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 Title Page
 Letter of transmittal
 Table of Contents
 List of Figures
 List of Tables
 Introduction
 Methods
 Study area and stratigraphy
 Zonation
 Distribution of siliceous...
 Discussion
 Summary and conclusions
 References
 Plates 1-13
 Copyright


FGS



Biostratigraphy of selected cores of the Hawthorn formation in northeast and east-central Florida ( FGS: Report of inves...
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 Material Information
Title: Biostratigraphy of selected cores of the Hawthorn formation in northeast and east-central Florida ( FGS: Report of investigation 93 )
Series Title: ( FGS: Report of investigation 93 )
Physical Description: viii, 68 p. : ill. (some col.) ; 23 cm.
Language: English
Creator: Hoenstine, Ronald W
Publisher: State of Florida, Dept. of Natural Resources, Division of Resource Management, Bureau of Geology
Place of Publication: Tallahassee
Publication Date: 1984
 Subjects
Subjects / Keywords: Geology, Stratigraphic -- Miocene   ( lcsh )
Micropaleontology -- Florida   ( lcsh )
Geology -- Florida   ( lcsh )
Hawthorn Formation   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Ronald W. Hoenstine.
Bibliography: Bibliography: p. 37-40.
 Record Information
Source Institution: 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: aleph - 000985852
oclc - 16684663
notis - AEW2268
lccn - 86620719
System ID: UF00001280:00001

Table of Contents
    Title Page
        Page i
        Page ii
    Letter of transmittal
        Page iii
        Page iv
    Table of Contents
        Page v
    List of Figures
        Page vi
    List of Tables
        Page vii
        Page viii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Methods
        Page 6
    Study area and stratigraphy
        Page 7
        Page 8
        Page 9
    Zonation
        Page 10
        Page 11
    Distribution of siliceous microfossils
        Page 12
        Page 13
        Page 14
        Page 15
        Page 15a
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
    Discussion
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
    Summary and conclusions
        Page 35
        Page 36
    References
        Page 37
        Page 38
        Page 39
        Page 40
    Plates 1-13
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
    Copyright
        Copyright
Full Text







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

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

BUREAU OF GEOLOGY
Steve R. Windham, Chief


REPORT OF INVESTIGATION NO. 93

BIOSTRATIGRAPHY OF SELECTED CORES OF THE HAWTHORN
FORMATION IN NORTHEAST AND EAST-CENTRAL FLORIDA

By
Ronald W. Hoenstine







Published for the
BUREAU OF GEOLOGY
DIVISION OF RESOURCE MANAGEMENT
FLORIDA DEPARTMENT OF NATURAL RESOURCES
TALLAHASSEE
1984















SCIENCE
LIBRARY
DEPARTMENT
OF
NATURAL RESOURCES



BOB GRAHAM
Governor


GEORGE FIRESTONE
Secretary of State


JIM SMITH
Attorney General


BILL GUNTER
Treasurer


GERALD A. LEWIS
Comptroller


RALPH D. TURLINGTON
Commissioner of Education


DOYLE CONNER
Commissioner of Agriculture


ELTON J. GISSENDANNER
Executive Director







LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
February 15, 1984


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

Dear Governor Graham:

The Bureau of Geology, Division of Resource Management, Depart-
S ment of Natural Resources, is publishing as Report of Investigation No.
93, "Biostratigraphy of Selected Cores of the Hawthorn Formation in
Northeast and East-Central Florida," prepared by Dr. Ronald W. Hoen-
stine, Bureau of Geology staff.

A knowledge of the paleoenvironmental conditions present during the
period of Hawthorn deposition is essential to an understanding of this im-
portant phosphate-bearing formation. This report identifies heretofore un-
described microflora and it attempts to both date Hawthorn sedimentation
and to reconstruct environmental conditions present along Florida's
northeast coast during the Middle Miocene and Early Pliocene.

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








iv







TABLE OF CONTENTS
Page
Introduction .......................................................... 1
Purpose of Study ........................................ .......... 1
Previous Work ...................................................... 5
Metric Conversion Factors ............................................. 6
Methods .............................................................. 6
Sample Preparation .......................... ........... ........... 6
Counts ......... ... .... ..... ....... ............................ 6
Study Area ............................................................ 7
Stratigraphy ................... ........................................ 7
Stratigraphic Relationships ....................................... 7
Lithology ........................... ... .. .............. ........... 10
Zonation ................. .. ...... ......................... ........... 10
Microfossll Correlation....................... ..... .......... 10
Distribution of Siliceous Microfossils .. ............ ....... ............. 12
Discussion ............................ ... .......... ..... ... ........... 22
Zone Occurrences.................. ........................... 22
Delphinels penelliptica Zone ............................................ 22
Cosclnodiscus pllcatus/Delphlneis penelllptica Zone ......................... 25
Cosclnodiscus plicatus Zone ..................... ... .. .............. 25
Upwelling/Cool Water Current ............. ... ....... ............. 28
Pliocene Data ............... .............. .. .. .... .............. 28
Diatom Molds ........................ ......... .............. 34
Paralla sulcata ................. ................................. 34
Summary and Conclusions ...................... ................. 35
References ................................ ........................ 37






LIST OF FIGURES
Figure Page
1. Location of study area ............................................. 3
2. Location of core and well cuttings........... .................. .... 4
3 Generalized ibopach of the Hawthorn Formation In the study area, contoured in
(sat ...... ....... ......... .... ......... .. ..... ... .8
4. Abbott's Atlantic Miocene Siliceous Microfossil Zones showing the substitution
of Rh/piones ancetfula and the marker diatoms, sllicoflagellate species and
ptanktonic diatons found associated with the zones (Abbott, 1978) ......... 11
SCorreation of diatom zones defined by Cavallero (1974); Schrader (1973);
Andrews (1976); Planktonic Foraminlferal Zones of Blow (1969); Calcareous
Nannofortl Zones of Martini and Worely (1970) and Siliceous Microfossll Zones
of Abbott (1979) (from Abbott, 1978) .................................. 13
6 Location of diatomaceous cores .................................. 14
7. Location of cores with diatom mold occurrences ...................... 15
& Chart showing the distribution of blostratlgraphic zones, dissolution
assembtage, foraminifera, diatom molds and formatlonal contacts ......... 16
9. Distribution of diatoms in terms of brackish, upwelling, and warm water
indictors and numbers of species for the Cumberland Island Core ........ 20
10 Distribution of diatoms in terms of brackish, upwelling, and warm water
indicators and numbers of species for W-670 .............. .......... 21
11. Ditribution of diatoms in terms of brackish, upwelling, and warm water
indicators and numbers of species for W-13751 ....................... 23
12. Distribution of diatoms in terms of brackish, upwelling, and warm water
indicators and numbers of species for W-13744 ......................... 24
13 Major currents of the North Atlantic .................................. 28
t4. Distribution of diatoms in terms of brackish, upwelling, and warm water
indicators and numbers of species for W-5906 ......................... 29
15. Distribution of diatoms in terms of brackish, upwelling and warm water Indicators
and numbers of species for W-13958 ...................... ... 30
16. Distribution of diatoms in terms of brackish, upwelling, and warm water
indicators and numbers of species for the St. Lucle core ................ 31







TABLE
1. Diatom species utilized as environmental indicators in this study ............ 19

PLATES

1. Actinocyclus octonarius, Actinocyclus Ingens, and Actinocyclus ellipticus ...... 43
2. Actinoptychus senarlus, Actinocyclus level, Actinoptychus aff. A. mlnutus,
and Blddulphia rhombus ..................... .................. 45
3. Blddulphia tuomeyl, and Biddulphla rettculum ........ ................. 47
4. Cosclnodiscus aplculatus, Coscnodiscus vetustissimus, and Coscinodiscus
lewislanus ........... .. ................... ...... ... 49
5. Coscinodiscus pertoratus, and Cosclnodiscus asteromphalus ................ 51
6. Cussla praepaleacea, and Cymatogonia amblyoceras ...... ............ 53
7. Delphlnels penelliptica, Delphineis angustata, Delphinels surirella, Delphinels
biserlata, Diplonels smith, and Diplonels bombus ....................... 55
8 Navicula of. N. directs, Navicula pennate, and Navicula hennedy .......... 57
9. Paralla sulcata, Melosira westil, and Podosira of. R stelliger .............. 59
10. Rhaphoneis amphiceras, Rhaphonels fatula, Rhuphonels gemmifera,
Rhaphonels f. R. angularis, Rhaphonels lancetulla, and
Rhaphonels adamentea ............................................. 61
11. Tlceratlum reticulum, Ticeratium condecorum, and Triceratium spinosum ...... 63
12. Xanthlopyxis sp., Thalasslothrix longissima, Trachynels aspera, Thalassionema
nltzscholdes, and Fragilaria sp ... ................................. 65
13. Distephanus stauracanthus, Mesocena circulus, Distephanus crux, Dictyocha
rhombica, and Distephanus o. D. boliviensis......................... 67






