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Fossil hunters guide to the geology of southern Florida ( FGS: Open file report 66 )
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Title: Fossil hunters guide to the geology of southern Florida ( FGS: Open file report 66 )
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Table of Contents
    Title Page
        Title Page 1
        Title Page 2
    Main
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
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    Reference
        Page 12
Full Text











STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Virginia Wetherell, Secretary







DIVISION OF ADMINISTRATIVE AND TECHNICAL SERVICES
Nevin G. Smith, Director







FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief






OPEN FILE REPORT 66






A FOSSIL HUNTER'S GUIDE TO THE GEOLOGY OF SOUTHERN FLORIDA

By

Thomas M. Scott and Frank R. Rupert


FLORIDA GEOLOGICAL SURVEY

Tallahassee
1994


k,*" -n- ,1! -- *-* 7,, ,i









' A Fossil Hunter's Guide to the

Geology of Southern Florida
Thomas M. Scott, P.G. #99 and Frank R. Rupert, P.G. #149


The Florida peninsula is the exposed portion of
the much broader feature known as the Florida
Platform. The exposed portion lies almost all to the
east of the axis of the platform. The axis of the
Florida Platform occurs approximately along the
present-day western coast of the peninsula.
The southern Florida peninsula, for the purposes
of this discussion, extends southward from the
southern boundaries of Pasco, Sumter, Lake, and
Orange Counties. In general, the southern peninsula
is characterized by flat plains and coastal lowlands.
Hilly uplands occur only in the central northern area
in portions of Polk and Highlands Counties. Figure 1
illustrates a geomorphic map of southern Florida.
Puri and Vernon (1964) recognized two broad
physiographic regions in the southern peninsula, the
Central Highlands and the Coastal Lowlands. The
rolling hills of the Central Highlands extend into the
southern region from the north and occupy only a
small portion of the area. The highlands include the
Lake Wales Ridge, the Polk Uplands and several
lesser ridges (Figure 1; White, 1970). The highest
elevations in southern Florida occur in the Central
Highlands (along the Lake Wales Ridge) where
elevations of more than 300 feet above mean sea
level (MSL) are present. The Coastal Lowlands cover
most of the southern portion of the state with
elevations generally below 100 feet above MSL.
Within the Coastal Lowlands, White (1970) recognized
a number of smaller geomorphic features including
the Gulf Coastal Lowlands, Eastern Valley, Osceola
Plain, De Soto Plain and the Everglades (Figure 1).
The Central Highlands exhibits a rolling
topography characterized by numerous sinkhole
lakes. Paleo-sand dunes are present along the flanks
of the Lake Wales Ridge in many areas. The higher
portions of this zone are characterized by thick sand
deposits lying on Eocene or Oligocene limestones or
the Hawthorn Group sands and clays. On the Polk
Uplands, a thin sand cover blankets the phosphate-
bearing, very fossiliferous sediments of the upper
Hawthorn Group. The phosphate-rich sediments are
mined in Polk, Hillsborough and Hardee Counties
exposing a plethora of vertebrate fossils. A variable
thickness of sand also covers the Hawthorn Group on
the Desoto Plain.
The Gulf Coastal Lowlands are underlain by
Oligocene to Miocene carbonate sediments. Varying


thicknesses of Neogene and Quaternary sediments
blanket the older rocks. The contact between the
carbonate rocks and the younger sediments is often
marked by a lag deposit of phosphate gravel
containing water-worn fossil fragments. Large quartz
pebbles are occasionally found in this lag deposit.
These unusually large clasts are thought to have been
transported southward from the piedmont trapped in
root clusters of trees. The often fossiliferous
sediments that overlie the rubble zone contain a
diversity of mollusk species.
Bounding the Central Highlands on the east and
south are the Osceola Plain, the Okeechobee Plain
and the De Soto Plain. The Osceola Plain is a beach
ridge plain formed during a previous sea level
highstand. The paleo-beach ridges exert strong
control on the drainage on the eastern half of the
plain. This is readily evident on the 7.5 minute
topographic quadrangles covering the area. The
beach ridges are not as evident on the western,
higher portion of the Osceola Plain. Elevations on the
Osceola Plain range from approximately 30 feet to 80
feet above MSL. A thick sequence of sands with
some shell underlies the Osceola Plain. These
Pleistocene deposits include a lithified coquina
representing an ancient beach deposit.
The De Soto Plain lies to the west of the Osceola
Plain and the southern tip of the Central Highlands.
The elevations on the De Soto Plain are similar to
those of the Osceola Plain. However, the De Soto
Plain does not appear to be an ancient beach ridge
plain. A variably thick sequence of sands with some
shell lies on the Hawthorn Group with the Hawthorn
at or near the surface in some areas.
The Okeechobee Plain occurs between the
Osceola and De Soto Plains at lower elevations. The
elevations of the Okeechobee Plain range from 20 to
30 feet above MSL. The plain is very flat and was
considered by White (1970) to be a northem
extension of the Everglades. It is underlain by sands
with some very fossiliferous zones. Shell pits near
Lake Okeechobee yield abundant late Pleistocene
mollusk shells.
To the east of the Osceola Plain lies the Eastern
Valley. This valley is low lying and swampy with shell
beds near the surface. The Eastern Valley is a paleo-
lagoon that extended far to the north. The St. Johns
River headwaters occur in the Eastem Valley in Indian


