Seismic stratigraphy of the western Florida carbonate platform and history of Eocene strata

MISSING IMAGE

Material Information

Title:
Seismic stratigraphy of the western Florida carbonate platform and history of Eocene strata
Physical Description:
xii, 215 leaves : ill. ; 29 cm.
Language:
English
Creator:
Jee, Jonathan Lucas, 1955-
Publication Date:

Subjects

Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1993.
Bibliography:
Includes bibliographical references (leaves 195-213).
Statement of Responsibility:
by Jonathan Lucas Jee.
General Note:
Typescript.
General Note:
Four folded ill. in pocket.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001897885
notis - AJX3182
oclc - 29809572
System ID:
AA00003662:00001

Full Text










SEISMIC STRATIGRAPHY OF THE
WESTERN FLORIDA CARBONATE PLATFORM
AND HISTORY OF EOCENE STRATA





















By

JONATHAN LUCAS JEE


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


1993
































Copyright 1993

by

Jonathan Lucas Jee












ACKNOWLEDGMENTS

I am indebted to Dr. Anthony F. Randazzo, committee

chairman, for his guidance and encouragement. I also thank

the other committee members, Dr. Douglas L. Smith, Dr. Paul F.

Ciesielski, Dr. David Hodell, and Dr. Thomas Crisman.

I am grateful to Mr. Hank Hamilton, Mr. Earl Hale, and

Mr. Jerry A. Watson of GECO Geophysical Company, Inc., Mr.

Carl B. Hutchins and Ms. Lori Price of Digicon Geophysical

Corporation, and Mr. Marc A. Lawrence and Ms. Carol Ellis of

Fairfield Industries for proprietary reflection seismic data

used in this study. Thanks go to Dr. John P. Riola, Ms. Jean

Anderson and Mr. Thomas M. Torrey of Texaco USA for assistance

in obtaining seismic data and for supplying data from

exploratory wells. I thank Dr. Tillman Cooley, Mr. Lee

Entsminger, Ms. Leigh Anne Salathe, and Mr. Everett Kastler of

Mobil Exploration and Producing U.S., Inc., for release of

cores and additional well information. Thanks also go to Mr.

Phil Ware of Coastal Petroleum for sharing well data with me.

Many others in various capacities have given support,

cooperation, assistance and advice, all greatly appreciated.

Dr. James A. Miller and Mr. Mahlon Ball of the United States

Geological Survey (USGS) supplied copies of USGS well and

seismic data. Craig Byar of Petroleum Information also


iii







provided information on offshore wells. Ms. Joan Ragland of

the Florida Geological Survey (FGS), Oil and Gas Section,

helped in the search for core information. Dr. Brad Macurda

of The Energists gave guidance in the initial phase of this

project, facilitating the search for seismic data. Dr. Albert

C. Hine and Dr. Larry J. Doyle of the Department of Marine

Science, University of South Florida, St. Petersburg, Mr.

George O. Winston, consulting geologist, and Dr. Richard T.

Buffler of the University of Texas Institute for Geophysics

shared helpful ideas on the project. Mr. Stephen M. Greenlee

of Exxon Production Research Company assisted with the

correlation of sequence boundaries and Mr. Stuart Grossman of

Exxon Exploration Company provided biostratigraphic data. Mr.

Frank Rupert of the FGS assisted with interpretation of data

on benthonic foraminifers.

Financial support, in the form of grants-in-aid of

research, was contributed by Sigma Xi, the Scientific Research

Society (1989), and the Geological Society of America (1990

and 1991). I have also been supported as a research assistant

working on various projects funded by grants from the USGS.

Additionally, I received (Fall 1990) a fellowship associated

with this dissertation research from the Space Assistantship

Enhancement Program of the Florida Space Grant

Consortium/National Aeronautics and Space Administration.

Special recognition is due Susan, my wife, for her love,

support, and inspiration.













TABLE OF CONTENTS
page

ACKNOWLEDGMENTS.... .................................. ... iii

LIST OF FIGURES.......... ...... ............... ......... vii

ABSTRACT................. ... ...... .......... ......... x

INTRODUCTION........................................... 1

Purpose and Scope........................ .. ......... 1
Stratigraphic Concepts.............................. 2
Seismic Stratigraphy ............................. 4
Sequence Stratigraphy.............................. 4
Genetic Stratigraphic Sequences................... 8
Allostratigraphy.................................. 11
Discussion......................................... 11
Geologic Setting....................................... 14
Stratigraphy.................. ........ .. ......... 14
Major Geologic Features.......................... 15
Pre-Late Cretaceous Geologic History.............. 23
Late Cretaceous-Cenozoic Geologic History.......... 27
Exposition of Problems Investigated.................. 50

METHODS AND MATERIALS.... ........................... 57

Data Base.............................................. 57
Reflection Seismic Data........ ........................ 57
Well Data.................. ................... 59
Seismic Stratigraphic Interpretation Procedure...... 64
Chronostratigraphic Interpretation Procedure...... 69
Well-Log Correlation Procedure.................... 73

RESULTS AND DISCUSSIONN.............................. 75

Chronostratigraphic Framework..................... 75
Time-equivalence of Lithostratigraphic Units...... 81
MCSB....................................... ....... 82
Upper Cretaceous................................. 83
Paleocene-Eocene..................... ..... ....... 85
Oligocene-Lower Middle Miocene.................. 88
Upper Middle Miocene-Holocene..................... 88
Seismic Stratigraphic Framework..................... 89
MCSB..... ...... ......... ............ ..... .... 89
Upper Cretaceous.................................. 131








Paleocene-Eocene................. ................... 142
Oligocene-Lower Middle Miocene................... 150
Upper Middle Miocene-Holocene..................... 153

SYNTHESIS AND INTERPRETATION.......................... 156

CONCLUSIONS.................. .. ....................... 166

APPENDIX A REFLECTION SEISMIC ACQUISITION PARAMETERS
AND PROCESSING SEQUENCES............................ 170

APPENDIX B BIOCHRONOSTRATIGRAPHIC AND
MAGNETOBIOCHRONOSTRATIGRAPHIC INTERPRETATIONS....... 180

REFERENCES ............................................ 195

BIOGRAPHICAL SKETCH................................... 214













LIST OF FIGURES
Figure page

1. Map of the study area............................. 3

2. Distribution of carbonate lithofacies in a
sequence framework.... ........................... 9

3. Middle Jurassic through Holocene stratigraphy in
the vicinity of this study....................... 17

4. Major geologic features of the Florida Carbonate
Platform.......................................... 18

5. Diagram of major Middle to Upper Cretaceous
sequence boundaries and maximum-flooding surfaces
from Wu and others (1990a)....................... 31

6. Contrast between (a) an idealized drowned carbonate
platform and (b) a subaerially exposed carbonate
platform......................................... 34

7. Synthesis of chronostratigraphy, biostratigraphy,
sequence stratigraphy, and eustatic curves
(modified from Haq and others, 1988) correlated
with the Upper Cretaceous formations and genetic
packages, central and eastern Coastal Plain of
Alabama.......................................... 36

8. Chart of lithostratigraphic units (Group,
Formation, Member) of the Gulf Coastal Plain,
Alabama, in the center, with the sequence
stratigraphic interpretations of Baum and Vail
(1988), Donovan and others (1988)on the right and
those of Mancini and Tew (1990a and b, 1991a and
b) on the left................................... 41

9. Map of previous seismic/sequence stratigraphic
studies of Upper Cretaceous and Cenozoic strata
in the vicinity of this study..................... 43

10. Chart comparing previous seismic/sequence
stratigraphic interpretations of Upper Cretaceous-
Cenozoic strata in this study area................ 45

11. Map of reflection seismic profiles and wells..... 61

vii








12. Seismic facies of carbonate depositional
environments.................................... 68

13. Geomagnetic polarity timescale for the Late
Cretaceous and Cenozoic with correlation to
planktonic foraminiferal zonations and and the
last appearance data of key planktonic
foraminifers.................................... 71

14. Well-log cross-section A-A' (caption)............ 76
(Figure in pocket)

15. Well-log cross-section B-B' (caption)............ 77
(Figure in pocket)

16. Well-log cross-section C-C' (caption)............ 78
(Figure in pocket)

17. Well-log cross-section D-D' (caption)............ 79
(Figure in pocket)

18. Part of seismic section F15,
a. uninterpreted................... ............ 91
b. interpreted .................. .................. 93

19. Part of seismic section F3,
a. uninterpreted............................... 95
b. interpreted.................................. 97

20. Northern part of seismic section G12,
a. uninterpreted............................... 99
b. interpreted.................................. 101

21. Southern part of seismic section G12,
a. uninterpreted............................... 103
b. interpreted.................................. 105

22. Part of seismic section G11,
a. uninterpreted............................... 107
b. interpreted.................................. 109

23. Part of seismic section Gl,
a. uninterpreted............................... 111
b. interpreted.................................. 113

24. Part of seismic section G3,
a. uninterpreted............................... 115
b. interpreted................... ............... 117

25. Part of seismic section G6,
a. uninterpreted............................... 119
b. interpreted.................................. 121


viii







26. Parts of seismic sections G17 and G18,
a. uninterpreted............................... 123
b. interpreted................................. 125

27. "Thickness" map of the entire Upper Cretaceous
through Cenozoic section contoured in 2-way
traveltime... ...... ........................ .. ... .. 126

28. Map of the configuration of the mid-Cretaceou
sequence boundary (MCSB) surface contoured in
2-way traveltime.................................. 128

29. "Thickness" map of the seismic subunit
contoured in 2-way traveltime.................... 133

30. "Thickness" map of the seismic subunit
contoured in 2-way traveltime.................... 138

31. Map of the configuration of the top of the
Cretaceous contoured in 2-way traveltime......... 141

32. "Thickness" map of the Paleocene-Eocene seismic
unit contoured in 2-way traveltime............... 145

33. Map of the configuration of the top of the Eocene
contoured in 2-way traveltime.................... 146

34. "Thickness" map of the Oligocene-lower Middle
Miocene seismic unit contoured in 2-way
traveltime........................................ 151

35. Map of the configuration of the top of the lower
Middle Miocene contoured in 2-way traveltime..... 154














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

SEISMIC STRATIGRAPHY OF THE
WESTERN FLORIDA CARBONATE PLATFORM
AND HISTORY OF EOCENE STRATA

By

Jonathan Lucas Jee

May 1993

Chairman: Anthony F. Randazzo
Major Department: Department of Geology

The stratigraphy of the western Florida Carbonate

Platform above the mid-Cretaceous Sequence Boundary (MCSB) is

defined using 9,600 km of multifold reflection seismic data

tied to 29 wells. Concordant reflections at the MCSB deny

subaerial exposure of the platform. A drowning unconformity

related to an oceanic anoxic event is a more likely cause of

the MCSB. Preexistent structures influenced the MCSB surface

which in turn affected subsequent deposition.

Biostratigraphic data tied to magnetobiochrono-

stratigraphic interpretations provide a time-stratigraphic

framework of four main units: Upper Cretaceous, Paleocene-

Eocene, Oligocene-lower Middle Miocene, and upper Middle

Miocene-Holocene. The Upper Cretaceous has two subunits Ku

(Cenomanian-Santonian) and K2 (Campanian-Maastrichtian). Ku

has continuous, parallel reflections and thickens in lows on

x







the MCSB. In the Apalachicola Basin, YK2 has uniform

thickness, discontinuous, subparallel, even-to-wavy

reflections, and is intensely faulted. Sonic velocity of K2

shows a southeastward change from siliciclastics to more

carbonate rock. Hummocky-to-contorted seismic facies and

thickening of KY2 on an MCSB high suggest a deep-water

carbonate buildup.

The Paleocene is thin and Danian strata absent from the

Destin Dome to Apalachee Bay. The Eocene margin marked by a

north-south belt of west-prograding clinoforms at 850W

developed from a homoclinal ramp to a flat-topped shelf.

Landward this margin, a seismic "marbled zone" suggests

dolomitic facies. In the Apalachicola Basin, Ypresian-

Lutetian (?) sequences form a wedge that thickens to the west.

Basinward of the margin Lutetian-Priabonian sequences with

lenticular shape and wavy, subparallel to hummocky seismic

facies are stacked to form broad, en echelon mounds. Near the

Florida Escarpment, an Eocene, elongate mound with disrupted

seismic facies restricted progradation of post-Eocene

clinoforms.

Post-Eocene strata are of continuous, parallel seismic

facies and drape the Eocene surface, thickening in the lows.

In the Tampa Embayment, Oligocene-Lower Middle Miocene strata

form sets of progradational clinoforms that steepen to the

southwest as they impinge upon the escarpment. Truncation of

clinoforms has been reported beneath a mid-Miocene








unconformity, but apparent truncation of clinoforms can also

be observed at the tops of other, older sequences.


xii













INTRODUCTION

Purpose and Scope

The goal of this investigation is to understand better

the geologic history of the western Florida Carbonate Platform

by refining the tectonic and stratigraphic framework of the

Upper Cretaceous through Quaternary sedimentary section in the

northeastern Gulf of Mexico.

The following are specific objectives of this study:

1. The use of seismic stratigraphic analysis of

multichannel seismic reflection profiles integrated with

available geological and geophysical data from wells to

a. Identify depositional sequences and delineate their

external geometry and areal extent,

b. Characterize seismic faces within depositional

sequences,

c. Relate depositional sequences to cycles of relative

sea level change, and

d. Compare the local and global patterns of sea-level

fluctuation.

2. The evaluation of conceptual models, especially those

predicting the responses of carbonate systems to fluctuations

of relative sea level, and those pertaining to carbonate-to-

siliciclastic facies transitions.







2

3. Interpretation of the depositional and diagenetic

history of Eocene carbonate deposits with particular attention

to the role of early post-depositional fluctuations of

relative sea level.

The area of investigation (Figure 1) extends offshore of

the present coastline from just east of Mobile Bay to

Charlotte Harbor, across the easternmost portion of the

Mississippi-Alabama Shelf to the De Soto Canyon, and over the

West Florida Shelf and Terrace to the Florida Escarpment

(Martin and Bouma, 1978).

Stratigraphic Concepts

This study involves the recognition and interpretation of

unconformity-bounded stratal units, known as "depositional

sequences." The term, depositional sequence, was coined as

part of "seismic stratigraphy" as expounded in a series of

papers by Vail and others (1977). Although the idea of

unconformity-bounded sequences developed over many years

(Sloss, 1988), Walker (1990) recognizes four "new

stratigraphies" that subdivide rocks into genetic packages on

this basis. These are seismic stratigraphy (Vail and others,

1977), sequence stratigraphy (Vail, 1987; Van Wagoner and

others, 1987, 1988), genetic stratigraphic sequences

(Galloway, 1989), and allostratigraphy (North American

Commission on Stratigraphic Nomenclature [NACSN], 1983). A

complete review would be redundant with voluminous literature,

but a brief synopsis is appropriate.










88 86" 84* 820 800
Mobile,



J SHELFn BiSS
on FJackonloill lorida

--30






280











,Bouma, 1978, Figure 2).
1 26 0

\;a; Howell /,

-- el *, -. --- .-


PLAIN_


Figure i. Map of the study area (modified from Martin and
Bouma, 1978, Figure 2).