BIOSTRATIGRAPHY OF SELECTED CORES OF THE HAWTHORN
FORMATION IN NORTHEAST AND EAST-CENTRAL FLORIDA

By
Ronald W. Hoenstine

INTRODUCTION

PURPOSE OF STUDY

Historically, the Hawthorn Formation has been a catch-all for Miocene
sediments in peninsular Florida, Georgia, and parts of South Carolina
(Abbott and Andrews, 1979). This extremely complicated formational unit
which consists generally of clay, carbonates (primarily dolomite), and
clayey, quartzose, phosphatic sand, was named by Dall and Harris (1892)
after the town of Hawthorne, Florida. During the last few years consider-
able interest has been focused on these sediments because of the forma-
tion's phosphate content.
Investigators have relied primarily on highly weathered surface out-
crops, spoil banks, or auger holes for obtaining fossil specimens from the
Hawthorn Formation. These outcrops are frequently so deeply weathered
that even fossil molds have been obliterated. When present, common fos-
sils include the oyster Ostrea normalls, a scallop Pectenacanlkas sp., and
large heads of the colonial coral Siderastraea sp. (Cooke, 1945). In addi-
tion, the fullers earth mines at Quincy and Midway, Florida, have yielded
bones identified as that of the dugong (manatee-like) HesperoSiren
crataegensis (Cooke, 1945). Primarily, the early Hawthorn studies were
based on field observations that emphasized mineral identifications and
geographic distribution with minimum attention given to microscopic ex-
amination and subsequent biostratigraphic analysis. Thus, very little work
has been done on determining the age of the sediments or the paleoenvi-
ronmental conditions present during the period of Hawthorn deposition,
except in relatively general terms.
Factors which hindered these early workers included the minimal bio-
genic carbonate content, extensive dolomitization, and in northeast Flor-
ida, the predominantly siliceous nature of the Hawthorn sediments. As a
consequence, biostratigraphic information in this paper is tied to siliceous
organisms whose stratigraphic value have been recognized and devel-
oped only in recent years. The presence of more widely understood
groups such as foraminifera or coccoliths, are of secondary correlation
value due to their sporadic occurrences in the Hawthorn. Another prob-
lem in past years was the paucity of core coverage that resulted in a
strong dependence on well cuttings, which were usually taken at 10-foot
intervals. Hence, biostratigraphic information, confined to a narrow inter-
val, could be overlooked.
Recent advances in worldwide diatom and silicoflagellate biostrati-
graphic correlation, especially the sequence of events in the sediments
of the Atlantic Coast for the Miocene (Abbott, 1978; Andrews, 1979), have





BUREAU OF GEOLOGY


now made possible comparative studies of such deposits as the
Hawthorn Formation. The extremely close relationship found to exist be-
tween oceanic diatom assemblages and diatomaceous sediments of sim-
ilar age from coastal regions has enhanced the value of coastal donations
in biostratigraphic studies (Abbott, 1978). Diatom blostratigraphic zona-
tions developed for the Pacific Ocean (Burkle, 1972) and for the Indian
Ocean (Schrader, 1973) have also proved invaluable.
Cores recently obtained by the Florida Bureau of Geology through a co-
operative study with the United States Bureau of Mines represent a signif-
icant attempt in recent years to investigate the subsurface stratigraphy of
the Hawthorn Formation. This augmented data base, in addition to num-
erous well cuttings on file at the Bureau of Geology, coupled with the re-
cent advances in diatom stratigraphy, present an opportunity to under-
take a detailed biostratigraphic study of selected cores from this complex
and little understood formation. The study area for this report is shown
in figure 1.
Located primarily in northeastern and east-central Florida, these cores
were drilled through Hawthorn sediments into the underlying limestone
(figure 2). The cores offered a number of unique opportunities: 1) to ex-
amine complete sections of Hawthorn sediments, 2) to observe and de-
termine the sequence of diatom assemblages, and 3) to determine the
existence, if any, of a relationship between microfossil occurrences and
sediment types.
Well-preserved assemblages of diatoms and silicoflagellates were ob-
served in five cores, and two sets of water well cuttings, occurring along
the coast. In addition to these cores and wells, diatom molds were ob-
served in several inland cores in Putnam and Clay counties. Two cores
had co-occurrences of coccoliths, diatoms, silicoflagellates, and forami-
nifera which offered an opportunity to correlate marker species of diverse
groups.
This paper presents an outline of new biostratigraphic data and its in-
terpretation using Hawthorn microfossils. The intention is to shed light on
the environmental conditions that existed during the deposition of Haw-
thorn sediments within the study area. A discussion of inferred paleoenvi-
ronmental changes which occurred during the period of Hawthorn depo-
sition relative to modern conditions is presented with an explanation of
assumptions.
This study is regarded as a preliminary investigation. Further micro-
scopic examination and analysis of additional cores, especially in south
Florida, is anticipated in order to determine the extent of the Pliocene age
that has been newly assigned to some "Hawthorn-like" sediments.






REPORT OF INVESTIGATION NO. 93


50 0 50 IOOMILES
50 0 50 1OOKILOMETERS


Figure 1. Location of study area.






BUREAU OF GEOLOGY


ISLAND CORE


*W-670


13815


-W-14477


4354


* CORES -,
*-CUTTINGS'




N _






10 0 10 20 30 40M
I O 10203040i0KM
-.-Qr KM


W-13551
-W-13881


--"W-13964
W- 13958

-ST. LUCIE CORE


Figure 2. Location of cores and well cuttings.







REPORT OF INVESTIGATION NO. 93 5

PREVIOUS WORK

Dall and Harris (1892) referred to beds of phosphatic rock and greenish
clays observed at Nigger Sink, Newnansville well, and Sullivan's Ham-
mock as the "Hawthorne beds" after the town of Hawthorne, Alachua
County, Florida. These same beds had been referred to earlier by L. C.
Johnson (1888) in an unpublished report for the United States Geological
Survey. Though Dall and Harris mentioned the mining of phosphatic lime-
stone for use as fertilizer near Hawthorne, they did not erect a type sec-
tion. Matson and Clapp (1909) included part of the underlying Cassidulus-
bearing limestone, now called the Suwannee Limestone, with the Haw-
thorne beds of Dall and Harris. Vaughan and Cooke (1914) felt that the
Hawthorn was nearly synonymous with the Alum Bluff Formation as de-
fined by Matson and Clapp (1909) and recommended that the name
"Hawthorn" be dropped. Cook and Mossom (1929) redefined the Haw-
thorn Formation to include the Hawthorne beds and the Sopchoppy Lime-
stone of Dall and Harris (1892), in addition to the Alum Bluff Formation
and the Duplin Marl as defined by Matson and Clapp (1909).
More recently, Cooke (1945) transferred some Late Miocene age beds,
recognized by Matson and Clapp (1909) as part of the Hawthorn, to the
Duplin Marl. Bishop (1956) identified marine and nonmarine Hawthorn
deposits in Highlands County. More recent contributions include: Ketner
and McGreevy (1959), Carr and Alverson (1959), Reynolds (1962), Wilson
(1977), Miller (1978), Riggs (1979a,b), Reik (1980), Leroy (1981), Scott and
MacGill (1981), and Scott (1982, 1983). Although others have discussed
this formation, the contributions of the above mentioned authors are es-
pecially significant in their attempts to define or redefine the Hawthorn
Formation.
Fossils previously reported from the Hawthorn Formation in the study
area (figure 1) include molluscs, benthic foraminifera, diatoms, and some
well-preserved vertebrate remains. Sellards (1916) identified bones and
teeth of Mesocyon (?) iamonensis Sellards (a dog), and Parahippus leo-
nensis Sellards (a three-toed horse) found near Tallahassee in the Haw-
thorn Formation. The most notable investigations of molluscs are those
of Gardner (1926) and Puri (1953).
Although no comprehensive microfossil investigations of the Florida
Hawthorn Formation have been reported, several studies of Atlantic
Coastal sediments have been undertaken. The first records of siliceous
microfossils from the Atlantic Margin began with the diatom studies of
Bailey (1841, 1844) and Ehrenberg (1844, 1854).
More recent studies of the Atlantic Coastal Plain include a discussion
of diatom molds from opaline cristobalite (Wise and Weaver, 1973) and a
sparse collection of fish teeth and diatoms (W. K. Posser in Johnson and
Geyer, 1965) from the Coosawhatchie Clay occurring in South Carolina.
Abbott (1974a) reported on the occurrence of a well-preserved diatom as-
semblage in the Coosawhatchie Clay of Jasper County, South Carolina.






BUREAU OF GEOLOGY


Emissee (1976) identified a number of dinoflagellates from the same unit.
Abbott and Andrews (1979) related the Coosawhatchie Clay in South Car-
olina and time equivalent strata at Berry's Landing, Georgia, to the North
Pacific zonation of Schrader (1973) utilizing diatoms and silicoflagellates.
Specific siliceous zonations of Atlantic coastal sediments include: Cav-
allero (1974), Andrews (1979), and Abbott and Ernissee (1977). These
attempts were influenced and in part derived from zonations developed
earlier in the Pacific Ocean by Martini (1971), Burkle (1972), and Schrader
(1973). Abbott (1978) published the first significant microfossil zonation of
Miocene strata along the Atlantic Margin of North America using diatoms
and silicoflagellates. This zonation, along with Andrews' (1979) correlation
of Miocene strata of the Chesapeake Bay region of Maryland, was utilized
in this study.


METRIC CONVERSION FACTORS
The Florida Bureau of Geology, in order to prevent duplication of paren-
thetical conversion units, inserts a tabular listing of conversion factors to
obtain metric units.


