center region of the core. The MS
core also has higher Na+ values in its lowest portion.
These areas of higher Na+ values could be the result of
diagenesis by solutions more saline than that which affected
other portions of the core at other times.
62












Table 8. Sodium and Sr2+ contents of calcite for all cores


Calcite


Strontium ppm
Range Mean


279-968
89-520
264-507
274-546
259-408
244-639
297-444
297-639
279-368


505
285
388
359
322
486
366
377
322


Sodium ppm
Range Mean


140-432
37-296
150-970
138-735
125-286
71-843
85-176
85-152
77-127


238
143
389
295
189
202
136
113
96


Cores


Nos of
Samples








Table 9. Sodium and Sr2+ contents of stoichiometric and
non-stoichiometric dolomite for all cores.


Dolomite

Strontium ppm


39-43 mole-percent-MgCO3
Group


Nos of
Samples


Range

215-319
215-314
201-370
192-334
201-289
210-403
170-262
210-279
201-275


Mean

256
246
246
246
234
282
236
240
229


44-50 mole-percent-MgCO3
Group


Nos of
Samples

0
1
6
17
9
8
17
2
10


Range




150-211
141-183
132-173
258-354
132-157
162-183
119-266


Mean


254
174
152
149
314
140
173
159


Sodium ppm


39-43 mole-percent-MgCO3
Group


Nos of
Samples


Range


Mean


44-50 mole-percent-MgCO3
Group


Nos of
Samples


Range


Mean


363-1,075
548-1,285
557-1,088
897-1,767
290-1,527
566-1,520
504-1,329
517-867
766-1,426


690
754
810
1,143
907
975
1,061
701
1,029


344-862
223-1,963
281-599
857-1,323
205-889
50-693
233-1,575


Cores


Cores


984
581
1,134
377
1,037
335
372
556










Table 10.


Sodium values in carbonate rocks reported in
previous works.


Description and Reference


Modern marine reef calcite and
aragonite sediments (Land and
Hoops, 1973)

Holocene dolomites (Land and
Hoops, 1973)

Pleistocene dolomite of Jamaica
Pleistocene calcite of Jamaica
(Land, 1973)

Eocene dolomite of Egypt (Land
et al., 1975)


Sodium (ppm)


1,140-2,520


1,010-3,050

400

less than 200


213-475


Table 11. Strontium values in carbonate rocks reported in
previous works.


Description and Reference Strontium (ppm)

Modern marine reef calcite and
aragonite sediments (Land, 1973) 1,200-4,140

Modern dolomite from the Persian
Gulf (Land and Hoops, 1973) 640

Pleistocene dolomite of Jamaica 220
Pleistocene calcite of Jamaica
(Land, 1973) 440

Carboniferous dolomite of Northumber-
land, England 132
Carboniferous calcite of Northumber-
land, England (Al-Hashimi, 1976) 618

Eocene dolomite of Egypt (Land et
al., 1975) 90

Platteville Formation, Ordovician,
dolomite 37
Platteville Formation, Ordovician,
calcite (Badiozamani, 1973) 228









Importance of Strontium


Kinsman (1969) has concluded that the Sr2+ concen-
tration of precipitated carbonate minerals is mainly deter-
mined by the Sr2+/ Ca2+ ratio of the precipitating solution.
The crystal structure of individual carbonate minerals also
affects the Sr2+ concentration. The Sr2+ content of sea
water is higher than that of fresh ground water. Odum
(1951a, b) reported an average Sr2+ concentration of 8.1 ppm
for sea water and less than 1 ppm for fresh ground water of
Florida. Because of this difference in Sr2+ content between
sea water and fresh water, carbonate minerals may reflect
the relative degree of mixing of fresh and saline subsurface
waters in the environment that produced them. Kinsman (1969
p. 488) found sea water to have a fairly constant Sr2+/ Ca24
ratio of (0.860.4) X 10-2 except where influenced by continental
waters nearshore. The Sr2+ content of sea water can be
concentrated in the supratidal environment to a Sr2+/ Ca2+
range of (0.8 to 1.2) X 10-2 over a range of solutions from
normal sea water to nine times concentrated sea brines
(Kinsman, 1969, p. 490). Kinsman (1969, p. 490) reported a
median Sr2+/ Ca2+ ratio of 3.2 X 10-2 for surface continen-
tal waters. Subsurface continental waters have a wide range
of Sr2+/ Ca2+ values depending upon the mineralogy of the
rocks through which they flow, but are generally less than
sea water (Kinsman, 1969, p. 490).

The Sr2+ in carbonate rocks is also reflected in the
mineralogy present. The aragonite crystal structure can
accommodate high amounts of Sr2+ (Bathurst, 1975, p. 241).
Modern marine sediments are composed chiefly of aragonite
and high-Mg calcite and have average Sr2+ concentrations of
more than 3,000 ppm (Land, 1973). The carbonate minerals in
ancient carbonate rocks are mostly low-Mg calcite and dolomite,
which do not incorporate as much Sr2+ as aragonite (Bathurst,
1975, p. 241). Table 11 presents Sr2+ values for some modern
and ancient marine carbonates. The ancient carbonate rocks
have much less Sr2+ than the modern carbonate sediments,
indicating later and continuing diagenesis in water less
saline than sea water. The lower Sr2+ content of ancient
marine carbonates also reflects the lesser ability of calcite
and dolomite to incorporate Sr2+ into their crystal structures
than aragonite.

Strontium in Calcite

The partitioning coefficients for precipitated aragonite
and calcite are determined by the Sr2+/ Ca2+ ratio of the
minerals formed. The partitioning coefficient for calcite
is K =0.140.02 at 25 Cand is dependent upon faunal mineralogy
as well as temperature (Kinsman, 1969, p. 488). Based on
the Sr2+/Ca2+ ratio of sea water, and the calcite partitioning
coefficient, calcite precipitated from sea water should have about








2+ 2+
1,200 ppm Sr2. Calcites with less Sr2+ would have been
precipitated from water less saline than sea water. This
would occur in sediments in an open system with solutions
less saline than sea water. The calcites in this study have
a Sr concentration range of 89-968 ppm with an average of
403 ppm (Table 8). This is comparable with other values
reported for ancient marine limestones (Table 11).

Strontium in Dolomite

Synthesis of dolomite at low temperatures has never
been accomplished because of very slow kinetics involved in
its formation (Berner, 1971). Therefore, the partitioning
coefficient is undefined and cannot be used to predict the
Sr2+ content of dolomite precipitating from sea water as was
done with calcite. However, as stated earlier, the dolomite
crystal structure should contain approximately half the
amount of Sr+ as would calcite precipitated from the same
solution (Behrens and Land, 1972). This would be approximately
600 ppm Sr a value supported by Land and Hoops (1973,
Table 4).

The Sr2+ values of the dolomites in this study range
from 119-403 ppm with an average of 239 ppm (Table 9). This
suggests that the latest diagenetic solution in which the
dolmite formed was less saline than sea water. The average
Sr content of the calcites is 403 ppm. The Sr2+ content of
the dolomites is approximately 59% of that in the calcites.
This is some 9% more than the amount predicted by Behrens
and Land (1972) based on the incorporation of Sr'+ into the
dolomite crystal structure. Land (1973) stated that this
difference in the Sr2+ content was caused by an outside
source and suggested sea water as that source. This would
indicate a greater relative amount of salt water present in
the dolomitizing zone and is compatible with the Na+ data,
indicating a more saline diagenetic environment for dolomite
than calcite. Calcites show considerably higher Sr2+ concentrations
than the dolomite because of the greater ability of calcite
to incorporate Sr into its crystal structure.

Strontium and Sodium in Relation to Mole-Percent-MgCO3

The relationship between the Sr2+ and Na+ concentrations
and the mole-percent-MgCO3 of dolomite was a means by which
the diagenetic model of dolomitization was evaluated. The
same data for calcite was used to interpret the chemistry of
the diagenetic environment. In the Floridan Aquifer, there
is a brackish zone between fresh and saline phreatic waters
(both saturated with calcite). This brackish zone is under-
saturated with calcite and supersaturated with dolomite
(Hanshaw et al., 1971). Dissolution of calcite can occur in
the undersaturated zone and physical mixing of the brackish
waters can cause CO2 to degas, enabling dolomite to precipitate.








Badiozamani (1973) found that when undersaturation of
calcite and degassing of CO2 occur, a solution with as
little as 3-30% sea water can cause replacement by dolomiti-
zation. Folk and Land (1975) proposed that with a Mg2+/Ca2+
ratio of at least 1, dolomitization can occur. Also they
found that lower salinities produced more ordered dolomites
with higher mole-percent-MgCO3 because there are fewer ions
competing for positions in the dolomite structure. This
suggests that hi h mole-percent-MgCO3 dolomites should have
lower Na+ and Sr2+ concentrations and would indicate the
relative salinity of the latest diagenetic solution.

Sections of the cores in this study contained both
calcite and dolomite. These sections of mixed mineralogies
could have resulted from the depletion of Mg2+ ions in the
solution by precipitation of dolomite and the subsequent
formation of low Na+ and Sr2+ calcite as more fresh water
flushed through the system (Land, 1973). The Na+ and Sr2+
concentrations associated with various mole-percent-MgCO3
contents of carbonate rocks are an indication of the relative
salinity of the environment during neomorphism.

The mixing zone model of dolomitization would be able
to produce the thick dolomite sequences in Florida because
"...sea level changes, climatic changes, and/or the occasional
uplift or downwarp of the Florida platform ..." (Hanshaw et
al., 1971, p. 722) could cause the brackish zone to move
within the system and contact large volumes of rock inland
and bring about substantial lateral migration of the sea
water/fresh water coastal zone of mixing.

Calcite

Nearly all of the calcite in this study is low-Mg
calcite with less than 4 mole-percent-MgCO3 It has much
lower Sr2+ and Na+ concentrations than modern marine carbonate
sediments (Tables 8 and 10). This may be the result of
diagenesis in an open system with fresh or slightly saline
water because calcite formation is inhibited by Mg2+ ions
(Berner, 1966). The slight changes of mole-percent-MgCO3
that did occur in the calcites had no corresponding changes
in Na+ and Sr2+ concentrations. However, the ranges of Na+
and Sr2+ values in the calcites could be caused by the
original mineralogy of the sediments (Veizer and Demovic,
1974) or by the position of the core in relation to the flow
patterns of the aquifer (Kinsman, 1969). If the original
sediments were aragonite, a higher content of Sr2+ should be
inherited by the precipitated calcites (Veizer and Demovic,
1974). If the calcites were in the down flow direction or
discharge area of the aquifer, they should have higher Sr2+
concentrations (Kinsman, 1969). These two factors, along
with the salinity of the diagenetic solutions, could cause
the wide variation of Sr2+ in the calcites.









Dolomite

As stated earlier, the dolomites in this study fall
into two groups, more nearly stoichiometric and non-sto-
ichiometric dolomite. Both groups have distinct Sr2+ and Na+
ranges (Table 9).

The more nearly stoichiometric dolomite (44-50 mole-
percent-MgCO3) occurs mainly in the lower portions of the B,
RS, CP, LE, MS and HS cores.

The higher mole-percent-MgCO3 dolomites generally have
a narrower range of Sr2+ concentrations than the non-
stoichiometric dolomites (Table 9). This may suggest a
longer resident time for the diagenetic fluids and possibly
a greater approach to equilibrium between crystals and
solution. The Sr2+ values for the 44-50 mole-percent-MgCO3
group are generally less than the 39-43 mole-percent-MgCO3
dolomites. Folk and Land (1975) attributed this type of
relationship to the formation of higher mole-percent-MgCO3
dolomite in less saline water allowing slower, more precise
ordering to occur with less inhibition by competing ions.

The data in this study show a positive correlation
between Na+ and Sr2+ in the dolomites of the B, RS, CP, GH,
MS and LE cores. These cores are in an area of "...large
discharge of artesian water..." (Stringfield, 1966, p. 130).
This large discharge could flush most of the trapped and
absorbed Na+ from the rocks. The LA, H and HS cores do
not show this positive correlation between the Sr2+ and Na+
values (Metrin, 1979). The Na+ concentrations vary over a
wide range, while the Sr2+ values are fairly constant. The
LA core is in an area of local recharge (Stringfield, 1966,
p. 126). The H and HS cores are in an area of local recharge
where the aquifer is at the surface. However,water also
discharges as large springs along the coast and on the floor
of the gulf (Stringfield, 1966, p. 130). This high discharge
(5.376m /sec for Homosassa Springs; United States Geological
Survey, 1974) in the area of these cores could cause fluctuations
in the ground water geochemistry, as the large amounts of
fresh water discharge lower the salinity of sea water. This
could cause the salt/fresh water interface to move seaward.
These variations in the salinity of the diagenetic fluids
could cause the wide ranges of Na+ values in these cores.
Also, Na+ could be contributed by trace amounts of clay pre-
sent in the original sample.

The changes in salinity that produced the distinct
ranges of Na+ and Sr2+ concentrations of the two dolomite
groups may have been caused by movement of the dolomitizing
fluids through the system. In response to climatic and/or
tectonic changes, inland brackish fluids would pass through
the aquifer as the phreatic zone fluctuated vertically. The
coastal salt/fresh water interface would migrate laterally
as changes in sea level occurred. This could cause changes









in the Na+ and Sr2+ concentrations of the dolomites of a
core as the dolomitizing solutions flowed through the aquifer
producing later and continuing dolomitization of the Floridan
Aquifer (Randazzo et al., 1977, p. 501).

The variations between Sr2+ and Na+ ranges in coastal
and inland cores are the result of the mineralogy of the
original sediments and/or the high discharge of fresh water
in the area of the coastal cores in this study, causing
modification of the three dimensional shape of the salt/fresh
water interface and consequent fluctuations of the ground
water geochemistry.

The results of this geochemical study of the distribution
of Na+ and Sr2+ within Eocene carbonate rocks of the Floridan
Aquifer support a mixing zone model of dolomitization, which
dolomitizes this sequence of rocks, with solutions less
saline than sea water. These dilute saline solutions can
be formed at the coastal salt/fresh water interface, modified
by fresh water discharge, or in an inland regime in the
brackish zone of the phreatic system.

SUMMARY

The carbonate units comprising the Floridan Aquifer in
the northern portion of the Southwest Florida Water Manage-
ment District were deposited in a shallow marine environment
and represent a complex history of deposition and diagenesis.
A number of lithofacies have been recognized and examination
of the vertical distribution of lithologies among cores has
enabled the recognition of cyclic sedimentation patterns in
the strata.

The Lake City Formation is represented by two distinct
depositional cycles. An open marine environment changed to
intertidal and supratidal environments. Shallow water is
indicated by the presence of algal boundstones and wackestones
and slightly deeper water by foraminiferal wackestones. The
upper portion of the last cycle is represented by lagoonal
deposition of mudstones, gypsum-bearing clay beds and a
significant amount of carbonaceous matter.

The carbonate rocks of the Avon Park Formation provide
evidence of deposition in an environmental complex consisting
of subaerially exposed tidal mudflats and intervening,
protected, shallow-water lagoons. A number of carbonate
facies have been recognized and examination of the vertical
distribution of lithologies within cored intervals has
enabled the recognition of cyclic sedimentation patterns in
Avon Park strata.

Subtidal facies show a general lack of sedimentary
structures and are represented by a greater abundance and
wider diversity of fossils than associated intertidal and
supratidal deposits. The lithologic and paleontologic charac-
teristics of these subtidal rocks suggest that they were
70







deposited in environments ranging from a broad carbonate
shelf or platform to a low energy lagoonal setting. Inter-
tidal rocks are characterized by a predominance of micrite,
indicative of the low tidal and wave energies which pre-
vailed in the depositional environment. Fossils are sparse
and the low faunal diversity of intertidal rocks may be a
reflection of unstable ecologic conditions which had limited
the presence of organisms in this tidal zone. Sedimentary
structures preserved in intertidal rocks include: vertical
burrows; root casts and molds; sediment mottling; and thin,
micritic beds. The most characteristic feature of the
supratidal rocks is thin, algal and sedimentary laminations.
Crinkled and flat laminar morphologies similar to those
found in the modern carbonate deposits of Andros Island,
Bahamas are abundantly represented in supratidal facies. A
scarcity of desiccation structures and evaporite minerals in
supratidal beds may suggest that deposition had taken place
under general humid paleoclimatic conditions.

