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The geomorphology, geology and hydrogeology of Lafayette County, Florida ( FGS: Open file report 46 )
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 Material Information
Title: The geomorphology, geology and hydrogeology of Lafayette County, Florida ( FGS: Open file report 46 )
Series Title: ( FGS: Open file report 46 )
Physical Description: 10 p. : ill., maps ; 28 cm.
Language: English
Creator: Arthur, Jonathan D
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee
Publication Date: 1991
 Subjects
Subjects / Keywords: Geomorphology -- Florida -- Lafayette County   ( lcsh )
Geology -- Florida -- Lafayette County   ( lcsh )
Hydrology -- Florida -- Lafayette County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Jonathon D. Arthur.
Bibliography: Includes bibliographical references (p. 9-10).
General Note: Cover title.
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: aleph - 001754162
oclc - 26615230
notis - AJG7151
System ID: UF00001045:00001

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Table of Contents
    Title Page
        Title Page 1
        Title Page 2
    Geomorphology and geology
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
    Hydrogeology
        Page 8
        Page 7
    Mineral and energy resources
        Page 8
        Page 9
    References
        Page 9
        Page 10
        Copyright
            Main
Full Text










STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Don E. Duden, Acting Executive Director




DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director





FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief






OPEN FILE REPORT 46





THE GEOMORPHOLOGY, GEOLOGY AND HYDROGEOLOGY OF
LAFAYETTE COUNTY, FLORIDA

By

Jonathan D. Arthur, P. G. 1149


FLORIDA GEOLOGICAL SURVEY

Tallahassee
1991














qq





LI5~cRA!I








THE GEOMORPHOLOGY, GEOLOGY AND
HYDROGEOLOGY
OF LAFAYETTE COUNTY

Jonathan D. Arthur, P.G. No. 1149


GEOMORPHOLOGY

Lafayette County lies within both the
Northern and Central geomorphic zones of White
(1970). The Northern Zone is described as broad
highlands spanning from the east coast across
the Florida Panhandle. The Central Zone
generally consists of a series of valleys which
separate coast-parallel ridges, however, none of
the Central Zone ridges are located within the
county. Accordingly, maximum elevations in
Lafayette County lie within the Northern Zone.
These elevations are in excess of 120 feet above
mean sea-level the National Geodetic Vertical
Datum (NGVD). Lowest elevations (less than 25
feet NGVD) occur within the Suwannee River
Basin along the southeast part of the county as
well as along the Steinhatchee River in the
southwest corner of the county.

The Gulf Coastal Lowlands is a major
geomorphic province which lies within both the
Northern and Central Zones and encompasses all
of Lafayette County. This geomorphic province Is
typically a flat, sandy plain commonly incised by
river and stream valleys. It also contains relict
beach ridge deposits and wetlands. In Lafayette
County, however, the only paleo-coastal feature is
the relatively flat topography due to terracing by
PlIo-Pleistocene seas. Healy's (1975) map of
Florida's terraces and shorelines indicates that
most of the county lies within the elevation range
of the Wicomico marine terrace (70-100 feet
above NGVD).

Wetlands comprise roughly one half of
Lafayette County (Figure 1). In addition to the
flat, low-lying topography of the county, the
location of these swampy areas is also controlled
by hydrogeological factors. Refer to the
HYDROGEOLOGY section for discussion of the
relationship between hydrogeology and the
wetlands of Lafayette County.

The most extensive wetlands are San
Pedro Bay and Mallory Swamp. San Pedro Bay
lies along the western margin of the county and


Mallory Swamp lies In the south-central third of
the county. Limited surface drainage of Mallory
Swamp is toward the south and southwest where
the waters eventually enter the Stelnhatchee River
In Dixie County via Eight Mile Creek. Drainage
from Mallory Swamp into the Suwannee River is
limited to one or two Intermittent tributaries. San
Pedro Bay is drained via tributaries of the
Steinhatchee River including Reedy Creek, Wolf
Creek, Owl Creek and Kettle Creek, all of which
are located in southwestern Lafayette County.
Headwaters of the Steinhatchee River itself
originate in the clayey sands of central Lafayette
county.

The Suwannee River comprises the entire
eastern border of the county. The Suwannee
River Valley extends three to five miles Into
Lafayette County and is floored by limestone.
These Eocene limestones are observed in outcrop
along the river, especially during the dry season.
Due to artesian conditions within the Floridan
aquifer system (see HYDROGEOLOGY section),
numerous springs are located along both the
Suwannee and Steinhatchee Rivers.