Seismic Stratigraphy

The key tenet of seismic stratigraphy is that primary

seismic reflections parallel stratal surfaces and

unconformities and follow chronostratigraphic correlations

(Vail and others, 1977). The basic unit for seismic

stratigraphic analysis, the depositional sequence, is defined

as "a stratigraphic unit composed of a relatively conformable

succession of genetically related strata and bounded at its

top and base by unconformities or their correlative

conformities" (Vail and others, 1977, p. 53). A "conformity"

is a bedding surface along which there is no significant

hiatus. "Sequence boundaries" are determined objectively by

the discordance of strata (onlap, downlap, toplap, and

truncation) manifested in seismic sections as reflection

terminations. By measuring "coastal onlap" (the progressive

landward onlap of coastal deposits in a given stratigraphic

unit), seismic stratigraphy was used to interpret sea-level

histories along continental margins and has been hailed as a

breakthrough for regional and global chronostratigraphic

correlations (Vail and others, 1977; Haq and others, 1987,

1988).

Sequence Stratigraphy

The concepts of sequence stratigraphy (Vail, 1987; Van

Wagoner and others, 1987, 1988), the study of rock

relationships within a chronostratigraphic framework of

repetitive sequences, evolved from seismic stratigraphy.







5

Application of sequence stratigraphy has spread beyond the

realm of seismic data, and detailed geologic data from wells

and measured sections can afford resolution of cycles higher

than the third order (Vail and others, 1977). Sequence

stratigraphy can provide information on lithofacies and facies

changes, relief and topography of unconformities,

paleobathymetry, chronostratigraphic correlation, and

depositional and burial history (Boggs, 1987).

A tenet of sequence stratigraphy is that, among four

major variables affecting stratal patterns and lithofacies

distributions (tectonic subsidence, eustacy, sediment supply,

and climate), relative change of sea level (the combination of

eustacy and tectonic subsidence) is "the key to understanding

stratigraphy," (Vail, 1987, p. 3). Vail (1987) fundamentally

revised the concept of a depositional sequence from that of

seismic stratigraphy (Vail and others, 1977). Whereas in

seismic stratigraphy one or more depositional sequences could

be deposited during one cycle (or paracycle) of relative rise

and fall of sea level, in sequence stratigraphy "A [single]

sequence is interpreted to be deposited during a [single]

cycle of eustatic change of sea level starting and ending in

the vicinity of inflection points on the falling limbs of the

sea level curve" (Vail, 1987, p. 3). To accommodate this

revision, the reflection termination criteria for the

recognition of sequence boundaries were restricted to onlap

above and truncation below, and the redefined "sequence"







6

subdivided into "systems tracts." Downlapping reflection

terminations were associated with systems-tract boundaries (at

the top of a "basin-floor fan," at the top of a "slope fan,"

or at the "maximum-flooding surface" within a "condensed

section").

Systems tracts are interpreted to be deposited during

specific time intervals within a eustatic cycle. A systems

tract is a linkage of contemporaneous "depositional systems"

(Brown and Fisher, 1977). A depositonal system is a three-

dimensional assemblage of lithofacies (Fisher and McGowan,

1967). Certain depositional environments and lithofacies are

associated with different systems tracts. Systems tracts are

defined by their position within the sequence, and by the

stacking patterns of "parasequence sets" and "parasequences"

bounded by "marine-flooding surfaces" (surfaces across which

there is evidence of an abrupt increase in water depth) (Vail,

1987; Van Wagoner and others, 1987, 1988).

The fluctuation of relative sea level, along with

depositional setting and climate, affect basin water chemistry

(salinity, nutrients, temperature, oxygen content) and

carbonate productivity (Sarg, 1988). Assuming that

depositional geometry, facies distribution and early

diagenesis of shallow-marine carbonate rocks are controlled

primarily by relative changes in sea level, sequence

stratigraphy has been proposed as a tool for characterizing







7

and delineating shallow-marine carbonate depositional

sequences (Sarg, 1988).

Both seismic stratigraphy and sequence stratigraphy have

significantly altered the language of stratigraphy, not only

by adding to the vocabulary, but also by redefining some terms

to restrict or even change their traditional meanings. In

sequence stratigraphic usage, an unconformity is "a surface

separating younger from older strata, along which there is

evidence of subaerial erosional truncation or subaerial

exposure, with a significant hiatus indicated" (Van Wagoner

and others, 1987, 1988). This is more restrictive than an

earlier definition (Vail and others, 1977) that encompassed

both subaerial and submarine surfaces. This restricted

definition of an unconformity is necessary, because otherwise

the presence of a maximum-flooding surface (a submarine

unconformity, in the strict sense) in the middle of a sequence

would violate the definition of a sequence as a "relatively

conformable succession of genetically related strata" (Vail

and others, 1977, p. 53).

Vail and Todd (1981) recognized two types of sequences

distinguished by the type of sequence boundary at the base of

the sequence. As applied to carbonate depositional regimes

(Sarg, 1988), a type 1 sequence boundary is marked by

subaerial exposure and erosion of the platform, concurrent

submarine erosion on the foreslope, onlap of overlying strata,

and a downward shift of coastal onlap. A type 2 sequence







8

boundary is characterized in carbonate systems by subaerial

exposure of inner-platform peritidal areas and platform

shoals, a downward shift in coastal onlap that may occur to a

position at the preceding platform/bank margin, and onlap of

overlying peritidal strata in platform lows and at the margin

(Sarg, 1988).

Four systems tracts are recognized in sequence

stratigraphy (Van Wagoner and others, 1987, 1988; Sarg, 1988):

lowstand, shelf margin, transgressive, and highstand. A type

1 sequence boundary is overlain by a lowstand systems tract,

whereas the shelf margin systems tract overlies a type 2

sequence boundary. The transgressive systems tract lies above

the transgressivee surface" that occurs at the top of either

the lowstand or shelf margin systems tract. The top of the

transgressive systems tract is a "condensed section," and the

upper boundary is the "downlap surface" (maximum-flooding

surface, MFS) above which lies the highstand systems tract

which completes the sequence. Figure 2 shows the distribution

of carbonate lithofacies in a sequence framework (Sarg, 1988).

