Citation
Neogene stratigraphy and geologic history of the Apalachicola Embayment, Florida ( FGS: Bulletin 58)

Material Information

Title:
Neogene stratigraphy and geologic history of the Apalachicola Embayment, Florida ( FGS: Bulletin 58)
Series Title:
Florida Geological Survey: Bulletin
Creator:
Schmidt, Walter, 1950-
Florida -- Dept. of Natural Resources
Florida -- Division of Resource Management
Florida -- Bureau of Geology
Place of Publication:
Tallahassee, Fla.
Publisher:
State of Florida, Dept. of Natural Resources, Division of Resource Management, Bureau of Geology
Publication Date:
Copyright Date:
1984
Language:
English
Physical Description:
146 p. : ill., maps ; 23 cm.

Subjects

Subjects / Keywords:
Geology, Stratigraphic -- Neogene ( lcsh )
Apalachicola Embayment (Florida) ( lcsh )
City of Apalachicola ( local )
Town of Suwannee ( local )
City of Chattahoochee ( local )
City of Ocala ( local )
City of Vernon ( local )
Gulf of Mexico ( local )
Geology ( jstor )
Limestones ( jstor )
Sediments ( jstor )
Quartz ( jstor )
Counties ( jstor )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (p. 73-80).
General Note:
Series Statement: Bulletin State of Florida, Bureau of Geology
Statement of Responsibility:
by Walter Schmidt.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
AAA1658 ( LTQF )
AEH5063 ( LTUF )
024079597 ( AlephBibNum )
20493136 ( OCLC )

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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Elton J. Gissendanner, Executive Director

DIVISION OF RESOURCE MANAGEMENT
Charles W- Hendry, Jr, Director


BUREAU
Steve R.


OF GEOLOGY
Windham, Chief


BULLETIN NO. 58

NEOGENE STRATIGRAPHY AND GEOLOGIC HISTORY OF THE
APALACHICOLA EMBAYMENT, FLORIDA

by
Walter Schmidt















Published for the FLORIDA GEOLOGICAL SURVEY

TALLAHASSEE 1984



















DEPARTMENT
OF
NATURAL RESOURCES



BOB GRAHAM
Governor


GEORGE FIRESTONE
Secretary of State

BILL GUNTER
Treasurer

RALPH D. TURLINGTON
Commissioner of Educatron


JIM SMITH
Attorney General

GERALD A. LEWIS
Comptro/ler

DOYLE CONNER
Commissioner of Agriculture


ELTON J. GISSENDANNER
Executive Director





BULLETIN NO. 58


TABLE 1.-Metric conversion factors for terms used In this report.
MULTIPLY BY TO OBTAIN acres 0.4047 hectares acres 4047.0 sq. meters cubic yards 0.7646 cu. meters feet 0,3048 meters inches 2.540 centimeters inches 0.0254 meters mires 1.609 kilometers sq. miles 2.590 sq. kilometers
PREVIOUS INVESTIGATIONS
Much of the previously applied nomenclature from the Miocene and Pliocene of the Florida panhandle is confusing and commonly misleading. Published stratigraphic names have included: deposits, beds, members, formations, groups, marls, b4ofacies, magnafacies, parvafacies, zones, and stages. This confusing situation was largely due to inadequate knowledge of the stratigraphic and paleoenvironmenta framework of the deposits. Much of the confusion resulted from the fact that there was no detailed mapping of these sediments. Most comprehensive descriptions of "facies" were confined to the sediments in the immediate vicinity of the various type localities. In addition to the lack of detailed studies, the inadvisable procedure of using the term facies was used to refer to divisions which are in actuality faunizones.
The nomenclatural history of these exposed deposits is too lengthy to include here and the reader is directed to Schmidt and Clark (1980) for the history of the Alum Bluff Stage (Middle Miocene) and the history of the Choctawhatchee Stage (Upper Miocene).
Studies dealing with the shallow stratigraphy (within about 600 feet of the surface) in the Apalachicola Embayment area are far less abundant and will be summarized below.
Sellards and Gunter (1918) published two geologic reports, one on the area between the Apalachicola and Ochlockonee rivers and a second on the area between the Choctawhatchee and Apalachicola rivers. Their reports described various geologic sections and they attempted to make some downdip interpretations.
Cole (1938) reported on the stratigraphy and micropaleontology of a well in Gulf County at Port St. Joe. His report identified species of foraminifera from various depths from the well cuttings, and his stratigraphic names conformed to prior usage from updip exposed sections. The next year two Masters Theses were completed under Dr. Cole's supervision. The first (Bernhagen, 1939) discussed the stratigraphy and micropaleontology of a well in Calhoun County (W-7 of the Florida Bureau of Geology's collection); and the second (Hobbs, 1939) discussed the stratigraphy and micropaleontology of two wells in Bay County (W- 140, W-151) and one well in Franklin County (W-228). They also identified species of foraminifera.





BUREAU OF GEOLOGY


Schnable and Goodell (1968) published an excellent report on the Pleistocene and Recent Stratlgraphy, Evolution, and Development of the Apa/achicola Coast, Florida. Although their report emphasizes coastal morphology, they do include some shallow geologic cross sections (generally within 100 feet of the surface) and a "surface geology" map.
Huddlestun (1976a) compared the updip and downdip sections in Walton County, which is located on the western-most fringe of the Apalachicola Embayment. Cameron and Mory (1977) reported on the mineral resources of Bradwell Bay, a small wilderness area in Wakulla County on the eastern edge of the embayment. Also in 1977, Trapp discussed an exploratory water well from St. George Island in Franklin County. Schmidt (1978,1979) published two environmental geology maps that cover the area on a 1:250,000 scale.
Schmidt and Clark (1980) published a geologic bulletin on Bay County, Florida, located on the western side of the embayment. Patterson, Schmidt and Crandell (1982) wrote on the geology and mineral resource potential of a part of the Apalachicola National Forest in southern Liberty County.
Other geologic reports on the area include heavy mineral identification of coastal and river deposits and sand-size analyses of present coastal features and surficial deposits inland. One study by Tanner (1966) commented on the Tertiary history of the Apalachicola River Region, as inferred from physiographic and terrace evidence.

DATA COLLECTION AND MODE OF ANALYSIS
Because of the gentle dip (less than 0.5 degree) of the strata and the thin veneer of Pleistocene terrace deposits throughout the coastal regions of the Apalachicola Embayment, there are very few locations where rock unts crop out at the surface. This regional study is, therefore, based mainly on subsurface information consisting of cuttings from water and oil test wells, stratigraphic core tests, drillers logs, and down-hole geophysical information (primarily gamma logs).
Surface exposures are usually found along the northern limits of the Neogene sediments associated with river bluffs or stream cuts. The Ochlockonee, Apalachicola, Chipola, Choctawhatchee, and Shoal rivers, along with many of their tributaries, have cut numerous steep bluffs into these clayey, sandy, shell beds. It is these surface exposures that have been extensively described and cited in the geologic literature. Most of these locations, in addition to other exposures such as road-cuts and borrow pits, have been visited and sampled so that they can be tied-in with the downdip subsurface data.
Water and oil test well cuttings are stored by the Florida Bureau of Geology in Tallahassee, Florida. Hundreds of sets of cuttings from the study area are available. Most have samples at 1 0-foot intervals; however, irregular intervals are not uncommon. The cuttings were examined with a binocular microscope, and such parameters as major rock type, color, estimated porosity, grain type, grain size, induration, cement type, sedimentary structures, accessory minerals, and fossils were described.





BULLETIN NO. 58


Stratigraphic core tests have been drilled throughout the area by the Florida Bureau of Geology. Sixty-six cores have been recovered in the vicinity of the embayment area, 26 of which are within the area of Neogene sediment thickening. All cores were drilled with a Failing 1500 truckmounted core rig and are generally from 200 to 500-feet deep. Cores are 14 inches in diameter. Recovery varied from 100 percent to app roximately 50 percent in the cavernous limestones. All but seven of the cores in Bay, Calhoun, Gulf, Liberty, and Franklin counties were drilled for this regional study. Drilling site locations were selected after assessing existing geologic data along with stratigraphic trends.
Geophysical well logs were run in most of the core holes by the Florida Bureau of Geology and/or the Northwest Florida Water Management District. Other geophysical logs are on file at both these agencies from scattered water wells located throughout the district. Although individual wells or core holes may have had a complete suite of logs run on them (including natural gamma, neutron, gamma-gamma, electric, caliper, and others), theone which seemed most useful for stratigraphic correlation was the natural gamma log. This is also the most commonly available well log. The natural gamma logs respond to natural gamma radiation (U, Th, K) present within the sediments. This is often associated with the mineral components present within the various rock units. The specific reason for the various activity levels present within the Neogene sequence of rocks in the Florida panhandle has been investigated by Kwader (1982). These logs proved useful in estimating the depth and thickness of the lithologic units especially in areas where cuttings or core control was sparse.
Information from cores was relied on most heavily in stratigraphic interpretations because cores offer a higher level of confidence for depth correlation. Upon completion of the lithologic descriptions of the cores and cuttings, formation contacts were picked and the lithologic package that made up each unit was defined. In addition, the cores were sampled for mineralogical and micropaleontological information. Samples were collected from the cores from major lithologic units. An x-ray diffraction study was carried out on these samples to estimate the dominant minerals present. Samples were also collected for smear slide analysis for microfossil content. Calcareous nannofossils and diatoms were found to be present in different formational units. This information, along with foraminiferal data from Walton, Bay, and Gulf counties, was used to aid both in the estimation of the time of deposition of the formations and in constructing biostratigraphic correlations.
Thin sections were prepared from selected samples to aid in rock descriptions and to assist in the assessment of depositional environment.

GEOLOGIC STRUCTURE
The Apalachicola Embayment (Pressler, 1947) is the dominant geologic structure Influencing the sediments in the central part of the Florida panhandle. The shallow deposits are gently down-warped about an axis that plunges to the south-southwest (Fig. 3).





BUREAU OF GEOLOGY


The southern extent of the embayment is not studied here due to the lack of off-shore data. However, it is postulated to continue to dip and thicken gradually to the south-southwest.

STRATIGRAPHY

INTRODUCTION
The downdip, predominantly subsurface stratigraphy of the Neogene sediments in the Apalachicola Embayment has never been well understood. As the rock units trend into the deeper parts of the embayment away from the two structural highs (the Ocala and Chattahoochee) their lithologic character changes. This downdip relationship was first recognized in Walton County by Hendry (1972) and Huddleston (1976a) and subsequently described and mapped in Bay (Schmidt and Clark, 1980) and Okaloosa counties (Clark and Schmidt, 1982), the latter of which is located in the western transition zone between the Gulf of Mexico Basin sedimentary infill and the more local Apalachicola Embayment sediments.
The present study maps and defines these Neogene units from Okaloosa County on the west to Wakulla and Leon counties on the east.
The Paleogene formations down to the Upper Eocene Ocala Group limestones are also identified in some cores and cuttings. These correlations appear on geologic cross sections shown later as Figures 13-18, although these older units were not mapped or described in detail because less data is available from these deeper horizons. A generalized, north-south, geologic cross section is shown in Figure 4, to demonstrate the updip-downdip stratigraphic relationships.

LATE PALEOGENE UNITS

Ocala Group
Upper Eocene (Jackson Stage) strata in Florida were divided by Puri (1957), on the basis of a detailed, biostratigraphic study, into three formations comprising the Ocala Group; they are, in ascending order, the Inglis, the Williston, and the Crystal River. The literature pertaining to the nomenclature of the Ocala Group leading up to the current usage is extensive and has been adequately reviewed in previous publications; it will not be repeated here. Summaries are contained in Vernon (1942), Cooke (1945), Pur (1957), and Puri and Vernon (1964).
In the Florida panhandle, the Ocala crops out along the Alabama state line (Figures 3 and 4) in Jackson and Holmes counties. This unit is brought to the surface as a result of the Chattahoochee Anticline in which older, deeper formations approach the ground surface. The Ocala in this area has been described both from surface exposures (Vernon, 1942; Moore, 1955; Schmidt and Coe, 1978) and downdip in core holes (Schmidt and Clark, 1980; Clark and Schmidt, 1982). In general, only two lithologic facies can be recognized. A lower facies consists of greenish-gray, glauconitic, sandy


10





BULLETIN NO. 58


thickness of clastics to the west during the Middle and Late Miocene. From benthic foraminiferal studies, they interpret a depositional setting dominated by shallow water (40-60m), nearshore, mud-rich habitats. They interpret depositional and faunal patterns to indicate an isostatic downwarp to the west of the present study area. Increased clastic sedimentation beginning with the deposition of the Pensacola Clay may have triggered this downwarp. The clastic material appears to have originated in the Alabama piedmont and coastal plain.
MIOCENE COARSE CLASTICS-The informal term Miocene coarse clastics" was introduced in the western Florida Panhandle by Marsh (1966). He described a deposit of sand, gravel, clay, and shell beds which he believed to be Miocene in age.
Clark and Schmidt (1982) showed that the Miocene coarse clastics lithologically grade into the undifferentiated Alum Bluff Group and the Intracoastal Formation in the western Okaloosa County area. They further note that because the underlying Pensacola Clay was dated as latest Miocene, the Miocene coarse clastics may be Pliocene in part, especially where the unit overlies the Pensacola Clay. This unit represents a continuation of clastic deposition as the region isostatically adjusted to the increased sediment load.
HAWTHORN FORMATION-The Hawthorn Formation is a series of marine, deltaic, and prodeltaic beds of diverse lithology. The co-type areas are in the Alachua and Bradford counties area (Scott, 1982).
Near the present study area, the Hawthorn has been mapped in Leon and Gadsden counties, located north and northeast of the main part of the embayment during the Neogene. In Leon County, it is composed of fine-to-medium grained quartz sand, sand-size phosphorite, silt, kaolinite, montmorillonite, palygorskite, and sandy, phosphoritic limestone (Hendry and Sproul, 1966).
The Hawthorn Formation was encountered in cores from northern Liberty and western Leon counties (Figure 18). It consists of light gray to pale orange quartz sands and clays. Occasionally, sandy, dolomitic calcilutite with minor amounts of phosphorite is recorded. This is considered a Middle Miocene formation, therefore it would correlate chronostratigraphically with the Bruce Creek and Intracoastal formations downdip,

PALEOENVIRONMENTAL ANALYSIS

FORMATIONAL OBSERVATIONS
OCALA GROUP LIMESTONES (Late Eocene)-Fossils from the three formations of the Ocala Group (the Inglis, Williston, and Crystal River formations) have been studied by many authors (Vernon, 1942; Applin and Applin, 1944; Purl, 1957; Cheetham, 1963; and many others). A wide range of marine fauna including mollusks, foraminifera, bryozoans and corals have been described.
In peninsular Florida, where the type localities of these formations are located, Cheetham (1963) suggested that water depths did not exceed 150


49





BULLETIN NO. 58


clastic deltaic sequence can be observed to have slowly invaded the marine environment and finally covered it, leaving the delta as we see it today (Figure 20).

GEOLOGIC HISTORY OF THE APALACHICOLA EMBAYMENT REGION

PRELIMINARY STRUCTURAL MAPPING
In preparing regional, structural contour maps of the top of the Cretaceous, the Middle Eocene, the Late Eocene, the Oligocene, and Early Miocene sediments, the author and Jim May (who was, at the time, on the staff of the Northwest Florida Water Management District) noticed some distinct recurring features. Two positive areas persisted throughout the sequence. The first is the Ocala High east of the present study area in the northwest part of the Florida peninsula and the other is in the Chattahoochee Anticline in the Jackson, Holmes, and northern Washington counties area.
Adjacent to each of these two positive or "high" areas are two low areas. The first is in the western three-to-four counties of the state, along the western flank of the Chattahoochee Anticline. This is the eastern-most limit of the Gulf of Mexico Sedimentary Basin. The second is located between the two relative high areas. In this region the typical southwesterly dipping strata are slightly depressed, forcing the structural contour lines to be deflected slightly northeastward. This feature is known as the Apalachicola Embayment, and it is relatively minor in size when compared to the more regional Gulf of Mexico Sedimentary Basin.
Mapping was generated from geologic well log and core descriptions stored at the Florida Bureau of Geology in Tallahassee. There are many problems inherent in using many different geologists' well log descriptions (such as discrepancies in formation definitions, and formation contacts, age assignments, etc.) as the data base for mapping. There were, however, some noted differences in the various horizons mapped. The orientation and placement of the gently plunging axis of the Apalachicola Embayment shifts northwest higher in the section.
The discovery of this feature led to several questions relating to its origin and its geological history. How did it originate? Was it a structural feature (a graben)? Was it depressed from the thick sediment load, or was it due to non-deposition? The feature seemed to migrate. What was the evidence for this? Why did its axis shift? Are there several different structural elements present that are superimposed on each other, compounding its interpretation? A literature search was carried out to obtain as much information as possible.

LITERATURE REVIEW
The first point that becomes readily apparent in a literature review of this topic is that many different names have been used in referring to this





BUREAU OF GEOLOGY


From the foregoing discussion it is obvious that the origin of the trough in Tertiary times is not well-defined. The interpretations which rely on faulting, although possible, can not be documented using available data. As a result, the paleogeographic interpretation of a strait or Tertiary channel comparable to the present Florida Strait Is preferred.

CONCLUSIONS
1. The downdip Neogene lithologic units along the coast of Panhandle Florida are different lithologic packages from the contemporaneous units exposed undip.
2. These units can be defined and mapped using well cuttings, cores, and geophysical well logs.
3. The Upper Eocene Ocala Group limestones identified are generally penetrated only by deeper water wells. The three formations of the Ocala Group cannot be differentiated, and, as a result, the unit is referred to as Ocala Group undifferentiated.
4. Although not present along the coastal areas of West Ftorida, the Oligocene Marianna Limestone is present in the northern, updip parts of the Apalachicola Embayment.
5. The Oligocene Suwannee Limestone is present throughout the study area. It is generally the deepest formation penetrated by water wells. In the western part of the study area, the formation is undifferentiated from the downdlp Chattahoochee Formation.
6. The Chattahoochee Formation, an Oligocene-Miocene unit, is present in the updip northern parts of the Embayment. In the western and southern parts of the study area, it is indistinguishable from the Suwannee Limestone.
7. The St. Marks Formation (Early Miocene) is present on the eastern flank of the Apalachicola Embayment. Downdip towards Gulf County, the St. Marks cannot be distinguished from the younger Bruce Creek Limestone.
8. The Bruce Creek Limestone is a Middle Miocene formation, present downdip throughout the embayment. The unit can be mapped using cores and well cuttings. ft is predominantly a subsurface unit. Faunal and lithologic evidence suggest it was deposited under shallow, near-shore marine conditions. The top of the Bruce Creek Formation contains a zone rich in algal oncolites. This implies a shallowing of the water depth near the end of Bruce Creek deposition.
9. A clayey dolosilt bed is present over the Bruce Creek Limestone in the central and eastern parts of the embayment. This massive unit may have been deposited In a supratidal or tidal flat environment. The massive, clayey nature of this bed is probably important for its hydrologic implications. This clay would act as an aquiclude and create artesian conditions in the underlying Bruce Creek Limestone.
10. The Intracoastal Formation is a Miocene-Pliocene unit. It is mappable throughout the embayment area and is the downdip equivalent of


70



































































































































































































m






LETTER OF TRANSMITTAL


Bureau of Geology Tallahassee, Florida December 31, 1984


Governor Bob Graham, Chairman
Florida Department of Natural Resources Tallahassee, Florida 32301

Dear Governor Graham:

The Bureau of Geology, Division of Resource Management, Department of Natural Resources is publishing as Bulletin 58 "Neogene Stratigraphy and Geologic History of the Apalachicola Embayment, Florida," prepared by Walter Schm[dt with our Geologic Investigations Section.

The panhandle of Florida wiJI be experiencing rapid population growth in the future. This report fulfills a need for information on the stratigraphy of the area, which is the foundation for responsible growth in community planning. Groundwater resource investigations, landfill siting, mineraJ deposits mapping, and foundation design are but a few of the disciplines r,*uiring geologic data such as this.

