Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
    Introduction
        Page 1
    The age of the rocks at Jackson Bluff
        Page 2
    Rocks and kinds of rocks
        Page 2
        Page 3
        Page 4
    Fossils
        Page 5
        Page 6
    Rock formations
        Page 7
        Page 8
        Page 9
    Rock uses
        Page 10
    Suggested advanced exploration for boy scouts
        Page 11
        Page 12
    Additional references
        Page 13
        Page 14

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY


FLORIDA GEOLOGICAL SURVEY
Robert 0. Vernon, Director








SPECIAL PUBLICATION NO. 14






ADVENTURES IN GEOLOGY AT JACKSON BLUFF






By
J. William Yon, Jr.




Tallahassee
1965














QE

















115479



7,,



A
cj'












Completed manuscript received
October 19, 1965
Printed by the Florida Geological Survey (114)
Tallahassee
1965









CONTENTS


Introduction ............................ .... ................ 1
The age of the rocks at Jackson Bluff ........................ 2
Rocks and kinds of rocks .................................... 2
Igneous rocks ........................................... 3
Metamorphic rocks ...................................... 3
Sedimentary rocks ....................................... 3
Marls .............................................. 4
Clays ................. ............................ 5
Sands ............................................. 5
Fossils ..................... ................. .............. 5
Class Gastropoda ....................................... 5
Class Pelecypoda ...................................... 7
Rock formations ............................................ 7
Rock layers ............................................ 7
Geologic history of deposition ............................ 9
Rock uses ...................................... ........... 10
Suggested advanced exploration for boy scouts ................. 11
Additional references ........................................ 13
Books or booklets of general interest ...................... 13
Rocks and fossils ........................................ 13



ILLUSTRATIONS


Figure
1 Map showing location and suggested routes to Jackson
Bluff ................................................. 1
2 Shell marl exposed near top of section at Jackson Bluff .... 4
3 Gastropods from the Jackson Bluff formation ............. 6
4 Pelecypods from the Jackson Bluff formation ............. 8
5 Diagrammatic section of roc ks exposed at Jackson Bluff,
Leon County, Florida ................................. 9
6 Unconformity between the Miccosukee and Jackson Bluff
form nations .......................................... 11
7 West bank of Ochlockonee River as seen from Jackson
Bluff ................................................ 12








ADVENTURES IN GEOLOGY AT JACKSON BLUFF

By
J. William Yon, Jr.

INTRODUCTION

The rocks exposed at Jackson Bluff on the Leon County side
of the Ochlockonee River just below Lake Talquin Dam, figure 1*,
provide a fascinating chapter in the story of Florida's geologic
history and can be of great interest to anyone interested in earth
science.

The rocks you see exposed at Jackson Bluff are sediments
that were laid down in ancient seas and by river deltas that once




G E O R G I A


(


,QUINCY


EON COUNTY

r !
/
j


TA L TALLAHASSEE r
JACKSON BLUFF.



5 0 5 10 15 Mile.
Approx. Scale


Figure 1. Map showing location and suggested routes to Jackson Bluff.

*Note: Jackson Bluff is located on property owned by the Florida Power
Corporation and is not accessible to the public except by special per-
mission from the Florida Power Corporation.


1





115 479








FLORIDA GEOLOGICAL SURVEY


covered this area. The many remains of former life (called fossils)
which you see at Jackson Bluff indicate that marine animals lived
in abundance in the ancient sea that covered the area.

The intent of this booklet is to help beginning students of
rocks investigate the geology of one of Florida's more famous
outcrops. It will also provide an opportunity for Boy Scouts to
work on the Geology Merit Badge.

THE AGE OF THE ROCKS AT JACKSON BLUFF

The rocks exposed at Jackson Bluff range in age from one to
twenty million years and these rocks were deposited during the
Miocene Epoch of the Tertiary Period and the Pleistocene Epoch
of the Quaternary Period. The rocks exposed at the base of the
bluff at river level are the oldest, and as you climb the bluff,
you pass across millions of years in the geologic time scale.
The table below shows how the section at Jackson Bluff fits into
the geologic time scale.