I

















-N-


i

100 10 4'
0 60
SCALE

EXPLANATION


COASTAL


LOWLANDS


Figure 1. Generalized geomorphic map of southern Florida
[from Scott et al. (1991) as modified from White (1970)]


-, ,







River County. The Atlantic Coastal Ridge borders the
valley on the east. The persistent coastal ridge
feature is composed of sands and lithified coquina.
The southern portion of the state, south of a line
trending east-west through Lake Okeechobee, is quite
flat exhibiting very little relief. The Immokalee Rise
and its southern extension, the Big Cypress Spur,
formed as submarine sand shoals during the
Pleistocene covering older limestones. The
Southwestern Slope lies to the west of the Rise. On
the slope, the limestones are covered by only a thin
veneer of sand.
The Everglades occur between the Immokalee
Rise, Big Cypress Spur, and Southwestern Slope on
the west and the Atlantic Coastal Ridge on the east.
The Everglades is a unique and interesting
geomorphic feature. It has been called the "river of
grass" formed as water sheet-flowed south from Lake
Okeechobee to Florida Bay. Peat and organic
sediments overlie Pleistocene limestones throughout
much of the region. In some areas, such as at Rock
Reef Pass in the Everglades National Park, highly
karstified limestones are exposed at the surface. Peat
and organic sediments fill the dissolutional
depressions. White (1970) felt that the Everglades
formed in a trough developed by dissolutional
lowering of the limestone surface of southern Florida.
The Atlantic Coastal Ridge of southeastern
Florida is composed of sands and coquina north of
the Palm Beach-Broward County line and
predominantly limestone in Broward and Dade
Counties. The northern portion formed as a barrier
island or shoal while the southern portion formed as
an oolite shoal. This persistent topographic feature
provided the high ground upon which the cities of
southeastern Florida developed.

Geology

The surficial geology and geomorphology of
southern Florida is, in general, not strongly affected
by subsurface structural features (Figure 2). This is
direct contrast with northern Florida where the
structural features strongly affect the outcrop pattern
of the Eocene through Miocene sediments. The
northern portion of the area under consideration
exhibits the effects of the structures that influence the
geology of northern peninsular Florida. The most
prominent of these is the Ocala Platform which can
be seen in the northwestern portion of Figure 2. Here
the Oligocene Suwannee Limestone and the
Hawthorn Group sediments are exposed on the
southeastward plunging nose of the Ocala Platform.
Younger formations lap onto the flanks of the
structure. Cross section A-A' in Figure 3 illustrates
how the younger Suwannee Limestone and Hawthorn
Group lap onto the structurally high Ocala Limestone.


Where the carbonate rocks are near the surface, karst
features are common.


-N-






100 10 40 MI

0 60KM
SCALE

,N AXIS OF NEGATIVE FEATURE

SAXIS OF POSITIVE FEATURE
A:?b


Figure 2: Geologic structures In southern Florida
(from Scott et al., 1991)
Other structural features affecting the sediments
in southern Florida include the Brevard Platform, the
Osceola Low, and the Okeechobee Basin. The
Brevard Platform occurs in the northeastern portion of
this area. This structure brings the Eocene
limestones within a hundred feet of the surface and
the Hawthorn Group sediments are thinned to absent
over its crest. The Brevard Platform plunges to the
south-southeast and affects the formations as far
south as Martin County.
The remaining two structural features are basins
where the sediments are thicker. The Osceola Low is
a relatively small basin in Osceola County and part of
Brevard County. The post-Ocala Limestone
sediments thicken in the basin to a maximum of more
than 350 feet. The Okeechobee Basin is a broad
south and south-southeast dipping structure. Within
the basin, the post-Ocala sediments thicken to the
south to more than 1300 feet (Figure 3, Section C-C').
Our discussion of the lithostratigraphy of the
southern Florida peninsula will begin with the Ocala
Limestone, the oldest unit shown on the geologic










i A'




Do SI,, KOS
ii hi ii Sl i



UNDIFFERENTIATED
SAND ANHD CLAY


OCALA ---- ----
LIME OfHE-r


t,


- 200
- 160
-120
- 80
- 40
- 0
- -40
--80
--120
- -160
--200
--240
- -280
- -320
- -360
- -400


100 10 40 MI

I II 1 II
0 60 KM

SCALE

FOR SECTIONS


0 SCA
SCALE


CROSS SECTION LOCATIONS


,,

40
S0
--40
-80
-120
-160
--200
--240
-280
--320
- -360
--400
- -440
- -480
- -520
- -560
- -600
-640
-680
-720
- -760
--800
--840
- -880
- -920
--960
- -1000
- -1040
- -1080
- -1120
- -1160
- -1200


.4

.. .. ...I~
.n r


v- -- ----
I I


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


'4

UNDIFFERENUATED
SHELL CDS

ANASTASIA FWr*


-- -- ----------- -----
----- --- -- -------- ---
-- ----1--- ------ --- -- - - ---=- -

