Geothermal nature of the Floridan Plateau ( FGS: Special publication 21 )

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Harmon Shields, Executive Director

DIVISION OF RESOURCE MANAGEMENT
Charles M. Sanders, Director

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

SPECIAL PUBLICATION NO. 21

THE GEOTHERMAL NATURE
OF THE FLORIDAN PLATEAU

Editors
Douglas L. Smith and George M. Griffin

Prepared for the
BUREAU OF GEOLOGY
DIVISION OF RESOURCE MANAGEMENT
FLORIDA DEPARTMENT OF NATURAL RESOURCES

TALLAHASSEE, FLORIDA
1977

DEPARTMENT
OF
NATURAL RESOURCES

REUBIN O'D. ASKEW
Governor

BRUCE A. SMATHERS
Secretary of State

PHILIP F. ASHLER
Treasurer

RALPH D. TURLINGTON
Commissioner of Education

ROBERT L. SHEVIN
Attorney General

GERALD A. LEWIS
Comptroller

DOYLE CONNER
Commissioner of Agriculture

HARMON W. SHIELDS
Executive Director

LETTER OF TRANSMITTAL

Bureau of Geology
Tallahassee
January 23, 1978

Governor Reubin O'D. Askew, Chairman
Florida Department of Natural Resources
Tallahassee, Florida 32304

Dear Governor Askew:

The Bureau of Geology, Division of Resource Management, De-
partment of Natural Resources, is publishing as its Special Publica-
tion No. 21, "The Geothermal Nature of the Floridan Plateau."

These selected papers edited by Douglas L. Smith and George
M. Griffin represent a broad regional evaluation of geothermal data
which should be of substantial interest to agencies and/or persons
involved with the assessment of the potential for energy development
from the geothermal resource base. ,

Respectfully yours,

Charles W. Hendry, Jr., Chief
Bureau of Geology

Completed Manuscript received
1976
Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology
Tallahassee
1977

iv

THE GEOTHERMAL NATURE OF THE FLORIDAN PLATEAU

CONTENTS

1. Introduction; C. W. Hendry, Jr., and S. R. Windham. ................ vii
2. Hydrogeology Related to Geothermal Conditions of the Floridan Plateau;
F. A. Kohout, H. R. Henry, and J. E. Banks. ........................ ix
3. Heat Flow in Florida Oil Test Holes and Indications of Oceanic Crust
Beneath the Southern Florida Bahamas Platform; G M. Griffin, D. A.
Reel, and R. W. Pratt............................................ 43
4. Spatial Distribution of Ground-water Temperatures in South Florida; C. R.
Sproul. ........................................................ 65
5. Terrestrial Heat-Flow Values in Florida and the Thermal Effects of the
Aquifer System; D. L. Smith and W. R. Fuller. ...................... 91
6. Uranium Series Isotopic Anomalies in Thermal Ground Waters from
Southwest Florida; J. K. Osmond and R. B. Cowart. ................ 131
7. Thermal Model for the Florida Crust; R. P. Lowell and L. T. Long. .... 149

vi

INTRODUCTION

The increased public awareness of the reality of the diminishing
hydrocarbon energy base has stimulated inquiry into alternative
sources of energy. One of the alternatives receiving considerable at-
tention is the heat from deep inside the earth geothermal energy.
U. S. Geological Survey Circular 726, 1975, defines the geothermal
resource base as heat above 150C which is stored in the ground to
depths of 10 kilometers and geothermal resources are defined as that
portion of this stored heat that is recoverable using present technol-
ogy, regardless of cost. Three categories of geothermal resource base
have been recognized:
1. Conduction dominated areas, in which the heat content is
indicated by the geothermal gradient.
2. Hot igneous systems, in which heat is produced by magmatic
sources.
3. Hydrothermal convection systems, in which sources are found
at shallow depths and relatively high temperatures.
There is not available for Florida sufficient data to define geo-
thermal systems or to estimate the geothermal resources. This dearth
of information is the stimulus for the Bureau of Geology publishing
this collection of papers entitled the "Geothermal Nature of the
Floridan Plateau."
The Bureau of Geology has exerted no editorial restrictions on
the reports and the conclusions represent the opinion of each in-
dividual author. As the State Geologist, however, it is appropriate to
offer a preliminary assessment of the future economical and techno-
logical feasibility of the contribution of geothermal energy as an
alternate energy source to Florida. From the data presented herein
and from our general knowledge of the subsurface geology of the
State the potential for geothermal energy to provide substantial
energy resources appears quite remote.

viii

HYDROGEOLOGY RELATED TO GEOTHERMAL CONDITIONS
OF THE FLORIDAN PLATEAU

By

F. A. KOHOUT(a), H. R. HENRY(b), AND J. E. BANKS(c)

(a) U. S. Geological Survey, Woods Hole, Massachusetts
(b) University of Alabama, Tuscaloosa, Alabama
(c) Coastal Petroleum Company. Tallahassee, Florida

HYDROGEOLOGY RELATED TO GEOTHERMAL CONDITIONS
OF THE FLORIDAN PLATEAU
CONTENTS
Page
Abstract ............ ................ ........................ 1

Introduction ....... ............. .......................... 2

Geologic and Geomorphic Setting ..................................... 3

The Floridan Aquifer System ... ................................... .. 5

The Principal Artesian Zone ..................................... 6

The Boulder Zone .... .......... ..... ...... ............. 6

Injection Sites in Florida ................... ................... .... 14

The Geothermal Regime of the Floridan Plateau ........................ 16
Vertical Temperature Profiles in Floridan Aquifer System .......... 16

Geographic Distribution of Temperature in
Floridan Aquifer System ................................... 19
Surface Evidence of Thermal Upwelling ........................... 21
Humble-Lowndes-Treadwell No. 1 ............................. 21

Warm Mineral Springs Sinkhole ........................... 22
The Mud Hole Submarine Spring ............................. 25

Hydraulic and Mathematical Model Studies ...................... 28

Comparison of Theoretical and Field Studies .................. 29
The Dolomite Question and Cavity Formation ...................... 32

Geothermal Gradients Below the Floridan Aquifer System .......... 35

Summary ............................. ........................ 36

Acknowledgments ................................................. 37
References ................... ........ ..................... 38

ILLUSTRATIONS
Figure Page
1 Map showing prominent hydrogeologic features of the
Floridan Plateau .... ............ ............. ............ 3

2 Index map showing localities referred to in this report .............. 4
3 Map showing the piezometric surface of the Principle Artesian
Zone as of 1960 ........................ ....................... 7

ABSTRACT
Temperature surveys in oil exploratory and waste-injection wells
indicate that geothermal gradients underlying the Floridan Plateau
are affected by the presence of cold sea water in the adjacent deeps
of the Gulf of Mexico and the Florida Straits. The geothermal gradi-
ent is negative (the ground water becomes colder) to a depth of
about 3,000 feet near the edge of the Plateau. In the horizontal di-
rection, the temperature increases toward the central axis of the
Plateau. The horizontal and vertical temperature distributions sug-
gest that cold, dense sea water flows inland through the cavernous
dolomite in the deep part of the aquifer where it becomes progressive-
ly warmed by geothermal heat flow. The reduction of density pro-
duces upward convective circulation. After mixing with fresh water
in the upper part of the aquifer, the diluted salt water flows seaward
to discharge by upward leakage through confining beds or through
submarine springs on the, Continental Shelf.
The focal point for the deep sea-water flow, and the hottest
water, should occur along the central axis of the Floridan Plateau,
farthest from the cold sea-water bodies. Upwelling of warm saline
water at Warm Mineral Springs sinkhole and the Mud Hole sub-
marine spring near the west coast of Florida provides field evidence
that a convective flow cell exists. Mathematical and laboratory model
studies demonstrate a remarkable similarity to the patterns of
salinity and temperature observed in the field.
Below the Floridan aquifer system the permeability of the rock
is relatively low and geothermal gradients are more "normal." How-
ever, bottom-hole temperatures recorded during geophysical logging
of oil exploratory wells indicate that the geothermal regime even as
deep as 15,000 feet below sea level is affected by lateral heat flow to
adjacent ocean depressions. The circumstances are considered in
detail by other papers in this volume.

BUREAU OF GEOLOGY

INTRODUCTION
In 1965 Kohout adopted the term "Boulder Zone" to identify
the deep, saline part of the Floridan aquifer system consisting of
cavernous limestone and dolomite. Since that time the shallow and
deep parts of the Floridan aquifer system have come under practical
development for the following uses (Klein and others, 1975; Meyer,
1971; and references therein):
(1) Storage of industrial and municipal liquid wastes in the
Boulder Zone.
(2) Production and desalination of low salinity brackish water
from the Principal Artesian Zone.
(3) Temporary storage in and recovery of fresh water from,
saline parts of the Principal Artesian Zone.
(4) Possible use of brackish artesian water to promote wildlife
survival in Everglades National Park.
Clearly, knowledge of how the system operates must be available in
order to predict and avoid conflicting uses.
Additional temperature and water quality data have become
available since 1965 as a result of new wells drilled for waste dis-
posal. The data support Kohout's hypothesis (1965) that cyclic
flow of salt water related to geothermal heating is occurring in the
Floridan Aquifer. The high permeability of the cavernous limestone
in the Boulder Zone permits cool ocean water from the Gulf of
Mexico and the Florida Straits to move inland, causing a reversal in
the normal geothermal gradient at depths of 1,000 to 3,000 ft. or
more. Normal gradients are present below 3,000-4,000 ft., extending
to the oil producing zones at about 11,500 ft.
This report is a review and extension of earlier studies related to
the mechanism of salt-water encroachment in the shallow Biscayne
Aquifer of southern Florida. Certain aspects provide background,
and the following reports are recommended to the reader: Cooper
(1959); Cooper and others (1964); Henry (1959, 1960); Kohout
(1960a, 1960b); Pinder and Cooper (1970); Segol and Pinder
(1976); and Rubin (1976). It was shown, both mathematically and
by field observation, that salt water flows inland from the floor of
the sea through the lower part of the Biscayne Aquifer into a zone
of diffusion, then upward and back to the sea through the upper
part of the aquifer.
In the Biscayne Aquifer this cyclic circulation is caused chiefly
by density differences related to hydrodynamic dispersion of salt
(Cooper and others, 1964). In the thicker Floridan aquifer system,
geothermal heat is believed to be an important additional energy
source for the cyclic flow mechanism.

SPECIAL PUBLICATION NO. 21

GEOLOGIC AND GEOMORPHIC SETTING
Peninsular Florida is the above-sea-level part of a much larger
landmass called the Floridan Plateau or Florida-Bahama Platform
(Fig. 1). On the west, this plateau is flanked by abyssal depths of
about 12,000 ft. in the Gulf of Mexico, roughly equivalent to the
depths of oil-producing wells in southern Florida at the Felda, Sun-
niland, and Forty Mile Bend oil fields (Fig. 2).
The dominant structural control of the deep sediments in Florida
is an anticline in Paleozoic rocks called the Peninsular Arch, which
crests in northern Florida (Puri and Vernon, 1964). Sea water in the
Gulf of Mexico sweeps southward around the southern end of the
Florida Peninsula and then eastward and northward through the
Straits of Florida. The water depth decreases from about 5,000 ft.
between Key West and Cuba to about 1,800 ft. between the Floridan
Plateau and the Bahama Banks, northeast of West Palm Beach. A
trench having a maximum depth of about 2,880 ft. occurs in the
Florida Straits east of Miami, Florida (Fig. 1). Pratt (1966, p. 62)
suggests that this trench was formed by erosion; Ball (1972, p. 65)

Figure 1. Map showing prominent hydrogeologic features of the Floridan
Plateau.

P1E

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GN

C--

MILES
0 20 40 60 80 100

KEY
WEST %

Figure 2. Index map showing localities referred to in report.

suggests that it was formed by tectonic action. A third possibility is
that it was formed by solution and collapse of limestone. Caverns
and flowing artesian zones deeper than 3,500 ft. occur on the east
coast of Florida adjacent to this bathymetric anomaly in the Florida

SPECIAL PUBLICATION NO. 21

Straits. Great solutional activity and cavern collapse in the Oldsmar
Limestone of central Florida and the Florida Keys supports a con-
jecture that the anomaly results from submarine development of
karst (Puri and Winston, 1974).
Southward from the crystalline rocks (Fig. 1) that occur in cen-
tral Florida at a shallowest depth of about 6,000 ft., the basement
rock deepens to an indicated depth of more than 30,000 ft. below
sea level in the Florida Keys, based on seismic, gravity, and magnetic
information (Meyerhoff and Hatten, 1974). Only about half of these
sediments have been penetrated by the drill. In the oceanic bodies,
water below the thermocline (at about 300 ft. below sea level) is
relatively cold. Thus, the Gulf of Mexico and the Florida Straits act
as hydraulic boundaries where aquifer materials of the Floridan
Plateau are partly or completely truncated and exposed to cold
sea water (40 -450 F).

THE FLORIDAN AQUIFER SYSTEM
The Floridan aquifer system is an extensive group of Tertiary
artesian limestone aquifers that supply water to thousands of munici-
pal, industrial, and irrigation wells in Florida and parts of South
Carolina, Georgia, and Alabama. In Florida recharge to the system
occurs through sinkhole lakes and by direct infiltration of rainfall
where the limestone crops out or lies near the surface in the karst
region of north-central Florida (shaded area in Figure 1). Lake-
control and drainage wells, estimated by Vernon (1970, p. 3) to
number more than 6,500, also provide recharge to the aquifer. After
moving downward into the aquifer, the fresh water then moves
laterally seaward beneath clay, silt, and marl confining beds toward
discharge points beyond the shoreline. The piezometric surface of
an artesian aquifer is the imaginary surface that coincides with the
height to which water will rise in tightly cased wells that tap the
aquifer. This surface for peninsular Florida was first mapped by
Stringfield (1936, Plate 13), whose work of nearly 40 years culmi-
nated in his important summary, published as Geological Survey
Professional Paper 517 (Stringfield, 1966). Over the years he used
the name "principal artesian aquifer." Parker and others (1955, p.
199) used the name "Floridan Aquifer." Stringfield (1964, p. C164)
described it as follows:
"In Florida, it is known as the Floridan Aquifer . The aquifer in-
cludes as many as seven geologic formations, ranging in age from
middle Eocene to middle Miocene. In Florida the basal unit of the
aquifer is the Lake City Limestone of middle Eocene age."
From temperature and hydraulic evidence to be presented later,

BUREAU OF GEOLOGY

the lower Eocene Oldsmar Limestone also is a participating unit of
the artesian aquifer system in southern Florida, at least as far north
as Ocala (Fig. 1). This has more than doubled the thickness of the
aquifer system, from about 1,000 ft. to about 2,300 ft. in southern
Florida.
Confirming with Stringfield's original definition, the upper part of
the Floridan Aquifer (900 to 1,900 ft. below sea level in southern
Florida) is referred to as the Principal Artesian Zone (See Figs. 9
and 10); note that the name is capitalized. The lower part of the
aquifer system (about -1,900 to -3,300 ft.) is referred to as the
Boulder Zone because of distinctive hydrologic properties. Although
confining beds may separate the two zones locally, thermal and
water-quality evidence indicates that regionally the aquifer acts as
a single hydrologic entity in the region between recharge areas in
the karst region of central Florida and the hydraulic boundaries
formed by deep sea-water bodies along the perimeter of the Floridan
Plateau (Fig. 1). The geologic column in Table 1 gives formation
tops and hydrologic properties observed at the Forty Mile Bend oil
field. (See Fig. 2 for location.)

THE PRINCIPAL ARTESIAN ZONE
In southern Florida the piezometric surface may be more than
40 ft. above the land surface, and a fresh- or brackish-water flow is
usually encountered 1,000 to 1,300 ft. below sea level. This flow zone
correlates with the Ocala and/or Avon Park limestones at the top of
the Principal Artesian Zone. The piezometric map of Figure 3 rep-
resents the pressure head for this upper part of the Floridan aquifer
system, the Principal Artesian Zone. The inset map shows the ap-
proximate depth to the base of potable water as mapped by Klein
(1971). In the shaded area the water is salty throughout the aquifer.
The altitude of the top of the Principal Artesian Zone ranges from
about sea level in central Florida to about 1,000 ft. below sea level
in southern Florida. Hydraulic information to map pressure-head
gradients in the deep saline (Boulder Zone) parts of the aquifer
system is lacking and direction of water movement can only be in-
ferred indirectly from temperature, chemical, and isotopic data.

THE BOULDER ZONE
The Boulder Zone in southern Florida is defined as the lower
part of the Floridan Aquifer, consisting of cavernous dolomite and
limestone (Kohout, 1965, p. 260). The term originated in the oil
industry from the drilling action of the bit and is a misnomer because

SPECIAL PUBLICATION NO. 21

Figure 3. Map showing the piezometric surface of the Principle Artesian
Zone as of 1960. After Stringfield (1964, p. C166) based on maps
by Healy (1962), Stewart and Counts (1958), and Stewart and
Croft (1960), inset after Klein (1971).
the main body of the rock does not consist of boulders, although
collapse breccias may be present. Chunks of dolomite break off from
the roofs and sides of caverns and these chunks fall under and around
the bit to produce very rough drilling conditions. A photo of one of
the "boulders" showing two sets of drill-tool marks is given by Puri
and Winston (1974, Fig. 23). The difficult drilling conditions gained
such notoriety in the oil industry that the name Boulder Zone took
on quasi-official status by common usage (Burke, 1967) and was

BUREAU OF GEOLOGY

TABLE I
GEOLOGIC AND HYDROLOGIC CHARACTERISTICS NEAR FORTY MILE BEND

FORMATION

SYSTEM SERIES Name Top Thickness LITHOLOGY HYDROLOGIC( IIARACTI R
(II.) Itt.)