Multiply by to obtain

feet 0.3048 meters
inches 2.5400 centimeters
inches 0.0254 meters
miles 1.6090 kilometers

METHODS
SAMPLE PREPARATION
Siliceous samples were prepared following procedures as recom-
mended by Abbott (1978). Procedures for calcareous samples were simi-
lar except that HCI was not used and caedex was utilized as the mounting
medium. A total of 780 slides mounted in either hyrax or caedex were
made using this procedure. These were examined by making systematic
traverses with a mechanical stage under a magnification of 600 X.
COUNTS
Frequencies of taxa were analyzed quantitatively using counts of 300
specimens whenever possible. Individual specimens were frequently
noted by recording the coordinates of the mechanical stage. Recorded in-
formation included species identification and counts.







REPORT OF INVESTIGATION NO. 93


STUDY AREA
The area of investigation is located in northeastern and east-central
Florida bounded to the north by the Florida-Georgia boundary, to the
south by St. Lucie County, to the east by the Atlantic Ocean, and to the
west by a centerline that approximates the center of the Florida peninsula
(figure 1). Although cores and well cuttings were examined throughout
the study area, a total of 17 cores and two well cuttings were found to be
especially productive in terms of yielding biostratigraphic data from
various microfossil groups including diatoms, silicoflagellates,
foraminifera, coccoliths, and ostracoda (figure 2). This report is primarily
concerned with diatoms and silicoflagellates. The most complete core
coverage was in the northern part of the study area, reflecting in part the
presence of thick Hawthorn sediments in that region.
STRATIGRAPHY
STRATIGRAPHIC RELATIONSHIPS
The Hawthorn Formation, which is present in the subsurface over
much of the study area, is missing in parts of Flagler, Volusia, Seminole,
and Lake counties. The thickness of this formation is extremely variable
with maximum values occurring in Duval County in the northeastern part
of the study area (figure 3). An observed thickness of at least 420 feet was
present in Duval County (W-14619), a core which did not completely pene-
trate the Hawthorn. This may be compared to well cuttings from W-10920,
located in Duval County, which penetrated through a Hawthorn section
measuring 491 feet in thickness.
The noted absence or thinning of Hawthorn sediments in specific areas
may be attributed in part to nondeposition or attenuation along the flanks
of a past structural high. The occurrence of an apparently shallow water
microfossil assemblage near the top of the Hawthorn in Brevard County
(W-5906), in contrast to a deeper water assemblage southward, may be
supportive of this premise. Alternatively, the missing sediments may be
attributed to deposition and subsequent erosion. Deposition of the Haw-
thorn Formation beyond its present limits has been postulated by Scott
and MacGill (1981) and Scott (1981).
Throughout the study area, the Hawthorn Formation is unconformably
overlain by undifferentiated sands and clays of Plio-Pleistocene age,
except for coastal areas of Flagler County, where the overlying sediments
are those of the Anastasia Formation, a coquinoid limestone also of
Pleistocene age. The contact between the undifferentiated sands and
clays and the underlying Hawthorn is generally gradational with the top
of the Hawthorn being placed at the first significant occurrence of
phosphorite in conjunction with a sandy, clayey dolomite or dolomitic,
clayey sand (Scott, 1983). A problem frequently encountered in the
identification of this contact is the presence of phosphorite in amounts
greater than 2 percent in the overlying sediments. This occurrence is







BUREAU OF GEOLOGY


100'


200'


300'

400'


Figure 3. Generalized isopach of the Hawthorn Formation in the study
area, contoured in feet.


I0 0 20 30 40 M
._ .


100







REPORT OF INVESTIGATION NO. 93


primarily attributed to reworking of Hawthorn sediments. Within the study
area, the top of the Hawthorn is usually a clayey, sandy, phosphatic
dolomite or a clayey, dolomitic, phosphatic sand. In addition, the
sediments lack shell material and are normally an olive-green color
(Scott, 1983).
An additional problem in picking the Hawthorn top was encountered in
the W-12958 and St. Lucie cores. These diatomaceous sediments which
included diatoms of Early Pliocene age were more calcareous than the
Middle Miocene diatomaceous sediments; an observation in part attri-
buted to the absence of dolomitization which might remove included co-
occurrences of calcareous nannoplankton and foraminifera. This was the
primary observed difference in lithology. Clay analyses done by Dabous
(personal communication, 1981) revealed the presence of montmorillonite
and palygorskite, common constituents of the Middle Miocene Hawthorn
Formation. Palygorskite has rare, sporadic occurrences in sediments
younger than the Miocene. Phosphorite content, which averaged a few
percent, was similar in abundance to that found in the Miocene age
sediments in the northern part of the study area.
The formal stratigraphic classification of these sediments remains in
question. These younger sediments may prove to be a new formation
possessing many of the Hawthorn lithologic characteristics. However,
Fogle (personal communication, 1981) identified the Hawthorn Formation
in the St. Lucie core as occurring in the interval from 150 to 547 feet
(below land surface). This would place the Pliocene assemblage de-
scribed in this study (-282 to -387 feet) well within the Hawthorn.
Therefore, considering the extreme variability of the Hawthorn sediments
and the similarity in mineralogy, phosphorite content, and relative diffi-
culty in distinguishing between the younger sediments and the Miocene
Hawthorn, the writer has been inclined to treat these "Hawthorn-like"
sediments as a lithofacies of the Hawthorn Formation (Huddlestun and
others, 1982). Future drilling is planned which should more fully identify
and delineate the areal extent of these sediments.
The Hawthorn Formation in the study area overlies unconformably the
Ocala Group limestones of Late Eocene age. An exception occurs in
Indian River and St. Lucie counties where Hawthorn sediments are
underlain by limestone sediments that may be of Oligocene age based
on foraminiferal occurrences.
In contrast to the contact separating undifferentiated sands and clays
from the underlying Hawthorn, the boundary between the Hawthorn For-
mation and the underlying Eocene age limestones was readily apparent.
This distinctive lithologic boundary offered a sharp contrast between the
dolomitic sediments of-the lower Hawthorn and the underlying richly fos-
siliferous, white-to-cream colored Ocala Group limestones. The Avon
Park Limestone is often distinguished from the younger Ocala Group by
the occurrence of numerous conical-shaped foraminifera, such as
Dictyoconus cooked (Applin and Jordan, 1945). The generally porous and
permeable limestones comprising the Ocala Group and Avon Park






BUREAU OF GEOLOGY


Limestones and local permeable zones of the lower Hawthorn form the
upper part of the Floridan Aquifer. Conversely, the clayey sands of the
upper Hawthorn may act as an aquiclude retarding downward water
seepage and in places (i.e., eastern Orange County) retarding the upward
movement of water.
LITHOLOGY
Hawthorn sediments throughout the study area are extremely variable,
ranging from phosphatic, clayey sands, and dolomitic, clayey silts to car-
bonates. In addition to common occurrences of clay or sand lenses, a
basal dolomite is also present in the Hawthorn sediments, represented
best in the northern cores (Scott, 1982; 1983).
Common to the Hawthorn Formation and an important lithologic guide
to its identification is the presence of phosphorite. This constituent, with
occasional occurrences in excess of 50 percent of the sediment sample,
is generally disseminated throughout a sandy carbonate or silt-clay ma-
trix. The phosphorite is present in variable amounts that commonly range
from less than one percent to 35 percent of the sample with average val-
ues of approximately five percent (visual estimate).
A number of Hawthorn samples in the study area have been studied
by x-ray diffraction in order to identify the clay components for paleo-
environmental inferences (Reik, 1980; 1982). These clay analyses indi-
cated the presence of palygorskite, sepiolite, montmorillonite, chlorite,
and kaolin. Palygorskite and montmorillonite were the most abundant
clays.
ZONATION
MICROFOSSIL CORRELATION
The diatom correlation and zonation scheme used in this study was pri-
marily based on Abbott's (1978) zonation of Miocene strata along the At-
lantic margin of North America and Pliocene fauna described by Lohman
(1938), Burkle (1972), and Jouse (1974). Additional emphasis was given to
the stratigraphic ranges of various species of Rhaphonels developed by
Andrews (1975) for the Chesapeake Bay area.
Diagnostic species utilized in the zonal correlations of the Florida diato-
maceous sediments were numerous and especially resistant to dissolu-
tion. Consequently, flora with similar ranges to species in Abbott's zona-
tion scheme are here utilized as index markers for the Florida Miocene
correlation.
Diatomaceous sediments encountered in three cores and one set of
cuttings from the northern half of the study area generally corresponded
to three Atlantic Miocene siliceous microfossil zones proposed by Abbott
(1978). These three Middle Miocene zones recognized in the cores in-
clude Abbott's Delphlnels penelliptica, Delphlnels penelllptical
Cosci iscus plicatus, and Coscinodlscus pilcatus zones (figure 4).
Abbott's correlations were found to be generally applicable to diatoma-










REPORT OF INVESTIGATION NO. 93


MIOCENE
AGE

EARLY MIDDLE


Actinoptychus
helioplto


Delphlnels Delphlnals
Delphinels ovota Delphlnals penelliptico Coclnodiscwu
ovoto Delphlneli penelliptica Coscinodlicul plicoatu
penelllpltic plicatus


4. --.
4.-..


