The Hawthorn Formation of northeastern Florida ( FGS: Open file report 1 )

OPEN FILE REPORT OFR 1

THE HAWTHORN FORMATION OF NORTHEASTERN FLORIDA

PART I- THE GEOLOGY OF THE HAWTHORN FORMATION
OF NORTHEASTERN FLORIDA

By
Thomas M. Scott
Florida Bureau of Geology

1982

This open file report is the first of a series of reports instituted by the Florida Bureau of
Geology to allow for quicker dissemination of results of research projects. This report
contains the results of Part I of the proposed two-part Bureau of Geology's Report of
Investigation No. 94, to be published according to availability of funds. For more
information contact:

Thomas M. Scott
Florida Bureau of Geology
903 West Tennessee St.
Tallahassee, FL 32304

904/488-9380

Additional xerox copies of this report are available for $1.00, prepaid, from:

Publications Office
Florida Bureau of Geology
903 West Tennessee St.
Tallahassee, FL 32304 904/488-9380

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

DIVISION OF RESOURCE MANAGEMENT
Casey J. Gluckman, Director

BUREAU OF GEOLOGY
C. W. Hendry, Jr., Chief

REPORT OF INVESTIGATIONS NO. 94

THE HAWTHORN FORMATION OF NORTHEASTERN FLORIDA

PART I THE GEOLOGY OF THE HAWTHORN FORMATION
OF NORTHEASTERN FLORIDA

by
Thomas M. Scott
Florida Bureau of Geology

PART II CHARACTERIZATION AND BENEFICIATION OF THE NORTHEASTERN
THE PHOSPHATE-BEARING HAWTHORN FORMATION

by
B. E. Davis, G. V. Sullivan, and T. 0. Llewellyn
U.S. Bureau of Mines, Tuscaloosa Research Center
Tuscaloosa, Alabama

1982

Part II is missing

CONTENTS

Page

Part I -

Part II -

The Geology of the Hawthorn Formation of

Northeastern Florida............ ... .... 111

Characterization and Beneficiation of

Northeastern Florida Phosphate-Bearing

Hawthorn Formation.............. ........... 44

THE HAWTHORN FORMATION OF NORTHEASTERN FLORIDA

PART I

THE GEOLOGY OF THE HAWTHORN FORMATION OF
NORTHEASTERN FLORIDA

by

Thomas M. Scott
Florida Bureau of Geology
Tallahassee, Florida

TABLE OF CONTENTS

Page

Abstract ..... ......... .... ................................... 1

Acknowledgements..... ............................. 2

Introduction .............................................. 3

Purpose and Scope ............ ...................... 3

Methods.... ...... ........ ............. .. .......... ........ 3

Previous Work ... ........................ .................. 5

Ocala Group ...................... ........................ 5

Hawthorn Formation ......................................... 5

Undifferentiated Post-Hawthorn Sediments................... 9

Lithologic Characteristics of the Hawthorn Formation......... 11

Stratigraphy.................. ................ .... ........ 18

Geophysical Interpretation ............. ....... o..... ........ 26

Structure ........... ............ .... ....................... 26

Geologic History.... ................. ....... ............... 34

Summary and Conclusions...................................... 37

References .................................................. 39

Appendix .............. .. ............... .. .................. 43

Figures

1 Study Area Location. .......... .. ... .................. .. 4

2 Percentage of Dolomite Units in the Hawthorn Formation... 15

3 Percentage of Sand Units in the Hawthorn Formation....... 16

4 Percentage of Clay Units in the Hawthorn Formation...... 17

5 Location of Cross-Sections............................... 20

6 Cross-Section A-A'...................................... 21

7 Cross-Section B-B'....... ..... ..... ............ .. .... 22

8 Cross-Section C-C'... .. ... .. ................... ...... .. 23

9 Cross-Section D-D'................. ...... ................ 24

10 Typical Geophysical Log................................ 27

11 Structure Map of Ocala Group............................ 29

12 Features Expressed on Ocala Group Surface................ 30

13 Structure Map of Hawthorn Formation..................... 32

14 Isopach Map of Hawthorn Formation...................... 33

TABLES

1 Nomenclature Chart... ..6.......... ................ .. .... 6

Page

ABSTRACT

The Hawthorn Formation in northeastern Florida consists of
widely varying mixtures of clay, quartz sand, carbonate and
)hosphate. Phosphate is virtually ubiquitous throughout the
lawthorn sediments and occurs primarily as allochemical grains.
Che carbonate component consists predominantly of dolomite.
Limestone is generally less than 5 percent of the total
hawthorn carbonates. Clays are present in much of the Hawthorn.
?alygorskite and montmorillonite are the most common clay
minerals.
The Hawthorn Formation unconformably overlies the Upper
Eocene Ocala Group limestones. It is unconformably overlain by
sediments referred to as Post-Hawthorn Undifferentiated
Sediments.
The stratigraphy of the Hawthorn is both complex and
variable. However, a generalized three-part subdivision of
the Hawthorn is recognized in northeastern Florida. In general,
there is a basal dolomite unit overlain by a sand and clay member
(containing some dolomite) which is, in turn, overlain by a dolo-
itic unit. A fourth unit is recognized in the western part of
:he study area. This unit is a clayey, sandy, phosphatic unit
thought to be, at least in part, reworked.
The study area appears to have been affected by episodes of
tructural movement. Both minor warping and faulting are
recognized.

2

ACKNOWLEDGMENTS

The author of this report would like to express his grati-
:ude to the staff of the Bureau of Geology for their assistance
Ln drafting illustrations, typing, proofing, and editing the
manuscript. I gratefully acknowledge the contribution of the
;taff geologists and graduate student assistants for their
suggestions and discussions during the preparation of this
report. The writer is grateful to the many private landowners
#ho granted permission to drill stratigraphic core holes.
The author appreciates the assistance of the United States
Bureau of Mines in providing funding for core and data acquisi-
tion under contract Grant Number G0166038.

INTRODUCTION

The Florida Bureau of Geology in cooperation with the U.S.
bureau of Mines began to study the phosphate bearing sediments of
:he Hawthorn Formation in peninsular Florida in 1975. The first
phase looked at the phosphatic sediments in southwestern central
Florida (Scott and MacGill, 1981). The second phase, a con-
:inuation of the U.S. Bureau of Mines grant (Grant Number
00166038), studied the Hawthorn Formation in northeastern
Florida. This report on the second phase presents the results of
| detailed lithostratigraphic study of the Hawthorn Formation and
pf the overlying and underlying sediments.

PURPOSE AND SCOPE

The purpose of this study is to provide an understanding of
the geologic framework of the phosphatic Miocene Hawthorn
Formation in northeastern Florida and its relation to the
overlying and underlying units.
The Florida Bureau of Geology drilled 33 core holes in the
study area. These ranged from 140 to 500 feet (43 to 152 meters)
in depth. Core data obtained during this study were supplemented
by water well cuttings drilled prior to the investigation. All
cores and cuttings are on permanent file at the Bureau of
Geology in Tallahassee. This data provided the basis for
construction of the geologic cross sections and structure and
isopach maps of the various geologic horizons throughout the
area. The study area includes 10 counties: Alachua, Baker,
Bradford, Clay, Duval, Flagler, Marion, Putnam, St. Johns and
Union (figure 1).

METHODS

Thirty-three core holes were drilled in the study area
utilizing a Failing 1500 Drill Master drill rig recovering 3 inch
and 1 3/4 inch (7.6 and 4.4 cm) cores. The core diameter varied
with the type of tools required to sample a particular interval.
Washed samples of the post-Hawthorn sediments were collected at
5 foot intervals. Continuous coring began at the top of the
Hawthorn Formation and continued into the Eocene limestones. All
cores from Bradford, Clay, Putnam and western St. Johns counties
were split and half sent to the U.S. Bureau of Mines in
Tuscaloosa, Alabama for chemical analysis. The remaining split
is stored at the Florida Bureau of Geology in Tallahassee. All
core holes had gamma-ray logs run to facilitate correlations.

0

at
0

Figure 1. Study area location.

r
r

" ~rqC~t~Plb

This information plus well locations and total depth are listed
in the Appendix.
The cores were examined by a geologist, described and then
entered into the Bureau's computer data files. The computer
program is designed to aid the geologist in the interpretation of
lithologic parameters. Color coded strip logs were constructed
and correlated with the gamma ray logs. This aided in the visual
correlation between cores. The strip logs and gamma ray logs
were then used to construct geologic cross sections. Samples
were taken from the cores at various depths for x-ray analysis to
determine the dominant minerals present. The analysis was done
for both bulk samples and oriented clay samples.

PREVIOUS WORK

Ocala Group

The limestones presently incorporated in the Ocala Group
were originally placed in the Eocene by Conrad (1846). Smith
(1881) correlated the exposed limestones of Florida with the
Vicksburg Limestone of Mississippi and Alabama and applied that
name to them. Dall and Harris (1892) referred to these sediments
as the Vicksburg Group. The term Ocala Limestone was first used
by Dall and Harris (1892) in reference to the rock being quarried
and best exposed near Ocala in Marion County. Dall (1896) lumped
the Eocene and the "Old Miocene" of Florida into the Oligocene.
Dall (1903) proposed the term "Peninsular Limestone" for the
lower division of the Vicksburg Group in the Florida peninsula.
Cooke (1915) discovered that the Ocala Limestone and the
Peninsular Limestone were identical and older than the Vicksburg
Limestone. He placed the Ocala Limestone back into the Eocene
(Jackson Age). Applin and Applin (1944) divided the Ocala
Limestone into an upper and lower member. Vernon (1951)
restricted the Ocala Limestone to the upper member of the Applins
and referred to the "basal 80 feet of the Ocala Limestone of
Cooke (1945)" as the Moodys Branch Formation. Vernon's Moodys
Branch Formation was subdivided into the Williston Member and the
Inglis Member. Puri (1957) raised the Ocala Limestone to group
status and included three formations: the Crystal River,
Williston, and Inglis. The Florida Bureau of Geology currently
accepts and uses Puri's terminology (Table 1).

Hawthorn Formation

The Hawthorn Formation was originally described by L. C.
Johnson (1888), who referred to the phosphatic beds in Alachua
and Columbia counties as the Waldo Formation. Dall and Harris
(1892) using much of Johnson's work, abandoned Johnson's Waldo
Formation and described the phosphatic beds as the "Hawthorne

TABLE 1: Nomenclature of previous authors and this report.