In addition, interpretations of the geologic history of the area are presented. This information will be useful to geologic researchers throughout the State to aid in a better understanding of the prehistoric development of Florida.
Respectfully yours,

Steve R. Windham, Chief
Bureau of Geology

















































Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology

Tallahassee
1984













TABLE OF CONTENTS

Page
A b stra ct.................. ............................ .................................................................................. ix
Acknowledgements ......................................... Xi
Introduction .................................................. ....... 1
Previous Investigations ............................................ 3
Data Collection and Mode of Analysis ................................. 6
Geologic Structure ................................................................................ ......................... 7
Stratigraphy ................................................................................................................ 10
Introduction ................................................................................................... 10
Late Paleogene Units .................................................................................................10
Ocala Group ........................................................................ ................................... 10
Marianna and Suwannee Limestones .................................................................... 12
Neogene Formations .............................................13
Chattahoochee and St. Marks Formations ........................... 13
Nomenclatural History ..............................................................................................13
Lithology ............................................................................................................. 13
Thickness and Distribution ............................... ... 14
Paleontology and A g ................................................................................... 15
Bruce Greek Limestone .......................................................................................... 15
Nomenclatural History.......... ................................ 15
uthology .................................... ................. 16
Overlying and Underlying Units...................................................16
Thickness and Distribution.... ............................................................................... 17
Paleontology and Age ................. ................................................................. 20
Intracoastal Formation ..................................... 20
Nomr nclatural Hislory .......... .............................. 20
Lithology ....................................................................................................... ........ 21
Four-Mile Village Member .................................... 21
Overlying and Underlying Units ....................................................................... .. 21
Thickness and Distribution .................................................................................. 24
Paleontology and Age ....................................... 24
Chipola Formation .................................... 29
Nomenclatural History ................................................................ 29
IU tholog y ........................................................... ................... ................................ 30
Overlying and Underlying Units ............... .......................................................... 31
Thickness and Distribution.................................................................................. 31
Paleontology and Age ................................... 32
Jackson Bluff Formation........................... ..................... .................................... 32
Namenclatural History .......................................................................................... 32
Llhology ................................................................ .............................................. 33
Overying and Underlying Units ......................................................................... 33
Thickness and Distribution ................................................................................... 35
Paleontology and Age ........................................................................................ 37
Pleistocene Sediments ................................... 37
Undifferentiated Sands and Clays ......................................................................... 37
Nomenclatural History .................................... 37
Lithology ...............................................................................................................38
Overlying and Underlying Units.... .................................................................... 38
Thickness and Distribution ................................................................................... 39
Paleontology and Age ..................................... 39








Adjacent Stratlgraphic Units ....................................... ............................................ ........ 48
Chickasawhay Limestone ............................................................................... 48
St. Marks Formation ............................................................................................... 48
Pensacola Clay ........................................................................................................ 4
Miocene Coarse Clastics ........................................................................................ 49
Hawthorn Formation .................................................. 49
Paleoenvironmental Analysis......... ....................................... 49
Formational Observations ....................................................................................... 49
Ocala Group Limestones ............................................ 49
Marianna and Suwannee Umeslones .................................................................... 50
Chattahoochee and St. Marks Formations ............................................................. 51
Bruce Creek Limestone ........... .......................... 51
Clayey Dolosilt ......................................................................................................... 52
Intracoastal Formation ............................................................................................. 52
Chipola Formation ................................................................................................... 53
Jackson Bluff Formation ..................................... 55
Massive Clays and Clayey Sands ......................................................................... 56
Graded Quartz Sands ............................................................................................. 56
Quartz Sand Residuum and Soil Zone .................................................................. 56
D isc u ss io n ................................................................... ....................................... .......... 56
Geologic History of the Apalachicola Embayment Region ..... ....................59
Preliminary Structural Mapping ......................................... 59
Literature Review ......... . .. ........................ 59
Sequenlial Trends from the pre-Jurassic to the Recent ............................................ 62
Structural History of the Apalachicola Embayment ......... ........................................ 67
Tertiary Structural Movements ....................................................................................... 68
C o nclusio ns ............................................................................................... .......................... 70
R efe re nces .................................................................... ... .............................................. 73
Appendiices
Appendix I. Diatoms From The Pleistocene Clay Beds ............................................ 81
Appendix II. X-ray Data Table ................................................................................... 96
Appendix Ill. Columnar Sections of Core Holes ............................. 105








LIST OF FIGURES


Page
Area of Study ............................................... 4
Location of Stratigraphic Core Tests In the Vicinity of the Study Area ............... 5
G eo logic S tructures................................................................................................... . 8
Generalized North-South Geologic Cross Seclion ............................................... 11
Dolosilt. Algar Bed, Bruce Creek Limestone from Core W-14890, and Algal Bed,
Bruce Creek Limestone from Core W-14844...................................................... 18
Top of Bruce Creek Umestone .............................................................................. 19
Intracoastal Formation from Core W-8873, and Four-Mile Village Member of
Intracoastal Form ation ......................................................................................... . 22
Thickness of Intracoastal Formation ..................................................................... 25
Top of Intracoastal Formation ........................................................................... 26
Top of Jackson Bluff Formation type sediments ............................ 34
Bedded quartz sands from Core W-14925, and Jackson Bluff Formation Shell Bed
from C ore W -1 4993 ............................................................................................. .3 6
Location of Geologic Cross Sections ....................................................................... 41
G eologic Cross Section A-A ................................................................................... 42
Geologic Cross Section B-B .................................... 43
Geologic Cross Section C-C' and D-D' .......... ................................................ 44
Geologic Cross Section E-E' and F-F .................................. 45
Geologic Cross Section G-G' and H-H ....................................... 46
Geologic Cross Section I-I' and J-J' ...................................................................... 47
Generalized Palsoenviron mental Trend .................................................................. 54
Generalized Paleogeographlic Trend, Eocene-Pleislocene .......................................... 58
A xis of "Low A rea" ............................................................................................... . 61
Sequential Plots of the AxIs of the Embayment ........................................................... 64
Simplified Structural History of the Apalachicola Embayment ............................... 69
Well Cuttings and Cores From Which Diatoms Were Found in the Pleistocene Clay
B ed s ................... ... ............................. ...... ...... ........................ 8 3


Number of Cores and Cuttings Sampled for X-ray Analyses ........ 97 W-6599, Jackson Bluff Core ............................ 108


Rock Bluff #1 Core ........................... 109
Alum Bluff # 1 Core ....................................................... 110
Wall #1 Core .......................... 111
CH-2 Core.............................. 112
St. George Island # 1 Core ........................................... 113
Alum Bluff # 2 Core ....................................................... 114
R yan # 1 C ore ................................................................ 1 15
Fenton Jones #1 Core .......................... 116
Bayview #1 Core ............................ 117
Mack #1 Core .............._ ......... ............. 118
Price #1 Core ........................................... 119
B ruce # 1 C ore .............................................................. 120
C offeen # 1 C ore .......................................................... 121
Intracoastal # 1 Core.................................... ........... 122
Sam #1 Core .................................. 123
Lalonde # 1 C ore ............................. ........................ 124
Ten Mile Creek #1 Core ............................................. 125
St. Joe # 1 Core .................. ............. ....................... 126
Schm idt # 12 Core ....................................................... 127
Schm idt # 13 Core ....................................................... 128
Mejefle #1 Core ........................................ 129
Williams Bay #1 Core ....................1..... 30
O tter C reek # 1 Core ................................................... 131
Warmouth Pond #1 Core ........................................... 132


25 Location and "W" 26 Columnar Section,


Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar Columnar


Section, W-661 1 Section. W-6901, Section, W-7457, Section, W-7524, Section, W-7574, Section, W-7616, section, W-8355, Section, W-8477, Section, W-8478, Section, W-8587, Section, W-8591. Section, W-8592, Section, W-8865, Section, W-8873, Secti6n, W-8876, Section, W-8877. Section, W-1 1270 Section, W-12051 Section, W-13617 Section. W-1 3622 Section, W-13965 Section, W- 14077 Section, W-14101 Section, W-14108


) .)


|








Columnar Columnar Columnar Columnar Columnar Columnar Columnar
Colu mnar Columnar
Columnar Columnar Columnar Columnar Columnar


Section, Section,
Section, Section, Section, Section, Section, Section, Section, Section, Seclion, Section, SecUon, Section,


W-14125, W-14704, W-14719, W-14746, W-14781, W-14799, W-14844, W-14876, W-14890, W-14906, W-14925, W-14969, W-14993, W-14996,


Bee Bay #1 Core .............................. 133
Luke Ford Creek #1 Core .......................................... 134
Indian Swamp #1 Core .... .................... 135
Depot Creek #1 Core ................................................. 136
Tates Hell #1 Core ........................ ., 137
Tates Hell # 2 Core ..................................................... 138
Tates Hell # 3 Core .................................................... 139
Crooked River #1 Core ............................................. 140
Tates Hell # 4 Core .................................................... 141
New River # 1 Core ..................................................... 142
Dead End #1 Core ................................................... 143
Gregory Mill Creek #1 Core ....................................... 144
Jackson Camp #1 Core .......................................... 145
Queens Bay #1 Core .......................... 146


LIST OF TABLES

Metric conversion factors for terms used in this report .................................................... 3
Partial list of Planktonic Foraminifera Identified from the Intracoastal Formation ..... 27 Partial list of Calcareous Nannofossils Identified from the Intracoastal Formation ....... 28 Partial list of Benthic Foraminifera Identified from the Intracoastal Formation ........ 29 Partial list of Diatoms Identified from the shallow clay beds within the undifferentiated sands and clays unit .................................................................................................. 40
Formation abbreviations from geologic cross sections A-A' to J-J' ......................... 40
Names used to describe the structural "low" feature near the Big Bend of Florida.... 60

UST OF PLATES

Diatoms Plate 1 .............................................................................................................. 85
Diatoms Plate 2 ........................ .............. ................................... .................. 87
Diatoms Plate 3 ............................................................................................................... 8
Diatoms Plate 4 ................................................................................................... 91
Diatoms Plate 5 ........................................................................................................ 93
Diatoms Plate 6 .............................................................................................................. 95











ABSTRACT


Neogene units lie near the surface in the Florida panhandle in a narrow band extending from 20 miles west of Tallahassee, Leon County, northwest to Oak Grove in north-central Okaloosa County. These sediments are primarily clayey, sandy (quartz), shell beds exposed along a number of stream or river bluffs.
Downdip towards the Gulf of Mexico these units thicken and change in lithologic character. Although subsurface units, these contemporaneous lithologic packages can be defined and mapped throughout the region using stratigraphic core tests, water-well cuttings, and geophysical well logs. The Bruce Creek Limestone and Intracoastal Formation are two units, predominantly subsurface, mapped from this area. It is also noted that the Chipola and Jackson Bluff formations are younger downdip in the subsurface than where they are exposed updip. Pleistocene quartz sands, gravels, and massive silty clay beds are mapped in Gulf, Franklin, and southern Liberty counties. These units were deposited in brackish and fluvial environments as the Apalachicola delta system advanced to the south.
The Neogene and Pleistocene sequence of sediments thickens and dips along a gently plunging axis that descends gulfward through central Gulf County. This thickened sequence of sediments is called the Apalachicola Embayment.
The lithologic and faunal characteristics of the formations, from the Upper Eocene to the Pleistocene are, summarized. This information is then used to suggest paleoenvironments for the various units. A generalized paleoenvironmental sequence is postulated from the mid-Tertiary to Recent.
Differing opinions on the nature and origin of the Apalachicola Embayment have been expressed by numerous geologists. By incorporating interpretations from the Neogene (this paper) with sequential structural contour maps from the Upper Cretaceous to the Lower Micoene (unpublished maps by May and Schmidt, 1974), and Jurassic mapping by Pontigo (1982), with the large volume of published literature on the area, a geologic history has been synthesized.
The low feature (embayment) resulted from a graben which had its origin in Triassic to Early Jurassic time. This graben slowly filled with sediments until it ceased to exist as an embayment at the end of the Early Cretaceous. From Early Cretaceous through Early Eocene a "low" or depression occurred east of the Jurassic axis. During Early through latest Eocene the axis of this "low" shifted to the northwest until the Oligocene, when it was repositioned once again over the Jurassic axis. This Late Cretaceous-Tertiary feature is considered to be due to slow deposition in a current-swept strait similar to the present Florida Straits. During the Early







and Middle Miocene, the strait apparently began to fill in as carbonates from the Florida platform on the southeast infringed on the shallow channel, and clastics from the northwest spilled over onto the shallow shelf. From the Late Miocene to Pleistocene the strait completely filled and the prograding coastal plain migrated over the area. The feature does not currently exist as a topographic low since the Apalachicola River Delta has prograded over the area.









ACKNOW LE DGEM ENTS


I would like to express my sincere gratitude to several people who offered helpful suggestions and assistance throughout the course of this research,
Assistance in microfauna identification and interpretation was graciously provided by Ronald W. Hoenstine and Bill Miller, who discussed the diatom data; and Sharon Boiling, Murlene Clark, and Richard Hummell, who identified planktonic and benthic foraminifera.
X-ray diff ractograms were run by Jon Arthur, Sharon Boiling, and Adel Dabous. Drafting and photographic reductions were prepared by Pauline Hurst, Jim Jones, and Simmie Murphy. A special thanks goes to Julia Jones and Josie Smith for typing and assisting with the manuscript.
Thanks go to several colleagues who offered numerous stimulating discussions on stratigraphic correlations and paleogeography. They include Paul Huddlestun, Muriel Hunter, Tom Kwader, John Meeder, Phil Pontigo, Tom Scott, Richard Strom, Sam Upchurch, and Jeff Wagner. I would also like to express my gratitude to Rami; Wright for his valuable criticism and advice during the writing of the manuscript. Bill Burnett, Ken Osmond, Bill Parker, and Sherwood Wise, al with the Florida State University, also reviewed the text and offered helpful suggestions.
I also want to extend my appreciation to C. W. Hendry, Jr., of the Florida Department of Natural Resources, Division of Resource Management, who supported and encouraged the completion of this project.










NEOGENE STRATIGRAPHY AND GEOLOGIC HISTORY OF THE
APALACHICOLA EMBAYMENT, FLORIDA
By
Walter Schmidt
INTRODUCTION
The geology of the Florida panhandle has been as thoroughly studied by geologists as any comparable area in the state of Florida. No less than eight of its counties have been singled out for study by the Florida Bureau of Geology in its Bulletin Series. Five of the ejght (Jefferson, Leon, Jackson, Holmes, and Washington) are located where the older formations approach the land surface (updip) and have significant surface relief and available rock outcrops on which to base studies. Two of the counties (Santa Rosa and Escambia) are located in the vicinity of active oil fieIds, and as a result, a large amount of subsurface data in the form of well cuttings and geophysical well logs is available. The most recently completed county study (Bay) was prepared as a direct result of the first stages of research towards the present regional study.
The Miocene and Pliocene deposits that crop out in the panhandle of Florida have been studied since the late 1800's. They have frequently been described and have received the greatest attention from paleontologists who have been attracted to their well-preserved mollusk and foraminiferal assemblages.
Burns (1889) and Langdon (1889) were the first to record descriptions of the shell beds along the Chipola and Apalachicola rivers, respectively. Since these initial reports, other authors have described or named these units primarily based on their fossil assemblages. Stratigraphic correlations, however, have been questionable due to poor, sporadic exposures and lithologic heterogeneity of the various deposits. For a history of the nomencratural changes leading up to modern usage see Schmidt and Clark (1980).
The Miocene-Pliocene deposits are exposed in a narrow band which extends from 20 miles west of Tallahassee, Leon County, Florida, west-northwest to DeFuniak Springs, Walton County, Florida, a distance of about 90 miles. South of these exposures, toward the Gulf of Mexico, stratigraphic interpretations have been based on relatively few sets of well cuttings. It is no surprise that the coastal stratigraphy has never been well understood since very few reliable data points exist on which correlations may be based. Indeed, lithologic complexity is such that stratigraphic problems of the outcropping units to the north remain unsolved. This thickened sedimentary sequence downdip of the exposed region occurs mainly in the subsurface and is known as the Apalachicola Embayment.
Many geologists in the past, when assigning formation names from





BUREAU OF GEOLOGY


well cuttings in the Apalachicola Embayment, would use the nearby outcrop formational descriptions. This seemed logical since the subsurface unit penetrated by the well would probably be exposed updip to the north. Thus, formation names from exposed units in the north were applied to the downdip rocks even though it was clear that these subsurface sediments were dissimilar from the described, exposed material.
In the late-1 9601s, the Florida Bureau of Geology undertook a stratigraphic coring program in Walton County. Twenty-five cores were drilled from the surface down to the Oligocene or Eocene age sediments. The cores were well-spaced throughout the county and extended from the Florida-Alabama border to the coastal margin. The wide arear extent of core control offered a unique opportunity to describe and map the lithologic units throughout the area of near-surface exposure as well as downdip where the Neogene units are entirely subsurface. Hendry (1972) and Huddlestun (1976a) utilized these data to map formation and chronostratigraphic units throughout Walton County.
It became readily apparent to them that the downdip Neogene sequence of sediments is an expanded section, thicker than the contemporaneous updip units. These deposits also are more calcareous, trending towards sandy (quartz) limestones and sandy (quartz) biocalcarenites, whereas the updip units are dominantly argillaceous, sandy (quartz), shell beds.This calcareous wedge of sediments contains, along with common macrofossils, a prolific and diverse microfauna, dominated by benthic and planktonic foraminifera and calcareous nannofossils.
Subsequent to the Walton County study, the downdip Neogene stratigraphic mapping program was extended eastward into Bay County (Schmidt and Clark, 1980) and westward into Okaloosa County (Clark and Schmidt, 1982). Although relying primarily on water-well cuttings, the stratigraphic sequence was definable and mappable, both east-west and north-south (updip/downdip).
Recently, the Florida Bureau of Geology drilled 20 stratigraphic core tests in Bay, Calhoun, Gulf, Franklin, and Liberty counties. These additional data enables this regional mapping project to be extended to the eastern terminus of these Neogene units.
This combined core coverage (66 cores in all, in or near the Apalachicola Embayment), along with hundreds of sets of water-well cuttings and geophysical well logs, has allowed the author to make regional correlations and interpretations regarding the Neogene and Quaternary sediments which fill in the Apalachicola Embayment (Figs. 1 and 2).

METRIC CONVERSION FACTORS
In order to prevent much awkward duplication of parenthetical conversion of units in the text of reports, the Florida Bureau of Geology has adopted the practice of inserting a tabular listing of conversion factors. For the use of those readers who may prefer to use metric units rather than the customary U.S. units, the conversion factors for terms used in this report are given in Table 1.





BULLETIN NO. 58


TABLE 1.-Metric conversion factors for terms used In this report.
MULTIPLY BY TO OBTAIN acres 0.4047 hectares acres 4047.0 sq. meters cubic yards 0.7646 cu. meters feet 0,3048 meters inches 2.540 centimeters inches 0.0254 meters mires 1.609 kilometers sq. miles 2.590 sq. kilometers
PREVIOUS INVESTIGATIONS
Much of the previously applied nomenclature from the Miocene and Pliocene of the Florida panhandle is confusing and commonly misleading. Published stratigraphic names have included: deposits, beds, members, formations, groups, marls, b4ofacies, magnafacies, parvafacies, zones, and stages. This confusing situation was largely due to inadequate knowledge of the stratigraphic and paleoenvironmenta framework of the deposits. Much of the confusion resulted from the fact that there was no detailed mapping of these sediments. Most comprehensive descriptions of "facies" were confined to the sediments in the immediate vicinity of the various type localities. In addition to the lack of detailed studies, the inadvisable procedure of using the term facies was used to refer to divisions which are in actuality faunizones.
The nomenclatural history of these exposed deposits is too lengthy to include here and the reader is directed to Schmidt and Clark (1980) for the history of the Alum Bluff Stage (Middle Miocene) and the history of the Choctawhatchee Stage (Upper Miocene).
Studies dealing with the shallow stratigraphy (within about 600 feet of the surface) in the Apalachicola Embayment area are far less abundant and will be summarized below.
Sellards and Gunter (1918) published two geologic reports, one on the area between the Apalachicola and Ochlockonee rivers and a second on the area between the Choctawhatchee and Apalachicola rivers. Their reports described various geologic sections and they attempted to make some downdip interpretations.
Cole (1938) reported on the stratigraphy and micropaleontology of a well in Gulf County at Port St. Joe. His report identified species of foraminifera from various depths from the well cuttings, and his stratigraphic names conformed to prior usage from updip exposed sections. The next year two Masters Theses were completed under Dr. Cole's supervision. The first (Bernhagen, 1939) discussed the stratigraphy and micropaleontology of a well in Calhoun County (W-7 of the Florida Bureau of Geology's collection); and the second (Hobbs, 1939) discussed the stratigraphy and micropaleontology of two wells in Bay County (W- 140, W-151) and one well in Franklin County (W-228). They also identified species of foraminifera.




