The sediments of the Ocala Limestone were deposited
under warm and open marine conditions on a relatively flat
and broad carbonate shelf or platform similar to the present
day Great Bahama Bank. The Ocala Limestone is composed of
two major lithologies, separating the strata into distinct
upper and lower lithologic units. Deposits representing
shallow subtidal to intertidal, comparatively high energy,
open or slightly restricted marine conditions occur in the
lower unit where deposition is interpreted to have taken
place relatively close to the shore. As a lithology, the
Lower Ocala is characterized by thickly bedded fossiliferous
limestone consisting predominantly of cleanly washed skeletal
packstones to grainstones.

The carbonate deposits of the Upper Ocala represent a
transition into progressively deeper water, lower energy
environments of sedimentation. The unit is characterized by
the presence of a deeper-water faunal assemblage, including
abundant whole and fragmented tests of large foraminifera,
and the deposition of wackestones and muddy packstones over
the cleanly washed deposits of the lower unit.

The change from the tidal-flat and restricted subtidal
deposits of the Avon Park to the offshore, high and low
energy marine deposits of the Ocala Limestone is indication
of an overall transgressive sequence of sedimentation. The
vertical succession and cyclic alternations of lithologies
is interpreted to be the result of periodic sea level fluctuations
characterized by local and repeated seaward shifts in the
shoreline environment.

The Suwannee Limestone and "Tampa Formation," as they
occur in the subsurface of Hillsborough and Manatee Counties,
south Florida, were deposited on a shallow marine carbonate
bank. The Suwannee Limestone is a white, whitish-gray to
yellowish-gray, allochemical limestone characterized by its
abundance of fossils and relative importance of pore-filling
sparite. The Suwannee Limestone consists of three lithofacies
and represents a series of rock types deposited mostly in an
agitated water, shallow subtidal zone above wave base.
71











The microcrystalline limestone and autochthonous algal
limestone of the Suwannee are only present near the top of
the sequence. These rock types can be attributed to their
deposition in the supratidal environment.

The disconformable erosional surface between the Suwannee
Limestone and the "Tampa Formation" represents a depositional
hiatus. Furthermore, a few micro-disconformities are found
within both of these formations, each representing local
diastems.

The "Tampa Formation" is a gray or dark gray, sandy,
clayey, allochemical limestone characterized by its abundance
of micrite, extra-basinal materials and local concentrations
of fossils. Microcrystalline limestone, dolomite and partly
dolomitized limestones are found only in the middle part of
the sequence. The sequence was deposited mostly in the
supratidal and intertidal environments.

In all, the Suwannee Limestone in the area records a
general transgressive-regressive sequence which ended with
subaerial exposure and erosion. The erosional surface is
overlain by a basal limestone conglomerate which was followed
by another phase of sedimentation during which the "Tampa
Formation" was deposited.

Diagenetic (crystallization) fabrics can be classified
on the basis of constituent crystal size distributions (uni-
or multi-modal) and combination of textural types. Basic
categories are:

(a) Equigranular
(i) peloidal
(ii) sutured mosaic
(iii) sieve mosaic

(b) Inequigranular
(i) spotted mosaic
(ii) fogged mosaic
(iii) contact-rhomb porphyrotopic
(iv) floating-rhomb porphyrotopic
(v) poikilotopic

(c) Aphanotopic

Consideration of natural associations and genetic
relationships of crystallization fabrics makes it possible
to deduce the original uncrystallized fabrics in many cases.
Type of porosity development is directly related to type of
crystallization fabric, except in the case of vug or cavernous
porosity (nonfabric selective). Vug porosity occurs sporad-
ically in dolomitized fabrics. Cavernous porosity is associated
with formational contacts and may be caused by gross mineralogic
changes in the rocks (e.g., the change from dominantly
calcitic to dominantly dolomitic rocks).










The close agreement of depositional cycles, patterns of
crystallization fabric distribution, and patterns of porosity
development in these cores suggests that predictive models
of mineralogy, fabric, and porosity development can be
constructed. The viability of such models will depend upon
reproducibility and recognition of these patterns in other
wells.

Atomic absorption spectrometry measurements of Sr2+, Na+
and mole-percent-MgCO3 have allowed the recognition of
distribution patterns related to depth, geographic position,
and diagenetic mineralogy.

Sodium and Sr2+ concentrations provide evidence in
support of a mixing zone model of diagenetic dolomitization
as presented by Hanshaw et al. (1971) and Land (1973). This
mixing zone can occur on the coast at the salt/fresh water
interface or in the brackish zone of the phreatic system
farther inland. Diagenesis occurred within a dynamic open
system in the Floridan Aquifer resulting in dolomitization
when sufficient Mg2+ ions were available and calcitization
when the supply of Mg2+ ions was lacking.

Higher concentrations of Sr2+ and Na+ in dolomite than
in calcite indicate a more saline diagenetic environment
during the formation of dolomite. The Sr2+ and Na+ con-
centrations and mole-percent-MgCO3 in calcite indicate
diagenesis in a uniform environment less saline than sea
water. Comparison of the Sr2+ and Na+ concentrations of the
Eocene dolomites with modern marine dolomites indicates
diagenesis in an environment less saline than sea water. Sr2+
and Na+ concentrations in dolomite are generally lower in
the higher mole-percent-MgCO3 dolomites, indicating a less
saline environment of formation with fewer ions competing
for sites in the dolomite structure. The Sr2+ values in
calcite could be inherited from original aragonitic sediments
or could be the result of formation in the discharge area of
the aquifer.

Some of the coastal cores of this study have lower Na+
and Sr2+ concentrations than the inland cores, suggesting a
less saline diagenetic environment for the coastal cores.
The large springs with high fresh water discharge near the
coastal cores of this study could account for this difference
by lowering the salinity of sea water and causing a seaward
shift of the salt/fresh water interface. The Sr2+ values
for the LA, H and LE cores reflect the presence of calcite
or dolomite. The LA and H cores have higher Na+ values in
their lower portions. The LE core has higher Na+ values in
its center region. This suggests fluctuations in the chemistry
of the diagenetic environment as the dolomitizing solutions
moved through the aquifer in response to climatic, tectonic,
and/or sea level changes.







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Full Text

PAGE 1

WATER IiRESOURCES researc center Publication No. 46 GEOHYQROLOGIC MODEL OF THE FLORIDAN AQUIFER IN THE SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT By Anthony F. Randazzo (Principal Investigator) Department of Geology University of Florida Gainesville UNIVERSITY OF FLORIDA

PAGE 2

GEOHYDROIOGIC IDDEL OF THE FLORIDAN AQUIFER IN THE SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT By Anthony F. Randazzo Publication No. 46 FLORIDA WATER RESOURCES RESEARCH CENTER RESEARCH PROJECT TECHNICAL CCMPLEl'ION REPORT OWRT Project Number B-032-FLA Matching Grant Agreerrent Number 14-34-0001-7148 Report Submitted: January 7, 1980 The work upon which this report is based was supported in part by funds provided by the United States Depa.rt:rrent of the Interior, Office of Water Research and Technology as authorized under the Water Resources Research Act of 1964 as a:rrended

PAGE 3

TABLE OF CONTENTS Abs tract .............................................. i v Introduction. . . . . . . . . . .. 1 Methods of Study................................. 1 Previous Work.................................... 3 Manatee Springs and Homosassa Springs ................. 4 Stratigraphy. . . . . . . . . .. 4 Sedimentology-Lithofacies. . . . . .. 4 Cyclic Sedimentation ........................ lO Depositional Environments ................... lO Diagenesis ....................................... 12 Crystallization Texture and Fabric Classification ............................. 12 Porosity .................................... 16 Fabric Selectivity of Dolomitization ........ 24 Summ.ary ......... 1 32 Romp Cores ........................................... 33 Avon Park Formation ............................. 33 Cyclicity ................................... 33 Recognition of Depositional Environments in Avon Park Strata ........................ 37 General Lithology .......................... 38 Depositional Facies ........................ 43 Ocala Limestone .................................. 44 Lower Ocala Limestone ..................... 44 Upper Ocala Limestone ................... 45 Ballast Point, Brandon, and Duette Cores ............ 47 Stratigraphy ..................................... 48 Stratigraphic Interpretation ............... 48 Diagenesis ....................................... 52 Geochemistry .......................................... 58 Importance of Sodium .......................... 60 Sodium in Calcite .......................... 62 Sodium in Dolomite .......................... 62 ii

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Importance of Strontium ........................... 66 strontium Strontium in in Calcite Dolomite. Strontium and Sodium in Relation to .. 66 . .67 Mole-Percent-MgC03. . . . ............ 67 Calcite .. Dolomite .68 .. 69 Summary ................................................ 70 References Cited ....................................... 74 iii

PAGE 5

ABSTRACT Nineteen cores from the northern portion of the Southwest Florida Water Management District and three counties adjacent to it were analyzed by megascopic, microscopic, x-ray diffraction, and atomic absorption spectrometry techniques for the determination of lithofacies, paleontology, mineralogy, and geochemistry. These wells penetrate biozones representative of the "Tampa", Suwannee, Ocala, Avon Park, and Lake City Formations. The Avon Park and Lake City Formations are characterized by interbedded massive, fossiliferous carbonate (limestone and dolomite) rocks (wackestone to grainstone) and thinly bedded peloidal and carbonaceous rocks (mudstone and wackestone). These represent subtidal (open marine and lagoonal), intertidal, and supratidal deposition. The Ocala Limestone is characterized by thickly bedded, fossiliferous limestone (mostly packstone and grainstone), representing subtidal and some intertidal depositional environments. The Suwannee Limestone consists of interbedded fossiliferous, partly dolomitized carbonate rocks (mudstone to grainstone) and an algal boundstone facies. These Suwannee deposits represent subtidal, intertidal and supratidal sedimentation. The "Tampa" Formation represents deposition in shallower marine waters and contains substantial quantities of clay and quartz and phosphatic sand, interbedded with carbonate rocks (mudstone to packstone). Numerous depositional cycles were recognized by cyclic occurrences of rock types and depositional environments. A wide range of diagenetic fabrics from early to late stages of development occur. Fabrics are classified descriptively as equigranular (uni-modal) or inequigranular (multi-modal). Fabrics composed of crystals
PAGE 6

The distribution of Na+ and Sr2 + ions and mole-percentMgC03 in carbonate rocks of the Floridan Aquifer supports a mixing zone model of diagenetic dolomitization. The inland phreatic zone consists of brackish solutions in the Floridan Aquifer. A coastal mixing zone exists at the salt/fresh water interface, but the flow patterns of the Floridan Aquifer can modify the three dimensional shape of this interface. Areas of locally high discharge, such as artesian springs, move the interface seaward. Variations in sea level and fluctuations of the phreatic zone related to climatic and tectonic changes could cause the dolomitizing solutions to contact large volumes of rock through time, resulting in the thick sequences of dolomite in the Floridan Aquifer. The Na+ content of carbonate rocks is an approximate indicator of the salinity of the latest diagenetic solution. Sodium concentrations of the calcites are 37-970 ppm, indicating a slightly saline diagenetic fluid. Dolomite has 281-1963 ppm Na+ and was formed in a slightly more saline solution. Strontium concentrations of carbonate rocks reflect the salinity of the latest diagenetic fluid and the diagenetic mineralogy. The Sr2+ concentration range of the calcites is 89-968 ppm, demonstrating diagenesis in a slightly saline solution, probably in an open system. The average Sr2 + content of the dolomites is approximately 59% of that in the calcites, indicating a more saline diagenetic environment for dolomite than calcite. The more nearly stoichiometric dolomite generally has a narrower range of Sr2 + concentrations than non-stoichiometric dolomite indicating a more saline diagenetic environment for the non-stoichiometric dolomite where a greater number of competing ions inhibit dolomite ordering. The formation of dolomite and its influence on rock texture and porosity are directly related to past and present hydrologic regimes interacting with aquifer limestones. v

PAGE 7

INTRODUCTION The Floridan Aquifer represents one of the world's finest aquifer systems and is relied upon as Florida's principal supply of fresh water. Detailed geologic knowledge of the Tertiary limestones comprising the aquifer is only now beginning to be compiled. Identification of the type and distribution of minerals, the arrangement, character and quantity of lithologic constituents,and the correlation of stratigraphic horizons would aid greatly our understanding of groundwater flow systems. The inaccuracies and uncertainties of our geologic knowledge of the Floridan Aquifer could be resolved by establishing a petrogrphic and geohydrologic model. Such a model would demonstrate the lithologic evolution of the aquifer and would be of fundamental importance in water management practices. This research effort was concentrated in the northern portion of the Southwest Florida Water Management District where drill-cored materials were most available for study (Figure 1). The principal stratigraphic formations studied were the Lake City, Avon Park, Ocala, Suwannee, and "Tampa" units. Rocks from this area were compared with those studied in an earlier investigation (Randazzo, 1976b). The petrologic characteristics of the Floridan Aquifer in the current study area have been described. The original depositional environments of the rocks were deduced and the effects of diagenesis have been recognized. Results have been applied to the clarification of stratigraphic problems. Geochemical analyses of the rocks have revealed the history of water/rock interactions. A better understanding of how porosity evolved has been achieved. Petrologic and geochemical parameters which control the functioning of hydrologic systems have been evaluated and may be useful in the prediction or deduction of future aquifer changes. Methods of Study In this study nineteen cored sections were examined from the northern portion of the Southwest Florida Water Management District and three counties adjacent to it (Figure 1). Numerous samples were also taken from quarries in the area. More than 1,000 thin sections were prepared and analyzed to determine the constituents of the rocks and the diagenetic changes that have occurred. The composition of the rocks was determined by point counting with approximately 250-300 point counts made on each thin section. Mineralogy was determined by X-ray diffraction analysis. Where calcite and dolomite were present in the same sample, a thin section of that sample was stained (Friedman, 1959) to determine which constituents of that rock were of calcite 1

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I ]I GH REPRESENTS 8 CLOSELY SPACED CORES o LEVY 25 SCALE MARION .CP HERNANDO PASCO HILLSBOROUGH eaR -0 MANATEE 50 km Figure 1. Index map of the study area showing core locations (B = Bell, MS= Manatee Springs, GH = Gulf Hammock, LE = Levy County-ROMP #124, RS = Rainbow Springs, CP = Cotton Plant, HS= Homosassa Springs, H = Hernando County-ROMP #107, LA = Lake CountY-ROMP #101, BP = Ballast Point, BR = Brandon, 0 = Duette). 2

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and which were dolomite. A1azarin red-S in a solution of NaOH was used to distinguish dolomite from calcite. The scanning electron microscope was also employed for minute textural studies and the determination of Mg/Ca ratios of selected a11ochemica1 constituents. Atomic absorption spectrometry was used for strontium and sodium detection and quantification. Mole-percent MgC03 of calcite and dolomite were calculated from data obtained by X-ray diffraction and atomic absorption spectrometry. The rock classification used herein is that proposed by Folk (1962). Grain-supported and matrix-supported distinctions have been made and the classification scheme of Dunham (1962) is used where appropriate. Previous Work The petrology and depositional environments of the carbonate units comprising the Floridan Aquifer have only recently been investigated. The broadly defined works of Vernon (1951) and Chen (1965) have been utilized in an attempt to relate modern carbonate shoreline processes to the sedimentologic environment represented (Randazzo and Saroop, 1976; Randazzo et a1., 1977). Several studies have been concerned with the nature and diagenetic alteration of carbonate rocks (Bricker, 1971; Purser, 1973; Folk, 1974; Folk and Land, 1975; Veizer et a1., 1977). The geochemical history and characteristics of these rocks and their relationship to hydrologic conditions have been addressed by Randazzo (1976b) and Randazzo and Hickey (1978). The oldest exposed rocks in Florida are Late Middle Eocene (Avon Park Formation). These rocks crop out on the crest of the Ocala Arch and are surrounded by rocks of Late Eocene age (Ocala Limestone) which occur on the flanks of the arch. These formations are the principal units composing the Floridan Aquifer. The Suwannee Limestone of Oligocene age, often exposed at the surface, is an important part of the aquifer in certain areas of Florida. The Lake City Formation of Middle Eocene age occurs only in the subsurface but is also a significant component of the Floridan Aquifer. This investigation involved a number of graduate students who made noteworthy contributions to the total research effort. The reader is directed to the works of Saroop (1974), Stone (1975), Hickey (1976), Liu (1978), Zachos (1978), and Fenk (1979) for elaborate details on the lithologic and paleontologic characteristics of the various lithofacies recognized. Hickey (1976), Sarver (1978), Zachos (1978), and Metrin (1979) discussed the diagenetic and geochemical aspects of the important carbonate rock-forming minerals, calcite and dolomite. Our combined efforts have resulted in the verification of a model of dolomitization by groundwater in the peninsula of Florida as postulated by Hanshaw et a1., (1971). Some of the results of our studies are summarized in a number of recent pUblications (Randazzo and Saroop, 1976; Randazzo, 1976a; and Randazzo and Hickey, 1978). References to other important contributions regarding stratigraphy, petrology, geochemistry and hydrology are presented in later sections of this report. 3