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

-=HAWTHORNi gGROUP --


-----ZZ -- --------




.u --. - - - - - -
- - - - - - - - - - - - - - - - - - - -. .
. . . . . . . . . . . - - - - - - - - - - - -
..........................---


,-- LIESTO
N ,


C8 ,
o 6



UNDIFFERENTIATED
200 SAND AND CLAY
160
120

-40 --

-40 -- ----______---------
-240
-120 -II-----------;--- ;---
------- ---------------------




-320
-400 --20 ----------


-4 -80A I- -
S::o0 -LIM.--ESTONE- -,
-58 I I i i i --, --I--I-- I-- T-- -------



-8600

--680


- 00 I I I I I 1- --
--840 '
I I I I I [ I I I I I I --- --- --- ,








- -880 I O l -
-920
-960
-1000
-1040
-1080


~8 8. .
0 0
C; g3 -11e


Figure 3. Geologic cross sections in southern Florida


AVON PARK
rFOMAION


C'








TQ


r


. .


I







map of the area (Figure 4). The map in Figure 4 is
constructed to show the extent of the formations as
they occur within 20 feet of land surface. Each
formation may be more extensive in the subsurface,
but because each eventually dips below the arbitrary
20 feet depth or pinches out, their entire extent is
hidden by shallower units shown on the map. Areas
underlain by more than 20 feet of undifferentiated
Pleistocene and Holocene sands are shown as white
areas on the map.
The Late Eocene (approximately 38 to 35 million
years ago [mya] Ocala Limestone is a very
fossiliferous limestone containing mollusks, echinoids
and foraminifers. It forms an important portion of the
major water-bearing unit, the Floridan aquifer system,
in Florida and parts of Alabama, Georgia and South
Carolina. Where the Suwannee Limestone is present,
the Ocala underlies it. The Suwannee is missing due
to erosion or nondeposition in the northeastern
portion of the southern Florida peninsula. As a result,
the Hawthorn Group immediately overlies the Ocala
Limestone. The Ocala Limestone is absent under
portions of Broward, Dade and Monroe Counties.
Presumably, it was removed by the erosive forces of
the Gulf Stream when it impinged upon the Florida
Platform during sea level fluctuations.
The Lower Oligocene (approximately 35 to 30
mya) Suwannee Limestone is exposed in a very
limited area in Hillsborough and Polk Counties (Figure
4). The Suwannee is a very fossiliferous limestone
containing foraminifers, mollusks and echinoids. One
characteristic fossil of the Suwannee Limestone is the
echinoid Ryncholampus gouldii which occurs in
abundance in some locations. This limestone
formation constitutes an important part of the Floridan
aquifer system in southern Florida. In general, the
Hawthorn Group overlies the Suwannee throughout
southern Florida.
Prior to the mid-Oligocene, the Florida Platform
was a broad carbonate depositional environment with
only a minor influx of siliciclastics (quartz sands, silts,
and clays). The siliciclastic sediment source, the
Appalachian Mountains, had been subjected to
erosion for millions of years and had been reduced
considerably in elevation. As a result, little sediment
was being shed and entering the carbonate-
depositing environment of the Platform. A broad,
regional uplift of the southern Appalachians occurred
during the mid-Oligocene (some 30 mya),
rejuvenating the erosional cycle. The renewed
erosion supplied siliciclastic sediments to the marine
depositional environment. These sediments were
transported onto the Florida Platform, first mixing with
the carbonates then, subsequently, replacing
carbonate deposition. This dramatic transformation
occurred during the deposition of the Hawthorn


Group and represents the first major sedimentation
change on the Florida Platform in millions of years.
While this shift in sedimentation was taking
place, another unique and interesting geologic event
was occurring. Phosphate was forming
(phosphogenesis). The deposition of abundant
phosphate is a geologically infrequent event requiring
a very specific set of circumstances. Cold,
phosphorous-laden ocean waters upwelled onto the
shallow continental shelf allowing many organisms to
flourish. The organic-rich sediments that resulted
allowed the precipitation of phosphatic minerals.
Subsequent sea level fluctuations concentrated the
phosphate grains and created the phosphate deposits
of the Hawthorn Group.
The Hawthorn Group in southern Florida consists
of two formations, in ascending order, the Arcadia
Formation and the Peace River Formation. The
Upper Oligocene to Middle Miocene (approximately
30 mya to 16 mya) Arcadia Formation is
predominantly a carbonate unit comprised of
dolostone/limestone with highly variable percentages
of quartz sand, clay and phosphate. Based on the
variable lithologies, the Arcadia has two named
members, the Nocatee and Tampa Members. The
Nocatee Member is a sand and clay unit with variable
phosphate. The Tampa Member is a sandy limestone
with only minor phosphate. The Arcadia Formation,
in general, is fossiliferous containing abundant
mollusks and other marine fossils with the rare
inclusion of vertebrates. The Arcadia Formation
occurs at or near the surface in portions of
Hillsborough, Pinellas, Manatee Sarasota and
Charlotte Counties (Figure 4). Late Pleistocene shell
beds overlie the Arcadia in part of this area. A well
developed rubble zone containing phosphate gravel,
vertebrate fossils and quartz cobbles and pebbles
occurs between the units.
The Middle Miocene to Lower Pliocene (16 mya
to 4 mya) Peace River Formation is predominantly a
siliciclastic unit with only scattered carbonate beds.
The phosphate content is highly variable with some
beds containing economically valuable
concentrations. The most phosphatic beds within the
Peace River Formation occur within the Bone Valley
Member. The Bone Valley Member, previously
referred to as the Bone Valley gravel or the Bone
Valley Formation, occurs in a restricted area that
includes portions of Polk, Hillsborough, Manatee and
Hardee Counties. This area comprises the main
portion of the Central Florida Phosphate District and
has been the site of phosphate mining activities since
the turn of the century. The name is derived from the
common occurrence of terrestrial and marine
vertebrate fossils within the deposit. A wide variety of
vertebrate fossils are found in this deposit ranging













