-4I


4 -


ZONES


Aclinoptychus hellopello
Novlculopsis ipp.
Oelphnels ovoato
Delphinel~ penelliptico
Cotclnodiscul pllcatus
Ditelphanu stlouroconthut
Actinocyclus ellipllcus
Annollus colifornicus
Bruniopsis mlrobills
Cosclnodlicus lewlilonus
Coaclnodiscus proayobel
Cosicnodiscus yabel
GuIslo proepoleoceo
Denticula hustedil
Denticulo louto
Mocroro itello
Modiorao splendldo
Raphidodiscus morylondicus
Rhophonels f(otile
Rouxio colifornico
Rouxlo diploneldes
Rouxlo novlculoldes


_ ...A


Figure 4. Abbott's Atlantic Miocene Siliceous Microfossil Zones showing
the substitution of Rhaphonels lancetulla and the marker diatoms,
silicoflagellate species and planktonic diatoms found associated with the
zones (Abbott, 1978).


- -- --- ~ ~I- -- --~~~~----- --*----


- --------- -- --- .
- I--


-- -- ----------.
---
-------- ---r

--- -- ---- --






BUREAU OF GEOLOGY


ceous sediments present in the northern half of the study area. However,
his correlation scheme was modified in part to make it more adaptable
to the observed flora (Abbott, personal communication, 1981). This
departure from Abbott's zonation involved the substitution of Rhaphonels
lancettulla for Coscinodiscus plicatus in Abbott's Cosclnodlscus plicatus/
Delphinels penelliptica and Coscinodiscus plicatus zones. These species
have a similar range; but possibly due to the environment of deposition
and associated selective weathering related to structure, the diatom
Coscinodiscus plicatus had an extremely sporadic occurrence in contrast
to the more abundant Rhaphoneis lancettulla. Many species, including
Coscinodiscus plicatus, which belong to the genus Cosclnodiscus, are
particularly susceptible to the effects of dissolution due to their fragile
structure. Consequently, the utilization of Rhaphonels lancettulla, a
species with some resistance to dissolution, was necessary in order to
meet desired criteria ascribed to index species, that is, being both
widespread and abundant.
Abbott's Miocene Atlantic margin zonation is shown in figure 5 along
with a notation underscoring the substitution of Rhaphonels lancetulla for
Coscinodiscus plicatus. Figure 5 is a correlation of planktonic foramini-
fera zones of Blow (1969) and calcareous zones of Martini and Worsley
(1970) to Abbott's Atlantic Margin zones (Abbott, 1978).
DISTRIBUTION OF SILICEOUS MICROFOSSILS
The siliceous microfossil groups included diatoms, sillcoflagellates,
and dinoflagellate species. In addition, phytoliths were noted throughout
the study area.
The distribution of diatomaceous cores in the study area was found to
be limited to near the present coast (figure 6). However, nine cores, the
majority of which were located further inland, contained diatom molds
(figure 7). Several of the cores (W-13958, W-13751, W-13844) had diatom
molds present in sediments below diatomaceous sediments. In all occur-
rences, the diatom molds were present in sediments of the middle or low-
er Hawthorn (figure 8). These molds were primarily circular structures be-
longing to the centrales group of diatoms. Diatom molds in W-14477, a
core located in Putnam County, occurred in sediments consisting primar-
ity of a poorly indurated, very fine-grained, clayey dolomite. Similarly, dia-
tom molds in W-14354, another core located In Putnam County, were
present in sediments consisting of a poorly indurated clay with associated
dolomite.
Additional cores with sediments containing diatom molds occur in Clay,
Duval, St. Johns, and Brevard counties. Miller (1978) has observed diatom
molds in Columbia and Baker County cores. In general, these molds
occurred in single short intervals in sediments ranging from moderately
indurated clays to fine-grained dolomite.
Hawthorn diatomaceous sediments were present in five cores and two
sets of well cuttings (figure 6). These cores and well sites are all located
within a few miles of the coast. W-13751 had special significance in that







REPORT OF INVESTIGATION NO. 93


EUROPEAN ABBOTT BLOW MARTINI a
M.Y. / STANDARD U.S. EAST FORAMINIFERAL WORSLEY
NANNOPLANKTON
STAGE COAST ZONES 1969 ZONES
_ZONES 1970


N 12






Nil


12






13



14





15


Burdigollon


Actinoptychus
heliopelto .


Sarrovollion


Longhian


Coscinodiscus
plicatus*.


Dalphinels
panalliptico
Cosclnodiscus
plicatus *


Delphinals
panelliptico


Delphlnals
ovato
Delphineis
penalliptico


Delphlnels
ovoto


N 10



N 9




N 8


NN4


NN3


NN6


NN5


* Rhaphoneis lancetulla substituted for
in this study.


Coscinodiscus


Figure 5. Correlation of diatom zones defined by Cavallero (1974);
Schrader (1973); Andrews (1976); Planktonic Foraminiferal Zones of Blow
(1969); Calcareous Nannofossil Zones of Martini and Worsly (1970) and
Siliceous Microfossil Zones of Abbott (1979) (from Abbott, 1978).


plicatus


- __~~ ___,


- ----- --- IL--- L --- LL ___ _~


N6 NT






BUREAU OF GEOLOGY


t'


/.
/'
i .. ..


; CORES
CUTTING


O1 0 10 20 30 40M
1 2 I0203040 OKM


-CUMBERLAND ISLAND CORE

-W-670



-W-13751


W-13844







W-5906








... W-13958


ST. LUCIE
CORE


Figure 6. Location of diatomaceous cores.





REPORT OF INVESTIGATION NO. 93


N




10 0 10 26 30o 4K M
10 0 10 20 30 40 OKM


-W- 14619
--W-14193
--W-13751
----W-13769


3744


-13964


13958


Figure 7.Location of cores with diatom mold occurrences.





REDUCTION


RATIO


12x









BUREAU OF GEOLOGY


W-13815


~LL
Lca
up ia
urr r-


Figure & Chart showing the distribution of biostratigraphic zones, disso-
luticn assemblages, foraminifera, diatom molds and formational contacts.








REPORT OF INVESTIGATION NO. 93


/-13769




2'"


-205.5


Pllo-Plelstocene undiff. sands and. clays

D Pliocene "Hawthorn like" sediments

] Cosclnodlscus plicatus zone

U Cosclnodlscus pllcatus / Delphlneus penelllptica zone

D Delphlneus penelllptica zone

SDiatom molds

Mollusk frags,foram molds and frags ,burrows

SForamlnlferal counts

* Dissolution assemblage

Hawthorn Formation contact (Top & Bottom)

SWell cuttings


W-13551
+45 1


W-13957


ST. LUCIE
CORE


-386





BUREAU OF GEOLOGY


Pliocene-age diatoms were found in the overlying, undifferentiated sand
and clays.
Diatomaceous sediments ranged in thickness from a minimum value
of 13 feet (W-13744) to a maximum value of 150 feet in the St. Lucie core
(figure 8). Diatomaceous sediments in the northern part of the study area
were predominantly dolomitic, silty clays with minor amounts of sand and
phosphorite. In contrast, the sediments with included diatoms in the
southern cores consisted of dolomitic, clayey silts with calcareous sands
present as important components (up to 40 percent).
The siliceous microfossils identified totaled 170 species of diatoms, 13
species of silicoflagellates, and two species of dinoflagellates. Diagnostic
diatoms in Hawthorn sediments of the northern cores were of Middle Mio-
cene age while diatoms in "Hawthorn-like" sediments of the southern two
cores were entirely Pliocene in age.
Diatoms occurring in the northern cores and well cuttings (Cumberland
Island, W-670, W-13751, W-13844) can be placed in one or more of
Abbott's three late Middle Miocene zones. These biostratigraphic zones
included the Delphlnels penelllptica, Coscinodiscus plicatis/Delphineis
penelliptica, and Coscinodiscus plicatus zones.
The distribution of fossiliferous intervals sampled in the cores and well
cuttings is shown in figure 8. Several of the intervals with sparse assem-
blages (W-13958, 148-150 ft., and the St. Lucle core, 370-371 ft.) occurred
between intervals of abundant diatoms, a circumstance for which no ex-
planation was readily apparent based on lithology.
The diatoms in the northern cores could be divided into two distinct
groups: a predominant temperate-to-warm-water assemblage and
another group associated with cool, upwelling waters. The temperate-to-
warm-water assemblage was the only group present in the diatomaceous
sediments of the southern cores.
The cool, upwelling species (table 1), which averaged approximately 12
percent of the total assemblage, attained a maximum value of 26.5 per-
cent of the assemblage in the 223-foot interval of W-13751 (figure 11).
These forms were completely absent from the Pliocene-age sediments of
the southern two cores. Apparently, the conditions necessary for their
presence were either absent or substantially diminished to a point that
upwelling-water forms were totally absent in the Pliocene environment.
Conversely, brackish water species (table 1) were present in both the Mio-
cene and Pliocene sediments.
Other microfossil groups (phytoliths and dinoflagellates), although less
abundant, are present throughout the study area, as noted in several
cores. Their occurrence has been reported by Abbott (1974b) in diatoma-
ceous clay units of the Hawthorn Formation of South Carolina and
Georgia.
Dinoflagellate occurrences, though few, were widespread. Their bio-
stratigraphic value has yet to be realized; however, a better under-
standing of the diversification experienced by this group beginning in the
Middle Miocene may prove invaluable to future biostratigraphic studies.







REPORT OF INVESTIGATION NO. 93


Table 1. Diatom species utilized as environmental indicators
in this study, compiled from Abbott and Andrews (1978),
and Abbott (personal communication, 1981).