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MANATEE SPRINGS AND HOMOSASSA SPRINGS Stratigraphy Rock cores were drilled at Manatee Springs (MS) and Homosassa Springs (HS) by the Florida Bureau of Geology. The oldest of the three formations penetrated in these wells is the Lake City Formation which is recognized by the following combination of features: presence of highly carbonaceous beds; clay beds; common quartz; glauconite and gypsum; and by poiki1otopic fabric seen in thin section. Fabu1aria mat1eyi, Archaias co1umbiensis, and Dictyoconus americanus occur together 14.68m above the top of the Lake City in the MS core, and F. mat1eyi and A. co1umbiensis occur together 22.56m below the top in the HS core. Dictyoconus americanus has not been positively identified in the HS well. Two distinct depositional cycles are recognized in the Lake City Formation in the study material. The Avon Park Formation overlies the Lake City Formation in both wells. The top of the Avon Park is determined by the first occurrence downward of a mudrock lithofacies which corresponds with the first occurrence of dolomite. The top is also marked by cavernous porosity; increased amounts of quartz, gypsum, and metallic sulfides; by poiki1otopic fabric seen in thin section; and by the first occurrence of Dictyoconus cookei in both cores. Five distinct depositional cycles are differentiated in the Avon Park represented by the study material. The Avon Park Formation is overlain by the Ocala Limestone. The Ocala Limestone has been biostratigraphica11y zoned by many authors using many different taxonomic groups and types of zones. A comparision of various zonations is shown in Table 1. Both wells enter the Ocala Limestone at an erosional unconformity with overlying Pleistocene or Holocene sands and do not represent the entire formation. Problems concerning recognition of the top of the entire unit will not be considered here (see Hunter, 1976). The Ocala Limestone is represented by one depositional cycle. Sedimen to1ogy -Li tho facies Rocks of the MS and HS cores can be divided into four major lithofacies (Table 2). Mudrocks [represented by mudstone (Dunham, 1962)J have grain contents of less than 10%, and for the most part contain less than 5% grains. Rocks with 10% or more grains [represented by wackestone, packstone and grainstone (Dunham, 1962)J are divided here on the basis of grain type. Skeletal grains (Leighton and Pendexter, 1962) and peloids (McKee and Gutschick, 1969) make up the most significant grains volumetrically (Figure 2) and the variation in their ratios can be used to differentiate most of the rocks. A few samples contain 4

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Table 1. Ocala biofacies. Pur; (1957) Cheetham (1963) McCullough (1969) Nicol & Shaak (1973) Zachos & Shaak (1978) Williams et al. (1977) Lepidocyclina chaperi Spondylus dumosus faunizone faun; zone Asterocyclina-Spirulaea Spi rul aed. vernoni 01iJ1.Q.P19US wetherbyi vernoni faunizone Floridina antigua biozone biozone I.. ... Nummulites vanderstoki faunizone Amusium range zone {=Camerina willcoxi}-biolone-faunizone Lepidocyclina-Pseudophragmina' faunizone Exputens ocalensis i Ul biozone Spiroloculina newberryensis Oligopygus haldeman; faunizone Tubucellaria nodifera biozone fauni zone Opercul;noides mood)branchensis (=Camerina willcoxi faunizone Operculinoides jacksonensis (=Camerina willcoxi)' faunizone Concurrent range zone Periarchus lyel'i floridanusPeriarchus lyelli Plectofrondicularia? faunizone Oligopygus phelan; inglisiana faunizone bi ozone

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Table 2. Lithofacies terminology. Dunham Mudstone Wackestone, Packstone, Grainstone (1962) <10% Grains Grains I <: 0 :;::; Other Grains >75% Other Grains .,... '" 0 0-E 0 Skeletal/Peloidal Grain Ratio '-' <1 II thofaci es Mudrod Peloidal Rock Tenn Skeletal Rock Characterized By Major Constituent 6

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-....J 0/0 Other Groins 0" 100 Peloidal Rocks Skeletal Rocks % .. !laa I ., Grains Figure 2. Distribution of grain types in the MS and HS cores. '10 Sketetal Graihs

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LEGEND Peloidal Rock Skeletal Rock D Mud rock Clay a Quartz Sand [Z] ..... ... .... .... .. .. Figure 3. Skeletal/Peloidal grain ratios and lithofacies distrubution iri the MS and HS cores. 8

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MS Skeletal/Peloidal Rctio 0 3: 30 "t-0, a. 3: o Q) m CII) '-0 r r-.r= Q,. Q) o 150 co .(0 u 0 0 .r::. ..J en CD c -.... 0 .t::. ..J Cycle VIII Cycle Vii Cycle VI Cycle IV CycJe II Cycle I 9 HS Sit.lctal/Peloidal Ratio 0 I C) 0 .c. Co CD C

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greater than 75% grains other than skeletal Or peloidal, and these are referred to minor lithofacies named according to the major constituent. Skeletal grains include all recognizable remains of hard parts secreted by organisms. They can generally be divided into fragmental and non-fragmental gnains, but the distinction is difficult to determine from thin section. Peloids are allochems composed of non-structured, micro-or cryptocrystalline material. They may represent wholly micritized skeletal grains, mud aggregates, pellets, and, in diagenetically altered rocks, the problematic clotted fabric or structured grumeleuse of Cayeaux (1935) (see especially Bathurst, 1975, p. 511-513). The term is very useful in that no genetic origin is assumed in its usage. Peloidal rocks are characterized by skeletal/peloidal grain ratios less than 1; skeletal rocks by ratios of 1 or greater. The distribution of lithofacies in the two cores is shown in Figure 3. Cyclic Sedimentation The variation in the skeletal/peloidal grain ratios are shown diagrammatically in Figure 3. Plotted values are restricted to samples containing 10% or more grains. Values were measured from point-counts of thin sections, and sample only certain portions of the cores (i.e., the diagrammed variation is only a sample of the real variation in the cores). The similarity in trends is, nevertheless, close. Corresponding variations in the sense if not the actual magnitude of the ratios is used as a basis of correlation. The mudrock lithofacies mayor may not be correlatable, which is in part caused by the diagenesis of otherwise recognizable skeletal or peloidal rocks which results in fabrics lacking original grains. Correlation of the study cores on this basis makes possible the recognition of repeated cycles of generally peloidal to skeletal sedimentation. Closer examination of these grossly defined cycles and consideration for finer grain-type distinctions, assessory minerals, and sedimentary structures suggests that these may in face represent actual cycles or carbonate sedimentation, with more than local significance. Depositional Environments Four major depositional environments can be recognized by a combination of criteria, including grain size and type, mineralogy, and sedimentary structures. Open Marine: This is the normal marine environment, represented by waters of average salinity, temperature, and composition, and with a bottom environment characterized by slightly oxidizing conditions. Sediments deposited in this environment are characterized by a lack of thin stratification or lamination, visible organic material, gypsum, or significant amounts of clay minerals. Large echinoids, mobile pelecypods, bryozoans, and abundant benthic foraminifera are diagnostic. The extensive dolomitization of these rocks makes it difficult to distinguish low and high energy deposits 10

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(i.e., deep and shallow subtidal), but corals and coralline algae, when present, indicate fairly shallow, agitated waters (Purdy, 1963). Skeletal packstones and grainstones are dominant, with some wackestones. Lagoonal: This environment is characterized by salinities, temperatures, and bottom Eh different from the open marine environment, from which it is isolated by actual barriers or by restriction of circulation by shallowness. It is analogous to the shelf lagoon environment described by Purdy (1963) and includes the adjacent subtidal environment discussed by Shinn et ale (1969). Salinities generally are higher than open marine, temperatures may rise infrequently as high as 40C (Glynn, 1968), and bottom conditions may be slightly oxidizing or reducing. Sediments consist mainly of pellets or mud aggregates (Shinn et al., 1969; Purdy, 1963), combined here under the term peloids. Water is quiet and non-agitated, since, as Purdy (1963) notes: ... the preservation as well as the formation of pellets is dependent upon minimal bottom agitation" (p. 484). Visible organic matter may be present, and its decomposition may have induced strong reducing conditions in the sediment, and thus restriction of infauna. Lamination and stratification are not common, but may be present in deeper and quieter parts of the shelf or lagoon. Generally the faunas will show less diversity; mudstone, wackestone, and pellet grainstone predominate, and the rocks are mostly peloidal. Intertidal: This environment is characterized by an abundance of preserved sedimentary structures. Evans (1965) in a detailed study of a tidal flat deposit, delineated six major zones parallel to coastal strike. In a vertical sequence, coarsest beds are at the bottom, well-sorted sands are in the middle, and fine silts and muds at the top. The deposits are characterized by laminated sands, silts, and muds. Well-developed burrows may be present and some portions of the deposits may be completely bioturbated (Shinn et al., 1969). Park (1976) in studies along the Persian Gulf, stated that ... optimum conditions for stromatolite development in the Trucial Coast are restricted to the mid and upper intertidal areas" (p. 382). Thin beds of organic debris may be present. The lowest portion of the tidal flat may be characterized by abundant rock and metazoan fragments (Evans, 1965). Tidal creeks cross the flats and have distinctive sedimentary characteristics analogous to those described for fluvial (point bar) deposits, though on a much smaller scale. According to Evans (1965): "The meandering of the creeks gives rise to cross-stratification on a scale not seen in the other sub-environments (of the tidal flat). Erosion of the concave outer bank is accompanied by the deposition of inclined strata with dips up to 20 on the convex inner bank. The meandering creek produces a planar surface of erosion, commonly covered by a layer of shells and mud pellets, derived from the banks, which is buried 11

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beneath the cross-stratified deposit of the prograding bank" (p. 226). Shinn et ala (1969) include the tidal creeks in the subtidal zone, but they are obviously characteristic of the tidal flat environment, and their deposits are intimately associated with intertidal deposits. Supratidal: This environment may include salt marshes, beaches and beach ridges, and sabkhas. Salt marsh deposits are typically well-laminated, fine-grained, and very carbonaceous (Evans, 1965; Shinn et al., 1969). They may be marked by root casts, fenestral porosity (Shinn, 1968a; Shinn et al., 1969), algal stromatolites, and laminate crusts (Multer and Hoffmeister, 1968). Supratidal ponds may result in deposits of fine clays and evaporite minerals. Creeks in the supratidal marsh, according to Evans (1965), may differ from creeks in the intertidal zone, with the base of the cross-stratification ... marked by a bed of jumbled angular blocks of marsh sediments, produced by undercutting of the creek walls. The overlying set of strata is again wedge-shaped and individual laminae may show dips of up to 800 (p. 226). Beach ridges are generally characterized by graded laminae and cross-beds, and the deposits are very well-sorted, though ranging from fine to coarse in grain size. Sabkha-type deposits are evaporitic in character, and contain gypsum and halite or crystal molds, and are generally laminated by algal stromatolites. Diagenesis Crystallization Texture and Fabric Classification The basic terminology described and defined by Friedman (1965) is used here. His terms for crystallization textures are retained. The definitions of euhedral, subhedral, and anhedral are those of general usage by North American geologists and do not require explanation. The terms are defined by Friedman (1965), following Cross et ala (1906). There are three major groups of crystallization fabrics (Table 3): equigranular and inequigranular, distinguished by uni-modal and multi-modal crystal size distributions, respectively; and aphanotopic, composed of crystals smaller than 0.002mm in diameter (unresolvable). The first two groups are further divided into idiotopic (mostly euhedral textures), hypidiotopic(mostly subhedral textures), and xenotopic (mostly anhedral textures) The Friedman classification of fabrics is expanded here by finer distinction of types, particularly inequigranular types (Table 3). Equigranular fabrics are divided into mosaic and peloidal fabrics, inequigranular into porphyrotopic, poikilotopic, and mosaic fabrics. Aphanotopic fabrics can not be further subdivided by use of the optical microscope. Porphyrotopic fabrics are further divided into floating-rhomb (Figure 4a) and contact-rhomb (Figure 4b). Floating-rhomb and contact-rhomb fabrics are characterized by isolated or loosely aggregated euhedral or subhedral crystals, respectively, 12

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I-' W Table 3. Crystallization fabric terminology (modified after Friedman, 1965). Peloidal Peloidal Equigranular Inequigranular Mosaic Mosaic Porphyrotopi c Sutured Sieve Fogged ContactFloatingMosaic r40saic r10saic ---Size classes O.256mm O.016mm diameter O.016mm O.002mm diameter
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Figure 4. a) b) c) d) e) f} HS 62, 28.65mbt (meters below top). Plane light. Peloidal lithofacies, partially dolomitized. Inequigranular, idiotopic floating-rhomb porphyrotopic. Small, euhedral dolomite rhombohedra in aphanotopic calcite groundmass. Large foraminifer is Dictyoconus cookei. MS 299, l45.85mbt. Plane light. Skeletal lithofacies, partially dolomitized. Inequigranular, hypidiotopic contact-rhomb porphyrotopic. Pockets of aphanotopic calcite surrounded by coarse, subhedral dolomite crystals. MS 106, 52.65mbt. Plane light. Mudrock lithofacies, dolomitized. Inequigranular, xenotopic fogged mosaic. MS 60, 35.66mbt. Plane light. Skeletal lithofacies, dolomitized. Inequigranular, xenotopic spotted mosaic. Spots are micritized foraminifera. MS 266, l30.00mbt. Crossed polars. Mudrock lithofacies, partially dolomitized. Inequigranular, poikilotopic. Small, anhedral to subhedral dolomite crystals embedded in coarse calcite groundmass. MS 266, l30.00rnbt. Crossed polars. Same as above, slide rotated to extinction of calcite. 14