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I '
9VYV~~VVV








It-li-


OCALA LIMESTONE


Figure 4. Geologic map of southern Florida
(compiled from county geologic maps by
various authors as listed in refences)


UNDIFFERENTIATED QUATERNARY SAND AND CLAY --- -

-- -- -- ---N

ANASTASIA FORMATION


O e b .."

KEY LARGO LIMESTONE -




MIAMI LIMESTONE ke."e bee Okchobee >
"9v I ..... -I vvvvvvvvvw T v
7VS 'VI #... , ... v........ .


I............ .......
UNDIFFERENTIATED SHELL BEDS, INCLUDING THE CALOOSAHATCHEE, ,', V
FORT THOMPSON, AND NASHUA FORMATIONS. .--....v.


YPRE AD FR...... N ...I............................








SUWANNEE LIMESTONE V
100 10 40 Mt \ ^ iBiii .'jj






SUWANNEE LIMESTONE J


4'







from shark's teeth to dugong, whale, horse, and
many others.
The Bone Valley Member consists of quartz
sand, clay and phosphate. The phosphate occurs as
silt- to gravel-sized clasts of the mineral francolite, a
carbonate fluorapatite. Phosphatic gravel beds are
interbedded with finer grained, sand-sized phosphate
beds. The phosphatic sediments contain highly
variable admixtures of quartz sand and clay.
Overlying the Hawthorn Group in the central
portion of the peninsula is the Upper Pliocene
(approximately 3 mya) Cypresshead Formation
(Figure 4). This unfossiliferous unit is composed of
clayey, occasionally gravelly quartz sands and forms
the higher ridges of the Central Highlands. Reworked
Cypresshead sands and younger undifferentiated
sands make up the remainder of the highlands.
Overlying the Hawthorn Group sediments in
much of southern Florida is the Tamiami Formation.
The Upper Pliocene Tamiami Formation consists of
limestones, sands and clays. Some portions of the
Tamiami, for example the Pinecrest beds, are
extremely fossiliferous containing a very diverse
molluskan fauna that attracts both professional and
amateur paleontologists. The Tamiami Formation is
exposed or occurs in the shallow subsurface in
southwestern peninsular Florida.
Plio-Pleistocene sediments overlie the Tamiami
Formation and the Hawthorn Group (where the
Tamiami is absent) and consist of limestones and
sands with variable fossil content. These units have
been recognized as the Caloosahatchee "formation",
Bermont "formation" and the Fort Thompson
Formation (Figure 4) by many paleontologists.
Although a particular lithology may occur in a
formation, problems arise from the practice of
identifying the units based on the incorporated
molluskan faunas. Currently, a particular fauna with
its guide fossils is used to determine whether a unit is
the Caloosahatchee "formation" or the Bermont
"formation". This practice does not conform with the
North American Stratigraphic Code. The Code is a
set of guidelines adopted by geologists that specify
how to identify various types of stratigraphic units.
Under the Code, formations are lithostratigraphic units
which should be identified based on the sediment
types, not on the recognition of the incorporated
fossils. In an attempt to rectify the situation, Scott
(1992) suggested placing the Caloosahatchee,
Bermont and Fort Thompson formations in the
Okeechobee formation (informally). Lithologically,the
Okeechobee formation consists of limestone, sands
and clays with varying shell content. Currently,
drilling is being conducted in southern Florida to
determine the validity of this approach.
The Atlantic Coastal Ridge in southern Florida is


constructed of the Anastasia Formation north of the
Palm Beach/Broward County line and the Miami
Limestone to the south. The Anastasia Formation is
a coquina composed of variably lithified shell and
sand. The Miami Limestone consists of oolitic
limestone and bryozoan-rich limestone that is variably
lithified. Excellent exposures of the Anastasia occur
along the coast at numerous locations including The
Refuge in Martin County and Blowing Rocks in Palm
Beach County. The Miami Limestone is well exposed
at Silver Bluff and along canals transecting the
coastal ridge.
The Florida Keys are constructed of upper
Pleistocene limestones. The upper keys are
composed of Key Largo Limestone, essentially a fossil
coral reef. Fossil corals of many species and sizes
are enclosed in a carbonate matrix. The Key Largo
Limestone is well exposed along some of the canals
in the upper keys. The State of Florida has
purchased the old Windley Key Quarry site where the
Key Largo Limestone was quarried for building and
decorative facing stone. The site is being preserved
as a State Geological Site and will be open to the
public in the near future. The lower keys are
composed of Miami Limestone oolite facies similar to
the southern portion of the Atlantic Coastal Ridge in
Dade County.