Quaternary Pleistocene Pleistocene 0 20 Shelly limestone Water-table aqutler
and Pliocene and sand
deposits
Tamiami 20 180 Marl, clay, and Conlninng bed, low permeability
I:ormation and limestone

Miocene Hawthorn 200 400 Green clay, mnirl, C'olnlinln bed, low pernmiability
I formation and sand

Tampa 600 250 Sandy limestone Conl ming bedfairly low per-
Limestone il bilhty. Wells may flow
small amount owing to upward
leakage Irom underlying
tornt tions.

Suwannee 850 350 Limestone I airly low permeabilit. wells
Oligocene Limestone usually l now owing to upward
leakage Irom under lng
torlnations.

Ocala 1,200 100 White limestone I-loridatn lqtit/
Tertiary Limestone Known as "rone of lost circula-

Avon Park 1,300 500 Chalky limestone ion" in the oil industry. Oil
Limestone well drillers' comments frequently
are as follows:

Eocene Lake City 1,800 250 Tan dolomltic 1,200 ft "I resh-watr flow"
Limestone limestone, or "lost circulation"
cavernous
1,900 ft "Lost circulation"
Oldsmar 2,050 1,250 Limestone with 2,300 ft "Bolders"
Limestone brown dolomite 2,700 1t -"Strong salt-water
developed adja- low
cent to large
caverns

Paleocene Cedar Keys 3,300 1.950 Dolomite and The thirstt anhydrite" near top
Limestone anhydrite ol Cedar Ke, s Limestone
(about 3.300 It) is the base of
Sthe I loridan Aquifer.
Upper Lawson 5,250 150 Porous limestone
Cretaceous Limestone
Unnamed 5.400 2,300 White chalk and
Deposits shale

Atkinson 7,700 100 t Silly limestone
cretaceous ormation and shjle

Lower Undifferen- 7,800 4,000 t Limestone, anhy- Lost circulation Irequently
Cretaceous tiated units drite, dolomite reported at 8,500 to 9,000 ft.
and shale. Sunni- Solution holes 1-inch in
land pay vone. diameter at 11,400 ft. in
reef-like formation at
I oriv Mile Bend.
11,800 Deepest well at Forty Mile Bend.

SApplin and Applin, 1944, Ipgure 22.
t Banks, Joseph E., 1960, p. 1739.

appropriate to identify the lower part of the Floridan Aquifer by

Kohout (1965).

Distinct zones (Table 1) in the deeper part of the aquifer were

SPECIAL PUBLICATION NO. 21

recognized and defined mainly from drilling experiences in wildcat
wells spread throughout southern Florida. Generalizations concern-
ing the average drilling times for most wells were as follows:
0- 1,900 ft. About 4 days
1,900- 3,500 ft. Variable as little as 3 days to as much as 3 months,
according to the amount of trouble; in the average
wildcat well, a month was required to overcome
drilling difficulty in the "Boulder Zone."
3,500-11,500 ft. Discounting coring and testing time, the brine
aquifer (oil zone) at about 11,500 ft. could be
reached 10 to 14 days after the 9%-inch casing
was cemented in place at about 4,000 ft.
The top of the Boulder Zone can be recognized frequently in the
oil company driller's log by the reports of an increase of flow or lost
circulation both of which imply a significant increase of perme-
ability. (The term "lost circulation" refers to the loss of return drill-
ing fluid and cuttings in hydraulic-rotary drilling operations and
implies very high permeability or caverns.) The hydrologic change
occurs about 900 ft. below the top of the Floridan Aquifer at an
average depth of about 2,300 ft. below sea level. At -2,700 ft. "large
cavities", "boulders," and a "strong salt-water flow" form an identi-
fiable hydrologic marker. The 1,200- and 2,700-foot flow zones are
consistent enough to be marked by heavy dashed lines on the geo-
logic section (Fig. 4).
Depths at which strong salt-water flows have been reported are
mapped in Figure 5. From these and other less tangible data the
following generalizations appear to be valid:
1. The depth of most of the reported flows seems to cluster
between -2,600 and -2,700 ft.
2. In the area southwest of Lake Okeechobee the reports of
heavy flows tend to cluster around 2,300 ft. below sea level.
3. Along the east coast flows as deep as -4,000 ft. are reported.
4. No flows have been reported in the westernmost Keys near
Key West, but "300% to 500% returns" that is, return of drilling
fluid were reported in the Marquesas Key drilling tract (B. W.
Folger, oral commun., 1964). These excessive returns may be evi-
dence of artesian flow under heads too low to rise to the derrick
floor, 30 to 50 ft. above sea level.
The lithologic character of the Boulder Zone was poorly known
because of lost circulation. However, the Gulf Oil Corp. recovered
boulders as large as 8 inches in diameter with a Globe junk basket
as it drilled through the Boulder Zone at Gulf State Lease 826-G in

BUREAU OF GEOLOGY

oa52

Figure 4. West-east geologic section through southern Florida and the
Bahamas from the Gulf of Mexico to the Atlantic Ocean. Adapted
from J. E. Banks (Ginsburg, et al., 1964, Figure 1).

SPECIAL PUBLICATION NO. 21

Figure 5. Depth of strong salt-water flows reported in oil exploratory wells.

Florida Bay (Well No. 17 in Fig. 6). The rock consisted of black to
brown vuggy, finely to coarsely crystalline dolomite.
After losing several sets of drill collars and pipes in Red Cattle
32-2 at its oil-field discovery at Felda (Fig 2), the Sun Oil Co.
obtained three-dimensional borehole photographs. The photographic
stereo pair taken at a depth of -2,442 ft. is shown in Figure 7.
By viewing the pair stereoscopically, one can obtain a most fasci-
nating geological and hydrological insight into the nature of the
Boulder Zone. Toward the upper right, two dark boulders can be
seen hanging at the top of a cavern. Fracturing and breaking-out of
such boulders during drilling allows the boulders to fall under and
around the bit. This would account for the wallowing drill action
and twist-off of the drilling pipe. In this same well (Red Cattle 32-2)
a 90-foot cavern was encountered from 2,522 to 2,612 ft. below land
surface. In the photos, the twisted-off and bent-over remnants of the
drill pipe could be recognized in the clear water of the cavern. Puri
and Winston (1974) describe the cavity occurrences in Red Cattle
32-2 and give additional photos. After the problems were identified

12 BUREAU OF GEOLOGY

EXPLANATION
10
WELL LOCATION AND INDEX NUMBER

1 SUMNER #1
2 AMERADA-COWLES MAGAZINES #1
3 HUMBLE-LOWNDES-TREADWELL#1
4 GULF-STEVENS #1
5 AMERADA-SOUTHERN STATES #1
6 CALIFORNIA CO. 2248-1
7 HUMBLE-KIRCHOFF #1
8 GULF-CONSOLIDATED NAVAL STORES #1
9 SUN-COLLIER #1; 9A SUN-RED CATTLE 32-3
10 HUMBLE-SUNNILAND FIELD
11 COMMONWEALTH-COASTAL 1055
12 GULF 340-1
13 MODEL LAND CO. 'C'
14 ROBINSON
15 COASTAL-WILLIAMS
28 STUART, FLORIDA STP
29 W PALM BEACH STP (PB-782)

16 SINCLAIR-WILLIAMS
17 GULF 826 G
18 COASTAL 363
19 CALIFORNIA CO. 1011-1
20 GULF 373
21 GULF 826Y
22 CALIFORNIA CO. 1011-3
23 CALIFORNIA-GULF 46-1
24 CALIFORNIA-GULF 44-1
25 SERIO #1 (S-1463)
26 GENERAL WATEP WORKS--I
PENINSULA UTILITIES CORP
DISPOSAL WELL (GW-1)
27 SUGAR CANE GROWERS COOPERATIVE,
#2 DISPOSAL WELL (SCG-2)
30MARGATE UTILITIES AUTH. STP
31 FLORIDA KEYS AQUEDUCT AUTH.
DESALINATION SUPPLY (FKAA)

Figure 6. Index map showing locations of oil exploratory wells that pro-
vided data for this report.

SPECIAL PUBLICATION NO. 21 13

Figure 7. Stereo photograph of Boulder Zone caverns and fractures taken
at 2,442 feet below land surface in Red Cattle 32-2. The length
of the rods extending from the camera downward to the square
light-shield is approximately 4.5 feet. Courtesy of Sun Oil Com-
pany. Photo taken by Layne Texas Company.

from the photos, new drilling techniques were devised by Mr. Bennie
Franks of Sun Oil Company to cope with the Boulder Zone (Burke,
1967); subsequently, drilling time through the zone averaged about
4 days.
Cavities occur at greater depth in the Florida Keys. During drill-
ing of the Coastal-Williams well on Key Largo (Fig. 6) a 2,000 gpm
water-flow commenced shortly after a cavity from -3,490 to -3,540 ft.
was penetrated (Joseph E. Banks, personal observation). From -3,510
to -3,540 ft., the cavity may have been much larger than indicated
by the caliper log because the caliper becomes fully extended and
loses calibration at a hole diameter of 32 inches.
The depths of reported flows (Fig. 5) and the existence of caverns
at depths only slightly greater than the 2,880-foot trench in the
Florida Straits suggest that there may be a direct correlation between
the sub-surface and surface features. This trench, as well as many
others that exist in the Florida Straits, would seem to be logical
places to look for discharge from the Floridan Aquifer. Mr. Art Mar-
kel of the Reynolds Submarine Services Corp. (oral commun., July,
1967) reports that the Aluminaut deep-sea submersible lost buoyancy
while investigating a small hole off the northern Florida coast and
was forced to jettison 2,000 pounds of ballast. This loss of buoyancy
might be explained by passage of Aluminaut from sea water into the
less dense, relatively fresh water associated with discharge from a
submarine spring (Kohout, 1966; Manheim, 1967).
Jordan and others, (1964) and Mulloy and Hurley (1970, p.
1970) also suggest that there may be a genetic relationship between
discharge from the Floridan Aquifer and karst features (sinkholes)
found on Pourtales Terrace and along the Florida Straits east of

BUREAU OF GEOLOGY

Miami (Fig. 1). Meyer (1974) demonstrated by tidal water-level
fluctuations and mathematical analysis that a cavity at -2,947 ft.
in waste-injection well GW-1 at Miami, Florida, is hydraulically
connected to sea water in the Florida Straits east of Miami.

INJECTION SITES IN FLORIDA
The potential beneficial uses of zones of high transmissivity in
the Florida subsurface for fresh-water storage and waste disposal
were described by Vernon (1970) and Garcia-Bengochea and Vernon
(1970). Impetus for the development of the aquifer for these pur-
poses was provided under U. S. Environmental Protection Agency
interstate regulatory powers over discharge of industrial pollutants
and sewage into surface waters. Much of the recent data about the
deep part of the Floridan Aquifer resulted from requirements of
several Florida State Agencies for permits to install subsurface
liquid-waste disposal facilities and for documentation of disposal
activities. The locations of underground waste injection systems
drilled prior to late 1976 are shown in Figure 8.
The oldest site is at Sunniland (Fig. 2) where oil-field brine,
produced at about 11,500 ft. below sea level, is reinjected into cavern-
ous dolomite at about 3,000 ft. below sea level. Injection of acidic in-
dustrial waste has been observed by the U. S. Geological Survey
under its Subsurface Waste Storage Program through the coopera-
tion of Monsanto Chemical Company at Pensacola, Florida, since
1964. Papers by Barraclough (1966), Goolsby (1971, 1972), Kauf-
man (1973), and Faulkner and Pascale (1975) represent one of the
most complete, continuing series of studies ever made concerning
buildup of pressure and geochemical changes as observed in nearby
monitor wells. Vernon (1970) described injection of hot, acidic waste
in the Sugar Cane Growers Association well (SCG-2) at Belle Glade
on the southeast corner of Lake Okeechobee (Figs. 2, 6, 8). Dissolu-
tion of dense limestone overlying the injection horizon and upward
migration of the acidic wastes have been described by Kaufman and
others, (1973) and Kaufman and McKenzie (1975). The deepest
active injection system is at a depth of nearly 5,000 ft., 30 miles east
of Tampa, Florida, where acidic, high-chloride waste is injected at
the Kaiser Aluminum and Chemical Plant (Wilson, and others,
1973).
Temperature and chlorinity data collected under the supervision
of J. I. Garcia-Bengochea (Black, Crow, and Eidsness, 1970, in
cooperation with the Florida Bureau of Geology) during the drilling
of the General Water Works-Peninsula Utilities Co. injection well

SPECIAL PUBLICATION NO. 21 15

P
o
rr.
c
o

INJECTION SITES

1964, Acidic, 1500'
1971, Acidic, 1500'
1963, Unsuccessful, 3500'
1975, Tertiary treated sewage, 1000'
1972, Sewage, 2500'
1972, Acidic, 4500'
1975, Sewage, 2500'
1975, Sewage, 3000'
1975, Freshwater storage, 1200'
1943, Oil field brine, 3000'
1976, Acidic, 3000'
1966, Acidic, 1900'
1975, Sewage, 3300'
1975, Sewage, 3200'
1959, Sewage, 1100', Retired
1975, Freshwater storage, 1,100'
1971, Sewage, 3000'
1975, Desalination, 2100'

Q

a: qvbPB

0 miles 50

0 5A L'

Figure 8. Location of deep injection and desalination production sites show-
ing year of installation, type of waste or use, and approximate
depth of well.

-- an -..0. c. monov

BUREAU OF GEOLOGY

(GW-1) at Miami, Florida, are among the best collected to date and
are used in a later section of this report. Temperature profiles were
obtained from wells recently drilled at the West Palm Beach sewage
treatment plant (STP), well PB-782, and at a test well drilled by
the Florida Keys Aqueduct Authority (FKAA) for a desalination
plant supply well at Marathon in the Florida Keys. These data, along
with the bottom-hole temperatures at the Stuart, Florida, STP and
the Margate, Florida, STP (wells 28, 29, 30, 31, Fig. 6) are the most
recent data to become available (courtesy of F. W. Meyer, U. S.
Geological Survey, Miami, Florida), and are used in Figures 10 and
11. Thus, temperature data obtained formerly as an incidental
part of cementing casing in oil exploratory wells (see example Gulf
340-1, Fig. 10) are now being obtained as a recognized, important
factor in evaluating the Floridan Aquifer for waste disposal.

THE GEOTHERMAL REGIME OF THE FLORIDAN PLATEAU
VERTICAL TEMPERATURE PROFILES
IN FLORIDAN AQUIFER
The first indication of an abnormal depth-temperature profile
underlying the Floridan Plateau was presented by Kohout (1965, p.
264) from a survey made in Gulf-Florida State Lease 340-1 at Forty
Mile Bend. The temperature curve for this well is plotted in the
idealized cross-section of Figure 9 at its proper geographical position
at Forty Mile Bend, 40 miles west of Miami.
Geothermal gradients of about 1F increase per 50- to 100-foot
increase in depth below 1,000 feet are commonly observed and can
be considered "normal." It is noted that Schneider (1964, p. 210)
attributes observations of very flat gradients in Texas, Maryland,
and Idaho and a negative gradient in the Union of South Africa to
ground-water circulation. Starting with 780F at a depth of -1,000 ft.
at Gulf 340-1 at Forty Mile Bend (Fig. 9) and assuming the "nor-
mal" geothermal gradient, the theoretical temperature at a depth of
3,300-ft. below sea level, at the base of the permeable zone, should
be between 101'F and 124'F. In contrast, the upper part of the
temperature profile of Gulf 340-1 showed a slight increase to 78F
at -1,000 ft., the contact between the upper confining bed and the
top of the aquifer. Below that, the temperature profile remains at
780 to a depth of -1,600 ft., and below that it decreases to 740 at
-3,100 ft. This negative temperature gradient is abnormal on two
counts: (1) it is contrary to the adiabatic compressional heating
effect of water percolating to this depth from the recharge area in
central Florida, and (2) it is contrary to the increase of temperature
that would be expected due to upward heat flow from the interior of

SPECIAL PUBLICATION NO. 21

DISTANCE IN MILES

150 T10 d 50o <
I i i I I I I I I I I ,
SINK HOLE 80" ra z
GULF OF MEXICO REGION < S -
POEMETR RE_ S RATS OF FLORIDA
CONFINING
BEDS
/-// 59 -000
PRINCIPAL ARTESIAN
FLORIDAN -2000
AQUIFER BOULDER ZONE

-W
CEDAR KEYS ANHYDRITE -4o

GEOTHERMAL HEAT FLOW oo
TEMPERATURE PROFILE W
(APPROXIMATE BELOW 7000
4000 ft)
60 80 100 I,0 , ,00
TEMPERATURE *E -8000

Figure 9. Idealized section through Miami showing concept of cyclic flow
of seawater induced by geothermal heating.

the Earth. The isotherms in the Florida Straits (Fig. 9, adapted from
Sverdrup and others, 1942) show that sea water having a tempera-
ture of about 44 OF is present where the Floridan Aquifer (in theory)
is truncated by the channel of the straits. The inference was made
in 1965 that the negative temperature gradient at Forty Mile Bend
in the Gulf 340-1 hole was related to the cold water in the Florida
Straits east and south of the Florida Peninsula.
Because dolomite and anhydrite rock have about the same ability
to conduct heat, it was inferred further that the contrasting thermal
gradients above and below the base of the Floridan Aquifer (Fig. 10)
relate to relatively rapid water movement in the aquifer as opposed
to very slow water movement in the low-permeability anhydrite un-
derlying the aquifer. The low permeability anhydrite can be com-
pared to a hotplate. Geothermal heat raises the temperature of
the aquifer water just above the anhydrite, and cold sea water from
the Florida Straits becomes progressively warmed and less dense as
it flows horizontally inland through the cavernous dolomitic lime-
stone in the deep part of the aquifer.
The loss in density as the water warms eventually produces a

1000

2000

U)

3000
O

I-~
LU
LU
u-
Z 4000
I
i-
LU-
Q

5000

6000

BUREAU OF GEOLOGY

TEMPERATURE F
1000 90

7000 '.I

Figure 10. Graph showing temperature profiles in oil-exploratory and waste-
disposal wells. See well locations in Figure 6.

thermal convection cell not unlike the familiar circulation in a teapot
being heated on a stove. The convective circulation in the deep part
of the aquifer should be eastward from the Gulf of Mexico, northward
from the southern Florida Straits, and westward from the eastern
straits. The focal point for this deep sea-water flow, and the hottest

SPECIAL PUBLICATION NO. 21

water, should occur along the axis of the Floridan Plateau farthest
from the cold sea-water bodies.
Vernon (1970) was critical of the temperature data and offered
an alternative suggestion related to geochemical reaction whereby
the cooling anomaly was involved with intensified solution of lime-
stone and dolomitization in the freshwater-saltwater transition zone.
The reader is referred to a rebuttal too extensive to be appropriate
in this paper (Henry and Kohout, 1972, p. 207-212).
The curve for Gulf 340-1 is plotted along with nine additional
temperature profiles in Figure 10. (See locations, Fig. 6). The tem-
perature data for well GW-1 were collected by the reverse-rotary
method of drilling, which permits the continuous collection of rock
and native water samples as they are returned to the surface by
upward circulation through the drill stem. The temperature de-
creases from 74 F at 1,000 ft. to 61F in a cavity encountered at
2,947 ft. below sea level. The difference represents a negative thermal
gradient of 13 F in a 2,000-ft. interval a startling phenomenon in
comparison to the normal positive ("textbook") thermal gradient of
about 1F for each 50- to 100-ft. increase in depth (i.e., an increase
of 200F in 2,000 ft. would be a minimum expectation).
During 1975 additional temperature information was obtained
from a test well for sewage injection at the West Palm Beach STP
plotted as PB-782 and from a test well for a desalination supply
well (FKAA) at Marathon in the Florida Keys. Both sites confirm
that a negative thermal gradient approaching 200F in 2,000 ft. is
present in wells close to the Florida Straits. This strong negative
thermal gradient (i.e., decrease in temperature with depth) should
be expected only for a limited distance inland from the cold sea-
water bodies. Beyond this distance, the thermal profile would be
expected to become positive (i.e., warmer with depth), because the
upward geothermal heat flow continually warms the sea water as it
flows inland.