Figure 1. Area of Study.












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BUREAU OF GEOLOGY


Schnable and Goodell (1968) published an excellent report on the Pleistocene and Recent Stratlgraphy, Evolution, and Development of the Apa/achicola Coast, Florida. Although their report emphasizes coastal morphology, they do include some shallow geologic cross sections (generally within 100 feet of the surface) and a "surface geology" map.
Huddlestun (1976a) compared the updip and downdip sections in Walton County, which is located on the western-most fringe of the Apalachicola Embayment. Cameron and Mory (1977) reported on the mineral resources of Bradwell Bay, a small wilderness area in Wakulla County on the eastern edge of the embayment. Also in 1977, Trapp discussed an exploratory water well from St. George Island in Franklin County. Schmidt (1978,1979) published two environmental geology maps that cover the area on a 1:250,000 scale.
Schmidt and Clark (1980) published a geologic bulletin on Bay County, Florida, located on the western side of the embayment. Patterson, Schmidt and Crandell (1982) wrote on the geology and mineral resource potential of a part of the Apalachicola National Forest in southern Liberty County.
Other geologic reports on the area include heavy mineral identification of coastal and river deposits and sand-size analyses of present coastal features and surficial deposits inland. One study by Tanner (1966) commented on the Tertiary history of the Apalachicola River Region, as inferred from physiographic and terrace evidence.

DATA COLLECTION AND MODE OF ANALYSIS
Because of the gentle dip (less than 0.5 degree) of the strata and the thin veneer of Pleistocene terrace deposits throughout the coastal regions of the Apalachicola Embayment, there are very few locations where rock unts crop out at the surface. This regional study is, therefore, based mainly on subsurface information consisting of cuttings from water and oil test wells, stratigraphic core tests, drillers logs, and down-hole geophysical information (primarily gamma logs).
Surface exposures are usually found along the northern limits of the Neogene sediments associated with river bluffs or stream cuts. The Ochlockonee, Apalachicola, Chipola, Choctawhatchee, and Shoal rivers, along with many of their tributaries, have cut numerous steep bluffs into these clayey, sandy, shell beds. It is these surface exposures that have been extensively described and cited in the geologic literature. Most of these locations, in addition to other exposures such as road-cuts and borrow pits, have been visited and sampled so that they can be tied-in with the downdip subsurface data.
Water and oil test well cuttings are stored by the Florida Bureau of Geology in Tallahassee, Florida. Hundreds of sets of cuttings from the study area are available. Most have samples at 1 0-foot intervals; however, irregular intervals are not uncommon. The cuttings were examined with a binocular microscope, and such parameters as major rock type, color, estimated porosity, grain type, grain size, induration, cement type, sedimentary structures, accessory minerals, and fossils were described.





BULLETIN NO. 58


Stratigraphic core tests have been drilled throughout the area by the Florida Bureau of Geology. Sixty-six cores have been recovered in the vicinity of the embayment area, 26 of which are within the area of Neogene sediment thickening. All cores were drilled with a Failing 1500 truckmounted core rig and are generally from 200 to 500-feet deep. Cores are 14 inches in diameter. Recovery varied from 100 percent to app roximately 50 percent in the cavernous limestones. All but seven of the cores in Bay, Calhoun, Gulf, Liberty, and Franklin counties were drilled for this regional study. Drilling site locations were selected after assessing existing geologic data along with stratigraphic trends.
Geophysical well logs were run in most of the core holes by the Florida Bureau of Geology and/or the Northwest Florida Water Management District. Other geophysical logs are on file at both these agencies from scattered water wells located throughout the district. Although individual wells or core holes may have had a complete suite of logs run on them (including natural gamma, neutron, gamma-gamma, electric, caliper, and others), theone which seemed most useful for stratigraphic correlation was the natural gamma log. This is also the most commonly available well log. The natural gamma logs respond to natural gamma radiation (U, Th, K) present within the sediments. This is often associated with the mineral components present within the various rock units. The specific reason for the various activity levels present within the Neogene sequence of rocks in the Florida panhandle has been investigated by Kwader (1982). These logs proved useful in estimating the depth and thickness of the lithologic units especially in areas where cuttings or core control was sparse.
Information from cores was relied on most heavily in stratigraphic interpretations because cores offer a higher level of confidence for depth correlation. Upon completion of the lithologic descriptions of the cores and cuttings, formation contacts were picked and the lithologic package that made up each unit was defined. In addition, the cores were sampled for mineralogical and micropaleontological information. Samples were collected from the cores from major lithologic units. An x-ray diffraction study was carried out on these samples to estimate the dominant minerals present. Samples were also collected for smear slide analysis for microfossil content. Calcareous nannofossils and diatoms were found to be present in different formational units. This information, along with foraminiferal data from Walton, Bay, and Gulf counties, was used to aid both in the estimation of the time of deposition of the formations and in constructing biostratigraphic correlations.
Thin sections were prepared from selected samples to aid in rock descriptions and to assist in the assessment of depositional environment.

GEOLOGIC STRUCTURE
The Apalachicola Embayment (Pressler, 1947) is the dominant geologic structure Influencing the sediments in the central part of the Florida panhandle. The shallow deposits are gently down-warped about an axis that plunges to the south-southwest (Fig. 3).








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BULLETIN NO. 58


A summary of the literature about this feature is given by Patterson and Herrick (1971) and May (1977). The feature was first named the Chattahoochee Embayment (Johnson, 1891), but has been referred to most commonly as the Apalachicola Embayment and will be recognized as such here. This embayment, which is a relatively shallow basin between the Ocala and Chattahoochee highs, is narrowest in the northeast and opens to the south and southwest.
It has been estimated that the deeper parts of the embayment, together with adjacent portions of the Gulf Basin, cover an area of approximately 30,000 square miles (Pressler, 1947). The magnitude of the basin appears to increase with depth, which would indicate a long continued development. However, the geologic history of the embayment appears to be a complicated sequence of events.
The near-surface Quaternary and Neogene deposits are gently downwarped, whereas the older Paleogene and Mesozoic rocks are downwarped to a progressively greater extent. Correspondingly, the older strata are thicker (Murray, 1961). As the embayment deepens toward the Gulf, the sedimentary fill attains a thickness of nearly 15,000 feet. The sediments, which range in age from Triassic to Recent (Applegate et al, 1978; Schmidt and Clark, 1980) are very similar to those of southern Mississippi and Alabama, except that the Tertiary formations become progressively more calcareous to the east.
The sedimentary fill rests on metamorphic rocks of probable Paleozoic Age (Applegate et a/., 1978). On the top of the Paleozoics, the Mesozoic deposits reach a thickness of over 10,000 feet, while the Cenozoic sediments are generally less than 3,000 feet in thickness.
To the north and northwest of this embayment is a positive structural feature caned the Chattahoochee Anticline (Veach, 1911; Pur and Vernon, 1964), a broad flexure mapped in the tri-state area of Alabama, Flodda, and Georgia. This "high" brings Oligocene and Eocene rocks to the surface, while the younger units either pinch out or are truncated against the high. The feature is an elongated anticline that trends northeastsouthwest, crests in Jackson County, and plunges to the southwest. It is this southern extension of the Chattahoochee Anticline that separates the Apalachicola Embayment from the more regionally extensive Gulf of Mexico Sedimentary Basin to the west. This transition zone between two negative features occurs in the Okaloosa County area (Clark and Schmidt, 1982) and corresponds to the western limit of the coastal Neogene carbonates.
To the east of the Apalachicola Embayment is another relatively high feature, the Ocala Arch. As the shallow sediments trend from the central part of the embayment towards the Ocala Arch, they again truncate at the surface as the older formations approach the more shalJow depths. This truncation, which marks the eastern extent of the shallow Neogene units in the embayment, occurs in western Wakulla, eastern Liberty, and eastern Franklin counties.





BUREAU OF GEOLOGY


The southern extent of the embayment is not studied here due to the lack of off-shore data. However, it is postulated to continue to dip and thicken gradually to the south-southwest.

STRATIGRAPHY

INTRODUCTION
The downdip, predominantly subsurface stratigraphy of the Neogene sediments in the Apalachicola Embayment has never been well understood. As the rock units trend into the deeper parts of the embayment away from the two structural highs (the Ocala and Chattahoochee) their lithologic character changes. This downdip relationship was first recognized in Walton County by Hendry (1972) and Huddleston (1976a) and subsequently described and mapped in Bay (Schmidt and Clark, 1980) and Okaloosa counties (Clark and Schmidt, 1982), the latter of which is located in the western transition zone between the Gulf of Mexico Basin sedimentary infill and the more local Apalachicola Embayment sediments.
The present study maps and defines these Neogene units from Okaloosa County on the west to Wakulla and Leon counties on the east.
The Paleogene formations down to the Upper Eocene Ocala Group limestones are also identified in some cores and cuttings. These correlations appear on geologic cross sections shown later as Figures 13-18, although these older units were not mapped or described in detail because less data is available from these deeper horizons. A generalized, north-south, geologic cross section is shown in Figure 4, to demonstrate the updip-downdip stratigraphic relationships.

LATE PALEOGENE UNITS

Ocala Group
Upper Eocene (Jackson Stage) strata in Florida were divided by Puri (1957), on the basis of a detailed, biostratigraphic study, into three formations comprising the Ocala Group; they are, in ascending order, the Inglis, the Williston, and the Crystal River. The literature pertaining to the nomenclature of the Ocala Group leading up to the current usage is extensive and has been adequately reviewed in previous publications; it will not be repeated here. Summaries are contained in Vernon (1942), Cooke (1945), Pur (1957), and Puri and Vernon (1964).
In the Florida panhandle, the Ocala crops out along the Alabama state line (Figures 3 and 4) in Jackson and Holmes counties. This unit is brought to the surface as a result of the Chattahoochee Anticline in which older, deeper formations approach the ground surface. The Ocala in this area has been described both from surface exposures (Vernon, 1942; Moore, 1955; Schmidt and Coe, 1978) and downdip in core holes (Schmidt and Clark, 1980; Clark and Schmidt, 1982). In general, only two lithologic facies can be recognized. A lower facies consists of greenish-gray, glauconitic, sandy


10





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SOUTH





BUREAU OF GEOLOGY


limestone and contains a lower Jackson fauna. The upper and more typical facies is a light-yellow to white, massive, porous, often silicified, abundantly microfossilllerous limestone (packed biomicrite or packstone to wackestone).
Very few wells reach the top of the Ocala Group and even fewer penetrate the entire thickness of the Ocala. As a result only a small number of the northern cores or cuttings described for this study included any Ocala. No formations or lithofacies could be ascertained for the unit. The group was identified as a light orange to white packstone to wackestone with high porosity in which both micrite and sparry calcite are common, along with small amounts of glauconite, quartz sand, and abundant fossils. Dominant fossils include foraminifera, mollusks, echinoids, bryozoans, and corals.
Contours drawn on top of the Ocala Group in the central part of the Florida Panhandle (Toulmin, 1952; Chen, 1965; Weaver and Beck, 1977; and Gelbaum and Howell, 1979) show a distinct deflection northeastward implying that the embayment feature existed at the close of the Late Eocene Series or that subsequent downwarping has occurred. Information presented later will argue for the former.

MARIANNA AND SUWANNEE LIMESTONES
The Oligocene Series (Vicksburg Stage) in the Florida Panhandle consists of the Chickasawhay, the Marianna, and Suwannee limestones and the Bucatunna Clay. The Marianna and Suwannee limestones are exposed in Jackson, Holmes, Washington, and Walton counties, (Vernon, 1942; Moore, 1955; Reves, 1961; Yon and Hendry, 1969; Schmidt and Coe, 1978). Although the Chickasawhay Limestone was named for exposures of limestone along the Chickasawhay River in Mississippi, Marsh (1966) extended this limestone unit into the Florida Panhandle; it is not however, exposed at the surface.
In addition to these three limestone formations Cooke and Mossom (1929), and Puri and Vernon (1964) recognized an additional Oligocene formation, the Byram Formation. Later authors, however, (Moore, 1955; Vernon, 1942; and Schmidt and Coe, 1978) included the Byram with the younger Suwannee Limestone because of its lithologic similarity. Marsh (1966) did map a Bucatunna Clay Member of the Byram Formation in the subsurface of Escambia and Santa Rosa counties in western Florida. Also Clark and Schmidt (1982) were able to identify this clay member in a limited number of well cuttings in western Okaloosa County. As is the case with the older Ocala Group, the Oligocene Series limestones are only encountered in the subsurface within the present study area. These deeper horizons are penetrated rarely and only by updip (more northerly) wells.
The Bucatunna Clay and the Chickasawhay Limestone do not occur within the bounds of this study. They occur on the western flank of the Chattahoochee Anticline and are, therefore, part of the eastern edge of the sediment wedge thickening westward into the Gulf of Mexico Sedimentary Basin (Figure 3). The Marianna and Suwannee limestones are often the





BULLETIN NO. 581


deepest formations penetrated in the northern limits of this study and their lithology is briefly summarized here.
MARIANNA LIMESTONE-From the few sets of well cuttings that contain the Marianna, it can be characterized as a light gray, massive, chalky, fossiliferous, moderately to well-indurated biomicrite or wackestone. Commonly present are large foraminifera of the genera Lepidocycina. Minor accessory minerals include glauconte, quartz sand, and pyrite. One core (W-6901, Liberty County) also appeared to contain some dolomite and a trace of montmorillonite, based on x-ray diffraction analysis.
SUWANNEE LIMESTONE-The Suwannee is present as the basal unit penetrated in many cores and water wells. It consists of light gray to yellow-gray, well indurated, chalky, sucrosic, fossiliferous biomicrite to biosparite, or a packstone to wackestone. The limestone is often dolomitized and contains highly altered, recrystalized fossils. X-ray analysis identified calcite, dolomite, quartz sand, and a minor amount of clay.
The top of the Suwannee, long considered the top of the Oligocene Series (more recently the Oligocene-Miocene boundary has been placed within the overlying Chattahoochee Formation by Poag, 1972; and Huddlestun, 1976a), dips to the south-southwest towards the city of Apalachicola (Toulmin, 1952; Weaver and Beck, 1977). The Suwannee approaches the surface to the east, as the older formations onlap onto the Ocala Arch, and to the north and northwest as the older formations again onlap the Chattahoochee Anticline.
Contours drawn on top of the Suwannee Limestone show a northeast deflection similar to the trend of the underlying Ocala Group (May and Schmidt, 1974). This implies that throughout the Oligocene a southwesterly opening embayment may have existed similar to that which is postulated for the Eocene. This sequence of events wilt be expanded on in a Iater section.

NEOGENE FORMATIONS
Chattahoochee and St. Marks Formations
NOMENCLATURAL HISTORY-The Chattahoochee and St. Marks formations are two limestone units of the Lower Miocene (Tampa Stage) as defined by Pur (1953). The first to use the term Chattahoochee Formation, however, was Dail and Stan ley-Brown (1894).
It was not until Purl and Vernon (1964) published their comprehensive Summary of the Geology of Florida that the Chattahoochee and St. Marks formations were established. They included type localities for both formations but did not attempt to map their area extent. A more complete nomenclatural history of the Tampa Stage in Florida is given in Schmidt and Clark (1980, pp. 33-35).
LITHOLOGY-Uthologic units that correspond to previous descriptions of both of these formations were encountered in many cores and cuttings throughout the study area. The St. Marks occurs along the south and eastern parts of the embayment and the Chattahoochee occurs along the north and western parts of the study area. Because the underlying


13





BUREAU OF GEOLOGY


Suwannee Limestone and the overlying Bruce Creek Limestone are also both carbonates that have undergone a considerable amount of secondary alterations due primarily to groundwater, these four formations occasionally cannot be separated. This lithologic trend is shown later on the geologic cross sections (Figures 13-18).
The Chattahoochee Formation can be summarized as follows: It is generally a very pale orange to very light gray, moderately to well-indurated, dolomitic, calcilutitic, mudstone to fossiliferous micrite. Quartz sand is often present, as are minor amounts of phosphorite. Some zones can be described as a fine-grained, sucrosic dolomite.
This wide range of lithotypes has resulted in the Chattahoochee/ Suwannee formations and the Chattahoochee/St. Marks formations sometimes being lumped into one undifferentiated unit (see Appendix 11l).
The St. Marks is a very pale orange to light gray to white, moderately to well-indurated, fossiliferous, dolomitic, calcarenitic limestone, or a packed biomicrite to a wackestone. Quartz sand is common, as are occasional greenish, clay blebs. Fossils are common, generally as molds and casts. The St. Marks is often indistinguishable from the overlying, younger Bruce Creek Limestone. These two formations are probably laterally equivalent in the deeper parts of the embayment (Figure 15).
THICKNESS AND DISTRIBUTION-The type locality of the St. Marks Formation is located about two miles south of Crawfordville in Wakulla County, along the eastern edge of the Neogene embayment as defined in this study.
The St. Marks is exposed throughout eastern Wakulla County and is generally associated with karst features such as sinks and springs. The western-most exposures are common along the Sopchoppy River where rock outcrops are found intermittently along the banks of the southern half of the river. (This limestone was recently informally named the Sopchoppy Limestone by Huddlestun and Hunter, 1980).
The thickness of the St. Marks ranges from zero east of Wakulla County, where it rests on karst formed on the Suwannee Limestone, to over 200 feet near the axis of the Apalachicola Embayment in the Gulf County area (Cameron and Mory, 1977). It dips towards the southwest from the outcrop area. Elevations range from 10-20 feet above sea level in Wakulla County to deeper than 600 feet below sea level in Gulf County.
Near the axis of the embayment the limestone of the St. Marks becomes indistinguishable from the younger Bruce Creek Limestone that has been described on the western flanks of the embayment. For this reason, a structural map of the St. Marks could not be constructed.
The type locality of the Chattahoochee Formation is at the Jim Woodruff Dam on the Apalachicola River. Here the Chattahoochee has an elevation of 169 feet (Tampa Formation of Moore, 1955). To the south the unit dips into the embayment and drops below present sea level in Washington, Calhoun, and Liberty counties (Moore, 1955; Schmidt and Coe, 1978). To the north the unit pinches out as the older Suwannee


14





BULLETIN NO. 58


Limestone nears the land surface approaching the axis of the Chattahoochee Anticline (Figure 4).
Downdip in Bay, Gulf, and southern Liberty counties the Chattahoochee Formation becomes locally indistinguishable from the St. Marks and Bruce Creek limestones (Schmidt and Clark, 1980). As a result, a structural map could not be constructed for the Chattahoochee.
PALEONTOLOGY AND AGE-Since Puri and Vernon (1964) defined the Tampa Stage, Poag (1972) and Huddlestun (1976 a, b) raised the Oligocoene-Miocene boundary into the Chattahoochee Formation based on planktonic foraminifera. The St. Marks, however, is still considered Lower Miocene.
The fossils described from the Tampa Stage sediments (Chattahoochee and St. Marks formations) are mostly found within the St. Marks; the Chattahoochee has relatively few fossil remains. Mansfield (1937) described the mollusks and Pur (1953) described the foraminifera and ostracoda.

Bruce Creek Limestone
NOMENCLATURAL HISTORY-The Bruce Creek Limestone was named by Huddlestun (1 976a). He included it in a group of three subsurface formations that he proposed from the southern half of Walton County. The three formations, of which the Bruce Creek Limestone was the basal formation, comprised his Coastal Group. Huddlestun explained that this group was a new name for Alum Bluff equivalent carbonate units that underlie the coastal area of Walton County and vicinity.
Huddlestun's (1976a) descripton of the Coastal Group states there are two lithologic types within the group. The first type is usually a welr-indu rated, coarsely calcarenitic, light colored, poorly microfossiliferous limestone (the Bruce Creek Limestone); and the second type is a younger (and therefore overlying), unconsolidated to moderately indurated, extremely microfossiliferous, less coarsely calcarenitic, argillaceous, glauconitic, and phosphatic limestone (his St. Joe and Intracoastal limestones).
Lithologies from the Bruce Creek Limestone have been referred to previously as a limestone facies of the Chipola Formation (Gardner, 1926; Cooke and Mossom, 1929). Limestones of similar description have been reported by Sellards and Gunter (1918); Cooke and Mossom (1929), and Vernon (1942) in southwestern Washington County near the Choctawhatchee River and in Walton County in White Creek.
The type locality of the Bruce Creek Limestone, as informally designated by Huddlestun (1976a), is several hundred feet downstream from the county road bridge over Bruce Creek in T1 N, R18W, north-half of section 2, Walton County, Florida. At this location, one-to-two feet of pale bluish-green, unconsolidated, soft, slightly argillaceous, sandy, slightly macrofossiliferous limestone is exposed. It is primarily a subsurface unit with the type loca fty being the only known exposure.