Fossil Hunting Localities

Southern Florida offers the fossil enthusiast some
of the finest Miocene to Recent collecting
opportunities in the state. Vertebrate fossils may be
found in abundance in the Hawthorn Group
sediments, and this area of Florida is also noted for
its Pliocene and Pleistocene shell bed deposits, as
well as the outstanding Recent shell collecting
opportunities at Sanibel Island, near Ft. Myers.
Figure 5 is a generalized location map for the
geographic areas mentioned in this article. Some of
the classic geologic localities are also illustrated in
Figure 6. The latter figure is some 30 years old, so
bear in mind that the land ownership and access
information is likely obsolete.
With southern Florida's burgeoning population,
many potential fossil sites are becoming developed or
otherwise off limits. Other popular sites such as the
Newbum or APAC pit near Sarasota are closed.
Many private mines and quarries are no longer willing
to bear the liability in allowing the public into their
pits. In at least one instance, a shell pit was closed
to all collectors due to unauthorized entry by a group
of thoughtless fossil hunters. It has therefore become
even more imperative to conduct all collecting in a
responsible manner, no matter where one hunts.
Respect the private property rights of others, and
















CLEARWATER 60 Gr Lawke ales 7. V
SMu be ry t 6
ST. PETERS 7. 37 i F
37T F"- ( INDIAN
t Meade RIVER
POLK Vero
75 MARDEE \ HIGHLANDS
MANATEE 'JChula OKEECHOBEE
Zolfosprn s ST.
17 LUCIE
SARASOTAl 701 /ardne- 27
41 72 Arcadia
SARASDTA Nocatee
Venice DESDTO
HAO L- TE GLADES Lke MARTN
64 \ Ok*eehobr
\75 71 m PALM BEACH
8 La Belle r Belle Glod*
MYERS HENDRY
LEE it 27
Sonibel
Island B|-----
BROVARD
Naples 75
COLLIER
co 41L DADE
Marco<
iwlond
MNRDE
100 10 40 MI

0 60 KM .

SCALE
Key Le
Windley
W QUARRY OR MINE AREAS Key

Key
West Big Pine Key









Figure 5. Generalized location map for southern Florida

8.


WEST PALM BEACH
-t


A
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4 STOP 62
STOP 63

Acline

S Start


D. oo a.to o' norm-- th .nd not-went

O. 20 C.llll.. r d.



0.I 4 Road lork. lk* road to rIlhl.
0.20
0.0 DO rln t oill ( ,lop 62),

1.0 o ur0 o d d o ork turn eIrl tI
0. 4o ,

1.50 Small pi.t (Stop 61).


STOP 58 Start

STOP83 S.o
S art




.2r Myers
41
0.00 function State Highway. 80 nd
T *bout 2 mile, ***( of Fort Myar
C por0 d e I on St* H.,Ihway S
8.80 Turn rhllt (aoutl) on unimpro.ve


.0. 4 .
3.9 0 stop car,. The ,eztion it on ,o
*ide of s-s0 aend i oversron.

0.00 JunctlLo U.S. Hl|hwy 4r and St

eait o Stat Hilbh*y 82.
6.20
20 Junction State Hihway 2*. Iak
(ellt) on State Hilhway 82A.
).60
9.80 Section in dr&liu0 ditch, t00' N
of old railrod Ird in SWIl NW
1. T44. S. R26E,. Le Coun


STOP64 Start Start STOP76



0-0'- A .LO Belle




0.00 Junction St.te Hlihw. ys 29 and 80.
In LBelle proceed west on State

0, 60 -
0.60 00rt flo.. .0. 4, n r0001000
2. So Road turn rllhtl itop Jult beforee bend
in road, walk in a hrai toward the
LB.tllt Chimber of Commerce Pcnic.
grounds.

S 70 0L 0. .





0.20
1.70 Gt. on bo- .0d. o. ro..d, 0ak. 0.0t



I. 90 Thil is th typ locality of Fort Thomp-on
orrmtLon. and it Sittion A-1S of D.Br
(195.). The *eclion .i aboul 0 o y.rd.
t of the bI i. p through the -pi| bnk.


I


STOP57 1

Sso start1 Sunnilond

" 0.00 n Communty0 of Sunnllad, proc 0d
donorth on sd.t Hashwy 29. .
h 0. 40 Q0urris of lhe Smuiltd Limeton3 0
Coaneyt on 0.0 0.0t 7ld0 o0 thb ro0d.

SSo










STOP 56 29 I

Start STOP60
41 0.00 1 L,3.-H00d .. no.n iS_.
soI, proved estl on StrIe High-ay 80.
COrn town .O Turn left (north) on -rded road.