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c. d. e. f.15

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contained in a fine-grained matrix. Mosaic fabrics are divided into fogged (Figure 4c) and spotted (Figure 4d) mosaic fabrics. Fogged mosaic fabric is characterized by irregular or diffuse areas of very fine crystals contained in a coarse mosaic groundmass. Isolated and well-defined peloids ("spots" or "blebs") of fine to very fine crystals in a coarse mosaic groundmass are characteristic of spotted mosaic fabric. Poikilotopic fabric (Friedman, 1965, p. 651) is relatively rare in the study material, but is distinctive when it occurs. Wholerock poikilotopic fabric is characterized by fine dolomite crystals contained in large sparry calcite 6rystals (Figures 4e, fl. The term can also be used to describe the small-scale fabric of calcitic micrite contained in sparry calcite overgrowths on skeletal grains (Figure Sa). Equigranular mosaic fabrics can be further divided into sutured (Figure 5b) and sieve (Figure 5c) mosaic fabrics. Tightly packed anhedral crystals, generally with little or no intercrystal porosity, are characteristic of sutured mosaic fabric. Sieve mosaic fabric, on the other hand, is characterized by loosely packed anhedral to euhedral crystals and high moldic and intercrystal porosity. It is in part analogous to the sucrosic or "sugary" texture of many authors. Peloidal fabric is distinctive but problematic, and characterized by distinct to indistinct "clotting" of crystals of essentially uni-modal size distribution (Figure 5d). A combined texture and fabric nomenclature is used to describe any crystallized rock sample, e.g., idiotopic floatingrhomb fabric; or xenotopic sutured mosaic fabric. The size scales recommended by Friedman (1965, p. 653) are arbitrary and do not conform to natural size breaks in the study material. Crystals in this material fall into three major size classes (according to length of major diameter) : (l) O.256mm to O.Ol6mm, (2) O.Ol6mm to O.002mm, and (3) less than No term is used to describe the first size classi the second size class is indicated by the prefix micro-added to the fabric term, and crystals in the third size class are termed aphanotopic. For example, the term microxenotopic fogged mosaic indicates that the crystals in the groundmass are anhedral and fall in the size range O.016mm to O.002mm. Crystals in the aphanotopic size range can not be resolved well enough for textural classification. Porosity Classification The Choquette and Pray (l970) classification of porosity is followed, with the following exceptions. No distinction is made between intraparticle porosity and growth-framework porosity of solitary corals or bryozoa or shelter porosity inside echinoids. No distinction is made between channel or cavern porosity. Root moldic porosity is considered to be simple moldic. 16

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The process of grinding thin sections alters the amount of intercrystal porosity, the actual amount varying according to the original grain size, texture, and fabric of the rock. A significant amount of intercrystal porosity may also be submicroscopic, particularly in rocks with a large percentage of aphanotopic grains. Errors in estimation are not known, but may range over 100%; for this reason only visible porosity is reported here. Distribution Excluding cavernous porosity, total visible porosity in the MS and HS cores appears to vary randomly (Figure 6), although the amount of porosity is generally low at depositional cycle boundaries. Cavernous porosity, on the other hand, is clearly associated with the formational contacts as selected in this study. Difference in the dissolution characteristics of calcite and dolomite probably accounts for caverns at the Avon Park-Ocala formational contact (see Goodell and Garman, and suggests its formation during the telogenetic stage (Choquette and Pray, 1970) of diagenesis. Enhanced solution beneath the clay beds marking the top of the Lake City Formation in the HS core may account for cavernous porosity here. Porosity is dominantly fabric selective (Table 4), a conclusion arrived at also by Textoris et ale (1972) and Randazzo et ale (1977).Interparticle porosity is greatest in rocks in which the original depositional fabric is preserved, whether dolomitized or not, but intraparticle porosity is greatest in those not dolomitized. Moldic porosity varies greatly, since it is dependent on original skeletal content, but is found predominantly in crystallized fabrics and is greatest in equigranular sieve mosaic fabric. Fenestral porosity is rare in the study material, and is restricted to equigranular fabrics only. Non-fabric selective vug porosity is restricted to crystallized fabrics, but is distributed among them and shows no apparent fabric selectivity other than occurrence in dolomite. The fabric selectivity of the porosity suggests that interpretable distribution of porosity can be seen in the cores. Manatee Springs Core Distribution of porosity types in the core (Figure 7) correlates closely with fabric distribution and also with the depositional cycles described. Cycles I and VIII, both represented by significant amounts of calcite, are characterized by interparticle porosity [primary (Choquette and Pray, somewhat modified by pore filling and cementation [mesogenetic (Choquette and Pray,)1970)]. Crystallized fabrics are for the most part characterized by moldic porosity [eogenetic or mesogenetic (Choquette and Pray, 1970)], although vug development may be important. Moldic porosity is generally greatest in the upper portions of the depositional cycles, directly related to the distribution of the skeletal rock lithofacies (see Figure 3). Sieve mosaic fabrics often have a significant amount of moldic porosity, and, coupled with their inherent high intercrystal porosity, are often soft and may form zones of high transmissivity. Moldic porosity in inequigranular mosaic fabrics may not lead to 17

PAGE 24

Figure 5. a) b) c) d) e) f) HS 35, 20.73mbt. Crossed polars. Skeletal lithofacies, undolomitized. Aphanotopic calcite embedded in sparry calcite overgrowth on echinoid grain (between arrows). MS 284, 140.21mbt. Plane light. Mudrock lithofacies, dolomitized. Equigranular, hypidiotopic sutured mosaic. MS 263, 128.40mbt. Plane light. Hudrock lithofacies, dolomitized. Equigranular, xenotopic sieve mosaic. Dolomite crystals, some of which are hollow (arrows), contain dark nuclei. MS 262, 127.86mbt. Plane light. Peloidal lithofacies, dolomitized. Equigranular, microxenotopic peloidal. MS 279, 137.46 mbt. Plane light. Mudrock lithofacies, dolomitized. Equigranular microxenotopic sutured mosaic. MS 151-B, 71.63mbt. Plane light. Skeletal lithofacies, dolomitized. Inequigranular, hypidiotopic spotted mosaic. Spot is transverse section of micritized foraminifer. 18

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a. b. c. d. e. f. 19

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Table 4. Fabric selectivity of porosity. Q.J Q.J Q.J ....-.->, u U ..Q +oJ ..... .... ..... ..... +oJ +oJ .VI VI 1'0 .... 0 1'0 1'0 c.. c.. U +oJ 0 1'0 ..... VI Q.J "C Q.J 1'0 +oJ +oJ ..-:: 0', +oJ :: :: 0 Q.J :;, 0 ..... :E: ::> Peloidal 0.06 a 5.5 1.3 7.1 Sutured tosa i c 0 0 4.8 O. 1 0.9 5.8 Sieve Mosaic a 0.03 13.3 0.3 1.2 14.8 Spotted Mosaic 0 0 5.0 0 3.0 8.0 Fogged Mosaic 0 0 7.3 0 2.2 9.5 Contact-Rhomb 0 0.6 3.3 a 1.5 5.4 Porphyrotopi c Floating-Rhomb 3.4 2.2 0.4 a 0.6 6.7 Porphyrotopi c Uncrysta 11 i zed 9.4 1.9 3.0 a a 14.4 Fabri cs All values in area percent of total rock. 20

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MS HS % Porosity % Porosity 1) .! "" 20 40 60 80 100 <.JO "" 0 I I I I I <.JO 20 40 60 10 I Caverns) caverns) Figure 6. Distribution of total visible. porosity in the and HS cores. 21 100 I

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Iype of Porosity. Interparticle Intrapartict e Moldie Fenestra.! .. Vuq LEGEND .!ysta lliz otion Fabric ............. Equigranular .--.----. Sutured Mosaic Sieve Mosaic .-. ... --.-.-,. Peloidal ........... Ineq,uigranuicr Ftoating-Rhomb Porphyrotopic Contact-Rhomb Porphyrotop i c Fogged Mosaic Spotted Mosaic Poikilotopi c Aphanotopic. Original Fabric Preserved IXXI 10001 -I rz Z ZI WmLa [I i I [I -[ ] Figure 7. Distribution of porosity types (excluding cavernous) in the Manatee Springs core and comparison with distribution of crystallization fabrics. 22

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o --o Q.. :c o cg CD CI) l.. Q;) cg ::E. c o o .. ... 10 .. ... . ... .. .... .. ... ... Porosity 20 .... :... ........ 4 .. .......... ;":00 .. ....... ... I. 23 30

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better permeability since the pores are often not interconnected. Vug porosity is probably necessary for high permeability in these fabrics. Highest permeabilities are suggested at the base of Cycle I (vug development in mosaic fabric) and in the center of Cycle I (interparticle porosity in the calcitic fabrics) i in the upper part of Cycle IV and Cycle V (moldic and vug porosity in sieve mosaic fabric); and in the parts of Cycle VIII with high interparticle porosity (Figure 7). Homosassa Core Distribution of porosity types in the HS core (Figure 8) also correlates closely with the depositional cycles, although it differs from the distribution found in the MS core (Figure 7). Cycle VIII, represented entirely by calcite, is characterized by interparticle porosity. Crystallized fabrics are for the most part characterized by moldic porosity, but vug development is more significant in this core than in the MS core. Highest permeabilities are suggested in Cycle III, the upper part of Cycle IV, and in Cycle V (moldic porosity in sieve mosaic and aphanotopic fabrics); the lower part of Cycle IV and lower part of Cycle VI (vug porosity in peloidal and inequigranular mosaic fabrics); and in Cycle VIII (interparticle porosity) (Figure 8) Fabric Selectivity of Dolomitization The sequence and association of crystallization fabrics and porosity evidenced in the HS and MS cores reveal much about their mode of origin and their genetic relationships. Heterogeneous Dolomitization A continuous spectrum of dolomite fabrics ranging from early stage floating-rhomb porphyrotopic (Figure 4a) to later stage contact-rhomb porphyrotopic (Figure 4b) fabrics is clearly revealed in the study rocks. These fabrics often grade into mosaic fabrics (Figures 4c,d), which appear to represent the completion stage of dolomitization in the rock (Figure 9). This process of dolomitization is multistage, and a full range of fabrics is present in the study rocks. Dolomite porphyrotopes are almost invariably restricted to aphanotopic (mud) calcite matrix, and therefore the appearance of the final fabric is dependent upon the occurrence and distribution of mud matrix in the original fabric (Figure 10). Because of this restriction, the process is here termed heterogeneous dolomitization. This process is initiated by nucleation of isolated dolomite crystals in an aphanotopic matrix consisting of calcite (or possibly aragonite). The preservation of a full range of fabrics indicates the process takes place during a geologically significant period of time (probably on the order of a thousand years or more). Heterogeneous dolomitization of mudstone leads to the formation of sutured mosaic fabric (Figure 10). Heterogenous 24

PAGE 31

dolomitization of wackestone leads to spotted mosaic fabric if the allochems are also dolomitized, or to sutured or sieve mosaic fabrics if they are dissolved (Figure 10). The large number of allochems present in a packstone causes the dolomite porphyrotopes to penetrate the grains and destroy original outlines, resulting in diffuse patches of finer-grained crystals and fogged mosaic fabric, or to sutured or sieve mosaic fabrics if the allochems are dissolved (Figure 10). No true grain-stones were observed that had more than 1% porphyrotopic dolomite; presumably grains tones can not be dolomitized by heterogeneous dolomitization since they contain no mud matrix. Homogeneous Dolomitization The process of heterogeneous dolomitization can not explain the origin of aphanotopic or peloidal fabric, or of dolomitized grainstones. The excellent preservation of original grainstone fabric in some dolomite samples is not possible if dolomitization proceeded by porphyrotopic growth, and heterogeneous dolomitization of a mudstone or peloidal grainstone would lead to sutured mosaic fabric. These particular fabrics are always composed of fine or very fine dolomite crystals, generally with mean diameters less than 0.016mm, and they are here referred to as micro-textured fabrics. Some mosaic fabrics are also composed of crystals in this size range, and these are also referred to as micro-textured. Dolomitization of micro-textured fabrics is not dependent upon the occurrence of mud matrix and the process is termed homogeneous dolomitization. Micro-textured fabrics are always composed of 99+% dolomite and no full range of fabrics is preserved as for heterogeneous fabrics. The process is, therefore, single-stage and nucleation of dolomite crystals occurs at a large number of sites throughout the rock and growth is completed in a geologically insignificant period of time. Destruction of allochems is probably minimized, and original fabrics often preserved. Fogged and spotted micro-textured mosaics are uncommon. Homogeneous dolomitization of mudstone leads to micro-textured sutured mosaic fabric, or, if the rate of nucleation is very high (essentially spontaneous throughout the rock), it can lead to aphanotopic fabric (Figure 11). Wackestone and packstone are generally dolomitized to micro-textured sieve mosaic fabric, although fogged or spotted mosaic fabrics might be developed (Figure 11). Homogeneous dolomitization preserves the original fabric of peloidal grainstone to a large degree (Figure 11). Poikilotopic Fabric The origin of poikilotopic fabric is problematic. This type of fabric is rare in the study rocks and its isolated occurrences provide little evidence of mode of origin. The character of the mixed mineralogy and the association with unconformities or zones of weathering suggest that it might originate by dedolomitization of crystallized fabrics (see Friedman, 1965, p. 651). 25

PAGE 32

lype of Porosity. Interparticle Intraparti cl e Maidie Fenestral Vug LEGEND Fabric E qui granular Sutured Mosaic Sieve Mosaic Peloidal Inequigranular Floatin 9 -Rhom b Porph yroto pic Contoct-Rhom b Porphyroto pic Fogged Mosaic Spotted Mosaic Poikilotopic Aphonotopic Original Fabric Preserved LXXI [0001 1 VI21 Wi/@ lS"1 [II I tl -( : Figure 8. Distribution of porosity types (excluding cavernous) in the HS core and comparison with distribution of crystallization fabrics. 26

PAGE 33

o .... 0 3 0 CD III en "-CD CD :E c .c > 0. CD 0 --c .9 o N ::0 '-O..Q -0 U 0 000 00 000 00 .. 000 .-. 10 .............................. .. .. ...... --.-... -------27 Porosity 20 30 40

PAGE 34

LEGEND Lithofac ie s Peloidal Rock VI/ZIl Skeletdl Rock I I Mudrock Clay & Qu ortz Sand D % Dolomite :: Dolomite Dolomite -I-Calcite x 100 Fabric Equigranufor Sutured Mosaic Sieve Mosaic Peloidal Inequi;ranuJ a r Floating -Rhomb Porphyrotopic Confact
PAGE 35

N V)-g Depth g In Meters Below Top Of g Well 0 I. I I fJ 10 (") \! '< n CD o o o 2. '\ I ..J 100 CD (f) I 11 J \ (") '< '< n 0 CD
PAGE 36

Co) Q.. 0 0 .c Q.. 0 a. (J .o tn. o :E Original Fabric Floatin;-Rhomb Stage ContactRhomb Stage Completion Stave Wackestone Mudstone Packstone 1 Spotted Moaalc Fog gad Mosaic Sieve Mosaic Figure 10. Genesis of crystallization fabrics by heterogeneous dolomitization. 30 c 0 .-0 .!:::! :: E 0 0 e 04-0 CD CD 0' CD e es c en 0 CD (J c

PAGE 37

w I-' Mudstone Original Fabric .. .. .... ( ..' '. ". J a .. .... .. Nucleation u -7 ... 3 (;' (;j 'q .: o. tIi 'd to Packlton., Waok ton. .. '... .... ;: .... II 41. 0' '4 ir D. 6, 0.'''' e .. __ .=a ... .. E o .c .U Peloidal Grainstone c c .!:! .... J E 0 0 0 _. :; r.-Ot Q) 0 Ot 1 T ... 0 c Completion ( '. ... -.' .J ::I .-. 0-U) a!II_ (1)4 0 A phonotoplc fA Icro textured Sutured MOlOle Mlcrotextured FoggedMoaolc Micro -textured Sieve MOlaic Figure 11. Genesis of crystallization fabrics derived by homogeneous dolomitization. Q) .... 0 .s 1 Peloidal

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Summary There is a descriptive basis for the classification of crystallization fabrics (primarily dolomites). Categori-zation of the rock fabrics found in the two study cores reveals patterns similar to those of the depositional cycles deduced from sedimentologic considerations. Type and distribution of porosity also occur in patterns that can be associated with the depositional cycles. The various crystallization fabrics caused by dolomitization can be placed into a genetic framework and there is a fabric dependency upon both the process of dolomitization and the original fabric. Unless the rock has undergone repeated neomorphism of dolomitized fabrics, it is generally possible to deduce the original depositional fabric (and thus the lithofacies) from even highly crystallized fabrics. Only in the case of sutured mosaic fabric is the original fabric in great doubt, primarily because repeated neomorphism will lead to this fabric. 32