Principal subdivisions of geologic time Time in
represented by the rocks at Jackson Bluff millions
of years
Era Period Epoch
Quaternary Recent
Pleistocene 1
N
o Unconformity
( Pliocene rocks
Tertiary missing 10
Miocene 10

ROCKS AND KINDS OF ROCKS

The crust of the earth or the earth's surface is composed of
many kinds of rock-forming minerals. Rocks occur everywhere,
and almost any plot of ground will yield them. They can occur as
rocky outcrops in soils of plowed fields, or as sands and gravels
in a river bottom.








FLORIDA GEOLOGICAL SURVEY


covered this area. The many remains of former life (called fossils)
which you see at Jackson Bluff indicate that marine animals lived
in abundance in the ancient sea that covered the area.

The intent of this booklet is to help beginning students of
rocks investigate the geology of one of Florida's more famous
outcrops. It will also provide an opportunity for Boy Scouts to
work on the Geology Merit Badge.

THE AGE OF THE ROCKS AT JACKSON BLUFF

The rocks exposed at Jackson Bluff range in age from one to
twenty million years and these rocks were deposited during the
Miocene Epoch of the Tertiary Period and the Pleistocene Epoch
of the Quaternary Period. The rocks exposed at the base of the
bluff at river level are the oldest, and as you climb the bluff,
you pass across millions of years in the geologic time scale.
The table below shows how the section at Jackson Bluff fits into
the geologic time scale.


Principal subdivisions of geologic time Time in
represented by the rocks at Jackson Bluff millions
of years
Era Period Epoch
Quaternary Recent
Pleistocene 1
N
o Unconformity
( Pliocene rocks
Tertiary missing 10
Miocene 10

ROCKS AND KINDS OF ROCKS

The crust of the earth or the earth's surface is composed of
many kinds of rock-forming minerals. Rocks occur everywhere,
and almost any plot of ground will yield them. They can occur as
rocky outcrops in soils of plowed fields, or as sands and gravels
in a river bottom.







SPECIAL PUBLICATION NO. 14


By studying rocks, geologists have come to know a great
deal about the composition, forces that shape the earth's surface,
and the history of the earth.

Geologists have divided all rocks into three main types: ig-
neous, sedimentary, and metamorphic.

Igneous Rocks

Igneous rocks are formed from molten material that originated
deep within the earth. As the molten rock material rose to shallow-
er depths, or to the earth's surface during volcanic eruptions,
it cooled and became solid. Because of the difference in cooling
rates and chemical composition, there are many varieties of ig-
neous rocks. Some of these varieties are granite, obsidian, and
basalt.

Metamorphic Rocks

Metamorphic rocks are sedimentary or igneous rocks that have
been acted upon and changed by intense heat and pressures.

This change takes place while the sedimentary and igneous
rocks are buried deep beneath the earth's surface. Some examples
of metamorphic rocks are gneisses, schists, and slate.

Sedimentary Rocks

Sedimentary rocks can be composed of material derived from
the weathering and eroding of older sedimentary, metamorphic and
igneous rocks. They are also derived from the precipitation of
chemical material and from the accumulation of organic matter.
Sedimentary rocks are deposited in layers that are generally paral-
lel to the earth's surface.

The rocks exposed at Jackson Bluff are sedimentary. Con-
sequently, they will be the only one of the three previously men-
tioned rock types discussed in more detail. Quite likely the marls,
clays, and sands (sedimentary rocks) we see at the bluff were
derived from igneous, metamorphic and sedimentary rocks in Ala-
bama and Georgia.