GEOGRAPHIC DISTRIBUTION OF TEMPERATURE
IN THE FLORIDAN AQUIFER
The geographic distribution of temperature near the bottom of
the Floridan Aquifer is illustrated in Figure 11. The temperature-
depth correlations were selected from the profiles of Figure 10 by
best judgment related to various conditions of the well when the
measurements were made. For example, a temperature of 108F at
-2,800 ft. in well 224B-1 was selected in preference to a temperature
of 1120F at 3,000-3,200 ft. (Fig. 10) because of the possibility that
the deeper zone might have been affected by heat from the hardening

BUREAU OF GEOLOGY

Figure 11. Map showing geographic distribution of temperature related to
depth near the bottom of the Floridan Aquifier system (Boulder
Zone).

cement below the aquifer base (about -3,300 ft.).
Bottom-hole temperatures obtained for sewage injection test
wells at the Stuart STP and the Margate STP are also plotted in
Figure 11 (complete temperature profiles not available). The Mar-
gate temperature of 590 F is the lowest of all wells and this correlates
with a relative location closest to the edge of the sharp dropoff into

SPECIAL PUBLICATION NO. 21

the deep water of the Florida Straits (indicated by the dashed edge
of the Floridan Plateau, Fig. 11). The temperature at the Stuart site
is relatively high and probably correlates with greater distance from
the edge of the plateau (edge of Florida Straits). Lichtler (1960,
Fig. 21, p. 61-63) has mapped temperatures in relatively shallow
artesian wells (900-1,300 ft. deep) in Martin County (Stuart area,
Figs. 6, 8), and notes that wells in the eastern part of the county
(nearer to the ocean) average about 70 cooler than those in the
western part of the county. The relationships are not clear but
upwelling of relatively cooler water from the Boulder Zone would be
a possible explanation.
The data in Figure 11 show that there is an overall increase of
water temperature in the deep part of the Boulder Zone from 59-
610F at Miami on the southeast, near the edge, to more than 108F
near the axis of the Floridan Plateau south of Tampa.

SURFACE EVIDENCE OF THERMAL UPWELLING
HUMBLE-LOWNDES-TREADWELL NO. 1
Several physical examples of increased temperature near the axis
of the Floridan Plateau cannot be plotted in Figure 11 because the
depth from which the waters rise is not known directly. Figure 12
shows the Humble-Lowndes-Treadwell No. 1, an abandoned oil-
exploratory well about 20 miles southeast of Warm Mineral Springs

Figure 12. Photograph of natural flow from Humble-Lowndes-Treadwell No.
1. Photo by D. H. Boggess, August 1966.

BUREAU OF GEOLOGY

Figure 13. Photograph of natural flow from Humble-Lowndes-Treadwell No.
1 after development into a warm-spring spa in 1967.

(Fig. 2), flowing at a reported rate of 7,000 gpm in August 1966.
The chloride content of the water was 18,700 mg/1, which is close
to the concentration in sea water (about 19,000 mg/1); the tempera-
ture of the water was 96 F. In 1967, the well was developed into a
warm-spring spa (Fig. 13), demonstrating how quickly a new con-
ceptual application changed the seemingly worthless saline-water
flow into commercial value (Kohout, 1970, p. 1446).
The depth from which the water originates is not known, but the
temperature of 96F is close to the 1000F temperature in Stevens
No. 1, located about 10 miles to the east (Figs. 10, 11). The high
chlorinity suggest that the water originates very deep in the Boulder
Zone.

WARM MINERAL SPRINGS SINKHOLE
Warm Mineral Springs (Figs. 2, 14) is a commercially developed
spa. The lake is actually a sinkhole about 250 ft. in diameter at the
surface and more than 200 ft. deep. The sink was originally named
"Warm Salt Springs" or "Big Salt Springs" (Parker and Cooke,
1944, p. 32-35; Ferguson, et al., 1947, p. 148). Discharge through an

SPECIAL PUBLICATION NO. 21

Figure 14. Oblique aerial photograph of Warm Mineral Springs sinkhole, a
commercially developed spa. White spots in Lake are bathers.
Overflow stream is at upper left corner of photo. Photo courtesy
of William R. Royal.

outflow creek has been measured periodically over the years by the
U. S. Geological Survey at 7 to 11 cfs (cubic feet per second).
Warm Mineral Springs sinkhole is unusual compared to most
Florida sinks because warm, hydrogen-sulfide-rich saline water flows
upward from depth. Stalactite-hung caves at 20-45 ft. bpwl (below
present water level) were occupied by humans during lowered sea
level of the glacial Pleistocene Epoch. The high H2S content (no
oxygen) is a probable factor in the excellent preservation of the
human bones which have been dated by carbon-14 analysis of sur-
rounding leaf material at about 10,000 years before present (Royal
and Clark, 1960, p. 286; Clark, 1969, p. 175-176; Clausen et al., 1975).
The sinkhole has been investigated by SCUBA divers. All walls
overhang to form a cathedral-shaped cavity about 400 ft. in diameter
near the bottom. In the north wall, at a depth of 215 ft., saline water
with a temperature of 90 F discharges from a cave. Flow through
the cross-section area shown in Figure 15 was measured by using
fluorescein dye as a tracer over a measured distance of 15 linear ft.
along the tunnel. The velocity of the water was about 1 fps (foot per

BUREAU OF GEOLOGY

Figure 15. Underwater photograph of cave cross section through which
discharge was measured by using fluorescein dye as a tracer.
Size of cross section can be judged from a 3-ft measuring stick
extending from floor to roof and a 5-ft surveyor's rod extending
left from meter stick. Ropes tied off on rock projections enter
picture from left and right. White object at right side of photo
is a polystyrene ball floating against roof for a marker buoy.
Photo by William R. Royal.

second) (W. R. Royal, oral commun., November 22, 1971). Thus,
about 30 cfs of warm salt water entered the main sinkhole through
this cave. The flow is variable, however; at the end of a very dry
season in May, 1974, the discharge from the cave was greatly reduced.
A velocity of possibly 0.1 fps at the cave mouth measured with
fluorescein by Kohout was inconclusive for determining discharge.
In October, 1973, a sampling hose was carried deep into the cave
to minimize contamination from shallow, fresh ground water which
enters at various levels in the main sinkhole. A large sample of
water was collected for tritium, carbon-14, and uranium-isotope
analysis. Tritium concentration was negligible indicating that the
discharge emanating from the cave comes primarily from the Floridan
Aquifer (i.e., a tritium component would indicate that shallow ground
water had been mixed into the warm water rising from the Boulder
Zone). The carbon-14 analysis (F. J. Pearson, U. S. Geological
Survey, written commun., 1976) indicates that a maximum of 4%
of modern water might be present in the blend. The water cannot
be age-dated because the end-point source waters that are present

SPECIAL PUBLICATION NO. 21

in the blend are not known, either as to original carbon-14 content
or salinity. The fact that the water exiting from the cave has a
temperature of 90F strongly suggests that the source is relatively
deep in the Boulder Zone (see temperature profile for Gulf-Stevens
No. 1 located about 10 miles east of Warm Mineral Springs, Fig. 10).
The water undoubtedly cools to some extent during its rise from
depth; also, the presence of 4% modem water indicates that the
blend contains an admixture of ground water (possibly fresh) from
the Principle Artesian Zone or possibly a small admixture from
shallow aquifers in the 200-500 ft. depth range. In any case, the
source-water deep in the Boulder Zone would necessarily have a
higher temperature and a higher salinity than the water which we
are able to measure in the cave (before its entry into the main
sinkhole). We have no way to give better quantitative information
but it is clear that warm salt water has sufficient head to flow into
the sinkhole where the water level is maintained by an overflow
dam at about 5 feet above sea level.
This upwelling of warm saline water appears to be another ex-
ample of the discharge of geothermally heated water along the
central axis of the Floridan Plateau. Also, Kaufman and Dion
(1967, Fig. 11) have mapped a zone of high-temperature saline water
in wells tapping the relatively shallow part (-1,200 ft.) of the
Floridan Aquifer along the Peace River 30 miles northeast of Warm
Mineral Springs.

THE MUD HOLE SUBMARINE SPRING
A submarine spring (Kohout, 1966) located about 12 miles off
the southwest shore of Florida (Fig. 11) has been an important
fishing spot for local fishermen for many years. The spring (Fig. 16)
was explored recently by SCUBA diving. It was discovered that the
discharge was taking place from a sink-like depression about 200 ft.
in diameter at a maximum depth of about 65 ft. below sea level. The
bottom consists of grey silt and mud, warm to the touch when the
hand is pushed a few inches under the surface. Under the slime and
mud, the bottom consists of sand and limestone gravel. When the
bottom is disturbed, clouds of mud are thrown into suspension and
seepage increases; this probably accounts for the name "Mud Hole"
(name used by local fishing captains, Munson, 1961).
Prominent orifices occur at several points. The temperature of
the water from each of these orifices was measured with a human
fever thermometer at 96.60F. A birefringent (heat-wave) mixing
plume extends about 5 ft. above the orifice. The diver's vision is
blurred in this mixing plume but upon penetrating into the orifice,

BUREAU OF GEOLOGY

Figure 16. Photograph of surface slick produced by upswelling of warm
seawater at the Mud Hole submarine spring, Oct. 26, 1972.

vision becomes dramatically clear; the lower part of Figure 17 demon-
strates this observation. In comparison to the cool sea water, the
outflowing spring water is sufficiently warm to cause apprehension.
The velocity of the water was estimated at 2 fps from debris
moving through the orifice (3 ft. x 1 ft.), half visible in Fig. 17. The
discharge is thereby estimated at about 6 cfs. The total discharge
from the whole depression is much larger than this but estimates are
not possible at this time. However, the Energy Research and De-
velopment Administration (ERDA) has provided a grant to further
define the discharge, chemistry, and thermal aspects of the spring
(Thomas E. Pyle, University of South Florida, Department of Ma-
rine Sciences, Oral commun., 1976).
The concentration of major ions is about the same as that of sea
water, e.g. chloride 19,000 to 20,000 mg/1 on several samplings. A
large volume sample was collected by inserting 400 ft. of garden hose

SPECIAL PUBLICATION NO. 21 27

Figure 17. Photograph of one of the orifices in the sink-like depression of
the Mud Hole submarine spring. Turbulent mixing zone above
changes to clear discharge where water of 96.60F exits toward
reader from orifice. Handheld camera at left indicates scale of
photograph.

with taped joints into the orifice and pumping water into three 15-
gallon drums on board the anchored survey boat. Tritium content
was 0.4 + 0.2 TU (F. J. Pearson, U. S. Geological Survey, 1976)
indicating the possibility of contamination from the surrounding sea
water. Carbon-14 analysis indicated that a maximum of 17% of
modern sea water might have been mixed into the discharging water.
The temperature represents prima facie evidence that the water
comes from considerable depth. If 17% of cool sea water (estimated
at a maximum of 700F for bottom water in the area) was mixed
with 83% of warm spring water of unknown temperature to yield a
100% blend of water measured at 96.6 F, a simple calculation can
be made:

BUREAU OF GEOLOGY

0.17 (70) +0.83T = 1.00 (96.6)
T 96.6 0.17(70)
0.83
T = 102.10F
The calculation suggests that water rising up from depth in
the aquifer might be expected to exceed 1020F. The temperature
profile in well 224B-1 (Fig. 10, 11), located in the general area of
the Mud Hole submarine spring, lends credence to this possibility.
Sea-level head exists along all shorelines of the Florida peninsula.
Therefore, although Figure 9 implies complete recycling of the in-
flowing warmed sea water to the eastern Florida Straits, it would
be possible for cold sea water to enter the Floridan Aquifer where
it is truncated at depth by the eastern and southern Straits of
Florida, and then to flow entirely beneath the above-sea-level part of
the Floridan Plateau toward discharge points along the west coast
of Florida. Though no wells have been drilled far out on the western
part of the plateau, presence of the cavernous Boulder Zone and
truncation by deep water in the Gulf of Mexico might also permit
eastward flow of sea water toward the central axis of the plateau.
The Mud Hole submarine spring may be evidence of upwelling from
the western or southern hydraulic boundaries as well as from the
eastern boundary in the Straits of Florida.

HYDRAULIC AND MATHEMATICAL MODEL STUDIES
Three sets of gradients control ground-water movement: the
hydraulic-pressure gradient, the geothermal gradient, and the salt-
concentration gradient. In thick aquifers, interaction of these gradi-
ents induces gravity convection currents. Under a grant from the
U. S. Geological Survey, the University of Alabama investigated the
mechanics of flow in deep saline aquifers affected by geothermal
heating (Henry and Kohout, 1972; Henry and Hilleke, 1972). The
study was for the purpose of determining theoretically whether
patterns of flow or circulation exist in the deep parts of such aquifers
which cannot be inferred from the piezometric gradient (as is shown
in Figure 3 for the upper Floridan Aquifer), but which might be
significant in leading to undesirable movements of liquid wastes in-
jected into these regions. Mathematical prediction of the direction
and rate of movement of the native water and the entrained waste is
the ultimate goal. However, the results are pertinent to considera-
tions of the influence of ground-water flow on geothermal heat flow
and visa versa. The above reports are summarized herein but the
reader is referred to the original papers for the mathematical support.
The above reports are summarized herein but the reader is referred

SPECIAL PUBLICATION NO. 21

to the original papers for the mathematical support.
The investigations consisted of experimental measurements on a
hydraulic model of the Floridan Aquifer and theoretical analyses of
the system based on solutions of the governing differential equations.
The hydraulic model yielded temperature distributions, salinity dis-
tributions, and flow patterns which were used for qualitative com-
parison with field conditions and with theoretical solutions. These
comparisons established the validity of solutions of the governing
equations which were then utilized for prediction of temperature,
salinity, and flow distributions for comparison with field conditions.
The two-dimensional hydraulic model made of sand was built to
simulate some aspects of the Floridan Aquifer. Systems were pro-
vided for supplying fresh-water recharge at ambient temperature
(approximately 70 F) and for maintaining a constant concentration
of salt water in the simulated ocean at approximately 430 F. Heating
pads were installed on the bottom and fresh-water end of the model
to simulate the geothermal heating which occurs in the field. The
physical dimensions of the simulated sand aquifer were 6 inches in
width, 12 ft. in length, and 3 ft. in depth. The corresponding length
and depth of the aquifer in the field are approximately 167 miles and
2,500 ft., respectively.

COMPARISON OF THEORETICAL AND FIELD STUDIES
The kinds of field data of particular interest for comparison with
theoretical studies are the temperature and chloride concentrations
obtained at various depths from drilling records. Information on
pressure-head distribution is only available from wells near the top
of the Floridan Aquifer (Fig. 3), and data that would permit de-
termination of flow direction in the deep, Boulder-Zone part of the
aquifer are non-existent.
The section line shown in Figure 18 is positioned to take advan-
tage of the largest amount of field data presently available. Figure
19a was obtained by translocating the temperature data of Figure
10 to an appropriate position along the section line of Figure 18.
The theoretical isotherms for one set of variables (Henry and Hilleke,
1972, Fig. 28) are plotted for comparison (Fig. 19b). In the deep
part of the aquifer, the isotherms in both diagrams are displaced in-
land and form a concave seaward pattern. This concavity strongly
suggests that cold ocean water moves inland in the deeper part of
the aquifer. Other evidence related to uranium isotope ratios (Os-
mond and Cowart, this volume) support this indication of inland
flow.

BUREAU OF GEOLOGY

Figure 18. Map showing section line and locations of wells used in Figures
19 and 20.