DALL & HARRIS (1892) MATSON & CLAPP (1909) COOKE (1945) PURI & VERNON (1964) THIS REPORT

PLEISTOCENE Sands Terrace and Coastal Terrace and Terrace deposits
Deposits Coastal Deposits Caloosahatchee beds
Undifferentiated
Post-Hawthorn
PLIOCENE Caloosahatchee Nashua and Caloosa- Caloosahatchee Sediments
beds hatchee beds and Citronelle Fms.

MIOCENE Newer
Miocene
Jacksonville Ls. Choctawhatchee Marl Duplin Marl Ft. Preston-Coarse Hawthorn Fm.
and Clastics
Older Jacksonville Fm. (Ls.) Hawthorn Fm.
Miocene Hawthorne

EOCENE Ocala Ls. g Hawthorne Fm. Ocala Ls. Ocala Group Ocala Group
(Nummulitic beds)
Ocala Ls.
"Peninsular" Ls.
O ____

beds." Even though Dall did not describe a type locality or use
the term "formation," later workers have credited him for naming
the Hawthorn Formation and describing the type locality around
Hawthorne, Alachua County. The Devil's Millhopper, near
Gainesville, as discussed by L.C. Johnson (1888) Dall and Harris
(1892), and Cooke (1945), and Brook's Sink in Bradford County, as
described by Cooke (1945), are accepted as cotype localities for
the Hawthorn Formation (Pirkle, 1956). Scott (1982) discusses
the cotype localities and equates them to cores taken nearby,
designating the cores as cotype cores for the Hawthorn Formation.
In 1909, Matson and Clapp designated Dall's "Hawthorne beds"
as a formation and considered it to be at least in part contem-
poraneous with the Tampa and Chattahoochee formations. They
included the Hawthorn, Tampa, Chattahoochee and Alum Bluff for-
mations in the Apalachicola Group. Matson and Clapp's descrip-
tion did include some limestone containing the echinoid
Cassidulus sp. This limestone is now referred to as the Suwannee
Limestone.
Vaughan and Cooke (1914) correlated the Hawthorn Formation
with the Alum Bluff Formation in northwest Florida as defined by
Matson and Clapp (1909, p. 91) and suggested the name Hawthorn be
dropped. In later publications, Matson and other authors
referred to the Hawthorn Formation as the Alum Bluff Formation.
In 1929, Cooke and Mossom reinstated and redefined the
Hawthorn Formation to include Dall's (1892) "Hawthorne beds," the
Sopchoppy Limestone and the Alum Bluff Formation of peninsular
Florida as defined by Matson and Clapp (1909). This new defini-
tion excluded the Cassidulus-bearing limestone that had been
described by Matson and Clapp (1909).
Very early in the nomenclatural history of the Hawthorn
Formation it was considered to be of "older Miocene" age by Dall
and Harris (1892). They observed the Hawthorn Formation in
Alachua County lying unconformably on rocks of supposed Vicksburg
age and thought it contemporaneous with the Chipola Formation. A
short while later, they altered their concept of the
Oligocene-Miocene boundary and positioned the Tampa, Hawthorn,
and Chipola formations, previously called "Older Miocene," in the
iOligocene. Matson and Clapp (1909) continued this age assign-
iment, equating the Tampa and Chattahoochee formations in the
panhandle of Florida to the Hawthorn Formation.
Vaughan and Cooke (1914), in describing several sections
near White Springs on the Suwannee River, thought the Hawthorn
Formation was contemporaneous with the Alum Bluff Formation.
Faunal and stratigraphic data formed the basis for their correla-
tion.
Cooke (1945) correlated the Hawthorn Formation with the
Chipola Formation and parts of the Shoal River Formation in the
Florida panhandle. He tentatively transferred some beds of Late
Miocene age that were previously included in the Hawthorn by
Matson and Clapp (1909) to the Duplin Marl. Cooke considered

-heir contact unconformable and postulated that the Hawthorn was
deposited by an expanded Tampa sea and that the Tampa/Hawthorn
contactt was conformable.
Pirkle (1956) studied the types of sediments in the Hawthorn
Formation. He stated that the dominant sediment types found in
the Hawthorn in Alachua County include quartz sand, clay, car-
Donate and phosphate. He further stated, "The proportions of
these materials vary from bed to bed and, in cases, even within a
few feet both horizontally and vertically in individual strata."
Pirkle, et al. (1965) studied the Hawthorn sediments in more
detail paying particular attention to the heavy mineral suites.
Reynolds (1962), in studying the relationship of the
Tampa-Hawthorn sequence in peninsular Florida, identified litho-
somes and used clay mineralogy to conclude that the two for-
mations interfingered. He identified a western carbonate
lithosome (Tampa), an eastern plastic lithosome (Hawthorn), and a
central Florida shelf where these two lithosomes interfingered.
The carbonate lithosome contained a palygorskite-montmorillonite-
sepiolite suite, whereas the plastic lithosome contained a
montmorillonite-illite suite.
Espenshade and Spencer (1963) included all the phosphate
bearing sediments overlying older carbonate rocks in North
Florida in the Hawthorn Formation. This included the reworked
phosphorites. They divided the Hawthorn into an upper phos-
phorite unit and a lower phosphatic dolomite unit.
Brooks (1966) proposed raising the Hawthorn to group status
based on the complex stratigraphy that has been discussed by many
authors (Pirkle, 1956; Espenshade and Spencer, 1963; Brooks, et
al., 1966). Brooks (1967) later reiterated this adding that the
youngest formation to be included in his Hawthorn "Group" would
be the Bone Valley Formation.
Sever, et. al., (1967) were able to divide the Hawthorn into
four recognizable lithologic units in the South Georgia North
Florida area. They state, however, that all these units are not
present over the entire area.
Puri and Vernon's (1964, p. 145) statement concerning the
Hawthorn expresses the feelings of many geologists. They state
that the Hawthorn Formation "...perhaps is the most misunderstood
formational unit in the southeastern United States. It has been
the dumping ground for alluvial, terrestrial, marine, deltaic and
pro-deltaic beds of diverse lithologic units in Florida and
Georgia that are stratigraphic equivalents of the Alum Bluff
Stage."
The North Florida phosphate district (as delineated by
Williams, 1971) includes the western part of the present study
area. Williams (1971) studied the phosphate deposits and
included part of them in the Hawthorn Formation.
Cooke (1945) divided the Miocene series into three different
stages in peninsular Florida: Early, Middle and Late. He
believed that the age of the Hawthorn Formation was Middle

4iocene. In the past, this type of definition has been general
practice in defining both the age and boundaries of Florida for-
nations. However, the lack of diagnostic data has made it dif-
ficult to determine the exact age and boundaries of the
formations. As a result, the age assignment of the Hawthorn
Formation has varied considerably since its inception. Recent
data indicates that the deposition of the Hawthorn began in the
earliest Miocene as shown by foraminifera in W-13815 in Nassau
County (R. Hoenstine, Fla. Bur. Geol., personal communication).
A core (W-13958) in Indian River County, Florida, suggests that
Hawthorn deposition continued into the Early(?) Pliocene south of
the study area ibidd).
The areal extent of the Hawthorn Formation was extended by
Cooke (1945) from Dall and Harris' (1892) descriptions of sec-
tions in central Florida to include strata occurring east of the
Apalachicola River, northward to Berkeley County, South Carolina,
and southward to cover almost all of the peninsula of Florida
except where it has been completely eroded. The Hawthorn
Formation is present in the subsurface of the study area except
where it is absent due to erosion or possibly nondeposition near
the southeast, south and southwest edges of the study area.
The authors mentioned in this section were those who defined
or redefined the Hawthorn Formation. Many others have published
on the Hawthorn Formation but have followed the authors mentioned
for their definition of the Hawthorn Formation. They are too
numerous to discuss in this report.

Undifferentiated Post-Hawthorn Sediments
The undifferentiated post-Hawthorn sediments consist of a
variety of lithologies. These include fine to coarse quartz
sands, occasionally containing quartz gravel, sandy clay, clay,
shell beds, marl and limestone. Formational assignments have
been as varied as the lithologies. Formation names applied, from
oldest to youngest, include: Fort Preston Formation,
Jacksonville Limestone, Choctawhatchee Formation, Duplin Marl,
Nashua Marl, Caloosahatchee Marl, unnamed coarse clastics and
terrace deposits.
The Upper Miocene Jacksonville Limestone was named by Dall
and Harris (1892) for a limestone exposed in an excavation near
Jacksonville. It was described as a "...porous, slightly
phosphatic, yellow rock...contains numerous molds of fossil
shells belonging to the new Miocene." Dall and Harris noted
occurrences of the Jacksonville Limestone on Black Creek in Clay
County and Preston Sink in Alachua County.
Matson and Clapp (1909) called the Jacksonville Limestone
:he Jacksonville Formation and described it as a clayey, sandy
imestone with zones of abundant fossils. They differentiated it
rom the Choctawhatchee Marl in that the Jacksonville Formation
contained mica, more lime and less sand.