FLORIDA GEOLOGICAL SURVEY


MARLS

Marls are exposed in most of the section at Jackson Bluff.
Marl is the term geologists apply to rocks that are composed of
essentially equal parts of clay and calcium carbonate (limestone).
At the bluff there are many shells present in the Jackson Bluff
formation. These shells, composed of calcite limestone particles
and associated with a clay, make this a special type of marl called
shell marl, shown in figure 2. The marls at Jackson Bluff vary in
color from very pale orange to bluish gray, and they contain abun-
dant fossil shells.


-IiS~ I4r r-


Figure 2. Shell marl exposed near top of section at Jackson Bluff.








SPECIAL PUBLICATION NO. 14


CLAYS

Clay is a generally plastic, natural material composed of clay
minerals that are too small to be seen without the aid of a very
high powered microscope or x-ray equipment. There are several
clay beds in the Jackson Bluff section and the color of these clays
varies from gray, yellow-orange to dark blue-green.

When clay is wet, it is often very soft and gummy. If clay
is present in a rock, it will generally have an "earthy" smell
when the rock is slightly moistened.

SANDS

Sands are composed of the mineral quartz and in Florida they
are generally unconsolidated. Sand can range in size from 2 milli-
meters (size of lead in pencil) to 0.05 millimeters (smaller than
a pin point). Sands that are cemented together are called sand-
stones. The quartz, making up sands in the section at Jackson
Bluff is crystalline silica (Si02) and is a stained, greenish gray
to light gray color.

FOSSILS

Fossils (evidence of past life) are important to geologists
because they help determine the time in the earth's history when
a rock was deposited. The presence of fossils in the rocks at
Jackson Bluff (fig. 2) show that during the time these animals
lived, ocean conditions were favorable for marine-animal growth.
The most common fossils in the rocks at Jackson Bluff come under
the zoological classification of Phylum Mollusca. The Molluscan
group can be further subdivided into the Classes Gastropoda and
Pelecypoda.

Class Gastropoda

Gastropods, such as snails, conchs, and whelks live today in
lakes, on land, and in the oceans. Fossil Gastropods are common
in the rocks at Jackson Bluff and can be identified. Pictures of
the fossils with their names are included for reference in figure
3.









FLORIDA GEOLOGICAL SURVEY


CL I ''


Figure 3. Gastropods from the Jackson Bluff formation. 1. Ptychosalpinx
laqueata (Conrad); 2. Cancellaria propevenusta Mansfield; 3. Dorsanum?
plicatilum (Bose); 4. Peristernia filicata (Conrad); 5. Solenosteira vaug-
hani Dall; 6. Eupleura miocenica Dall; 7. Ecphora quadricosta umbili-
cata Wagner; 8. Polinices coensis Dall; 9. Tegula exoleta (Conrad).
After Cooke and Mossom, 1929, pl. 16.


F.'':.I.C








SPECIAL PUBLICATION NO. 14


Class Pelecypoda

The group Pelecypoda includes what are commonly known as
oysters, clams, mussels and scallops. Pelecypods, like Gastro-
pods, live today in fresh and salt water. Fossil Pelecypods are
common at Jackson Bluff, and the pictures in figure 4 include
some of the Pelecypods that can be observed in the rocks at Jack-
son Bluff.

ROCK FORMATIONS

Sedimentary rocks are generally deposited as layers. If these
layers or units are distinctive and extend over a large geographical
area, geologists call them formations. Formations quite often are
given names so that geologists can refer to them without a long
description each time the rock unit is mentioned.

There are four rock units or formations exposed at Jackson
Bluff. Beginning at the top of the Bluff and going from youngest
to oldest, these units are Pleistocene deposits, Miccosukee for-
mation, Jackson Bluff formation and the Hawthorn Formation.

The Pleistocene deposits are primarily light gray sands. The
Miccosukee formation consists of yellow-orange, clayey sands.
The Jackson Bluff formation is a vari-colored, sandy marl con-
taining many fossils. The Hawthorn Formation contains layers
of vari-colored, sandy clays, marls and clayey quartz sands.