PAGE 39

ROMP CORES Three cores were extracted by the Southwest Florida Water Management District from locations in north central and northwestern peninsular Florida as part of its Regional Observation and Monitor-Well Program (ROMP). The location of these cores (#101, #107, #124) are shown in Figure 1. At the writing of this report some ten additional ROMP cores are in various stages of investigation. The major stratigraphic units encountered are the Avon Park and Ocala Formations (F igure 12). Avon Park Formation The Avon Park Formation exhibits many features which are strikingly similar to carbonate sediments produced in modern tidal-flat environments. These features include: flat, millimeter-thick laminations; undulating stromatolites; vertical burrows; desiccation cracks; "birdseye" structures; root casts and molds, flat pebbles; sediment mottling; evaporite mineral molds; and thin, micritic beds. These features have been described as being products of tidal-flat accretion over adjacent shallow marine deposits. Petrographic examination has revealed the presence of eleven commonly occurring subfacies representative of the supratidal, intertidal and subtidal zones. The repetitive vertical arrangement of these rock types has enabled the recognition of cyclic sedimentation patterns in Avon Park strata. Cyclicity The vertical sequence of interbedded lithologies found in the Avon Park Formation depict a complex model of sediment accumulation in which the recognition of cyclic depositional patterns proves to be, ... the single most illuminating factor in making sense of the seemingly bewildering vertical parade of subfacies" (Reinhardt and Hardie, 1976). The vertical organization of lithologies represents a repetition of sedimentation cycles in which the basic Avon Park depositional cycle is represented by an offlapping or progradational facies sequence (Figure 13). Subtidal facies represents the lowest unit in most depositional cycles. This is often in sharp contact with a bed which represents the top of the underlying cycle. Periods of submergence to subtidal levels were followed by shoaling and progradation of intertidal and supratidal deposits over subtidal sediments. Interruptions in these progradational trends are indicated by numerous incomplete cycles marked by minor unconformable contacts found along cyclic boundaries. 33

PAGE 40

LEGEND THINLY BEDDED AND LAMINATED MUDSTONE FLATLY LAMINATED, PELLETED MUDSTONE TO PACKSTONE ALGAL BIOLITHITE ROOTED AND MOTTLED FORAMINIFERAL WACKESTONE PELLETED WACKESTONE TO PACKSTONE ROOTED AND BURROWED MUDSTONE BIOCLASTIC WACKESTONE TO MUDSTONE FORAMINIFERAL-ECHINOID WACl
PAGE 41


PAGE 42

-I OJ c c:: 1J... CORE SEDIMENTARY FEATURES ./ EROSIONAL CONTACT LITHOLOGY: Algal biolithites; thinly bedded and laminated mudscones to wackestones. STRUCTURES: Thin algal and sedimentary laminations, des iccation cracks, fenestral cavities, rare burrows. -.. _o---!!:, --:.. ---FOSSILS: Sparse to absent ,-=--J. LITHOLOGY: Skeletal and pel if letal mudstones, wackestones II \ 0 1and packs tones. DEPOSIT10NAL ENVIRONMENT Shallow Lagoon Supratidal Mudflat ;-[ __ 0 STRUCTURES: Vertical burrows, J
PAGE 43

Recognition of Depositional Environments in Avon Park Strata Although each of the ROMP cores used in this study displayed its own unique set of interpretive problems, similarities were found to exist which enabled the recognition of the supratidal, intertidal and subtidal zones within the Avon Park strata. The most characteristic feature of supratidal deposits in the Avon Park is thin, algal and sedimentary laminations. Crinkled and flat laminar morphologies similar to those described by Hardie and Ginsburg (1977) are abundantly represented in supratidal facies. Many beds consist of laminated fine and medium crystalline dolomites which presumably have replaced original, finely bedded or laminated, muddy sediments. Supratidal rocks are largely mud-supported. Invertebrate skeletal remains are sparse and pellets usually represent the dominant allochemical constituent. Burrow structures are rare and, where they do occur, they stand out in vivid contrast against the well-preserved, laminated matrix of the rock. Desiccation structures are found in supratidal beds and include laminoid fenestral cavities ("birdseye" vugs), algal mat deformation structures, flat pebbles and vertically oriented cracks disrupting algal laminations and thin micritic beds. No evidence of evaporite minerals were found in the ROMP cores although small amounts of gypsum and the presence of evaporite mineral molds have been previously reported from supratidal facies within the Avon Park (Saroop, 1974; Hickey, 1976). The boundary between rocks representing the supratidal and the underlying intertidal zones is typically gradational (Figure 13). Changes in the nature of preserved sedimentary structures and a relatively greater abundance and diversity of fossils serve to distinguish these tidal deposits. Intertidal rocks are characterized by a predominance of micrite, indicative of the low tidal and wave energies which prevailed in the depositional environment. Fossils consist of a sparse number of individuals and relatively few species (mostly foraminifera and ostracods with fewer gastropods) These beds are further distinguished by the presence of preserved sedimentary structures including vertical burrows, open root tubules and a churned-to-wispy-sediment mottling. These features are of debatable value as primary indicators of a particular subenvironment within a shallow nearshore regime of sediments. They do, however, provide clues to the role of organisms in the paleoenvironment which may have exerted some control over sediment disrupting processes and allowing for the preservation of these structures. Recognizable transition in fossil communities, as seen in vertical sequence, was the most useful criteria enabling the differentiation between subtidal and intertidal facies. 37

PAGE 44

The fauna of subtidal rocks is represented by a larger number of individuals and wider diversity of fossils than associated intertidal and supratidal deposits. A general lack of stratification in subtidal rocks may be an indication of early bioturbative processes; the activities of burrowing and sediment-ingesting organisms result in the destruction of primary sedimentary structures and in the homogenization of the ambient sediment body (Shinn, 1968b; Heckel, 1972). Locally, wave and current energy was strong enough to winnow interstitial muds and reorganize the sediments into flat to low angle, current laminations. General Lithology The general distribution of Avon Park lithologies in the ROMP cores is shown in Figures 14, l5 and l6. The lower part of the Avon Park in these cores (unit A) shows a dominance of supratidal-intertidal ("tidal-flat") sedimentation over accompanying subtidal phases. Vernon (l95l, p. 96) had described this lithology as a ... tan to brown, thin-bedded and laminated very finely crystalline dolomite ... Wellpreserved, thinly laminated deposits, interpreted as algal stromatolites, are abundantly represented in this lowermost unit. These distinctly laminar rocks were originally described by Vernon as varve-like features with the implication that they represented organic and plant residues in a relatively deep body of water. Dolomitization is more extensive in this unit than in overlying strata, often to a degree such that the original microfabric of the rock is largely obscured and sometimes obliterated. Desiccation features in algal bedding structures are generally more abundant than in overlying lithologies. The central portion (unit B ) of the formation is similar in many aspects (particularly in the ROMP core #l24 to the Avon Park unit designated by Randazzo and Saroop (l976) as Lithofacies I. Vernon's (l95l, p. 96) description of this lithology is repeated below: Cream to brown, pasty and fragmental, peat flecked and seamed, very fossiliferous marine limestone. This bed is extremely rich in well-preserved bryozoa, foraminifers and ostracods, and the fauna is concentrated and somewhat deformed along thin beds that are interbedded with peat and more barren pasty limestone seems to give the rock a laminated and mottled appearance, to which the term 'molasses and butter' has been applied by some geologists. The interbedding of rock types observed by Vernon may be expressed in terms of cyclic depositional patterns. Subtidal beds, characterized by their abundant and distinct microfauna, are interlayered with sparsely fossiliferous carbonate rocks of tidal-flat origin. The lack of a conspicuous 38

PAGE 45

LEGEND THINLY BEDDED AND LAMINATED MUDSTONE -=---=--==1 FLATLY LAMINATED, PELLETED MUDSTONE TO PACKSTONE f I ALGAL BIOLITHITE H ROOTED AND MOTTLED FORAMINIFERAL WACKESTONE PELLETED WACKESTONE TO PACKSTONE ROOTED AND BURROWED MUDSTONE BIOCLASTIC WACKESTONE TO MUDSTONE FORAMINIFERAL-ECHINOID WACKESTONE TO PACKSTONE FORAMINIFERAL PACKSTONE TO GRAINSTONE D1CTYOCONID WACKESTONE TO PACKSTONE MILlOLID i'ACKSTONE PELOID-MILlOLlD PACKSTONE COMPOSITE GRAIN-MiXED SKELETAL GRAINSTONE TO PACKSTONE FRAGMENTAL GRAINSTONE TO PACKSTONE FRAGMENTAL PACKSTONE TO WACKESTONE LARGE FORAMINIFERAL WACKESTONE TO PACKSTONE NUMMULlT1D WACKESTONE TO PACKSTONE LIMESTONE :0 DOLOMITE .. .. CHERT .. .. ... AI. ... ... ... .' .It. ... ... Symbolic patterns for Figures 14, 15, and 16. 39

PAGE 46

25 -4: 30-4: U 0 a: 35W a. a. Z ::::l 40-f2 (Jj 4eW I---1 4:
PAGE 47

35 40 45 50 (J) 55 I-IJJ :E 60 IJJ. a:: o
PAGE 48

5 10 -15 -202.5 30-65 701 I (J) ...J MINERALOGY LllMOlOGY TIDAL ZONES sup inter sub FAUNIZONES (from Hunter) 1976) Spirolocl.llina seminolensis Ampnistegfna pinorensis cosdeni Zone Lijl.lonel/(l flon'dana, Oicfyoconus floridanus, O. cooke;' Zone Figure 16. ROMP well #124 (LE). Mineralogy, lithology, tidal zones, biozonations. 42

PAGE 49

fauna imparts a "barren" appearance to these rocks. Por tions of this unit have been partially or completely dolomitized. Dolomitization is more extensive in ROMP core #124. This portion of the Avon Park records a gradual net change in sea level. Subtidal facies predominate in the lower portion of the unit. Cycles become shorter and less regular in the upper portions of the lithology where tidal-flat carbonates dominate. Vernon (1951, p. 96) describes the uppermost lithology of the Avon Park as a ... cream to brown, highly fossiliferous, miliolid rich, marine, fragmental to pasty limestone .... He remarks that this unit sometimes appears as a coquina of "cones" (Le., dictyoconid foraminifera) with locally abundant specimens of the small echinoid, Neolaganum (=Peronella) dalli. The unit (unit C) is characterized by wide vertical and lateral variations in character. This lithology, as it is represented in the ROMP core #124, bears a close resemblance to the carbonate rocks designated by Randazzo and Saroop (1976) as Lithofacies II. The unit has been extensively dolomitized in this locality. Lenses of peat and carbonaceous plant remains are abundant in the upper beds of this core. Dolomite represents only a small portion of this unit in ROMP core #107 and is absent in ROMP core #101. The preservation of fossils is typically poor in these beds and often molds or impressions are all that remain of the original tests. Subtidal deposits in the lower portion of this unit are characterized by a low diversity fauna dominated by species of dictyconid and large miliolid foraminifera. These beds become highly fossiliferous towards the top of the unit and support a diverse array of fossils. Depositional Facies Eleven commonly occurring subfacies representing the supratidal, intertidal and subtidal zones have been recognized in these cores of the Avon Park Formation. These include: I. Supratidal rocks a. thinly bedded and laminated mudstone b. flatly laminated, pelleted mudstone-wackstone c. algal biolithite II. Intertidal rocks a. rooted and mottled, foraminiferal wackestone b. pelleted wackestone to packstone c. rooted and burrowed mudstone d. microlaminated, bioclastic wackestone to mudstone III. Subtidal rocks a. foraminiferal-echinoid wackestone to packstone b. foraminiferal packstone-grainstone c. dictyoconid wackestone to packstone d. miliolid packstone 43

PAGE 50

All lithologies have been partially to completely replaced by dolomite. The distribution of facies in the three cores is shown in Figures 14, 15, and 16. The depositional environments and possible water depths of subfacies in the Avon Park Formation are described in Table 5. Figure 17 illustrates the generalized distribution of depositional environments. Ocala Limestone In contrast to the complex cyclic sequences expressed by the Avon Park strata, the rocks of the Ocala Limestone are interpreted as products of a more constant and stable depositional environment. The presence of an abundant and diverse marine fauna signifies a transition to less-restricted, more normal, open marine conditions. In general, the change from the tidal-flat and restricted subtidal deposits of the Avon Park to the offshore, high and low energy marine deposits of the Ocala Limestone is indicative of an overall transgressive sequence of sedimentation. Chen (1965, p. 76) has concluded that the sediments of the Ocala had been deposited under warm and shallow water marine conditions on a relatively flat and broad carbonate shelf or platform similar to the present day Great Bahama Banks. The ROMP cores reveal that the Ocala Limestone is composed of two major lithologies, separating the strata into distinct upper and lower lithologic units (Figures 3 and 7). Deposits representing shallow-water, moderately high energy conditions occur in the lower unit where deposition is interpreted to have taken place relatively close to shore. These grade into slightly deeper water, lower energy deposits which characterize the upper unit. Data from the ROMP cores are most consistent with the interpretation of Applin and Applin (1944), dividing the Ocala Limestone into an upper and a lower member. Lower Ocala Limestone The Lower Ocala unit occupies the same stratigraphic interval recognized by the U.S. Geological Survey as the Lower Ocala, and would include the Williston and (at least part of) the Inglis designations of Puri (1957). This portion of the Ocala has been generally described as a light cream to tan colored miliolid limestone, porous, friable, microcoquinoid in appearance, often chalky and generally harder than strata characterizing the upper unit. Petrographic examination reveals that this lower unit consists predominately of cleanly washed skeletal packs tones to grains tones in marked contrast to the overlying muddier deposits of the Upper Ocala. The contact between rocks of the Upper and Lower Ocala is gradational. 44

PAGE 51

Depositional Facies Three commonly occurring depositional subfacies have been identified in the rocks of the Lower Ocala, on the basis of lithology, textures, constituent grain composition and grain attributes. These are: Peloidal/miliolid packstone (subtidal sand flat facies) Composite grain/mixed skeletal grainstone-packstone (detrital shoal facies). Fragmental grainstone-packstone (intertidal shoal facies) These subfacies delineate distinctive depositional subdivisions of the open shelf environment. The vertical arrangement of lithologies in Lower Ocala strata is shown in Flgures 14, 15 and 16. The depositional environments and possible water depths of subfacies in the Lower Ocala Limestone are described in Table 5. Figure 17 illustrates the generalized distribution of depositional environments. Upper Ocala Limestone The carbonate deposits of the Upper Ocala Limestone represent a transition into progressively deeper water environments of sedimentation. A continuation of the general transgressive sequence is suggested by the presence of a deeper-water faunal assemblage and the deposition of wackestones and muddy packestones over the cleanly washed deposits of the lower unit. Megascopically, the unit is very pale orange in color. Beds are uniformly textured and range from sparsely granular to coquinoid in appearance. The rock is friable and generally softer than the lower unit. The Upper Ocala is characterized by the presence of abundant whole and fragmented tests of large foraminifera. Specimens which have been identified from the ROMP cores include: Nummulites willcoxi ocalana Heterostegina ocalana Spiroloculina newberryensis Sphaerogypsina globula Textularia sp. Whole tests of small, thin-shelled foraminifera, ostracods, echinoid plates and spines, small gastropids and fragments of pelecypids and bryozoans are also present. Grain sizes range from coarse silt-sized (O.04mm) bioclasts to coarse pebble-sized grains measuring from several millimeters to 45