Springs of Lafayette County which flow
into the Suwannee River include: Alan Mill Pond,
Blue, Convict, Fletcher, Mearson, Owens, Perry,
Ruth, Troy and Turtle Springs. Iron Spring and
Steinhatchee Spring are associated with the
Steinhatchee River. Of the 12 springs reported
for Lafayette County, Troy Spring Is the only one
classified as a first magnitude spring (Rosenau, et
al., 1977). This classification denotes that the
spring has an average discharge greater than or
equal to 100 cubic feet per second.

GEOLOGY

Lafayette County is underlain by several
thousand feet of sedimentary rocks. The
basement rocks beneath the region are
comprised of Paleozoic (Ordovician through
Devonian) quartz sandstones and shales (Applln,
1951) which are found at depths greater than
4000 feet below land surface (bls). These rocks
have been penetrated by oil test wells and are
part of the Paleozoic Suwannee Basin. The
oldest geologic unit penetrated by water wells is
the Eocene Avon Park Formation. The Eocene
through Oligocene units comprise the upper
portion of the Floridan aquifer system in the
region the county's main source for drinking


1


UNIVERSITY OF FLORIMA I7'AARIES












t "- EXPLANATION
S" 'A'',ST'E CU: Y Rc ;;

WE.I LOCATIO.i
S. A --..CROSS SECTION LCCAT:C-
4942 SWAMP
SA SPRING 3 ^

0 2 4
W-6534 N SCA



W-3014


W-400
* SAN MAYO
PEDRO .A AAY





-----~o ^-----------------------
A BC AY AO N A1
-2000 W-1576 0






A dk A AL4A& W-1866
AL Z k W-15951 & A
,0-,_ Ak /NORTHERN ZONE&




Ak W-157 8 B Ah 9 J&- J&3



DIXIE COUNTY


Figure 1. Lafayette County geomorphic features and geologic cross section locations.


1--

I-


4 MILES

6 KILOM ERS
LE








water. The following summary of Lafayette
County geology will be limited to these Eocene
age and younger rocks. Figure 1 shows the
location of geologic cross sections (Figures 2 and
3) depicting subsurface relationships of these
geologic units. Interpretations in the cross
sections are based on analysis of wells shown in
Figure 1 In addition to data from wells not shown.
Figure 4 Is a generalized geologic map showing
the extent of near-surface (20 feet bis or less)
stratigraphic units.


Eocene Series

Avon Park Formation

The Avon Park Formation (Miller, 1986)
underlies all of Lafayette County and generally
consists of tan to buff dolostones and dolomitic
limestones with occasional organic-rich
laminations. This formation ranges in age from
approximately 47 to 43 million, years old (mya),
which corresponds to the Middle Eocene Epoch.
The Lower to Middle Eocene Oldsmar Limestone
lies beneath the Avon Park Formation In Lafayette
County at depths exceeding 900 feet bis.
Examination of well cuttings Indicates that the
uppermost portion of the Avon Park Formation is
typically a tan to grayish-orange sucrosic
dolostone. The most diagnostic fossils recognized
in cuttings are the foraminifera Dlctyoconus sp.
and Cosk/nollna florldana. A variety of echinoids
is also found in this unit. The Avon Park
Formation is fairly uniform in thickness beneath
Lafayette County, ranging from 500 to 700 feet
(Miller, 1986). It thickens to more than 800 feet in
the south-bordering counties (Dixie and Gilchrlst;
Purl, et al., 1967). The top of the formation is
between 110 to 160 feet bis and is unconformably
overlain by the Ocala Limestone.

No samples were recovered from intervals
at or very near the top of the Avon Park
Formation in three wells utilized in this study.
These Intervals may be Indicative of cavities
formed from carbonate dissolution at the
formation boundary. Alternatively, the lack of
recovery may be the result of wash-out of
uncorsolidated, possibly organic-rich sediments
which are occasionally found at this stratigraphic
position.


Ocala Limestone

The Ocala Limestone, first named by Dall
and Harris (1892), consists of white to light gray
limestone with a diverse fossil assemblage. This
formation is Late Eocene in age (approximately 40
to 38 mya) and contains characteristic fossils
such as the foraminifera Lepidocyclina sp. and
echinoids such as Eupatagus antillarum. Other
fossils observed in the unit include pelecypods,
bryzoans, gastropods and additional foraminifera
such as Nummulltes. The top of the Ocala
Limestone is either a surface exposure or an
unconformable contact with one of the following:
the Suwannee Limestone, the Hawthorn Group or
undifferentiated sands and clays. Accordingly,
depths to the top of the formation range from 0 to
approximately 90 feet bis. An analysis of well
cuttings and core selected for this study suggests
that the Ocala Limestone ranges in thickness from
70 to 160 feet.