HIGH BRACKISH
SALINITY WATER


COOL
UPWELLING


Biddulphia toumeyi X
Coscinodiscus nodulifer X
Coscinodiscus rothil X
Diplonels crabro X
Hemidiscus ovalis X
Hyalodiscus laevis X
Rhaphonels amphiceros X
Thalassionema nitzschoides X
Thalasslothrix longisslma X
Trachynels aspera aspera X


SPECIES


WARM
WATER







r--' ~--\ ] ,





I
O COM DEPTH (FET.


&.#*tes UPWELUNQ 8PECES
-- BRACKISH SPECIES
.***"" WARM WATER SPECIES



C.p.
D.p. Zone D.p. Zone

S''f i


-270 -0 -290 -300 3S10 -320 -330 -340 -350 -360
CORE DEPTH (FEET, MSL)
Figure 9. Distribution of diatoms in terms of brackish, upwelling, and warm water indicators and numbers of
species for the Cumberland Island Core.











30.0



25&0

I-
Z
M 20.0
0

LL
o 15.0.
I-

I0.
0'


5.0.




-270


Figure 10. Distribution
species for W-670.


I / ,
/ \
-v
/r
IA


-270


.........UPWELLING SPECIES

---BRACKISH SPECIES
***** WARM WATER SPECIES


COCE Wpm ('EET. ULSU


D.p.


D.p. Zone


w.... @*.e...
.,.
9.........-* *.



*e 1
,**
e '"o



4r
o
o *
*
*****
F
"****
F
"****
P
"
r
"*


-280 -290 -300 -3 -320
CORE DEPTH


-330 -340
(FEET, MSL)


-350 -360


of diatoms in terms of brackish, upwelling, and warm water indicators and numbers of


. .......... ....... .... ..... ..... m-- -- --- ---- .. --






BUREAU OF GEOLOGY


DISCUSSION
ZONE OCCURRENCES
The diatomaceous Hawthorn sediments present in cores in the north-
ern part of the study area were all of late Middle Miocene age (figure 8).
These dates and associated paleoenvironmental data were derived al-
most exclusively from diatoms. An important exception occurred In Nas-
sau County (W-13815) where sediments near the base of the Hawthorn
were determined to be of Early Miocene age on the basis of planktonic
foraminifera.
In the Atlantic Coastal Plain, Abbott found that the Early and early Mid-
die Miocene sediments were restricted, with one exception, to the shelf
north of Cape Hatteras. The one exception was the occurrence of diato-
maceous sediments belonging to the Delphineis ovata/Delphlneis penel-
liptica Zone (Middle Miocene) in Georgia. The Early and early Middle
Miocene strata south of Cape Hatteras may be represented by unfossili-
ferous sediments.
These Early and early Middle Miocene zones were, with one exception
(W-13815), entirely absent from sediments studied in Florida. This could
be accounted for in a number of ways including: nondeposition, deposi-
tion and subsequent erosion and/or strata of this age being represented
by unfossiliferous sediments. The presence and appearance of poorly-
preserved diatoms in strata at the top of the diatomaceous Hawthorn sed-
iments and in the overlying post-Hawthorn diatomaceous sediments of
W-13751 (-33 to -43 ft.) are suggestive of dissolution. In like manner,
the absence of flora below the Delphineis penelliptica Zone in sediments,
many of which were dolomitized, may be due to the total dissolution of
diatoms in early Middle Miocene and older sediments.
DELPHINEIS PENELLIPTICA ZONE
.Numbers of species (figures 9, 10, 11) were high throughout the recog-
nizable portion of the Delphinels penelllptica Zone for the three northern
cores (Cumberland Island, W-670, W-13751). However, W-13744, which
had the longest section of Delphinels penelliptica zonal sediments, had
markedly fewer species for this zone relative to the other cores (figure 12).
A similar trend was noted with respect to the upwelling assemblage (fig-
ures 9, 10 11). Upwelling species had occurrences averaging more than
17 percent of the total assemblage in this zone; a trend analogous to total
species numbers. In contrast, the upwelling species recorded in the
Defphtnes penelliptica Zone of W-13744, with one exception (seven per-
cent), accounted for less than one percent of the assemblage (figure 12).
Brackish water species, which reached a maximum value of 11.6 per-
cent in W-670, averaged less than four percent for all other cores in the
Delphinels penelilptica Zone (figures 9, 10, 11, 12). Upwelling species (ex-
cept for W-13744) greatly outnumbered brackish-water forms throughout
this zone.






REPORT OF INVESTIGATION NO. 93


The above observations show a fluctuation in species numbers and a
distinct decline of upwelling forms in the Delphinels penelliptica Zone for
W-13744, the most southern core in which this zone was recognized. This
is indicative of a stressed environment and associated reduced
assemblage.
Several explanations may account for the reduced flora at W-13744.
Specifically, the sharp decline in upwelling species at this site during the
Middle Miocene suggests that the effects of a postulated offshore, cold-
water current (Abbott and Andrews, 1979) may not have reached this far
south or that it may have moved further seaward. Conversely, if upwelling
was the source of these cool-water species, an alternate explanation
would suggest a reduction in upwelling intensity due to locally shallow
conditions as opposed to deeper water further north. It is also possible
that the sediments represented by these cores were not deposited syn-
chronously. Consequently, the period represented by a reduced flora in
W-13744 and the noted absence of this assemblage in other cores may
be due to synchronous sediments in the latter cores having been re-
moved through erosion. Evidence supportive of this latter premise in-
cludes the higher elevation of -132 feet recorded for the top of the
0
.a.. / "* UPWELLING SPECIES
30.0. / BRACKISH SPECIES
f /n """"WARM WATER SPECIES

,.o. i D.p.
3 90 CORE DEPTH (PET, M8L) D

00 **

00 0 *
LL
.1.5.C0 p.
w D.P. I %

_ 0o.. A. I *:: be





-.10 .1lo -120 .77 |30 -.0 .So ft
CORE DEPTH (FEET, MSL)
Figure 11. Distribution of diatoms in terms of brackish, upwelling, and
warm water indicators and numbers of species for W-13751.







...... "UPWELLING SPECIES
---- BRACKISH SPECIES
.***.,. WARM WATER SPECIES


K


Zone


D.p. Zone


CORE DEPTH (FEET, MSL)


Figure 12. Distribution of diatoms in terms of brackish, upwelling, and warm water
species for W-13744.


*144 -146 -148 -150

indicators and numbers of


30.0


- ,r \


-124 GORE DEPTH (FEET,MBL) -1






REPORT OF INVESTIGATION NO. 93


Delphineis penelliptica zonal sediments present in W-13744 as compared
to 168 feet at W-13751, 335 feet at W-670, and 342 feet at the Cum-
berland Island core to the north.
COSCINODISCUS PLICATUS/DELPHINEIS PENELLIPTICA ZONE
This zone has special significance in that sediments belonging to this
zone in W-13751 appear to form a complete section; that is, continuous
sedimentation without a break. If all sediments are present this gives a
maximum calculated sedimentation rate at this site of 3.2 cm/1000 years.
Species numbers remained high throughout the Coscinodiscus
plicatus/Delphineis penelliptica Zone in all cores except W-13751 (figure
11). This core experienced several major reductions in species numbers
which were not observed in the other cores.
The cool, upwelling species in this zone made up 10 percent or more
of the assemblage for sampled intervals in all cores except W-13751. This
latter core recorded both maximum and minimum values for all cores in
this zone. Of significance was the marked increase in upwelling species
from one percent and lower values observed in the underlying Delphineis
penelliptica Zone to over 15 percent in the Coscinodiscus plicatus/
Delphineis penelliptica Zone for W-13744.
Brackish-water forms reached values from five percent to a maximum
of 11.6 percent at certain intervals in the Coscinodiscus plicatus/
Delphineis penelliptica Zone in all of the cores. These were maximum
core values for the three northern cores (Cumberland Island, W-670,
W-13751). In addition, a general reduction in brackish-water species
counts occurred from W-670 southward to W-13744 in this zone.
The above data suggest that changes in the environment of deposition
during the time represented by the Coscinodiscus plicatus/Delphineis
penelliptica Zone were probably local in extent. Several of these changes
in the environment were quite conspicuous as indicated by the sharp de-
cline of all species in sediments of W-13751 in the middle part of the zone.
COSCINODISCUS PLICATUS ZONE
The Coscinodiscus plicatus Zone was recognized at only one site
(W-13751, figure 11). This one occurrence in St. Johns County, with one
exception at (-116 ft.), showed a general decrease of brackish species
in going upcore, reaching a maximum value of 9.5 percent of the assem-
blage in that zone (figure 11). The absence of this zone both north and
south of this core, may be attributed to erosion or non-deposition of these
sediments at other core sites. Support for this premise includes the mark-
edly higher elevation (-115 ft.) recorded at W-13751 for the top of the
underlying Coscinodiscus plicatus/Delphineis penelliptica Zone as com-
pared to 310 feet for W-670 and a closer value of 129 feet for W-13744.
In general, the Coscinodiscus plicatus Zone showed an increase in
species numbers. The species present in this zone were suggestive of a
restricted lagoonal assemblage.