PAGE 52

" .. \ .. ',. :':. :?III ,.' INTERTlDAL 1 ;;:ri:. : .. -':.. :,-:, :=.--_ ..c, :';'::":-, -.' AND 1 RESTRICTE01 '1---=.::= SUPRATlDAL 1 LAGOON I SHALLOW : -::'_'-":.y.:'.,; .. ,::., ":. MUDFUTS 1 ISUBTlDA.1.. ,0 1 SHALLOW SU8T1DALI (INTERTIDAL I SANOF1-ATS I ":''):'''::Y;": I SHOALS 1 (OFFSHORE, OPEN CYCLIC SEDIMENTATION: NEARSHORE SHELF : SHELF Figure 17. Generalized relationship among depositional environments interpreted for the Avon Park Formation and the Ocala Limestone. Table 5. Depositional environments and probable water depths of subfacies in the ROMP cores. FACIES a. ntiHl.'f BEDOED AND LAMINATa) MUDSiONE I b. F1..ATLY MUDSTONE TO Co AI.GA.L. BIOLiTHITE a. ROOTED AND FORAMINIFERAL WACKESTONE IT b. FEl.l.tTED WACXESTONE TO PACKSTONE C. ROOTED AND BURROWED MUDSTONE d. 310CLASTIC WACXESTOHE TO hlUDS'TOHE a. FORAhlINIFE.:tAL. -!0IIN010 WACXESTONE TO P*.CXSTONE rrr b. FORAhllMIFERAL PACXSTONE TO GR4INS'TONE C. OICT'1OCONID WACXESiONE TO PI\CXSTONE Ii IiIIUOl..1D PACXS"':"CNE a. PE1.0ID-..aI..IOl..ID ITo. 'COMPOUND GRAIN-MIXED SKEI.TAI. GRAINSTONE TO FRAGMENTAL GRAINSTONE TO P*.CXS'TCNE O. FRAGhlENTAL. ?!lCXSTOHE TO WACXES'TCNE Y b. L.ARGE, FORAMINIFERAL WACXES"':"CNE TO c. HU .. hlULlT10 WACXESTOHE TO PACXSTONE 46 ENVIRONMENTS OF OE?OSIT10N AND WAnF! OE?T'HS r INTERTIDAL MUDFLAT PRCTCTEO, SHAU.O""WAToR L.AGOON. WATER DEPTH THAN 10 METERS. }-SHALl.OW SUBTIDAL SANOF1...ATS. WATER OEPTH LSS THAN to METERS !'H ALLOW SUBTI DAl.. TO INTERT1DAI. SHOAL.S. W4Ta! OEPT'''' O-iO METtRS. OFnHORE, OPEN SHE1.F. WAitH OEPTH GREATtF! THAN METtRS. \I. ...J LI.I -en LI.I c::: 0 :::: en c::: '" LI.I ..J z

PAGE 53

a few centimeters or more along their long axis. Some of the larger tests have been broken and extensively fragmented; however, they show little signs of mechanical abrasion in that grain boundaries tend to be ragged or angular in shape. The evidence suggests that most fragments were derived through biologically controlled processes. Some large burrow structures are encountered which are probably of crustacean origin. These are preserved as open tubes which show a characteristic dense micritic lining. Similar burrows have been attributed to crustaceans by Shinn (1968b). The upper unit is characterized by a largely mudsupported fabric. The matrix is composed of micrite and very finely crystalline microspar often cluttered by silt-sized bioclasts. It sometimes displays a clotted fabric although discrete pellets are rarely observed. Depositional Facies The limestone of the Upper Ocala can be subdivided into its component subfacies. Three primary depositional subfacies are recognized. These are: Bioclastic packstone to wackestone Large perforate foraminiferal wackestone to packstone Nummulitid wackestone to packstone Subdivisions were based primarily upon paleontologic criteria including the relative abundance and identity of the various faunal constituents. The vertical arrangement of lithologies in Upper Ocala strata is shown in Figure 14. The depositional environments and possible water depths of subfacies in the Upper Ocala Limestone are described in Table 5. Figure 17 illustrates the inferred distribution of depositional environments. BALLAST POINT, BRANDON, AND DUETTE CORES Drill cores, located at Ballast Point and Brandon in Hillsborough County, and at Duette in Manatee County, were obtained from the Florida Bureau of Geology. These cores penetrate the "Tampa Formation" and Suwannee Limestone (Figure 18). The Suwannee Limestone is of Oligocene age, and defined as a biostratigraphic unit rather than a lithostratigraphic unit. In the area of study, it is lithologically conformable with the underlying Late Eocene Ocala Limestone. An unconformity is present toward the north in Hernando County (Yon and Hendry, 1972, p. 30) and Citrus County (Vernon, 1951, p. 177). The pelecypod ocalanum, which is apparently present at and below the depth of about 116m from sea level within the Ballast Point core, is utilized herein as a biostratigraphic marker of the Upper Ocala (McCullough, 1969, p. 1) 47

PAGE 54

Because the Suwannee Limestone and Tampa Formation have been defined on the basis of biostratigraphic evidence, confident recognition and correlation have been difficult at best. These traditional formational names are invalid on the basis of the Code of Stratigraphic Nomenclature (Randazzo, 1976a). King and Wright (1979, p. 1605) have defined the Tampa Formation from biostratigraphic and geochronologic criteria. The Tampa Formation is lithologically similar in places to other "post-Suwannee" units. The Tampa Formation described in the cores studied may actually be the Hawthorn Formation. Because of the uncertainity of its identity, references made to the Tampa Formation in the remaining part of this report will be offset in quotation marks. Stratigraphy The regional stratigraphy of the "Tampa Formation" and Suwannee Limestone is summarized by Applin and Applin (1944) and Puri and Vernon (1964). The Ballast Point, Brandon and Duette drill cores were used in making a northwest-southeast correlation of the "Tampa Formation" and Suwannee Limestone (Figure 18). The correlation was done on the basis of petrographic similarities between cores. As an aid to correlation, vertical variation diagrams of orthochemical, allochemical, and terrigenous constituents were constructed and compared with one another. Although neomorphism and silicification are locally intensive within the cores, orthochemical components (micrite, microspar, pseudospar and sparite) and ghosts of allochemical grains are generally recognizable. Among these diagrams, the similarities in vertical variation of contents of fossils, pellets, and micrite (and microspar) among cores proved most useful in correlation. From the correlation, a composite vertical sequence (Figure 19) was constructed to show the changes in lithology and stratigraphic relationships of the various lithologic types. There are four lithofacies distinguished from one another by macroscopic appearance. These lithofacies are further divided into 19 subfacies on the basis of microscopic and macroscopic attributes. The distinctions among these subfacies reflect differences in the energy levels represented (Figure 19, Table 6). Stratigraphic Interpretation Petrographically derived subfacies classifications are listed in Figure 19 with their inferred depositional environments (i.e., supratidal, intertidal, shallow subtidal and deep subtidal) The sequence is subdivided into four distinct lithofacies representing different environments of deposition. Lithofacies I together with lithofacies II makes up the major sequence of the Suwannee Limestone which has a distinct 48

PAGE 55

\.0 SE A LEVEL BALLAST PT. o If) 0: W tt30 w 60 --.]:-_ T-IX r -=r BRANDON KEY '-' '-....... o 6 12 L I I KILOME TERS '-'-....... ....... '-IHf1tllimestone of "Tampa Formation" Suwannee limestone Crystal River Formation D Part of core not studied fV\N'J\ Disconformities DUETTE ....... ....... '-....... ....... Figure 18. Stratigraphic sections and correlations of the "Tampa Formation" and Suwannee Limestone.

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I .. I g '0 g, E 0 I "" 5 I I :;r;1 I I I : I ...... i w I ,-:' I-'" w 1m it ;j -l I u I w w I z z iP I :J tr) II I Deposltionot Environment s I-I --' ..J --'I g 1<" ;:: !-0.0 i tC SlOSl'O.RI TE SANOY INTlI .. ""OI. TE INTRAMiC/IUl)'TE 00l.0""TI2EO :No. 8101.ITHlTE 015(;ONFOII'" T T M.CRO OISCO"FO"M' TV v'v' o [] I I 1 ... tf.:JHJCSS 1:1 r-;:--l _____________________ _______ __ .. _R __ I Figure 19. mation" Ba 11 ast Generalized columnar section of the "Tampa Forand Suwannee Limestone, based on data from the Point, Brandon, and Duette cores. 50

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Table 6. Characteristics of depositional environments of the "Tampa Formationll and Suwannee Limestone. ENVIRONNNTS CHARACTERI STI CS SUPRATIDAL INTERTIDAL SUBTIDAL DEEP SUBTIDAL Foss i 1 fragments )t -Intraclasts '-----.....;..----....:i-----......... Pellets ..... 41. ----+-----..01-_ .. Terrigenous quartzl____ ..... _____ ____ 5 E Terri genous !:: cl avs J... -------i---.... --........... .....J )-.' ----....:-----_ ... -_ ....... ......... Micrite Sparite f-." ... .-. -.- "1 Do 1 omi te I I --. ........... ............ ; ................ _____ ( SWl r 1 eo and ver-:-____ _____ ................ 1 5 ti ca 1 burrO\,iS 1 c::::: I MicriteVl envelopes Peat seams Arti c. cora 1-1 i nes & codiaceans Dasyclad ca 1 ci spheres l:.ncrustose Coral lines >-C.!l Mo 11 us cs o I j ...... --1" ........... I ............ III r-.... --,....-----! I --I-------! .--.-.. -----.. III 4 f------..., I .. ... +0-----...,1 ..... ................ ........ 5 1-__ __ _+_-------_i_I----'--.,-"-"--+-" -. -" -" -" -" -" ----"+r--------------I1' UoiCl'l I j __ .41---------+----------+r-------------------+1_._ .. _._._. ____ Bryozoans .. +---_. _I "'1 j t I jl Algal II I __ ___________ _________ ___________________ ---Abundant ---Common ........ Rare 5l

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Late Oligocene fauna. This section can be subdivided into nine subfacies. Lithofacies III is the top unit of the Suwannee Limestone and is subdivided into three subfacies. This lithofacies is interpreted as a shoreline sequence with oscillations in sea level which cause changes in the type of deposition from time to time. In all, the Suwannee Limestone consists of lithofacies I-III which recorded a general transgressive phase with minor episodes of regression, and lithofacies III recorded a general regression with a later transgressive phase. The boundary between the Suwannee Limestone and the overlying "Tampa Formation" is represented by a disconformity, indicating sub-aerial exposure and erosion. This may be related to the Ocala Uplift which Vernon (1951) dated as post-Oligocene in age. Upon an erosional surface was deposited lithofacies IV of the "Tampa Formation" which is typical of the Lower Miocene Series and characterized by a lithology and fossil assemblage different from that of the underlying beds. Lithofacies IV, making up the limestone portion of the "Tampa Formation" studied, is subdivided into seven subfacies and represents two carbonate cycles of sedimentation. Diagenesis The most important processes of diagenesis within the varied facies of the Ballast Point, Brandon and Duette are those of calcitization, dissolution, micrite-envelope formation, micritization, compaction, cementation, neomorphism and replacement (dolomitization and silicification). All of the microfacies found within the cores reflect the effects of several of these processes, acting either simultaneously or sequentially (Liu, 1978). Table 7 lists the prominent diagenetic features developed in the Suwannee Limestone and the "Tampa Formation." There are only four common porosity types present in the Ballast Point, Brandon and Duette cored sections, although nearly all porosity types described by Choquette and Pray (1970) were encountered. These four basic types are inter-particle, intraparticle, moldic and non-fabric-selective vugs. Usually a combination of different pore types is found in a subfacies (Figure 20). The visible porosity in different microfacies varies mostly between 3 to 22% (yigure 21). Sizes of pores generally vary from micropores (less than 0.06mm) in interparticle to intraparticle types to small megapores (less than 32mm) in vugs, molds and interparticle types. Textoris et al. (1972) felt that dissolution of the skeletal allochems, especially in sediments with interparticle pores, would provide for the reprecipitation of low-Mg calcite nearby as cement and at times invert location of 52

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Table 7. Prominent diagenetic features displayed within the subfacies of the SUvJannee Limestone and !tTampa Forma ti on. II Subfacies Diagenetic Features IVg ExtensivE recrystallization of micrite to microspar. Dissolution of fossils. Two generations of cementation. IVf Dissolution of fossils and infilling of the resultant molds with two generations of sparry calcite cementation. Fossi1s commonly coated by micrite envelopes. rVe In Ballast Point and Duette cores: completely do10mitized with preservation of original texture; oartial coalescive neomorphism of dolomite with texture or destroyed. In Brandon core: partly dolomitized by coalescive neomorphism without preservation of original texture. IVd In the lower portions; extensive recr'ystall;zation of micrite to microspar and pseudospar; partial replacement of detrita1 grains by sparry taleite. IVe Mieritized allochems coated by micrite envelopes. Dissolution of fossils. Partia1 replacement of sparry calcite cement by silica (cl1ert) IVb Dissolution of fossils and infilling of the resultant molds Ivith sparry calcite cement. Fossils coated by micrite envelopes. IVa Allochemical grains coate
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Table 7. (continued) Subfacies Diagenetic Features IlIa A high degree of micritization completely destroying the original algal cellular structure (Banner and Wood, 1964). Cementation of fenestral pores by sparry calcite. lIe Recrystallized fOS$11 grains, especially dasyclad algal segments. Dissolution of fossils and infilling of the resultant molds with sparry calcite cement. In Brandon core, high degree of silicification. lId Micritized allochems. High degree of cementation developed in intergranular pores. Compacti on and mecnani ca 1 breaJ
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Table 7. (continued) Subfacies Diagenetic Features Ib Micritized allochems. 1a Very high degree of cementation developed in interand intra-granular pores. Micritized a1lochems. High degree af cementation. Partial replacement af echinoid fragments by silica (chert). 55

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>I--V1 o c::: o a.. -l c:t: Io I-w.... o I..LJ <..!:l c:t: Iz I..LJ U c::: I..LJ a.. Suwannee Suwannee Bi ospari te Subfacies Biomicrite Subfacies (Subfacies Ic) (Subfacies II Ic) 60 6 34.9 45 45 II 37.5 I I 11 I I 11 30 30 I II! 19.6 I I I 15,7 1 I 13 J5 12.5 I III 9.8 I /1 --. I I 1 I Q....J rn Q 0 0 0 m o Suwannee Biomicrite Subfacies (Subfacies Ire) 48.0 20.0 "Tampa" Sandy Clayey Microsparite Subfacies (Subfacies IVd) 53.9 15.4 3C.e t I II I I II m W 9.0 ::1 15 m-= = -oj ==-= I I ill I II LLL.G Suwannee Biosparite (Subfaci es 24.5 -Subfaci es Ira) 50.8 40 16.9 20 m7.7 o Inter-Intra-Moldic Vug and Particles Channel TYPES OF PORES "Tampall Pelecypod Biomicrudite Subfacies (Subfacies 1.3 6.3 5!l Inter-Intra Particles \ \1 \1 12.S [lTiI] Vug and Channel Figure 20. Major types of pores and relative percentages in selected subfacies of the "Tampa Formation" and Suwannee Limestone. 56

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SEA BALLAsr POINT LEV E L 0 r---"'r-r--,....--,....--r-r--1"--' CORE BRANDON DUErrE (Jj a:: I.J.J f-w Z I f-a... w a 30 \ 50 60 110 :20 130 1401 I I o :0 I I [ ( I I 1 I I 20 30 40 0 10 20 30 40 0 PERCENT POROSITY I I 1 I 20 30 40 Figure 21. Variations in visible porosity in the "Tampa Formation" and Suwannee Limestone. 57

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original pore spaces. The moldic porosity type (maximum up to 17% of a rock unit) is completely controlled by the abundance of original skeletal allochems which have been dissolved. This pore type is common in both sparites and micrites (Figure 20 ). Skeletons may be completely dissolved and the resultant voids subsequently solution-enlarged, or filled with low-Mg sparry calcite to varying degrees. Interparticle pores are common in sparites. The pore spaces may reach as high as 21% in volume. Original porosity was higher and dependent on packing and shapes of allochems. Interparticle porosity still exists commonly in molluscbearing beds (Figure 20) because of the differences in the shapes of fossils and packing. The intraparticle pore type may be found in any skeletal grains which originally had open chambers (foraminifera and bryozoans). It is common in the various rock types of both sparites and micrites, and may be as much as 5% of the rock volume. The two rather common, non-fabric-selective vug and channel pore types are grouped together due to their normally common genesis. Most vugs are probably solution-enlarged molds, and some channels are often simply connections between them. Vug porosity may reach as much as 24% in rock volume. Many channels are solution-enlarged cracks of various origins, including fractures. Vugs and channels may be in various stages of infilling and are more common in the micritic subfacies. GEOCHEMISTRY The Na+ and Sr2 + concentrations and mole-percent-MgC03 of selected pure calcite or dolomite samples from 16 of the Eocene carbonate rock cores studies (Figure 1) were measured and the results were used to evaluate a model of diagenetic dolomitization. In the process of evaluating this model of dolomitization, an attempt was made to delineate new, and/or confirm reported relationships between Sr2 + and Na+ and mole-percent-MgC03 and the latest diagenetic solution affecting the rocks. The geographic position of each core and its Na+ and Sr2 + content were considered in determing the affect, if any, of groundwater flow patterns of the Floridan Aquifer on the Na+ and Sr2 + content of diagenetic carbonate minerals formed within the aquifer. The distribution of Sr2 + was evaluated to determine if the original mineralogy of the sediments has any control over the present diagenetic products. The geochemical significance of Sr2 + and Na+ in calcite and dolomite stems from their ability to substitute in the cation layers of the crystal structures of these minerals. The calcite crystal structure consists of alternating layers of Ca2 + ions and C032 -radicals. The dolomite crystal structure has alternating layers of Ca2 + and Mg2 + ions with layers of CO 3 2 -radicals in between them. High-Mg calcite 58