Dolostones observed at the top of the
Ocala Limestone may be part of the Steinhatchee
Dolomite Member. Purl et al., (1967) describe the
Steinhatchee Dolomite as a tan, granular, Impure
dolostone occurring in the basal position of the
Crystal River Formation (upper Ocala Limestone)
outcropping near Horseshoe Beach, Dixie County.
Scott (personal communication, 1991), however,
has observed dolostones similar in appearance,
Interbedded with and at the top of the upper
Ocala Limestone in the region. He notes that
other unpublished field studies have found
Oligocene-age fossils within some of these
dolostone lithologies. In order to better
understand the age, occurrence and extent of the
Steinhatchee Dolomite Member, further study is
required.

Oligocene Series

Suwannee Limestone

The occurrence of the Lower Oligocene
Suwannee Limestone (Cooke and Mansfield,
1936) beneath Lafayette County is sporadic. This
unit, which ranges in age from 38 to 33 mya, is a
thin discontinuous layer above the Ocala
Limestone and Is unconformably overlain by
Hawthorn Group sediments. The lithology of the
Suwannee Limestone as observed from well
cuttings ranges from a light to tannish gray
limestone to a tan sucrosic dolostone. Fossils in































'-
r 53



\!SL 0





-25
-100




-5 1

-200



-75



-300


Undifferentiated
Sand and Clay I
- /


0
0 0


Limestone


Limestone


SCALE f
, 2 4 MILES Avon Park H Formation
0 2 4 6 KILOMETERS
VERTICAL EXAGGERATION
284 TIMES TRUE SCALE
- NO SAMPLES TD 1111' BLS


TO 1113' BLS


NNW


SSE


Figure 2. Geologic cross section A A'.




















































SCALE
0 2 4 MILES
0 2 4 6 KILOMETERS
VERTICAL EXAGGERATION
264 TIMES TRUE SCALE
NO SAMPLES

TO = 4560' BLS TD 11 00' BLS


TD 3507' BLS


Figure 3. Geologic cross section B B'.


MSLt0


--100


-25 -





-50 -





-75


--200







--300












EXPLANATION

POST-MIOCENE CLAYEY SAND

S-- [ MIOCENE HAWTHORN GROUP -N-

S EOCENE OCALA LIMESTONE


-- 0 2 4 MILES

...-. 0 2 4 6 KILOMETER"

































DIXIE COUNTY



FIgure 4. Geologic map of Lafayette County (modified from Knapp, 1978a, 1978b Uoyd and
Campbell, 1986). Map reflects geologic formations encountered less than or equal to 20
feet bis.
..........*. .-. '* .-. -- .- .**- *f ^ i ^... _- -..- .. -. .. .- .- .. -.. -. ...1..'.


61
Y
(I


S








the unit include gastropods, pelecypods,
echinolds (e.g. Rhyncholampusgouldii), abundant
milliolids and other benthic foraminifera such as
Dictyoconus sp. The top of the Suwannee
Limestone Is found between 30 and 80 feet bis.
Thickness of the unit ranges from 0 to 25 feet.
The formation eroslonally pinches out to the
northeast against the Ocala Limestone where the
Ocala occurs as a stratigraphic high, cropping out
In a band paralleling the Suwannee River (Figures
2 and 4). Toward the west-central part of the
county, as evidenced by W-15954 (Figure 3), the
formation is also absent. Existing data suggest
that the extent of the Suwannee Limestone is
limited to the central portion of the county.

Miocene Series

Hawthorn Group

Hawthorn Group sediments (Scott, 1988)
are Miocene in age (approximately 25 to 5 mya)
and generally consist of phosphatic siliciclastics
(sands, silts and clays) and carbonates. In
Lafayette County, the Hawthorn Group sediments
are noticeably less fossiliferous than the
underlying Eocene and Oligocene carbonates.
Samples of Hawthorn in Lafayette County include
lithologies of white sandy, phosphatic carbonate
and very pale orange to light gray phosphatic
clay. Some of the clayey lithologies could be
considered "hard rock" phosphate. The
subsurface extent of Hawthorn sediments
approximately coincides with that of the
underlying Suwannee Limestone. In limited areas,
the Hawthorn Group may lie unconformably
above the Ocala Limestone (Figure 2). Depth to
the top of the Hawthorn Group, where present,
ranges from 5 to 45 feet bls. Available data
indicate that all of this unit is overlain by Post-
Miocene sediments. Figure 4 shows three
locations where Hawthorn Group sediments lie
within 20 feet of land surface in the Northern
geomorphic zone. The Hawthorn Group averages
20 feet thick and ranges from 0 to 40 feet thick in
the subsurface of Lafayette County.