In Figure 20, the theoretical field isochlor pattern is compared
with the few chloride data that have been obtained from wells tapping
both shallow and deep parts of the Floridan Aquifer. The sparse
data were collected mostly as blends of water from long sections of
open hole, rather than as point sources of water from a specific
depth. Nevertheless, there is correspondence to the calculated chlo-
rinity pattern of Figure 20b.
As previously noted, sufficient synoptic pressure-head data from
wells tapping the deep, saline part of the aquifer are non-existent
and direction of water movement in these regions cannot be deduced
directly from field measurements. In lieu of this, the hydraulic lab-
oratory model studies and the mathematical solutions applied to the
Floridan Aquifer as a field model demonstrate a remarkable similarity
of temperature and chloride distribution. Confidence, then, can be
placed in solutions of streamline pattern as shown in Figure 21.
This model assumes, however, that a hydraulic boundary represented
by recharge of fresh water exists at the inland end of the model. The

SPECIAL PUBLICATION NO. 21

150 100
I , I

A
224B-1 STEVENS #1 COLLIER #1

(b)

1.0

y' 0.5

0-

DISTANCE IN MI

50

340-1

LES

0
, | i i i
A'
GW-1
I STRAITS OF FLORIDA

Figure 19. (a)
(b)

I I I I
0 0.5 1.0
X'
Temperature distribution in Floridan aquifier system.
Theoretical field isotherms for variables Nc=10, N -=3, NT=I
(After Henry and Hilleke, 1972, Fig. 28, for aquifier 167 miles
long and 2,500 feet thick).
The dimensionless units for temperature have the following
equivalents: 1.00 = 1100F, 0.85 = 1000F, 0.75 = 930F, 0.5
750F, 0.25 = 580F, 0.15 = 510F, 0.1 = 470F, 0.0 = 400F.

field situation is more complicated than this because, in fact, sea-
level head exists along all shorelines of the Florida peninsula. Cold
sea water can enter the Floridan Aquifer at depth where it is truncated
by the eastern Straits of Florida, and then flow entirely beneath the
peninsula toward shallow discharge points along the west coast of
Florida. The warm, saline effluents at Warm Mineral Springs sink-
hole and the Mud Hole submarine spring are field evidences that

BUREAU OF GEOLOGY

DISTANCE IN MILES

150 100 50 0
I i i i I i i. i i i i i i
A COLLIER SERIO A'
#1 SCG-2 #1 GW-1
SSTRAITS OF FLORIDA
CHLORIDE
-o1
CONFININGQ BEDS CLOR
19,800+
2 88 MG/L
4000
17900
15600 4000 18400
10300 19300 3
CEDAR KEYS ANHYDRITE -4

SAMPLED BY BLENDED E ER COLLECTED BY DR
THIEF METHOD 7100 mg/I AT REVERSE ROTARY DRILLING 5
SUN OIL CO 6500 GPM FLOW (Vrnon, 1970, Fig 8)
(Vernon, 1970. --6
p 27) BLENDED 2000 GPM FLOW
OPEN HOLE FROM -1360' TO
POINT OF DATA PLOT -7
S(Kohout, 1967, p 352)
-8

(b)

1.0-

y' 0.5-

0- o

000

000 <,

000 f
000
o

000 o
1-

z
000
Z

000

000

0I .0
0.5 1.0

Figure 20. (a) Chloride distribution in the Floridan aquifier system.
(b) Theoretical field isochlors for variables Nc = 10, N -= 3,
NT = 1 (After Henry and Hilleke, 1972, Fig. 26, for aquifier
167 miles long and 2,500 feet thick).
The dimensionless units for chloride have the following
equivalents in mg/1: 0.00 freshwater, 0.05 = 990, 0.2 =
3,960, 0.5 = 9,900, 0.8 = 15,840, 0.95 = 18,810, 1.00 = 19,800.

such circulation exists.

THE DOLOMITE QUESTION AND CAVITY FORMATION
Though seemingly remote to the subject matter of this volume,
continuous chemical diagenesis of the limestone matrix of the Flori-
dan Aquifer may be involved with the geothermally-motivated cyclic

SPECIAL PUBLICATION NO. 21 33

- t"- ------ ----- .I --.2 -

I OI M I
0 0.5 1.0
X'

Figure 21. Theoretical streamlines for variables Nc = 10, N -= 3, NT = 1
(After Henry and Hilleke, 1972, Fig. 27, for aquifier 167 miles
long and 2,500 feet thick).

flow of sea water. The amount of dolomite that is present in the
geologic column worldwide continues as one of the enigmas of
carbonate geochemistry (Fairbridge, 1957; Bathurst, 1971) because
dolomite has not yet been synthesized under laboratory conditions
that are characteristic of sedimentary environments (Deelman, 1975,
p. 471). Hanshaw, Back, and Deike (1971, p. 710) point out that
although the oceans are at or beyond saturation with respect to pure
calcite and dolomite, modern marine sediments are composed pri-
marily of aragonite, high-magnesium calcite, and low-magnesium
calcite. Concerning the source of magnesium ion for dolomite under-
lying the Florida Platform, they succinctly state:
"Mass balance calculations by Hsu (1963) indicate that simply mov-
ing magnesium ions (obtained from high-magnesium calcites) from
the recharge area to a downgradient area cannot dolomitize a signifi-
cant portion of the Floridan Aquifer. Our mineralogic studies concur
with this; there is obviously insufficient magnesium from magnesium
calcites available today to accomplish widespread dolomitization."
Puri and Winston (1974, p. 56) in discussing the origin of cavities
in the Floridan Aquifer state:
"Dolomitization is critical to the formation of the cavities, as all cavities
occur in dolostone. All hypotheses stand or fall on the time of dolomiti-
zation. So far, there is no evidence to conclusively prove when this
took place.
Previously expressed hypotheses include those of Vernon (1947, 1951,
1970) and Kohout (1965), and Hanshaw, Beck and Dieke (1971).
Vernon (1970) proposed a geochemical reaction that follows the mix-
ing of two bodies of water that contrast in concentration of salts. The
interface is the locus of dolomitization and of an intensified solution
and removal of solids.

BUREAU OF GEOLOGY

Kohout proposes a convection current, generated by geothermal heat-
ing of sea water freshly intruded into the high transmissivity zone
from the rock outcroppings in the Straits of Florida at the east, south,
and west sides of the Floridan Plateau. Dolomitizing magnesium-rich
water is thus continuously circulated into the aquifer to provide the
magnesium for continuous dolomitization.
A geochemical hypothesis for dolomitization by ground water was
offered by Hanshaw, Back, and Deike (1971). Their study was based
on chemistry of the Floridan ground water and the mineralogic
composition of the artesian aquifer. They observed that there was a
systematic change in the magnesium to calcium ratio from 0.5 in the
potable water to 1 from the recharge area down-gradient into the deep-
er part of the aquifer system. They examined stable carbon isotope
composition of calcite-dolomite and found that the calcite 8C13 compo-
sition is always that of normal marine limestone; however, the 8C13 of
the associated dolomite was not formed under marine conditions but
was formed under the effect of ground water, perhaps saline.
From our incomplete data in this study, we observed that the base
and top of cavity zones in cores are usually bounded by peaty partings,
or other impediments to vertical migration of fluids. The dolomitizing
fluids then were forced to spread laterally, creating the horizontally
oriented cavities and zones of cavities."
In contrast to the above references to inadequate supply of mag-
nesium for dolomitization, the cyclic flow mechanism can occur
purely by dispersion of salt as in the Biscayne Aquifer of the Miami,
Florida area or as postulated here, by dispersion of salt augmented
by convection from geothermal heat flow as in the Floridan Aquifer.
The possibility therefore exists as noted by Folk and Land (1975)
for continuous dolomitization and continuous formation of voids
below sea level, as well as by the commonly recognized mode of
above-sea-level solution. One may even speculate that the orientation
of the cavities may not be completely horizontal as implied in the
above quotation from Puri and Winston (1974). Although horizon-
tally oriented in a localized sense, the flow of sea water from the edge
of the deep sea-water bodies must also have a vertical upward com-
ponent because of the convective circulation. Assuming contempo-
raneous continuing dolomitization to be a valid process, intergranular
flow initiated by geothermal heating in a homogeneous, isotropic
limestone matrix could be expected to ultimately superimpose a
system of dolomite-lined voids and cavities on the original layer of
rock. The cavities would form a pattern that would duplicate the
original streamline pattern of the hydraulic flow. Indeed, the creation
of the first voids would increase the permeability of the matrix, thus
increasing the rate of flow of the dolomitizing fluids, and in turn
augmenting cavity formation. The diagenetic change should be a
self-perpetuating, accelerating phenomenon. In geologic time, changes

SPECIAL PUBLICATION NO. 21

of sea level, natural differences in the original sedimentation, struc-
tural movement, collapse of caverns, etc., would provide great vari-
ability. However, Puri and Winston (1972, p. 3) note that "cavities
tend to rise stratigraphically away from the Florida Straits in a
northerly direction." Also, it is interesting to note that the deepest
flows in Figure 5 occur in the Florida Keys adjacent to the Straits
of Florida at depths of 3,500 to 4,000 ft. The occurrence of strong
salt-water flows as reported during drilling becomes progressively
shallower toward the central axis of the Floridan Plateau to a depth
of about 2,300 ft., representing a rise of over 1,000 ft. relative to the
Florida Keys. No evidence exists that these cavern systems are inter-
connected but can the above hydrologic and geologic evidence be
entirely circumstantial and misleading?

GEOTHERMAL GRADIENTS BELOW
THE FLORIDAN AQUIFER
There is some evidence that the geothermal temperature distribu-
tion at the foot of the Floridan Plateau is affected by cold sea-water
circulation. In Figure 10, adjacent to the bottom of each tempera-
ture curve, the bottom-hole temperature as shown on Schlumberger
electric logs is correlated with the depth of measurement. These
temperature data are in no way connected with the temperature
curve except that they represent the end point for the temperature
profile in the relatively low permeability rock below the Floridan
Aquifer. The data suggest that the heat sink formed by cold water
in the Gulf of Mexico at depths of about 12,000 ft. (about 400F)
affects the horizontal temperature distribution even at the roots
of the plateau. For example, a temperature of 164 F at 15,290 ft.
in California 46-1, nearest to the Gulf of Mexico, is about 740 cooler
than the 238 temperature in well 224B-1 near the central axis of
the Floridan Plateau. Although many inconsistencies can develop
in measurement of bottom-hole temperatures because of the circu-
lation of mud in the borehole before measurement, it appears that
the large temperature differentials between wells 46-1 and 826Y,
near the edge of the cold sea-water bodies, and those in the interior
of the plateau are too large to be explained by such inconsistencies.
Rather, the data suggest that there exists under the plateau a three-
dimensional temperature regime that is consistent with upward heat
flow from the interior of the earth, modified by material heat flow to
the cold sea-water in the adjacent ocean basins. Other papers in this
volume give detailed consideration to geothermal gradients and
heat-flow in beds underlying the Floridan Aquifer (also see Reel
and Griffin, 1971).

BUREAU OF GEOLOGY

SUMMARY
This paper presents evidence that the geothermal regime of the
Floridan Plateau is modified by presence of cold sea water (40-
450F) in the Gulf of Mexico and the Florida Straits.
From about 1,500 ft. to 3,000 ft. below sea level the ground
water in the Floridan Aquifer system becomes colder with depth.
In the horizontal direction, the average temperature at -3,000 ft.
increases from about 600 near the cold sea-water bodies to more
than 1080F along the central axis of the Floridan Plateau. The water
at these same depths approximates the salinity of sea water as evi-
denced by samples obtained during drilling of waste injection wells
along the east coast of Florida. Mathematical and laboratory model
studies indicate that the anomalies may be caused by a geothermal
convection cell which causes sea water to flow inland through caver-
nous dolomite near the bottom of the aquifer. After becoming
warmed, the water flows upward where it mixes with fresh water re-
charged through sinkholes in the karst region of central Florida, and
thence seaward through the upper part of the aquifer to discharge
by upward leakage through confining beds or through submarine
springs on the Continental Shelf and Slope. The convective circula-
tion in the deep part of the aquifer should be eastward from the
Gulf of Mexico and northward and westward from the Straits of
Florida. The focal point for this deep sea-water flow, and the
hottest water, should occur along the central axis of the Floridan
Plateau (Fig. 1), farthest from the cold sea-water bodies. The Mud
Hole submarine spring which discharges warm sea water from a
sink-like crater about 65 ft. below sea level off the west coast of
Florida (Fig. 11) provides field evidence that the convective flow
cell exists.
In the low-permeability rock below the Floridan Aquifer system,
geothermal gradients are more "normal"- that is, the temperature
increases with depth in a manner consistent with upward heat flow
from the interior of the earth. However, bottom-hole temperatures
recorded in Schlumberger electric logs indicate that even at the foot
of the Floridan Plateau, as deep as 15,000 ft. below sea level, the
temperature regime is modified by lateral heat flow to cold sea-water
circulating through the adjacent ocean depressions.
The possibility of cyclic circulation of cold sea water into perme-
able corbonate rocks underlying the Florida-Bahama Plateau has
practical importance because the coolness may represent a funda-
mentally important control on the occurrence of hydrocarbons -
i.e., the temperature of the rocks may have been too low except in
specific places to convert organic matter to oil and gas (Reel and

SPECIAL PUBLICATION NO. 21

Griffin, 1971), Subsequent papers in this volume give consideration
to these problems.

ACKNOWLEDGMENTS
Data and logs were supplied by the California Co., Coastal Pe-
troleum Co., Gulf Oil Corp., Humble Oil Co., Mobil Oil Co., Serio
Oil Co., Sun Oil Co., and the Florida Bureau of Geology. The hy-
draulic model and theoretical studies were a part of the Master of
Science degree of Mr. Jeff Hilleke of the University of Alabama. His
contributions are manifest in the report. Leonard A. Wood, coordi-
nator for U.S. Geological Survey Subsurface Waste Storage Program,
provided guidance; funds for the theoretical studies by the University
of Alabama were provided under this program. Field hydrological
studies were made by the U.S. Geological Survey under the general
supervision of Clyde S. Conover. Geologic framework studies by the
Florida Bureau of Geology were made under Robert 0. Vernon and
later, Charles W. Hendry, Jr. Over more than 10 years the following
individuals contributed data or helped in other ways: William R.
Royal, Roy Worrell, Bennie Franks, Charles A. Appel, Robert E.
Hill, Les Koher, John Stamer, Charles Holmes, J. I. Garcia-Bengo-
chea, Muriel Hunter, F. W. Meyer, R. L. Nace, D. H. Boggess, V. T.
Stringfield, H. H. Cooper, Jr., M. I. Rorabaugh, C. L. McGinnis,
N. D. Hoy, Wilburn A. Cockrell, F. J. Pearson, I. J. Winograd,
Gerald Meyer, J. K. Osmond, J. L. Cowart, Glen Faulkner, Don
Goolsby, M. I. Kaufman, Harbans O. Puri, H. K. Brooks, Robert
Kirkland, J. S. Rosenshein, Larry Farnell, Lee Miller, James Ed-
wards, John McDonald, Thomas E. Pyle, F. T. Manheim, Warren
Leve, C. B. Sherwood, Howard Klein, Lyle McGuinnis, and Mahlon
Ball. Laine Kohout aided by several typings of this report. The Mote
Marine Laboratory provided vessel support on two visits to the Mud
Hole submarine spring.

BUREAU OF GEOLOGY

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SPECIAL PUBLICATION NO. 21

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39

BUREAU OF GEOLOGY

1966, Submarine springs, in Encyclopedia of Earth Sciences Series,
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40

SPECIAL PUBLICATION NO. 21

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41

HEAT FLOW IN FLORIDA OIL TEST HOLES
AND INDICATIONS OF
OCEANIC CRUST BENEATH THE SOUTHERN
FLORIDA-BAHAMAS PLATFORM1

By

George M. Griffin2, David A. Reel3, and Richard W. Pratt4

1 Based on research performed in the Geology Departments of the University
of Florida and the University of South Florida. The financial assistance of
Cities Service Oil Co., Texaco Inc., and Coastal Petroleum Co. is sincerely
appreciated as is the personal assistance of Mr. Joseph E. Banks of Coastal
Petroleum Co.
2 Present address: Dept. of Geology, University of Florida, Gainesville, FL
32611
3 Present address: Getty Oil Co., Offshore Div., P. O. Box 1404, Houston, TX
77001
4 Present address: Law Engineering Co., Tampa, FL

43

CONTENTS
Page
A abstract ................................ .. ........................ 45
Introduction ........................................ ............ 46
Results and Discussion ........................ .................... 47
Conclusions ...................................................... 50
Appendix ................. ............................ ... 51
References ................... ................. .. ... ......... 63

ILLUSTRATIONS
Figure Page
1 Heat-Flow Values Extant upon Completion of this Project .... 48
2 Empirical Working Curves of Thermal Conductivity vs.
Porosity for Various Lithologies ............................ 55

Tables
1 Heat-Flow Measurements in Florida Oil Test Holes ............ 49
2 Geothermal Gradients ...................................... 52
3 Procedure for Measuring Porosity by Cutting Samples by the
Varsol Absorption M ethod ........................... ...... 56
4 Depth, lithology, bulk density, porosity, and thermal con-
ductivity of rock samples from California-Coastal Petroleum
Company No. 2 State Lease 224-A, offshore Franklin
County, Florida ................... ...................... 57-59
5 Depth, lithology, bulk density, porosity, and thermal con-
ductivity of rock samples from Humble Oil Company No. 1
State Lease 1004, Palm Beach County, Florida ............... 59-61
6 Depth, lithology, and thermal conductivity of samples from
Commonwealth No. 1 Wisehart State Board of Education ... 62

ABSTRACT
Heat-flow was determined for three deep oil-test holes, yielding
values of 0.71 and 0.76 HFU for south Florida and 0.92 HFU for
north Florida. Both the magnitude and trend of the values are similar
to those previously known for the eastern Gulf of Mexico. The very
low heat flow of the southern part of the peninsula supports the
concept that oceanic crust, with very low heat generating potential,
underlies the southern part of the Florida-Bahamas Platform.