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has more than 4 mole-percent-MgC03 and low-Mg calcite has less than 4 mole-percent-MgC03. Dolomite in carbonate rocks of the Floridan Aquifer has been classified as more nearly stoichiometric if it contains 44-50 mole-percent-MgCo3 and non-stoichiometric if it has 39-43 mole-percent-MgC03 The geochemical significance of ions such as Sr2+, Na+, and Mg2+ in the formation and diagenesis of carbonate rocks has been discussed by a number of authors (Odum, 1957; Kinsman, 1969; Beherns and Land, 1972; Land and Hoops, 1973; Viezer and Demovic, 1974; Folk and Land, 1975; Randazzo and Hickey, 1978; Sarver, 1978, Metrin, 1979). Odum (1957) reported Sr2T/ca2 + ratios in ancient rocks much lower than materials of modern sediments, suggesting that the sediments had been replaced. Kinsman (1969, p. 487) stated that "The Sr2+/ Ca2 + ratio of a precipitating solution plays a dominant role in determining the Sr2 + concentration of precipitated carbonate minerals." Kinsman (1969, p. 501) also found that calcites precipitated from a single solution in the down flow areas had higher Sr2+values than those formed in the up flow areas. Beherns and Land (1972, p. 159) proposed .. that if the Ca-planes in dolomite behave like calcite and the Mg-planes exclude the larger Sr2+ion nearly completely, dolomite should contain approximately half the amount of strontium as would a calcite co-existing at equilibrium ." Land and Hoops (1973, p. 613) indicated that, "The bulk sodium content of carbonate rocks is a crude but useful indicator of the salinity of genetic and diagenetic solutions," and that Na+ substitutes with equal facility into Ca2 + and Mg2+ lattice positions in dolomite. Viezer and Demovic (1974) suggested that the Sr2 + content of carbonate rocks is facies controlled with the high Sr2 + concentrations inherited from predominately aragonitic sediments. Folk and Land (1975) found that lower salinities enabled more stoichiometric dolomite to form because of the lower concentrations of other ions competing with Mg2+ and Ca2 + for sites in the dolomite crystal structure. In this study, a model of diagenetic dolomitization involving the mixing of fresh and salt water to produce a dolomitizing solution as addressed by Hanshaw et ale (1971), Badiozamani (1973), and Randazzo et ale (1977) was evaluated. This zone of mixing can occur at the interface between fresh and saline subsurface waters in a coastal regime and farther inland in a brackish zone (Hanshaw et al., 1971; Land, 1973). This model has been proposed for a ... later and continuing stage of dolomitization ... for the Eocene Ocala and Avon Park rocks of the Floridan Aquifer (Randazzo et al.,1977). 59

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The sixteen cores analyzed include the Bell (B-Gilchrist County), Rainbow Springs (RS--Marion County), Cotton Plant (CP--Marion County), and eight from Gulf Hammock (GH--Levy County) as well as ROMP #101 (LA--Lake County), #107 (H--Hernando County), #124 (LE--Levy County) and Homosassa Springs (HS--Citrus County) and Manatee Springs (MS--Levy County). Detailed geology for these cores is contained in Stone (1975--GH cores) ,Hickey (1976--B, RS, CP cores), Zachos (1978--HS, MS cores), and Fenk (1979--LA, H, LE cores). Pure calcite and dolomite samples from these cores were analyzed by X-ray diffraction and atomic absorption spectrometry. Samples were ground .to a powder, dissolved and diluted to appropriate volumes. Analysis was done on a Perkin-Elmer 403 Model Atomic Absorption Spectrophotometer. An Amdahl-470 V62 model computer was used to calculate parts per million (ppm) of each element analyzed. Magnesium data were calculated in terms of mole-percent-MgC03' The data were plotted to determine significant trends. Methods for quantitative analysis of Sr2+, Na+, Mg2+ and Ca 2 + are presented in Sarver (1978) and Metrin (1979). Importance of Sodium The most abundant cation in sea water is Na+ (Land et al., 1975). The partitioning coefficients of Na+/Mg2 + and Na+/Ca2 + for natural carbonate has not been defined sufficiently to be employed confidently in the determination of the paleosalinity at the time of deposition. However, the overall Na+ content may be a rough indicator of the salinity of the latest diagenetic fluid (Land and Hoops, 1973; Viezer et al., 1978). In the model of diagenetic dolomitization evaluated in this study, dolomitization occurs in the mixing zone of fresh and saline subsurface waters. In Florida, the coastal mixing zone is formed at the interface of the fresh water lense and sea water at the depth based on the GhybenHerzberg relation (Walton, 1970) (Figure 22). Sea water in the vicinity of Miami Beach has 10,970 ppm of Na+ and fresh ground water from the interior of the Florida peninsula has combined Na+ and K+ concentrations ranging from a few parts per million to about 40 ppm (Stringfield, 1966, p. 155). In the zone of mixing, the Na+ concentration will be directly proportional to the degree of mixing (Badiozamani, 1973). Land and Hoops (1973) pointed out that the trapped and absorbed Na+ could affect the determination of the Na+ in the crystal structure of calcite and dolomite. However flushing of the Floridan Aquifer with fresh ground water would remove most of the Na+ ions released into solution during the dissolution and replacement of the original sediments. 60

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I ---, .. 0. .' /. J. .. ... ,_ .... ..... . .. .. .. ... '.' .... : .... ;,' .. .. ... .. .. ..... :,' .. .... .. -ft""' .. -.. ... ('.. '. ..-.. ... .. 0 o .. .. .... -... f' .. .--. : ..... .. . Figure 22. The coastal zone of mixing environment of peninsular Florida. 61

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Sodium in Calcite Removal of aragonite and high-Mg calcite sediments from the marine environment where they are stable, can bring about their replacement by more stable low-Mg calcite and/or dolomite. Whether the change is to low-Mg calcite or dolomite is dependent upon the mineralogy of the original sediments, early-formed diagenetic products and the chemistry of the diagenetic environment. Pure calcite samples from the cores in this study have a Na+ content range of 37-970 ppm and an average of 196 ppm (Table 8). Land and Hoops (1973) reported Na+ concentrations of 1,010 ppm or more for Holocene marine carbonate sediments (Table 10). Data from these two studies show a lower Na+ content for the Eocene carbonates, indicating that the formation of low-Mg calcite took place in an environment less saline than sea water. This environment may have been the inland brackish zone of the Floridan Aquifer or the coastal salt/fresh water interface. Sodium in Dolomite Land and Hoops (1973) suggested that Na+ is able to substitute into the Ca 2 + and Mg2+ positions of the dolomite structure with equal facility. Therefore, the Na+ concentrations of calcite and dolomite may be compared directly. The replacement of aragonite and high-Mg calcite by dolomite reflects the environment of diagenesis. TheNa+ concentration of the dolomite studied ranged from 50-1,963 ppm, with an average of 887 ppm (Table 9). Comparison of this average with the 196 ppm average Na+ content of the calcites, indicates that the dolomites were precipitated in a more saline environment than the calcites. When the Na+ concentrations of the Eocene dolomites in this study are compared to modern marine dolomites with Na+ concentrations of 2,000 ppm and more (Land, 1973; Land and Hoops, 1973), a diagenetic environment considerably less saline than sea water is indicated. These low Na+ values for the calcites and dolomites in this study indicate that even slight mixing of hypersaline and fresh water can cause dolomitization. A modern dolomite with 2,000-5,000 ppm Na+ can form by reaction with hypersaline brines, but, if 5-30% of the brine is mixed with fresh water to form a more dilute dolomitizing solution, the resulting dolomite will have only 100-1,500 ppm Na+. Badiozamani (1973, p. 769) stated that 5-30% sea water is enough to cause undersaturation of CaC03 and oversaturation of CaMg(C0 3)2. Land (1973) found that as little as 3-4% sea water would also cause oversaturation of CaMg(C03)2, resulting in dolomitization. Vertical variation diagrams of Na+ concentrations are presented by Sarver (1978) and Metrin (1979). They show higher Na+ concentrations in the lower portion of the LA, H, HS, B, CP, RS and several of the GH cores. LE and MS cores show higher Na+ values in the center region of the core. The MS core also has higher Na+ values in its lowest portion. These areas of higher Na+ values could be the result of diagenesis by solutions more saline than that which affected other portions of the core at other times. 62

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Table 8. Sodium and Sr2+ contents of calcite for all cores Calcite Nos of Strontium ppm Sodium EEm Cores Samples Range Mean Range Mean LA 31 279-968 505 140-432 238 H 23 89-520 285 37-296 143 LE 5 264-507 388 150-970 389 HS 8 274-546 359 138-735 295 MS 9 259-408 322 125-286 189 GH 21 244-639 486 71-843 202 RS 6 297-444 366 85-176 136 CP 11 297-639 377 85-152 113 B' 7 279-368 322 77-127 96 63

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Table 9. Sodium and Sr2+ contents of stoichiometric and non-stoichiometric dolomite for all cores. Dolomite Strontium ppm 39-43 mo1e-percent-MgC03 44-50 mo1e-percent-MgC03 Group GrouE Nos of Nos of Cores Samples Range Mean Samples Range Mean LA 11 215-319 256 0 H 6 215-314 246 1 254 LE 14 201-370 246 6 150-211 174 HS 13 192-334 246 17 141-183 152 MS 20 201-289 234 9 132-173 149 GH 50 210-403 282 8 258-354 314 RS 12 170-262 236 17 132-157 140 CP 11 210-279 240 2 162-183 173 B 12 201-275 229 10 119-266 159 Sodium ppm 39-43 mo1e-percent-MgC03 44-50 mo1e-percent-MgC03 Group Group Nos of Nos of Cores Samples Range Mean Samples Range Mean LA 11 363-1,075 690 0 H 6 548-1,285 754 1 984 LE 14 557-1,088 810 6 344-862 581 HS 13 897-1,767 1,143 17 223-1,963 1,134 MS 20 290-1,527 907 9 281-599 377 GH 50 566-1,520 975 8 857-1,323 1,037 RS 12 504-1,329 1,061 17 205 ... 889 335 CP 11 517-867 701 2 50-693 372 B 12 766-1,426 1,029 10 233-1,575 556 64

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Table 10. Sodium values in carbonate rocks reported in previous works. Description and Reference Modern marine reef calcite and aragonite sediments (Land and Hoops, 1973) Holocene dolomites (Land and Hoops, 1973) Pleistocene dolomite of Jamaica Pleistocene calcite of Jamaica (Land, 1973) Eocene dolomite of Egypt (Land et al., 1975) Sodi urn (ppm) 1,140-2,520 l,010-3,050 400 less than 200 213-475 Table 11. Strontium values in carbonate rocks reported in previous works. Description and Reference Modern marine reef calcite and aragonite sediments (Land, 1973) Modern dolomite from the Persian Gulf (Land and Hoops, 1973) Pleistocene dolomite of Jamaica Pleistocene calcite of Jamaica (Land, 1973) Carboniferous dolomite of Northumberland, England Carboniferous calcite of Northumberland, England (Al-Hashimi, 1976) Eocene dolomite of Egypt (Land et al., 1975) Platteville Formation, Ordovi.cian, dolomite Platteville Formation, Ordovician, calcite (Badiozamani, 1973) 65 Strontium (ppm) 1,200-4,140 640 220 440 132 618 90 37 228

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Importance of Strontium Kinsman (1969) has concluded that the Sr2 + concen t:ation of precipitated dete: mlned by the Sr2+/ Ca2 + ratlo of the preclpltatlng Solutlon. The crystal structure of individual carbonate minerals also affects the Sr2 + concentration. The Sr2 + content of sea water is higher than that of fresh ground water. Odum (1951a, b) reported an average Sr2 + concentration of 8.1 ppm for sea water and less than 1 ppm for fresh ground water of Florida. Because of this difference in Sr2 + content between sea water and fresh water, carbonate minerals may reflect the relative degree of mixing of fresh and saline subsurface waters in the environment that produced them. Kinsman (1969+ p. 488) found sea water to have a fairly constant Sr2+/ ca2 ratio of (0.86.4) X 10-2 except where influenced by continental waters nearshore. The Sr2 + content of sea water can be concentrated in the supratidal environment to a Sr2+/ Ca2 + range of (0.8 to 1.2) X 10-2 over a range of solutions from normal sea water to nine times concentrated sea brines (Kinsman, 1969, p. 490). Kinsman (1969, p. 490) reported a median Sr2+/ Ca2+ ratio of 3.2 X 10-2 for surface continental waters. Subsurface continental waters have a wide range of Sr2+/ Ca2 + values depending upon the mineralogy of the rocks through which they flow, but are generally less than sea water (Kinsman, 1969, p. 490). The Sr2 + in carbonate rocks is also reflected in the mineralogy present. The aragonite crystal structure can accommodate high amounts of Sr2 + (Bathurst, 1975, p. 241). Modern marine sediments are composed chiefly of aragonite and high-Mg calcite and have average Sr2 + concentrations of more than 3,000 ppm (Land, 1973). The carbonate minerals in ancient carbonate rocks are mostly low-Mg calcite and dolomite, which do not incorporate as much Sr2 + as aragonite (Bathurst, 1975, p. 241). Table 11 presents Sr2 + values for some modern and ancient marine carbonates. The ancient carbonate rocks have much less Sr2 + than the modern carbonate sediments, indicating later and continuing diagenesis in water less saline than sea water. The lower Sr2 + content of ancient marine carbonates also reflects the lesser ability of calcite and dolomite to incorporate Sr2 + into their crystal structures than aragonite. Strontium in Calcite The partitioning coefficients for precipitated aragonite and calcite are determined by the Sr2+/ Ca2 + ratio of the minerals formed. The partitioning coefficient for calcite is KSr=0.14.02 at 25 COand is dependent upon faunal mineralogy as we 1 as temperature (Kinsman, 1969, p. 488). Based on the Sr2+/ca2 + ratio of sea water, and the calcite partitioning coefficient, calcite precipitated from sea water should have about 66

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1,200 ppm Sr2+. Calcites with less Sr2 + would have been precipitated from water less saline than sea water. This would occur in sediments in an open system with solutions less2saline than sea water. The calcites in this study have a Sr + concentration range of 89-968 ppm with an average of 403 ppm (Table 8). This is comparable with other values reported for ancient marine limestones (Table 11). Strontium in Dolomite Synthesis of dolomite at low temperatures has never been accomplished because of very slow kinetics involved in its formation (Berner, 1971). Therefore, the partitioning is undefined and cannot be used to predict the Sr + content of dolomite precipitating from sea water as was done with calcite. However, as stated earlier, the dolomite crystal should contain approximately half the amount of Sr + as would calcite precipitated from the same solution and Land, 1972). This would be approximately 600 ppm Sr +, a value supported by Land and Hoops (1973, Table 4). The values of the dolomites in this study range from 119-403 ppm with an average of 239 ppm (Table 9). This suggests that the latest diagenetic solution in which the formed was than sea water. The average Sr content of the calc1tes 1S 403 ppm. The Sr2 + content of the dolomites is approximately 59% of that in the calcites. This is some 9% more than the amount predicted by Behrens and Land (1972) based on the incorporation of into the dolomite crystal strQcture. Land (1973) stated that this difference in the Srl+ content was caused by an outside source and suggested sea water as that source. This would indicate a greater relative amount of salt water present in the dolomitizing zone and is compatible with the Na+ data, indiciating a more saline diagenetic environment for dolomite than calcite. Calcites show considerably higher Sr2 + concentrations than the because of the greater ability of calcite to incorporate Sr + into its crystal structure. Strontium and Sodium in Relation to Mole-Percent-MgC03 The relationship between the Sr2 + and Na+ concentrations and the mole-percent-MgC03 of dolomite was a means by which the diagenetic model of dolomitization was evaluated. The same data for calcite was used to interpret the chemistry of the diagenetic environment. In the Floridan Aquifer, there is a brackish zone between fresh and saline phreatic waters (both saturated with calcite). This brackish zone is undersaturated with calcite and supersaturated with dolomite (Hanshaw et al., 1971). Dissolution of calcite can occur in the undersaturated zone and physical mixing of the brackish waters can cause CO2 to degas, enabling dolomite to precipitate. 67