41 -.8 40 Brida on BaBn Cire.,
29 4.20 0Turn lt on dirt ro d.
o. Id
Junction U.S. High.-y 41 .nd st0t. 4.00 Coanunc. oO C-l. ..ohlch. Rivr,
0Higbwy 29, at C..r 0to.n. exp30res *nd 3 a0nn Cre. k. Section on l(t bank.
pIn ,:rs .on Ft. Lr-m..


i-Im


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(from Purl and Vernon, 1964)


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always seek permission before entering anyone's
land. To ensure your being allowed to return, avoid
littering or destructive digging, and leave it as you
found it.
The mines of the Central Florida Phosphate
District, nearby and south of Bartow, have yielded
some of the richest Miocene and Pliocene vertebrate
fossils found in Florida. This region is world famous
for its fossils, and has been dubbed the "Bone Valley".
Shark teeth and bones from a variety of both
terrestrial and marine vertebrates are common finds.
Unfortunately, access to the few remaining mines is
difficult to come by. Most are closed to the public
and many have regular security patrols. At last
checking two mining companies still allowed escorted
groups (primarily fossil clubs) in to collect: Cargill
Fertilizer, Inc., P.O. Box 1035, Ft. Meade, FL, 33841,
(813) 285-8125, and IMC Agrico, P.O. Box 867,
Bartow, FL 33830. (813) 533-1121. Most collecting
is done on the large mine spoil piles, in certain
designated inactive areas of the mines.
Individuals may collect fossil material similar to
that found in the phosphate mines at numerous sites
along the Peace River. This stream is incised into
Miocene Hawthorn Group sediments, and yields
Miocene to Pleistocene fossils. It flows in a leisurely
southwestward course from Bartow to Charlotte
Harbor on the west coast. The best fossils occur in
the stretch from Zolfo Springs to Nocatee. Here
stream bottom sediments are composed of
fossiliferous sands and gravels, and screenwashing is
the preferred method of recovering the fossils. The
Peace River is shallow enough to wade over much of
its course, and a canoe or boat allows travel to
collecting sites away from popular access points.
Public boat ramps are available at Arcadia, Gardener
and Zolfo Springs. Canoes may be rented at the
Canoe Outpost in Arcadia.
For collectors who are landlubbers, several
bridges and public parks provide pedestrian access
to the river. The following land access sites are
suggested by the Fossil Club of Miami in their June,
1994 newsletter. Fossils may be sifted with a
hardware cloth screen from the streambed of Joshua
Creek, a tributary to the Peace River which passes
under State Road 17 a few miles south of Arcadia.
Park on the east side of 17 and wade the shallows
100 yards downstream of the bridge. Just west of
Arcadia, car parking is available on the north side of
the highway 70 bridge over the Peace River. Locals
collect shark teeth, vertebrate bones, Indian beads,
and old bottles in a gravel bar under the sand in the
river bottom near the bridge. A similar collecting
opportunity occurs about 100 yards downstream from
Crews Riverside Park, at the Wachula bridge over the


Peace River (County Road 636, just west of Wachula).
Shark teeth and other small fossils are found by
digging and sifting in the gravel streambed. Another
possibility is Brownville Park, located on a dirt road
just south of Brownville Road (take highway 17 north
from Arcadia 4.5 miles, then west on Brownville road
to the dirt road on the left just before the river).
Fossils have been found in the stream bed 100-150
yards north and south of the park.
Many other local creeks and streams in and west
of the phosphate district may yield similar finds.
Brown (1988) recommends Horse Creek in De Soto
County (10 miles west of Arcadia on State Road 72)
for fossils similar to those in the Peace River. Hunt in
shallow water south of the bridge. A mask and
snorkel will help locate fossils in the bottom
sediments.
Shallow sediments of the Hawthorn Group
extend westward from the phosphate district to
coastal portions of Pinellas and Manatee Counties
(see Figure 4). This unit lies at shallow depth in
portions of the Tampa Bay area. Many of the stream
banks which once exposed this unit have long since
been encased in concrete during Tampa's urban
expansion. One site in Tampa, near the eastern
terminus of Gandy Boulevard on Hillsborough Bay, is
Ballast Point. It is famous in mineralogical circles for
its prized agatized coral geodes which erode out of
Hawthorn Group sediments near the shore. These
geodes represent silicified Oligocene-Miocene coral
heads whose hollow interiors have become lined with
variously-colored agate or chalcedony, a finely-
crystalline form of quartz. Now a park, the site was
effectively picked clean over the years by collectors.
The city performed the coup de grace when they
constructed a concrete seawall along the shore,
covering the remaining outcrop. Today small pieces
of agatized coral and small agatized mollusk shells
may still be found with diligent searching among the
rock rubble covering the beach and offshore area.
Similar agatized corals have been found in dredge
material along the causeways to the coastal barrier
islands in northern Pinellas County and in some of the
streams along the eastern shore of Tampa Bay.
Future finds of similar material could occur during
dredging or excavation work in the Tampa area, and
the interested collector should make it a routine to
check such sites.
The Hawthorn Group extends offshore on
Florida's Gulf Coast onto the broad continental shelf.
Shark teeth and fossils from submarine outcrops of
the Hawthorn and younger units wash ashore on
beaches from Clearwater south to Venice. Venice
Beach and nearby Caspensen Beach are famous for
their extremely abundant shark teeth. These may be