BUREAU OF GEOLOGY


More recently, the Bruce Creek Limestone has been mapped in the subsurface in Bay County east of the type area (Schmidt and Clark, 1980) and in Okaloosa County west of the type area (Clark and Schmidt, 1982). Further mapping of this formation (Schmidt et a/., 1982; and Boiling, 1982) has shown the unit to be a wedge-shaped deposit and that its eastern extent coincides with the eastern boundary of the Neogene Apalachicola Embayment. As stated in a prior section, the lithology of the Bruce Creek becomes indistinguishable from that of the St. Marks Formation on the eastern flank of the embayment.
LITHO LOGY-The Bruce Creek Limestone has proven to be an easily recognizable stratigraphic unit and a useful marker, Samples from the type outcrop on Bruce Creek In Walton County can be correlated lithologically and stratigraphically with well cuttings and cores from areas east and west of the type area.
Towards the west in Okaloosa County and vicinity, the Bruce Creek Limestone is a white to light gray, moderately indurated, calcarenitic limestone. It ranges from a wackestone to a packstone or a sparse to packed biomicrite. The Bruce Creek contains planktonic and benthic foraminifera, echinoid fragments, ostracods, and mollusks. Fossils are generally preserved as molds which can be observed from cores throughout the unit. Common accessory minerals include quartz sand, pyrite, phosphorite, mica, clay, and glauconite. Quartz sand ranges from one to 20 percent with higher values coinciding with the northern limits of the formation. Other accessory minerals occur in quantities less than one percent. The Bruce Creek becomes dolomitic towards the south and west.
From the type area eastward towards the Apalachicola Embayment, the Bruce Creek is a white to light yellow-gray, moderately indurated, calcarenitic limestone. The Bruce Creek is dominated by macrofossil molds; but microfossils are also present, including planktonic and benthic foraminifera, ostracods, bryozoans, and calcareous nannofossils. Accessory minerals are about the same in the west with the addition of some heavy minerals. The limestone seems to become less indurated towards the east, although in the area of Gulf County the unit is often highly indurated and dolomitic (often sucrosic).
X-ray analyses of selected core samples showed the Bruce Creek to be predominantly calcite with a trace of montmorillonite in the Walton County area. To the east in Bay, Calhoun, Gulf, Liberty, and Franklin counties, calcite is still dominant; however, dolomite, quartz and montmorillonite are also common. Palygorskite and aragonite were also present in minor amounts (see Appendix II). It should be noted here that many accessory minerals observed under the microscope are not recorded by the x-ray diffractometer because they occur in small amounts (less than one percent). For this reason both the observed accessory minerals and the x-ray results will be discussed.
OVERLYING AND UNDERLYING UNITS-The Bruce Creek Limestone ovedles the Chickasawhay Limestone near the western limit of the unit in Okaloosa and Santa Rosa counties (Clark and Schmidt, 1982). In


16





BULLETIN NO. 58


Walton, Bay, Calhoun, and Gulf counties it overlies the Chattahoochee Limestone or a Chattahoochee/Suwannee undifferentiated unit. In Liberty and Franklin counties, the St. Marks Formation underlies the Bruce Creek, although the Bruce Creek and St. Marks become difficult to distinguish from each other east of the Apalachicola River.
In general, the Chickasawhay and Suwannee Limestone are well indurated, sucrosic dolomites, commonly grayish-orange in color, whereas the Bruce Creek is a white to gray, calcarentic limestone and is much less dolomitized. Quartz sand is rare in the Chickasawhay and Suwannee and common in the Bruce Creek.
In central Okaloosa County, the Bruce Creek occurs as a tongue extending northward from the coastal area into the sediments of the Alum Bluff Group. The Bruce Creek, therefore, overlies and underlies this unit. The Alum Bluff Group consists of quartz sands, clayey sands, and motlusk shell beds.
The undifferentiated Alum Bluff Group overlies the Bruce Creek Limestone in the northwestern comer of the study area in Santa Rosa, Okaloosa, and Walton counties. The Intracoastal Formation overlies the Bruce Creek throughout most of the embayment area. The Intracoastal is easily distinguished from the Bruce Creek by the olive-green, poorly indurated, foraminiferal, biocalcarenitic nature of the Intracoastal when compared to the white to very pale orange, well to moderately indurated, granular limestone of the Bruce Creek. The Intracoastal Formation also contains greater quantities of quartz sand, phosphorite, and clay than does the Bruce Creek.
In the central part of the Apalachicola Embayment, the basal part of the Intracoastal consIsts of a massive, clayey, dolosilt (Figure 5, core 1). This bed will be discussed with the Intracoastal Formation in a later section.
THICKNESS AND DISTRIBUTION-The Bruce Creek Limestone is a wedge-shaped deposit that thins to the north and thickens to the south (see geologic cross sections, Figures 13-18). It pinches out in north-central Okaloosa and Walton counties (Clark and Schmidt, 1982; and Huddlestun, 1976a), in northern Bay County (Schmidt and Clark, 1980), in central Calhoun and Liberty counties, and western Wakulla County (Figure 6). The regional trend throughout the study area is a west-northwest to east southeast strike, although on the eastern flank of the embayment it curves to a north-south strike (Figure 6).
The highest elevations occur in Walton County where it lies more than 50 feet above sea level. The top of the formation is deepest, just over 600 feet below sea level, in southwestern Okaloosa County. The regional dip for the unit is to the south-southwest at a gentle dip of approximately 12 feet per mile (0. 13 degrees). The Bruce Creek Limestone has been estimated to be up to 86-feet thick in coastal Walton County (Huddleston, 1 976a) and about 300-feet thick towards the axis of the embayment in southwest Bay County (Schmidt and Clark, 1980). Because very few wells penetrate the entire thickness of the Bruce Creek along the coast, an Isopach map of the limestone was not constructed.


17






BUREAU OF GEOLOGY


Figure 5.


CORE 1: Dolosilt, algal bed; Bruce Creek Limestone from Core W-14890, 176 feet to 188 feet. CORE 2: Algal bed; Bruce Creek Limestone from Core W-14844, 55 feet to approximately 74 feet. (The top of each core is towards the bottom of the page.) Core diameter is 1 N inches.


Is


w lw-w. 1 ,
1A;
ldppl















lo ..% 2_,-2-1 "
0-.L 1 -or ---z IIL I


so r






A' L r,,I



Figure 6. Top of the Bruce Creek Limestone.






BUREAU OF GEOLOGY


PALEONTOLOGY AND AGE-The Bruce Creek Limestone contains numerous fossils, mostly preserved as molds and casts of mollusk shells. In addition, both benthic and planktonic foraminifera are present, as are ostracods, bryozoans, echinoids, and algal remains. Calcareous nannofossils have been reported (Schmidt and Clark, 1980); however, due to the crystalline and moderate to well-indurated nature of the rock, their preservation is poor.
Huddlestun (1976a) dated the time of deposition of the Bruce Creek Limestone from the Watton County area as Middle Miocene, based on planktonic foraminifera identified from a clay bed within the unit. In Bay County, the fossiliferous clay unit is absent; but on the basis of the presence of some G/ob/gerinoides sp., Schmidt and Clark (1980) also concluded the unit was Middle Miocene. The same age (Middle Miocene) was also assigned to the Bruce Creek in Okaloosa County (Clark and Schmidt, 1982) and in Gulf County (Bolling, 1982) based on planktonic foraminifera.
The upper part of the Bruce Creek (a zone that varies in thickness from less than one foot to about 20 feet) consists of an algal-rich limestone, where algal oncolites are common to abundant (Figure 5, core 2). This may suggest a permanently submerged shoal environment (Logan, et a]., 1964) or at least a shallowing of water near the end of Bruce Creek deposition. The fauna preserved in the deeper limestone (deposited prior to the algal zone) seems to suggest an offshore shallow marine environment associated with a shallow carbonate platform. This may represent a slight shallowing from the marine carbonates of the warm shallow seas that existed prior to the Miocene in the Oligocene and Eocene epochs (Yon and Hendry, 1972).

Intracoastal Formation
NONMENCLATURAL HISTORY-The Intracoastal Formation was first described by Huddlestun (1 976a, b). He used the name Intracoastal Limestone to describe a "soft, sandy limestone of Pliocene age that underlies the coastal area of western Florida." His discussion pertained mostly to the Walton County area. Huddlestun placed the Intracoastal Limestone in his "Coastal Group." (For a historical account of the Coastal Group, see the history section on the Bruce Creek Limestone in this paper).
Huddlestun took the name Intracoastal from the Intracoastal Waterway #1 core (W-8873), located in Walton County, Florida, in T3S, R18W, northeast quarter of the southwest quarter of sec. 11 (Figure 40).
Schmidt and Clark (1980) expanded the definition of the Intracoastal Limestone to include lithologically Indistinquishable sediments underlying the unit described by Huddlestun and named that sediment package the Intracoastal Formation. Their mapping resulted in correlations between Bay County and Walton County. Later, Clark and Schmidt (1982) mapped the formation westward into Okaloosa County and named the Four-Mile Village Member from the middle of the formation. Their Four-Mile Village Member equates to the informal phosphatic sand unit described by Huddlestun (1976a) from Walton County.


20





BULLETIN NO. 58


Finally, Schmidt et aL (1982) reported that the Intracoastal Formation was mappable eastward to eastern-most Franklin and Liberty counties and northward to central Calhoun and Liberty counties.
LITHOLOGY-The Intracoastal Formation is an easily recognizable stratigraphic unit, with well-defined upper and lower contacts. The formation is predominantly a subsurface unit with only two known surface exposures, one in northern Bay County and another in central Franklin County. As a result, the formation descriptions and mapping have been carried out using water well cuttings, stratigraphic core tests, and geophysical well logs.
The Intracoastal lithology varies only slightly throughout its areal extent. It is a very sandy, highly microfossiliferous, poorly consolidated, argillaceous, calcarenitic limestone (Schmidt and Clark, 1980). The dominant lithologic components include microfossil material, quartz sand, clay, micrite, and phosphorite. It contains minor amounts (generally one percent or less) of glauconite, pyrite, heavy minerals, and mica. It can generally be referred to as a poorly consolidated wackestone or a packed biomicrite. Unwashed samples of the Intracoastal Formation are yellowgray when dry and dark olive-green when wet. Washed samples are buff to speckled gray in color.
X-ray analyses of selected core samples did not yield clear-cut trends in mineral constituents (Appendix II). As a result, a lithofacies plot yielded no interpretable patterns. As a general rule, calcite and quartz (sand) are the dominant minerals present. Also present, but in lesser amounts are aragonite, dolomite, montmorillonite, kaolin, and phosphorite (apatite). Mineral grains that make up less than a few percent of the sample often are not represented on the x-ray diffractogram; however, their presence is observed through microscopic examination of the core samples (Figure 7).
FOUR-MILE VILLAGE MEMBER-A phosphatic sand unit that is present within the Intracoastal Formation was informally described by Huddlestun (1 976a). This phosphatic sand has been designated the Four-Mile Village Member of the Intracoastal Formation by Clark and Schmidt (1982). The Coffeen #1 core (W-8865) was used by them as the best example of the unit. The Four-Mile Village Member is a pale yellow-brown to yellow-gray, poorly consolidated, calcareous, slightly argillaceous, microfossiliferous, glauconitic, phosphoritic, quartz sand or sandstone. The member extends from near the Bay-Walton county line westward along the coast into central Okaloosa County. To the north in Okaloosa and Walton counties, it pinches out (or loses definition) rapidly and is rarely found north of Choctawhatchee Bay. West of the Fort Walton Beach area, the member loses definition as the Intracoastal Formation thickens and dips toward the Gulf of Mexico Sedimentary Basin (see geologic cross sections Figures 13 and 14).
OVERLYING AND UNDERLYING UNITS--The Intracoastal Formation overlies the Bruce Creek Limestone throughout most of its areal extent; and in the Liberty County area, it overlies a sedimentary section which resembles the Hawthorn Formation. Overlying the Intracoastal are






BUREAU OF GEOLOGY


Figure 7.


CORE 1 : Intracoastal Formation from Core W-8873, 85 feet to 92 feet. CORE 2: Four-Mile Village Member, Intracoastal Formation, from Core W-8873, approximately 177 feet to 185 feet. (The top of each core Is towards the top of the page). Core diameter is 14 inches.


22





BULLETIN NO. 58


Pliocene-Recent sands: the undifferentiated Alum Bluff Group sediments and the Jackson Bluff or the Chipola Formation, both molluscan shell beds.
The olive-gray, poorly consolidated, clayey, sandy foraminiferal biocalcarenitic nature of the Intracoastal differs from the white to pale orange, well-indurated, granular limestone of the Bruce Creek. The upper part of the Bruce Creek often contains an algal zone with many oncolites which provides a marked contrast with the Intracoastal. In the east and central part of the Apalachicola Embayment, specifically in Liberty, Gulf, and Franklin counties, there is a dark gray, massive, plastic, dolosilt between the base of the Intracoastal Formation and the Bruce Creek Limestone. X-ray analysis shows the dominant minerals present in this thin, massive "clay" bed to be dolomite, quartz, montmorillonite, and palygorskite. Smear slides of this unit yield no microfauna, but do reveal abundant dolomite rhombs in the very fine sand to sift-size range. This horizon may be an important unit for its hydrogeologic implications as well as for its paleoecologic interpretation. Hydrologically, it may hinder vertical groundwater migration and, therefore, create artesian conditions in the underlying Bruce Creek Limestone. The fine grained, clayey nature of the unit with incorporated unetched, noncemented, dolomite rhombs may imply a tidal flat with the in situ dolomite obtaining its magnesium from eroding Oligocene and Early Miocene dolomitic limestones exposed just north or east of the area in Jackson, Leon, or Wakulla counties. How this may fit into the sequence of events that led to the present stratigraphic sequence will be discussed in a later section.
Overlying the Intracoastal near the northwestern extent of the Formation in Walton and Okaloosa counties is the undifferentiated Alum Bluff Group. This is a clayey, fine-grained quartz sand unit with some mica and small amounts of fossil material. Further updip, it becomes more clayey and fossil mollusks are common. Along the coast from central Bay County westward, an unconsolidated, fine to coarse-grained, relatively clean, quartz sand unit overlies the Intracoastal. Its lack of fossil material, clay and carbonate easily distinguishes it from the Intracoastal. To the east in the Apalachicola Embayment, either the Jackson Bluff Formation or Chipola Formation cover the Intracoastal. Both of these formations are predominantly argillaceous, sandy, mollusk beds. The Chipola is normally a well-indurated, molluscan shell bed, whereas the Jackson Bruff is non-indurated and poorly consolidated. Both of these formations, with their abundant lithified or unlithified molluscan shell material contrast sharply with the medium grained, mollusk-poor, Intracoastal Formation.
Occasionally, when core data or well cuttings are not available, natural gamma logs can be used to approximate upper and lower contacts of the Intracoastal Formation (see Appendix III). In general, the units overlying the Intracoastal are lower in gamma activity and logs record very low counts per second (cps). In addition, the Jackson Bluff shelly clay beds have low activity, although there are more counts per second than in the overlying quartz sands. Gamma activity in the Intracoastal commonly increases going down hole, until near the base of the formation where peak counts


23





BUREAU OF GEOLOGY


over 200 cps are often recorded. Highs and low peaks in the gamma trace are common between the base of the Intracoastal and the top of the Bruce Creek Limestone. Going below the Intracoastal into the Bruce Creek, activity drops off again, but it is not as consistently low as in the cleaner sands near the surface. This is probably due to pore space and cavity inf ill of higher-count material from above. As a general rule, the limestone units deeper than the Intracoastal are lower than it in gamma activity.
THICKNESS AND DISTRIBUTION-The Intracoastal Formation is a low-angle, wedge-shaped deposit (see Figures 8 and 9). its greatest thickness occurs in the southwest part of Okaloosa County where it is just over 400-feet thick. This occurs as the formation dips towards the Gulf of Mexico Sedimentary Basin where most stratigraphic units expand as they plunge westward. The Intracoastal, however, lithologialy grades into the Pensacola Clay and/or the Miocene-Pliocene Coarse Clastics near the Okaloosa-Santa Rosa county line. Along the axis of the Apalachicola Embayment in southwestern Gulf County, the formation exceeds 300-feet in thickness and appears to continue to thicken offshore. The unit pinches out against the older units as they approach the surface. This up-dip limit line is approximated in Figure 8.
The regional dip of the top of the Intracoastal Is to the south-southwest. Local changes occur in that regional trend, especially on the east flank of the embayment (Figure 9). The regional dip is approximately eight feet per mile (0.09 degree) in the Bay County area and less than three feet per mile (0.03 degree) in Liberty and Franklin counties.
The Intracoastal Is present in the subsurface from western-most Okaloosa County eastward to the Ochlockonee River area in western Wakulla County, The updip limit extends northward through northern Liberty, central Calhoun, and northern Bay counties (Figure 8). It is postulated to continue to dip and thicken offshore to the south and southwest.
Mitchum (1976) reported Miocene-Pliocene unlithified dolomites in the offshore area. His description of well-formed euhedral rhombs, varying in size from microcrystalline to medium crystalline, and having sharp corners showing no abrasion, is a good description of the dolosilt horizon at the base of the Intracoastal from onshore cores. His published seismic profile lines seem to verify this correlation.
PALEONTOLOGY AND AGE-Fauna from the Intracoastal Formation is prolific and abundant. The two surface exposures of the Intracoastal, along Econfina Creek in Bay County and near Carrabelle in Franklin County, have been referred to as the Cancel/aria zone and described by Cooke and Mossom (1929), Cooke (1945), and Puni (1953). Their descriptions generally refer to it as a shelly limestone.
The Intracoastal is a richly microfossiliferous calcarenite or wackestone including calcareous nannofossils, planktonic and benthic foraminifera, echinoid fragments, spicules, mollusks, shark teeth, ostracods, and relatively rare fossil fragments that appear to be parts of diatoms.
In Walton County, Huddlestun (1 976a) identified numerous plan ktonic


24











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lp
i s In




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PD*ACL* "Ay a41
.# '. -q~B a.AI;L


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"A


T' CKESI OF INTrlACoASAL FO1ATON





COlYTMIJt INTERVAL qr.


4CL.iE~.
cC .J. .It4~7Efl~


Figure 8. Thickness of the Intracoastal Formation.


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P IL CA SI
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Figure 9. Top of the Intracoastal Formation.


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CI





BULLETIN NO. 58


foraminifera from the Intracoastal Limestone; and, by using various zonation schemes (Berggren, 1973; Blow, 1969; and Lamb and Beard, 1972), dated the Intracoastal from late Early Piocene to Late Pliocene (Huddlestun's Intracoastal Limestone was only the upper half of the presently defined Intracoastal Formation).
In Bay County, Schmidt and Clark (1980) zoned planktonic foraminifera using the schemes of Bolli (1957), Lamb and Beard (1972), and Berggren (1973, 1977). Their estimated time of deposition began with the late Middle Miocene (N 1I-N1 2) and ended in the early part of the Late P1iocene (N1 8-N21 ). They point out that a hiatus occurs in the middle of the formation. This was graphically displayed by Clark and Wright (1979), who also estimated sediment accumulation rates above and below missing planktonic foraminiferal zones from well cuttings in the Bay County area.
In Okaloosa County, Clark and Schmidt (1982), again using planktonic foraminifera, dated the Intracoastal as late Middle Miocene to Pliocene. They also noted the missing foraminiferal zones which indicate a probable hiatus, BoIling (1982) also found that to be the case in Gull County, although she did state that, due to poor preservation, the exact timing of the hiatus could not be conclusively established.




Table 2. Partial list of planktonic foraminifera Identified from the Intracoastal
Formation (from Schmidt and Clark, 1980).