Genetic Stratigraphic Sequences

The genetic stratigraphic sequence (GSS) theory

(Galloway, 1989) was modeled on marine basins filled by

episodes of progradation of terrigenous plastic sediments

punctuated by marine transgressions. While there is no

expressed applicability to carbonate depositional regimes, the

















SEQUENCE SRAMTI6RAPHY DEPOSIflONAL MODEL
$OWNW SUM= SYSIR=S UACTS AND LDIDFAO5


I
IWYAW


3 TICTCAW
~~~1
.ATm
4" OtIffTLAt.


S52


SI CONDENSED SECTION




SUBAERIAL HIATUS L


SIST) /

DISTANCE-1

B) IN GWLUDC WME


SURFACES
(SB) SEQUENCE BOUNDARIES
ISB 1 TYPE-1
(SB 2) TYPE-2
IDLSI DOWNLAP SURFACES
(ms) mam loading surfa
ITS) TRANSGRESSIVE SURFACE
(Fr floodng surfIa above murnum
NgNnm .


SYSTEMS TRACTS
HST HIGHSTAND SYSTEMS TRACT
TST TRANSGRESSIVE SYSTEMS TRACT
LST LOWSTAND SYSTEMS TRACT
LSF LOWSTAND FAN
LSW LOWSTAND WEDGE
SMW SHELF MARGIN WEDGE SYSTEMS TRACT


UTHOFAIES
SSUPRATIDAL
PLATFORM
SPLATFORM-MARGIN
GRAINSUPPORTSTONE/REEFS
[ MEGABRECCIAS/SAND
]FORESLOPE
n TOE-OF-SLOPE/BASIN


Figure 2. Distribution of carbonate lithofacies in a
sequence framework (Sarg, 1988).







10

concept has important implications for sequence stratigraphy

that warrant its discussion.

The GSS idea is based on the conceptual framework of

Frazier (1974) for the recognition and description of

boundary-defined genetic units deposited during successive

regional "depositional episodes." A GSS consists of

genetically related "depositional systems" (Fisher and

McGowen, 1967) and their component "facies sequences"

(Frazier, 1974) and is the stratigraphic record of a

depositional episode. Depositional episodes are punctuated by

regional flooding events, and the GSS is bounded by hiatal

surfaces (submarine unconformities or condensed sedimentary

veneers) that record maximum marine flooding of the basin

margin. Some elements of the GSS concept have analogs in

sequence stratigraphy. The flooding surfaces and condensed

sections that bound genetic stratigraphic sequences are

equivalent to the "downlap" or "maximum-flooding" surfaces

(MFS) and condensed sections at the tops of transgressive

systems tracts. Although both a GSS and a systems tract are

said to consist of depositional systems (Fisher and McGowen,

1967), the GSS is said to be analogous to a parasequences set

(Galloway, 1989, p. 137), rather than a systems tract, and a

facies sequence is considered analogous to a parasequence

(Galloway, 1989, p. 128).

Key differences, however, distinguish the GSS paradigm

from sequence stratigraphy. First, the eustacy is not







11

regarded as the dominant stratigraphic variable, but only a

part of an ongoing interplay with sediment supply and basin

subsidence. Second, the boundaries (maximum-flooding

surfaces) of the GSS are 1800 out of phase with the boundaries

(subaerial unconformities) of sequences (sensu Vail, 1987).

Allostratiqraphy

"An allostratigraphic unit is a mappable stratiform body

of sedimentary rock that is defined and identified on the

basis of its bounding discontinuities" (NACSN, 1983, p. 865).

From this definition, it might seem that allostratigraphy

qualifies as an alternative to seismic stratigraphy, sequence

stratigraphy, and the concept of genetic stratigraphic

sequences; Walker (1990, p. 780) is of this opinion. In the

North American Stratigraphic Code (NASCN, 1983) remarks in the

Preamble (p. 849), the stated purpose (p. 865), and the

examples given (p. 866-867) all indicate that the category be

limited, as specified, to alluvial, lacustrine, and glacial

deposits, and probably to those of the late Cenozoic.

Discussion

Walker (1990) discusses problems with the application of

both sequence stratigraphy and genetic sequence stratigraphy.

He emphasizes the extent to which depositional patterns can

and will change across both subaerial unconformities and

maximum-flooding surfaces and rejects both Vail (1987) and

Galloway (1989) in favor of an approach that uses

allostratigraphic units. I agree with Walker (1990) that both








12

sequence boundaries and maximum-flooding surfaces (Vail, 1987;

Van Wagoner, 1987, 1988) are surfaces of comparable

stratigraphic significance. Furthermore, I share the doubt

expressed by Schlager (1992, p. 28) as to whether one can

unequivocally differentiate between subaerial and submarine

surfaces of erosion or nondeposition, especially in carbonate

rocks. I prefer, as Schlager (1992) recommends, to return to

the approach of seismic stratigraphy (Vail and others, 1977)

in which both surfaces were considered to be depositional

sequence boundaries, without regard to whether they are

subaerial or submarine. Vail and others (1977, p. 64) state,

Two or more sequences may be deposited during a
cycle or paracycle. After a rapid rise of sea
level, a surface of non-deposition [sic] may be
developed before the progradational deposits of the
stillstand are laid down. The surface should be
marked by downlap of the overlying progradational
deposits. Frazier (1974) recognized such surfaces
in defining depositional episodes during the
Pleistocene of the Gulf of Mexico. Each sequence
of transgressive sandstones is overlain by a
sequence of upward coarsening, progradational
strata.

The example described here (Frazier, 1974) is the very work

upon which Galloway (1989) bases the concept of genetic

stratigraphic sequences. Per Galloway (1989), the surface

"marked by downlap" is the boundary of a GSS, but to Vail

(1987) and Van Wagoner and others (1987, 1988) it would be the

"surface of maximum flooding" in the midst of the sequence.

In a seismic stratigraphic scheme (Vail and others, 1977),

however, this surface is simply another depositional sequence

boundary.







13

Another issue is the sequence stratigraphic depositional

model for carbonate rocks (Figure 2); this model is virtually

identical to that for a siliciclastic regime (Vail, 1987), but

for the substitution of carbonate lithofacies. Considering

the complex array of carbonate platform facies models (Read,

1985), this is simplistic. Handford and Loucks (1991, in

press) recognize that the depositional and diagenetic

responses of carbonate sediments to relative changes of sea

level and several other factors can result in significant

variations in systems tract geometries and unusual and perhaps

unique stratal patterns.

Jacquin and others (1991) present an example of the

successful application of sequence stratigraphic concepts

(systems tracts and depositional sequences) to carbonate rocks

in outcrops at the scale of seismic lines. Commonly, however,

the identification of systems tracts is beyond the limits of

seismic resolution (Schlager, 1992, p. 28). Nevertheless, it

is generally possible to recognize unconformities as sequence

boundaries and sediment packages with internally coherent

bedding patterns as sequences.

The critical observations of Miall (1986, 1991, 1992)

include many well-made points about the problems with sequence

stratigraphy. It is my intention to apply all techniques of

stratigraphic analyses (including that of seismic sequences)

objectively to evaluate data obtained from detailed local

research.









Geologic Setting

The Florida Carbonate Platform projects southeastward

from adjacent parts of the Atlantic and Gulf Coastal Province

of North America and forms the northeastern margin of the Gulf

of Mexico. Along this margin, the platform consists of the

emergent Florida Peninsula, a broad area of shallow shelf, and

a gently inclined upper slope (terrace) fronted by the steep

Florida Escarpment (Figure 1).

Stratigraphy

A thick section of sedimentary rock, ranging from

Jurassic to Holocene, underlies the region. Figure 3 is a

chart of the Middle Jurassic through Holocene stratigraphy in

the vicinity of this study. The chart is largely derived from

that of Salvador (1991, Plate 5) with the minor modification

of certain lithostratigraphic boundaries and the addition of

Gulf Coast Provincial chronostratigraphic units according to

the schemes of 1) Huddlestun and others (1988), and 2) Wu and

others (1990a).

The establishment of Florida's stratigraphic nomenclature

is reviewed by Gohn (1988) and more specifically in sections

of Salvador (1991). The former offers some alternative

interpretations regarding the age and correlation of certain

units shown in Figure 3 (e.g., Atkinson, Cedar Keys, Oldsmar,

and Suwannee Formations). Important contributions to Florida

stratigraphy include Applin and Applin (1944, 1965, 1967),

Applin and Jordan (1945), Chen (1965), Winston (1971a, b,







15

1976a, 1977, 1978), Meyerhoff and Hatten (1974), and Miller

(1986).

Major Geologic Features

The major geologic features of the region are shown in

Figure 4. Review of the literature reveals numerous

discrepancies in the names, locations, shapes and orientations

of the major geologic features of Florida (e.g., Chen, 1965;

Martin, 1978; Klitgord and others, 1984; Shaub, 1984; Locker

and Sahagian, 1984; Pindell, 1985; Buffler and Sawyer, 1985;

Ball and others, 1988; Salvador, 1991). Figure 4 attempts to

reconcile these various interpretations and is based, as much

as possible, on observations of the seismic data used in this

study. Features discussed here are the Peninsular Arch, Ocala

"uplift," Middle Ground Arch, Sarasota Arch, Destin Anticline,

South Florida Basin, Tampa Basin, Apalachicola Basin and

Embayment, Suwannee Channel, Gulf Trough, DeSoto Canyon, and

Florida Escarpment.

The Florida Platform is effectively divided into eastern

and western parts by the southeast-plunging Peninsular Arch.

Although it has been called a "basement" structure (Shaub,

1984), the Peninsular Arch actually overlies, and is distinct

from, more than one "basement" feature (Klitgord and others,

1984, p. 7756). The Peninsular Arch was "continuously

positive from Jurassic until Late Cretaceous time and was

intermittently positive during Cenozoic time" (Miller, 1986,

p. B11).











U,


>I 4J
V

w 9)
4)00


r-I
0'I
CQ





.6-4 >
9 0 r.~
U 13




*H -l co
totr




~4.) U
U)J







-I -4 H )

.~0

.0 0)
04 r.6-
(ISU
k-rq~









4-)

V4) W~
COV ))









40 W




P tV k
P-r Eiu
OH















OO4 4J
04









4) H- -r


'$4 0 4U)C
Z %4 0 5-I
4)H4
EU -( V
Uct2rU
*e- l
w~u~4




U) '44-64 -



U) HU









Z O I C


-I
NUEVOLEONIAN z WASHITAN-
5; FREDRICKSBURGIAN


-I
NUEVOLEONIAN z WISHITAN-
F Ff i:DRICKSBURGIAI
Z


SAUSTINIAN


m0
-< >
SAUSTINIAN 0 m
z m m


I a -1 a ---- AI I T


C 1 N O


01: C


ERATHEM


T E R T I A R Y 0
JURASSIC C R E T A CE N E O U S G E E-QUATERNARY SYSTEM
MIDDL U P PALEOCEN EOCENE OLIGOCENE MI OCENE ES
U P PERP E 0 C P E R LIOCENEPLSERIES
MIDDLE U P P E R L O W E R PPER LOWER UPPER LOWER MIDDLE UPPE LOWER UPPER LOWER MIDDLE UPPER LOCENEPLEISTOCENE SERIES



.- 3> >->_z-zzr z- z-r ,--z> zZ
5; Z 5; a




-4 CI A mim


~~ m


ZULOAGAN
C"


I;


N AHULUHA0 COMANGEN


l U L Ir IH


VICKS- CHICA-
BURGIAN SAWHAYAN


CHICASAWHAYAN
TE, CHICASAWHAYAN
Z


Cr -


-r


ziL
I :' Selma Midway Wilcox Claiborne V- kbu
9 I I II A0


(f C /I o1=0 -:c, 00 WC.r0
r::::CL =3 25.c -


I II

0 Wilcox CClaiboneZJacnn>
CD00 _
-W' W 00
KC0z0 r o
-- C U) C=r
ts -nCDCD < I >2in
I~ oF?' -~

C: 10 D -V 0E = CD
3 iF)
I + Hwtor.-
a;=r W cc 030
CL-E O p 0n









00CD0
9 I a,0Pesaoa n
~ aCD 03 CD=3










~~CC
U) -0 U)







0 0 8

C 0Z
CI) !!5: o rn v
5 1; CLI
W U) Va U'll e' ~
r 0 -n::;:.::::,:.a g



C~~; Caibrne Jak'n ~ U) Hawthornm luf--
...: .. :. CD g > > -
CD r- M (g v
C --a =)0 Q0 W-
U):OII)ma mCn f
:. C~ o ~ o~zor'
o ~ n arCD
CL. -
O p, ~ >


Fort Pierce


0 .,j1cc,"0


S BasaltL


II

CD
U) CD


CD
-0 C


0 c
U) 1CD
0003 0C
a. cCm
. 00-0


---- Hawthorn ---



.. 00
; "...: ".''::':. ":: -

9t ED:."" : '


M E S O


ZULOAGAN


Sn 0

mg


I .I


i -------------- = 1 I I I I I I --T-----T





Ir





I :!_-


i 4---


I


II


::;::;


SERIES
















































Figure 4.


Major geologic features of the Florida
Carbonate Platform: AB = Apalachicola Basin,
AE = Apalachicola Embayment, BFZ = Bahamas Fracture
Zone, CFZ = Cuba Fracture Zone, DD = Destin Dome,
GT = Gulf Trough, MGA = Middle Ground Arch, OH =
Ocala High, PA = Peninsular Arch, SA = Sarasota
Arch, SC = Suwannee Channel, SFB = South Florida
Basin, TE = Tampa Embayment, KU = position of Upper
Cretaceous facies boundary, EU = position of Upper
Eocene facies boundary.






19

The area of outcropping Eocene rocks in west-central

Florida has been called Ocala "uplift," but this feature does

not affect rocks older than the middle Eocene and, therefore,

is not truly an uplift (Winston, 1976b). In the literature,

the Ocala "uplift" and Peninsular Arch are sometimes confused

(Salvador, 1991, Figure 2.)

The northern boundary of the Florida Carbonate Platform

is, essentially, a facies transition to terrigenous clastic

sediments derived from the Appalachian Mountains. The

carbonate-siliciclastic facies relationship existed since the

late Mesozoic (Salvador, 1987; Late Jurassic, Ball and others,

1983; Early Cretaceous, Corso and others, 1989). The facies

change in Upper Cretaceous through Upper Eocene strata

migrated progressively to the northwest (Chen, 1965; Miller,

1986). In Upper Cretaceous, Paleocene, and Lower Eocene

rocks, the location of the facies transition is associated

with the Suwannee Channel (Chen, 1965), also known as the

Suwannee Strait (Dall and Harris, 1892; Pinet and Popenoe,

1985; Popenoe, 1985; Miller, 1986). In Middle Eocene and

Upper Eocene strata, the facies change is located in the

vicinity of the Gulf Trough (Popenoe and others, 1987).

McKinney (1984) proposes a "carbonate suppression"

sedimentologic model (Walker and others, 1983) as an

alternative to structural control of the Paleogene facies

transitions.







20

Based on a carbonate-to-siliciclastic facies change

interpreted from seismic refraction profiles, Antoine and

Harding (1965) extend the Suwannee Strait southward, beneath

the continental shelf under Apalachee Bay. A change in the

character of reflection seismic data led Antoine and Jones

(1967) to locate the facies change along the Florida

Escarpment at 270 30' N and to project the Suwannee Strait

toward that point. Chen (1965), however, projects the

Suwannee Channel more toward the west, linking the channel

with the Apalachicola embayment and extending it across the

Apalachicola Basin toward the west side of the DeSoto Canyon.

Mitchum (1978) presents the DeSoto Canyon, "an area of

nondeposition and some sediment erosion since the Late

Cretaceous," as the westward extension of the Suwannee Strait

visible on seismic sections.

The Florida Escarpment, stretching from the DeSoto Canyon

to the Straits of Florida, is the western boundary of the

Florida Platform. The escarpment formed by aggradation of an

Early Cretaceous rimmed carbonate platform (Bryant and others,

1969; Corso and Buffler, 1985; Corso and others, 1989), but,

south of 270 N, the escarpment has been modified by erosion

(Freeman-Lynde, 1983; Corso and others, 1988; Paull and

others, 1990; Twichell and others, 1986, 1990, 1991).

East of the Florida Escarpment, a number of basins and

arches (Middle Ground Arch, Sarasota Arch, Destin Anticline,

Tampa Basin, Apalachicola Basin and Embayment) are recognized.







21
Most of these features are "basement"-related but have

expression in younger Mesozoic strata and influence that

persist into Cenozoic strata (Ball and others, 1988).

At the northwestern end of the study area are the

Apalachicola Basin (Northeast Gulf Basin of Locker and

Sahagian, 1984) and its onshore extension, the Apalachicola

Embayment. A large northwest-trending anticline in the

Apalachicola Basin, the Destin Anticline or Destin Dome is

related to a salt swell uplifted during the Late Cretaceous

and early Cenozoic (Ball and others, 1982).

Southeast of the Apalachicola Basin, the Middle Ground

Arch (Winston, 1969) is a broad, southwest-plunging nose that

can be traced onshore into the west flank of the Peninsular

Arch (Ball and others, 1988). Some studies (Locker and

Sahagian, 1984; Lord, 1987; Dobson, 1990) recognize a distinct

high on the basement surface, to the southwest of the Middle

Ground Arch and refer to it as the "Southern Platform." It is

unclear whether in younger strata this feature is

distinguishable from the Middle Ground Arch. The name is