BUREAU OF GEOLOGY

INTRODUCTION
By 1968, a moderate number of heat-flow values had been pub-
lished for the marine areas of the Gulf of Mexico and northwestern
Caribbean Sea (Epp et al., 1970; Langseth and Grim, 1964). Four
measurements in the deep eastern Gulf averaged 0.88 HFU, indicat-
ing below-average heat flow for the region as a whole. Individual
values increased from 0.7 in the southeastern Gulf to approximately
1.0 in the northeastern Gulf. If extrapolated across the untested
continental shelf and coastal plain of Florida, Georgia, and Alabama,
this trend appeared to continue northward into the continent, where
values of 0.95, 1.02, 0.97, and 1.00 (avg.=0.99 HFU) had been re-
ported in the Piedmont of Alabama, Georgia, and South Carolina
(Lee and Uyeda, 1965; Roy, et al., 1968).
Remarkably, in 1968 no published heat-flow measurements
existed for any of the land areas surrounding the eastern Gulf or
northwestern Caribbean, including the Florida-Bahamas Platform,
Cuba, and Yucatan. Therefore, between 1968 and early 1971, we
partially filled this gap with the measurements reported herein for
three deep oil-test holes.
The methods used in this study are detailed in the appendix.
Generally, thermal gradients were calculated from the "maximum"
or "bottom-hole" temperatures recorded on electric log headings.
Thermal conductivities of well samples were determined in one hole
by the Beck (1957) divided-bar method. In the other two holes,
published relationships between lithology, porosity, and thermal
conductivity were used to estimate the conductivity parameter of
the heat-flow equation.

SPECIAL PUBLICATION NO. 21

RESULTS AND DISCUSSION
The heat flow measurements and related data resulting from this
project are listed in Table 1 and plotted on Figure 1, where all other
heat flow values known to exist for the region at the time of comple-
tion of our experimental work are also indicated. The values result-
ing from this project suggest that heat flow is least in the southern
part of the Florida Peninsula (0.71 and 0.76 HFU) and increases
toward north Florida (0.92 HFU). The general trend on the land
therefore parallels the previously known trend in the offshore part
of the region and is similar in magnitude. The principal point of
interest is the very low heat flow through south Florida and the
adjacent part of the eastern Gulf of Mexico.
As Roy et al., (1968) have pointed out:
Q= a + bA
(eq. 1)
where:
Q = total heat flow,
a = the fraction of heat flow produced by transfer
from the lower crust and upper mantle, = 0.79
HFU in the eastern United States,
b = the depth of radiogenic sources of heat in the
upper crust, = 7.5 km in the eastern United
States, and
A = heat produced by radioactive crustal rocks at a
depth of b.
Recalling that the average value for the two boreholes in south
Florida is Q = 0.735 HFU, the observed heat flow is entirely ac-
counted for by that portion produced by conductive transfer from
the lower crust and upper mantle. That is, in south Florida:
Q N a,
and the contribution to heat flow by upper crustal radioactive sources
is negligible, i.e.:
bA 0
The implication from this is that south Florida is underlain by
oceanic crust in which the heat-generating potential is quite low
when compared to sial (approximately one-sixth). Such an interpre-
tation is consistent with the continual subsidence of the area, which
over its approximately 150 million year (age from Khudoley, 1967)
history of sedimentation is calculated to average 200 ft. per million
years at Cay Sal Bank, its southern tip.
Dietz et al. (1970) have previously postulated from other types
of geophysical evidence that the Bahama Platform is underlain by
oceanic crust, an hypothesis agreed to by Uchupi et al. (1971).

BUREAU OF GEOLOGY

0.97
0

l \\0

0 100 200
Miles

0.8

\
0.7'

, A

Figure 1. Heat Flow Values extant completion of this project. (Asterisks in-
dicate new values; black dots are measurements prior to 1971 as
reported by Lee and Uyeda, 1965; Roy et al, 1968; and Epp et al,
1970.)

Table 1 -- Heat Flow Measurements in Florida Oil Test Holes

Well Name Examined
and Location Depth Interval

California-
Coastal Petrol-
eum Co. -- No.2
State Lease 224
-A. (Franklin
Co., Offshore,
27.79250N, 84.
3619W)

1,300 -
10,510 ft
(397-3206m)

Average
Thermal Gradient

0.99'F/100ft
(18.030C/km)

Thermal Conductivity** (Rock Type, Mean Con-
ductivity, Thick- Average Heat Flow
ness of this lithology) (10-6cal/cm2sec)
Rock Type Wegiht ed an Thickness of Lithology
Limestone 2.21 240 ft ( 73m)
Dolomite 2.55 380 ft (116m)
Argillaceous 2.98 890 ft (271m)
Cherty Ls. 5.53 1230 ft (375m)
Sandstone 13.046 70 ft ( 21m)
Argill. Ss. 9.71 610 ft (186m)
Ss + Red SH 5.15 5320 ft(1595m)
Ss + Gray SH 4.62 650 ft (650m)
Weighted Mean 5.13 9300 ft(2837m) 0.92

Humble Oil and 4,650 0.980F/100ft Limestone 3.00 2790 ft (851m)
Ref. Co. -- 12,800 ft (17.850C/km) Dolomite 3.69 710 ft (217m)
No.l State (1418-3904m) Anhydrite 7.40 270 ft ( 82m)
Lease 1004 Ls. + Dol. 3.79 92Q ft (281m)
(Palm Beach Co, Ls. + Anhyd. 4.84 670 ft (204m)
2-485-35E) Dol. + 4.52 2470 ft (735m)
Dol. + Ls.+
Anhyd. 4.06 810 ft (247m)
Weighted Mean
Average 3.95 8640 ft(2635m) 0.71

Commonwealth 6,085 *0.98F/100ft Limestone 3.51 956 ft (292m)
Oil Co. -- 11,558 ft (17.850C/km) Argillaceous 3.26 150 ft ( 46m)
No. 1 Wisehart- (1856-3525m) Dolomite 4.67 856 ft (261m)
St. Board of Anhydrite 5.57 401 ft (122m)
Education (Dade Weighted Mean 4.26 2363 gy (729m) 0.76
Co., 16-54S-35E)

Composite gradient for 3 wells in the same township as Commonwealth No. 1 Wisehart, but not in this well.

** 10-3cal/cm secC

BUREAU OF GEOLOGY

However, Sheridan (1971) has proposed a model based on crust of
the Red Sea type, which includes 9.9 mi. of an intermediate layer
(density 2.15), overlain by 2.1 mi. of oceanic crust (density 2.95),
overlain by about 1.9 miles of sediment with a density of 2.35, and
topped by about 3.1 mi. of limestone (density 2.50). The Sheridan
model yields a mantle depth of 18 mi., which he believes is more in
keeping with gravity data for the area. In neither the Dietz et al.,
Uchupi et al., or Sheridan models is the crust considered as con-
tinental, therefore the heat-flow data seem comparable with either
of their proposals.

CONCLUSION
The data of this project support the general concept that oceanic
crust, with very low heat-generating potential underlies the southern
part of the Florida-Bahamas Platform. However, clear distinction
between the models proposed by Dietz et al. (1970) and Sheridan
(1971) is not possible from the heat-flow data; if Sheridan's inter-
mediate layer (density 3.15) does in fact exist between the mantle
and the oceanic crust, its heat generating potential must be very low.

SPECIAL PUBLICATION NO. 21

APPENDIX
A. Generalities of Heat-Flow Measurements
The rate at which the earth's internal heat moves toward the
surface is reported most commonly in terms of HFU (heat flow
units), wherein 1 x 10-6cal/cm2 sec = 1 HFU. The average heat flow
from continental areas of all types centers at about 1.5 HFU.
Terrestrial heat flow measurements have generally been con-
sidered to require a borehole extending beneath the zone of climatic
fluctuations and ground-water movement. If rigidly applied, this
requirement restricts geothermal temperature measurements in Flor-
ida to depths approximately greater than 1000 ft. in north Florida
and 5000 ft. in south Florida, that is, depths below the Floridan
aquifer system. The three heat-flow measurements reported in this
paper abide by this restriction, including only temperature and
conductivity data collected below the Floridan Aquifer. However, as
Smith and Fuller have shown in their work (1976, this volume),
although the aquifer system affects subsurface temperatures marked-
ly, it is possible to make high quality heat-flow measurements in
shallow boreholes once the thermal effects of the aquifer are under-
stood. Thus, the heat flow values reported herein for deep holes cor-
relate very well with the values reported by Smith and Fuller except
in areas of active ground-water recharge and similar disturbances of
the thermal flow pattern.
B. Computation of Heat Flow and Measurement of the Thermal
Parameters Used in this Study
Heat flow is defined by the relationship:

Q K (AT/AZ), (eq. 2)
where, Q heat flow in 10-6cal/cm2 sec,
K = thermal conductivity of the rock between depths of tem-
perature measurements in 10-3cal/cm sec0c, and
(AT/AZ) = the rate of increase in temperature between mea-
surement depths (i.e. the geothermal gradient),
with T in C, and Z in cm.
Because it is never possible to measure both of the basic parameters
in the heat flow equation under ideal, equilibrium, in situ conditions,
various assumptions must always be made; those made in this study
are explained below.
Geothermal gradients (Table 2) were calculated from the series
of "bottom hole temperatures" or "maximum temperatures" re-
corded by oil well service companies during standard electric logging
runs. These temperatures are assumed to represent near-equilibrium
conditions at the bottom of the hole at the time of the probe in-

Table 2 -- Geothermal Gradients

Depth Interval

Geothermal Gradient

California-Coastal Petrol,Co.--
No. 2 St. Lse, 224A
(Franklin Co., FL.)

Humble -- No. 1 St. Lse. 1004
(Palm Beach Co., FL)

Commonwealth -- No. 1
Wisehart- St. Bd. of Educ.
(Dade Co., FL)

0-5000 ft (0-1525m)
5000-10,560 ft (1525-3221m)
Average*:0-10,560 ft (0-3221m)

4600-7800 ft (1403-2379m)
7800-9000 ft (2379-2745m)
9000-10,800 ft (2745-3294m)
10,800-12,800 ft (3294-3904m)
Average*: 0-12,800 ft (0-3904m)

Average**: 0-11,558 ft (0-3525m)

1.140F/100
0.920F/100
0.990F/100

1.40F/100
0.60F/100
1.080F/100
0.600 F/100
0.980F/100

0.980F/100

ft (20.760c/km)
ft (16.750c/km)
ft (18.030c/km)

ft (25.490c/km)
ft (10.93c/km)
ft (19.670c/km)
ft (10.930c/km)
ft (17.850c/km)

ft (17.850c/km)

* Visual estimate from plotted T/Z data.
** Based on 6 subsurface temperature measurements in 3 other wells within the same township; data from
Wisehart No. 1 appeared erroneous and were not used; see text.

Well Name

SPECIAL PUBLICATION NO. 21

sertion. Difficulties inherent in using temperatures of this type have
been discussed previously (Griffin et al., 1969). The temperatures
are "uncorrected" in the sense of the AAPG Geothermal Survey of
North America. Temperatures at Z = 0 were taken from the average
ambient surface temperature map of the U.S. Weather Bureau.
The geothermal gradient for the Commonwealth No. 1 Wise-
hart was determined differently from the other two wells. The only
temperature recorded for the well, 226 F at 11,558 ft., when plotted
with the surface temperature of 750 F, yielded a gradient of 1.31 F/-
100 ft. Because this gradient is very much higher than gradients in
the surrounding area, as shown on the geothermal gradient map of
the state (Reel and Griffin, 1971; Reel, 1970), it was considered
suspect and was not used. Instead, the composite average gradient
for 6 subsurface measurements in 3 other wells in the same 54S-35E
township was used in the heat-flow calculation; this composite gradi-
ent is 0.980F/100 ft. (Reel, 1970). The composite 3 well, 6 measure-
ment thermal gradient for an adjacent township (54S, 36E), in the
same 40-Mile Bend Oil Field, was also calculated to be 0.98, lending
additional credence to our assumption.
Thermal conductivity was determined by two different methods:
(1) In the California-Coastal No. 2 State Lease 224A, and in
the Humble No. 1 State Lease 1004, conductivity was estimated
from empirical relationships between lithology, porosity, and thermal
conductivity. These relationships were examined by Bullard et al.
(1956), Diment and Robertson (1963), Ratcliff (1960), Woodside
and Messmer (1961), and Zierfuss (1969). Figure 2 is a composite
plot of the published relationship, assuming that salt water saturates
the pore network, which is true of our samples.
Entry into the working curves (Fig. 2) requires prior determina-
tion of lithology and porosity. For this purpose, regularly spaced
core samples from these two wells were categorized into lithologies,
and the porosity of each sample was measured by the "Varsol absor-
tion method," described in detail in Table 3. The depth, lithology,
porosity, bulk density, and derived thermal conductivity for each
sample are listed in Tables 4 and 5. Weighted mean-conductivities
were calculated for each lithology using the relationship:
(eq. 3)
where, K = the mean thermal conductivity for this lithology,
lx weighted in proportion to the thickness and con-
ductivity of each segment of this lithology,
k the arithmetic mean thermal conductivity of a par-
lx ticular segment, based on equally spaced measure-
ments of porosity within this segment, and

53

BUREAU OF GEOLOGY

li the thickness of a particular segment divided by the
11 i total thickness of all segments of this lithology.
Similarly, the weighted mean thermal conductivity for each well
was calculated from the relationship:
(eq. 4)
where, K_ = the mean thermal conductivity for the well, weighted
x in proportion to the thickness and mean conductivity
of each Lithology,
K_ = the mean thermal conductivity of a particular lithol-
lx ogy, and
Li = the thickness of a particular lithology divided by the
YL i total thickness of the stratigraphic section examined
in the well.
(2) In the Commonwealth No. 1 Wisehart, the thermal con-
ductivity of 33 core samples was measured directly with a divided-
bar device similar to that described by Beck (1957). The apparatus
was built so as to duplicate the Beck device as closely as possible,
and the only deviations were: (a) instead of a single thermocouple
at each level, three were used; these were arranged radially at 1200
intervals; readings from the three thermocouples were averaged,
thus improving the precision; (b) the size of the required sample was
scaled down to 0.875 in. so that the only available well samples could
be used; and (c) a Lexan plastic disc (General Electric Co.) was used
for calibration because a quartz standard was not available.
Samples were cut with a 0.875 in. diamond corer, with the long
axis of the disc parallel to the bedding. The discs were lapped with
extreme care to produce smooth, parallel surfaces and a thickness of
approximately 5mm. Each finished disc was soaked in saturated
NaCI brine for several days immediately prior to measurement of
thermal conductivity. The device was calibrated with the Lexan
standard before and after each run. Resulting thermal conductivities
are listed in Table 6. The mean thermal conductivity for the well,
weighted in proportion to the approximate thickness of each major
lithology (using equation 3) was 4.26 x 10-3cal/cm secc.

54

SPECIAL PUBLICATION NO. 21

12-
E
i -

S10-
I-
u
5 9.
a
Z *
0
u

55

Thermal Conductivity

vs

Porosity

\
\

40 50 60
POROSITY (%)

70 / 80

Figure 2. Empirical working Curves of Thermal Conductivity vs Porosity
for Various Lithologies, based on Published Data. Extrapolations
indicated by dashed lines. 1: Limestone, Archie Class II, Zierfuss
(1969). 2: Limestone, Archie Class III, Zierfuss (1969). 3: Lime-
stone, Archie Class I, Zierfuss (1969). 4: Dolomite, Zierfuss (1969).
5: Calcareous Shale, Bullard, Maxwell, and Revelle (1956) and
Diment and Robertson (1963). 6: Anhydrite, Zierfuss (1969). 7:
Sandstone, Woodside and Messmer (1961).

56 BUREAU OF GEOLOGY

Table 3. Procedure for Measuring Porosity of Cutting Samples by the Varsol
Absorption Method.

(1) Select a representative 10 g sample and break into fragments one to four mm
in diameter.

(2) Saturate with Varsol.1

(3) Dry at 1000C for fifteen hours.

(4) Cool in a dessicator and weigh ("dry weight").

(5) Re-immerse in Varsol and saturate for two hours in a dessicator.

(6) Roll quickly and briefly onto a paper towel to remove excess Varsol from
the exterior.

(7) Weigh quickly ("wet weight").

(8) After weighing place immediately in a burette containing a known volume
of Varsol, and determine the "bulk volume" of the sample by displacement
of the Varsol.

(9) Subtract the "dry weight" from the "wet weight" to determine the "weight
of Varsol" in the pores.

(10) Divide the "weight of Varsol" by 0.772 (its density) to yield the "volume
of Varsol in the pores.

(11) Divide the "volume of Varsol" in the pores by the "bulk volume" to yield
the ratio of the pore volume to total volume; multiply this ratio by 100
to yield percent porosity.

(12) Divide the "dry weight" by the "bulk volume" to yield the "bulk density"
of the rock.

1Varsol is a cleaning naptha manufactured by Humble Oil Company. It has a
density of 0.772 g/cm3 and is able to displace water from pores because of
its greater attraction to pore walls.

SPECIAL PUBLICATION NO. 21 57

Table 4. PDpth, lithology, bulk density, porosity, and thermal
conductivity of rock samples from California-Coastal
Petroleum Company N.o. 2 State Lease 224-A, offshore
Franklin Comity, Florida.