G/obigerina dutertre/ G. nepenthes G/obogerinoides congiobatus G. obliquus G. obliquus extrernus
3. quadr/llobatus sacculiter G. quadri//obatus tri/obus G. tuber G/oborotalla acostaensis G. continuosa G. crassaformis G. exi/is G. fohsi fohsi G. fohsi /obata G. fobs! peripheroronda G. fohsi robusta G. humerosa G, inf/eta G. lenguaensis G. margaritae


G. menardil G, merotumida 0, mu/ticamercata G. p/esiotumida G. praemiocenica G. praehirsuita G. praemenardi/ G. puncticulata G. ronda G. scitula G. siakensis G. tumida
G/oboquadrina a/tispira G. dehiscens Hastigerina siphonifera Orbu/ina blobata
0. sutura/is 0. universa Sphaeroidine//a dehiscens Sphaeroidinel/opsis seminullna S. subdehiscens


27





BUREAU OF GEOLOGY


Wiggs and Schmidt (1978) and Schmidt and Clark (1980) listed some stratigraphically significant discoasters and coccoliths from the Walton and Bay County vicinity. Although they did not zone the various samples, the general assemblage agreed with the planktonic foraminifera evidence. West of the areal extent of the Intracoastal Formation is the stratigraphically equivalent Pensacola Clay. Clark and Schmidt (1982) identified Cretaceous nannofossils as well as Miocene forms from this unit. Cretaceous limestones, presently exposed north of the area in Alabama, are the apparent source of the reworked fauna. No older reworked forms have been found from the Intracoastal.


Table 3. Partial list of the calcareous nannofoslls idnt fled from the Intracoatal
Formation (from Schmidt and Clark, 1900).

Braarudosphaera bigelowi D. quinqueramus
Catinaster coalitus D. surculus Coccolithus pelagtcus D. variabilis
CyclosoccoI/thina macintyrei Disco/ithina sp.
Discoaster brouweri Heicopontosphaera sp.
D. calcaris Reticulofenestra pseuD. challenged doumbiica
D. kugleri Reticulofenestra sp.
D. neohamatus Spenolithus abies
D. pentaradiatus Spenolithus sp.



Faunal evidence points to a middle to outer shelf environment for the Intracoastal Formation. Planktonic foraminifera commonly comprise about 50 percent of the foraminiferal fauna, the same percentage which occurs today in the eastern Gulf of Mexico between depths of 100m 190m (Wright, 1979). There are changes in the fauna in some cores near the top of the formation, The proportion of planktonic tests decreases and mollusks, echinoid spines, and shallow water ostracods increase. Benthic foraminiferal data tends to yield more shallow depths (5 m to 1 00m) than the ptanktonic proportion would indicate (Hummell, 1982).
Lithologic evidence, such as the presence of glauconite, phosphorite, kaolinite, quartz sand, and heavy minerals also supports a near-shore, open marine environmental interpretation.


28





BULLETIN NO. 58


Table 4. Partial List of benthic foraminifera Identified from the Intracoastal
Formation (from Hummell, 1982).


Amphistegina lessonii Anomatina sp. Bigenerina ftoridana S. nodosar/a textu/aroidera So/ivina perca Bolivina sp.
B. marginata mutticosta Bu/iminella elegantissima S. carseyae Bulinel/a curta Cancris communis Cibic/del/a var/abilis C/bic/des /obatu/us C/bicidies sp. Cibicides sp. Dental/ina pyrula D. communis Discorbis sp. Discorbis subauracana E. ro/shauseni F. punctata F/orlus grateloupi Fursenkoina exilis Globufina inaequa/is G. gibba G. rotundata Gyroidinoides sp. Hormosina sp. Lenticulina degolyeri


L. americana spinosus L. vaughani Marginuina dubia M. howei Massi/ina mansfie/di Nonion sp. Nonione/la scapha P/anul/ina sp. Po/ymorphina sp. Pseudopo/y morphina rutiia Pu//enia salisburyi Recto bo/iuina vicksburggensis
monssoun Reyssella sp. Reyssella miocenica Rotalia beccari Siphogenerina lame/lata Siphonina jacksonensis Textularia articulatus T. gramen T. f/oridana T. warreni T. aggutinans Uvigerina pivlata U. irettensis U. subperegrina U. auberiana U. byramensis Virgulina (virgulne/la)
miocenica


Chipola Formation
NOMENCLATURAL HISTORY-The name Chipola Formation was first suggested by Burns (1889, in DalI, 1892). He collected and described mollusks from exposures on the Chipola and Apalachicola rivers. Dal and Stanley-Brown (1894) later called these beds the Chipola shell marl. Matson and Clapp (1909) included these beds as a member in their Alum Bluff Formaton, and Gardner (1926) later promoted the member to a formation. Puri (1953) referred to the Chipola as a facies of the Alum Bluff Stage which he placed within the Middle Miocene. It was redefined as a formation once again by Pur and Vernon (1964).
The lithologic characteristics of the Chipola have not been well-defined. In the type area, Puri and Vernon (1964) described it as a blue-gray to yellowish-brown, highly fossiliferous marl studded with molluscan shells.


29





BUREAU OF GEOLOGY


They further state that this marly facies exists only in the vicinity of the Chipola and Apalachicola rivers. Cooke (1945) described two other facies: a sandy limestone found primarily in the subsurface and a light colored, coarse, sandy facies that contains cay, Huddlestun (1 976a) stated that the lithology at the type locality of the Chipola is atypical for the formation. He further stated the Chipola lithology is varied and heterogeneous. Huddlestun described three lithofacies for the Chipola Formation: an updip shell bed, a downdip nonshelly calcareous sand, and a sandy limestone, which lies even further downdip. This type of lithofacies mapping results in the merging of contemporaneous depositional units, not lithologic packages or formations.
The author has attempted in this study to establish a stratigraphic unit by correlating nearby core holes with the type area, namely the exposure at Alum Bluff. The Chipola Formation exposed at Alum Bluff has been described by numerous authors; most of whom were interested in paleontology as evidence of age and paleoecology (Gardner, 1926-1950; Cushman and Ponton, 1932; Pur and Vernon, 1964; Banks and Hunter, 1973). As a result, the Chipola has been placed in the Middle Miocene, Aum Bluff Stage; and it has become a chronostratigraphic or biostratigraphic unit rather than a lithostratJgraphic formation.
The Chipola Formation, as defined in this paper, uses the lithotype and stratigraphic position of the described Chipola at Alum Bluff in Liberty County. From that area, correlations using cores and well cuttings are made to the southeast and southwest into the deeper, thicker sequence of sediments. As a result, the age of the Chipola Formation does not correspond only to the Middle Miocene (the age near the type area) but crosses time lines and is younger toward the Gulf Coast (Figure 4).
LITHOLOGY-As previously stated, the Chipola Formation has been described by many authors. They were mostly interested in the well-preserved mollusk and foraminiferal assemblages from exposures along the Chipola and Apalachicola rivers. Because of the lithologic variability described in the past literature, a well-defined, concise description of the formation does not exist to the extent that it could be used to identify and map the unit. The present definition, therefore, will utilize the hithologic type described from the stratigraphic interval present at Alum Bluff in Liberty County. The described lithology will be from that stratigraphic horizon as it is mapped in cores and well cuttings throughout the subsurface in the Apalachicola Embayment.
Near the type area, the Chipola is a very light gray to white, sandy (quartz), fossiliferous calcarenite or wackestone. Mollusks, particularly gastropods, and foraminifera are abundant. It is poorly to moderately indurated and accessory minerals include quartz sand (10 to 50 percent), micrite, and small amounts of heavy minerals, mica, and phosphorite. Downdlip towards the Gulf of Mexico some slight changes are noted which may be due to different groundwater conditions, The most noticeable difference is the slightly better indurated nature of the unit and a decrease in sand content.


30





BULLETIN NO. 58


Cores from downdip commonly contain this Chipola unit, described as a yellowish-gray to light gray, moderate to well-indurated sandy (quartz), fossiliferous limestone. Although there is a considerable amount of clastic material present, it could be classified as a wackestone or a packstone. The fossil content and accessory mineral suite is the same as that described updip. X-ray analyses of samples from cores identified calcite, aragonite, quartz, dolomite, and some montmorillonite clay as the dominant minerals present.
OVERLYING AND UNDERLYING UNITS-The Chipola Formation overtlies the Intracostal Formation throughout most of its area] extent. Only updip near the outcrop area where the Intracoastal is not present does the Chipola overlie a different unit. There, it is underlain by the Chattahoochee Formation.
The Chattahoochee Formation contrasts markedly with the Chipola in that the former is a very pale orange to very light gray, moderate to well-indurated, calcilutitic, dolomitic limestone or fossiliferous mudstone, with fossils being present but not abundant. The Chipola is a more poorly indurated, molluscan-rich, sandy, clayey caicarenite or wackestone. The Intracoastal also is easily distinguished from the Chipola, although locally the contact appears gradational. The Intracoastal is a yellow-gray to olive-green, sandy (quartz), slightly phosphatic, biocalcarenite or wackestone. It is poorly consolidated, and microfossils are abundant, with mollusks being common but not abundant.
Overlying the Chipola Formation is the Jackson Bluff Formation or the Hawthorn Formation. The Jackson Bluff, present throughout most of the downdip sequence, is similar to the Chipola but differs in being much less consolidated, more sandy (quartz), and clayey, and pelecypods are dominant over gastropods. The difference in induration is the most obvious difference in core samples. In the northern Liberty County area, the Hawthorn Formation overlies the Chipola. The Hawthorn is predominantly a quartz sand with a clayey and micritic matrix, and phosphorite is also present in trace amounts.
The gamma log signatures do not show a distinct enough change to warrant their use for upper and lower picks of formation contacts. There are, however, a few general trends (see Appendix Ill). The Intracoastal is commonly higher in gamma counts than the Chipola, and the overlying Hawthorn is commonly lower in activity. Where the Jackson Bluff overdes the Chipola, there is no noticeable change in the gamma log.
THICKNESS AND DISTRIBUTION-The Chipola, as defined in this study, Is restricted within the Apalachicola Embayment in Bay, Calhoun, Liberty, and Gulf counties. It Is not present in the Franklin County area. Near the outcrop area north of Bristol in Liberty County, it averages 60 to 70 feet in thickness. Downdip it Is usually the same thickness, although it is sporadically thinner and at times absent. When it is absent, the Jackson Bluff shell beds are mapped as the entire mollusk-rich zone above the Intracoastal.
Near the outcrop area, the Chipola is about 75 feet above present sea





BUREAU OF GEOLOGY


level; downdip the deepest recorded Chipola lies about 140 feet below sea level in southern Gulf County and dips to the south at about 3.5 feet per mile (0.04 degree) (see geologic cross sections for regional trends, Figures 1318).
PALEONTOLOGY AND AGE-As previously stated, the exposed part of the Chipola has received a considerable amount of attention from geologists and paleontologists. Burns in 1889 (in Dall, 1892) was the first to record molluscan collections from the shell beds on the Chipola River. Gardner (1926) collected samples from a number of outcrops throughout the Florida Panhandle and published a comprehensive description of the fauna. Vokes (1965) decribed the gastropods. A number of additional reports on the fauna of the Chipola Formation have been published in the Tulane Studies in Geology and Paleontology Series by E. H. Vokes and H. E. Vokes (1969-1982).
The benthic foraminifera of the Chipola Formation were described by Cushman (1920), Cushman and Ponton (1932), and Purl (1953). Purl also included a list of identified ostracod species. Planktonic foraminifera were described by Gibson (1967), Akers (1972), and Huddlestun (1 976a). They estimated the time of deposition to be in the Globigerinatel/a insueta Zone, which is from the late part of the Early Miocene. Huddlestun suggested it was transitional in age between the Early and Middle Miocene.
Akers (1972) reported the presence of calcareous nannofossils in Chipola material. Coral species were described by Vaughan (1919) and Weisbord (1971). Finally, Bender (1971) dated corals from the Chipola using the He/U ratio method. He estimated a concordant age of 14-18 million years. This would put the Chipola in the late Early Miocene or early Middle Miocene.
The present study did not identity fauna from the Chipola Formation; fossils were used only as lithologic elements. There were, however, time lines estimated for the underlying Intracoastal formation. The uppermost Intracoastal near the coast was estimated to be early Late Pliocene. This would probably put the downdip Chipola near the present coast in the Late Pliocene. The Chipola was dated as Early to Middle Miocene where it is exposed (see above). It can, therefore, be concluded that the presently defined Chipola Formation is younger downdip near the present coast than it is updip, where it is exposed. This relationship is displayed in Figure 21.

Jackson Bluff Formation
NOMENCLATURAL HISTORY-The Jackson Bluff Formation was named by Puri and Vernon (1964). They combined the Ecphora and Cancel/aria biofacies of Purl (1953) into one formation because both are exposed at Jackson Bluff in Leon County. This is the only exposure at which more than one of Puri's four biofacies has been observed. Purl and Vernon (1964) included the Jackson Bluff Formation in the Choctwhatchee Stage of Purl (1953), which included all Miocene sediments of post-Alum Bluff age in the Florida Panhandle and their equivalents in the central and western Gulf states. This stage is approximately equivalent to the Upper Miocene Series.


32





BULLETIN NO. 58


The sequential changes in nomenclature leading up to the current usage is extensive and will not be repeated here. For a complete history of the use of the terms Jackson Bluff Formation and Choctawhatchee Stage, see Schmidt and Clark (1980, pp. 41-44).
The type section, as designated by Pur and Vernon (1964), is in the face of an old road-metal borrow pit, about 150-yards south of the dam at Jackson Bluff along the Ochlockonee River (T1 S, R4W, S20, bbb). The site is currently owned by the State of Florida, and is managed by the Department of Natural Resources. The section exposed here is about 40 feet in thickness, of which the upper 12 feet are Jackson Bluff Formation (except for a two-foot soil zone).
The Jackon Bluff Formation, like the Chipola, was also defined in the past on the basis of its fauna and not on its lithologic characteristics. As a result, the Jackson Bluff has been considered a paleoecological facies and a chronostratigraphic unit.
As was the case for the Chipola Formation, the northern Liberty County area (a geographic area between the "Type" at Jackson Bluff and the exposed sediments at Alum Bluff along the Apalachicola River) is used to identify the stratigraphic position and lithologic character of the unit. This interval is mapped downdip in cores and well cuttings.
LITHOLOGY-The Jackson Bluff Formation at the type locality has been described as consisting of three clayey, sandy, shell beds (Pur and Vernon, 1964). The beds are differentiated on slight lithologic variation and their mollusk assemblage.
This clayey, sandy, shell bed is exposed along a number of stream or river bluffs throughout the Florida Panhandle. Sediments that are lithologically similar lie near the surface in a narrow band extending from 20 miles west of Tallahassee, Leon County, northwest to the Oak Grove area of north-central Okaloosa County, a distance of about 100 miles (Figure 10). The shell beds vary from tan to orange-brown to gray-green, sandy clays and clayey sands with abundant mollusk shells. The outcrops are generally poorly exposed and of limited extent. As a result, true stratigraphic relationships have been poorly understood and most past mapping has emphasized faunal or chronologic characteristics.
Well cuttings and core descriptions allow this unit to be mapped downdip, where it is covered by younger sands and clays. These shell beds have not previously been called the Jackson Bluff Formation west of the Washington County area (it appears as undifferentiated Alum Bluff Group on the geologic cross sections Figure 13-18). In the cores, the unit is generally a light gray, poorly-consolidated, clayey, quartz sand with abundant micro and macrofossils. Mollusk shells dominate the fossil fauna; however, foraminifera, ostracods, bryozoans, echinoids and worm tubes are also common. X-ray analyses show the common minerals to be quartz, calcite, aragonite, montmorillonite, kaolinite, phosphorite, mica and pyrite.
OVERLYING AND UNDERLYING UNITS-The Jackson Bluff type sediments overlie the Chipola Formation in the central and western updip


33
















UP a
-- LiN"T


T


f


TOP OF JACUKSON J FCMATION TVPF 8EEMN"T


Figure 10. Top of the Jackson Bluff Formation type sediments.





BULLETIN NO. 58 35

parts of the Apalachicola Embayment. In Wakulla and southern Liberty counties, where the Chipola is not differentiated from the Jackson Bluff, the Intracoastal Formation is the underlying unit. In the updip eastern parts of the embayment, the Hawthorn Formation underlies the Jackson Bluff Formation.
The Chipola Formation is generally more consolidated, has less quartz sand, and more carbonate than the Jackson Bluff. The Intracoastal is easily distinguished by its olive-gray color, its lack of mollusks, and by being a medium to fine-grained biocalcarenite or wackestone. The Hawthorn, only present at the northeast comer of the study area, is a clayey, calcareous, quartz sand. Fossils are not present in the Hawthorn except in localized limestone beds further north in Gadsden County (outside the present study area).
Unnamed clayey sands, clays, and coarse sands overlie the Jackson Bluff Formation (Figure 11), In areas of higher elevations (updip), the coarse sands and gravels are associated with the Citronelle Formation or reworked Citronelle. In the east-central part of the embayment (downdip) in southern Liberty and Franklin counties, there is a massive clay bed over the Jackson Bluff; this bed appears to be locally mappable (Figure 18). Both the poorly-sorted sands and the massive clay bed are easily distinguished from the shell-rich Jackson Bluff Formation.
Gamma logs do not offer much assistance in picking these formation contacts. The overlying sands tend to have low activity (50 counts per second or less) and the clay beds generally are higher (up to 100 cps). The Jackson Bluff, however, exhibits variable gamma intensity. The contact is often gradational and may be difficult to ascertain without samples.
Below the Jackson Bluff Formation, the Intracoastal Formation generally has higher gamma counts, although this contact is also gradational; and, therefore, only a zone of transition is evident. The Chipola is also slightly higher in counts than the Jackson Bluff; but, again, the change (or contact) Is subtle; and samples probably would be needed for positive contact picks.
THICKNESS AND DISTRIBUTION-The Jackson Bluff Formation type sediments, as defined in this study, Include the undifferentiated Alum Bluff Group from Okaloosa and Walton counties. Their lithologic similarity and stratigraphic position is the basis for their being combined. As a result, the areal extent of this formation extends from western Leon County to northwestern Okaloosa County (Figure 10). The regional dip is to the south-southwest and ranges from about three feet per mile (0.03 degree) on the east side of the embayment to just over eight feet per mile (0.09 degree) In Okaloosa County. The unit ranges from a high of 220 feet above sea level in Walton County to a low of 148 feet below sea level in Gulf County. The greatest thicknesses occur downdip near the present Gulf coast, where it approaches 150 feet in thickness. From this vicinity northwestward, the unit thins, and in some locations is not present at all. This is most likely caused either by irregular deposition due to undulatory bottom conditions, or by post-depositional erosion, or both.





BUREAU OF GEOLOGY


Figure 11. CORE 1 : Bedded quartz sands from Core W-14925, from about
11 feet to 18 feet. CORE 2: Jackson Bluff Formation from Core W-14993, from about 40 feet to 48 feet. (The top of each core is towards the bottom of the page). Core diameter is 13/4 inches.