ambiguous as to its location and its nature; it is easily

mistaken for a south-Florida feature, and is erroneously

suggestive of a carbonate platform.

South of the Middle Ground Arch, the Tampa Basin

(Klitgord and others, 1984) is also called the Tampa Embayment

(Shaub, 1984; Dobson, 1990), the St. Petersburg Basin (Locker

and Sahagian, 1984), and the Florida Elbow Basin (Pindell,







22

1985). Ball and others (1988) did not observe convincing

evidence in seismic sections of the Tampa Embayment's

existence, but Dobson (1990) and Lord (1987) do recognize this

feature on coverage farther downdip.

The Sarasota Arch, also called the Pinellas County Arch

(Shaub, 1984, Lord, 1987) or Tampa Arch (Pindell, 1985),

separates the Tampa Embayment to the north from the South

Florida Basin to the south. The Sarasota Arch rivals the

Peninsular Arch in relief (Ball and others, 1988, Ball, 1991).

Ball and others (1988) could not clearly observe the Sarasota

Arch on seismic sections, but well data suggest a major down-

to-the-north fault between the Mobil OCS-G3341 and Shell OCS-

G3912 wells (Figure 11, Wells 17 and 18) that may be related

to the northwest flank of this granitic high (Ball, 1991).

South Florida Basin, also known as the Sunniland Basin

(Locker and Sahagian, 1984) is considered to be a basement-

controlled structure (Sawyer and others, 1991) and contains

more than 8,000 m of uppermost Jurassic through Quaternary

strata (Ewing, 1991). Galloway and others (1991) regard the

basin as an area of rapid Cenozoic subsidence and sediment

accumulation. They state (Galloway and others, 1991, p. 313)

that the entire Florida Platform was exposed at the end of the

Cretaceous (Figure 3), but others (Chen, 1965; Winston, 1971a,

b) report that sedimentation in the South Florida Basin was

continuous from the Cretaceous into the Tertiary. Shaub

(1984) discusses the internal framework of this basin.









Pre-Late Cretaceous Geologic History

To set the stage for the evolution of the Florida

Carbonate Platform one must look back to the rifting of Pangea

and the beginnings of the Atlantic Ocean and the Gulf of

Mexico in the Late Triassic. Many alternative interpretations

exist for the origin of the Gulf of Mexico/Caribbean region

(e.g., Anderson and Schmidt, 1983; Van Siclen, 1984; Klitgord

and others, 1984; Pindell, 1985; Buffler and Sawyer, 1985;

Salvador, 1987; Sheridan and others, 1988; Buffler, 1989;

Reitz, 1991b). Among the models there is general agreement

that the crust beneath the Florida Platform is continental,

although many (Klitgord and others, 1984; Pindell, 1985;

Buffler and Sawyer, 1985; Sheridan and others, 1988; Buffler,

1989; Reitz, 1991a) consider this continental crust to be

attenuated. Some investigators (Klitgord and others, 1984;

Van Siclen, 1984; Pindell, 1985; Buffler and Sawyer, 1985;

Sheridan and others, 1988; Buffler, 1989; Dobson, 1990)

believe that a major crustal boundary occurs along a line

trending northwest-southeast across the West Florida Shelf

(Bahamas Fracture Zone, BFZ, of Klitgord and others, 1984; Jay

Fault of Pindell, 1985). To the northeast of this line, the

crust is continental, and to the southwest, the crust is

attenuated (thick, transitional of Buffler, 1989). Ball and

others (1988) and Ball (1989, 1991), however, report that

Paleozoic sedimentary or metasedimentary rock underlies the

entire platform north of 260 N, and though deep faults do







24

exist at some locations identified by others (e.g., Klitgord

and others, 1984; Pindell, 1985) as hinges or fracture zones,

these are not boundaries between isolated blocks of

continental crust.

The specific character of the BFZ (or analogous

northwest-southeast faults) is ambiguous. Among those who

consider it a right-lateral wrench-fault zone, Van Siclen

(1984) interprets it in relation to the Paleozoic Ouachita

orogeny, but Miller (1982) regards it as a result of north-

south compression that was active throughout the Jurassic.

Others (Klitgord and others, 1984; Pindell, 1985) speculate

that motion was left-lateral and related to Mesozoic sea-floor

spreading. Dobson (1990) does not cite evidence of strike-

slip movement on the BFZ but notes truncation of structural

features. Reitz (1991a) describes the BFZ as "an apparently

undisturbed northwest-southeast linear zone" that separates

northeast-trending rift basins to the northeast from

northwest-trending rifts to the southwest. Wu and others

(1990b, p. 337) observe "no major fault."

In Florida geology, the term, "basement," has been

variously defined as rocks beneath the "pre-Cretaceous

postrift unconformity" (Klitgord and others, 1984), "the top

of the Paleozoic section" (Ball and others, 1988), and "rocks

below, or older than, the Middle Jurassic Louann Salt"

(Dobson, 1990; Dobson and Buffler, 1991). The main types of

"basement" rocks of Florida are Jurassic igneous rocks in







25

South Florida, Paleozoic igneous rocks in central Florida, and

Paleozoic sedimentary rocks in northern and panhandle Florida

(Klitgord and others, 1984). Salient features interpreted

from seismic profiles and well control within the "basement"

of the northeastern Gulf of Mexico are discussed by Ball and

others (1988), Dobson (1990), and Dobson and Buffler (1991).

Progressive eastward marine invasion occurred during the

Jurassic, as the Gulf of Mexico opened (Salvador, 1987).

Along the northern flank of the Gulf of Mexico Basin,

deposition of evaporites (Louann Salt) in the late Middle

Jurassic (Callovian) was followed in the Late Jurassic

(Oxfordian-Kimmeridgian) by mixed siliciclastic and carbonate

deposition (Norphlet-Smackover, Haynesville), and in the

latest Jurassic (Tithonian) to earliest Cretaceous by

deposition of a thick wedge of coarse, fluvial-deltaic

sediments (Cotton Valley). Miller (1982) and Mitchell-Tapping

(1982) address the structure and stratigraphy of Jurassic

rocks, onshore Florida. Ball and others (1988), Dobson (1990),

Dobson and Buffler (1990a, b), and Reitz (1991a) investigate

the seismic stratigraphy and geologic history of Jurassic

rocks of the northeastern Gulf of Mexico. Structure of the

"basement" surface controlled the distribution, thickness, and

paleogeography of Jurassic units (Miller, 1982; Dobson, 1990;

Reitz, 1991a).

Carbonate/evaporite sediments of the Florida Platform

were deposited in the South Florida Basin in latest Jurassic







26

(Tithonian) time, while the northern part of the platform

remained emergent until the Early Cretaceous (Klitgord and

others, 1984; Salvador, 1987; Sheridan and others, 1988).

Seismic correlations (Dobson, 1990) suggest the presence of an

appreciable thickness of Smackover Limestone (Oxfordian) in

the Tampa Embayment with seismic faces interpreted as

shallow-marine, carbonate ramp with localized buildups. The

overlying Haynesville sequence (Kimmeridgian) onlaps even more

of the western Florida Platform, but Haynesville carbonate

deposits are limited to the western Apalachicola Basin

(Dobson, 1990; Dobson and Buffler, 1990a, b).

Carbonate/evaporite deposition occurred in the Tampa Embayment

and over the Sarasota Arch during the Tithonian (Salvador,

1987, Figure 10). In the Apalachicola Basin, the Knowles

Limestone, at the base of the Lower Cretaceous and the top of

the Cotton Valley Group, marks the transition from a carbonate

ramp to a rimmed carbonate platform (Corso, 1987; Corso and

others, 1989). Progradation of the Knowles Limestone

carbonate ramp extended to the southeast, toward the Tampa

embayment (Dobson, 1990).

During the Early Cretaceous, the western Florida

carbonate Platform developed a high-relief, rimmed margin

along the present Florida Escarpment (Bryant and others, 1969;

Corso and Buffler, 1985; Corso and others, 1989). A

discontinuous series of contemporaneous platforms nearly

encircled the deep Gulf of Mexico; Locker and Buffler (1983),







27

Winker and Buffler (1988), and McFarlan and Menes (1991)

provide comparisons of these Lower Cretaceous carbonate shelf

margins.

Late Cretaceous-Cenozoic Geologic History

In the U.S. Gulf Coastal Plain, the term "Upper

Cretaceous" is loosely applied to the mid-Cenomanian through

Maastrichtian section that has been called the provincial

"Gulfian Series." The boundary of the Gulfian with the

underlying Comanchean Series is a profound physical

stratigraphic break but does not correspond exactly to the

internationally accepted Lower Cretaceous-Upper Cretaceous

boundary (McFarlan and Menes, 1991; Sohl and others, 1991).

Throughout much of the Gulf Coast, the Upper Cretaceous

section is "strongly overprinted" by cyclic sea-level

fluctuations (Salvador, 1991, p. 421). These oscillations

should be reflected in the Florida Platform, as well, but as

yet they have not been reported (Salvador, 1991, p. 428).

After the Comanchean Epoch, there occurred a basin-wide change

in sedimentation (Winker and Buffler, 1988), and deep-water

carbonate sediment was deposited over the Florida Platform

(Bryant and others, 1969; Worzel and others, 1973, Mitchum,

1978; Freeman-Lynde, 1983). In the Florida panhandle, Gulfian

strata dominantly consist of calcareous clay; in peninsular

Florida, these rocks are chiefly chalk and fine-grained

limestone. The Upper Cretaceous through Cenozoic deposits

drilled along the Florida Escarpment are foraminiferal-







28

coccolith carbonate muds (oozes), suggesting that the west

margin of the post-Comanchean Florida Platform was a distally

steepened ramp (Read, 1985) dominated by pelagic to open-

marine shelf carbonate sedimentation (Winker and Buffler,

1988). The Gulfian Series occurs only in the subsurface in

the study area (Applin and Applin, 1967; Miller, 1986).

Paleogene strata in peninsular Florida are shallow marine

carbonate rocks intercalatedd with evaporites in the older

units); to the north and west, these grade into deposits of

clay and fine sand. Siliciclastic deposits are more prevalent

in Neogene strata. During the Miocene the Florida Carbonate

Platform received an influx of terrigenous sediments from the

north. Special conditions of marine chemistry, particularly

in middle Miocene time, resulted in the widespread deposition

of phosphatic sediments (Riggs, 1984; Scott, 1988; Compton and

others, 1990). Post-Miocene strata consist of shallow,

marginal-to-open marine beds overlain by sandy marine terrace

deposits that are in turn capped by a thin layer of fluvial

sand and/or residuum.

Beneath the Gulf of Mexico, Buffler and others (1980)

observe a major, regional unconformity and seismic

stratigraphic sequence boundary that corresponds to the

Comanchean-Gulfian boundary. Although its stratigraphic

expression varies, this prominent, high-amplitude reflection

is present on seismic profiles from the deep Gulf and along

its southern and eastern margins (Faust, 1986). Buffler and







29

others (1980) term the reflection the Mid-Cretaceous

Unconformity (MCU) and relate the event to a relative fall of

sea level that occurred in the Cenomanian (97 Ma, per Vail and

others, 1977). Addy and Buffler (1984) correlate the MCU with

the top of the Washita Group (Lower Cretaceous) on the West

Florida Shelf. Another idea on the origin of the MCU

(Schlager and Camber, 1986; Schlager, 1989, 1991) is that

growth of the carbonate platform was terminated through rapid

submergence (Schlager, 1981) that produced a "drowning

unconformity" associated with a rise or highstand of sea

level, not a lowstand.

Faust (1990) interprets the following geologic history to

explain the MCU. Sea level dropped below the shelf edge

during the Cenomanian, resulting in subaerial exposure,

meteoric leaching, and erosion of the Lower Cretaceous Florida

Carbonate Platform. Turbidity currents and debris flows cut

canyons in the Florida Escarpment. During the Late

Cretaceous, sea level rose well above the previous platform

margin. As platform carbonates tried to keep pace with rising

sea level, prograding clinoforms downlapped onto the MCU, but

the platform soon drowned and was buried by deep-water

carbonates. Faust (1990) comments that in the center of the

deep Gulf the MCU (or more precisely its correlative

conformity) might be better termed the Mid-Cretaceous Sequence

Boundary (MCSB); he also notes that the revised date of the

unconformity is 94 Ma (Haq and others, 1987).







30

Wu and others (1990a; Figure 5) endorse correlation of

the top of the Lower Cretaceous (Washita Group) with the

Middle Cenomanian (94 Ma) sea-level fall (Addy and Buffler,

1984), but declare that, basinward of the platform margin, the

MCU of Buffler and others (1980) correlates instead with the

91.5 Ma (Turonian) sea-level rise (Haq and others, 1987). On

the shelf, the 91.5 Ma maximum-flooding surface is reportedly

recognized as a downlap surface over the Middle Cenomanian

carbonate platform (Wu and others, 1990a). Thus, in the deep

basin, Wu and others (1990a) would replace MCU with MCFS

(Middle Cretaceous Flooding Surface). Feng and Buffler

(1991), however, point out that, in the northeastern corner of

the deep Gulf, the thickness of sequences in the stacked

condensed section between the MCSB and 30 Ma is beyond seismic

resolution. Although the mid-Cenomanian unconformity is

considered to be present over the entire Florida Platform

(Salvador, 1991, Figure 19), Salvador (1991, p. 422) notes

that, if it is due to a major lowering of sea level, the

unconformity is probably represented within the platform

interior by a disconformity or a very low angle unconformity

difficult to identify in a nearly horizontal section composed

of alternating limestones and evaporites, both above and below

the stratigraphic break. Indeed, confusion surrounds

precisely which reflector(s) various investigators identify as

the MCU. Wu and others (1990b) indicate that the 94-Ma MCSB

























BASINWARD


WELL 4


WELL 2


- major sequence boundary and -maximum flooding surface
in Ma of Haq oet al.( 1987) observed on seismic profile
- major sequence boundary and- -maximum flooding surface

in Ma of Haq et al. (1987)not observed on seismic profile
...." downlaps observed on seismic profile


Figure 5.


Diagram of major Middle to Upper Cretaceous
sequence boundaries and maximum-flooding surfaces
from Wu and others (1990a); MCFS is Mid-Cretaceous
Flooding Surface, TLC is Top of Lower Cretaceous.


WELL 5


WELL I


i1.5 IMCFS)
93
93.5
94 ITLCO


LANDWARD







32

(top of the Lower Cretaceous, TLC) and the 91.5-Ma MCFS are

recognizable as two separate surfaces on the western Florida

Carbonate Platform (Figure 5). Schlager (1989) regards age

estimates of the MCU as inconclusive, leaving the way open for

Wu and others (1990a) to interpret the "drowning unconformity"

(Schlager, 1989; Schlager and Camber, 1986) to be the MCFS

(91.5 Ma) rather than the MCSB/TLC (94Ma). The top of the

Washita Group (i.e., the MCU/MCSB/TLC) in the Exxon OCS-G2486-

3 well (Figure 11, Well 7) is picked 120 m deeper by Faust

(1990) than by Addy and Buffler (1984), yet both

interpretations identify a similar zone of transitional

deepening just below the respective picks for the MCU. Faust

(1990) does not recognize the MCSB and MCFS as two distinct

surfaces, but concludes that in the Florida Escarpment region

the MCU corresponds to a maximum-flooding surface. Faust

(1990, Figures 18 and 22), shows that over most of the

Apalachicola Basin, except over the Destin Dome, the

reflectors above and below the MCSB are concordant.

Truncation of underlying reflectors and onlap of overlying

reflectors is characteristic of the MCU over much of the area

to the south and east, across the Middle Ground Arch and in

the Tampa Embayment. Downlapping does occur in a zone of

sediment bypass along the platform margin and downlaps of

clinoforms prograding toward the basin center dominate the

outer Florida Platform (Faust, 1990). Corso and others (1989)

and Mitchum (1978) characterize the top of the Lower







33

Cretaceous (i.e., MCU/MCSB) by downlap of overlying

reflectors. This characterization adds to the confusion

between the MCSB and MCFS. The question of MCSB vs. MCFS

seems to reflect the issues of the relative importance of, and

distinctness of, subaerial-erosional unconformities and