BUREAU OF GEOLOGY


Upwelling/Cool Water Current
The co-occurrence of upwelling and temperate-to-warm-water species
in all three Middle Miocene biostratigraphic zones is significant, suggest-
ing the mechanism of upwelling or the existence and proximity of an off-
shore, cool-water current during the Middle Miocene. Supporting data
include the presence of well preserved siliceous microfossils, benthic for-
aminifera, and appreciable concentrations of phosphorite (Haass and
Schrader. 1979).
Upwelling, as it occurs today off the coast of Peru, requires a narrow
shelf and a continuous downwelling front. There is evidence for both a
Peru-type upwelling and an arid climate during the early Middle Miocene
for northwestern Africa (Haass and Schrader, 1979). As a consequence
of upwelling, deeper cold water and associated cooler water diatom spe-
cies are brought to the surface where they mix with temperate-to-warm-
water, coastal diatoms.
Common arguments against the operation of this mechanism off the
coast of Florida in the past include the following observations of modern
day upwelling: the occurrence of upwelling is primarily off of the western
sides of continents, presence of a narrow shelf, and wide circulation
(Smith, 1968). Recent studies (Manheim and others, 1975; Burnett and
Veeh, 1977) suggest that these arguments may not be as valid as once
thought. These studies and observations reveal that the majority of up-
welling off the coast of Peru occurs in water depths between 150 and 600
feet with minor upwelling operative in deeper water. In addition, intense
upwelling occurs in shallow waters on the Agulhas Bank off South Africa
(Summerhayes, 1970). Other evidence for upwelling off east coasts in-
cludes observations (Milliman and others, 1975; William Burnett, per-
sonal communication, 1981) of variable upwelling off the east coast of
Brazil. In addition, Wells and Gray (1960) have observed variable upwell-
ing off the coast of North Carolina. Riggs (1979a) postulates the existence
and movement of upwelling waters across a shallow Florida platform dur-
ing the Miocene. Taylor and Stewart (1959) reported present-day upwell-
ing off the northeastern coast of Florida. Consequently, some of the argu-
ments against the operation of upwelling off the east coast of Florida may
be unfounded.
Recent data (Hathaway and others, 1970) point to the existence of a rel-
atively broad shelf off this part of Florida during the Middle Miocene. Fur-
thermore, the diatoms in these Middle Miocene sediments were predomi-
nantly benthic and nearshore forms, many of which occur today in water
depths of 300 feet or less. Other factors present which are common to
areas of upwelling include: the excellent preservation of diatoms and sili-
coflagellates in coastal cores, a predominant benthic foraminiferal as-
semblage, and appreciable concentrations of phosphorite (Haass and
Schrader, 1979).
Another factor normally associated with upwelling on the eastern side
of oceans is an arid climate. This study noted the presence of phytoliths







REPORT OF INVESTIGATION NO. 93


of the Panicoid class in the Middle Miocene diatomaceous sediments.
Sporadic in occurrence, this group of microfossils suggests the presence
of grasslands or prairies in the region (Twiss and others, 1969). Such veg-
etation, if widespread, would be indicative of low rainfall, a characteristic
of arid climates (Odum, 1959). Alt (1974) and Abbott (1974b) have found
evidence for such a climate further north in the sediments of South
Carolina.
A variation in specimen size of included species was observed in sev-
eral of the cores. This was especially pronounced near the top of the
Coscinodiscus pllcatus/Delphlne/s penell/ptica Zone of the Cumberland
Island core (-285 ft.). This could be associated with an increase in
coastal upwelling intensity. Larger planktonic diatom specimens, which
are generally favored by high upwelling velocities and greater associated
productivity, provide a means to estimate past upwelling velocities and
productivity. Furthermore, studies by Richert (1976) have shown that
coastal upwelling with velocities of less than 2 m/day and without a con-
tinuous downwelling front are undetectable in sediments based on opal
content diatomss). Consequently, the decrease in specimen size ob-
served may indicate reduced upwelling Intensity. Such occurrences, as
in the Cumberland Island core, coincided with periods or cycles of dimin-
ishing deposition of diatomaceous sediments or, in the case with the 50
to 52 ft. and 99 to 102 ft. intervals of W-13744, with isolated occur-
rences of sparse floral assemblages (figure 8).
Alternatively, the attractiveness of an offshore, cool-water current as a
source of both upwelling diatom species and phosphorite cannot be dis-
missed. Upwelling genera such as Thalass/onema, Thalasslos/ra, and
Denticula may have been brought in by cool-water currents. Such a cur-
rent (Ancestral Labrador Current) has been postulated by Abbott and An-
drews (1979). This current may be extended as far south as the study area
if, as Abbott suggests, the Cape Fear Arch east of North Carolina was
subdued during the Middle Miocene (figure 13).
An open Isthmus of Panama was a major influence on circulation
patterns (especially in equatorial Atlantic waters). A flow of Pacific nutri-
ent-rich waters through this opening would result in increased diatom pro-
duction in areas near to these currents (Ramsey, 1971).
The noted absence of upwelling species in the Pliocene diatomaceous
sediments present in the southern part of the study area may be related
to the closing of the Isthmus of Panama during Pliocene times (Stokes,
1966). Such an event would have a dramatic effect on currents, especially
in the Caribbean Sea region. The cessation of strong westward flowing
ocean currents would divert increasing amounts of warm water north-
ward. Consequently, the presence of the course of Abbott's postulated
cool-water current and associated upwelling diatoms off the east coast of
Florida may have ceased or moved considerably offshore or northward;
the net effect being minimal or no influx of upwelling species. In sum-
mary, an open Isthmus permitting the flow of Pacific nutrient-rich waters
into Atlantic waters and a subdued Cape Fear Arch were real or postu-






BUREAU OF GEOLOGY


lated factors present in the Miocene that were either missing or signifi-
cantly changed by Pliocene time.
Pliocene Data
Dates obtained from the diatom flora for the "Hawthorn-like" sediments
south of Brevard County were unexpected. These diatomaceous sedi-
ments, which were present in two cores from Indian River and St. Lucle
counties, had diatoms of post-Miocene age (figure 8). If these sediments
are assigned to the Hawthorn Formation, this would represent a signifi-
cant age extension of the Hawthorn Formation based on flora from the
northern cores and heretofore accepted dates (Alt, 1974; Weaver and
Beck, 1977).
The Middle Miocene flora present in the northern part of the study area
is not present in these cores. Explanations for this noted absence in-
clude: nondeposition of Hawthorn sediments in this area during the Mid-


Figure 13. Major currents of the North Atlantic.

















O CORE D.P (EET, ML) -
-38 CORE EPTH (FEET, MSU S


- BRACKISH SPECIES
'******WARM WATER SPECIES


-40 -42 -44


-46 -48 -50 -52 -54


CORE DEPTH (FEET, MSL)


Figure 14. Distribution
species for W-5906.


of diatoms in terms of brackish, upwelling, and warm water indicators and numbers of











I ,^ \ --- WARM WATER SPECIES
Z *"***s'BRACKISH SPECIES
S- coRo DEPTH ET, MM 1 -
0

0
I--
'4.0
0
0 i


-100 -O -115 -1 -130 -135 -140 -145
CORE DEPTH (FEET, MSL)

Figure 15. Distribution of diatoms in terms of brackish, upwelling and warm water indicators and numbers of
species for W-13958.








******* BRACKISH SPECIES
- WARM WATER SPECIES


I-

0 /

o


a 0




-240 -20 -20 -300 -3. -340 -360 -38 -400 420
CORE DEPTH (FEET, MCSL)

Figure 16. Distribution of diatoms in terms of brackish, upwelling, and warm water indicators ana numbers of
species for the St. Lucie core. m






BUREAU OF GEOLOGY


die Miocene, deposition of Hawthorn sediments and subsequent erosion,
or strata of this age being represented by unfossiliferous sediments. Al-
though the first two explanations cannot be ruled out as possible causes,
the close similarity of these unfossiliferous sediments in lithology to the
SMiddle Miocene sediments in the northern cores and thickness (hun-
dreds of feet) are supportive of their presence as unfossilized sediments.
In addition, the absence of a Middle Miocene assemblage in these
southern cores may be the result of secondary dissolution or a depo-
sitional environment inhospitable to their presence. The presence of
carbonate below the Pliocene age flora, which invariably occurs as dolo-
mite (Scott, personal communication, 1981), does lend support to the
theory of alteration of initial sediments, erasing all evidence of included
microflora.
These younger Pliocene sediments were more calcareous than the
Middle Miocene diatomaceous sediments, an observation in part attri-
buted to an increase of calcareous nannoplankton and foraminifera. This
was the primary difference observed in the lithology. Clay analyses done
by Dabous in 1981 revealed the presence of sepiolite and palygorskite,
common constituents of the Middle Miocene Hawthorn Formation, in ad-
dition to montmorillonite. Sepiolite and palygorskite have rare sporadic
occurrences in sediments younger than the Miocene. Phosphorite con-
tent, which averaged a few percent, was similar in abundance to that
found in the Miocene sediments to the north.
The formal classification of these sediments remains in question. The
younger sediments may prove to be a new formation possessing many
of the Hawthorn lithologic characteristics. However, Fogle (personal com-
munication, 1981) identified the Hawthorn Formation in the St. Lucie core
as occurring in the interval from 150 to 547 feet. This would place the
Pliocene assemblage described in this study (-282 to -387 ft.) well
within the Hawthorn. Therefore, due to the extreme variability of the
Hawthorn sediments and the similarity in mineralogy, phosphorite con-
tent, and relative difficulty in distinguishing between these sediments and
the Miocene Hawthorn, the writer is inclined to treat these sediments as
a facies of the Hawthorn Formation (Huddlestun and others, 1982, in
press). Planned future drilling should more fully identify and delineate the
areal extent of these sediments.
A distinctively different assemblage was present in the Pliocene sedi-
ments of the southern cores. Upwelling species, which were so numerous
in the Middle Miocene diatomaceous sediments, were missing from these
sediments. The resultant assemblage indicates an environment of
temperate-to-warm temperatures and relatively shallow coastal depths.
This assemblage had occurrences in sediments of increased dolomitic
composition in which the effects of solution were apparent. The Indian
River core (W-13958) had several depths (- 112 ft., 122 ft., 130 ft.) in
which species displayed varying degrees of dissolution (figure 15). Dia-
tom species such as Paralia sulcata and Navicula pennata as well as cal-
careous Discoaster species displayed partially dissolved rims or edges.