Rock Layers

The diagram shown in figure 5 indicates how the rock layers
occur in the section at Jackson Bluff. As shown in the illustration,
the oldest (bottom) unit is the Hawthorn Formation, and overlying
the Hawthorn are progressively younger formations. The geologic
time span covered, from the basal Hawthorn Formation to the
Pleistocene sands at the top of the exposed section, is approxi-
mately 20 million years. Detailed study of this section by geolo-
gists has enabled them to gain knowledge about the geologic his-
tory of the rocks exposed at Jackson Bluff.








FLORIDA GEOLOGICAL SURVEY


Figure 4. Pelecypods from the Jackson Bluff formation. 1. Cardita (Car-
ditamera) vaughani Dall; 2. Anadara aresta Dall; 3. Anadara campsa
Dall; 4. Chione xesta Dall; 5. Chione ulocyma Dall; 6. Cardium virginia-
num Conrad; 7. Crassatellites meridionalis Dall. After Cooke and Mos-
som, 1929, pl. 17.









SPECIAL PUBLICATION NO. 14


PLEISTOCENE

-Unconformity--
MICCOSUKEE
formation
-Unconformity-



JACKSON
BLUFF
formation


LU 1-Unconformity--


HAWTHORN
Formation


::::::::::::::S: nd::::::::::::::::
.. . . .-

..C.ayey ..Sand


















.-.....-.. _. -ry Sandy Clay -. .- .
r- aon yjCla y






j, 'r,,,
C 1a 3.i J
~.--~lel ~ I a~s d


Figure 5. Diagrammatic section of rocks exposed at Jackson Bluff,
Leon County, Florida.

Geologic History Of Deposition


Geologists believe that the Hawthorn Formation at Jackson
Bluff was laid down in a shallow sea that received abundant sands
and clays from the land that was to the north of Jackson Bluff.
The cross-bedded sand in the Hawthorn Formation, exposed at the
bluff, indicates that the shore line was at or near Jackson Bluff
during the period of geologic time in which the Hawthorn Forma-
tion was being deposited.







FLORIDA GEOLOGICAL SURVEY


The Jackson Bluff formation was probably deposited in a
shallow sea that received sands and clays from a land area to the
north and northeast. These shallow, warm waters provided a good
environment in which abundant marine animal life such as clams
and conchs could live.

The rocks of the Miccosukee formation are believed to have
been deposited as a large delta that covered many square miles of
Florida. The Miccosukee formation, exposed at Jackson Bluff, is
thin compared to the thickness of the unit in other areas. Follow-
ing deposition of the Miccosukee formation at Jackson Bluff, the
land surface was exposed for many thousands of years and quite
likely a large amount of the Miccosukee rocks was eroded away.

During the time the last seas covered the land at Jackson
Bluff, the sands exposed at the top of the section were deposited.
These sands were laid down during the Pleistocene or Great Ice
Age.

As shown in the diagrammatic section (fig. 5), several lines
called unconformities separate the formations. These unconformi-
ties represent a break in the geological record. That is, they re-
present an interruption in the sequence of rocks that resulted from
an interval of erosion or non-deposition. Figure 6 shows an exam-
ple of an unconformity between the Miccosukee and Jackson Bluff
formations.

Jackson Bluff was formed through erosion by the Ochlockonee
River over a period of thousands of years, or during the time geo-
logists call the Recent. Looking toward the west side of the Och-
lockonee River, figure 7, from Jackson Bluff, you will notice the
bank of the river is much lower in height than where you are stand-
ing. During times of flooding, the water of the river spills out over
the west bank and deposits sand along the channel bank. The
sand forms small ridges along the bank and these are called natu-
ral levees. Lying behind the natural levees is a plain approxi-
mately one mile wide, which forms the flood plain of the Ochlocko-
nee River.