maximum-flooding surfaces.

The idealized drowned carbonate platform (Erlich and

others, 1990; Figure 6a), is characterized by any or all of

the following features: conformable seismic sequence

boundaries, good internal reflectors, horizontal to sub-

horizontal basinal marine onlap becomingg parallel to the

carbonate sequence boundary in basinal positions), and late-

growth reefs at some shelf margin locations. Chemical

sedimentation (usually glauconite or phosphate) is common

within the drowning sequence. Subaerially exposed platforms

(Figure 6b) may show any or all of the following:

unconformable sequence boundaries, erosional/karst surfaces

(may have hummocky or discontinuous nature and cause

attenuation of seismic data and/or shallow multiples), shelf-

to-basin reflector continuity, and divergent basinal onlap

patterns (possibly due to lowstand submarine fans).

King and Skotnicki (1990) examine the Upper Cretaceous

facies stratigraphy and biostratigraphy of the inner Coastal

Plain of Alabama. They then integrate the local stratigraphy

and the global synthesis of sea-level changes during the Late

Cretaceous (Haq and others, 1987, 1988; Figure 7).














(a)
Later Progradation





I Continuous Datai Cae


Conformabie Sequence Boundary


DROWNING EVENT


(b)


Uncontormab( e Sequence Boundary

....:-: : -Karsted/Eroded Sur-ace -
-Shett-to-flasin Reflector Continuity r .*. -- """.:": _
--..-- -D ".-




Lowstand Fan (?)4


SUBAERIAL UNCONFORMITY



Figure 6. Contrast between (a) an idealized drowned carbonate
platform and (b) a subaerially exposed carbonate
platform (Erlich and others 1990).










P 44 o to o(

0 0 0 U 0

."l4.) 0II r.
,C p0C P #

- 0 o 0 **(0 4

4- o -rl 4-i4 1 0 CO

+ 9 Cn I M U O. jc
to -H > o P4-4

S4 .A 0 -4 -4

-, )0 r 0 -, 1 0 P 04

4) 0 4 d 4H
00 4 W o r.



M -V W- o
C oM. IA I () v .m-4
4& 0 0
04 -- v g M 0 pC





4ON 4o a) o II .4J
4 -) V ., g



10j 0 0 I 4 r -4
0.C 0 0 o0


S H m Ord
S: *- I
(0 w 0 0

40>, ,-) to w to u
to C 4 r-4 CO u0



*> 'd gt CO
t) O^ l *o I a 1) co
-0$ o X 4 ro >) 00

04 C ) 0 0 9- 4-4



M E00-4 00
*M -H 0 t U 0 (O 0 0
0 0 0 ) C D4 4B 0
4 ) 4 -1 (1 r.I ) 4 -H
)0 0 HII H0 V0

rM O-E t 3l t o0
M -P ) c r-4 4
0 4J re r30 0 r-lg or M t 0




) ) Hu 4 E-io w 0 go







.r.
w)






















'4I I I 1
l I I
>I

c4 I I I


I 4I ai
all I I_
II 1_itII1


dl
I -







37

King and Skotnicki (1990) correlate the Eutaw Formation

to the Late Santonian-Early Campanian (85-83 Ma) sequence of

Haq and others (1987, 1988). The lower sequence boundary, at

the top of the Tuscaloosa Formation, is a high-relief surface

that corresponds to a type 1 sequence boundary, and the upper

sequence boundary, at the top of the Eutaw Formation is a low-

relief surface that equates to a type 2 sequence boundary. A

low-relief stratigraphic break within the Eutaw represents

the83.75 Ma maximum flooding surface (Haq and others, 1987,

1988).

The Mooreville Chalk and Blufftown Formation are coeval

(Lower Campanian) units of the basal Selma Group in central

and eastern Alabama, respectively. King and Skotnicki (1990)

correlate the top of the Mooreville-Blufftown interval to the

type 1 sequence boundary at 80 Ma (Haq and others, 1987,

1988).

The next overlying time-equivalent units of the Selma

Group in central and eastern Alabama are, respectively, the

Demopolis Chalk and Cusseta Sand. This interval spans the

Upper Campanian and contains three genetic packages that King

and Skotnicki (1990) correlate to the three Upper Campanian

sequences of Haq and others (1987, 1988). The tops of all

three packages (including the contact with the overlying

Ripley Formation) are low-relief breaks that relate to type 2

sequence boundaries.







38

The Ripley Formation of the Selma Group spans the

Maastrichtian and encompasses two genetic packages that

correspond to two sequences (Haq and others, 1988; King and

Skotnicki, 1990). The packages are separated by a low-relief,

intraformational break that relates to the 71 Ma type 1

sequence boundary of Haq and others (1988). A high-relief

break at the top of the Ripley Formation corresponds to the

major type 1 sequence boundary at 68 Ma (Haq and others, 1987,

1988).

The Prairie Bluff Chalk and Providence Sand are the

latest Maastrictian (68-67 Ma) equivalents at the top of the

Selma Group, in central and eastern Alabama, respectively.

The stratigraphic break at the top of the Prairie Bluff-

Providence interval is a low-relief surface in the area

studied by King and Skotniki (1990), but has greater relief

along strike where Baum and Vail (1988) describe it as a type

1 sequence boundary.

Sequence stratigraphic interpretations of outcrops in

Alabama (Figure 8) place the Cretaceous-Tertiary (K-T)

boundary at the maximum-flooding surface within the Pine

Barren Member of the Clayton Formation (Donovan and others,

1988) and divide the Paleogene section into depositional

sequences (Baum and Vail, 1988). These sequence stratigraphic

interpretations, however, are not undisputed. Notable

examples of controversy are interpretation of the Eocene-

Oligocene boundary as either a surface of maximum flooding







39

(condensed section) (Baum and Vail, 1988), or a sequence

boundary (Dockery, 1990) and explanation of the Gosport Sand

as either an incised-valley-fill deposit on a type 1 sequence

boundary (Baum and Vail, 1988), or a transgressive, marine

deposit (Dockery, 1990).

Mancini and Tew (1990b, 1991a, b) apply sequence

stratigraphic concepts to essentially the same stratigraphic

section as Donovan and others (1988) and Baum and Vail (1988),

but arrive at quite different interpretations (Figure 8).

Discrepancies include placement of the K-T (Hazel, 1990;

Mancini and Tew, 1990a, and Olsson and Liu, 1990) and

Oligocene-Miocene boundaries. Baum and Vail (1988) identify

only 19 depositional sequences, whereas Mancini and Tew

(1990b, 1991a, b) recognize 22 (Figure 8). Baum and Vail

(1988) regard the contact of the Gosport Sand with the

overlying Moodys Branch Formation as a surface of maximum

flooding (condensed section), whereas Mancini and Tew (1990b,

1991a, b) consider it a type 1 unconformity. Also, Mancini

and Tew (1990b, 1991a, b) place the base of the TO 1.2 cycle

at the top of the Glendon Limestone and consider this contact

a type 2 sequence boundary. Baum and Vail (1988), however,

identify it as a condensed section and consider the base of

the Glendon Limestone as the type 2 sequence boundary of the

TO 1.2 cycle. The recognition and "correct" interpretation of

the key stratigraphic surfaces (i.e., sequence boundaries and

maximum-flooding surfaces), a feat required to apply sequence




























Figure 8. Chart of lithostratigraphic units (Group,
Formation, Member) of the Gulf Coastal Plain,
Alabama (center) with the sequence stratigraphic
interpretations of Baum and Vail (1988), Donovan
and others (1988) (right), and Mancini and Tew
(1990a and b, 1991a and b)(left).










Mancini and Tew Baum and Vail (1988).
(1990a and b. 1991a and b) Donovan and others (1988)

Relative Change Formaton Relative Change "
Series Stage in Formation/ I Stage Series
c o 0 Coastal Onlap Member Coastal Onla Stage S u

a C_ Payne&s Aquitan. Miocene
0 Hammock C-

S e c- To c
S- Chickaeawhay


N Bucatunna o
0 Byram 0
C *_ C.- 0
1 Glendon
o \C----- Marianna -- ^
Mint Spring ------
\Red \Forest Hill
Td C---- Bluff\Bumonose-- Td
riabo Cocoa o Td
N N. Twistwood I
s C- Creek c-- ,.
a Moodys Branch "Z
C -
o ---- Gosoort 5

SCockfield
Ia a t ; C- Gordon Creek
a -----

0 -- Dobys Bluff -0 0
w c w
as Tc Tc

M\C ____ C0-------
N
Winona

--- __Meridian C -
Ypre- Hatchetigbee C pre
sian ,, k--- Ypre-
n- sin
--- -- Bashi \
S----- Bells Ee
a- \\ Landing o o i
Tb = -2 0 = T.
Ta Ca | Tb
C Graggs c----
S -Landig


SCe- Grampian Hills c
C" one nGravel Creek
Sc----- Coat Bluff c-----

o 0 Oak Hill o
a ,. c----- Matthews
\ \Landing

T a C----- Porters Creek Ta


c C----- McBryde c
Q 'Turritella o
CQ I -- rock' >*
Pine Barren 0

Upper Maas- \ C, Maps- Upper
Creta- trich- C- Prairie Bluff t---- rich- Creta-
ceous tan tian in ceous



Sequence Boundaries Type 1 --. Type 2 -
Condensed Section C-







42

stratigraphy successfully, seems even more subjective in

outcrops and well data than in the sequence analysis of

seismic data.

The pioneering seismic stratigraphic investigation of

Mitchum (1978) interprets 2500 nautical miles (4630 km) of

single-channel data (Figure 9) and focuses on the post-Early

Cretaceous geologic development of the western Florida

Platform. The seismic profiles are correlated to data from

15-ft (4.6-m) cores taken at 60-ft (18-m) intervals in each of

seven 1000-ft boreholes scattered along the West Florida

Slope, north of 260 30' N. Using seismic stratigraphic

procedures for sequence analysis (Vail and others, 1977),

Mitchum (1978) defines ten depositional sequences (Figure 10)

above the "K" sequence boundary that he identifies as the top

of the Lower Cretaceous. Mitchum (1978) does not explicitly

correlate his seismic stratigraphic interpretation to the

global sea-level curve of Vail and other (1977), but includes

a chronostratigraphic chart (Mitchum, 1978, Figure 2) with a

geochronometric scale.

The seismic stratigraphic framework of Addy and Buffler

(1984) for the shallow shelf in the Destin Dome area (Figure

9) identifies five seismic units, designated A through E

(Figure 10), above the MCU (correlated to the top of the Lower

Cretaceous and sequence boundary "K" of Mitchum, 1978). Age

determinations are made partly by ties to wells (Exxon OCS-

G2486-3 and Sun OCS-G2490) and partly by correlation to

















































Mitchum (1978)
Addy and Buffler (1984), Faust (1990)
Doyle and Holmes (1985)
Mullins and others (1987, 1988a and b)
Ball and others (1988)
Evans (1989)
Wu and others (1990a and b)


Figure 9. Map showing general locations of previous
seismic/sequence stratigraphic studies of
Upper Cretaceous and Cenozoic strata in
the vicinity of this study.


******o***o*******








p (D
0) 4.)
040~

~44


4-
o (o




4-H

$4J

r~.









-H


>11

*H4-)

4-)
to U)




Ol



tn-H





4-)


tn0




0)
5.4
















0



0-


z m
I'o

S2a
Sze


Co
0







co

A 0c
0 cm

z



w G
u

Z Z




-0 <
0















LL






LU
5 0
uj'
gl



1^


omm 4
on 10


I I II I


U)








46

seismic line 126 (Mitchum, 1978, Figures 3 and 4, p. 199) and

then to the sea-level curve of Vail and others (1980). The

sequence boundary ages shown in Addy and Buffler (1984, Table

1), therefore, differ somewhat from those of Mitchum (1978).

Doyle and Holmes (1985) investigate the shallow

structure, stratigraphy, and carbonate sedimentary processes

of the West Florida Upper Continental Slope (Figure 9) with a

high-resolution, shallow-penetration seismic survey. Doyle

and Holmes (1985) map the "top seismic unit," which, by

correlation to Mitchum (1978), they interpret to consist of

Pleistocene-Holocene sediments. South of 270 30' N, the base

of this upper seismic unit is interpreted to be an erosional

unconformity. Doyle and Holmes (1985) report that the unit

underlying this unconformity could be Pliocene, but that based

on a veneer of phosphorite, they consider it to be Miocene.

Despite a karst-like morphology over much of its extent, Doyle

and Holmes (1985) entertain submarine, as well as subaerial,

erosion as possible causes of this feature. This is another

example of the practical problems that arise in recognizing

sequence boundaries. The mechanism of the submarine erosion

postulated by Doyle and Holmes (1985) does not directly

involve the fluctuation of relative sea level, but action of

the Tertiary Loop Current.

A considerable amount of interpretation (Gardulski and

Mullins, 1985; Mullins and others, 1987, 1988a and b) has been

based on analysis of a set of approximately 1,500 km of high-







47

resolution, intermediate-penetration (500-750 m subsurface),

single-channel analog, reflection seismic data from a

relatively small (5,000 km2) area (Figure 9), ostensibly

representative of the entire western Florida Platform. The

seismic profiles are correlated to two of the coreholes (CH32-

45 and CH33-48) drilled by Exxon (Mitchum, 1978) and

additionally to piston cores and dredged samples. The

sequential post-Early Cretaceous stratigraphic evolution of

the carbonate ramp slope of central west Florida (Figure 10)

was determined by defining six "primary seismic depositional

sequences" (Mullins and others, 1988b). These sequences are

not as defined by Vail (1987) and Van Wagoner and others

(1987, 1988), for they do not correspond to individual cycles

of sea-level fluctuation. Neither are they "depositional

sequences" as defined by Vail and others (1977), for they can

include unconformable surfaces with significant lacunae (e.g.,

"sequences" IV and I, Mullins and others, 1988b; Figure 10).

Mullins and others (1988b) regard sea-level fluctuation as but

one of a suite of processes affecting sedimentation and

attribute a major change in deposition from progading

clinoforms ("sequence" II) to a pelagic slope-front-fill

system ("sequence" I) and the associated seismic-stratigraphic

break, about 12-15 Ma, to a paleooceanographic event, namely,

intensification of the Loop Current in the Miocene (Gardulski

and Mullins, 1985; Mullins and others, 1987). Mullins and

others (1988b) also recognize an unconformity within







48

"sequence" I, at about 10.2 Ma, which they interpret as a

surface of subaerial exposure and karst development and relate

to the unconformity identified by Doyle and Holmes (1985).

This correlation is problematic, because the minimum age of

the unconformity of Doyle and Holmes (1985) would be

approximately 1.6 Ma, if the underlying unit were Pliocene, or

about 5.5 Ma, if that unit were Miocene.

Gardulski and others (1991) interpret the Upper

Cretaceous to Pleistocene evolution of the deep-water

carbonate platform of west Florida (Figure 10) from detailed

analysis of samples from all seven of the Exxon coreholes

(Mitchum, 1978). Gardulski and others (1991) recognize

Pliocene sediments in CH30-43, CH31-44, CH35-46, and CH34-47

where Mitchum (1978) had reported their absence. This prompts

reconsideration of the age interpretations of Doyle and Holmes

(1985), for Pliocene strata must then be included either in

the Pleistocene-Holocene "top seismic unit" or in the

underlying "Miocene" unit. The "four major depositional

systems" of Gardulski and others (1991) do not correlate well

with the six "depositional sequences" of Mullins and others

(1988b) (Figure 10) and interpretations thereof differ, as

well. Gardulski and others (1991) interpret the Campanian-to-

Maastrichtian regime as progradational with a change by the

Maastrichtian to pelagic aggradation. This includes with

"sequence" V the lower part of "sequence" IV and necessitates

that yet another significant stratigraphic break occur within







49

the "reflection-free" interval of "sequence" IV (Mullins and

others, 1988b). Also, "sequences" II and III are not

distinguishable able in the corehole samples (Gardulski and

others, 1991).

In related work, Mullins and others (1988a) characterize

the modern carbonate ramp slope of west central Florida and

Gardulski and others (1986, 1990) ascribe carbonate mineral

cycles identified in piston cores of Pleistocene ramp slope

sediments to climatic changes. Analysis of Ocean Drilling

Project (ODP) Hole 625B, on the east flank of DeSoto Canyon

(Roof and others, 1991), shows a record of cyclic sedimen-

tation controlled primarily by sea-level fluctuations from the

present to 2.8 Ma and periodic fluctuations related perhaps

to Loop Current variations from 2.8 to 5.4 Ma.

Palynostratigraphy of the Cenozoic portion of Exxon

Corehole 32-45 (Wrenn and Satchell, 1988) permits subdivision

of seismic "sequences" I through IV (Mullins and others,

1988b) and evinces the erosional unconformity separating early

Miocene marls from those of the late Miocene. The abundance

of terrestrial palynomorphs and shelfal dinocysts in Neogene

samples, however, does not support the contention of Mullins

and others (1988b) that the intensified Loop Current acted as

an oceanographic barrier to off-shelf sediment transport.