BULLETIN NO. 58


PALEONTOLOGY AND AGE-Fossil mollusk shells are abundant throughout the Jackson Bluff sediments and have been discussed extensively in the literature (Mansfield 1930, 1932; Gardner 1926-1944; Cooke and Mossom 1929; and others). Corals from the Jackson Bluff were identified by Weisbord (1971). Microfossils are also abundant, with ostracods having been reported by Howe (1935) and foraminifera having been reported by Cushman (1920), Cushman and Ponton (1932), Pur (1953) and Been (1973). Akers (1972) and Huddlestun (1976a) examined the planktonic foraminifera from the outcropping and downdip Jackson Bluff. They both concluded that the Jackson Bluff Formation was deposited in the middle to earliest Late Pliocene. Akers (1972) and Akers and Koeppel (1973) also reported the presence of calcareous nannofossils from some horizons within the Jackson Buff. Their age correlates well with the planktonic foraminifera zones.
Downdip the fauna appears to include most of the previously reported fossil types. Scattered planktonic foraminif era, however, reveal that the age of the unit downdip may be latest Pliocene and may extend into the Pleistocene. This is also expected because of the Late Pliocene age obtained for the underlying Intracoastal Formation. This relationship is expressed in Figure 4.
Paleoecoogic interpretations from surface samples were published by Dubar and Beardsley (1961) and Dubar and Taylor (1962). They concluded that the lower part of the Jackson Bluff type sediment was deposited under open marine conditions with a water depth of no more than 120 feet. Depth of water near the top of the unit was less than 48 feet. Their interpretations were made from comparison of fossil molluscan and foraminiferal assemblages with extant communities in the Gulf of Mexico, western Atlantic, and Caribbean. Beem (1973), using a modern species distribution approach on 128 species of benthic foraminifera, estimated water depths to have been less than 100 meters (328 feet).
PLEISTOCENE SEDIMENTS
Undifferentiated Sands and Clays
NOMENCLATURAL HISTORY-A wedge-shaped clastic unit of quartz sands, gravels and clays overlies the shell beds of the Jackson Bluff Formation. This unit includes some clayey sand and gravel, which probably correlates with the Citronelle Formation (present along the northern edge of the study area where elevations are higher). Other beds contain reworked clayey sands, massive clay beds, coarse quartz sands, and Pleistocene to Recent coastal sands. This clastic wedge of sediments extends to the surface from the top of the Jackson Bluff Formation.
Because these deposits are relatively unfossiliferous and difficult to stratigraphically correlate, few reports have emphasized Pleistocene to Recent stratigraphy. The most comprehensive report (although of restricted areal extent) was that of Schnable and Goodel (1968). Their report discusses the Pleistocene to Recent stratigraphy and development of the coastal strip in Gulf and Franklin counties.


37





BUREAU OF GEOLOGY


Other studies that brief ly mention the shallow clastics include Schmidt and Clark (1980) and Clark and SchmIdt (1982). In addition, several theses (Huddlestun 1976a, Clark 1980, and Boiling 1982 from Walton, Bay, and Gulf counties, respectively) mention this group of sediments.
LITHOLOGY-There are several different lithologic packages within this undifferentiated sand and clay unit. Along the northern parts of the study area, associated with higher elevations, the sediments can be correlated with the Citronelle Formation. The type locality of the Citronelle Formation lies near Citronelle, Alabama. In northwest Florida, it generally consists of fluvial, cross bedded sands, gravels and clays, and post-depositional limonite. In the lower elevations towards the coast, reworked coarse sands and gravels are common in Walton, Bay, Calhoun, and Gulf counties.
In southern Liberty, Gulf, and Franklin counties, there are massive clay beds overlying the Jackson Bluff. These clay beds are locally interbedded with graded, coarse, quartz sands (Figure 11). These clay beds are generally greenish-gray to olive-gray, massive, plastic, and sandy (quartz). The dominant clay mineral is kaolinite, with montmorillonite and palygorskite also present. These clays are low in permeability and act as an impediment to vertical groundwater migration. The clay beds and graded sands are present in the central part of the Apalachicola Embayment. They are not known from the area of Bay, Walton, or Okaloosa counties.
Quartz sands and gravels are present in southern Liberty, Gulf, and Franklin counties. Mineralogically, they are predominantly quartz with minor amounts of heavy minerals and organic material. These sands range in size from very fine to gravel, and show cross-bedding and graded beds. The unconsolidated nature of these poorly-sorted sands and gravels make them an excellent local aquifer.
The lithologic unit that extends to the surface is a pale yellow-brown to light gray, unconsolidated, medium-grained clayey sand. The common minerals are quartz, clay, heavy minerals, and mica, in order of abundance. These clayey sands are usually unfossiliferous, although plant remains in the form of wood fragments and soil-zone roots are common.
OVERLYING AND UNDERLYING UNITS--The various clastic units that lie near the surface are easily distinguished from the underlying formations. On the western flank of the embayment and farther west in the study area, clayey sands overlie the Intracoastal Formation downdip near the Gulf Coast. The calcareous and abundantly microfossilifeous nature of the Intracoastal contrasts markedly with the rarely fossiliferous clastics above.
In the updip areas and in the central part of the embayment, the Jackson Bluff Formation type sediments underlie the clayey sands. The molluskan-rich nature of the Jackson Bluff is the major lithologic difference. This contact is often gradational over several feet.
Gamma logs are only marginally useful for separating the main lithologic types within this unit. The massive clay beds generally produce relatively high counts; however, the varying amounts of clay, mica, and heavy minerals (mineral material that also produce high gamma counts)


38





BULLETIN NO. 58


scattered throughout the section make it difficult to obtain distinct lithologic separations.
The coarse sands and gravel beds are usually low in gamma activity with occasional spikes or high counts where thin clay stringers occur (see Appendix Ill).
The contact with the underlying Jackson Bluff or Intracoastal formations can generaly be approximated; however, the specific signature varies from well to well. The base level of counts is usually higher in the clayey carbonates below than in the clastics above. The shallow clay beds often have thin spikes of high counts.
THICKNESS AND DISTRIBUTION-The clayey sands, which represent reworked deposits, are present over the entire study area. In the northern parts of the area, the Citronelle Formation comprises the hills of higher elevations. Only in the central part of the embayment in southern Liberty, Gulf, and Franklin counties can the massive clay beds and the graded coarse quartz sands be found (see Figures 15 and 18).
The thickness of these beds vanes from zero (where they have been eroded updip in the highlands) to over 110 feet along the axis of the embayment. The regional dip is to the south-southwest, although local changes do occur.
Pleistocene sea level fluctuations have reworked and homogenized these near surface sediments making outcrop localities similar.
PALEONTOLOGY AND AGE-The undifferentiated sediments are generally unfossiliferous. There are, however, some mollusk shell fragments within the unit near the present coast. Other fauna in these beds include rare finds of foraminifera, ostracods, echinoids, and bryozoans.
In the graded coarse sands and gravels, wood fragments are occasionally present. Rapid deposition in a fluvial or deltaic environment may be the reason for their preservation. In some cores, this graded unit seems to possess various sequences of foreset beds. All cross-beds are sloped south at approximately the same dip angle. This probably reflects the prograding Apalachicola Delta in the Late Pleistocene.
Schnable and Goodell (1968) used numerous radiocarbon dates to estimate the age of some shallow sediments (30-40 feet below present sea level) along coastal Franklin and Gulf counties. Their data suggest dates of 27,000 to 34,000 years before present for some organic, clayey sand beds.
Most of the clayey beds from the core holes and well cuttings throughout the study area were prepared for microfossil observation. Smear slides showed that calcareous nannofossils were rare and poorly preserved; however, diatoms were abundant in some shallow clay beds (Figure 24).
A mixture of fresh water and marina diatoms were identified (Appendix i). Certain species, such as Gomphonema parvu/eum and Cyclotela striata, are associated with nutrient-rich waters near river outlets. The overall assemblage indicates a fresh water input into a marine environment. This fits well with the prograding delta, as indicated by the stratigraphic information.


39





BUREAU OF GEOLOGY


Most of the diatom species found in these beds are living today and were common in the Pleistocene (W. Miller, personal communication, 1982). One location on St. George Island, where diatoms were recovered, occurs in a clay bed above a horizon dated by Schnable and Goodell (1968) as 27,620 to 40,340 years before present. This Late Pleistocene age fits well with the diatom data.


Table 5. Partlial list of diatoms identified
Undifferentiated Sands and


from the shallow clay beds within the Clays Units (Appendix I).


Actinocyc/us octonarius Actinoptychus austra/ius A. senarius Bid dulphia aurita B. rhombus Campyloneis grevillei Cocconeis placentulia Coscinodiscus sp. Cyc/otella striata Cymbella minuta Denticulia sp. Diploneis smithit


Epithemia argus E. ocellata Eupodoscis radiatus
Gomphonema parvulum Navicula lyra Paraia sulcata Podosira sp. Pseudauliscus sp. Rhapohoneis sp. Rhoplodia gibba Synedra ulua Triceratium favus


Table 6. Formation abbreviations for geologic cross sections A-A' to J-Jr.


A
AB BC CHATI
CHIP
CIT
CLAY
CS
CSDS
DS
4
GRAD HAW IC JB
MAR
MB
OCA
OY
SM SDS
SW


-Algal Bed
-Undifferentiated Alum Bluff
-Bruce Creek Limestone
-Chattahoochee Formation
-Chipola Formation
-Citronelle Formation
-Clay Massive
-Clayey Sands
-Coarse Sands
-Dolosit and Clay
-Four-Mile Village Member


SDS-Graded Sands
-Hawthorn Formation
-Intracoastal Formation
-Jackson Bluff Formation
-Marianna Limestone
-Mollusk Bed
-Ocala Group Undifferentiated
--Oyster Bed
-St. Marks Formation
-Sands (Quartz)
-Suwannee Limestone


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BUREAU OF GEOLOGY


ADJACENT STRATIGRAPHIC UNITS
CHICKASAWHAY LIMESTONE-The Chickasawhay Limestone was extended into the Florida Panhandle from its type exposure on the Chickasawhay River in eastern Mississippi by Marsh (1966). The Chickasawhay Limestone and the Chattahoochee Formation are I1thologically indistinguishable in the Okaloosa County area. As a result, these formations were combined in subsurface mapping by Clark and Schmidt (1982).
The Chickasawhay Limestone is primarily a tan, sucrosic dolomite; it may also occur as dolomitic, fossiliferous limestone. It extends from Escambia County eastward to Walton County, where it grades into the Suwannee Limestone. The Chickasawhay is confined to the subsurface in Florida.
Marsh (1966) and Poag (1972) placed the Chickasawhay in the Late Oligocene and correlated it chronostratigraphically with the lower Chattahoochee Formation and upper Suwannee Limestone in northern Florida.
ST. MARKS FORMATION-Puri (1953) revived the term St. Marks Formation and applied it to the calcareous facies of his Tampa Stage (Early Miocene). The type locality described by Pur and Vernon (1964) is in central Wakulla County. The formation was described as a pale to yellowish-gray, argillaceous, mod erately-indu rated massive limestone, with casts and molds of mollusks and abundant Sorites sp.
The St. Marks dips southwest from the type area and becomes totally subsurface in the Apalachicola Embayment. In cores and well cuttings, the St. Marks and Bruce Creek are difficult to separate lithologically. Near the axis of the embayment these two formations are indistinguishable in shallow sections. In deeper sections, the St. Marks lithology appears to predominate. On the west flank of the embayment, the Bruce Creek lithology is dominant. These two formations are probably conformable with a slight variation occurring from St. Marks (Lower Miocene) to Bruce Creek (Middle Miocene).
PENSACOLA CLAY-The Pensacola Clay was originally described by Marsh (1966) from three oil test wells in Baldwin County, Alabama. In Escambia and Santa Rosa counties, Florida, Marsh described it as a dark-to-light gray, silty clay, containing variable amounts of quartz sand, carbonized wood, pyrite, and mica.
Clark and Schmidt (1982) mapped the Pensacola Clay eastward to the western side of Okaloosa County. Their work correlates the Pensacola Clay with the lower part of the undifferentiated Alum Bluff Group and the lower part of the Intracoastal Formation.
The Pensacola Clay has been dated as Middle to Late Miocene by Marsh (1966) using benthic foraminifera. An age of late Middle Miocene was obtained by Clark and Schmidt (1982) using planktonic foraminifera. They tentatively dated the top of the Pensacola Clay as latest Miocene using calcareous nannofossils.
Wright and Clark (1982) noted the regional trend of increasing


48





BULLETIN NO. 58


thickness of clastics to the west during the Middle and Late Miocene. From benthic foraminiferal studies, they interpret a depositional setting dominated by shallow water (40-60m), nearshore, mud-rich habitats. They interpret depositional and faunal patterns to indicate an isostatic downwarp to the west of the present study area. Increased clastic sedimentation beginning with the deposition of the Pensacola Clay may have triggered this downwarp. The clastic material appears to have originated in the Alabama piedmont and coastal plain.
MIOCENE COARSE CLASTICS-The informal term Miocene coarse clastics" was introduced in the western Florida Panhandle by Marsh (1966). He described a deposit of sand, gravel, clay, and shell beds which he believed to be Miocene in age.
Clark and Schmidt (1982) showed that the Miocene coarse clastics lithologically grade into the undifferentiated Alum Bluff Group and the Intracoastal Formation in the western Okaloosa County area. They further note that because the underlying Pensacola Clay was dated as latest Miocene, the Miocene coarse clastics may be Pliocene in part, especially where the unit overlies the Pensacola Clay. This unit represents a continuation of clastic deposition as the region isostatically adjusted to the increased sediment load.
HAWTHORN FORMATION-The Hawthorn Formation is a series of marine, deltaic, and prodeltaic beds of diverse lithology. The co-type areas are in the Alachua and Bradford counties area (Scott, 1982).
Near the present study area, the Hawthorn has been mapped in Leon and Gadsden counties, located north and northeast of the main part of the embayment during the Neogene. In Leon County, it is composed of fine-to-medium grained quartz sand, sand-size phosphorite, silt, kaolinite, montmorillonite, palygorskite, and sandy, phosphoritic limestone (Hendry and Sproul, 1966).
The Hawthorn Formation was encountered in cores from northern Liberty and western Leon counties (Figure 18). It consists of light gray to pale orange quartz sands and clays. Occasionally, sandy, dolomitic calcilutite with minor amounts of phosphorite is recorded. This is considered a Middle Miocene formation, therefore it would correlate chronostratigraphically with the Bruce Creek and Intracoastal formations downdip,

PALEOENVIRONMENTAL ANALYSIS

FORMATIONAL OBSERVATIONS
OCALA GROUP LIMESTONES (Late Eocene)-Fossils from the three formations of the Ocala Group (the Inglis, Williston, and Crystal River formations) have been studied by many authors (Vernon, 1942; Applin and Applin, 1944; Purl, 1957; Cheetham, 1963; and many others). A wide range of marine fauna including mollusks, foraminifera, bryozoans and corals have been described.
In peninsular Florida, where the type localities of these formations are located, Cheetham (1963) suggested that water depths did not exceed 150


49





BUREAU OF GEOLOGY


feet and that the Late Eocene depositional environments were probably lagoonal with shoal water, tropical climate, and exceptionally uniform hydrographical conditions during the Late Eocene. In the Florida Panhandle, he suggested water depths of 100 to 300 feet.
Chan (1965), using a lithofacies mapping approach along with published faunal lists, reconstructed a regional pattern of sedimentary environments during the Paleocene and Eocene in Florida. He stated Florida was a stable carbonate platform bounded by submarine escarpments on both the Atlantic and Gulf of Mexico sides and separated from the continental shelf at the north by the "Suwannee Channel". The platform was characterized by shallow water, with reefs along its northern and eastern margins. Chen noted that, in the latest Eocene, pails of the platform may have been emergent based on the unconformable relationships mapped. This is also suggested by Randazzo (1972a, 1980) from petrographic evidence.
Chen (1965) noted the absence of shallow-water types of larger foraminifera and bryozoans in the "Suwannee Channel" area. He pointed out that deeper-water types are dominant there. Although well control in this deep r part of the section is poor, Chen suggested that a degree of interfingering between the clastic facies from the northwest and the nonclastic facies from the south must exist somewhere along the channel. The nonclastic facies steadily spread north and northwest during the Paleocene and Eocene. This occurred as a result of continued growth and migration of the calcareous fauna towards the warm, shallow marine current to the northwest.
Regional paleogeographic maps of the southeastern coastal plain (Chen, 1965), show a marine current crossing the Big Bend of Florida into southwest Georgia from southwest to northeast. The axis of this channel or current shifts northwestward through the Eocene until it was situated near the present-day Apalachicola River. Evidence for this current is also seen in the Georgia coastal plain (Schmidt, 1977).
MARIANNA AND SUWANNEE LIMESTONES (Ollgocene)-The Madanna and Suwannee limestones are similar to the undedying Ocala in that they are mostly calcium carbonate and are fossiliferous, chalky calcarenites. Yon and Hendry (1972) and Randazzo (1972b) briefly summarized some paleoenvironmental interpretations from the Suwannee Limestone in Hemando and Pasco counties. They concluded from the predominance of calcarenites, bedding characteristics, and paleontological evidence that the sediments of the Suwannee Umestone were deposited in a warm shallow sea. Petrographic observations showed a predominance of low energy, shallow water and higher energy, shallow subtidal environments.
The Suwannee in the panhandle has a different foraminiferal fauna than that in the peninsula. The two assemblages merge In the Tallahassee area. A physical boundary, such as a deeper, current-swept strait would have separated and isolated the fauna, creating the different assemblages observed.


50





BULLETIN NO. 58


The Marianna Limestone is of much less areal extent than the Suwannee. It is present in Jackson, Washington, and Holmes counties at the surface. In the subsurface in Bay and Walton counties, identification is difficult. The foraminiferal assemblage was considered to represent moderately deep water (60 feet or more)" by Todd (in Puri and Vernon, 1964). Chen (1965), however, interpreted the conditions to have been very shallow water, nearshore marine. From petrographic evidence, Randazzo (1 972b), Interpreted the type section at Marianna to represent a low energy, shallow water environment followed by higher energy and, probably, a marine transgression followed in turn by a regression at the top of the section.
CHATTAHOOCHEE AND ST. MARKS FORMATIONS (Late Oligocene-Early Miocene). The Chattahoochee and St. Marks formations were deposited in a warm (200 -300C) inner neritic (between low tide and 50 meters depth) environment (Pur, 1953). Sediments of the Chattahoochee Formation were considered by Purl (1953) to be nearer shore, based on a "meager" number of foraminifera species.
Puri considered the Tampa Stage (Early Miocene) seas to be transgressive over the eroded surface of Oligocene or older limestones. He concluded that early in the transgressive period a "limy" lithofacies (the St. Marks) was deposited downdip; and late during this transgression and the regression that followed, a more clastic (Chattahoochee) lithofacies was deposited updip.
Gremillion (1966) described the exposed section along the Apalachicola River near the city of Chattahoochee. He also suggested a shallow regressive sea and, from the presence of some rubble beds, thought that the shoreline was not very far away during that time.
The Chattahoochee Formation commonly contains quartz sand and some clay beds. The fossil assemblage is not abundant and generally only poorly preserved molds are found. This formation represents the first clastic influx into the embayrnent area after the regression of the warm carbonate seas of the Eocene and Oligocene.
The St. Marks Formation described from the east side of the embayment (Pur 1953; Pur and Vernon, 1964; Hendry and Sproul, 1966; Yon, 1966) is a sandy (quartz) caJcarenite. Fossils, mostly foram in ifera and mollusks, are abundant.
BRUCE CREEK LIMESTONE (Middle Miocene)-The Bruce Creek Limestone is described as a white to light yellow-gray, moderately indurated, granular to calcarenitic limestone (Schmidt and Clark, 1980). Quartz sand is common, as are minor amounts of phosphorite, glauconite, and pyrite. Fossil content is abundant and includes mollusks, bryozoans, echinoids, benthic and planktonic foraminifera, ostracods, and calcareous nannofossils. This wide array of marine fossils, along with the clastic mineral content, implies that the environment of deposition for this formation was shallow, nearshore marine. The upper few feet of the Bruce Creek often contain an algal-rich limestone, where algal oncolites are common. This suggests a permanently submerged shoal environment






BUREAU OF GEOLOGY


(Logan, et a., 1964) or at least a shallowing of the water depth near the end of Bruce Creek deposition.
Many authors have postulated depositional environments for the Miocene in north and northwest Florida (Puri, 1953; Tanner, 1966; Banks and Hunter, 1973; Weaver and Beck, 1977; and many others). In general, shallow marine carbonates dominated the Early Miocene. The Middle and Late Miocene saw increased clastics (quartz sands and clays), less fossil material, and some prodeltaic sediments.
In the panhandle Purl ( 953) described environments of deposition for the facies in the Alum Bluff Stage (Middle Miocene). The Hawthorn was deposited in continental and deltaic environments, the Chipola in warm marine waters in depths greater than 60 fathoms (360 feet). The Shoal River and Oak Grove fauna were considered mostly brackish with a slight influx of inner neritic forms.
CLAYEY DOLOSILT (Middle Miocene)-ln the central and eastern parts of the embayment a dark gray, massive, plastic, clayey dolosilt overlies the algal zone of the Bruce Creek Limestone. The environment of deposition for this unit is not as clearly understood as for some of the underlying and overlying formations. The fine-grained, clayey nature of the unit with incorporated unetched, non-cemented dolomite rhombs may imply a supratidal or tidal flat environment. The dolomite seems to have formed in situ because there is no abrasion evident, and it is all the same, very fine-grain size. There are no fossils evident.
Mitchum (1976) reported the same type of well-sorted, microcrystalline to medium crystalline, unetched dolomite, in approximately the same stratigraphic position from offshore; in addition, he also interpreted these as authigenic grains which replaced calcite sediments. He further stated that most of the magnesium would have been derived from interstitial water or from seawater during long exposure on the sea floor, These sediments are correlateable to the dolosilt bed from the onshore cores.
INTRACOASTAL FORMATION (Middle Miocene and Pliocene)-The Intracoastal Formation is a richly microfossiliferous calcarenite including calcareous nannofossils, planktonic and benthic foraminifera, echinoid fragments, spicules, mollusks, shark teeth, ostracods, and small unidentified fossil fragments that appear to be parts of diatom frustules.
With such a diverse group of marine organisms, it is no surprise that the precise environment of deposition is difficult to ascertain because of the varying environmental requirements for each fossil group. Because of the apparent abundance of benthic and plan ktonic foraminifera, this group was used to approximate water depths.
Planktonic/benthic ratios in the Bay and Walton counties area are about 0.5. This proportion occurs today in the eastern Gulf of Mexico between depths of 1 00m and 1 90m (Wright, 1979). Toward the upper half of the formation, the proportion of planktonic tests decreases; this was' probably caused by a shallowing of the water depth. A brief study of the benthic foraminifera from two cores by Hummell (1982) suggests depths between 5m and 100m from the Gulf and Franklin counties area.