DEPTH LITHOLOGY DENSITY POROSITY CONDUCTIVITY
(ft.) (g/cc) (%) (10-3cal/cm secoC)

1300-10 Limestone 1.65 43.9 2.06
1400-10 Dolomite 1.76 38.6 2.76
1500-10 Dolomite 1.70 50.3 2.39
1600-10 Dolomite 1.64 45.9 2.50
1710-20 Dolomite 1.74 42.1 2.62
1800-10 Limestone 1.91 33.6 2.26
1900-10 Limestone, Chert 2.11 23.5 3.48
2000-10 Limestone, Chert 2.13 21.9 2.90
2100-10 Limestone, Chert 2.13 21.2 4.12
2200-10 Limestone, Chert 2.14 20.0 6.56
2300-10 Limestone, Chert 1.94 28.2 4.76
2400-10 Limestone, Chort 2.15 21.2 3.86
2500-10 Limestone, Chert 2.14 17.8 9.94
2600-10 Limestone, Chert 2.12 20.6 6.82
2700-10 Limestone, Chert 2.10 21.7 7.95
2800-10 Limestone, Chert 2.12 20.5 6.29
2900-10 Limestone, Chert 2.02 24,0 6.39
3000-10 Limestone, Chert 2.10 21.6 5.57
3100-10 Limestone, Chert 2.06 24.1 3.43
3200-10 Limestone, Shale 2.03 24.9 2.74
3300-10 Limestone, Shale 1.99 26.7 2.87
3400-10 Limestone, Shale 2.03 25.7 2.97
3500-10 Limestone, Shale 2.06 24.5 3.01
3600-10 Limestone, Shale 2.11 22.5 3.16
3700-10 Limestone, Shale 2.00 26.4 3.26
3800-10 Limestone, Shale 1.97 28.3 2.93
3900-10 Limestone, Shale 2.06 24.1 2.79
4000-10 Sandstone 2.23 16.6 12.82
4100-10 Gray Shale, Sandstone 2.08 23.5 3.83
4200-10 Gray Shale, Sandstone 2.10 22.3 4.11
4300-10 Gray Shale, Sandstone 2.05 25.2 4.03
4400-10 Gray Shale, Sandstone 2.13 22.5 5.03
4500-10 Gray Shale, Sandstone 2.08 23.3 4.43
4600-10 Gray Shale, Sandstone 2.16 21.9 5.22
4700-10 Gray Shale, Sandstone 2.18 21.7 5.79
4800-10 Red Shale, Sandstone 2.17 20.9 6.91
4900-10 Red Shale, Sandstone 2.16 22.4 5.36

58 BUREAU OF GEOLOGY

Table 4 (con'd.)

DEPTI LITHOLOGY DDSITY PO0OSITY CODUCjT.TL'Y
(ft.) (-/cc) (e) (lcal/cn secC)

5000-10 Rod Shale, Sandstone 2,16 22.9 6.36
5100-10 Rod Shalc, San :,one 2,27 18.4 5.18
5200-10 Rod Shale, Sandston) 2.18 22.6 4.87
5300-10 Rod Shale, Sandstone 2.20 20.7 7.32
5400-10 Rod Shalo, S.:nd:':o n 2,20 23.5 5.90
5500-10 Rod Shalc, Sadn:tone 2.27 17.7 5.76
5600-10 Rod Shale, S:andtono 2.24 19.9 5.89
5700-10 Rod Shale, Sandstone 2.37 16.8 6.91
5800-10 Red Shalo, Sandstone 2.24 19.9 4.98
5900-10 Rod Sha2e, Sandatono 2.22 20.2 6.80
6000-10 Red Shale, Sandstone 2.37 15.4 6.31
6100-10 Rod Shale, Sandcstone 2.30 16.1 6.08
6200-10 Red Shalo, Sandstone 2.34 15.9 7.68
6300-10 Rod Shale, Sandstone 2.33 14,9 7.45
6400-10 Red Shale, Sandstone 2.31 17.1 5.12
6500-10 Red Shale, Sandstone 2.83 25.8 4.57
6600-10 Rod Shale, Sandstone 2.18 20.3 5.02
6700-10 Rod Shale, Sandstone 2.24 17.7 5.56
6800-10 Red Shale, Sandstone 2.24 19.5 5.33
6900-10 Red Shale, Sandstone 2.25 18.2 5.70
7000-10 Rod Shale, Sandstone 2.26 17.8 4.71
7100-10 Red Shale, Sandstone 2.23 19.1 4.38
7200-10 Red Shale, Sandstone 2.42 12.9 7.53
7300-10 Red Shale, Sandstone 2.17 21.7 4.14
7400-10 Red Shale, Sandstone 2.20 20.6 5.34
7500-10 Red Shale, Sandstone 2.39 13.7 7.25
7600-10 Red Shale, Sandstone 2.39 14.6 6.39
7700-10 Red Shale, Sandstone 2.31 17.8 4.79
7800-10 Red Shale, Sandstone 2.27 18.2 4.42
7900-10 Red Shale, Sandstone. 2.35 15.4 5.88
8000-10 Red Shale, Sandstone 2.35 15.6 6.59
8100-10 Red Shale, Sandstone 2.35 15.3 7.42
8200-10 Red Shale, Sandstone 2.34 16.4 4.90
8300-10 Red Shale, Sandstone 2.40 14.6 6.50
8400-10 Red Shale, Sandstone 2.31 16.4 5.52
8500-10 Red Shale, Sandstone 2.42 15.5 4.96
8600-10 Red Shale, Sandstone 2.41 13.5 6.25
8700-10 Red Shale, Sandstone 2.34 16.0 5.02
8800-10 Red Shale, Sandstone 2.36 15.4 4.71
8900-10 Red Shale, Sandstone 3.21 14.4 5.04
9000-10 Red Shale, Sandstone 2.45 13.4 4.65
9100-10 Red Shale, Sandstone 2.46 12,4 4.62
9200-10 Rod Shale, Sandstone 2.45 12.5 4.89
9309-10 Red Shale, Sandstone 2.44 12.2 4.64
9400-10 Red Shale, Sandstone 2.37 16.1 4.65
9500-10 Red Shale, Sandstone 2.44 13.1 4.78
9600-10 Rod Shalo, Sandotone 2.45 11,8 6.19

ERRATA

Bureau of Geology
Special Publication No. 21

Page x Figures 4 21 and Table 1 listings omitted. They are as follows:

Page

4. West-east geologic section through southern Florida
and the Bahamas from the Gulf of Mexico to the Atlantic
Ocean .......................................................... 10

5. Depth of strong salt-water flows reported in oil
exploration wells ........................................... 11

6. Index map showing locations of oil exploratory wells
that provide data for this report ........................... 12

7. Stereo photograph of Boulder Zone caverns and fractures
taken at 2,442 feet below land surface in Red Cattle 32-2 ... 13

8. Location of deep injection and desalination production
sites showing year of installation, type of waste or
use, and approximate depth of well .......................... 15

9. Idealized section through Miami showing concept of cyclic
flow of seawater induced by geothermal heating ............... 17

10. Graph showing temperature profiles in oil-exploratory
and waste-disposal wells .................................... 18

11. Map showing geographic distribution of temperature
related to depth near the bottom of the Floridan Aquifer
system (Boulder Zone) ..................................... 20

12. Photograph of natural flow from Humble-Lowndes-Treadwell
No. 1 ....................................................... 21

13. Photograph of natural flow from Humble-Lowndes-Treadwell
No. 1 after development into a warm-spring spa in 1967 ...... 22

14. Oblique aerial photograph of Warm Mineral Springs sink-
hole, a commercially developed spa .......................... 23

15. Underwater photograph of cave cross section through which
discharge was measured by using fluorescein dye as a
tracer ....................................................... 24

16. Photograph of surface slick produced by upwelling of warm
seawater at the Mud Hole submarine spring, October 26,
1972 .............. ...................................... ... 26

17. Photograph of one of the orifices in the sink-like depres-
sion of the Mud Hole submarine spring ....................... 27

18. Map showing section line and locations of wells used in
Figure 19 and 20 ............................................ 30

19. (a) Temperature distribution in the Floridan Aquifer
system ................... ............................. 31
(b) Theoretical field isotherms for variables Nc=10,
i~=3, NT=I (After Henry and Hilleke, 1972, Fig. 28,
for aquifer 167 miles long and 2,500 feet thick) ...... 31

20. (a) Chloride distribution in the Floridan Aquifer
system .............................................. .. 32
(b) Theoretical field isochlors for variables Nc=10,
NO=3, NT=I (After Henry and Hilleke, 1972, Fig. 26,
for aquifer 167 miles long and 2,500 feet thick) ...... 32

21. Theoretical streamlines for variables Nc=10, N(=3,
NT=1 (After Henry and Hilleke, 1972, Fig. 27, for aquifer
167 miles long and 2,500 feet thick) ....................... 33

Tables

1. Geologic and hydrologic characteristics near Forty
Mile Bend ..................... ............................ 8

SPECIAL PUBLICATION NO. 21

Table 4 (con'd.)

LITHOLOGY

DEPTHiI
(ft.)

9700-10
98300-10
9900-10
10000-10
10100-10
10200-.10
10319.5
10400-10
10500-10

DL"JSSITTYPOO Y COITDUCTIVITY
(c/cc) (0) (mcal/cm socoC)

2.40
2,o0
2.37

2.37
2.39
2.40
2.41
2.4-1

Weighted mean

9.7 13.07
12.6 9.34
12.2 8.97
10.1 8.63
13.0 9.49
9.5 8.89
10.7 14.4
12.5 9.43
12.8 9.04
conductivity = 4.62

Table 5. o)epth, litholo0y, bulk density, porosity, and thermal
conductivity of rock samples from Humble Oil Company -
No. 1 State Lease 1004, Palm Beach County, Florida.

LITHOLOGY

Dolomite, Anhydrite
Dolomite, Anhydrito
Dolomite, Anhydrite
Dolomite, Anhydrite
Dolomite, Anhydrite
Dolomite, Anhydrito
Dolomite, Anhydrite
Dolomite
Dolomite
Dolomite
Dolomite
Dolomite
Dolomite, Anhydrite
Dolomite, Anhydrito
Dolomite, Anhydrite
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone, Dolomite
Limestono, Dolomite
Limestone, Dolomite
Limestone
Limestone, Dolomite
Limestone, Dolomite
Limestone
Limestone
Limestone
Limestone

DENSITY POROSITY COIDUCTIVITY
(e/co) (%) (meal/cm secC)

2.59
2.31
2.41
1.98
2.94
2.07
2.50
1.97
2.15
2.38
2.16
2.10
2.32
2.28
2.26
2.31

1.80
2.14
2.12
2.37
2.24
2.20
2.04
2.11
2.21
2.26
2.00
2.02
1.97

12.1
20,2
13.9
10.3
8.2
40.8
15.1
28.1
25.2
14.9
23.8
27.6
22.4
21.0
5.5
18.1
21.0
49.9
30.5
35.0
15.4
19.0
17.3
21.2
21.3
20.7
17.3
26.2
25.5
28.8

5.48
4.08
4.69
5.33
6.28
2.95
4.60
3.25
3.38
4.09
3.47
3.27
3.71
3.73
5.20
3.02
2.81
2.00
2.37
2.22
3.62
3.36
3.29
2.80
3.07
3.05
3.07
2.53
2.55
2.42

Shaleo, Sandstono
Shale, Sandstone
Shale, Sand Otone
Shale, Sandl tonoi
Sha lo, Sand ctone
Shale, Sandstone
Sandstone
Shale, Sandstone
Shale, Sandstone

Red
Rod
Rod
Rod

Red

Red
Rod

DEPTH
(ft.)

4650-80
4740-70
4830-60
4920-50
5000-30
5090-20
5180-10
5240-50
5300-01
5350-51
5400-01
5450-51
5510-40
5600-30
5690-20
5780-1o
5870-00
5960-20
6050-80
6140-70
6230-60
6320-50
6410-40
6500-30
6590-20
6680-10
6770-00
6860-90
6950-80
7040-70

59

BUREAU OF GEOLOGY

Table 5 (con'd.)

DEPTH'
(ft.)
7130-60
7220-50
7310-40
7400-30
7490-20
7580-10
7670-00
7760-90
7850-80
7940-70
8030-60
8120-50
8210-40
8300-30

8390-20
8480-10
8570-00
8660-90
8750-80
8840-70
8930-60
9020-50
9110-40
9200-30
9300-01
9350-51
9400-01
9450-54
9500-01
9550-51
9600-01
9668-69
9700-01
9750-51
9800-01
9850-51
9900-30
9990-20
10080-10
10170-00
10260-90
10350-80
10440-70
10530-60
10620-50
10710-40

10800-30

Dolomite,
Dolomite,
Dolomite,
Dolomite,
Dolomite,
Dolomite,
Dolomite,
Dolomite,
Dolomite,

Anhydrite
Limestone
Anhydrito
Anhydrite
Limestone
Anhydrite
Limestone
Limestone
Limestone,

Anhydrite
Dolomite, Limestone,
Anhydrite

LITHOLOGY

Limestone, Dolomite
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone

Lime tone
Limostono
Limestone, Dolomite
Limostoone, Dolomite
Anhydrite
Dolomite, lAnhydrite
Limestone, Dolomite
Dolomite, Limestone
Dolomite, Anhydrito
Dolomite, Anhydrito,
Dolomite
Dolomite, Anhydrito
Dolomite, Anhydriite
Anhydrite
Dolomite, Anhydrite
Dolomite
Dolomite
Dolomite
Anhydrite
Dolomite
Dolomite
Limestone
Dolomite
Dolomite
Dolomite
Limestone
Limestone
Limestone

DE7iSITY

2.05
2.22
2.18
2.08
2.25
2.16
2.13
2.10
2.25
2.16
2.00
2.21
2.3*3
2.39

2.30
2.33
2.26
2.28
2,62
2.18
2.64
2,42
2.68
2.50
2.05
2.41
2.17
2.92
2.40
2.30
2.06
2.36
2.14
2,01
2.22
2.50
2.45
2.69
1.91
2.45
2.34
2.41
1.80
2.24
2.12
2.50

2.41

POTOSITY

25.9
19.9
21.8
23.4
20.8
21.4
20.1
22.4
17.6
19.4
25.2
18.4
17.4
16.0

43.8
15.0
21.4
20.1
10.7
18.3
9.6
19.3
12.8
14.2
28.6
13.9
31.4
.1.1
12.4
20.1
26.6
16.2
20.8
28.9
19.0
7.8
9.6
8.1
11.2
11.7
18.0
16.5
18.1
20.4
21.2
11.8

15.6

COITDUCTIVITY
(mcal/cm sooC)
2.95
2.88
2.88
2.67
2.83
2.78
2.87
2.55
3.05
2.92
2.57
3.00
3.37
3.58

2.93
3.48
3.36
4.12
5.72
3.84
5.94
4.85
6.00
4.39
3.22
4.16
3.08
7.83
4.31
3.70
2.97
4.00
3.67
3.19
3.72
4.60
4.42
6.01
4.39
4.63
3.99
3.85
3.97
3.32
3.61
4.47

4.02

60

SPECIAL PUBLICATION NO. 21

Table 5 (con'd.)

DESIT' Y POROSITY COlNDUCTIVITY
(c/co) () (mral/cm seccC)

10890-20

10980-10
11070-00

11160-90

11250-80
11340-70
11450-51
11500-01
11551-52
11600-01
11655-80
11740-70
11830-60
11920-40
12000-01
12030-93
12149-60
12200-01
12244-53
12300-12
12350-51
12400-01
12450-51
12500-01
12550-51
12590-20
12680-10
12770-00

Dolomite, Limestone,
Anhydrito
Dolomite, Limestone
Dolomite, Limestone,
Anhydrito
Dolomite, Limrestone,
Anhydrito
Limeostone, Anhydrito
Limos tone, Anhydrite
Limestone
Limcstono 0
Lime stone
Limestone
Limestone, Anhydrite
Limestone, Anhydrito
Limestone, Anhydrite
Limestone, Anhydrite
Dolomite, Anhydrcit e
Dolomite, Anhydrait Anhbydrite
Lime stone
Limestone
Anhydrit o
Anhydrito
Dolomite
Dolomito
Limestone
Limestone
Limestone
Limestone
Limestone

Weighted mean

2.42

2.33
2.39

2.60

2.50
2.35
2.63
2.15
2.21
2.65
2.52
2.38
2.40
2.46
2.68
2.83
2.97
2.48
2.40
2.88
2.72
2.62
2.27
2.44
2.62
2.30
2.29
2.31

LITHOLOGY

15.4

18.1
15.4

8.4

9.3
14.9
4.1
20.6
19.0
3.3
10.8
10.1
15.1
13.7
7.7
2.2
0.00
12.2
15.1
3.2
4.0
20.6
14.9
10.1
2.6
14.4
14.9
15.8
conductivity

4.35

3.81
4.19

4.96

5.38
4.10
4.89
3.36
3.50
4.98
5.42
4.56
4.39
5.31
4.99
6.92
8.15
3.49
3.25
0.81
7.19
3.68
4.09
3.68
5.62
4.03
4.01
3.97
= 3.95

61

62

BUREAU OF GEOLOGY

Table 6 -- Depth, lithology, and thermal conductivity of samples from Commonwealth
-- No. 1 Wisehart State Board of Education.

Gross Lithology

Conductivity
(10-3cal/cm secC)

Depth
(ft)

6085
6112
6148
6151
6156
6166
9195
9204
9208
9212
9260
9288
9290
9309
9321
9329
9820
9854
9872
9886
10,798
10,808
11,315
11,327
11,369
11,378
11,380
11,382
11,432
11,447
11,496
11,527
11,536

Note: Values in parentheses were based on inferior samples or mixed lithologies
and were not included in averages or heat flow calculations.