picked up in the strand line and swash zone of the
beach, or dredged in the shallows with a hand held
screen mesh. Local convenience stores market long-
handled screened scoops for just this purpose. Most
of the teeth found on the beach are small. Larger
teeth are sometimes found by scuba divers in the
bottom sediments offshore. This is one site worth
visiting as it is hard to avoid finding fossils here.
Florida's southwest coastal and south-central
peninsula areas are truly the realm of the invertebrate
fossil enthusiast. Molluskan fossiliferous units of the
Caloosahatchee, Bermont, Ft. Thompson, and
Pinecrest formations occur near or at the surface over
broad areas of the southern peninsula (see Figure 4).
These shallow units extend from St. Petersburg
southward through Lee County, then eastward in a
broad swath near Lake Okeechobee. They continue
up the east coast, eventually grading to the north into
the fossiliferous sediments of the Nashua Formation.
Their distribution reflects the extent of encroaching
Plio-Pleistocene seas, and the shelly units form a u-
shaped areal pattern around the generally
unfossiliferous undifferentiated Quaternary and
Cypresshead Formation sediments of the central
highlands (see Figure 4).
The Plio-Pleistocene shell units commonly
contain abundant well-preserved Pliocene and
Pleistocene mollusks, corals, and barnacles as well
as some freshwater forms. They occur at variable,
generally shallow depths along Florida's southwest
coast and portions of the east coast, and are best
observed in excavations. Abundant well-preserved
mollusks occur in the walls of a drainage ditch
around Fossil Park, at 9th Avenue and 71st Street in
St. Petersburg.
Shell beds are commonly mined as roadbase
material from pits in coastal counties. Prior to their
recent closings, such commercial pits provided
collectors with access to excellent fossil shells. Shell
pits are commonly in a state of flux, and changing
ownerships may one day bring more relaxed policies
on admitting avocational fossil hunters.
Invertebrate fossil hunters have a number of
collecting options open to them. Some general ideas
and suggestions are presented here. Manmade
canals, excavations and natural creeks which have
cut down into fossiliferous strata are likely places to
look. Brown (1988) describes a fossil mollusk site at
Shell Creek in Charlotte County (four miles west of I-
75 on S.R. 17 to County Road 764, then 4.4 miles
east to Shell Creek Park. Best collecting is from a
canoe launched at the park. Search the high banks
for shell-laden beds of the Plio-Pleistocene
Caloosahatchee formation. Other deeply-incised
streams in the area covered by shelly sediments
(Figure 4) are worth scouting out.


Shelly sediments are also exposed in abundance
along the Caloosahatchee River and its tributaries,
particularly in the 4 mile segment just east of La Belle
in Hendry County. The high banks are best explored
and collected from a boat or canoe. Boat access is
available at the Franklin Lock in Lee County, near the
State Road 78 State Road 31 junction, and at the
public ramp on S.R. 78 just west of La Belle.
The Plio-Pleistocene shelly units may contain
both land and marine vertebrate fossils. It is not
unusual to find fossil bird or horse material in the
shell-bearing strata. The famous Leisey shell pit,
located on the eastern shore of Tampa Bay near
Apollo Beach, gained national attention with the
discovery of a fantastically abundant and diverse
assemblage of Pleistocene vertebrate fossils in the
shell strata. These finds are described in Hulbert et
al., (1994).
Other Pleistocene vertebrate bearing strata are
present throughout southern Florida. The famous
canal bank site at Vero Beach and the similar
'Melboume Bone Bed", both discovered early in the
century in Pleistocene sands along the east coast,
attest to this fact. Abundant fossil sea bird fossils
were also recently discovered in a shell pit in
southwest Florida (Emslie, 1992).
Hunting for vertebrate material entails searching
in the same kinds of areas as fossil mollusks occur.
Check any areas where excavation or dredging is in
progress. Many collectors walk the sediment spoil
piles created by the dredging of canals. Similar
material is commonly pumped up as fill in
construction and beach renourishment projects. The
smaller vertebrate teeth and bones easily survive the
dredging process, and diligent searching may yield
good finds.
As with the Miocene fossils of the Peace River,
Pleistocene vertebrate material commonly occurs in
streambed deposits. Vertebrate fossil deposits may
be concentrated in holes or other natural
impediments on the streambed. Depending on which
part of the area one searches, a variety of fossil ages
may also be present, due to the stream having cut
downward through different ages of strata. Renz
(1993) describes his discovery of a nearly complete
Pleistocene sloth skeleton simply by wading a shallow
stream in southwest Florida.
Collecting opportunities generally decline in the
southernmost counties of this area, but fossils are still
available. Quarries and drainage ditches cut in the
Pliocene Tamiami Formation in Collier County may
contain mollusks and echinoids, including the
characteristic sand dollar Encope tamiamiensis.
Limestone portions of this formation are typically
more lithified than younger units, and many of the