Cooke (1945) dropped the name Jacksonville Limestone or
Formation and placed the rocks in the Duplin Marl which he
described as a sandy, shell marl. Cooke differentiated the
Duplin from the Choctawhatchee and restricted the Choctawhatchee
to the Florida panhandle.
Bermes, et al. (1963) in their study of Flagler, Putnam and
St. Johns counties simply called these lithologies "Upper Miocene
or Pliocene deposits." Clark, et al. (1964) extended the
Choctawhatchee Formation into Northeastern Florida and referred
the "late Miocene beds" in Alachua, Bradford, Clay and Union
counties to it.
The Miocene Fort Preston "formation" is an informal name
applied by Puri and Vernon (1964) to the coarse elastic material
of peninsular Florida. Puri and Vernon (1964) described these
sediments as "...poorly sorted quartz grains, ranging in size
from fine sand to small pebbles, in a clay matrix...usually red
or orange in color...to white or light yellow gray." Cooke
(1945) had placed these sediments in the Citronelle Formation.
Clark, et al. (1964) stated that their unnamed coarse plastics,
which Puri and Vernon (1964) identified as Fort Preston (Middle
Miocene), overlie the Choctawhatchee Formation which is younger
than the Fort Preston. Due to the nonfossiliferous nature of
these plastics, they have been assigned to several different
ages. This has given rise to the confusion which is evident from
the variety of names applied to them.
The Nashua Marl was named by Matson and Clapp (1909) for
"... Pliocene marls extensively developed in the valley of the
St. Johns River...". It was named for the town of Nashua in
Putnam County on the St. Johns River. Matson and Clapp state,
"The Nashua Marl bears a strong lithologic resemblance to the
Caloosahatchee Marl. There is the same alternation of sand beds
with shell marl. The matrix of the Nashua Marl, white, usually
calcareous, is always more or less sandy and sometimes consists
of nearly pure sand. The shells are commonly well preserved
though locally a marl consisting of broken and eroded fragments
of shells is not uncommon." Mansfield (1918) studied the
mollusks of the Nashua and decided they were very similar to the
Caloosahatchee Marl. Cooke and Mossom (1929) equated the Nashua
with the Caloosahatchee and discarded the term Nashua.
Dall and Harris (1892) described a unit of predominantly
sand and shells in south Florida, giving it the name
"Caloosahatchee beds." Matson and Clapp (1909) used the term
marl rather than beds. Cooke and Mossom (1929) brought the term
Caloosahatchee Marl into the present study area when they
discarded the Nashua as discussed above.
The unnamed coarse clastics of Clark, et al. (1964) are
described as a "...nonfossiliferous, deltaic deposit that is com-
posed mostly of varicolored sand and clayey sand that contains
quartz gravel locally." They placed it in the Pleistocene Epoch.
These are the same sediments that Cooke (1945) called Citronelle

(Pliocene) and Puri and Vernon (1964) called Fort Preston
(Miocene). This unit is mapped by Puri and Vernon (1964) as
Fort Preston (Miocene). Puri and Vernon mapped the Fort Preston
as occurring in the higher ridges of the study area.
The terrace deposits are often considered to be Pleistocene
in age and are related to the fluctuations of sea level. These
deposits include a wide variety of lithologies occurring at many
different elevations. Clark, et al. (1964) included sands,
clayey sands, clays, marls, and shell in this unit. Clark, et
al. (1964), and Bermes, et al. (1963), believed that this unit
blanketed the greater part of the present study area.
Pirkle (1956), in discussing the post-Hawthorn sediments,
placed the units above the Choctawhatchee shell marl in an undif-
ferentiated category. Pirkle believed these materials to be
Pliocene or Pleistocene. He states, "...a Pleistocene age is
considered far more likely."
In this report the term undifferentiated is used for the
sediments overlying the Hawthorn in the study area due to the
evident stratigraphic confusion that exists. These will be
referred to as Undifferentiated Post-Hawthorn Sediments.

LITHOLOGIC CHARACTERISTICS OF THE HAWTHORN FORMATION

The Hawthorn Formation in the southeast is probably one of
the most misunderstood units in the stratigraphic section. Such
glorified terms as "a garbage can" and "F.U.B.A.R." (Fouled Up
Beyond All Recognition) have been applied to it. The confusion
as to what actually constitutes the Hawthorn Formation is readily
understood since the variability of the sediments is the rule
rather than the exception.
The sediments of the Hawthorn Formation consist of widely
varying mixtures of clay, quartz sand, carbonate and phosphate.
Beds of end-member composition (i.e., pure clay) are not common
but do occur. The most common lithologies encountered in the
Hawthorn are dolomitic, clayey sands and clayey and/or sandy
dolomites.
Phosphate is virtually ubiquitous throughout the Hawthorn
sediments. The occurrence of phosphate is the most important
lithologic factor in the identification of the sediments grouped
in the Hawthorn. It is, however, not the only factor involved
since phosphatic material is commonly reworked into the
overlying, post-Hawthorn units.
The phosphates occur primarily as allochemical grains.
These can be divided into pelletal form and intraclasts. The
pelletal grains are the dominant phosphate form in the Hawthorn
of the study area. They are sand-sized and generally well
rounded with a smooth to polished surface. These grains contain
varying amounts of microscopic inclusions disseminated throughout
(Riggs, 1979a). The inclusions are dolomite rhombs, microfossil
debris and terrigenous plastic material. Riggs (1979a) suggests

that the pelletal phosphate was formed by benthic organisms
ingesting the phosphate mud along with the included con-
taminants and excreting these as fecal pellets. Miller (1982)
feels that gentle bottom currents were strong enough to cause
the pelletal phosphate to form from a phosphatic gel or mud.
The pelletal phosphates are generally black to dark gray but
range to tan and white in more weathered or reworked sections.
The lighter colors are generally found higher in the section near
the upper Hawthorn boundary.
Phosphatized skeletal debris and oolitic or pseudo-oolitic
grains are also found in the Hawthorn Formation. Miller (USGS,
1981 personal communication) reports oolitic phosphate grains in
the Hawthorn in the Osceola National Forest in the northwestern
section of the study area.
Phosphatic intraclasts occur scattered throughout the sec-
tion but are most common in the dolomites in the lower Hawthorn.
Two types of intraclasts are recognized in the study cores.
First are the phosphate intraclasts which Riggs (1979a) describes
as fragments of penecontemporaneous phosphate sediments that have
been torn up and redeposited. The intraclasts are abraded,
rounded and somewhat irregular. In some of the intraclasts, rem-
nants of.original bedding may be seen. Smaller intraclastic
grains may be difficult to separate from the pelletal forms.
The second type of intraclasts are phosphatized dolomite
intraclasts. These intraclasts show a zoned replacement of
dolomite by phosphate. The zonation trends from unreplaced dolo-
mite in the interior to replacement phosphate at the outer
edges. They are irregular and abraded with somewhat rounded to
very rounded edges. This type of intraclast is most common in
the lower Hawthorn dolomites.
Many "rubble" zones occur scattered through the Hawthorn
Formation. These zones consist of phosphate and dolomitic
intraclasts incorporated in a soft matrix of sand, clay, and
dolomite. They appear to represent periods when the phosphate
and carbonate muds were able to accumulate, become somewhat
lithified to well lithified, then were ripped up and redeposited.
The clasts commonly are bored by pelecypods and show varying
degrees of abrasion.
Phosphate concentrations in the Hawthorn range from zero
to greater than 40 percent. The higher concentrations are un-
common. Average phosphate concentrations in the Hawthorn range
from 5 to 10 percent based on visual estimates. Reworked
Hawthorn sediments form beds that often contain phosphate in
concentrations of 30 to 40 percent (W-14255, Mizelle #1, Bradford
County, for example). Units of this grade may one day be econo-
mically attractive.
The carbonate component of the Hawthorn Formation is com-
posed predominantly of dolomite. However, limestone and micrite
occur sporadically, both vertically and laterally throughout the
area. In general, limestones account for less than 5 percent of

the total Hawthorn carbonates. A notable exception to this
occurs in the study area well W-14255, Mizelle #1. The carbonate
sediments in the Hawthorn from Mizelle #1 core are predominantly
calcareous with only a minor dolomite component.
Dolomite is common throughout the Hawthorn Formation. It
occurs not only as a dolomite primary lithology but also as a
matrix material in other lithologies. As a result, dolomite is
found in virtually the entire Hawthorn section. Lithologies
lacking dolomite are not common but do occur, particularly as
clays.
Dolomitic sediments in the Hawthorn range from poorly con-
solidated to well indurated and contain widely variable amounts
of quartz sand, silt, clay and phosphate. They can be sub-
divided into two basic categories, dolosilts and dolomites.
Although they are both composed of the mineral dolomite and are
gradational with one another, they form two identifiable litho-
logies and will be discussed separately.
Dolosilts are composed of silt-sized dolomite rhombs with
varying percentages of accessory minerals. Induration is
generally poor to moderate. The accessory minerals are quartz
sand, silt, clay and phosphate. The phosphate occurrence is
related to the occurrence of sand. If no sand is present,
phosphate is generally not encountered. This is apparently due
to the plastic nature of the phosphate grains. The phosphate is
transported with the sand from areas of primary accumulation to
the areas of dolosilt formation or accumulation.
Dolosilts are often confused with clays by geologists and
others unfamiliar with the peculiarities of the Hawthorn
Formation. Admittedly, the dolosilts bear a resemblance to clays
particularly when first recovered and they often contain clay in
abundance. However, the silty texture and reaction to dilute HC1
indicate that clay is not the primary constituent. Examination
under a binocular microscope and X-ray analysis confirm the iden-
tity of the dolosilts.
Dolosilts occur throughout the Hawthorn section. However,
they commonly occur higher in the section. Color ranges from
yellowish gray (5Y7/2 or 5Y8/1, GSA Rock Color Chart) to olive
gray (5Y3/2 or 5Y4/1).
Dolomites in the Hawthorn Formation are composed of anhedral
to subhedral, crystalline dolomites with varying percentages of
accessory minerals. The dominant accessory minerals are the same
as those in the dolosilts; sand, silt, clays and phosphate. The
proportions of these minerals are highly variable. The dolomites
generally range from moderately to well indurated. Color ranges
from light gray (N7) to light olive gray (5Y5/2 or 5Y6/1).
Dolomites often occur interbedded with dolosilts. The two litho-
logies also appear to grade into each other. The gradational
nature and the more coarse, intergrown crystalline nature of the
dolomites suggest that some of these dolomites are the result of
aggrading neomorphism of the dolosilts.

Dolomites resulting from the replacement of limestone are
common in the Hawthorn particularly in the lower portion. These
dolomites contain fossil molds and fossil "ghosts" that are indi-
cative of an original limestone lithology.
The origin of the dolosilts is somewhat of an enigma. As
previously mentioned, they are composed of a poorly consolidated
dolomite in the form of discrete rhombs. They are often inti-
mately mixed with varying amounts of clay, quartz, pilt and
sand. Riggs (1979a) suggests that the dolosilts are detrital,
having been transported from source areas south and east of the
present landmass. However, no definitive work has been done con-
cerning the origin of this sediment type.
Figures 2, 3 and 4 show the relative percentages of dolo-
mite, sand and clay units within the Hawthorn. These maps are
constructed from core data only. Percentages of each rock type
were determined by adding the thickness of each unit of a
specific rock type and dividing by the total thickness of the
Hawthorn Formation in the core. Additional information from well
cuttings does not provide an accurate indication of the litholo-
ies due to the loss of softer and finer grained materials during
killing, sample collection and sample preparation.
The total dolomite component of the Hawthorn sediments
shows a trend of increasing abundance toward the south-central
part of the study area (figure 2). The greatest amount of dolo-
mite in the Hawthorn is in the southern Clay County northern
and western Putnam County area. Here cores contain from 50 to
more than 70 percent dolomite. The lowest percentage of dolomite
is found in westernmost Bradford County where less than 10 per-
cent of the Hawthorn Formation is dolomite. In the study area,
the percentage of dolomite is in the less than 10 to 70 percent
range. Riggs (1979a) places the present study area in a section
of the state in which the Hawthorn is dominantly terrigenous
sediments with subordinate carbonates. This suggests that the
abundance of dolomite in the Clay-Putnam county area is somewhat
anomalous and represents a possible carbonate bank. Carbonate
sediments increase in abundance south of the study area becoming
the dominant sediment type in central and southern Florida.
Sand, both as a rock type and as an accessory mineral, is a
major constituent of the Hawthorn Formation. It is the most
abundant rock type encountered in the Hawthorn in the study area.
Quartz sand also is the most common accessory mineral in the
Hawthorn. Accessory minerals in the sand-size range include
minor amounts of feldspar, heavy minerals and variable con-
centrations of phosphate. Pirkle, et al. (1965) studied
the Hawthorn sediments from the Devil's Millhopper (northwest of
Gainesville, Alachua County) and Brooks Sink (Bradford County).
They analyzed the insoluble residues for percent quartz sand,
clay, P205, type and abundance of heavy minerals and size dis-
tribution of the sands. In general, they showed the Hawthorn
sands to be in the medium to fine size classification with the

Figure 2. Percentage of dolomite units in the Hawthorn Formation.