The seismic investigation of Ball and others (1988)

comments only briefly on the Cenozoic section and concentrates

on older structure and stratigraphy. An impressive sequence







50

of basinward prograding reflections with vertical relief of as

much as 0.5 seconds two-way travel time (2-way TT) are

observed to make up a major portion of the middle to lower

Cenozoic section on the south flank of the Middle Ground Arch.

Prograding reflections are also noted in the Cenozoic section

in the Tampa Embayment, in the area studied by Mullins and

others (1987, 1988b).

High-resolution seismic reflection and associated data

reveal the Neogene and Quaternary stratigraphy of inner-shelf

and coastal areas of Florida (Locker and Doyle, 1987; Locker

and others, 1990; Evans, 1989; Evans and Hine, 1991). In the

Charlotte Harbor area, Evans (1989) recognizes six

depositional sequences lying between regional unconformities.

The sequences of oblique clinoforms prograde to the south-

southeast. The lower regional unconformity is correlated to

the 10.5 Ma sea-level fall.

Exposition of Problems to be Investigated

Despite the contributions of the aforementioned

investigations, many questions about the evolution of the

western Florida Carbonate Platform from a rimmed carbonate

shelf (Read, 1985) in the Early Cretaceous to a drowned,

distally steepened ramp (Read, 1985) in the Holocene remain

unanswered. In the summary of the recently published Decade

of North American Geology (DNAG) volume on the Gulf of Mexico

Basin, Salvador (1991, p. 548) includes the following







51
statement about the additional information and new studies

needed:

Considerable information about Cretaceous and
Cenozoic regional stratigraphic hiatuses or
unconformities may be obtained from detailed
lithostratigraphic and biostratigraphic studies
(and perhaps seismic-stratigraphic interpretation)
of the Florida and Yucatan carbonate platforms.
Their Cretaceous to Holocene stratigraphic section,
composed predominantly of shallow-water carbonates
and evaporites, and deposited under extremely
stable tectonic conditions, should reflect
admirably important eustatic changes in sea-level
[sic] and the corresponding stratigraphic hiatuses
and sedimentary cycles.

The thick and really extensive interval of Eocene shallow-

marine carbonate strata constitutes a significant portion of

the Florida Carbonate Platform. Onshore, these rocks, which

commonly have high primary and secondary porosity, form the

major part of the Floridan aquifer system (Miller, 1986), an

important ground-water supply. As an extant carbonate coastal

aquifer, these strata offer opportunities to investigate a

variety of on-going diagenetic processes, including

dissolution, cementation and dolomitization (Jee and others,

1991), but better understanding of their sedimentology and

stratigraphy is essential as a frame of reference for

interpretations of their subsequent diagenesis.

The depositional setting and shelf-margin profile of the

Eocene western Florida Carbonate Platform have yet to be fully

defined and, among the paleoenvironments interpreted thus far,

reefal and oolitic facies of a "shoal-water complex" (Read,

1985) are conspicuously lacking (Randazzo, 1987).







52

Winston (1978, 1989) reports the existence of the

"Rebecca Shoals Barrier Reef Complex" in strata of Late

Cretaceous through Paleocene age, onshore and offshore

Florida. The literature is not clear whether this "dolomite

reef" (Winston, 1989) is truly an ecologic reef (Dunham,

1970). If so, how did conditions change in the Eocene to

cause its demise? Considering the paradox of drowned

carbonate platforms (Schlager, 1981), one may wonder if change

in sea level played a role. After its end, did the "reef"

express an influence on subsequent sedimentation?

No Paleocene sediment was recovered in any of the Exxon

coreholes along the west Florida slope, but CH32-45 is

reported to have bottomed in Eocene calcareous nannofossil

ooze (Mitchum, 1978; Mullins and others, 1988b; Wrenn and

Satchell, 1988; Gardulski and others, 1991). Obviously, one

must look landward of this chalk, which is interpreted as an

open-ocean, marginal plateau deposit, to observe the

morphology and facies transitions of the Eocene shelf/basin

margin.

The global nature of the regional transgression recorded

by the regional lithostratigraphy of Paleocene and Eocene

rocks of Florida (Chen, 1965; Miller, 1986) is recognized, but

some controversy exists concerning its cause. Although Vail

and others (1977) interpret Eocene patterns of coastal onlap

to reflect worldwide rise in relative sea level, a sea-level

curve based on volume changes of the mid-ocean ridge system








53

(Pitman, 1978) indicates sea level fell persistently from Late

Cretaceous to Middle Miocene time. Pitman (1978, p. 1389)

points out that, "The shoreline tends to stabilize at that

point on a margin where the rate of rise (or fall) of sea

level is equal to the difference between the rate of

subsidence of the platform and the rate of sediment infill.

Under these conditions, if sea level is made to rise more

rapidly or fall more slowly a transgression will occur." On

this basis, Pitman (1978) attributes the marine transgression

in the Eocene to reduction in the rate of sea-level fall, at

that time.

McGowran (1990) presents the early Paleogene as a time of

episodic transition of global climate from Mesozoic

"greenhouse" to Cenozoic "icehouse." This transition affected

both oceanic circulation and sea level. McGowran asserts a

parallel between tripartite patterns evident in various

paleobiological and geochemical data drawn from marine and

terrestrial realms and plate tectonic events of the Paleocene

and Eocene epochs, but is unable to relate these clearly to

either eustatic or climatic changes. At the scale of his

investigation, McGowran sees no cyclic or rhythmic character

in the patterns.

Cyclic deposition and erosion have been observed in the

Eocene carbonate section of Florida (Randazzo and Saroop,

1976; Randazzo and others, 1977; Randazzo and Hickey, 1978)

but, as yet, these have not been completely explained and







54

related to global patterns of relative sea-level fluctuation.

Changes in the rate of sea-floor spreading cause sea level to

fluctuate at rates of less than 10 Mm/yr (Pitman; 1978). This

is too slow to explain many of the prominent features in the

stratigraphy of carbonate platforms (Kendall and Schlager,

1981, p. 185). The glacioeustatic mechanism is commonly

invoked to account for cycles of relative sea-level change

with frequencies higher than the third order of Vail and

others (1977). Although estimates of temperature change in

North America indicate alternating episodes of relative warmth

and coolness during the Eocene, it is believed that Antarctic

glaciation did not commence until the Late Eocene. "In fact,

global temperatures may never again have risen to the levels

that they attained in Eocene time" (Stanley, 1986, p. 541).

What, then, is the nature of the cycles that occur in the

Florida's Eocene carbonate section?

The depositional and diagenetic responses of carbonate

systems to relative sea-level rise and fall are modeled based

on the principles of seismic/sequence stratigraphy, by Kendall

and Schlager (1981), Sarg (1988), and Schlager (1992). Facies

models, in the sense of Walker (1990), are generalizations

that combine the features of many local examples to produce a

norm by which the significance of a new example can be

assessed. Through attempts to apply a model to a specific

case the existing model can be improved or a new one

constructed. The "new stratigraphies," Walker (1990) notes,







55

are largely conceptual with few actual geological examples.

It is of interest, therefore, to test the applicability of

such models to the carbonate system of the western Florida

Platform.

To varying degrees, the diagenetic features of Florida's

Eocene carbonate rocks have been characterized and

hydrogeochemical factors that influence diagenetic processes

have been analyzed (Randazzo, 1980; Randazzo and Cook, 1987;

Randazzo and Bloom, 1985; Randazzo and Zachos, 1984; Randazzo

and Hickey, 1978; Randazzo and others, 1983, 1977). The

diagenesis of these rocks has not, however, been interpreted

holisticallyy," within the context of the 33 to 55 million

years of geologic history since their deposition. Changes in

relative sea level influence the position of the coastal and

inland fresh water-salt water mixing zones and other factors

important to dolomitization, cementation and dissolution. The

Eocene carbonate rocks of Florida doubtlessly reflect such

changes, but the sequence, timing and duration of diagenetic

episodes is still speculative. For instance, although

evidence (Randazzo and Bloom, 1985) suggests that certain

diagenetic processes (i. e., dolomitization) have been active

within the last 30,000 years, the diagenetic role of early

post-depositional fluctuations in relative sea level is not

well understood.

Proponents of sequence stratigraphy believe that the rate

and direction of relative sea level changes have been







56

constrained within fairly narrow limits for most of the

Mesozoic and Cenozoic ocean margins and tied to an integrated

chronostratigraphic framework (Haq and others, 1988). The

general stratigraphy of the northeastern Gulf of Mexico has

been correlated (Greenlee, 1987; Greenlee and Moore, 1988; Wu

and others, 1990) to the major sequence boundaries associated

with eustatic sea-level changes (Haq and others, 1987, 1988).

The attempt is made here to extend and refine this correlation

in the Upper Cretaceous-Cenozoic section throughout the

western Florida Carbonate Platform.

Better understanding of the controls on spatial and

temporal variations in mixed carbonate and siliciclastic

deposition in settings like the previously mentioned facies

transition between peninsular and panhandle Florida has come

from viewing mixed sequences as part of a continuum between

the carbonate and siliciclastic end members (Doyle and

Roberts, 1988; Budd and Harris, 1990). An attempt is made

here to resolve differences in the interpreted extension of

the Suwannee Strait, or Channel, beneath the West Florida

Shelf (Antoine and Harding, 1965, Antoine and Jones, 1967;

Mitchum, 1978; Chen, 1965; Miller, 1986).













MATERIALS AND METHODS

Data Base

Much of the data used in this study were obtained from

petroleum industry sources. The American petroleum industry

still uses U.S. measurements rather than metric. Virtually

all data (well logs, seismic acquisition and processing

specifications, etc.) are not in metric units. Where

feasible, metric equivalents are provided, but wholesale

conversion of every measurement was not undertaken.

Reflection Seismic Data

Approximately 9,600 kilometers (6,000 miles) of multifold

reflection seismic data were used in this investigation. The

data were contributed by GECO Geophysical Company, Inc.,

Digicon Geophysical Corporation, and Fairfield Industries.

Since the commercial data are proprietary, lines were

renumbered for reference within this text, and only

generalized locations are shown (Figure 11). General

information on the recording parameters and processing

sequences can be found in Appendix A.

GECO Geophysical Company released (through Texaco Inc.)

approximately 3657 kilometers (2,273 miles) of selected

seismic data from the 1986-1987 GECO Eastern Gulf of Mexico

Regional Well-Tie program. The GECO lines supply regional







58

coverage from the eastern Apalachicola Basin to the northern

South Florida Basin. The GECO data are 96-fold common-depth-

point (CDP) coverage. The record sections obtained display

wave-equation-migrated data at a vertical scale of 2.5 inches

equals 1 second (2-way TT) and a compressed horizontal scale

of 1 inch equals 2.5 miles (1:158,275). This presentation

enhances the continuity of reflections and makes the data more

easy to interpret (Macurda, 1988).

Digicon Geophysical Corporation released selected seismic

data from the 1984/85 Destin Dome Spec Survey (80-fold CDP),

the 1986 Florida Middleground Spec Survey (80-fold CDP), and

the 1987/88 Florida Middleground Infill Spec Survey (90-fold

CDP). The Digicon data set amounts to approximately 3,459

kilometers (2,150 miles) of data. The record sections

obtained display migrated data at a vertical scale of 2.5

inches equals 1 second (2-way TT) and a horizontal scale of 1

inch equals 3,514 feet or 0.67 miles (1:42,171). The Digicon

lines provide a rectangular grid of coverage across the Middle

Ground Arch and Tampa Embayment.

Fairfield Industries released more than 2475 kilometers

(1538 miles) of selected 72-fold CDP seismic data from the

1984-85 Offshore Florida program. The record sections

obtained display migrated data at a vertical scale of 2.5

inches equals 1 second (2-way TT) and a horizontal scale of 1

inch equals 3,514 feet or 0.67 miles (1:42,171). Much of

these data were reprocessed with full-dip move-out migration







59

in 1988. The Fairfield lines furnish a rectangular grid of

coverage across the Apalachicola Basin. Fairfield lines

illustrated in Figures 19 and 20 have been displayed at a

compressed horizontal scale comparable to that of the GECO

lines.

Well Data

The seismic data are correlated with information from 29

offshore wells (Figure 11). Various geophysical logs,

biostratigraphic data, and some lithologic data were obtained

for these wells (Table 1). Synthetic seismograms and/or

velocity surveys were obtained for eight wells (Table 1).

West of 860 W, Wells 1 through 10 (Figure 11) are all

located on or near the grid of seismic profiles. Of the 13

key wells located in federal waters, on the outer continental

shelf (OCS), east of 860 W, 11 are tied by the layout of

selected lines (Wells 11, 12, 13, 14, 15, 16, 17, 18, 20, 21,

and 23; Figure 11). Wells 25 and 29, located in the state

waters of Florida (Table 1) can be projected toward seismic

lines G10 and G15 (Figure 11).

Data on certain wells from published sources (Addy and

Buffler, 1984; Lord, 1987; Greenlee, 1987; Greenlee and Moore,

1988; Wu and others, 1990a) are integrated into this study.

Wells 24, 26, and 29 are interpreted in stratigraphic cross-

sections by Miller (1986, Plates 15, 22, and 24,

respectively). In the case of near-shore wells, published

interpretations of nearby wells were also consulted (Applin













x r.
-4 > M0
0 0 4J
m 1 t
0 o 0

9 X-

Vn >4 W
- ) 9 0


. -o *-
0 H3

U 00 X 4-4
SW -rq 0





OH
1 (1) t









,-4 .H -H
M l C




O 4



O= s 0
5140 0

*H ul0






-H *H 0



44 >1 4H *
.4 4 )
S*P4 *> (10)

-u 4V 4)




44 ,- *H

(0 (a 4





-iH
4:1 s--
MUo1
.H ~f
P4 <








61














G16





















0 6,,
cy 0








200

to


II II








0 0 t
H H> 0
S 0 H -
H -o -Zc C
H E
0 CH 0 0 U C UC.





U H r H o H M H 1 H 1H HHr HUC /


lcc a. o S o0
O ccc HHOcO O CH a (n QQOU


u 0o o 0 0 m00 0m H 0 H 0(













S 0 o o OOOO o o o H 0 0
0 o o % w m W> m m -
4 aM r- O 0 ON D O O O O CO O r- O0





M, 0 0 N 0 0 0 M 0 0 00 0 010 H0 M 0oa 0


oO WON o mo oD -D %0












O o oNMOO'.D = oN O H C
So r-0 w 0 r- N N Ln o o 0 IN H
0rrHH N H, c r"4 rl o fo r-i H oH Ho





>I (1) 4) 4) W ) (1 (L l) ) (1) (1) I I
E-i R R 0 0 0 R H 9i L 0 r- 0 m M
S NOOOOOOOO O OHO O O O O OH
w in a Q a 0 Q a a a Q.4 4.) 4.
O (a > .4 .)P 4- 4-)

(A 4n to w W to w w oa O o 0 O o 0O-H 0 $4, M .o 4.





V CO CO CO N (*- %D N 0CON M %D0 %O r- m qr r-H N 01
m 0 w N o m r-' H LA M N -; v H- 0
Sv v n LA M m 0L oi
H N OCOw w N N N O N N N N w Nl Cl) m


o 00000000000 0 c00 0 0 0 0


E-4 0 0 U 0 0
m 0 0 0- 0 r-4 r-l r-Ol 0
> -4 0 0 U UH 0 0 > 0 Z (v -H o -ri rq r-l U

0 U M_ w_ P_ p_ M_ M cccc En z _c 0


n^c Cenm-oiS I I3 I I -E















U S

H CO


SQ Q 0 M






4 0 H 0 A 0
Im I a Ji NLH QIQ


o e ^o N PO m n 4




co r- H N In U n









H0 N'O 0 '-0 0 0 0O
0n r0 il n 0 U 00 r% (

r-I I r- I r-l ci -I H r-I







%C0



1 1 0 0 0





So I




o0 r0 0 O 0 P 0 i N--00&
pO A O O p 0 9 r. >4 >4 a
ti o p p (O p t t > >


O )4




> I 4 4 O O Q
0 U U) U) M N


0 0 0 0 )4 0

0 r-H



r-o H )N 0 0 4O r- 0 0


N N N NCM NNNNNN


0
0 0 0
04


VO 0 ON
til 6'001



0000' 0
0 H 0 r.
4OH 0mH o )
.--4 #0 PC 0 m > 1M
O*N M4 0 >1 4O 0H