fossils occur as molds and casts or are well-
cemented in the rock matrix.
Most of eastern Broward and all of Dade County,
as well as the lower Florida keys, are underlain by
shallow, generally unfossiliferous oolitic Miami
Limestone. The Miami Limestone has some
molluskan fossiliferous portions, and Pleistocene
vertebrate fossils have been found in sinkholes in the
unit. However, the area is sparse in fossils as a
general rule.
The upper Florida keys, from Key Largo to Big
Pine Key, are comprised of Key Largo Limestone.
This unit contains abundant and well-preserved
Pleistocene corals, which may be observed in
channel cuts on Key Largo. Most corals are
cemented in the rock matrix, but collectors have been
able to recover individual corals from areas where
new canals are being blasted and dredged.

References

Arthur, J., 1993a, Geologic map of DeSoto County, Florida:
Florida Geological Survey Open File Map Series 58.

1993b, Geologic map of Highlands County, Florida:
Florida Geological Survey Open File Map Series 52.

Arthur, J., and Campbell, K., 1993, Geologic map of Pinellas
County, Florida: Florida Geological Survey Open File Map
Series 44.

Brown, R., 1988, Florida's Fossils, Guide to Location,
Identification, and Enjoyment: Sarasota, The Pineapple
Press, 208 p.

Campbell, K, 1993a, Geologic Map of Polk County, Florida:
Florida Geological Survey Open File Map Series 46.

1993b, Geologic Map of ManateeCounty, Florida:
Florida Geological Survey Open File Map Series 50.

S1993c, Geologic Map of Glades County, Florida:
Florida Geological Survey Open File Map Series 60.

Campbell, K., and Arthur, J., 1993a, Geologic Map of
Hillsborough County, Florida: Florida Geological Survey
Open File Map Series 45.

1993b, Geologic Map of Sarasota County, Florida:
Florida Geological Survey Open Rie Map Series 57.

Duncan, J., 1993a, Geologic map of Broward County, Florida:
Florida Geological Survey Open File Map Series 64.

1993b, Geologic map of Collier County, Florida:
Florida Geological Survey Open File Map Series 63.

1993c, Geologic map of Dade County, Florida:
Florida Geological Survey Open File Map Series 67.

1993d, Geologic map of Monroe County, Florida:
Florida Geological Survey Open File Map Series 66, 2
sheets.


Duncan, J., and Scott, T., 1993a, Geologic map of St. Lucie
County, Florida: Florida Geological Survey Open File Map
Series 53.

1993b, Geologic map of Martin County, Florida:
Florida Geological Survey Open File Map Series 56.

Emslie, S., 1992, The Avifauna from APAC shell pit, Sarasota
County, Florida, in: Scott, T., and Allmon, W., 1992, The
Plio-Plelstocene Stratigraphy and Paleontology of
Southern Florida: Florida Geological Survey Special
Publication 36, 194 p.

Hulbert, R., Morgan, G., and Webb, S., 1994, Paleontology and
Geology of the Leisey Shell Pits, Early Pleistocene of
Florida: Bulletin of the Florida Museum of Natural History,
v. 37, pt. 1, 352 p., pt. 2, 324 p.

Missimer, T., and Scott, T., 1993, Geologic Map of Lee County,
Florida: Florida Geological Survey Open File Map Series
61.

Purl, H., and Vemon, R., 1964, Summary of the geology of
Florida and a guidebook to the classic exposures: Florida
Geological Survey Special Publication 5 (revised), 312 p.

Renz, M, 1993, Fossil Treasures In Florida's Creeks: Florida
Paleontological Society Newsletter, v. 10, n. 3, p. 14-16.

Scott, T., 1993a, Geologic map of Brevard County, Florida:
Rorida Geological Survey Open File Map Series 49.

,1993b, Geologic map of Hendry County, Florida:
Florida Geological Survey Open File Map Series 62.

,1993c, Geologic map of Indian River County,
Florida: Florida Geological Survey Open File Map Series
55.

,1993d, Geologic map of Okeechobee County,
Florida: Florida Geological Survey Open File Map Series
54.

1993e, Geologic map of Orange County, Florida:
Florida Geological Survey Open File Map Series 62.

,_ 1993f, Geologic map of Osceola County, Florida:
Florida Geological Survey Open File Map Series 48.

1993g, Geologic map of Palm Beach County,
Florida: Florida GeologikJ Survey Open File Map Series
65.

Scott, T., and Campbell, K., 1993, Geologic map of Hardee
County, Florida: Florida Geological Survey Open File Map
Series 51.

Scott, T., Uoyd, J., and Maddox, G., (eds.) 1991, Florida's
Groundwater Quality Monitoring Program,
Hydrogeologic Framework: Florida Geological Survey
Special Publication 32, 97 p.

Scott, T., and Missimer, T., 1993, Geologic map of Charlotte
County, Florida: Florida Geological Survey Open File Map
Series 59.

White, W., 1970, Geomorphology of the Forida peninsula:
Rorida Geological Survey Bulletin 51, 164 p.