REPORT OF INVESTIGATION NO. 93


Similar changes were observed in the St. Lucie core to the south.
The presence of extinct species, including Rhaphoneis fatula and Goni-
othecium odontella, which made their first appearance in the Pliocene
and Late Miocene respectively, were present in these sediments. The lat-
ter species range from the Late Miocene to Early Pliocene. The presence
of Thalassiosira oestrupi in these sediments is significant, since the first
appearance of this brackish-water species is generally accepted as the
base of the Pliocene. The co-occurrence of Discoaster brouweri and the
silicoflagellate Distephanus boliviensis is rare in Pliocene sediments; the
latter species was formerly thought to have reached extinction by the late
Early Miocene. Of further significance was the presence of Bogorovia tat-
sunokuchiensis, a diatom common to the Pacific and believed to range
from 2.9 to 4.9 million years before present (Abbott, personal communica-
tion, 1981). Consequently, an Early Pliocene date for these sediments is
strongly supported by the included flora.
Pliocene diatom assemblages examined in the cores from Brevard
County and southward exhibited no discernible trends in numbers of
warm-water species (figures 14, 15,16). Maximum recorded occurrences
in these cores varied from a 1.0 percent peak encountered in W-5906 to
a 2.2 percent peak observed in W-13958 near the southern end of the
study area. Distinct maxima and secondary maxima peaks were present
in the Indian River (W-13958) and St. Lucie cores.
Minimum occurrences generally coincided with minimum numbers of
species and brackish-water species, a finding suggestive of increased
environmental stress. Prominent minimum occurrences, which ap-
proached zero, were recorded in both cores in intervals between the max-
imum abundances of brackish-water species mentioned above.
Numbers of Pliocene brackish-water species were similar to those
found in the diatomaceous Middle Miocene Hawthorn sediments (figures
14, 15, 16). These species included the Pliocene forms Trachyneis aspera
aspera and Hemidiscus ovalis, in addition to Rhaphoneis amphiceras,
species also present in the Miocene.
Brackish-water species, which averaged less than four percent of the
Pliocene assemblage, had maximum occurrences greater than six per-
cent of the total assemblage in W-5906, W-13958, and the St. Lucie core.
Brackish flora in the two southern cores (W-13958 and St. Lucie) each ex-
hibit similar maximum abundances that were separated by an interval re-
flecting a sharp decline in numbers. The similarities in distribution of
brackish and warm-water species, abundances, and numbers of total
species versus depth are remarkably close. Specifically, the general coin-
cidence of two major brackish and warm-water species peaks (W-13958,
-117 ft., -137 ft., and St. Lucie core, -312 ft., -342 ft.) and minima
(W-13958, -125 ft. and St. Lucie core -332 ft.) are suggestive of a
regressive-transgressive sequence on at least a local scale. In general,
the flora denotes a shallow coastal or estuarine environment. This type
of environment has a range of depths at which a relatively minor drop in
sea level could dramatically affect the assemblage. This may be indicated






BUREAU OF GEOLOGY


by the occurrence of sparsely fossiliferous samples between two major
peaks in both cores.
Species diversity is extremely variable throughout the Pliocene diato-
maceous sediments. In general, diversity is less than that observed in the
Miocene sediments to the north. The reduction in numbers of included
species and absence of cool-water upwelling species are supportive of
significant environmental changes during the Early Pliocene.
Diatom Molds
Diatom molds were found at various intervals in eight of the cores (fig-
ure 8). These cores were located at both coastal and inland sites (figure
7). In general, these molds were present in the middle or lower part of the
Hawthorn section.
The explanation for these molds is probably a matter of time-related ki-
netics since the opal-A which forms the diatom frustules is inherently un-
stable. Alternatively, an increase in pH to values near 8 or 9 as a result
of groundwater action could enhance the dissolution process (Abbott,
personal communication. 1981).
The absence of both diatoms and molds in many of the cores could be
attributed to a general incompatibility of diatoms at the time of the deposi-
tion to such environmental factors as water temperature, salinity, and/or
a nutrients deficiency (especially nitrate and silica). Alternatively, their ab-
sence could be a function of selective solution both in the water column
and in the sediments.
The occurrence of only centrales-type molds may not represent the
past living assemblage (biocoenose). Studies in the equatorial Pacific
(Burkle. 1977) have shown significant alteration of the diatom death as-
semblage (thanatocoenose) by selective dissolution in both the water col-
umn and the enclosing sediments. Molds of the centrales would tend to
be preserved due to their generally larger and thicker valves. Conversely,
the occurrence of these centric forms, which tend to dominate the plank-
tonic species, may not have lived in situ. Diatoms, in particular planktonic
species, are susceptible to lateral transport and may have been brought
inland by currents to waters less conducive to plant growth resulting in
their subsequent burial and post-depositional alteration.
Paralla sulcata
The abundance of the diatom species Paralla sulcata in both Middle
Miocene and Pliocene sediments was notable. Indeed, this species was
usually the dominant member of both prolific and impoverished assem-
blages alike. The dominance of this species may be as Abbott suggests
(personal communication, 1979), a function of initial abundance at the
time of sediment deposition. However, the type and appearance of speci-
mens (resistant species, dissolution rims) and particularly the appear-
ance and abundances of Paralia sulcata in sparsely fossiliferous intervals
are suggestive of dissolution assemblages. Consequently, this species
may have value as a dissolution indicator.







REPORT OF INVESTIGATION NO. 93


SUMMARY AND CONCLUSIONS
1. Cores drilled during the late 1970's along Florida's east coast by the
Florida Bureau of Geology contain the most complete suite of Florida
Hawthorn microfossiliferous sediments currently available for biostrati-
graphic analysis. Hawthorn sediments in the northern part of the study
area range in age from Early Miocene to late Middle Miocene, while the
southern part of the study area from Brevard County southward contains
"Hawthorn-like" diatomaceous sediments of Early Pliocene age overlying
the "typical" Hawthorn sediments.
2. A diversity of microfossil groups including 170 species of diatoms, 13
species of silicoflagellates, in addition to a number of planktonic and ben-
thic foraminifera and several coccolith species, can be identified in the
Hawthorn sediments. Diatoms represent the most definitive group in
terms of both age resolution and environmental interpretation.
3. Three biostratigraphic zones of Middle Miocene to late Middle Mio-
cene age can be recognized in the Hawthorn sediments of three cores
and one set of well cuttings (Cumberland Island, W-670, W-13751,
W-13844). A departure from Abbott's zonation involved the substitution of
Rhaphoneis lancettulla for Coscinodiscus plicatus in the Coscinodiscus
plicatus/Delphinels penelliptica and Coscinodiscus plicatus zones in or-
der to make the Florida Hawthorn zonation more adaptable to the ob-
served flora.
4. Upwelling species occur with a predominant temperate-water flora in
the northern cores. The upwelling flora, which is believed here to be the
result of coastal upwelling or influx from a postulated offshore, cool-water
current (Ancestral Labrador Current), reaches a maximum value of 26.0
percent of the total assemblage in core W-13751.
5. The total absence of an upwelling flora in the Pliocene "Hawthorn-
like" sediments of the southern half of the study area may be related to
changes in the paleo-oceanographic environment by Pliocene time.
These changes may include the closing of the Isthmus of Panama during
the Early Pliocene, cessation of upwelling, or both.
6. Core W-13751, located in St. Johns County, has the longest diatoma-
ceous section which includes the Middle Miocene Coscinodiscus pli-
catus, Coscinodiscus plicatus/Delphineis penelliptica and Delphineis pen-
elliptica zones. Sediments belonging to the Coscinodiscus plicatus/
Delphinels penelliptica Zone appear to form a complete section, from
which a sedimentation rate of 3.2 cm/1000 years has been calculated. Al-
though this rate is higher than present deep-sea sedimentation rates (2
cm/1000 yrs.), it may be compared to shelf deposits which typically have
higher sedimentation rates.
7. In general, species diversity was less in the Pliocene sediments than
the Middle Miocene sediments, a reduction attributed in part to changes
in the depositional environment, degree of dissolution, and other external
influences.
8. Fluctuations in productivity, as expressed in terms of species diver-