BULLETIN NO. 58


These data suggest that the depositional environment was deeper than for the two lithologic units immediately below (Figure 19). This interpretation would represent a short-term reversal in the trend of shallowing water during late Bruce Creek deposition.
Lithologic evidence, however, points out that clastic input from the north increases in the younger sediments. The Intracoastal contains kaolinite, montomorillonite, palygorskite, heavy minerals, and abundant quartz sand. All of these minerals are present in older sediments exposed on the coastal plain to the north.
It is postulated here that the fluvial sources northward (during Intracoastal time, stiTl north of the study area) carried much of the clastic load from the southern Appalachians and narrow coastal plain. Heavy mineral analysis by Isphording (1971, 1977) pointed out that much of the heavy detrital minerals in the Florida Miocene originated from the high grade metamorphic rocks or from the igneous rocks of northern Georgia and east-central Alabama.
These sediment-laden fluvial sources also carried nutrients into the marine environment. It is probably this nutrient-rich, warm water that caused the planktonic and benthic communities to flourish. The phosphorite may be a result of high organic production both in the water column and in the bottom sediment. Riggs (1979, 1980) has reported on the Miocene phosphorites from the peninsula of Florida and discussed their mode of origin. He considered that the cold, upwelling water that moved across the Florida platform brought bacterially precipitated microcrystalline phosphorite mud to the shallow-water environment.
This microcrystalline phosphorite mud was populated by a benthic community that ingested and excreted the muds as fecal pellets. A shallow water microorganism hash with pelletal phosphorite also typifies the Intracoastal in Panhandle Florida. Riggs' interpretation seems valid; a fluvial nutrient source from the north was added to this phosphorite mud during the deposition of the Intracoastal Formation.
A hiatus exists in the middle of the Intracoastal Formation. This was discovered by zoning the various planktonic foraminifera using the schemes of Bolli (1957), Lamb and Beard (1972), and Berggren (1973, 1977). The entire Late Miocene and part of the Early Pliocene is absent from the Intracoastal, at least in the area where it could be zoned. This hiatus occurs in Bay and Gulf counties, as reported by Schmidt and Clark (1980) and Boiling (1982), Missing biostratigraphic zones such as this could imply a brief drop in sea level corresponding in part to the world-wide "Messinian event." This sea level drop has been further documented in Florida by Huddlestun and Wright (1977) from the Florida Panhandle, and by Peck et a. (1977) from south Florida.
There is, however, no apparent lithologic change across the hiatus. Why this occurs is not clear, although a rapid sea level decline and quick recovery could account for it (Figure 19). Such a sea level drop and rise is suggested by Vail and Hardenbol (1979).
CHIPOLA FORMATION (Middle Miocene to Late Pliocene)-Several


53








ECOLOGIC LEATI \ RELATIVE CHANGES OF SEA LEVEL SERIES FORMTIONtlIthology INTERPRETATION WATER DEPTH (Kodified from Vail et al. .- 1977) INTRPR p Low 1:0*- RISIN ,. FALLI 1G --r )
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' I --


%





BULLETIN NO. 58


authors have collected fossil material from the type area of the Chipola Formation, namely the Alum Bluff in Liberty County and the Chipola River, Ten Mile Creek, and Farley Creek in Calhoun County. The most comprehensive faunal descriptions include Gardner (1926); Pur (1953); Vokes (1965, 1972, 1977); and Weisbord (1971). Shallow marine fauna such as foraminifera, ostracods, mollusks, and corars have been the most common fossils recorded.
Purl (1953) stated that two-thirds of the foraminiferal species occurring in the Chipola are known to be living today in shallow warm waters and are generally restricted to a depth range of 60 fathoms (360 feet). He further estimated the waters to have been between 200 and 300 C.
More recently Furlong (1980) interpreted the depositional environment of the Chilpola from studying the detrital sand size sediments and their distribution within the formation. He concluded that the Chipola Formation was deposited in an unrestricted lagoon and nearshore bay environment similar to Florida Bay, but with considerably deeper water, probably 200 feet or more. A general shoreline was projected eastward beyond Alum Bluff in Liberty County and northward in the vicinity of Marianna in Jackson County.
The general faunal assemblage reported from the ChipoLa along its outcrops holds also for the subsurface samples recovered from cores and cuttings. As a resut, the environmental interpretations published also seem to be applicable downdip.
There is one important difference worth emphasizing. The Chipola Formation as mapped downdip into the Embayment crosses time lines and appears to be Pliocene near the present coast. This would call for the Chipola-type environment to migrate south as sea level slowly dropped.
JACKSON BLUFF FORMATION (Pliocene)--The Jackson Bluff Formation, like the Chipola, has been subject to a number of faunal studies. Some that include paleoecologic interpretations include Pur (1953), Dubar and Beardsley (1961), Dubar and Taylor (1962), and Beem (1973).
Dubar and Taylor (1962) specifically studied the "type" at Jackson Bluff in Leon County, identified macro and microfossils, and did a grain-size analysis of the sediments. They concluded that the sediments were deposited in an open marine, near-shore, shallow to intermediate shelf zone, at depths of less than 21 fathoms (126 feet). They went on to state that the formation was not a simple depositional unit. It apparently was transgressive near the bottom (representing maximum water depth for the section), then was deposited under shoaling conditions, and finally the top of the section became transgressive again, but was deposited at a depth of less than 8 fathoms (48 feet).
The clayey, sandy shell beds of the Jackson Bluff Formation from the exposed sections compare well with the unit as mapped downdip into the embayment. As was the case for the Chipola Formation, the Jackson Bluff Formation appears to cross time lines and become younger near the present coast. The unit downdip is probably Pleistocene in age.
Both the Chipola and Jackson Bluff formations show a complete suite





BUREAU OF GEOLOGY


of shallow water marine fossils and the lithologic components of the prograding coastal plain, They contain quartz sands, calcite, aragonite, montmorillonite, kaolinite, muscovite, and some heavy minerals. It appears that the shoreline was considerably closer to the study area than during the deposition of prior formations. This, it is assumed, is a result of the prograding clastics of the coastal plain and a general regressive trQnd (Figure 19).
MASSIVE CLAYS AND CLAYEY SANDS (Pleistocene)-Overlying the Jackson Bluff Formation in the central part of the Apalachicola Embayment are several massive clay beds and clayey sand beds. Some of the clay beds appear to be laterally continuous and, therefore, correlatable between core holes (see geologic cross sections Figures 13-18).
The clay beds are dominated by kaolinite with montmorillonite and palygorskite also present. Quartz sand, muscovite, and heavy minerals are also common. The massive, dark gray to black nature of the clays, along with commonly incorporated plant remains, implies a lagoonal or tidal flat environment. Fossil material is not readily evident. However, diatoms were found In abundance in several cores and well cuttings.
A mixture of fresh and marine water diatoms were identified from the assemblage. This mixture of fresh and marine species, and species associated with nutrient-rich waters near river outlets, fits well with the environmental interpretation of a prograding delta slowly migrating over and into the marine realm. These diatoms were only found near the present coast at relatively shallow depths (Appendix I).
GRADED QUARTZ SANDS (Pleistocene ?}-in the central part of the embayment in Franklin, Gulf, and southern Liberty counties, there is an unconsolidated, poorly sorted, quartz sand and gravel unit. These sands often exhibit graded bedding; and in some cores, foreset beds are apparent. There are sporadic, well-preserved wood fragments in these gravel beds. Rapid deposition in a fluvial or deltaic environment is the reason for the intact preservation.
This lithologic package represents the arrival of the clastic invasion over the study area. The shallow water, brackish and marine environment of the units deposited below this graded quartz sand have been displaced south and southwest into the present Gulf of Mexico.
QUARTZ SAND RESIDUUM AND SOIL ZONE (Holocene)-The clayey sands and silty sands that blanket the surface of the entire study area represent reworked and winnowed sediments from the last retreat of the sea. They are, generally, unconsolidated sifty sands with recent root accumulation in the present soil zone. They are terrestrial deposits with coastal dunes and other coastal features which are common throughout the near-shore area.

DISCUSSION
Due to poor preservation of marker species or the absence of zonable fauna being present, time lines are not readily obtainable. As a result, a direct correlation with the sea level curve of Vail et a/., (1977) and Vail and


56





BULLETIN NO. 58


Hardenbol (1979) cannot be attempted. There are, however, generaI trends that can be observed because some stratigraphic horizons have been zoned well enough to yield relative ages throughout the local geologic section.
The Late Eocene Ocala Group limestones and the Oligocene Marianna and Suwannee limestones represent a shallow, open marine carbonate platform or shelf environment. From the elevation where they are exposed in the panhandle, it can be concluded (without major tectonism) that sea level was considerably higher than it is at present.
The Late Oligocene and Early Miocene Chattahoochee and St. Marks form ations seem to have a more prolific shallow water fauna than the older units. A slight incidence of quartz sand and numerous shallow water mollusks imply that the sea level may have dropped some from earlier times.
The Bruce Creek Limestone (Middle Miocene) has much the same fauna as the St. Marks Formation. There is a slight increase in quartz sand and clay in the Bruce Creek. A very shallow environment near the end of Bruce Creek deposition is suggested by the faunal evidence (including abundant algal oncolites).
The Intracoastal Formation (Middle Miocene to Pliocene) represents a reversal of this shallowing trend and was deposited in deeper water than was the Bruce Creek. There is evidence that the coastal plain to the north was highly eroded during Intracoastal time because there are abundant clastic minerals present throughout the Intracoastal along with the open marine fauna.
The Chipola and Jacksor. Bluff Formations (Middle Miocene to latest Pliocene) were probably deposited in near-shore, shallow marine environments. Evidence for this are the numerous shallow water mollusk assemblages and the abundance of clastics, including quartz sands, clays, mica, and heavy minerals.
Overlying the Jackson Bluff are massive clays that were deposited in a brackish or prodeltaic environment. Over the clays are fluvial or prodeltaic sands and gravels. The sea level trend (although there have been several Pleistocene fluctuations) is generally regressive after the Intracoastal Formation.
This general trend is only a reflection of the regional lithologic packages mapped throughout the embayment. There are numerous sea level fluctuations recorded throughout the world from this time interval that can only be observed through detailed paleontologic analysis which was not attempted in this study.
Each of the cores taken near the central part of the Embayment records the entire sequence of environmental changes that occurred in this area from the Late Eocene to the Present. In moving up each core (going up section), the pure limestone from the marine environment at the base of the section becomes a slightly sandy limestone to a very clayey, sandy, poorly-consolidated calcarenite, then to an unconsolidated, clayey shell bed, to massive dark clays, and finally to fluvial or prodeltaic sands. The


57






BUREAU OF GEOLOGY


:CLA STICSL ::-


MARINE CURRENTS


EARLY EOCENE


HOOCHEE ANTICLINE


OLIGOCENE


APALACHICOLA f';
EMBAYMENT


LATE
MIOCENE


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Figure 20. Generalized Paleogeographic Trend
(Eocene to Pleistocene).


58


W-





BULLETIN NO. 58


clastic deltaic sequence can be observed to have slowly invaded the marine environment and finally covered it, leaving the delta as we see it today (Figure 20).

GEOLOGIC HISTORY OF THE APALACHICOLA EMBAYMENT REGION

PRELIMINARY STRUCTURAL MAPPING
In preparing regional, structural contour maps of the top of the Cretaceous, the Middle Eocene, the Late Eocene, the Oligocene, and Early Miocene sediments, the author and Jim May (who was, at the time, on the staff of the Northwest Florida Water Management District) noticed some distinct recurring features. Two positive areas persisted throughout the sequence. The first is the Ocala High east of the present study area in the northwest part of the Florida peninsula and the other is in the Chattahoochee Anticline in the Jackson, Holmes, and northern Washington counties area.
Adjacent to each of these two positive or "high" areas are two low areas. The first is in the western three-to-four counties of the state, along the western flank of the Chattahoochee Anticline. This is the eastern-most limit of the Gulf of Mexico Sedimentary Basin. The second is located between the two relative high areas. In this region the typical southwesterly dipping strata are slightly depressed, forcing the structural contour lines to be deflected slightly northeastward. This feature is known as the Apalachicola Embayment, and it is relatively minor in size when compared to the more regional Gulf of Mexico Sedimentary Basin.
Mapping was generated from geologic well log and core descriptions stored at the Florida Bureau of Geology in Tallahassee. There are many problems inherent in using many different geologists' well log descriptions (such as discrepancies in formation definitions, and formation contacts, age assignments, etc.) as the data base for mapping. There were, however, some noted differences in the various horizons mapped. The orientation and placement of the gently plunging axis of the Apalachicola Embayment shifts northwest higher in the section.
The discovery of this feature led to several questions relating to its origin and its geological history. How did it originate? Was it a structural feature (a graben)? Was it depressed from the thick sediment load, or was it due to non-deposition? The feature seemed to migrate. What was the evidence for this? Why did its axis shift? Are there several different structural elements present that are superimposed on each other, compounding its interpretation? A literature search was carried out to obtain as much information as possible.

LITERATURE REVIEW
The first point that becomes readily apparent in a literature review of this topic is that many different names have been used in referring to this





BUREAU OF GEOLOGY


feature(s). May (1977) addressed this nomenclatural problem and suggested the term Chattahoochee Embayment be used to refer to this structural element in northwest Florida. May went on to summarize the various names found in the literature, as shown in Table 7.

TABLE 7.-Narnes used to describe the structural "low" feature near the Big Bend of Florida (modified from May 1977).


AUTHOR
Johnson 1891 Dali and Harris 1892 Foerste 1893

Pressler 1947 Toulmin 1955 Braunstein 1957 Murray 1957 King 1961 Roberts and Vernon 1961 Herrick and Vorhis 1963 Sever 1966 Stringfield 1966


NAME
Chattahoochee Embayment Suwanee Strait Okefenokee Strait Apalachicola Embayment of the Gulf
Basin
Apalachicola Embayment Suwannee River Basin Southwest Georgia Basin Suwannee Basin Southwest Georgia Embayment Gulf Trough of Georgia Gulf Trough Apalachicola Basin


May (1977) preferred to use the term Chattahoochee Embayment because it is the original name and should have priority. This author, however, prefers to use the term Apalachicola Embayment for several reasons: 1) Apalachicola Embayment is the term currently used by the Florida Bureau of Geology, and it is used by most geologists familiar with the area; 2) The oil and gas industry also uses this term and it is well established in the literature; 3) Apalachicola (the city) is located approximately on the axis of the embayment as it opens to the south; 4) Chattahoochee (the city) is northwest of the embayment adjacent to a positive structural feature; 5) The term Chattahoochee Anticline is used for a positive structural feature next to the embayment; therefore, the use of the same name for both an anticline and an embayment seems undesirable; and 6) Chattahoochee is also the name of a local formation.
As would be expected with so many differing names and interpretations, there are also many differing opinions on the nature and origin of the feature. Some have favored the hypothesis that a graben is responsible. Others have preferred a downfaulted embayment, a syncline, a solution valley, a submarine valley, or a current-swept strait. When several axial plots are combined from different authors (Figure 21), a wide range of orientations and locations are apparent. The immediate question that arises is: Are these various authors mapping different features, or do their stratigraphic interpretations differ that much from one another? This type of confusion has resulted in one paper being entitled Chattah6ochee Antic/ine, Apa/achicola Embayment, Gu/f Trough and Related Structural


so





BULLETIN NO. 58


1'

If It
N


E rF


~. I; 'I-,


AXIS OF "LOW AREW'
COMPILED FROM NUMEROUS
PUBLICATIONS


Figure 21. Axis of "Low Area" as interpreted by various authors.
a. Chen (1965), Applegate (1978), Pontigo (1982)
b. Herrick and Vorhis (1963), Cramer (1974), Arden (1974)
c. Toulmin (1952), Weaver and Beck (1977), May (1977)
d. Chen (1965)
e. Applin and Applin (1944, 1967), Hull (1962)
f. Applin and Applin (1967)
g. Chen (1965)



Features, Southwestern Georgia, Fact or Fiction (Patterson and Herrick, 1971).
Depending on which stratigraphic horizon was being mapped or what geographic area was studied, various authors interpreted the origin and geological history of the feature differently. Some (Outler, 1979; Pontigo, 1979; Applegate et a., 1978; Cramer, 1974; Arden, 1974; Herrick and Vorhis, 1963; Hull, 1962; and Applin and Applin, 1944, 1967) studied the Mesozoic sediments, placed an axis through Port St. Joe, and implied that a graben caused the sediment thickening. Some (Gelbaum and Howell, 1979; Weaver and Beck, 1977; May, 1977; Chen, 1965; and Toulmin, 1952) studied the Paleogene horizons and plotted their axes farther east and interpreted that little or no deposition was due to a current-swept strait. Finally, other authors studying the Neogene (Banks and Hunter, 1973;





BUREAU OF GEOLOGY


Toulmin, 1952; and Schmidt, this paper) discussed sediment infill of an embayment or basin by a prograding, clastic deltaic sequence.
The variety of names used is explained by the fact that differing horizons were studied and various locations plotted. Each author chose a surface feature in the vicinity of the low axis, as interpreted by that author to name the subsurface feature. In addition, depending on the areal extent of their study, writers would choose to call the depressed sediments a basin, embayment, strait, or trough.
This varied and confusing summary of geologic interpretations can be sorted out and historical trends postulated, if the various data can be put in a chronological sequence. Unpublished information from the Florida Bureau of Geology files were used to verify and check the many formational contacts.