0- I o1 C>i *H
-COq -4 0 000 1 .0
O1 lOO r..O V ) 0 >

-) 10 0 0 010 U 0 O C
Sr Z 1 0 C 0 0-H
0 0 0'00'(0 M0 0 0 W-4 >1-4-
-4 -H C C C -H M () -4 t r-l *J 4- V (10
S4J-J 4-H H H 4 -J C V-H 0 43-0 a) m
V O OU 0 W 4) U O C. Or-l -
01 0 r-qr-lr-4 E 040 00) - C C 0 0 H-H 0 0 > 0) (0 -H
M I HHIQQQ IrU CO U) > C


OMU004ZZU 0
rlU)HHHQZHHOUUnC.-lH
MHHQQQ0aUCOCQ







64

and Applin, 1965, 1967; Winston, 1971a and b, 1976a, and

1977).

Samples from cored intervals interpreted to be Eocene

were obtained from Wells 17 and 21 (Figure 11 and Table 1).

The former well has two cored intervals interpreted to be in

Eocene strata, Core #1 (2,994 to 3,020 ft) and Core #2 (4,581

to 4,583 feet). The latter well has three cored intervals

interpreted to be in Eocene strata, Core #1 (1,659 to 1,692

feet), Core #2 (3,472 to 3,478 feet), and Core #3 (4,102 to

4,112 feet). Detailed analysis and interpretation of the

cores was not within the scope of this study.

Seismic Stratigraphic Interpretation Procedure

Seismic stratigraphic interpretation (Vail and others,

1977) has three principal steps:

1--(seismic) sequence analysis,
2--(seismic) faces analysis,
3--sea-level analysis.

Sequence analysis begins with recognition of the regional

setting and pertinent age relationships and entails definition

of depositional sequences and delineation of their extent by

mapping their external geometry. Facies analysis involves

identification and characterization of the lithofacies within

sequences based on seismic data, geophysical log character

and/or geologic data. Sea-level analysis includes

construction of a chronostratigraphic correlation chart and

geochronologic chart that shows regional cycles of relative

sea-level change (Vail and others, 1977).









Vail (1987) expands the seismic stratigraphic

interpretation procedure to seven steps:

1--seismic sequence analysis,
2--well-log sequence analysis,
3--synthetic, well-to-seismic ties,
4--seismic facies analysis,
5--interpretation of depositional environment and
lithofacies,
6--forward seismic modeling,
7--final interpretation.

Vail and Wornardt (1990) again revise the procedure for

well log-seismic sequence stratigraphic analysis. An eleven-

step process is now recommended:

1--Interpret lithology from log character (confirm with
cores and cuttings when possible),
2--Interpret depositional environments from
micropaleontology/ paleoecology and then from well log
character,
3--Interpret the condensed sections from faunal and
floral abundance and diversity to recognize:
Major condensed sections associated with
maximum flooding surfaces
Secondary condensed sections not associated
with maximum flooding surfaces
Base of lowstand prograding wedges
Base of lowstand slope fans
Minor condensed sections between attached
lobes of slope fans
4--Age date with high resolution biostratigraphy and
correlate with global sequence cycle chart,
5--Locate discontinuities on dipmeter log
6--Interpret sequence and systems tract boundaries from
log character,
7--Tie to seismic sections that have sequences and
systems tracts interpreted,
8--Interpret sequence boundaries, maximum flooding
surfaces and systems tracts on seismic data and tie the
seismic interpretation to the well logs,
9--Identify parasequences and marker beds,
10--Construct well log-seismic sequence stratigraphic
cross-sections,
11--Prepare a chronostratigraphic chart from key cross-
sections to summarize stratigraphic framework.







66

This investigation integrates all available information

from seismic and wells, but does not adhere strictly to the

procedure of Wornardt and Vail (1990), because there are few

wells in the study area, and geologic, biostratigraphic and

paleoecological data are even more scarce. As discussed by

Schlager (1992, p. 28), the restricted definitions of

"unconformity" and "sequence boundary" (Vail, 1987 and Van

Wagoner and others, 1988) are not acceptable, and the limits

of seismic resolution preclude the recognition of systems

tracts. Therefore, the criteria used for sequence boundary

recognition are those of Vail and others (1977).

As the first step, the boundaries of depositional

sequences were identified by reflection terminations and

traced throughout the grid of seismic sections. Then,

lithostratigraphic and biostratigraphic data from wells were

used to interpret the seismic data. The interpretations from

well data were tied to seismic sections either by synthetic

seismograms or using sonic logs.

The well-to-seismic ties for Wells 11, 12, 16, 17, 18,

and 21 (Figure 11, Table 1) were made using synthetic

seismograms. The conversions from depth (ft) to two-way

travel time (2-way TT, sec) for the well-to-seismic ties for

Wells 2, 4, 5, 8, 9, 10, and 11 (Figure 11, Table 1) are based

on sonic log interval transit time (At, gsec/ft). Sonic logs

were blocked and the average interval transit time (At,

Asec/ft) used to calculate the two-way travel time (2-way TT,







67
sec) for each blocked interval by dividing the interval

thickness (ft) by the average sonic velocity (ft/sec) of the

interval. The stacking velocity near the well was used to

calculate the 2-way TT to the top of the sonic log. The

cumulative 2-way TT below the seismic datum (sea level) was

calculated by summing the 2-way TT of each interval. The

cumulative 2-way TT of depths at which the change in At was

relatively great were correlated to reflections on the seismic

sections. A suite of well-log cross-sections (Figures 14

through 17) were constructed showing chronostratigraphic,

seismic-stratigraphic, and lithostratigraphic correlations.

Seismic facies analysis was approached as previously

described. The analysis incorporates the characterization of

seismic facies of carbonate rocks by Fontaine and others

(1987; Figure 12) and the models of Handford and Loucks (in

press).

A suite of "thickness" and "structure" maps of key units

were made, contoured in 2-way TT. Conversion to depth was not

attempted, because of sparse control on sonic velocity. In

general, a increase in sonic velocity occurs toward the

southeast with the change from siliciclastic to more carbonate

rock. The gradational nature of this change in sonic

velocity, however, means that locally the change is

negligible. Maps contoured in 2-way TT should be more easily

tied by future investigators than maps converted to depth on

the basis of speculative sonic velocity.




































0= .- Ia



0- O


.C c



C -2 ~. 2 :.o
tiM i .
silla'ilS____
C6
C6 v
v-- i I soj
CA">E oaS ug
cilitl
s w s asTo

CiL r
l'55-S Ei-i--3Cu


4.)







0


.H
0
*"-
-1



04
a)



co
0



) -4





4-J4

E)
oU
o-




4w














- tP
H 0




('4
0 -H








Chronostratigraphic Interpretation Procedure

Most sequence stratigraphic analyses (e.g., Baum and

Vail, 1988; Greenlee, 1988; Greenlee and Moore, 1988; King and

Skotnicki, 1990; Wu and others, 1990a; Dobson, 1990) employ

the Mesozoic-Cenozoic Cycle Chart (Haq and others, 1987, 1988)

as the standard for temporal correlations. Miall (1991, 1992)

suggests the need to revise this practice. Another reason for

change is a more accurate geomagnetic polarity time scale

(GPTS) for the Late Cretaceous and Cenozoic (Cande and Kent,

1992). The correlation of series and stage boundaries to

magnetopolarity chronozones by Haq and others (1987, 1988) is

different from that of other schemes (Kent and Gradstein,

1985; Breggren and others, 1985a, b, c; Aubry and others,

1988), particularly the GPTS of Cande and Kent (1992). Also,

the correlation by Haq and others (1987, 1988) of

biochronostratigraphic units, specifically the planktonic

foraminiferal (N/P) biochronozones, with magnetic polarity

stratigraphy is different from that of other schemes (Berggren

and others, 1985a, b, c; Aubry and others, 1988). As the GPTS

of Cande and Kent (1992) does not provide a magneto-

biochronostratigraphic correlation, the interpretations of

Berggren and others (1985a, b, c) as revised by Aubry and

others (1988) are used to tie the planktonic foraminiferal

zonations to this GPTS (Figure 13). One point of controversy,

the position of the Paleocene-Eocene boundary (Aubry and

others, 1988; Swisher and Knox, 1991, and Cande and Kent,





























Figure 13.


Geomagnetic polarity timescale for the Late
Cretaceous and Cenozoic (from Cande and Kent,
1992; black is normal polarity, white is
reversed) with correlation to planktonic
foraminiferal zonations and the last appearance
data (LAD) of key planktonic foraminifers (from
Kent and Gradstein, 1985; Berggren and others,
1985a, b, and Aubry and others, 1988). Six-letter
abbreviations for foraminifers are explained in
Appendix B.











CHRONO- 3 > LAD OF KEY

TIME STRATIGRAPHIC z PLANKTONIC ZONES TIME
UNITS FORAMINIFERS


PL IS TOCENE
2 -
PL10- L PIACENZIAN 2A--
CENE E ZANCLEAN 3
MESSINIAN 3A .
34 "
S L TORTONIAN 4A'

J 5-A--.
SERRAVALIAN
c: --M -- ...
LJ LANGHIAN 5..
o50--
BURIGALIAN SE:::
E 6 --.
6A--
AQUITANIAN 6B..-
6C..-

L CHATTIAN a
o 9-..


E E RUPELIAN 12.-
Q


-0 Mo






- 10






-20






-30






-40






-50






-60






-70






-80o


BARTONIAN 18 I
19.. -


LUTETIAN


21t.--


23 ...-
E YPRESIAN


25"
L SELANOIAN 26-.


- 27...
E DANIAN 2S8
29--


MAASTRICHTIAN


33 ..


CAMPANIAN


SANTONIAN


< GLR FPR




< GLR KUG
< GLB CAG


( GLR OOP
< CHL CUB
(< PHG MCR
(< HNK ALA,TBR
< GAK SMV
MZV SPN
ORN BKM
ACR BLO

(MZV ARA


< ACR PCM

(MZV SBB

< MZV VLC
< PRT PMI
( MZV AGA
< MZV PBU








< GTI ELE








-N23-
-N22-
-N21-
N19
N18
N17
N16


-N1 1-
N8
=N7=
N6
N5

N4

P22/N3

P21

P19ig
P18

-P16-
-i-
P15
P14
-P13-
P12

P11l

P10
P9
P8
-P7-
P6
-P5-
P4
P3
-P2-

P1


N13

4N10


- i a


L PRIABONIAN


-0 Mo






- 10o






-20






-30






-40






-50






-60






-70






-80







72

1992) is beyond the scope of this investigation, but is

addressed by Berggren and others (1992).

Chronostratigraphic control comes from reports of the

depths of the first down-hole occurrences (i.e., last observed

occurrences, LOO) of various planktonic and benthonic

foraminifers in wells (Appendix B). This study preferentially

uses the nomenclature of Bolli, Saunders, and Perch-Nielsen

(1985); Appendix B includes an informal synonymy of the taxa

listed in the reports.

The last appearance data (LAD) of certain of the

planktonic foraminifers are correlated to the magnetic

polarity stratigraphy (Kent and Gradstein, 1985; Berggren and

others, 1985a, b; Ciesielski, personal communication).The LOO

of these taxa in the wells studied can be considered equal to

or older than the LAD tie points shown in Figure 13.

The LOO of other taxa listed can be considered equal to

or older than their LAD relative to the planktonic

foraminiferal zonations as shown in Bolli, Saunders, and

Perch-Nielsen (1985). One discrepancy between the planktonic

foraminiferal zonation of Berggren and others (1985b) and that

used in Bolli, Saunders, and Perch-Nielsen (1985) is that the

top of the Truncorotaloides rohri zone, P14 is the LAD of the

nominate taxon in the latter scheme, but the first appearance

datum (FAD) of Porticulasphaera semiinvoluta (referred to here

as Globigerinatheka semiinvoluta) in the former.







73

The chronostratigraphic significance of still other taxa

listed in Appendix B is based on the previously published

interpretations of Applin and Applin (1944), Applin and Jordan

(1945), or Miller (1986).

Well-log Correlation Procedure

Outcrops of coastal plain strata are sparse, and much of

our knowledge of Florida stratigraphy is based on data from

wells. When subsurface investigations began, in the early

1940's, there was no code of stratigraphic nomenclature and no

distinction between biostratigraphic and lithostratigraphic

units. In most cases, "diagnostic foraminifera" were the

criteria for recognizing subsurface formations in Florida

(Applin and Applin, 1944; Applin and Jordan, 1945). In a

their study of the Comanche Series (Lower Cretaceous), Applin

and Applin (1965, p. 31) explain that, "provisional boundaries

of the stratigraphic units are arbitrarily determined on the

basis of lithologic and electric log characteristics that are

traceable from well to well, and which occur at, or slightly

above, the highest level of the diagnostic fossils." Although

Winston (1971a, b, 1976a, 1978) offers lithologic criteria

from sample and geophysical logs from "type" wells to

establish correlation of both newly proposed and "classic"

stratigraphic units, microfaunal assemblages remain the key to

the stratigraphic correlation in Florida. Miller (1986)

employs time-rock units correlated chiefly by means of







74

planktonic and benthonic foraminifers. A similar approach is

used in this study.

The suite of well-log cross-sections, A-A' through D-D'

(Figures 14 through 17), are constructed on datum levels

relative to mean sea level. In each case, the line of section

is more or less perpendicular to the present coastline. The

LOO of a "diagnostic" taxon is shown by the six-letter

abbreviation for that taxon alongside the well log. The

abbreviations are listed in Appendix B in general order of

first down-hole occurrence (i.e., increasing age) of taxa.

In the case of correlations based on magnetobiochrono-

stratigraphic and/or biochronostratigraphic interpretations,

the boundaries are chosen to coincide with lithologic changes

(from sample and/or geophysical logs) that are traceable from

well to well, and that occur at, or slightly above, the LOO

the diagnostic taxa. On the cross-sections, these boundaries

are shown by thick lines. Tentative correlations based only

on lithologic characteristics (from sample and/or geophysical

logs) that are traceable from well to well are shown on the

cross-sections by thin lines.

The positions of sequence boundaries interpreted from

seismic sections via sonic logs and/or synthetic seismograms

are also annotated on the well-log cross-sections. In the

specific case of the MCSB, the boundary is so labeled and

shown as a thick, wavy line.












RESULTS AND DISCUSSION

Chronostratigraphic Framework

Pertinent age relationships were interpreted as

previously described (Figure 13), and the LOO depths and

magnetobiochrono-stratigraphic or biochronostratigraphic

information on the taxa are listed in Appendix B and

illustrated in four well-log cross-sections (Figures 14, 15,

16, and 17). In some of the wells, the LOO depths of certain

taxa do not occur in an ideal stratigraphic sequence (Appendix

B, shaded blocks). Reworking, caving, and differences in

preservation can affect the observed sequence of microfossil

occurrences. Most instances in this study are of the sort

where the LOO of one taxon occurs beneath the LOO of other

taxa the LAD of which are supposed to be older. Such cases

could be attributed to caving. There are also a few cases

where the LOO of a taxon is among others whose LAD are

considered to be younger; this suggests reworking. Where

there are problems, the chronostratigraphic interpretation is

tentative.

Calibration of the occurrences of planktonic foraminifers

against Tkgnetostratigraphy (Miller and others, 1985, 1991)

indicates that some low-latitude taxa exhibit latitudinal



















Figure 14. (In pocket) Well-log cross-section A-A' showing
age interpretation based on the depths (from Exxon
Company reports) of the last observed occurrences
of key planktonic and several benthonic foramini-
fers in Wells 3, 7, 8, and 10 in the Destin Dome
Area. Well numbers refer to Figure 11 and Table
1. There is a change in datum of the two
southwesternmost (down-dip) wells, from -1,000
feet to -1,500 feet, subsea.

The LOO of a "diagnostic" taxon is shown by the
six-letter abbreviation for that taxon alongside
the well log. Abbreviations are listed in
Appendix B in general order of first down-hole
occurrence (i.e., increasing age) of taxa.

The positions of sequence boundaries interpreted
from seismic sections are also annotated. In the
specific case of the MCSB, the boundary is shown
as a thick, wavy line.

MCSB = Mid-Cretaceous Sequence Boundary.
Ku = Top of Cenomanian-Santonian subunit.
K2 = Top of Campanian-Maastrichtian subunit.
TEU = Top of Upper Eocene,
TML = Top of Lower Middle Miocene.

Correlations on magnetobiochronostratigraphic
and/or biochronostratigraphic interpretations