Figure 3. Percentage of sand units in the Hawthorn Formation.

Figure 4.. Percentage of clay units in the Hawthorn Formation.

greatest amount of sand retained on the 60 mesh (2 0) and 120
mesh (30 ) sieves. The heavy minerals found to be most common
were ilmenite, leucoxene, kyanite, sillimanite, staurolite, epi-
dote and garnet.
Figure 3 is a percent sand (rock type) map. The greatest
sand concentrations occur in north and northwestern portions of
the study area suggesting a source to the north and northwest.
Sand content generally decreases to the south and southeast. A
general decrease in average sand grain size followed the same
trend as abundance. The map shows a northwest-to-southeast trend
of a decreasing percentage of sand units within the Hawthorn in
the central portion of the study area.
Clays are present throughout much of the Hawthorn Formation.
Most often the clays are accessory mineral in another dominant
lithology, i.e., clayey, dolomitic sand or clayey, sandy dolo-
mite. However, clay beds are not uncommon. Figure 4 shows the
areal distribution of clays as a percentage of the total Hawthorn
section. The maximum percentage of clay beds present is greater
than 70 percent in W-14354 in east-central Putnam County. Clay
percentages of 30 to 40 percent are found along the eastern and
southeastern edge of the map. Lower percentages are dominant
over most of the remaining map area. Note the increase in clay
content in Alachua County.
The clay minerals present in the Hawthorn are palygorskite,
montmorillonite, sepiolite, illite, kaolinite and chlorite (Reik,
1982). Palygorskite and montmorillonite are the dominant clays
in the Hawthorn of the study area. Sepiolite, illite and
chlorite are uncommon. Kaolinite is found only in the more
weathered or leached sections of the Hawthorn.

STRATIGRAPHY

The Hawthorn Formation within northeastern Florida un-
conformably overlies the Eocene limestones of the Ocala Group.
The unconformity cuts increasingly older rocks toward the
southeast. Throughout most of the study area the first Eocene
limestone encountered is the Crystal River Formation, the
youngest unit of the Ocala Group. In eastern and southeastern
Putnam County and into Flagler County, the Williston Formation
underlies the unconformity in the southeastern most corner of the
study area (Bermes, et al, 1963; Reik, 1980; Leroy, 1981). The
entire Ocala Group is missing in central Volusia County,
southeast of the study area (Wyrick, 1960). The first Eocene
carbonate encountered in central Volusia County is the Avon Park
Limestone.
The Hawthorn Formation is unconformably overlain by several
different units. The location within the study area dictates
which of the units lies on the Hawthorn. These units are often
lumped into one of two categories 1) Upper Miocene to Pliocene
Deposits; 2) Post-Hawthorn to Recent Deposits (Bermes, et al,

(Pliocene) and Puri and Vernon (1964) called Fort Preston
(Miocene). This unit is mapped by Puri and Vernon (1964) as
Fort Preston (Miocene). Puri and Vernon mapped the Fort Preston
as occurring in the higher ridges of the study area.
The terrace deposits are often considered to be Pleistocene
in age and are related to the fluctuations of sea level. These
deposits include a wide variety of lithologies occurring at many
different elevations. Clark, et al. (1964) included sands,
clayey sands, clays, marls, and shell in this unit. Clark, et
al. (1964), and Bermes, et al. (1963), believed that this unit
blanketed the greater part of the present study area.
Pirkle (1956), in discussing the post-Hawthorn sediments,
placed the units above the Choctawhatchee shell marl in an undif-
ferentiated category. Pirkle believed these materials to be
Pliocene or Pleistocene. He states, "...a Pleistocene age is
considered far more likely."
In this report the term undifferentiated is used for the
sediments overlying the Hawthorn in the study area due to the
evident stratigraphic confusion that exists. These will be
referred to as Undifferentiated Post-Hawthorn Sediments.

LITHOLOGIC CHARACTERISTICS OF THE HAWTHORN FORMATION

The Hawthorn Formation in the southeast is probably one of
the most misunderstood units in the stratigraphic section. Such
glorified terms as "a garbage can" and "F.U.B.A.R." (Fouled Up
Beyond All Recognition) have been applied to it. The confusion
as to what actually constitutes the Hawthorn Formation is readily
understood since the variability of the sediments is the rule
rather than the exception.
The sediments of the Hawthorn Formation consist of widely
varying mixtures of clay, quartz sand, carbonate and phosphate.
Beds of end-member composition (i.e., pure clay) are not common
but do occur. The most common lithologies encountered in the
Hawthorn are dolomitic, clayey sands and clayey and/or sandy
dolomites.
Phosphate is virtually ubiquitous throughout the Hawthorn
sediments. The occurrence of phosphate is the most important
lithologic factor in the identification of the sediments grouped
in the Hawthorn. It is, however, not the only factor involved
since phosphatic material is commonly reworked into the
overlying, post-Hawthorn units.
The phosphates occur primarily as allochemical grains.
These can be divided into pelletal form and intraclasts. The
pelletal grains are the dominant phosphate form in the Hawthorn
of the study area. They are sand-sized and generally well
rounded with a smooth to polished surface. These grains contain
varying amounts of microscopic inclusions disseminated throughout
(Riggs, 1979a). The inclusions are dolomite rhombs, microfossil
debris and terrigenous plastic material. Riggs (1979a) suggests

1963). Clark, et al (1964) referred to the Post-Hawthorn units
as 1) Choctawhatchee Formation, 2) Older Pleistocene Terrace
Deposits, 3) unnamed Coarse Clastics. For the purposes of this
study formational names were not applied to these units. They
are shown on the cross sections as specific lithologies (figures
5-9).
Sandy, often clayey, shell beds overlie the Hawthorn east of
central Clay and Putnam counties (figure 9, DD'). Cross sec-
tions AA' and BB' (figures 6 and 7) clearly show how the shell
unit onlaps the Hawthorn. Also, the clayey sand overlying the
shell bed shows a similar relationship. Further west (inland),
the sediments overlying the Hawthorn are predominantly sands,
clays and clayey sands (figure 6 and 7). Scattered lenses or
erosional remnants of shell beds and limestone occur on top of
the Hawthorn (W-8400 BB'; W-14283 AA', CC'). The limestone
cropping out in Brooks Sink (Bradford County, T7S, R20E, S12,
SW1/4, of SW1/4) is an example of the scattered remnants or lenses of
carbonate. The limestone is absent from the cores east and west
of the sink (W-14255 and W-14280). Pirkle (1956) referred to
this limestone as lower Choctawhatchee (Upper Miocene) in age
based on ostracods identified by H.S. Puri of the Florida Bureau
of Geology.
The stratigraphy of the Hawthorn Formation is complex and
variable. However, lithologic patterns can be seen when litholo-
gies are grouped into four categories. These categories, based
on the dominant component, are dolomite, limestone, sand and
clay. As previously stated, the occurrence of end-member litho-
logies (i.e., pure sand, etc.) is uncommon. However, they do
occur, most often as clays and dolomites.
A generalized three part subdivision of the Hawthorn
Formation is obvious from the cross sections (figures 6-9). The
cross sections show an upper dolomite unit overlying a sand and
clay member which overlies a basal dolomite unit. These units
are gradational with each other. Each unit also contains thin
beds lithologically similar to the other units. A fourth unit is
recognized in wells in the western portion of the study area
(figure 6, AA', W-14255, W-14280). It occurs at the top of the
Hawthorn and is a unit of reworked clayey, sandy, phosphatic
material. Scott (1982) discussed this briefly.
The upper dolomitic unit consists of sandy to very sandy,
sometimes clayey, phosphatic dolomites. Induration is generally
poor to moderate, however, well indurated units do occur. Thin
sand beds are common and thicker sand units occur sporadically.
Clay layers also occur in this member. The upper dolomitic unit
is absent in the southeastern corner of the study area presumably
due to erosion (figure 9, DD'). It is also absent over at least
part of the St. Johns Platform (see structure section and
figure 12) again presumably due to post-Hawthorn erosion.
Westward across the study area, this unit appears to interfinger
with and grade into a more plastic unit similar to the middle

20

2-rT5,- u.Mam o FO
4 tllsl
0 EOR IA-

-- I e, I I / -LL -

-r *" -
f[ i ,-/ 7 _'_ ij--- .

7. v

Fig r- 5. oca I o cosssc i'o .
-- i .. Ii .- t. ,
Fiur 5 L o crs. s c t"o

Figure 5. Location of cross-sections.

8. See
CS-Clfq)S"ldy
SC Sao .Carty
Sh .__ 11Bid

LSC -l,.LMete,.o*Ctjl(y
$LCSodM.Col[o.otCleae
CLS-Chiol.caisSrdl
CSDClay.S"" lmatic
SOC...SondOoSrmo .Caero
OSC_...DolomJf.SOndy.Cl*oyf

- -Falt

Figure 6. Cross-section A-A'.

GC.....C4Ilovper
St..Jcftdet.sC

LIC-.m lv..t n01oWChIvl
SLCLblad.CreloeaciCfr
CL8.Cle.CoCkahsou0tndt
CSL.ClcnSodootommtc
8DCSB.A0ln.tt.Clot

- H#1VlWfln Fm bound0141a
*** 'F"(Oll(0hed ylea

Figure 7. Cross-section B-B'.