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Badiozamani (1973) found that when under saturation of calcite and degassing of C02 occur, a solution with as little as 3-30% sea water can cause replacement by dolomitization. Folk and Land (1975) proposed that with a M g2+/Ca2 + ratio of at least 1, dolomitization can occur. Also they found that lower salinities produced more ordered dolomites with higher mole-percent-MgC03 because there are fewer ions competing for positions in the dolomite structure. This suggests that hi1h mole-percent-MgC03 dolomites should have lower Na+ and Sr + concentrations and would indicate the relative salinity of the latest diagenetic solution. Sections of the cores in this study contained both calcite and dolomite. These sections of mixed mineralogies could have resulted from the depletion of Mg2 + ions in the solution by precipitation of dolomite and the subsequent formation of low Na+ and Sr2 + calcite as more fresh water flushed through the system (Land, 1973). The Na+ and Sr2+ concentrations associated with various mole-percent-MgC03 contents of carbonate rocks are an indication of the relative salinity of the environment during neomorphism. The mixing zone model of dolomitization would be able to produce the thick dolomite sequences in Florida because ... sea level changes, climatic changes, and/or the occasional uplift or downwarp of the Florida platform ... (Hanshawet al., 1971, p. 722) could cause the brackish zone to move within the system and contact large volumes of rock inland and bring about substantial lateral migration of the sea water/fresh water coastal zone of mixing. Calcite Nearly all of the calcite in this study is low-Mg calcite with less than 4 mole-percent-MgC03' It has much lower Sr2 + and Na+ concentrations than modern marine carbonate sediments (Tables 8 and 10). This may be the result of diagenesis in an open system with fresh or slightly saline water because calcite formation is inhibited by Mg2+ ions (Berner, 1966). The slight changes of mole-percent-MgC03 that did occur in the calcites had no corresponding changes in Na+ and Sr2 + concentrations. However, the ranges of Na+ and Sr2 + values in the calcites could be caused by the original mineralogy of the sediments (Veizer and Demovic, 1974) or by the position of the core in relation to the flow patterns of the aquifer (Kinsman, 1969). If the original sediments were aragonite, a higher content of Sr2+ should be inherited by the precipitated calcites (Veizer and Demovic, 1974). If the calcites were in the down flow direction or discharge area of the aquifer, they should have higher Sr2+ concentrations (Kinsman, 1969). These two factors, along with the salinity of the diagenetic solutions, could cause the wide variation of Sr2 + in the calcites. 68

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Dolomite As stated earlier, the dolomites in this study fall into two groups, more nearly stoichiometric and non-stoichiometric dolomite. Both groups have distinct Sr2+ and Na+ ranges (Table 9). The more nearly stoichiometric dolomite (44-50 molepercent-MgC03) occurs mainly in the lower portions of the B, RS, CP, LE, MS and HS cores. The higher mole-percent-MgC03 dolomites generally have a narrower range of Sr2 + concentrations than the nonstoichiometric dolomites (Table 9). This may suggest a longer resident time for the diagenetic fluids and possibly a greater approach to equilibrium between crystals and solution. The Sr2 + values for the 44-50 mole-percent-MgC03 group are generally less than the 39-43 mole-percent-MgC03 dolomites. Folk and Land (1975) attributed this type of relationship to the formation of higher mole-percent-MgC03 dolomite in less saline water allowing slower, more precise ordering to occur with less inhibition by competing ions. The data in this study show a positive correlation between Na+ and Sr2+ in the dolomites of the B, RS, CP, GH, MS and LE cores. These cores are in an area of n large discharge of artesian water ... n (Stringfield, 1966, p. 130). This large discharge could flush most of the trapped and absorbed Na+ from the rocks. The LA, Hand HS cores do not show this positive correlation between the Sr2 + and Na+ values (Metrin, 1979). The Na+ concentrations vary over a wide range, while the Sr2 + values are fairly constant. The LA core is in an area of local recharge (Stringfield, 1966, p. 126). The Hand HS cores are in an area of local recharge where the aquifer is at the surface. However,water also discharges as large springs along the coast and on the floor of the gulf (Stringfield, 1966, p. 130). This high discharge (5.376m3/sec for Homosassa Springs; United States Geological Survey, 1974) in the area of these cores could cause fluctuations in the ground water geochemistry, as the large amounts of fresh water discharge lower the salinity of sea water. This could cause the salt/fresh water interface to move seaward. These variations in the salinity of the diagenetic fluids could cause the wide ranges of Na+ values in these cores. Also, Na+ could be contributed by trace amounts of clay pre-sent in the original sample. The changes in salinity that produced the distinct ranges of Na+ and Sr2+ concentrations of the two dolomite groups may have been caused by movement of the dolomitizing fluids through the system. In response to climatic and/or tectonic changes, inland brackish fluids would pass through the aquifer as the phreatic zone fluctuated vertically. The coastal salt/fresh water interface would migrate laterally as changes in sea level occurred. This could cause changes 69

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in the Na+ and Sr2 + concentrations of the dolomites of a core as the dolomitizing flowed through the aquifer producing later and continuing dolomitization of the Floridan Aquifer (Randazzo et al., 1977, p. 501). The variations between Sr2 + and Na+ ranges in coastal and inland cores are the result of the mineralogy of the original sediments and/or the high discharge of fresh water in the area of the coastal cores in this study, causing modification of the three dimensional shape of the salt/fresh water interface and consequent fluctuations of the ground water geochemistry. The results of this geochemical study of the distribution of Na+ and Sr2 + within Eocene carbonate rocks of the Floridan Aquifer support a mixing zone model of dolomitization, which dolomitizes this sequence of rocks, with solutions less saline than sea water. These dilute saline solutions can be formed at the coastal salt/fresh water interface, modified by fresh water discharge, or in an inland regime in the brackish zone of the phreatic system. SUMMARY The carbonate units comprising the Floridan Aquifer in the northern portion of the Southwest Florida Water Management District were deposited in a shallow marine environment and represent a complex history of deposition and diagenesis. A number of lithofacies have been recognized and examination of the vertical distribution of lithologies among cores has enabled the recognition of cyclic sedimentation patterns in the strata. The Lake City Formation is represented by two distinct depositional cycles. An open marine environment changed to intertidal and supratidal environments. Shallow water is indicated by the presence of algal boundstones and wacke stones and slightly deeper water by foraminiferal wackestones. The upper portion of the last cycle is represented by lagoonal deposition of mudstones, gypsum-bearing clay beds and a significant amount of carbonaceous matter. The carbonate rocks of the Avon Park Formation provide evidence of deposition in an environmental complex consisting of subaerially exposed tidal mudflats and intervening, protected, shallow-water lagoons. A number of carbonate facies have been recognized and examination of the vertical distribution of lithologies within cored intervals has enabled the recognition of cyclic sedimentation patterns in Avon Park strata. Subtidal facies show a general lack of sedimentary structures and are represented by a greater abundance and wider diversity of fossils than associated intertidal and supratidal deposits. The lithologic and paleontologic characteristics of these subtidal rocks suggest that they were 70

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deposited in environments ranging from a broad carbonate shelf or platform to a low energy lagoonal setting. Intertidal rocks are characterized by a predominance of micrite, indicative of the low tidal and wave energies which prevailed in the depositional environment. Fossils are sparse and the low faunal diversity of intertidal rocks may be a reflection of unstable ecologic conditions which had limited the presence of organisms in this tidal zone. Sedimentary structures preserved in intertidal rocks include: vertical burrows; root casts and molds; sediment mottling; and thin, micritic beds. The most characteristic feature of the supratidal rocks is algal and Sedimentary laminations. Crinkled and flat laminar morphologies similar to those found in the modern carbonate deposits of Andros Island, Bahamas are abundantly represented in supratidal facies. A scarcity of desiccation structures and evaporite minerals in supratidal beds may suggest that deposition had taken place under general humid paleoclimatic conditions. The sediments of the Ocala Limestone were deposited under warm and open marine conditions on a relatively flat and broad carbonate shelf or platform similar to the present day Great Bahama Bank. The Ocala Limestone is composed of two major lithologies, separating the strata into distinct upper and lower lithologic units. ,Deposits representing shallow subtidal to intertidal, comparatively high energy, open or slightly restricted marine conditions occur in the lower unit where deposition is interpreted to have taken place relatively close to the shore. As a lithology, the Lower Ocala is characterized by thickly bedded fossiliferous limestone consisting predominantly of cleanly washed skeletal packstones to grainstones. The carbonate deposits of the Upper Ocala represent a transition into progressively deeper water, lower energy environments of sedimentation. The unit is characterized by the presence of a deeper-water faunal assemblage, including abundant whole and fragmented tests of large foraminifera, and the deposition of wackestones and muddy packstones over the cleanly washed deposits of the lower unit. The change from the tidal-flat and restricted subtidal deposits of the Avon Park to the offshore, high and low energy marine deposits of the Ocala Limestone is indication of an overall transgressive sequence of sedimentation. The vertical succession and cyclic alternations of lithologies is interpreted to be the result of periodic sea level fluctuations characterized by local and repeated seaward shifts in the shoreline environment. The Suwannee Limestone and "Tampa Formation," as they occur in the subsurface of Hillsborough and Manatee Counties, south Florida, were deposited on a shallow marine carbonate bank. The Suwannee Limestone is a white, whitish-gray to yellowish-gray, allochemical limestone characterized by its abundance of fossils and relative importance of pore-filling sparite. The Suwannee Limestone consists of three lithofacies and represents a series of rock types deposited mostly in an agitated water, shallow subtidal zone above wave base. 71

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The microcrystalline limestone and autochthonous algal limestone of the Suwannee are only present near the top of the sequence. These rock types can be attributed to their deposition in the supratidal environment. The disconformable erosional surface between the Suwannee Limestone and the "Tampa Formation" represents a depositional hiatus. Furthermore, a few micro-disconformities are found within both of these formations, each representing local diastems. The "Tampa Formation" is a gray or dark gray, sandy, clayey, allochemical limestone characterized by its abundance of micrite, extra-basinal materials and local concentrations of fossils. Microcrystalline limestone, dolomite and partly dolomitized limestones are found only in the middle part of the sequence. The sequence was deposited mostly in the supratidal and intertidal environments. In all, the Suwannee Limestone in the area records a general transgressive-regressive sequence which ended with subaerial exposure and erosion. The erosional surface is overlain by a basal limestone conglomerate which was followed by another phase of sedimentation during which the "Tampa Formation" was deposited. Diagenetic (crystallization) fabrics can be classified on the basis of constituent crystal size distributions (unior multi-modal) and combination of textural types. Basic categories are: (a) Equigranular (i) peloidal (ii) sutured mosaic (iii) sieve mosaic (b) Inequigranular (i) spotted mosaic (ii) fogged mosaic (iii) contact-rhomb porphyrotopic (iv) floating-rhomb porphyrotopic (v) poikilotopic (c) Aphanotopic Consideration of natural associations and genetic relationships of crystallization fabrics makes it possible to deduce the original uncrystallized fabrics in many cases. Type of porosity development is directly related to type of crystallization fabric, except in the case of vug or cavernous porosity (nonfabric selective). Vug porosity occurs sporadically in dolomitized fabrics. Cavernous porosity is associated with formational contacts and may be caused by gross mineralogic changes in the rocks (e.g., the change from dominantly calcitic to dominantly dolomitic rocks). 72

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The close agreement of depositional cycles, patterns of crystallization fabric distribution, and patterns of porosity development in these cores suggests that predictive models of mineralogy, fabric, and porosity development can be constructed. The viability of such models will depend upon reproducibility and recognition of these patterns in other wells. Atomic absorption spectrometry measurements of Sr2+, Na+ and mole-percent-MgC03 have allowed the recognition of distribution patterns related to depth, geographic position, and diagenetic mineralogy. Sodium and Sr2 + concentrations provide evidence in support of a mixing zone model of diagenetic dolomitization as presented by Hanshaw et al. (1971) and Land (1973). This mixing zone can occur on the coast at the salt/fresh water interface or in the brackish zone of the phreatic system farther inland. Diagenesis occurred within a dynamic open system in the Floridan Aquifer resulting in dolomitization when sufficient Mg2+ ions were available and calcitization when the supply of Mg2+ ions was lacking. Higher concentrations of Sr2 + and Na+ in dolomite than in calcite indicate a more saline diagenetic environment during the formation of dolomite. The Sr2 + and Na+ concentrations and mole-percent-MgC03 in calcite indicate diagenesis in a uniform environment less saline than sea water. Comparison of the Sr2 + and Na+ concentrations of the Eocene dolomites with modern marine dolomites indicates diagenesis in an environment less saline than sea water. Sr2 + and Na+ concentrations in dolomite are generally lower in the higher mole-percent-MgC03 dolomites, indicating a less saline environment of formation with fewer ions competing for sites in the dolomite structure. The Sr2 + values in calcite could be inherited from original aragonitic sediments or could be the result of formation in the discharge area of the aquifer. Some of the coastal cores of this study have lower Na+ and Sr2 + concentrations than the inland cores, suggesting a less saline diagenetic environment for the coastal cores. The large springs with high fresh water discharge near the coastal cores of this study could account for this difference by lowering the salinity of sea water and causing a seaward shift of the salt/fresh water interface. The Sr2 + values for the LA, Hand LE cores reflect the presence of calcite or dolomite. The LA and H cores have higher Na+ values in their lower portions. The LE core has higher Na+ values in its center region. This suggests fluctuations in the chemistry of the diagenetic environment as the dolomitizing solutions moved through the aquifer in response to climatic, tectonic, and/or sea level changes. 73

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Viezer, J., J. Lemieux, B. Jones, M. R. Gibling, and J. Savelle, 1977, Sodium: paleosalinity indicator in ancient carbonate rocks: Geology, v. 5, p. 177-179. Viezer, J., J. Lemieux, B. Jones, M. R. Gibling,and J. Savelle, 1978, Paleosalinity and dolomitization of a lower Paleozoic carbonate sequence, Somerset and Prince of Wales Islands,Artic Circle: Canadian Journal Earth Sciences, v. 15, p. 1448-1461. Vernon, R. 0., 1951, Geology of Citrus and Levy Counties, Florida: Florida Geological Survey Bull. 33, 256 p. Walton, W. C., 1970, Groundwater resource evaluation: New York, McGraw-Hill, 664 p. Williams, K. E., D. Nicol,and A. F. Randazzo, 1977, The geology of the western part of Alachua County, Florida: Florida Bureau of Geology, Report of Investigations 85, 98 p. Yon, J. W. and C. W. Hendry, 1972, Suwannee Limestone in Hernando and Pasco Counties, Florida: Florida Bureau of Geology Bull. 54, part 1, p. 1-42. Zachos, L. G., 1978, Stratigraphy and petrology of two shallow wells, Citrus and Levy Counties, Florida: M.S. Thesis, University of Florida, 105 p. Zachos, L. G. and G. D. Shaak, 1978, Stratigraphic significance of the Tertiary echinoid Eupatagus ingens Zachos: Journal Paleontology, v. 52, p. 921-927. 79