are shown by thick lines. Tentative correlations
based only on lithologic characteristics are shown
on the cross-sections by thin lines.




















Figure 15.


(in pocket) Well-log cross-section B-B' showing
age interpretation based on the depths of the last
observed occurrences of key planktonic and some
benthonic foraminifers in Wells 11, 12, 13, and 26
on the Middle Ground Arch. Well numbers refer to
Figure 11 and Table 1. Datum is mean sea level.

The LOO of a "diagnostic" taxon is shown by the
six-letter abbreviation for that taxon alongside
the well log. Abbreviations are listed in
Appendix B in general order of first down-hole
occurrence (i.e., increasing age) of taxa.

The positions of sequence boundaries interpreted
from seismic sections are also annotated. In the
specific case of the MCSB, the boundary is shown
as a thick, wavy line.

MCSB = Mid-Cretaceous Sequence Boundary.
Kl = Top of Cenomanian-Santonian subunit.
'Y2 = Top of Campanian-Maastrichtian subunit.
TEU = Top of Upper Eocene.
TL = Top of Lower Middle Miocene.

Correlations on magnetobiochronostratigraphic
and/or biochronostratigraphic interpretations
are shown by thick lines. Tentative correlations
based only on lithologic characteristics are shown
on the cross-sections by thin lines.


















Figure 16. (In pocket) Well-log cross-section C-C' showing
age interpretation based on the depths of the last
observed occurrences of key planktonic and some
benthonic foraminifers in Wells 14, 15, 16, 17,
and 28 on the southeast flank of the Tampa
Embayment. Well numbers refer to Figure 11 and
Table 1. Datum is mean sea level.

The LOO of a "diagnostic" taxon is shown by the
six-letter abbreviation for that taxon alongside
the well log. Abbreviations are listed in
Appendix B in general order of first down-hole
occurrence (i.e., increasing age) of taxa.

The positions of sequence boundaries interpreted
from seismic sections are also annotated. In the
specific case of the MCSB, the boundary is shown
as a thick, wavy line.

MCSB = Mid-Cretaceous Sequence Boundary.
Kl = Top of Cenomanian-Santonian subunit.
S2 = Top of Campanian-Maastrichtian subunit.
Tp = Top of Paleocene.
TEU = Top of Upper Eocene.
TML = Top of Lower Middle Miocene.
K. KLb, and KLc denote key seismic reflections
within the Lower Cretaceous section shown to
strengthen correlations of overlying units.

Correlations on magnetobiochronostratigraphic
and/or biochronostratigraphic interpretations
are shown by thick lines. Tentative correlations
based only on lithologic characteristics are shown
on the cross-sections by thin lines.





















Figure 17.


(In pocket) Well-log cross-section D-D' showing
age interpretation based on the depths of the last
observed occurrences of key planktonic and some
benthonic foraminifers in Wells 21, 22, 23, and 29
on the north flank of the South Florida Basin.
Well numbers refer to Figure 11 and Table 1.
Datum is mean sea level.

The LOO of a "diagnostic" taxon is shown by the
six-letter abbreviation for that taxon alongside
the well log. Abbreviations are listed in
Appendix B in general order of first down-hole
occurrence (i.e., increasing age) of taxa.

The interpretation of sequence boundaries on
seismic sections in this area is problematic.
Ka, KLb, and KLc denote key seismic reflections
within the Lower Cretaceous section shown to
strengthen correlations of the MCSB and overlying
units. The MCSB is shown as a thick, wavy line.

Correlations on magnetobiochronostratigraphic
and/or biochronostratigraphic interpretations
are shown by thick lines. Tentative correlations
based only on lithologic characteristics are shown
on the cross-sections by thin lines.







80

diachrony. More unexpectedly, however, 687Sr age equations

reveal that some planktonic foraminiferal datum levels,

specifically in the Oligocene, are diachronous along

longitudinal gradients (Hess and others, 1989). The

magnetobiochronostratigraphic correlation of the LOO of such

taxa (noted in Appendix B) are somewhat suspect.

The most detailed biostratigraphic data available are

from four Exxon wells (Wells 3, 7, 8, and 10) in the Destin

Dome Area (Figure 14). For wells to the southeast (Figures

15, 16, and 17), there is less information. It has been noted

(Applin and Jordan, 1945; Huddlestun, 1988) that the

microfauna of the subsurface formations of Florida are rather

distinct. Taxa noted in the near-shore wells (i.e., Well 26,

Well 28, and Well 29; Miller, 1986, 1988) are different from

those reported from wells farther offshore. This contributes

to some perplexing correlations (Figure 15, Figure 16, Figure

17). Some of the problem is due to the prevalence in the

shallow-marine facies of near-shore wells of benthonic rather

than planktonic taxa.

Notwithstanding these considerations, the data provide a

chronostratigraphic framework wherein it is possible to

identify the MCSB and group the overlying strata into four

main chronostratigraphic units, namely Upper Cretaceous,

Paleocene-Eocene, Oligocene-lower Middle Miocene, and upper

Middle Miocene-Holocene.









Time-equivalence of Lithostratigraphic units

Although the boundaries of many lithostratigraphic units

in the region are considered to be time-parallel (Baum and

Vail, 1988), with the data available in this study the ability

to specify lithologic characteristics is limited and

lithostratigraphic correlations cannot be made on the basis of

chronostratigraphic equivalence. Nevertheless, the following

information provided by Galloway and others (1991) on the

relationship of certain biostratigraphic markers to

lithostratigraphic units in the northern Gulf of Mexico is

worthy of note.

1. The top of the Midway Group (Paleocene) can be

reliably identified on the extinctions of Morozovella

(Globorotalia) velascoensis and Planorotalites (Globorotalia)

pseudomenardii.

2. The top of the subsurface Wilcox Group (Paleocene-

Eocene) in Louisiana and Texas can be identified most reliably

on the extinction of Morozovella acuta (Globorotalia

wilcoxensis).

3. In deep-water sections the top of the Claiborne Group

(Eocene) is marked by the extinction of Truncorotaloides

rohri.

4. The mid-dip portion of the upper Jackson Group

(Eocene) in Texas contains Marginulina cocoanensis. In down-

dip, deep-water sections the top of the Jackson Group is







82

picked on the extinction points of either Turborotalia

(Globorotalia) cerroazulensis or Hantkenina alabamensis.

5. The top of the Vicksburg Formation (Oligocene) in

deeper-water sections over the entire northern Gulf of Mexico

Basin can be picked at the extinction point of Globigerina

ampliapertura.

6. Where it ranges above the Vicksburg, the extinction

of Anomalina bilateralis can be used as a correlation point in

the Frio Formation of Texas and Louisiana.

7. Outcrops of the Chickasawhay Formation of southern

Mississippi and southwestern Alabama contain Nodosaria

blanpiedi, a marker for the Frio Formation (Oligocene) in the

subsurface of Texas and Louisiana.

8. The Anahuac Formation (Oligocene), found in the

subsurface of Texas, Louisiana, and southwestern Mississippi,

contains the Heterosteqina Zone and Marqinulina vaginata (M.

mexicana var. vaginata) in the underlying Marginulina Zone.

MCSB

As the lower stratigraphic boundary of this study, and in

light of the controversy discussed previously (Addy and

Buffler, 1984; Faust, 1990; Wu and others, 1990a; Feng and

Buffler, 1991), it is important to establish some basis

regarding the MCSB. In this study, the MCSB is identified as

the base of the Cenomanian shale that overlies the thick,

Lower Cretaceous section of interbedded carbonates and

evaporites. This contact is characterized on well logs by







83

relatively low gamma ray, high resistivity, and low sonic At

values, below, and an overlying interval of high gamma ray,

low resistivity, and very high At values (Figures 14, 15, 16,

and 17). Though in places reported as gray or black in color

(Wells 16, 17, 26, 28), this shale correlates to the "green

shale unit" reported by Applin and Applin (1965) and seems to

be present throughout the western Florida Carbonate Platform.

In Well 7 (Figure 14) the MCSB contact lies below the

corresponding pick of Addy and Buffler (1984) and above the

pick of Faust (1990). The MCSB pick recognized here (-3996

ft, subsea) lies within the Cenomanian section, whereas that

of Addy and Buffler (1984) lies near the top of section

considered here to be Turonian (-3707 ft, subsea), and Faust's

(1990) lies at the base of the Cenomanian (-4101 ft, subsea).

The abrupt change in sonic velocity at the contact picked in

this study makes it a more likely candidate to produce the

high-amplitude MCSB reflection than alternative picks

associated with gradational lithologic changes (Addy and

Buffler, 1984; Faust, 1990).

Upper Cretaceous

The Upper Cretaceous unit is equivalent to the provincial

Gulfian Series. Compared to the Upper Cretaceous stratigraphy

in the Coastal Plain of Alabama (King and Skotnicki, 1990;

Figure 8) where strata from lower Turonian to upper Santonian

are absent beneath a regional unconformity at the top of the

Tuscaloosa Formation (Figure 7), the section penetrated by







84

wells in the study area is more complete. In the Destin Dome

wells (Figure 14), it includes (in ascending order)

Cenomanian, Turonian, Coniacian, Santonian, Campanian and at

least some Maastrichtian strata. To the southeast, sparse

control variously affords recognition of Cenomanian, Turonian,

Santonian, Campanian and Maastrichtian strata in Wells 12, 13,

and 26 (Figure 15) and in Wells 14 and 15 (Figure 16). In the

southernmost wells (Figure 17) the Upper Cretaceous unit is

only tentatively subdivided by correlations based on log

character.

A mid-Paleocene age for the stratigraphic break at the

top of the Upper Cretaceous agrees with the interpretation of

Addy and Buffler (1984). The position of this contact in Well

7 (Figure 14) is also in agreement with the corresponding pick

by Addy and Buffler (1984). Curiously, Mitchum (1978) reports

the Paleocene is entirely absent in his study area, but

assigns an early Paleocene age to sequence boundary J (Figure

10).

The Cenomanian-Santonian strata correspond in age to the

Tuscaloosa-Eutaw lithostratigraphic units in the west and to

the Atkinson Formation and the lower Pine Key Formation in

peninsular Florida (Figure 3). This correlation agrees with

that shown for the Sun OCS-G2490 (Block 166) by Wu and others

(1990a, Foldout 2). The Campanian-Maastrichtian strata

correlate to at least part of the Selma Group in the west and







85

to the upper Pine Key and the Lawson Formation in peninsular

Florida (Figure 3).

Paleocene-Eocene

Lower Paleocene (Danian) strata, though reported in

outcrops in the Gulf Coastal Plain (Baum and Vail, 1988; King

and Skotnicki, 1990; Mancini and Tew, 1990a, b, 1991a, b;

Figures 7 and 8), are not identified in any wells in the study

area. Magnetobiochronostratigraphic interpretations indicate

that Paleocene strata in the Destin Dome wells (Figure 14) are

of the Selandian Stage. Selandian strata are also identified

in Wells 12 and 13, on the Middle Ground Arch (Figure 15), and

in Well 14 (Figure 16). The Selandian strata contain

Morozovella velascoensis and Morozovella pseudobulloides, taxa

characteristic of the "Tamesi fauna" (Applin and Applin, 1944;

Applin and Jordan, 1945). Information from Mobil on

nannoplankton biostratigraphy indicates Upper Paleocene strata

are also present in Well 16 (Figure 16).

The Paleocene section is thin in wells on the Destin Dome

(Figure 14) and Middle Ground Arch (Figure 15), ranging from

less than 50 to about 250 ft thick. Correlations suggest that

the Paleocene section increases to the east and south, to

about 500 ft thick in Well 26 (Figure 15), and from about 500

ft thick in Wells 14 and 16 to more than 1,200 ft thick in

Well 28 (Figure 16).

The Selandian (Thanetian in Figure 3) strata are age-

equivalent to the Midway Group, and possibly the lower Wilcox







86

Group, to the west (Gohn, 1988). On the Florida Peninsula,

the Cedar Keys Formation is traditionally regarded as

Paleocene. Gohn (1988) concludes the Cedar Keys is likely

Danian and early Selandian, but Salvador (1991, Plate 5)

indicates it is upper Thanetian to lower Ypresian (Lower

Eocene).

In Mississippi and Alabama, Lower, Middle, and Upper

Eocene strata are the Hatchetigbee Formation of the Wilcox

Group, the Claiborne Group, and the Jackson Group,

respectively (Figure 3). On the Florida Peninsula, the Lower,

Middle, and Upper Eocene strata are generally considered to

comprise, respectively, the Oldsmar, Avon Park, and Ocala

formations. Gohn (1988) states that it is possible that much

of the Oldsmar is late Paleocene, and that, based on

restriction of the biostratigraphic marker Helicostegina

gyralis to the middle Eocene, the upper part is probably

middle Eocene (Lutetian?). Salvador (1991, Plate 5) shows the

Oldsmar as upper Ypresian and lower Lutetian (Figure 3). The

Avon Park Formation is considered to be upper Lutetian and

lower Bartonian (Gohn, 1988; Salvador, 1991, Plate 5; Figure

3). Priabonian strata correlate to the Ocala Limestone

(Figure 3).

All four Eocene stages, (in ascending order) Ypresian,

Lutetian, Bartonian, and Priabonian, can be differentiated

from the biostratigraphic control in the Destin Dome wells

(Figure 14). The Eocene section is not as clearly defined in






87

wells to the southeast. Ypresian, Lutetian, and Bartonian

strata are variously identified in Well 12 (Figure 15) and in

Wells 14 and 16 (Figure 16), but data are sparse. In Core 1,

Well 21 (Figure 17), echinoid specimens were recovered and

identified as Neolaganum dalli, a taxon characteristic of the

Middle Eocene (Claibornian) Avon Park Formation (Toulmin,

1977).

For Wells 26, 28, and 29, published lithostratigraphic

(Winston, 1977) and/or chronostratigraphic (Miller, 1986,

1988) interpretations of these or nearby wells provide

information to subdivide the Eocene section. As already

noted, the units recognized in these wells are not readily

correlated to wells offshore (Figures 15, 16, and 17).

In each of Wells 3, 7, 8, and 10, the top of the Eocene

section is clearly marked. In Well 7, this contact occurs

some 188 feet (57.3 m) lower than the pick made by Addy and

Buffler (1984) for the corresponding contact of their units C

and D (Figure 10). Addy and Buffler (1984) relied on the

interpretation of Mitchum (1978) for the estimate of the age

of this boundary as middle Oligocene (Figure 10). The data of

this study, however, indicate that Lower Oligocene (Rupelian)

strata overlie the well-defined, top-of-Eocene boundary.

There are no biostratigraphic data available on the top-of

Eocene boundary in Wells 11 through 23 (Figures 15, 16, and

17).









Oligocene-Lower Middle Miocene

Chronostratigraphic subdivision of post-Eocene strata

(Figure 14) is problematic, because the LOO of Lower Oligocene

(Rupelian) and Upper Oligocene (Chattian) taxa are not all in

sequence (Appendix B). Similarly indistinct is the contact of

the Oligocene with overlying Miocene strata. This may be in

part due to the previously noted diachrony of certain

Oligocene taxa, but also reflects the fact that many of the

key Oligocene and Miocene indicators are benthonic taxa, the

temporal significance of which is recognized as suspect

(Galloway and others, 1991).

Magnetobiochronostratigraphic interpretations do permit

identification of the top of Langhian strata (lower Middle

Miocene) in Well 3 (Figure 14). This stratigraphic position

corresponds to a prominent reflection on the seismic sections

that has been previously identified elsewhere as a mid-Miocene

sequence boundary (Figure 10; Sequence Boundary D, 12 Ma,

Mitchum, 1978; contact of Seismic units B and C, 16 Ma, Addy

and Buffler, 1984; contact of Sequences I and II, 12-15 Ma,

Mullins and others, 1988b; TLM, 15.5 Ma Wu and others, 1990a).

Upper Middle Miocene-Holocene

This chronostratigraphic unit is defined rather by

default in that few wells are logged or sampled this high in

the section, consequently there is no biostratigraphic

control. The principal justification for recognizing this as

a distinct chronostratigraphic unit is its position overlying