'Figure9. Cross-section D-D'.

member of this study (figures 6 and 7, AA' and BB').
The middle plastic unit of the Hawthorn Formation in
northeast Florida consists of clayey, dolomitic, phosphatic
sands. These are generally poorly to moderately indurated. Clays
containing widely varying amounts of sand, dolomite and
phosphate are common, occasionally comprising the bulk of this
member. Thin dolomite beds are also often present. This unit is
present throughout the study area but appears to become less
distinct, merging with the upper and lower members, toward the
north (figure 9, DD').
The basal dolomitic member is present throughout northeast
Florida. It consists of sandy, sometimes clayey, phosphatic
dolomites that are poorly to well indurated. Sand and clay beds
also occur in this unit. This unit thins to the west in the
study area and thickens toward the Jacksonville Basin (figures
6-9).
Miller (1978) investigated the Hawthorn in the Osceola
National Forest in Baker and Columbia counties. He identified
five lithologic units within the Hawthorn. The units designated
A through E, compare well with the three units identified in this
report. Miller's basal member, E, is a carbonate unit comparable
to the lower dolomitic unit of this report. Unit D is a
complexly interbedded carbonate-clastic member representing a
transitional sequence between units E and C. Unit C is a plastic
unit comparable to the middle plastic unit of the present study.
Unit B is a plastic (clay) to carbonate member which appears to
correlate with part of the middle plastic unit. Unit A is a car-
bonate member and correlates to the upper carbonate rich unit of
this study.
The upper dolomite unit seen on the cross sections crops out
in Brooks Sink, Bradford County. This outcrop reveals the thin
bedded and lithologically variable nature of the upper Hawthorn
dolomites (Scott, 1982).
The lower boundary of the Hawthorn Formation is easily
picked based on a drastic lithologic change. The basal Hawthorn
s generally a brownish to greenish, sandy, phosphatic dolomite
and lies directly on a gray to white often recrystalized
limestone.
As stated previously, the upper surface of the Hawthorn
Formation is an unconformity. Large deposits of dolomitic and
phosphatic rubble often occur here. Variable amounts of
phosphate gravel and sand are often found in the sediments imme-
diately overlying the Hawthorn contact. These rapidly decrease
in abundance upward away from the contact until the post-
Hawthorn sediments contain only trace amounts of reworked
phosphate.
The upper boundary of the Hawthorn, however, has long been a
source of controversy and misunderstanding. The top of the unit
cannot be picked strictly on the occurrence of phosphate. As
previously mentioned, phosphate is commonly reworked into the

greatest amount of sand retained on the 60 mesh (2 0) and 120
mesh (30 ) sieves. The heavy minerals found to be most common
were ilmenite, leucoxene, kyanite, sillimanite, staurolite, epi-
dote and garnet.
Figure 3 is a percent sand (rock type) map. The greatest
sand concentrations occur in north and northwestern portions of
the study area suggesting a source to the north and northwest.
Sand content generally decreases to the south and southeast. A
general decrease in average sand grain size followed the same
trend as abundance. The map shows a northwest-to-southeast trend
of a decreasing percentage of sand units within the Hawthorn in
the central portion of the study area.
Clays are present throughout much of the Hawthorn Formation.
Most often the clays are accessory mineral in another dominant
lithology, i.e., clayey, dolomitic sand or clayey, sandy dolo-
mite. However, clay beds are not uncommon. Figure 4 shows the
areal distribution of clays as a percentage of the total Hawthorn
section. The maximum percentage of clay beds present is greater
than 70 percent in W-14354 in east-central Putnam County. Clay
percentages of 30 to 40 percent are found along the eastern and
southeastern edge of the map. Lower percentages are dominant
over most of the remaining map area. Note the increase in clay
content in Alachua County.
The clay minerals present in the Hawthorn are palygorskite,
montmorillonite, sepiolite, illite, kaolinite and chlorite (Reik,
1982). Palygorskite and montmorillonite are the dominant clays
in the Hawthorn of the study area. Sepiolite, illite and
chlorite are uncommon. Kaolinite is found only in the more
weathered or leached sections of the Hawthorn.

STRATIGRAPHY

The Hawthorn Formation within northeastern Florida un-
conformably overlies the Eocene limestones of the Ocala Group.
The unconformity cuts increasingly older rocks toward the
southeast. Throughout most of the study area the first Eocene
limestone encountered is the Crystal River Formation, the
youngest unit of the Ocala Group. In eastern and southeastern
Putnam County and into Flagler County, the Williston Formation
underlies the unconformity in the southeastern most corner of the
study area (Bermes, et al, 1963; Reik, 1980; Leroy, 1981). The
entire Ocala Group is missing in central Volusia County,
southeast of the study area (Wyrick, 1960). The first Eocene
carbonate encountered in central Volusia County is the Avon Park
Limestone.
The Hawthorn Formation is unconformably overlain by several
different units. The location within the study area dictates
which of the units lies on the Hawthorn. These units are often
lumped into one of two categories 1) Upper Miocene to Pliocene
Deposits; 2) Post-Hawthorn to Recent Deposits (Bermes, et al,

younger sediments. In northeastern Florida, the most consistent
method of recognizing the top of the Hawthorn is based on the
occurrence of a mixture of sand, clay, phosphate and dolomite (or
locally limestone). The sediment is most commonly a clayey,
sandy, phosphatic dolomite or a clayey, dolomitic phosphatic
sand. It lacks shell material and is normally an olive green to
gray-green color.

GEOPHYSICAL INTERPRETATION

Gamma ray logs are quite helpful in recognizing the approxi-
mate boundaries of the Hawthorn Formation. The Hawthorn, in
general, is marked by gamma ray activities that are significantly
higher than the overlying and underlying sediments (figure 10).
The Hawthorn-Ocala contact is always marked by a large decrease
in activity in the Ocala. The basal Hawthorn often has strong
gamma ray peaks (greater than 200 counts per second (cps) while
the underlying limestones have very low activities (less than 20
cps). Cavities in the limestones just below the Hawthorn Ocala
boundary are occasionally filled with Hawthorn sediments. This
produces a gamma ray peak which occurs below the contact and may
cause a misinterpretation of the boundary. However, when this
occurs the resulting peak is usually more subdued than the basal
Hawthorn peaks.
The gamma ray signature of the top of the Hawthorn Formation
shows strong peaks (often greater than 150 cps). The overlying
sediments produce gamma ray peaks that are much less intense than
those of the Hawthorn but greater than the Ocala Group lime-
stones. Immediately above the uppermost Hawthorn, the gamma ray
peaks may be quite variable due to the reworking of Hawthorn
sediments as previously mentioned and the occurrence of clays.
This can create confusion. However, these peaks are generally
less intense than the typical uppermost Hawthorn peaks.
While the upper and lower Hawthorn sediments tend to exhibit
strong gamma ray peaks, the sediments in between produce much
less intense peaks. Although peaks in these sediments may reach
200 cps they average much less (around 40 to 50 cps). This
contrast produces a general three part breakdown of the Hawthorn
based on gamma ray logs (figure 10) which can be traced
throughout much of the study area. However, this division based
on gamma ray activity does not always correlate closely with the
lithologic breakdown described earlier.

STRUCTURE

The Hawthorn Formation unconformably overlies the Ocala
Group limestones and is in turn overlain unconformably by sedi-
ments ranging from Upper Miocene to Recent. The unconformity on
top of the Ocala Group represents an interval of erosion or non-
deposition that includes the uppermost Eocene, the entire

27

POST HAWTHORN
SEDIMENTS
114

o E :._

I LOCALA

INCREASING ACTIVITY

Figure 10. Typical geophysical log.

Oligocene and, in some areas, the basal Miocene. Figure 11 shows
this unconformity and its relation to the structural features of
the study area. The unconformity encounters older rocks towards
the southeast. In the southeastern corner of the map area, the
Crystal River Formation (youngest formation of the Ocala Group)
is absent and the underlying Williston-Inglis Formation is
thinned (Leroy, 1981; Leroy and Scott, 1981). In general, the
top of the Ocala Group dips to the northeast toward the
Jacksonville Basin (figures 11 and 12). The direction of dip
becomes more northerly along the eastern edge of the map.
Structural features identified on the Ocala surface are
indicated on figure 12. These are the Nassau Nose, Jacksonville
Basin, St. Johns Platform, Baker-Bradford Slope, Marion Plain and
the Ocala High. The dominant structural elements are the Ocala
High, the St. Johns Platform and the Jacksonville Basin. The
remaining features represent transitional areas between these
major elements.
The Ocala High, often termed the Ocala Uplift (Vernon 1951),
is the dominant feature of west-central and northwestern penin-
sular Florida and is an area where the Ocala Group limestones are
well above sea level. The "crest" of the high is located south-
west of the study area where it is breached by erosion exposing
the Middle Eocene Avon Park Limestone. It trends northwest-
southeast, plunging gently in both directions. The eastern flank
of the Ocala High can be seen on the west side of figures 11 and
12.
The St. Johns Platform, named by Riggs (1979a), is a north-
ward dipping extension of the Sanford High. The Sanford High is
located south of the study area in Volusia and Seminole counties.
In a regional sense, the St. Johns Platform parallels the Ocala
High (figure 12).
The Jacksonville Basin (Riggs, 1979a) is the subsurface
extension of the Southeast Georgia Embayment in northeastern
Florida. It is separated from the onshore portion of the
Southeast Georgia Embayment in Georgia by the Nassau Nose. The
Nassau Nose is an eastward plunging apparently anticlinal
feature. The Southeast Georgia Embayment was named by Toulmin
(1955). Herrick and Vorhis (1963) state "...the embayment
appears to have originated in Middle Eocene time and continued as
a de-positional basin intermittently through Miocene time." The
Jacksonville Basin contains the thickest sequence of Miocene
sediments found in the northern two-thirds of the peninsula.
Maximum Hawthorn thickness is close to 500 feet (150 meters) in
the center of the basin,
The Baker-Bradford Slope lies west of the Jacksonville
Basin and the St. Johns Platform. It trends northwest-southeast,
terminating against the St. Johns Platform (figure 12). Miller
(1982) in discussing the phosphate in the Hawthorn under the
Osceola National Forest (Baker and Columbia counties), refers to
a "hinge line" which strongly affected the deposition of the

Figure 11. Structure map of Ocala Group.:

142

4ASSAIq 051

FF ORRp IC

-
F 1o
I

~. tw

-. -*--4-* -
I IL O

* I7
p,
.Lo ~ ~ *- i--- --*r

Figure3 12 Fetrsepesdo OaaGopsrae

phosphorites. This "hinge line" coincides with a portion of the
Baker-Bradford Slope. The Baker-Bradford Slope extends from the
Florida-Georgia border southeastward to northeastern Putnam
County. The extent of the slope in Georgia was not investigated
in this study.
South and west of the Baker-Bradford Slope and between the
Ocala High and the St. Johns Platform is the Marion Plain, named
by Riggs (1979a). The Marion Plain is a fairly broad, relatively
flat area underlying eastern Marion County extending northward
into Union County. The erosional surface of the Ocala Group dips
very gently towards the northeast where it terminates against the
St. Johns Platform to the south and merges with the Baker-
Bradford Slope to the north (figures 11 and 12).
The structure map of the Hawthorn Formation (figure 13)
indicates that by the end of Hawthorn deposition many of the
features noted on the Ocala Group structure map (figures 11 and
12) are no longer as pronounced. As is the case with the Ocala
Group, the top of the Hawthorn Formation is an unconformity.
This in turn, has modified the existing structures. The Hawthorn
dips gently to the east and northeast.
One notable structure shown on the Hawthorn structure map is
the low area over the Jacksonville Basin. This lies slightly
south of the thickest accumulations of Hawthorn sediments and may
represent a paleo-drainage pattern into the embayment. If this
feature is an ancient drainage system, it is interesting to note
that it nearly coincides with the present course of the St. Johns
River.
The isopach map of the Hawthorn Formation (figure 14) shows
the thickest accumulations to be in the northeast, coinciding
with the deepest portion of the Jacksonville Basin. The Hawthorn
ranges in thickness from zero in the southwest, west and
southeast parts of the study area to greater than five hundred
feet in the northeast. The Hawthorn thickens in a general
manner from the southwest to northeast throughout the study
area.
The paleoextent of the Hawthorn Formation beyond its
present erosional limits has been postulated by (1981). Based on
the assumption that much of the chert found in the limestones at
or near the surface on the Ocala High is the result of silica
released from the Hawthorn clays during weathering and erosion of
the sediments, the approximate extent of the Hawthorn can be
postulated. This line of investigation suggests that the
Hawthorn Formation was probably deposited over almost all of the
Florida peninsula. This approach appears to work well for the
areas west and southwest of the study area. However, it does not
appear to work well for the southeastern portion of the area due
to the apparent lack of chert in the subsurface. The author
believes that the paucity of chert in this area is directly
related to the faces present in the Hawthorn. Figures 2 and 4
show relative dolomite and clay contents of these sediments.

0 OR OIA
F 0'tlrrA

tYRK\1

o#*i
kx '
P( k

.1
/1

'M,IA... law

Vi/

AV

k )

'k'fl,:

-. ~ 4 ~4-f--4- 4~ --1~ 1 --* -

4 ---'9---.- t -

\ *

rJ -
14

W-oL C) tWinI r4 M

** S1
*~-w '**_ ay~ ----1--iI
r. ,

,4
^gP.^''

\ Vv~&-. rinK. *~~1

1)A .i f7i Z/7j >2/
^l~k \ / ^r ///.^--4j^

1II( '1)

(I'-

l- I

J7lSI-CJ)~

- sr.

~1

2

'vi
"I

0
"I

Figure 13. Structure map of Hawthorn Formation.

:I

i.1
4
t
I..

h
r~S"PP
^vi'.?

_-~6C

|

9.,

";

;
t i -~;---i
I ,

A~iV -1

j

9;
f~ ~~~s

'* I t I -" l i W _--t_

"I~"-'

_

PI~-~;d~""~""lxl

-~--

I

. .. __ UL=.-- === =

C

1--

I

I_._ II ~- -------------------- --

.I

-- ---

I

6-- '-" --"-""--""

- ---; --------

A

__~_~_

S111--

----~-U--*-r~

- k I

I

su r a-~ - -

- -

------------ --

!

ii r I 1 7

vMAL^K^^
\ t \KD ^ E^',y '^i
V\\ .^'^ ^----^

J

I

\ A.4
Off

us-]

SCO R GIA
OR

'

Figure 14. Isopach map of Hawthorn Formation.

I
f--Jl

mw

U)

K

U'

A'

0 IA

LO II

.-.--..-.-i-

>1

"1

J

I I

L

.rL- ..,

I

Figure 14. Isopach map of Hawthorn Formation,

-q .. .

B

k

n

- -25- C.MW.4. O I 3v 3 h F
wI-CIIIUW h
13 rolf aftAftwe' ad
W4411r

101

V.
7---L

trim,

I

These figures suggest an increased dolomite content and decreased
clay component when comparing southwest and west with the
southeast. With less clay present to be weathered, less chert
(or none) resulted on the Sanford High.

GEOLOGIC HISTORY

The study area has been affected by episodes of erosion,
nondeposition, faulting and warping. The result is an
interesting geologic history. Determination of the geologic
history is based almost entirely on subsurface data since there
are few outcrops within this area.
Although this study did not investigate the deeper subsur-
face units (Lake City Limestone, Avon Park Limestone, etc.),
other authors have done so. These include: Bermes, et al.
(1963); Clark, et al. (1964); Leve (1966); Fairchild (1977);
Reik (1980); Leroy (1981). The reader should consult these
studies for information on the deeper units.
The carbonates of the Upper Eocene Ocala Group were de-
posited unconformably on the Avon Park Limestone. The Ocala
roup attains a thickness greater than 300 feet (90 meters) under
Duval County in the Jacksonville Basin. It is probable that the
Jacksonville Basin existed at this time as a shallow basin. This
is indicated by a slight thickening of the Ocala in the basin
(Leve, 1966). However, the preservation of this thickness of
Ocala Group limestones was due less to the existence of the
basin at the time of deposition than it was to the subsequent
downwarping of the basin in late Ocala and post-Ocala time, as
indicated by the depth to the Ocala top and the increased
thickness of the entire group in the basin.
The Oligocene Suwannee Limestone was not deposited within
the study area. It was however deposited east of the present
shoreline and is found in the JOIDES 1 drill hole approximately
25 miles (40 km) east of Fernandina Beach, Nassau County. The
nondeposition of the Suwannee or equivalent units within the
study area is evident from the lack of erosional remnants in even
the deepest parts of the Jacksonville Basin while a quite thick
section of Ocala Group is present.
The surface of the Ocala Group was exposed to erosion and
dissolution prior to the deposition of the Hawthorn Formation.
In the Miocene, the Hawthorn seas began to encroach on the
exposed Florida Platform, transgressing across it. Accompanying
the transgression was an influx of clastics from the north which
filled the Suwannee Straits and began to enter the carbonate
environments of the platform. Within the study area, the flood
of clastics decreased from this time and carbonate-rich sedi-
ments became more important. This is shown by the general three
part breakdown of the Hawthorn that was discussed earlier in this
report and is seen in the cross sections (figures 6-9).
The Hawthorn Formation was deposited over most of the

Florida platform as is indicated by erosional remnants isolated.
from the main outcrop area and from subsurface data. Also, as
previously discussed, the occurrence of chert in the Eocene and
Oligocene limestones suggests that the Hawthorn covered a much
larger area in the past (Scott, 1981). Post-Hawthorn erosion
removed the Hawthorn from the Sanford High and the Ocala High and
thinned the unit over much of the remaining area.
Post-Hawthorn shell beds and limestones appear to have been
deposited during two separate depositional episodes. The
limestones and shell referred to as Choctawhatchee Age (Upper
Miocene) by Pirkle (1956) were possibly deposited prior to the
major regression that occurred in the Late Miocene (Messinian).
These were subsequently highly eroded during the regression
leaving only scattered remnants. These remnants have been
discussed by Pirkle (1956), Reik (1980) and Scott (1982). The
second episode of shell bed deposition occurred when the sea
transgressed onto the platform in the Pliocene. The shell units
deposited during this time are found in the eastern half of the
study area.
The post-Hawthorn shell beds and limestones lie on the
eroded surface of the Hawthorn. These units contain variable
percentages of reworked Hawthorn sediments. The most easily
recognized component of the reworked sediments is phosphate which
is common in the shell units and is generally most abundant in
the shell beds just above the Hawthorn contact.
In the areas where the shell beds are missing, the sediments
deposited on the Hawthorn are clayey sands and sandy clays. No
age assignment has been possible for the clayey sands and sandy
clays. These in turn are overlain by unconsolidated sands of
presumed Pleistocene age. The Pleistocene age for the sands is
based on the assumption that the Pleistocene sea levels fluc-
tuated widely and deposited sands as terrace deposits over the
entire state (MacNeil, 1950; Healy, 1975). It is most likely,
however, that the higher level terrace sands are older than
Pleistocene.
An episode of structural warping occurred during the period
from the end of the Eocene to the Early Miocene. The Ocala
Uplift (Ocala High of this paper) is postulated to have formed
during this event (Vernon, 1951). The warping that formed the
Ocala Uplift also may have formed the Sanford High, the St. Johns
Ridge and associated features. Also, as mentioned above, the
renewed downwarping of the Jacksonville Basin occurred during
this time. The results of this warping are seen in the erosional
thinning of the Ocala Group southward from the Jacksonville Basin
onto the Sanford High south of the study area. The Ocala Group
thins progressively onto the high and is absent over the crest of
the feature. Where the Ocala is absent, the Avon Park Limestone
is the first carbonate encountered below the undifferentiated
sands of Plio-Pleistocene (?) Age.
Many authors believe that faulting occurred during this epi-

sode of deformation. Faults in Duval (Leve, 1966), Clay (Clark,
et al, 1964; Fairchild, 1977; Reik, 1980), and Putnam (Bermes, et
al, 1963; Leroy, 1981) counties have been proposed. These have
been postulated in the Ocala Group, Avon Park Limestone and Lake
City Limestone. None of these faults have previously been iden-
tified displacing the Hawthorn Formation and younger units. This
suggests that the deformation ceased prior to Hawthorn time.
The author, however, sees evidence for displacement of the
Hawthorn and younger materials within the study area. This will
be discussed later. Faults proposed by previous authors and by
this author are shown on figures 6, 7, 9, 11, 13. Postulated
displacements of the faults are variable.
Core data from the study area suggest the existence of
faults which occurred during post-Hawthorn time. Figure 9 (cross
section DD') indicates where the faults are believed to exist.
The faults displace at least the Ocala group, Hawthorn Formation
and the Pliocene shell beds. It is also possible that the
undifferentiated sands overlying the shell beds were displaced
but there is no evidence at this point to support such a conclu-
sion. Displacement along these faults reaches a maximum of
approximately 100 feet (30 meters) and decreases northward on the
north-south faults (Leroy, 1981). This can be seen on figure 11.
It is interesting to note that the St. Johns River follows this
faulted course fairly well (figure 11). This seems to further
substantiate the ideas of Pirkle (1971) concerning the offset
course of the St. Johns River being affected by faulting.