ROCK USES

Many geologists earn their livelihood looking for rock depo-
sits that may be useful to man. This phase of geology is called
economic geology.








SPECIAL PUBLICATION NO. 14


Figure 6. Unconformity between the Miccosukee and Jackson Bluff
formations.

The Jackson Bluff formation is an economic deposit. The
formation has been mined by the Florida Power Corporation for use
as a road material. Observation of the embankments of the dam at
Lake Talquin show that the Jackson Bluff formation was used as
a construction material when the dam was built.

SUGGESTED ADVANCED EXPLORATION
FOR BOY SCOUTS

1. Measure at Jackson Bluff the thickness of the sands, clays,
and marls as shown in the diagrammatic section on page 9.

2. Observe and describe how the beds at the river level are
being eroded.







FLORIDA GEOLOGICAL SURVEY


.-. i.. 4;-
".::


Figure 7. West bank of Ochlockonee River as seen from Jackson Bluff.

3. How many different kinds of fossils are recognized in the
rocks at Jackson Bluff? List all identified fossils. Draw some of
the common fossils.

4. Discuss how the Jackson Bluff section fits into the over-
all scheme of geologic events as described in your Geologic Merit
Badge Pamphlet.









SPECIAL PUBLICATION NO. 14 13

ADDITIONAL REFERENCES

The publications listed below should be available at local
libraries.

Books Or Booklets Of General Interest

Cooke, C. Wythe
1939 Scenery of Florida interpreted by a geologist: Florida
Geological Survey Bulletin 17, 120 p., 58 figs.

Purl, Harbans S.
1964 (and Vernon, Robert 0.) Summary of the Geology of Florida
and a guidebook to the classic exposures: Florida Geolo-
gical Survey Special Publication No. 5 (Revised). 312 p.

Rocks And Fossils

Bishop, Ernest W.
1961 (and Dee, Lawrence L.) Rocks and Minerals of Floridaand
a guide to identification, occurrence, production and use:
Florida Geological Survey Special Publication, No. 8,
41 p.

Calver, James L.
1957 Mining and Mineral resources: Florida Geological Survey
Bulletin 39, 132 p., 35 figs., 12 tables.

Cooke, C. Wythe
1945 Geology of Florida: Florida Geological Survey Bulletin
29, 342 p., 1 pl., 47 figs.

Cooper, C.L.
1953 (and others) Geology: Merit Badge Series, Boy Scouts of
America, New Brunswick, New Jersey, 83 p.

Mansfield, W. C.
1930 Miocene Gastropods and Scaphopods of the Choctawhatchee
Formation of Florida: Florida Geological Survey Bulletin
3, 189 p., 21 pl.

1932 Miocene Pelecypods of the Choctawhatchee Formation
of Florida: Florida Geological Survey Bulletin 8, 240 p.,
34 pl., 3 fig.

1935 New Miocene Gastropods and Scaphopods from Alaqua
Creek Valley, Florida: Florida Geological Survey Bulletin
12, 50 p., 5 pl.








FLORIDA GEOLOGICAL SURVEY


Namowitz, S. N.
1960 (and Stone, D. B.) Earth Science: The World We Live In:
D. Van Nostrand Co., Princeton, N.J., 614 p., (High School
Text).

Olsen, Stanley J.
1959 Fossil Mammals of Florida: Florida Geological Survey
Special Publication No. 6, 74 p., 14 pl., 13 fig.

iRhodes, F. H.
1962 (and others) Fossils: A Guide to Prehistoric Life: Golden
Nature Guide, Golden Press, New York, N.Y., 160 p.,
(Paperback).

Zim, H. S.
1957 (and Shaffer, P. R.) Rocks and Minerals: A Guide to Fami-
liar Minerals, Gems, Ores and Rocks: Golden Nature Guide,
Golden Press, New York, N.Y., 160 p., (Paperback).











70375 '





















f