BUREAU OF GEOLOGY


sity and numbers of brackish-water species in both Middle Miocene and
Pliocene assemblages, are probably the result of sea level changes. The
degree of similarity of these fluctuations are especially pronounced in the
Ptiocene sediments of W-13958 and the St. Lucle core, an indication of
a transgressive-regressive sequence in at least a local area.
9. The diatomaceous sediments that are here described from Indian
River and St. Lucie counties, are tentatively designated as "Hawthorn-
like" sediments on the basis of lithologic similarities. If these sediments
are assigned to the Hawthorn Formation, this represents a significant
upward extension of the Hawthorn Formation's age of deposition in
eastern Florida.
10. The presence of the diatom Delphlnels biserlata, a highly definitive
index species in the Middle Miocene Coscinodiscus plicatus Zone, repre-
sents an extension of the previously accepted range for this species.
11. The presence of Melosira granulata, a fresh-water diatom, near the
top of the Hawthorn Formation in W-13744 may represent a lowering of
sea level associated with an extreme regressive cycle, or it may be attrib-
uted to influx from a nearby fresh-water source, such as a river.
12. The diatomaceous Hawthorn sediments in the study area are bio-
stratigraphically equivalent to the lower part of the Choptank Formation
and the top of the Calvert Formation of the Chesapeake Bay Area as well
as part of the Pungo River Formation of North Carolina.
13. The presence of the planktic foraminifera Globlgerina chipolensis
(Oligocene to earliest Miocene) and Globlgerinoldes quadrilobatus pri-
mordius (Early Miocene) in sediments near the bottom of the Hawthorn
Formation in W-13815 offers strong support for the initiation of Hawthorn
sedimentation in the deeper basins of north Florida during the Early
Miocene.
14. The co-occurrence of important Pliocene marker species represent-
ing several different microfossil groups foraminiferaa Globorotalla marga-
ritae; coccoliths, Discoaster broweri and Discoaster surculus; silicoflagel-
lates Mesocena circulus, and the diatom Rhaphoneis fatula) in sediments
of core W-13958 is significant in that this represents a rare, if not the only,
recorded co-occurrence of diverse microfossil groups of Pliocene age
along the Atlantic east coast..
15. The appearance and abundance of the diatom Paralla sulcata in
sparsely fossiliferous sediments suggests its utilization as a dissolution
indicator.







REPORT OF INVESTIGATION NO. 93


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REPORT OF INVESTIGATION NO. 93


PLATES 1-13


_ _I __
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42 BUREAU OF GEOLOGY

PLATE 1
Diatom photomicrographs; 400X

Figure 1 Actinocyclus octonarius (Ehrenberg)
diameter 40 to 114 pm

Figure 2 Actinocyclus ingens (Rattray)
diameter 22 to 39 pm


Figure 3 Actinocyclus ellipticus (Grunow)
length 20 to 79 pm






,REPORT OF INVESTIGATION NO. 93


2


PLATE 1






44 BUREAU OF GEOLOGY

PLATE 2
Diatom photomicrographs; 400X

Figure 1 Actinoptychus senarius (Ehrenberg) Ehrenberg
diameter 22 to 77 pm

Figure 2 Actinoptychus clevei (Schmidt)
diameter 33 to 83 pm

Figure 3 Actinoptychus aff. A. minutus (Greville)
diameter 29 to 44 pm

Figure 4 Biddulphia rhombus (Ehrenberg) Smith
length 54 to 105 pm







REPORT OF INVESTIGATION NO. 93 45
















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PLATE 2





46 BUREAU OF GEOLOGY

PLATE 3
Diatom photomicrographs; 400X

Figure 1 Biddulphia tuomeyi (J. W. Bailey) Roper
length 42 to 123 pm

Figure 2 Biddulphia reticulum (Ehrenberg) Boyer
length 35 to 95 pm







REPORT OF INVESTIGATION NO. 93 47r







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PLATE 3





48 BUREAU OF GEOLOGY

PLATE 4
Diatom photomicrographs; 400X

Figure 1 Coscinodiscus apiculatus (Ehrenberg)
diameter 74 to 117 pm

Figure 2 Coscinodiscus vetustissimus (Pantocsek)
diameter 58 to 67 pm

Figure 3 Coscinodiscus lewisianus (Greville)
length 30 to 106 pm, width about 2/5 of length in larger
specimens


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REPORT OF INVESTIGATION NO. 93 49


PLATE 4


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50 BUREAU OF GEOLOGY

PLATE 5
Diatom photomicrographs; 400X

Figure 1 Coscinodiscus perforatus (Ehrenberg)
diameter 57 to 102 pm

Figure 2 Coscinodiscus asteromphalus (Ehrenberg)
diameter 59 to 198 pm






REPORT OF INVESTIGATION NO. 93 51












1


PLATE 5






52 BUREAU OF GEOLOGY

PLATE 6
Diatom photomicrographs; 400X

Figure 1 Cussia praepaleacea (Schrader) Schrader
diameter 30 to 55 pm, width 7 to 9 pm

Figure 2, 3 Cymatogonia amblyoceras (Ehrenbergf.Hanna
length 35 to 55 pm .. :.










REPORT OF INVESTIGATION NO. 93 53


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PLATE 6


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BUREAU OF GEOLOGY


PLATE 7
Diatom photomicrographs; 400X

Figure 1 Delphineis penelliptica (Andrews)
length 28 to 82 pm, width 10 to 12 um

Figure 2 Delphineis angustata (Pantocsek) Andrews
length 31 to 50 pm, width 7 to 8 pm

Figure 3 Delphineis surirella (Ehrenberg)
length 15 to 46 pm

Figure 4 Delphineis biseriata (Grunow) Andrews
length 40 to 64 pm, width 6 to 9 pm

Figure 5 Diploneis smith (Brebisson) Cleve
length 50 to 77 pm

Figure 6 Diploneis bombus (Ehrenberg) Cleve
length 30 to 46 pm






REPORT OF INVESTIGATION NO. 93 55









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56 BUREAU OF GEOLOGY

PLATE 8
Diatom photomicrographs; 400x

Figure 1 Navicula cf. N. direct (Wm. Smith) Ralfs in Pritchard
length 53 to 77 pm, width 12 to 15 pm

Figure 2 Navicula pennata (Schmidt)
length 56 to 78 pm, width 13 to 18 pm

Figure 3 Navicula hennedyi (W. Smith)
length 48 to 58 pm, width 23 to 40 pm






REPORT OF INVESTIGATION NO. 93 57




















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PLATE 8





58 BUREAU OF GEOLOGY

PLATE 9
Diatom photomicrographs; 400X

Figure 1, 2 Paralia sulcata (Ehrenberg) Cleve
diameter 26 to 40 pm

Figure 3 Melosira westii (W. Smith)
diameter 16 to 30 pm

Figure 4 Podosira cf. P stelliger (Bailey) Mann
diameter 31 to 62 pm







REPORT OF INVESTIGATION NO. 93


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PLATE 9





BUREAU OF GEOLOGY


PLATE 10
Diatom photomicrographs; 400X

Figure 1 Rhaphoneis amphiceras (Ehrenberg) Ehrenberg
length 29 to 100 pm, width 18 to 25 pm

Figure 2 Raphoneis fatula (Lohman)
length 33 to 46 pm

Figure 3 Rhaphoneis gemmifera (Ehrenberg)
length 28 to 115 pm, width 15 to 20 pm

Figure 4 Rhaphoneis cf. R. angularis (Lohman)
length 50 to 150 pm, width 17 to 21 pm

Figure 5 Rhaphoneis lancetulla (Grunow)
length 38 to 114 pm, width 7 to 10 pm

Figure 6 Rhaphoneis adamantea (Andrews)
length 36 to 80 pm, width 20 to 30 pm







REPORT OF INVESTIGATION NO. 93 61










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62 BUREAU OF GEOLOGY

PLATE 11
Diatom photomicrographs; 400X

Figure 1 Triceratium reticulum (Ehrenberg)
length of side 30 to 62 pm

Figure 2 Triceratium condecorum (Ehrenberg)
length of side 40 to 82 pm

Figure 3 Triceratium spinosum (Bailey)
length of side 42 to 75 pm







REPORT OF INVESTIGATION NO. 93


PLATE 11





64 BUREAU OF GEOLOGY

PLATE 12
Diatom photomicrographs; 400X

Figure 1 Xanthiopyxis sp. (Ehrenberg)
length is generally less than 50 pm

Figure 2 Thalassiothrix longissima (Cleve and Grunow)
length of whole specimens unknown but fragments
observed reached a length of 175 pm, width 3 to 4 pm

Figure 3 Trachyneis aspera (Ehrenberg) Cleve var. aspera
length 44 to 180 pm, width 13 to 17 pm

Figure 4 Thalassionema nitzschoides (Grunow) Hustedt
length 30 to 126 pm, width 4 to 5 pm

Figure 5 Fragilara sp. (Lyngbye)
length 28 to 117 pm, width 3 to 4 pm






REPORT OF INVESTIGATION NO. 93 65






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PLATE 12






66 BUREAU OF GEOLOGY

PLATE 13
Silicoflagellate photomicrographs; 400X

Figure 1 Distephanus stauracanthus (Ehrenberg)

Figure 2 Mesocena circulus (Ehrenberg)

Figure 3 Distephanus crux (Ehrenberg)

Figure 4 Dictyocha rhombica (Ehrenberg)

Figure 5 Distephanus cf. D. boliviensis (Frenguelli)






REPORT OF INVESTIGATION NO. 93 67






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PLATE 13










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