These figures suggest an increased dolomite content and decreased
clay component when comparing southwest and west with the
southeast. With less clay present to be weathered, less chert
(or none) resulted on the Sanford High.

GEOLOGIC HISTORY

The study area has been affected by episodes of erosion,
nondeposition, faulting and warping. The result is an
interesting geologic history. Determination of the geologic
history is based almost entirely on subsurface data since there
are few outcrops within this area.
Although this study did not investigate the deeper subsur-
face units (Lake City Limestone, Avon Park Limestone, etc.),
other authors have done so. These include: Bermes, et al.
(1963); Clark, et al. (1964); Leve (1966); Fairchild (1977);
Reik (1980); Leroy (1981). The reader should consult these
studies for information on the deeper units.
The carbonates of the Upper Eocene Ocala Group were de-
posited unconformably on the Avon Park Limestone. The Ocala
roup attains a thickness greater than 300 feet (90 meters) under
Duval County in the Jacksonville Basin. It is probable that the
Jacksonville Basin existed at this time as a shallow basin. This
is indicated by a slight thickening of the Ocala in the basin
(Leve, 1966). However, the preservation of this thickness of
Ocala Group limestones was due less to the existence of the
basin at the time of deposition than it was to the subsequent
downwarping of the basin in late Ocala and post-Ocala time, as
indicated by the depth to the Ocala top and the increased
thickness of the entire group in the basin.
The Oligocene Suwannee Limestone was not deposited within
the study area. It was however deposited east of the present
shoreline and is found in the JOIDES 1 drill hole approximately
25 miles (40 km) east of Fernandina Beach, Nassau County. The
nondeposition of the Suwannee or equivalent units within the
study area is evident from the lack of erosional remnants in even
the deepest parts of the Jacksonville Basin while a quite thick
section of Ocala Group is present.
The surface of the Ocala Group was exposed to erosion and
dissolution prior to the deposition of the Hawthorn Formation.
In the Miocene, the Hawthorn seas began to encroach on the
exposed Florida Platform, transgressing across it. Accompanying
the transgression was an influx of clastics from the north which
filled the Suwannee Straits and began to enter the carbonate
environments of the platform. Within the study area, the flood
of clastics decreased from this time and carbonate-rich sedi-
ments became more important. This is shown by the general three
part breakdown of the Hawthorn that was discussed earlier in this
report and is seen in the cross sections (figures 6-9).
The Hawthorn Formation was deposited over most of the

SUMMARY AND CONCLUSIONS

The Hawthorn Formation in the Southeastern United States is
probably one of the most misunderstood units in the stratigraphic
section. The confusion as to what actually constitutes the
Hawthorn Formation is understandable since the variability of the
sediments is the rule rather than the exception.
The sediments of the Hawthorn Formation consist of widely
varying mixtures of clay, quartz sand, carbonate, and phosphate.
Beds of a single sedimentary component (i.e., pure clay) are not
common but do occur. The most common lithologies encountered in
the Hawthorn are dolomitic, clayey sands and clayey and/or sandy
dolomites.
Phosphate is virtually ubiquitous throughout the Hawthorn
sediments. The occurrence of the phosphate is the most important
lithologic factor in the identification of the sediments grouped
in the Hawthorn. It is, however, not the only factor involved
since phosphatic material is commonly reworked into the overlying
post-Hawthorn units.
The phosphates are generally sand-sized grains that are
well rounded and "polished." They normally contain varying
amounts of inclusions including dolomite rhombs, microfossil
debris and elastic grains (quartz). Phosphate also occurs as
intraclasts composed of phosphatic sedments or phosphatized dolo-
mites. Phosphate concentrations in the Hawthorn range from zero
to greater than 40 percent.
Dolomite is the predominant carbonate present in the
Hawthorn Formation. It occurs both as a matrix material and as a
primary lithology. The dolomitic sediments range from poorly
consolidated to well indurated and contain widely varying percen-
tages of quartz sand, silt, clay and phosphate. Dolosilt, a
sediment composed of silt-sized dolomite rhombs, is a common
constituent of the Hawthorn. The dolosilts often contain
variable amounts of clay and are commonly mistaken for clays.
Replacement dolomites are also common. Dolomites and dolosilts
comprise an average of 25 to 40 percent of the Hawthorn within
the study area.
Sand is a major constitutent of the Hawthorn Formation. It
is the most abundant lithologic type encountered in the Hawthorn
in the study area. Quartz sand is the most common accessory
mineral in the Hawthorn. Accessory minerals in the sand-size
range include minor amounts of feldspar, heavy minerals and
variable concentrations of phosphate.
Clays are present throughout much of the Hawthorn Formation.
Most often the clays are accessory minerals in another dominant
lithology, i.e. clayey, dolomitic sand or clayey, sandy dolomite.
However, clay beds are not uncommon. The clay minerals present in
the Hawthorn are palygorskite, montmorillonite, sepiolite,
illite, kaolinite, and chlorite (Reik, 1982). Palygorskite and
montmorillonite are the dominant clays in the Hawthorn of the

study area. Sepiolite, illite and chlorite are uncommon.
Kaolinite is found only in the more weathered or leached sections
of the Hawthorn.
Lithologic trends in the Hawthorn show that, within the
study area, dolomite content increases eastward. Sand content is
inversely proportional to the dolomite content in that it
decreases eastward. Clay content is greatest in northern St.
Johns County near the southern edge of the Jacksonville Basin.
Clay content is also high in central Alachua County.
The complex mixture of clastics and carbonates that comprise
the Hawthorn Formation unconformably overlie the Eocene Ocala
Group limestones. The Hawthorn is in turn unconformably overlain
by differing units depending on the location within the study
area. In the eastern half of the study area, the Hawthorn is
overlain by Pliocene shell beds. Sands and clayey sands overlie
the Hawthorn in the western half with occasional remnants of
Upper Miocene limestone and shell units.
The Hawthorn Formation in northeastern Florida can be
divided into three members. In general, the upper unit is predo-
minantly poorly consolidated dolomites and dolosilts with varying
amounts of sand, silt, clay and phosphate. The middle member is
largely plastic. It is a poorly consolidated dolomitic sand with
varying percentages of dolomite, clay, silt and phosphate. The
basal member is, once again, predominantly dolomite. Induration
varies from poor to good and percentages of sand, silt, clay and
phosphate vary widely. The three members are gradational with
each other and each member contains beds of lithologies similar
to that found in the other members. Occasionally, a fourth
member is present at the top. The fourth member consists of
reworked Hawthorn sediments. It is most commonly found in the
western half of the study area.
The dominant structural features affecting the Hawthorn
Formation are the Jacksonville Basin, Ocala High, Sanford High
and the St. Johns Platform. These features are manifested on
the Ocala Group and influenced the deposition of the Hawthorn
Formation. These structures are more subtle on top of the
Hawthorn.
The study area has been affected by episodes of warping and
faulting. The first episode of warping that is identified
occurred during the period from latest Eocene through Early
Miocene. This episode formed the Ocala High (Uplift), St. Johns
Platform, Sanford High and associated features. The Jacksonville
Basin is thought to have existed as a more shallow basin prior to
this time and was deepened considerably during the period of
deformation. Faulting occurred during this period displacing the
Ocala Group. An episode of faulting is postulated in eastern
Putnam County which occurred after the deposition of the Pliocene
shell beds. Faulting in the study area has a maximum dis-
placement of at least 100 feet. It is interesting to note that
the St. Johns River follows proposed fault zones fairly closely.

REFERENCES

Applin, P.L. and E.R., Applin, 1944, Regional subsurface
stratigraphy and structure of Florida and South Georgia:
Bulletin American Association of Petroleum Geologists, Vol.
28, No. 12.

Bermes, B.J., G.W. Leve, and G.R. Traver, 1963, Geology and
ground water resources of Flagler, Putnam and St. Johns
counties, Florida: Florida Geological Survey Report of
Investigation 32.

Brooks, H.K., 1966, Geological history of the Suwannee River: in
Miocene-Pliocene Series ot the Georgia Florida Area:
Southeastern Geological Society Guidebook 12.

Brooks, H.K., 1967, Miocene-Pliocene problems of peninsular
Florida: in Miocene-Pliocene Problems of Peninsular
Florida: Southeastern Geological Society Guidebook 13.

Clark, W.E., R.H. Musgrove, C.G. Menke, and J.W. Cagle, Jr.,
1964, Water resources of Alachua, Bradford, Clay and Union
counties, Florida: Florida Geological Survey Report of
Investigation 35.

Conrad, T.A., 1846, Description of new species of organic remains
from the Upper Eocene limestones of Tampa Bay, Florida:
American Journal of Science Series 2.

Cooke, C.W., 1915, The age of the Ocala Limestone: U.S.
Geological Survey Professional Paper 95.

Cooke, C.W. and S. Mossom, 1929, Geology of Florida: Florida
Geological Survey Annual Report 20.

Cooke, C.W., 1945, The Geology of Florida: Florida Geological
Survey Bulletin 29.

Dall, W.H. and G.D. Harris, 1892, Correlation paper Neocene:
U.S. Geological Survey Bulletin 84.

Dall, W.H., 1896, Descriptions of Tertiary fossils from the
Antillean region: U.S. National Museum Proceedings, Vol.
XIX, No. 1110.

Dall, W.H., 1903, Contributions to the Tertiary fauna of Florida:
Wagner Free Inst. of Sci. Trans., Vol. 3, Parts 1-6.

Espenshade, G.H. and C.W. Spencer, 1963, Geology of phosphate
deposits of northern peninsular Florida: U.S. Geological
Survey Bulletin 1118.

Fairchild, R.W., 1977, Availability of water in the Floridan
Aquifer in southern Duval and northern Clay and St. Johns
counties, Florida: U.S. Geological Survey Water Resources
Investigation 76-98.

Healy, H.G., 1975, Terraces and shorelines of Florida: Florida
Bureau of Geology Map Series 71.

Herrick, S.M. and R.C. Vorhis, 1963, Subsurface geology of the
Georgia Coastal Plain: Georgia Department of Mines, Mining
and Geology, Information Circular 25.