Limestone and dolomite (3.12)
Limestone 3.00
Limestone 2.90
Dolomite 5.10
Dolomite and anhydrite (3.50)
Limestone 3.00
Anhydrite 5.20
Dolomite 3.91
Dolomite 4.21
Anhydrite 5.28
Dolomite 4.23
Anhydrite 6.20
Dolomite 6.10
Limestone 4.53
Dolomite 4.38
Limestone 4.17
Limestone (4.90)
Anhydrite and dolomite (4.85)
Limestone 3.50
Limestone 3.56
Limestone 3.96
Limestone 3.60
Anhydrite and dolomite (4.87)
Limestone 3.23
Limestone 3.38
Limestone 3.17
Argillaceous limestone (3.15)
Limestone 3.35
Argillaceous limestone 3.26
Argillaceous limestone (2.74)
Argillaceous limestone (2.8 )
Anhydrite (4.5)
Anhydrite 5.6
Weighted mean conductivity 4.26

SPECIAL PUBLICATION NO. 21

REFERENCES
Beck, A., 1957, A steady state method for the rapid measurement of the thermal
conductivity of rocks: Jour. of Scientific Instruments, v. 34, p. 186-189.
Bullard, E. C., (Maxwell, A. E., and Revelle, R.), 1956, Heat flow through the
deep sea floor: in Landsberg, H. E. (ed.) Advances in Geophysics, v. 3,
p. 153-181.
Dietz, R. S., (Holden, J. C., and Sproll, W.P.), 1970, Geotectonic evolution and
subsidence of Bahama platform: Geol. Soc. American Bull., v. 81, p. 1915-
1927.
Diment, W. H. (and Robertson, E. C.), 1963, Temperature, thermal conduc-
tivity and heat flow in a drilled hole near Oak Ridge, Tennessee: Jour. of
Geophys. Research, v. 68, n. 17, p. 5035-5047.
Epp, David, (Grim, P. J. and Langseth, M. J., Jr.) Heat flow in the Caribbean
and Gulf of Mexico: Jour. of Geophys. Research, v. 75, p. 5655-5669.
Griffin, G. M., (Tedrick, P. A., Reel, D. A., and Manker, J. P.), 1969, Geo-
thermal gradients in Florida and Southern Georgia: Trans. Gulf Coast
Assn. Geologic Societies: v. 19, p. 189-193.
Khudoley, K. M., 1967, Principal features of Cuban geology: American Assoc.
Petroleum Geologists Bull., v. 51, p. 668-677.
Langseth, M. G. (and Grim, P. J.), 1964, New heat-flow measurements in the
Caribbean and western Atlantic: Jour. Geophys. Research, v. 69, p. 4916-
4917.
Lee, W. H. K. (and Uyeda, Seiya), 1965, Review of heat flow data: in Terres-
trial Heat Flow, Geophys. Monograph 8, American Geophysical Union,
ed. by W. H. K. Lee, p. 87-190.
Ratcliffe, E. H., 1960, The thermal conductivities of ocean sediments: Jour. of
Geophys. Research, v. 65, n. 5, p. 1535-1541.
Reel, D. A., 1970, Geothermal gradients and heat flow in Florida: unpublished
thesis, University of South Florida, Tampa, FL., 66p.
(and Griffin, G. M.), 1971, Potentially petroliferous trends in Florida
as defined by geothermal gradients: Trans Gulf Coast Assn. Geologic
Societies: v. 21, p. 31-36.
Roy, R. F., (Blackwell, D. D., and Birch, Francis), 1968, Heat generation of
plutnoic rocks and continental heat flow provinces: Earth and Planetary
Sci. Letters: v. 5, p. 1-12.
Sheridon, R. E., 1971, Geotectonic evolution and subsidence of Bahama plat-
form: Discussion: Geol. Soc. America Bull., v. 82, p. 807-809.
Smith, D. L. (and Fuller, W. R.), 1976, Terrestrial heat flow values in Florida
and the thermal effects of the aquifer system: this volume.
Uchupi, E., (Milliman, J. D., Luyendyk, B. P., Bowin, C. 0., and Emery, K.
0.), 1971, Structure and origin of southeastern Bahamas: American As-
soc. Petroleum Geologists Bull. v. 55, p. 687-704.
Woodside, W. (and Messmer, J. H.), 1961, Thermal conductivity of porous
media, II: Consolidated rocks: Jour. Applied Physics, v. 32, n. 9, p. 1699-
1706.
Zierfuss, H., 1969, Heat conductivity of some carbonate rocks and clayey sand-
stones: American Assoc. Petroleum Geologists Bull., v. 53, n. 2, p. 251-260.

SPATIAL DISTRIBUTION
OF
GROUND WATER TEMPERATURE
IN
SOUTH FLORIDA

BY

C. R. SPROUL1

'Black, Crow, and Eidsness Inc.
Gainesville, Florida 32602

CONTENTS
Abstract ......................................................... 67
Introduction ........................................ ........... 68
Hydrologic Setting ........................................... 69
Previous Studies .............................................. 73
Sources of Data .............................................. 74
Regional Temperature Distribution .................................. 74
Temperature Anomalies ............................................ 76
Local Anom alies .............................................. 77
Lee County .............................................. 78
McGregor Isles (Lee County) .............................. 80
Charlotte County "Hot Springs" ............................ 80
Martin County "Hot Well" ................................. 84
Peace River Valley ........................................ 86
East Coast Cooling Anomaly .................................... 86
References ..................................................... 89

ILLUSTRATIONS
Figure Page
1 Area of Study ............................................. 69
2 Elevation (in feet) of top of Floridan Aquifer ................ 71
3 Potentiom etric Surface ...................................... 72
4 Regional ground-water temperature .......................... 75
5 Map of Lee County showing the location of the McGregor Isles
area (from Sproul et al., 1972) .............................. 81
6 Map showing the effects of intrusion on water temperatures in
the lower Hawthorn aquifer (Sproul et al., 1972) .............. 82
7 Map of McGregor Isles showing the extent of saline-water intrusion
into the lower Hawthorn aquifer (Sproul et al., 1972) .......... 83
8 Temperature of water in artesian wells in Martin County ....... 85
9 Drilling and water quality data from a deep well at Stuart,
M artin County .......................................... 88
Tables
1 Well inventory data ........................................ 79

ABSTRACT
The Florida Aquifer in southern Florida is comprised of a thick
section of generally southward-dipping Tertiary (pre-Miocene) car-
bonates. The aquifer is layered, having in most places several distinct
water-producing zones. The producing zones are separated by less
permeable limestone and dolostone. Water in the aquifer is confined
under artesian pressure by younger Tertiary clastics.
Ground-water temperatures measured at the well frequently show
poor correlation with well depth, usually because of local variations
in the relative contribution of each producing zone penetrated. How-
ever, review of existing literature, and examination of a large amount
of ground-water temperature data, show some distinctly anomalous
distributions in ground-water temperature. Some of these anomalies
appear to be related to upwelling of warmer, highly mineralized water
along fracture systems.
A cooling anomaly along the east coast has been attributed to
the cooling effect of the deep bottom water offshore in the Atlantic
Ocean. Cooling by conduction and by cyclic inland flow of the cold
sea water have been suggested as mechanisms for the cooling effect.

BUREAU OF GEOLOGY

INTRODUCTION
At depths of 100 feet or so below the earth's surface, the tempera-
ture is not affected by seasonal variations of insolation. Below this
depth, the temperature of the rocks and contained water remains
nearly constant. The temperature is controlled by the relatively
constant flow of geothermal heat from the earth's interior, modified
by circulation of ground water, thermal properties of the rocks and
contained water, and volcanic and tectonic activity.
The temperature of ground water normally increases at a rate of
1 F per 50 to 150 feet of depth. The actual rate of increase is con-
trolled by the rate of geothermal heat flow and other factors, listed
above. In an artesian system in which the water is moving down-
gradient, at progressively greater depth, the temperature would be
expected to increase at a regular and constant rate. Any perturba-
tions in the rate of temperature increase or distribution of ground-
water temperature in this situation should be useful in interpreting
some of the flow characteristics of the aquifer.
This paper presents a synopsis of ground-water temperature data
and known temperature anomalies in the principal artesian aquifer
in south Florida.

68

SPECIAL PUBLICATION NO. 21

HYDROLOGIC SETTING
The area of study, shown in Figure 1, is approximately the
southern one-third of peninsular Florida. The dominant aquifer
system in this area is the Floridan Aquifer, a regional artesian system
which underlies all of Florida and adjacent parts of neighboring
states.

SSTUDY AREA

0

Figure 1. Area of Study

69

BUREAU OF GEOLOGY

The Floridan Aquifer in this area is comprised of 1,000 to 3,000
feet of southeast to southwest dipping Tertiary limestone and dolo-
stone. The elevation of the top of the Floridan Aquifer is shown on
Figure 2. The aquifer is layered, having in most places three or more
distinct zones of relatively high transmissivity, separated from one
another by relatively impermeable limestone or dolostone. It is over-
lain by several hundred feet of relatively impermeable clastics, also
mostly of Tertiary age, which confine the water under artesian
pressure.
Younger Tertiary and Neogene limestones and sands overlie the
confining beds of the Floridan Aquifer. These shallow strata produce
a second aquifer system that furnishes the potable fresh ground
water for much of south Florida.
Some recharge of the Floridan Aquifer occurs in the north central
part of the study area; however, the principal recharge area lies
further to the north, in the ridge area of central Florida. The ground-
water flow regime in the aquifer is dominated by a large potentio-
metric high situated in central Florida, as shown on Figure 3. Ground-
water flow is generally southward and toward both coasts. Discharge
from the aquifer is through springs, both onshore and offshore at
the submarine outcrop of the Tertiary limestones, and through a
large number of wells.
Over most of the study area, the artesian water is too highly
mineralized for direct use as a potable water source. Present use is
primarily for irrigation. Potential future uses of the aquifer, in which
interest is rapidly increasing, are: cooling, production of potable fresh
water by desalination, as a reservoir for the storage and recovery
of fresh water, and as a receptacle for liquid wastes.
In order to properly manage the resource and to accommodate
these sometimes conflicting uses, ground-water flow patterns within
the aquifer must be defined and understood. It seems clear that a
study of the geothermal regime in the aquifer will contribute signifi-
cantly to our understanding of these flow patterns.
Some of the regional geothermal features and local temperature
anomalies described herein have been studied in some detail, and
well-founded hypotheses can be proposed to account for them. In
other cases there is little factual data available, and the hypotheses
offered are quite tentative.

SPECIAL PUBLICATION NO. 21

0

Co

-800

(Modified from Vernon, 1973)

Figure 2. Elevation (in feet) of top of Floridan Aquifier

71

BUREAU OF GEOLOGY

S T E OL

ORAN

0

C320
TEE HAIGH ANDS

OK CHOBEE

Lake

CHARLOTTE GLADES Okeechobeg

LE HENDRY

COLLIE R

cs-

Figure 3. Potentiometric Surface

SPECIAL PUBLICATION NO. 21

PREVIOUS STUDIES
Over the past 30 years or so, geologists and hydrologists noted
the occurrence of seemingly anomalous ground-water temperatures
in the Floridan Aquifer in south Florida. Because the temperature
extremes reported (approximately 680 F to 910 F) had little bearing
on potential uses of the water, little attention was given to the ex-
planation of these anomalies. Many of the temperature data exist
only in unpublished form, as field notes and well inventory records.
Among the writers who have commented on the anomalies:
Lichtler (1960, p. 61-63) noted both hot and cool anomalies in
Martin County. He postulated that the cool temperatures in the
eastern (coastal) part of the area might be due to a cooling effect of
the nearby Atlantic Ocean, and that higher temperatures inland
might be due to radioactivity of the water.
Stringfield (1966, p. 152-153) noted temperature anomalies in
several areas of south Florida. Stringfield attributed most of them
to differences in the depth at which water entered the wells. He also
mentioned the possible cooling effect of sea bottom temperature at
the submarine outcrop of the aquifer as an explanation for low
artesian water temperatures along the coast in Dade County.
Kohout (1965, p. 249-271) described a regional cool temperature
anomaly in south Florida and presented a hypothesis as to its origin.
In Kohout's paper, it was first suggested that ground-water tempera-
tures might have significant implications with regard to ground-water
circulation patterns in the Floridan Aquifer. In his initial work, and
in a subsequent paper on the same subject (Kohout, 1967, p. 339-
354), he hypothesized a cyclic flow of water in the aquifer produced
by convection. According to this hypothesis, salt water moving inland
from the submarine outcrop of the aquifer becomes less dense due to
geothermal heating, rises, mixes with fresher water at a shallower
depth, and flows down-gradient to discharge.
Kaufman and Dion (1967) described a linear ground-water tem-
perature anomaly generally paralleling the Peace River in Hardee
and DeSoto counties. They suggest that this anomaly may be due to
the upcoming of deep artesian water along a fracture.
Sproul et al. (1972) described a high temperature anomaly in
Lee County which is associated with a fracture of fault system.
Upward migration of warmer and more mineralized water along an
open fracture is suggested.

BUREAU OF GEOLOGY

SOURCES OF DATA
The majority of the ground-water temperature data used in this
paper was obtained during an inventory of artesian wells in south
Florida conducted by the Florida Bureau of Geology between 1956
and 1971. Records of approximately 5,000 Floridan aquifer wells
were obtained during that period. The principle objective of the in-
ventory was to obtain data on the numbers and locations of uncon-
trolled flowing artesian wells. In the course of the inventory a sub-
stantial body of hydrologic data, including ground-water tempera-
ture, was accumulated.
Data collected during the inventory included, whenever possible:
location, depth, and sizes of wells; depth of casings; and use, yield,
artesian pressure, temperature, and chloride content of the water.
Inventory records were subsequently computerized to facilitate re-
trieval of the data.
Other sources of temperature data cited in this paper are pub-
lished reports of the U.S. Geological Survey and the Florida Depart-
ment of Natural Resources, Bureau of Geology, unpublished reports
and materials from the files of various state agencies, and data col-
lected by the writer in the course of hydrological investigations.

REGIONAL TEMPERATURE DISTRIBUTION
Ground-water temperature in the upper few hundred feet of the
Floridan Aquifer is shown on Figure 4. This regional temperature map
was constructed by plotting available ground-water temperature
data on a map at a scale of 1 inch = 10 miles and drawing isothermal
contours at a 50 F contour interval.
The density of temperature data points ranges from an average
of about 3 per township (36 square miles) in the northwestern two-
thirds of the area to only 3 or 4 per county in the southeastern one-
third (Palm Beach, Broward, Dade, Monroe, and Collier counties).
Only data whose reliability could be reasonably established was
used in the construction of Figure 4. For the present purpose, a data
point was considered reliable if the well depth was known to within
about 100 feet, and if the well had been flowing or pumped long
enough for the water temperature to stabilize. Practically all of the
wells used were drilled for water supply, predominantly for irrigation
water. The usual well construction practice in the area is to set steel
casing into the first competent rock and then continue drilling open
hole, penetrating a succession of permeable zones, until the desired
well yield is reached. In south Florida, at least one very prolific water
producing zone is usually penetrated between 200 and 500 feet below
the top of the aquifer, and this frequently determined the final depth

SPECIAL PUBLICATION NO. 21

0

EXPLANATION
Range of temperature in the
upper part of the Floridan
aquifer (oF)
E < 70
S700- 750
750-800
80 850
> 850

MONROE

(Modified from Vernon, 1973)

Figure 4. Regional groundwater temperature

75

BUREAU OF GEOLOGY

of the well. Therefore, the temperatures shown on the regional ground-
water temperature map are representative of a range of depths and
of several different producing zones in the aquifer.
Ground-water temperature data in the area shows a fairly large
amount of scatter, for reasons described above. Consequently, the
contours on Figure 4 are highly generalized.
Ground-water temperatures are relatively low (700 to 750 F) in
the north-central part of the study area, corresponding to the
southern edge of the recharge area of the aquifer. Temperatures in-
crease downdip, and in the direction of ground-water flow toward
the west, southwest, and southeast. The expected gradual, regular,
downgradient temperature increase is interrupted on the west by a
band of above-normal ground-water temperatures generally parallel-
ing the Peace River in Hardee and DeSoto counties. To the south-
east, the normally expected downgradient temperature increase is
interrupted by a reversal in gradient with temperatures decreasing
downgradient.
The lowest ground-water temperatures in the area occur along
the southeast coast, where a temperature of 690 F was recorded in
a 980-foot well at Miami Beach. In this same area, a bottom tempera-
ture of 59 F was recorded in a 3,100-foot well at Margate in Broward
County.
The highest ground-water temperatures mapped on Figure 4
are in the mid-80's and occur along the west coast from Fort Myers
to Punta Gorda, and up the Peace River Valley nearly into Hardee
County. Higher ground-water temperatures occur in several areas
which are too small to be shown on the regional map. Some of the
highest recorded ground-water temperatures, excluding those re-
corded in oil wells, are: 960 F in a 1,640-foot well near Punta Gorda,
930 F in a 710-foot well near Fort Myers, and 910 F in an 843-foot
well about 15 miles west of Stuart in Martin County.

TEMPERATURE ANOMALIES
It is apparent from Figure 4 that there are substantial deviations
from the expected distribution of ground-water temperatures in the
Floridan Aquifer. Examination of the well inventory data referenced
earlier reveals other cases of anomalous temperatures in certain
areas too small to be depicted on the regional map. Other references
to apparently anomalous ground-water temperatures are contained in
various published reports.
Ground-water temperature anomalies in south Florida may be
grouped into three major categories, as follows:

SPECIAL PUBLICATION NO. 21

1. Definite local temperature anomalies, or "hot spots," ranging
in size from a single well or small group of wells up to areas
of a few square miles, occur where ground-water temperatures
are about 5 to 10 degrees F higher than adjacent areas.
2. A region of above-normal temperatures occurs in a narrow
band paralleling the Peace River in DeSoto and Hardee coun-
ties. Temperatures in this region are generally 3 to 5 degrees F
higher than in adjacent areas.
3. A low temperature anomaly is present along the east coast
in which ground-water temperature decreases downgradient
and with increasing depth in the aquifer.
The latter described cooling anomaly along the east coast, in
which both lateral and vertical temperature distribution is the re-
verse of the normal distribution, is the most striking feature of the
ground-water temperature regime in peninsular Florida. This cooling
anomaly, along with the "hot spots," is probably also the most
significant of the above features with respect to implications regard-
ing ground-water circulation patterns.