SEQUENTIAL TRENDS FROM THE PRE-JURASSIC TO THE RECENT
The eadiest indication of a depression is evidenced by the top of the pre-Jurassic surface. Arden (1974) shows a plunging axis (Figure 22) to dip approximately southwest towards southern Gulf County from the southwest corner of Georgia. Arden considered this feature a tensionally controlled Late Triassic "down-warp" forming a broad basin. Subsequent to the development of this '4syncline1, further crustal tension created high-angle fractures, and a series of fault block basins appeared into which Triassic sediments began to be deposited. This interpretation was developed by Arden using seismic reflection surveys wfth associated gravity and vertical magnetic field measurements. Pontigo (1982) seemed to agree with Arden when he stated that the Apalachicola Embayment was initiated as a result of rifting during Late Triassic to Early Jurassic times associated with the opening of the Atlantic Ocean. Pontigo used well cuttings, geophysical well logs, and seismic reflection lines as his data base. Seismic lines show graben structures in basement reflections. A diabase intrusion in the Eagle Mills Formation (Triassic), dated as 180-200 million years (Barnett, 1975), provides a minimum age for the tensional features observed.
A structure contour map of the sub-Zuni erosional surface (approximately during the Early Jurassic) shows an embayment in the same vicinity as Arden's map (Bamett, 1975). Barnett also plotted several faults on that surface, including some in the Apalachicola area. Two of his faults which form a graben have been further documented by Pontigo (1982), who used better well control, in addition to seismic lines. Contour maps on top of the Norphlet Formation and several lithofacies in the Smackover Formation (both Late Jurassic) show the graben opening towards and centered around Gulf County and cutting into these Upper Jurassic formations (Pontigo, 1982). This may imply that structural activity continued through the Jurassic. From petrographic studies of these units, Pontigo concluded that the open sea was to the south with a possible exposed region to the north.
The Late Jurassic in this area is represented by the Cotton Valley


62






BULLETIN NO. 58


group. This group consists of mudstones and coarse sandstones and, as depicted on a structural cross section by Applegate et at. (1978), the embayment still existed through the end of the Jurassic (Figure 22). Herrick and Vorhis (1963) and Cramer (1974) mapped what was termed the pre-Cretaceous in southwest Georgia. Their maps showed the same trend of the embayment with its axis plunging towards the Gulf County area of Florida (Figure 22).
The Lower Cretaceous in the Apalachicola Embayment consists of shales and sandstones varying from about 4,200 feet to 5,800 feet in thickness. A structural cross section prepared by Applegate et at. (1978) shows the Lower Cretaceous thickest near the axis of the embayment. It also shows the embayment was filled in by the end of the Early Cretaceous. This is also shown by Outler (1979) and Pontigo (1979) on the structure contour maps prepared on the top of the Lower Cretaceous. Their maps show the regional dip of the beds to the south-southwest but do not have deflections in the contours to form an embayment. It is inferred here that subsidence had ceased or the sedimentation rate exceeded the rate of subsidence due to either compaction or the structural graben below.
Applin and Applin (1967) mapped the pre-Gulf rocks (the top of the Lower Cretaceous) throughout northern Florida, and their interpretation is in agreement with Outler (1979) and Pontigo (1979) in that the embayment is no longer present but apparently filled in. Applin and Applin (1967) do, however, show an embayment shifted eastward from the prior feature (Figure 22). The axis of this low also plunges towards southern Gulf County; but instead of rising towards the southwest corner of Georgia, it rises nearly due east, then turns northeast and runs along eastern Leon County, Florida, into Georgia, then turns east again. There it plunges towards southeast Georgia where geologists name the feature the Okefenokee Embayment. Between the Apalachicola and Okefenokee embayments, there is a relative high area (that separates the two low features) which the Applins called the Suwannee Saddle. This low structure, that seems to connect the northeast Gulf with the coastal Atlantic, was first noted by DalI and Harris (1892) who named the feature the Suwanee Strait, They concluded that this feature separated the continental border from the islands representing Florida (Dali and Harris did, however, discuss this as an Eocene and Miocene feature).
The top of the Upper Cretaceous sediments was mapped by Applin and Applin (1944, 1967), Hull (1962) and Chen (1965) (Figure 22). Their work not only showed the structure from contour mapping but they inferred paleogeographic relationships with the addition of isopach maps and lithofacies maps. Hull interpreted the thin Upper Cretaceous rocks as an area of slow sedimentation. He felt this was an area that separated the carbonate banks on the south from the source of terrigenous sediments on the north. Hull further stated, "This thinness, which is generally attributed to Post-Cretaceous erosion, can be explained as a result of differential sedimentation during Late Cretaceous time, when the Suwannee strait was a boundary between two distinct sedimentary facies."









BUREAU OF GEOLOGY


(



I...



U


/


'I


aHlt9l 9M1


2

TOP OF JURASS4C


*IYLEUA' t t f. th


C-- -.
a






a
mxii ow nineS
-or atu


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an


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TOP
A.MI V


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U)PPER cntTsCiOUS .3fj.%- WPLA 444 hL LfM


4
14






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Figure 22. Sequential plots of the axis of the Embayment, Pre-Jurassic to

Pleistocene. (Pattern on 10 and 13 represents area exposed

above sea level.)


I
AKPB Q0 "ADIN
PM-JURA$IC SURFACE


I


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65


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WIOOLF" IOIClWEq .rldr,T hI1: P.R.,


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12
LATE IItOCEF4E-PL.IOCKNE


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13
PLIOCINII-RECENT T"ULUIN I2Z Si-m r i' ;t PA"A'


BULLETIN NO. 58


L
OLICO-CENE





BUREAU OF GEOLOGY


Applin and Applin (1967) offered an alternative interpretation. They thought this area represented an upwarped barrier that separated the two provinces during the latest Cretaceous time. During Tertiary time, tectonic movements in Florida and Georgia brought about a relative depression of the uplift area (the barrier), forming the synclinal feature now seen in the stratigraphy.
The top of the Paleocene was mapped by Chen (1965) as part of his regional lithostratigraphic analysis of Paleocene and Eocene rocks in Frorida. Chen showed a synclinal axis (termed the Suwannee Channel) rising from the south Gulf County area towards the east-northeast, then shifting northeast until reaching the Florida-Georgia state line, thereafter, turning east-northeast again (Figure 22). Chen also showed, by use of a isopach map, the thin accumulation within the Suwannee Channel during the Paleocene. The location of the syncline as mapped by Chen (1965) is very close to the syncline as mapped by Applin and Applin (1967) from the top of the Lower Cretaceous. This implies a long, stable presence of the feature from Early Cretaceous through the Paleocene. Chen (1965) suggests that this relatively thin deposition within the channel is from continued strong current action during that time. The currents could have considerably reduced the rate of sediment accumulation within the channel and would have prevented the spread of terrigenous sediments over the peninsula to the southeast.
The Eocene series has received more attention by geologists than the older series, partially because of an increased data base in the more shallow sediments. Toulmin (1952), Chen (1965), Weaver and Beck (1977), and Gelbaum and Howell (1979) all mapped Eocene horizons in north Florida (Figure 22). Chen (1965) mapped contours on top of the Lower Eocene, the Middle Eocene, and the Upper Eocene. From that data, (isopach maps and lithofacies maps) Chen developed a regional paleogeographic interpretation of the Suwannee Channel during Late Cretaceous and Early Tertiary time. He stated that "... the Suwannee Channel was a bathymetric depression and a natural barrier, both sedimentational and ecologic, during Late Cretaceous and Early Tertiary time.'" By Middle and Late Eocene time, the channel was no longer an effective barrier in separating the clastic and nonclastic facies. The axis of the channel and facies boundary shifted northwestward through the Eocene (Figure 22). By the end of the Eocene, the axis shifted west and plunged towards Gulf County from the southwest corner of Georgia. This location and orientation is very close to the Triassic and Jurassic position of the axis (Figure 22).
The upper surface of the Oligocene series was mapped by Toulmin (1952). May (1977), Weaver and Beck (1977), and Gelbaum and Howell (1979). The structural map of the Oligocene is based on the top of the Suwannee Limestone by most authors. The structural maps show the synclinal axis to be similar to that of the top of the Eocene in general configuration. There does, however, appear to be a relative high in the trough. The Apalachicola Embayment is separated from the "trough" in


66





BULLETIN NO. 58


southwest Georgia. This high or "isill" has also been projected higher in the section Into the Early Miocene (Tampa Stage) sediments by Weaver and Beck (1977). There is no way to determine the width of the iLsill" from available well control.
If this relative high in the embayment-trough existed at the close of the Oligocene and during the Early Miocene, it may have acted as a bridge to transport clastics across the barrier channel. This was postulated by Banks and Hunter (1973) (Figure 22), although their "land bridge" is considerably farther south than would be called for by the interpretive stratigraphic data. The post-Early Miocene sediments throughout the Florida peninsula are dominated by terrigenous clastics, whereas prior sediments are predominately nonclastics (limestones, dolomites, and evaporites). This observation seems to support a "bridging" of the barrier channel or at least a diminished barrier effect by the Suwannee Current after Oligocene time.
The Miocene of the southeastern United States has been studied by many authors (too numerous to list here). Studies by Weaver and Beck (1977) and Riggs (1980) included regional paleogeographic maps of the area. Weaver and Beck connect the Gulf of Mexico with the Atlantic Ocean by means of a narrow trough near Gadsden County, Florida, that connects the Apalachicola Embayment with the southeast Georgia area which they call the Atlantic Embayment. The high "sill" in Gadsden County separates the Apalachicola Embayment from the trough area of the Atlantic Embayment.
Riggs (1980) also showed this same trough. Northwest of the trough is a terrigenous system labeled the Apalachicola Delta. Southwest of the trough are numerous shallow marine depositional basins.
The axis of the Apalachicola Embayment in the study area during Middle Miocene is shown on Figures 6 and 22.
The Late Miocene to Pliocene sediments have not been mapped throughout the area prior to this study. The structure contours prepared on the top of the Intracoastal Formation (Figure 9) and the Jackson Bluff Formation (Figure 10) define the orientation and relief of the synclinal axis on the respective horizons. It should be noted that the location of the axis seems relatively permanent after the latest Eocene. Also, the relief of the feature is less on the younger units, indicating that the embayment was filling in. When the Oligocene "sill" blocked the Suwannee Channel, the marine current was impaired so that lower velocities allowed sediment accumulation to take place. As more and more sediment filled in, the marine communication ceased betwen the Gulf and the Atlantic. From the Middle Miocene to the present, clastics filled in and began to prograde south. This is evident from the geologic cross sections and the geologic columnar sections in Appendix Ill.

STRUCTURAL HISTORY OF THE
APALACHICOLA EMBAYMENT
From the preceding discussion, a generalized summary of the structural history of the Apalachicola Embayment can be formulated. An


67





BUREAU OF GEOLOGY


embayment or low area existed in the Late Jurassic and Early Cretaceous and originated as a basement graben. This low area filled with sediments during the Jurassic and Early Cretaceous, and by the end of the Early Cretaceous was completely filled. This is evident from the down-to-Gulf dip of the overlying sediments with no deflection of the structural contours. The top of the Lower Cretaceous shows a synclinal axis again but shifted eastward. This feature is probably due to nondeposftion in a current-swept strait. The synclinal axis of this channel migrated westward until the Oligocene when it became located in the central Gadsden County area and dipped towards Gulf County. From Early Miocene until the Recent, the low feature slowly filled in and, in Pleistocene to Recent times became covered by the prograding Apalachicola River delta.
This simplified history is graphically illustrated in Figure 23. It seems the Neogene axis was situated over the Jurassic axis, with no apparent low or embayment in between. The deeper feature originated structurally, whereas the Paleogene-Neogene feature was due to slow deposition from a current-swept strait. It is probable, then, that the superimposition of the Jurassic and Cenozoic axis is concidental.
TERTIARY STRUCTURAL MOVEMENTS
Some authors feel that a graben is responsible for the Late Tertiary feature, although none have presented convincing evidence for the existence of faulting on a downthrown central block. Moore (1955), on the basis of a faunal discontinuity in three wells, postulated the Cypress Fault in Jackson County, Florida. Schmidt and Coe (1978) did not include a fault in their interpretation of the local stratigraphy. They did not rely on the faunal assemblage and contoured the formational units without a fault in their solution. Patterson and Herrick (1971) also reviewed the Cypress Fault and felt proof of such a fault was inadequate.
Sever (1966) cited a fault in the Thomas County area of Georgia. The Ochlockonee Fault, as named by him, was based on structure contour maps of the Suwannee and Tampa limestones. The current writer redrew these contour maps, using Sever's formation picks, and finds no reason to include a fault in the interpretation. Patterson and Herrick (1971), also looked at these data and stated "this fault is no more than a hypothetical possibility."
Another fault, the Bainbridge-Chattahoochee-Blountstown Fault of Tanner (1966), was also questioned by Patterson and Herrick (1971). Tanner uses surface physiography and "linears" as evidence for "dislocations." Core and well cuttings described by the author do not support offsets in the proposed areas.
Finally, Gelbaum and Howell (1979) hypothesize that "gravity faulting" along with downwarping caused the sediment thickening. They also point out that sediment infilling "healed" or "disguised" most fault traces. Their conclusions also are highly interpretive.


68





BULLETIN NO. 58


RECENT


TERTIARY


MID
CRETACEOUS



LATE
JURASSIC


PRE JURASSIC


Figure 23. Simplified Structural History of the
Apalachicola Embayment.


69





BUREAU OF GEOLOGY


From the foregoing discussion it is obvious that the origin of the trough in Tertiary times is not well-defined. The interpretations which rely on faulting, although possible, can not be documented using available data. As a result, the paleogeographic interpretation of a strait or Tertiary channel comparable to the present Florida Strait Is preferred.

CONCLUSIONS
1. The downdip Neogene lithologic units along the coast of Panhandle Florida are different lithologic packages from the contemporaneous units exposed undip.
2. These units can be defined and mapped using well cuttings, cores, and geophysical well logs.
3. The Upper Eocene Ocala Group limestones identified are generally penetrated only by deeper water wells. The three formations of the Ocala Group cannot be differentiated, and, as a result, the unit is referred to as Ocala Group undifferentiated.
4. Although not present along the coastal areas of West Ftorida, the Oligocene Marianna Limestone is present in the northern, updip parts of the Apalachicola Embayment.
5. The Oligocene Suwannee Limestone is present throughout the study area. It is generally the deepest formation penetrated by water wells. In the western part of the study area, the formation is undifferentiated from the downdlp Chattahoochee Formation.
6. The Chattahoochee Formation, an Oligocene-Miocene unit, is present in the updip northern parts of the Embayment. In the western and southern parts of the study area, it is indistinguishable from the Suwannee Limestone.
7. The St. Marks Formation (Early Miocene) is present on the eastern flank of the Apalachicola Embayment. Downdip towards Gulf County, the St. Marks cannot be distinguished from the younger Bruce Creek Limestone.
8. The Bruce Creek Limestone is a Middle Miocene formation, present downdip throughout the embayment. The unit can be mapped using cores and well cuttings. ft is predominantly a subsurface unit. Faunal and lithologic evidence suggest it was deposited under shallow, near-shore marine conditions. The top of the Bruce Creek Formation contains a zone rich in algal oncolites. This implies a shallowing of the water depth near the end of Bruce Creek deposition.
9. A clayey dolosilt bed is present over the Bruce Creek Limestone in the central and eastern parts of the embayment. This massive unit may have been deposited In a supratidal or tidal flat environment. The massive, clayey nature of this bed is probably important for its hydrologic implications. This clay would act as an aquiclude and create artesian conditions in the underlying Bruce Creek Limestone.
10. The Intracoastal Formation is a Miocene-Pliocene unit. It is mappable throughout the embayment area and is the downdip equivalent of


70





BULLETIN NO. 58


the exposed Alum Bluff Group and Jackson Bluff Formation. The Intracoastal is richly microfossiliferous and was estimated to have been deposited under marine conditions in less than 623 feet of water. The diverse group of marine organisms present, along with a significant amount of quartz sand, heavy minerals, clays, glauconite, and phosphate, leads to the concusion that the Intracoastal was seaward (shallow shelf) of a fluvial source. High amounts of nutrients from the exposed coastal plain to the north may have contributed to the high biological productivity in the area.
11. The Chipola formation has been mapped into the subsurface, downdip of the "type" area. It has been dated as Middle Miocene from fossiliferous outcrops. Downdip It is considered time-transgressive and is estimated to be Late Pliocene.
12. The Jackson Bluff Formation has been mapped Into the subsurface, downdip of the "type" area. It has been dated Late Pliocene from outcrops. Downdip it is estimated to extend into the Pleistocene.
13. Overlying the Jackson Bluff Formation are clay, clayey sand, quartz sand, and gravel beds. These sediments represent the clastic invasion of the fluvial delta over the shallow marine environment.
14. The massive clay beds appear to be correlative locally. They have yielded diatoms near the present coast. The fauna includes fresh-water and marine diatoms, and species associated with nutrient-rich waters near river outlets. This indicates a prograding delta during the time of deposition, Identified diatoms are found commonly in Pleistocene to Recent sediments.
15. Coarse quartz sands and gravels are common in the central part of the embayment. This unit is locally correlative, and represents the final stage in the fluvial elastic invasion over the shallow marine environment. The sand and gravel beds exhibit coarsening-upward sequences and unidirectional cross-bedding. The cross-bedding is tentatively correlated with prodettaic foreset beds. The coarse sands and gravels may locally be a shallow, fresh water source for domestic supplies. They also could be used as source of aggregate for the construction industry, although at present the area is considerably distant from population centers.
16. The synclinal axis for the embayment was established during Middle Miocene, Early Pliocene, and Late Pliocene times.
17. The approximate updip limits of deposition for the Neogene Formations were estimated.
18. Late Tertiary and Quaternary paleoenvironmental trends were estimated. This was accomplished using the literature, Identified fauna, sedimentary characteristics, and lithologic components.
19. The nomenclatural history and interpretive history of the Apalachicola Embayment was summarized. It was concluded that the embayment originated from a graben during pre-Jurassic times. The low area slowly filled with sediments and was filled by the end of the Early Cretaceous. A synclinal axis re-appeared at the top of the Lower Cretaceous series, but it was shifted eastward 50 or more miles. Through the Tertiary, this axis migrated westward until the Oligocene when it was once again aligned over the Jurassic-Cretaceous feature. The latter





72 BUREAU OF GEOLOGY

migrating feature is interpreted as a current-swept marine strait similar to the present Florida Strait. During Miocene times, the strait was bridged or "pinched off" due to the northwestward migration of the Florida carbonate platform and the southeastward migration of the clastics from the north. From Pliocene to Pleistocene times, the embayment slowly filled with sediment, until at present it is completely filled again and, therefore, no longer exists.






BULLETIN NO. 58


REFERENCES
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Neogene Formations, Northern Flotida and Atlantic Coastal Plain:
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I and Koeppel, P. E., 1973, Age of Some Neogene Formations, Atlantic Coastal Plains, Unfted States and Mexico: in Symposium on Calcareous Nannofossils, Proceedings, Gulf Coast Sect., Soc. Eoon.
Paleontol. Mineral., Houston, Texas, pp. 8-93.
Applegate, A. V., Pontfigo, F. A. Jr., and Rooke, J. H., 1978, Jurassic
Smackover Oil Prospects in the Apa/achicola Embayment: The Oil and
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AppliIn, Paul L., 1951, Preliminary Report on Buried Pre-Mesozoic Rocks in
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Arden, Daniel D., Jr., 1974, A Geophysical Profile in the Suwannee Basin,
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Georgia Coastal Plain, Ga. Geol. Survey Bull. 87, pp. 111-122.
Banks, J. E., and Hunter, M. E., 1973, Post-Tampa, Pre-Chipola Sediments
Exposed in Uberty, Gadsden, Leon, and Wakulla Counties, Florida:
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Barnett, R. S., 1975, Basement Structure of Florida, and its Tectonic
Implications: Trans. Gulf Coast Assoc. Geol. Socs., V. 25, pp. 122-142. Beem, K. A., 1973, Benthonic Foraminifera Paeoecology of the
Choctawhatchee Deposits (Neogene) of Northwest Florida: Unpublished Dissertation, Department of Geology, University of Cincinnati, 201
P.
Bender, Michael, 1971, The Reliability of He/U Dates on Corals: Amer.
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5407, pp.391-397.
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the Rio Grande Rise (South Atlantic): Madne Micropaleontology, V. 2,
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Bemhagen, Ralph J., 1939, Stratigraphy and Mcropaleontology of a Deep
Well in Calhoun County, Florida: unpublished thesis, Ohio State
University, 42 p.
Blow, W. H., 1969, Late Middle Eocene to Recent Planktonic Foramin/feral
Biostratgraphy: Proceedings of the First International Conference on Planktonic Microfossils, V. 1, Edizioni Tecnoscienza; Rome, Publisher,
pp. 199-421.


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Bolli, H. M., 1957, Planktonic Foraminifera from the Oligocene-Miocene C/pero and Lengua Formations of Trinidad, B. W /.: U.S. Nat. Mus. Bull, No. 215, pp. 97-123.
Boiling, Sharon, 1982, Neogene Stratigraphy of Gulf County, Florida: M. S.
unpublished thesis, Florida State University Geology Dept., 146 p.
Braunstein, J., 1957, The Habit of Oil in the Cretaceous of Mississippi and Alabama: in Frascogna, X. M., (ed.) Mesozoic Paleozoic Producing areas of Mississippi and Alabama: Miss. Geo. Soc., pp. 1-11. Bums, Frank, 1889, Unpublished Field Notes, U.S. Geological Survey
(Referenced in Cooke and Mossom, 1929, Geology of Florida, Florida
Geol. Survey, 20th Annual Report, 103 p).
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p.


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APPENDIX I

Diatoms from the Pleistooene Clay Beds




Full Text


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