Johnson, L.C., 1888, The structure of Florida: American Journal
of Science, 3rd Series, Vol. b6.

Leroy, R.A., 1981, The Mid-Tertiary to Recent lithostratigraphy
of Putnam County, Florida: Unpublished M.S. Thesis, Florida
State University, Taliahassee.

Leroy, R.A. and Scott, T.M., 1981, The Mid-Tertiary to Recent
stratigraphy in Putnam County, Florida: Abstract, Florida
Academy of Sciences Journal, Vol. 44, Supplement 1.

Leve, G.W., 1966, Ground water in Duval and Nassau counties
Florida: Florida Geological Survey Report ot Investigation
43.

MacNeil, F.S., 1950, Pleistocene shorelines in Florida and
Georgia: U.S. Geological Survey Professional Paper 221-F.

Mansfield, W.C., 1918, Molluscan faunas from the calcareous marls
in the vicinity of Deland, Volusia County, Florida: Florida
Geological Survey Annual Report 10-11.

Matson, G.C. and F.G. Clapp, 1909, A preliminary report on the
Geology of Florida: Florida Geological Survey Second Annual
Report.

Miller, J.A., 1978, Geologic and geophysical data from Osceola
National Forest, Florida: U.S. Geological Survey Open file
Report 78-799, p. 101.

SMiller, J.A., 1982, Structural and sedimentary setting of
phosphate deposits in North Florida and North Carolina:
Mocene or the Southeast United SCates, Froceedings of the
Symposium, T. Scott and S. Upchurch (eds.): Florida Bureau
of Geology Special Publication 25, in press.

Pirkle, E.C., 1956, The Hawthorn and Alachua Formations of
Alachua County Florida: Florida Academy of Sciences,
Vol. 28.

Pirkle, E.C., W.J. Yoho and A.T. Allen, 1965, Hawthorn, Bone
Valley and Citronelle sediments of Florida: Florida Academy
of Sciences, Vol. 28.

Pirkle, W.A., 1971, The offset course of the St. Johns River,
Florida: Southeastern Geology, Vol. 13, No. 1.

Puri, H.S., 1957, Stratigraphy and zonation of the Ocala Group:
Florida Geological Survey, Bulletin 38.

Puri, H.S. and R.O. Vernon, 1964, Summary of the geology of
Florida and a guidebook to the classic exposures: Florida
Geological Survey Special Publication No. 5 (revised).

Reik, B.A., 1980, The Tertiary stratigraphy of Clay County,
Florida with Emphasis on the Hawthorn Formation: Un-
published M.S. Thesis, Florida State University,
Tallahassee.

1982, Clay mineralogy of the Hawthorn Formation in
northern and eastern Florida: Miocene of the Southeastern
United States Proceedings of the Symposium, T. Scott and
S. Upchurch (eds.): Florida Bureau of Geology Special
Publication 25 (in press).

Reynolds, W.R., 1962, The Lithostratigraphy and Clay Mineralogy
of the Tampa-Hawthorn Sequence of Peninsular Florida:
Unpublished M.S. Thesis, Florida State University, p. 126.

Riggs, S.R., 1979a, Phosphorite sedimentation in Florida A
model phosphogenic system: Economic Geology, Vol. 74,
No. Z.

1979b, Petrology of the Tertiary phosphate system
of Florida: Economic Geology, Vol. 74, No. 2.

Scott, T.M., 1981, The paleoextent of the Miocene Hawthorn
Formation in peninsular Florida: Abstract, Florida Academy
of Sciences Journal, Vol. 44, Supplement 1.

1982, A comparison of the "cotype" localities and
cores of the Miocene Hawthorn Formation: Miocene of the
Southeastern United States Proceedings of the Symposium,
T. Scott and S. Upchurch (eds.): Florida Bureau of Geology
Special Publication 25 (in press).

and P.L. MacGill, 1981, The Hawthorn Formation of
Central Florida: Florida Bureau of Geology Report of
Investigation 91.

Sever, C.W., J.B. Cathcart and S.H. Patterson., 1967, Phosphate
deposits of south-central Georgia and north-central
peninsular Florida: South Georgia Minerals Program, Project
Report 7.

Smith, E.A., 1881, On the geology of Florida: American Journal
of Science, Series 3, Vol. 21.

Toulmin, L.D., 1955, Cenozoic geology of southeastern Alabama,
Florida and Georgia: American Association of Petroleum
Geologists Bulletin 39, No. 2.

Vaughan, T.W. and C.W. Cooke, 1914, Correlation of the Hawthorn
Formation: Washington Academy of Sciences Journal, Vol. 4,
No. 10.

Vernon, R.O., 1951, Geology of Citrus and Levy counties, Florida:
Florida Geological Survey Bulletin 33.

Williams, G.K., 1971, Geology and geochemistry of the sedimentary
phosphate deposits of northern Peninsular Florida:
Unpublished c n.D. Dissertation, Florida State university,
Tallahassee.

Wyrick, G.G., 1960, The ground water resources of Volusia County,
Florida: Florida Geological Survey Report of Investigation
ZZ.

APPENDIX

CORES USED IN THIS STUDY*
(Sea Level Datum)

ALACHUA COUNTY

LOCATION

TOP OF TOP OF GEOPHYSICAL**
ELEV TD HAWTHORN OCALA LOGS

11486 Hawthorne #1
14641 Devils Millhopper #1

10S 22E 3 SW NE 100
9S 19E 15 NW SE 178

- 45 89 34.5
+ 46 +167.5 + 69

BAKER COUNTY

Trail Ridge #3
ONF-5
ONF-7

2S 22E 15 SE SE
2S 19E 2 NW NW
2S 19E 30 NW SW

167 -121
132 -162
141 67

- 13 ---
+ 98 -140
+121 41.5

BRADFORD COUNTY

Ralford #1
Mizelle #1
Varnes 1\
Walnwrlght

Dupont 11
Harris #1
Long Branch 11
Fox Meadows #1
Jennings #1
ValldeJul #1
Kuhrt #1
Miss J #1

DUVAL COUNTY

14619 Carter 11 .

IS 27E 42

12 -488 68

NASSAU COUNTY

13815 Cassldy #1

3N 24E 32 NW NW 80

-410

- 52 -402

PUTNAM COUNTY

Baywood #1
Nichols #1
Moody #1
Merritt #1
East Palatka #1
Devils Elbow #1
Bostwick #1
Atchenlson #1
Hall-Putnam #1

9S 25E
13S 28E
9S 24E
11S 26E
9S 27E
10S 27E
8S 27E
10S 24E
9S 23E

18 SW
7 SW
9 NE
27 SW
49
41
26 SW
3 NE
18 NE

- 92
- 94
- 92
- 80
-134
-238
-225
-146
- 64

+ 36
- 4.4
+ 20
+ 5
- 27
-127
- 94
+ 5
+ 66.5

- 87
- 5.5
- 77
- 57
- 90.7
-187
-204
-120.5
- 64

ST. JOHNS COUNTY

Scott #1
Scott 12
Scott 13
Zonker #1
Parker Farms #1

38 NW
11 SW NE
14 NE NW
37
20 NE NE

-224
-281
-211
-168
-239

- 37
- 43
- 68
- 89
- 97

-209
-239
-201
-127
-223

* Data In feet. To convert multiply feet x 0.3048 to get meters.
* G = Gamma ray, C = Cullper, E = Electric

WELL
NUMBER

NAME

10473
13805
13812

13813
14255
14280
14283

21E 26
19E 1
21E 4
22E 24

NE NW
SE NW
SW NE
SE SW

-144
- 7
- 35
-101

+ 88
+115
+113
+ 93

-143.5
+ 22
-0-
+ 15

10488
13769
14179
14193
14219
14301
14476
14521

CLAY COUNTY

- 93
-222
-234
-307
-402
- 87
-363
-305

98.5
37
18
20
30
60
52
60

- 96
-205.5
-206
-275
-340
- 62
-341
-273

G
C,E,G
G
C,E,G
C,E,G
G
G
G

8400
14318
14346
14353
14354
14376
14477
14566
14594

13744
13751
13765
13844
14413

FLRD GEOLOSk ( IC SUfRiW

COPYRIGHT NOTICE
[year of publication as printed] Florida Geological Survey [source text]

The Florida Geological Survey holds all rights to the source text of
this electronic resource on behalf of the State of Florida. The
Florida Geological Survey shall be considered the copyright holder
for the text of this publication.

Under the Statutes of the State of Florida (FS 257.05; 257.105, and
377.075), the Florida Geologic Survey (Tallahassee, FL), publisher of
the Florida Geologic Survey, as a division of state government,
makes its documents public (i.e., published) and extends to the
state's official agencies and libraries, including the University of
Florida's Smathers Libraries, rights of reproduction.

The Florida Geological Survey has made its publications available to
the University of Florida, on behalf of the State University System of
Florida, for the purpose of digitization and Internet distribution.

The Florida Geological Survey reserves all rights to its publications.
All uses, excluding those made under "fair use" provisions of U.S.
copyright legislation (U.S. Code, Title 17, Section 107), are
restricted. Contact the Florida Geological Survey for additional
information and permissions.

	Front Cover
	Title Page
	Table of Contents
	Part I. Geology of the Hawthorn...
	Part I - Table of Conatents
	Abstract
	Acknowledgement
	Introduction and methods
	Lithologic characteristics of the...
	Stratigraphy
	Geologic history
	Summary and conclusions
	References
	Appendix: Cores used in study

MILLISECOND	CLASS.METHOD	MESSAGE
0	sobekcm_page_globals.constructor
0	sobekcm_page_globals.constructor	Application State validated or built
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.constructor	Navigation Object created from URI query string
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.display_item	Retrieving item or group information
0	sobekcm_page_globals.get_entire_collection_hierarchy	Retrieving hierarchy information
0	sobekcm_assistant.get_entire_collection_hierarchy
0	cached_data_manager.retrieve_item_aggregation
0	cached_data_manager.retrieve_item_aggregation	Found item aggregation on local cache
0	item_aggregation_builder.get_item_aggregation	Found 'all' item aggregation in cache
0	system.web.ui.page.page_load (ufdc.page_load)
0	sobekcm_page_globals.constructor.on_page_load
0	html_echo_mainwriter.add_style_references	Adding style references to HTML
0	html_echo_mainwriter.add_text_to_page	Reading the text from the file and echoing back to the output stream
28	html_echo_mainwriter.add_text_to_page	Finished reading and writing the file