LOCAL ANOMALIES
As used in this report, the term "hot well" or "hot spot" refers
to an individual well or a small area wherein the ground-water tem-
perature is abnormally high for that area. This definition excludes
cases in which the high temperature can be attributed to well depth
alone or to local permeability changes within the aquifer.
Most of the data on ground-water temperature in south Florida
are measurements taken at the well mouth of either flowing or
pumped wells. As such, the temperatures measured represent a
composite of the temperature in all producing zones penetrated by a
well. Since ground-water temperature generally increases with well
depth, a reasonable correlation would be expected between well
depth and temperature, at least for small areas. However, in most of
the area of this report, this correlation is very poor, making the
delineation of actual anomalies difficult.
Most wells penetrate several producing zones in the artesian
aquifer. Since permeability in limestone aquifers is typically some-
what randomly distributed within each producing zone, wells in
the same area and of the same depth may derive the majority of
their flows from different depths. Thus, temperatures measured at
the well mouths would be different but would not be reflecting a
geothermal anomaly. Apparent "hot spots" may also occur where
permeability in the upper part of the aquifer is locally poorly de-
veloped. Wells in such areas will, as a group, produce water having

BUREAU OF GEOLOGY

a higher temperature than identically-constructed wells in surround-
ing areas.
High-temperature anomalies which are "real," as opposed to
those produced by local permeability changes, have been identified
in several areas of south Florida. Almost all are thought to be due
to upwelling of artesian water from deep sources feeding a shallower
aquifer zone. Most, but not all, high-temperature anomalies are
associated with high chlorides in the ground water, another indication
of the deep source of the warmer water.
So far as is known, none of the ground-water temperature anoma-
lies reflect a geothermal heat flow anomaly.
A discussion of specific "hot wells" and "hot spots" which have
been investigated by the writer and others follows.

LEE COUNTY
Table 1 is a tabulation of well data for one township (36 square
miles) in western Lee County. This tabulation demonstrates at once
the mass of data available and the difficulties involved in identifying
real versus apparent anomalies.
Well 5 in the table, 1,045 feet deep, temperature 800 F, is less
than 1,000 feet from well 6 of almost the same depth (919 feet) pro-
ducing water at 860 F. Well 6 appears anomalous on the basis of its
temperature alone, when compared with temperature in other wells
in the area. Its chloride content, however, is not unusual for wells of
this depth in the area. The geothermal gradient in the area is about
1 F per 70 feet of depth (Sproul et al., 1972, p. 16). Thus, if well
5 produces most of its water from near the top of the aquifer (400 to
500 feet) and well 6 produces mostly from the bottom (800 to 900
feet) both wells could reflect normal ground-water temperatures
for the area.
Well 19 also has a higher temperature than most wells in the
area, though not as high as in well 6. However, the chloride content
in well 19 is clearly higher than normal. Since this well is not unusual-
ly deep, it is highly likely that a communication is present between
the upper part of the Floridan aquifer and a deeper saline aquifer
in the vicinity of well 19.
Further investigations to confirm this hypothesis cannot be un-
dertaken, since the wells involved are reported to be plugged with
cement.

SPECIAL PUBLICATION NO. 21

TABLE 1

WELL INVENTORY DATA
Township 44 South, Range 23 East, Lee County, Florida

Well Location Depth of Depth of Chloride Temp.
No. Sec. Twp. Rge. Well, ft Casing, ft mg/l F

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36

37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64

SE SE 1
NE SE 1
SE SE 2
SE SE 3
NE NE 3
SW NE 3
SE NE 3
SE NE 3
NE NW 6
SW NE 6
NE SE 6
NW NE 6
SE NE 7
SW SE 8
NE SE 9
NE SE 10
NW NE 11
NW NE 11
SE NE 11
NE NE 11
NE SW 12
NE SW 12
NE NW 13
NE NW 13
NW SE 13
NW NE 13
SE NE 13
SW SW 14
NW NW 15
SE NW 15
SW NE 15
SE SW 15
SW SE 16
SW SE 15
SE SE 15
NE SE 15

SW NW 17
SW NW 17
SW SW 17
SW SE 17
NW SE 18
NW NW 19
SE NE 19
NE SW 19
NE SE 20
NE NE 21
NE SW 21
SE SW 21
NE NW 22
SE NE 22
NW NE 23
NW SE 24
NW NE 25
SW SW 25
NE NW 27
NW NW 27
SW NW 27
NE NW 28
SE NW 28
SW SE 32
SE SE 32
NE SW 33
SW SW 33
SE SE 36

44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S

44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S
44S

23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E

23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E
23E

619
1,001
706
511
1,045
919
642
510

832
468
601

800

515
835
857

512
585

300
700
815

225

683
800
790
796

468

390
978

1,000

700
700

660

808
590
1,000
1,000
157
444
630

1,000
----
--_
----

133
157
143
155
159
137
157
155

122
128
156

164
162
170

117
151

156
132

159

163

126

117

70

133
177

42
112
__
__

-__
__
__
__
-__
--_
--_
_-_

1,000

655

880
980
640
900
900
900
840

960
940
---
-_

820
670
2,380

670
740

720
240

540
84
660

600
640

1,200
620
--_
-_
-_
780
640
640
360
480
600
220
800
520
--_

880
560
---
--_

560
240
620
600
600
560
600
1,000

79

83

83

80
86
84
83
82
80
82
-_

78
__
83
77
82
82
85
__

82
80
--
80
78
__
__
82
81
80
82
82
__
84
83
__

81
76
-_

83
77
82
84
79
79
81
74
83
82
__
--

85
84
__
__

81
74
78
79
79
78
78
__

BUREAU OF GEOLOGY

McGREGOR ISLES (LEE COUNTY)
An investigation by Sproul et al. (1972) of a group of high-
salinity wells south of Fort Myers led to the delineation of a "hot
spot" in this area. The location of the area is shown on Figure 5.
Normal ground-water temperature in the surrounding area ranges
from 81 F to 83 F in wells 500 to 700 feet deep. The highest
temperature measured in the anomalous area was 930 F in a 710-foot
well.
The "hot spot" encompasses about two square miles. Within
this area, 25 wells exhibiting abnormal temperature and water quality
characteristics were found. Data from an intensive geophysical log-
ging program suggests that the anomaly is associated with a series
of faults, as shown on Figures 6 and 7. Other later data (Boggess,
personal commun., 1975) suggests that the structurally high area is
an anticline rather than a faulted structure.
Whether or not faulting is involved, it appears certain that this
thermal anomaly is produced by warm, salty water from a deep
artesian aquifer invading a shallower brackish aquifer. The hypo-
thesis best fitting the observed data is that a conduit is present near
the center of Section 16, Township 45 South, Range 24 East, con-
necting the deep aquifer with shallower aquifers. The shape of the
body of intruding warm water (Figure 6) suggests that the conduit
may be developed along complementary components of a fracture
system. The pattern exhibited by the spread of high-chloride water
(Figure 7) is even more suggestive of fault or fracture acting as a
line source of intruding saline water.
The conduit most probably is a zone of increased permeability
produced by solution along a fault or fracture plane at a time when
the base level of solution was much lower than at present. The
depth to which the conduit extends is estimated to be 1,600 to
1,700 feet, on the basis of ground-water temperatures. The intrusion
of warmer water was probably initiated by heavy withdrawals of
irrigation water from the Floridan Aquifer in the area.

CHARLOTTE COUNTY "HOT SPRINGS"
A deep well in Charlotte County has been flowing salt water at a
temperature of 960 F for many years. The location of this well, which
was once the subject of a commercial development as a spa, "Hot
Springs of Florida," is shown on Figure 5.
Since this well is at least 90 F warmer than any other well in the
vicinity, it might be considered a likely candidate as an anomalous
"hot well." However, geophysical logging of this well shows it to be
1,640 feet deep. The well terminated in a large solution cavity from

SPECIAL PUBLICATION NO. 21

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LEE COUNTY
LOCATION MAP

15 Miles

Figure 5. Map of Lee County showing the
area (from Sproul et al., 1972)

location of the McGregor Isles

-~-~--~-~--~-~;---------";--~---1~'----

81

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BUREAU OF GEOLOGY

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Figure 6. Map showing the effects of intrusion on water temperatures in the
lower Hawthorn aquifier (from Sproul et al., 1972)

82

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LLJ

SPECIAL PUBLICATION NO. 21

z
0

z

-J
a-
x
LLU

CL
a)

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a)
0,
E

(3E

EC

o
-o

c J
OC

-0

C'Ilo

C
C
o L
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0- a

(L)
OZ- Q)
a-() -0L
C)L
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Figure 7. Map of McGregor Isles showing the extent of the saline-water in-
trusion into the lower Hawthorn aquifier (from Sproul et al., 1972)

83

BUREAU OF GEOLOGY

which most of the well flow emanates. Records of this well in the files
of the Florida Bureau of Geology indicate that it was abandoned by
the driller due to a large flow of salt water that prevented further
progress.
Most of the other wells in this area are 500 to 600 feet deep and
have a temperature of about 820 F. If a geothermal gradient of 10
F per 70 feet, as determined for the aquifer in Lee County, prevails
here, a 1,640-foot well would be expected to have bottom hole
temperature of about 970 F. The "hot springs well" represents an
unusually deep well for the area, but not an anomalous "hot well."

MARTIN COUNTY "HOT WELL"
An apparently anomalous "hot well" in the northern part of
Martin County is described by Lichtler (1960, p. 62). The location
of this well is shown on Figure 8. The reason for the high tempera-
ture (910 F) in this well has not been established. Lichtler (p. 63)
speculates that radioactivity may be responsible. However, String-
field (1966, p. 152) feels that this is unlikely. An analysis of radio-
active elements in the water from this well, presented in Lichtler's
report (p. 52), does not indicate the presence of any unusual concen-
tration of these elements.
Water from the well does not have, for this area, any apparent
unusual chemical properties such as high chlorides that would indi-
cate a deep source. Nevertheless, its temperature is clearly anomalous.
Normal ground-water temperatures in the area are about 820 F at 500
feet and 850 F at 700 feet, a gradient of 10 F per 67 feet. Even if all
of the well flow came from the bottom of the well (843 feet) the
temperature would be only 870 F.
No investigations have been undertaken to explain the anomalous
temperature in this well. A working hypothesis is suggested as
follows: The well is in close proximity to a vertical conduit con-
necting with a deeper artesian aquifer. If this is the case, the deeper
aquifer contains brackish water similar in quality to the aquifer
zones between 500 and 900 feet. An aquifer zone at a depth of ap-
proximately 1,100 feet would satisfy both temperature and salinity
requirements to fit the criteria of this hypothesis. The "hot well"
may only be the warmest of a group of wells affected by such a
connection with a deeper zone. The latter is suggested by tempera-
tures in surrounding wells, as shown on Figure 8.

SPECIAL PUBLICATION NO. 21 85

\4- .

I
CD 0 S| !r -|
0 -- 1 --- -0
l?, o \ ']

U-) Lc) r- 0
(c) )0)

LoI
L co[ o o oI

c-"0 ) I0
rI-
_D m o 0
Ln00

(a n N0

Figure 8. Temperature of water in artesian wells in Martin County
M o b-Loc0CC

co lEo

Figure) 8t
Q) Q)O

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BUREAU OF GEOLOGY

PEACE RIVER VALLEY
A generally north-south trending area of high ground-water
temperatures was mapped by Kaufman (Kaufman and Dion, 1967)
in DeSoto and Hardee counties. This apparent anomaly follows
generally the valley of the Peace River. Coincident with the thermal
anomaly are trends in several water quality parameters, including
concentrations of total dissolved solids, sulfate, and hardness.
The occurrence of a thermal anomaly in conjunction with highly
mineralized water is consistent with an upwelling of deep artesian
water in this area. Kaufman postulates that the deeper water is
ascending along a linear fracture zone or fault paralleling the Peace
River. A more intensive study of ground-water conditions in the
area (Wilson, 1975) shows the anomalous conditions less sharply
defined than mapped by Kaufman. In his study, Wilson found no
evidence of faulting in the area; likewise, test drilling data across the
area obtained by an electric utility company did not show any
evidence of faulting.
It is suggested here that the thermal anomaly along the Peace
River is due to a combination of the following factors:
1. The area of the apparent anomaly coincides generally with
the area of artesian flow. Thus, the river valley is a ground-
water discharge area with recharge to the aquifer occurring on
the adjacent uplands. This situation results in a temperature
and water quality contrast between the valley and uplands.
2. The upper producing zones of the Floridan Aquifer are less
productive along the Peace River Valley than elsewhere in
these counties. Thus, the average depth to the first major
water-producing zone penetrated by wells in the area is
greater and the temperature of the water higher.
Downhole temperature measurements made by the author in
northeast DeSoto County indicate a vertical temperature gradient of
10 F per 107 feet. If this gradient is applicable to the river valley
area, a temperature between 840 and 85'F would be predicted for a
depth of 800 to 900 feet. These values are consistent with actual
temperatures and well depths in the area.

EAST COAST COOLING ANOMALY
Due to the kinetics of ground-water flow, ground-water tempera-
ture in a confined aquifer normally increases with distance down-
gradient and depth in the aquifer. However, as Figure 4 shows,
ground-water temperatures decrease downgradient along the east
and southeast coast. The downgradient decrease in temperature is
accompanied by a reversed vertical gradient with temperature de-

SPECIAL PUBLICATION NO. 21

creasing with depth.
The cooling anomaly is evident at least as far north as St. Lucie
County and extends down the coast to the upper Keys. The lowest
temperature measured to date has been 590 F in a 3,100-foot deep
well at Margate, near Fort Lauderdale. The lowest temperature
measured in a well in the upper part of the aquifer is 690 F in a
980-foot well at Miami Beach.
At least two hypotheses have been proposed to account for this
cooling anomaly. Early investigators, cited by Stringfield (1966, p.
153), suggested that low temperatures observed in Dade County
were due to cooling of the aquifer water by the cold ocean water
present at the submarine outcrop of the aquifer. Lichtler suggested
the same mechanism to account for a seaward cooling anomaly in
Martin County (see Figure 8). Vernon (1970, p. 13) also cited heat
loss to the cold ocean water as a likely cause of the generally lower
temperatures of ground water along the southeast coast.
A hypothesis involving cyclic convective flow of cold ocean water
has been proposed by Kohout to account for the cooling anomaly.
According to this hypothesis, geothermal heating causes cold ocean
water (430 to 400 F) to move inland along the base of the aquifer,
where it would become warmer and less dense, rise, mix with less
saline water, and flow back toward the ocean.
At present, there is insufficient data to fully support either hy-
pothesis. The cyclic flow mechanism suffers from three principle dif-
ficulties:
1. In order for the cyclic flow proposed by Kohout to occur,
there must be at some depth in the aquifer system a landward
gradient. No such gradient has been measured to date. It
should be noted, however, that most determinations to date
of the potentiometric gradient are rather imprecise.
2. The cyclic flow proposed by Kohout should be accompanied
by an increase in salinity with depth. This seems to be true
in extreme south Florida, but not in Martin and St. Lucie
counties. Figure 9 shows the temperature and chloride con-
tent at different depths in a deep well at Stuart in Martin
County. These data show a reversed temperature gradient ac-
companied by less saline water in the lower part of the
Floridan Aquifer. Obviously, mixing of Floridan Aquifer water
with cold salt water cannot be responsible for both. Freshen-
ing of water with depth in the aquifer has also been observed
by the author and confirmed by drill-stem testing and geo-
physical logging in St. Lucie County.

BUREAU OF GEOLOGY

Figure 9. Drilling and water quality data from a deep well at Stuart, Mar-
tin County

3. Within the aquifer system there are extensive beds having
low permeability which would seem to prevent the develop-
ment of a convective cell, as proposed by Kohout.
A quantitative analysis of the conductive cooling hypothesis will
require data on the thermal properties of the aquifer system which
are not now available, along with rates of ground-water movement
in various components of the system.

88

SPECIAL PUBLICATION NO. 21 89

REFERENCES
Kaufman, M. I. (and Dion, N. P.), 1967, Chemical character of water in the
Floridan Aquifer in southern Peace River Basin, Florida: Florida Bureau
of Geology Map series 27.
Kohout, F. A., 1967, Groundwater flow and the geothermal regime of the
Floridan plateau: Trans. Gulf Coast Assoc. Geol: Soc., v. 17, p. 339-354.
1975, A hypothesis concerning cyclic flow of salt water related to
geothermal heating in the Floridan Aquifer: Trans. New York Acad. Sci.,
v. 28, p. 249-271.
Lichtler, W. F., 1960, Geology and ground-water resources of Martin County,
Florida: Fla. Geol. Survey, Report of Inv. 23.
Sproul, C. R., (Boggess, D. H., and Woodward, H. J.), 1972, Saline-water in-
trusion from deep artesian sources in the McGregor Isles area of Lee
County, Florida: Florida Bureau of Geology Inf. Circ. 75.
Springfield, V. T., 1966, Artesian water in Tertiary limestone in the south-
eastern states: U. S. Geol. Survey Prof. Paper 517.
Vernon, R. 0., 1970, The beneficial uses of zones of high transmissivities in the
Florida subsurface for waste storage and waste disposal: Florida Bureau
of Geology Inf. Circ. 70.
1973, Top of the Floridan artesian aquifer: Florida Bureau of
Geology Map Series 56.
Wilson, W. E., 1975, Ground-water resources of DeSoto and Hardee Counties,
Florida: U. S. Geol. Survey, Open File Report 75-428.

	Title Page
	Front Matter
	Table of Contents
	Introduction
	Main

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