Post-Miocene Series

Undifferentiated Sands and Clays

The distribution of post-Miocene series
(younger than 5 mya) clayey sands is shown in
Figure 4. Deposits greater than 20 feet thick are


limited to the central and western portions of the
county. These sediments lie above either
Hawthorn Group sediments, Suwannee
Limestone, or Ocala Limestone (Figure 2 and 3)
and are generally moderate yellowish brown to
brown in color with variable amounts of organic
material. Thicknesses range from 0 to 45 feet and
average about 25 feet.

HYDROGEOLOGY

Ground water is water within the pore
spaces of rocks and sediments in the subsurface.
When these pore spaces are interconnected
(permeable), ground water is free to flow under
the influence of gravity or pressure. If the pore
spaces are not present or not interconnected,
such as in clay-rich strata, the flow of the ground
water is restricted. These physical parameters of
rocks as they relate to ground water movement
and storage have given rise to a classification of
hydrogeologic units in Florida (Southeastern
Geological Society Ad Hoc Committee, 1986). In
Lafayette County, the pertinent units include the
surficial aquifer system, the intermediate confining
unit and the Floridan aquifer system. An aquifer
system is "a heterogeneous body of intercalated
permeable and poorly permeable material that
functions regionally as a water-yielding hydraulic
unit" (Poland, et al., 1972).

The extent of the surficial aquifer system
in the county has not been well defined. This
aquifer system is a water-table aquifer
(unconfined) within post-Miocene clayey sands of
the central and western part of the county. In the
San Pedro Bay area of adjacent Taylor County, a
surficial (water table) aquifer system reaching
maximum thicknesses of 50 feet has been
reported (Burnson, 1982).

The intermediate confining unit, where
present, is comprised of clayey Miocene
(Hawthorn Group) sediments and in some cases
the relatively clay-rich post-Miocene sediments.
A map showing general hydrogeologic conditions
of the region (Burnson, 1982) delineates a "Class
II semiconfined Floridan aquifer" which roughly
corresponds to the distribution of clayey sands
shown in Figure 4. Burnson's "Class II" area
includes the central and western parts of
Lafayette County and presumably the surficial
aquifer system, which may in places lie above the
confining unit. He also reports a thin (less than 5









feet thick) Miocene confining unit beneath the
surficial aquifer system in the San Pedro Bay area
of Taylor County.

As noted earlier, the Floridan aquifer
system is the major source of drinking water In
Lafayette County. The Floridan aquifer system
underlies the entire county and is between
approximately 1250 and 1475 feet thick (Miller,
1986). Depths to this aquifer system range from
0 to about 60 feet bis. Along the Suwannee River
and the southern border of the county, the
Floridan aquifer system is unconfined (Burnson,
1982; see also the extent of the Ocala Limestone,
Figure 4). The uppermost geologic formations of
this system include either the Suwannee
Limestone (where present) or the Ocala
Limestone.

The potentiometric surface of an aquifer
system reflects the surface (or elevation) to which
the ground water would rise due to hydrostatic
pressure. When an aquifer system is confined by
overlying impermeable beds, the potentiometric
surface may be situated above land surface.
Under such (artesian) conditions, if an unconfined
path exists between the aquifer system and the
surface, ground water will flow freely at land
surface in the form of seeps and springs. As
noted in the GEOMORPHOLOGY section and
shown in Figure 1, numerous springs occur along
the Suwannee and Steinhatchee Rivers, indicating
that those ground waters are under some amount
of pressure from within the Floridan aquifer
system with respect to the river stage.

In addition to the presence of springs, the
potentlometric surface is also one of the variables
influencing the location and extent of wetlands in
the county. Figure 4 shows that carbonates of
the Floridan aquifer system comprise the majority
of the bedrock in the region. Approximately half
of the county lacks a significant aquifer confining
unit (Burnson, 1982) and the potentiometric
surface of the Floridan aquifer system is at or
near land-surface elevation (Barr, 1987). These
combined factors cause standing water conditions
(i.e. wetlands) when drainage and evaporation do
not counter the effect. In areas where wetlands
lie above the intermediate confining unit clayeyy
sands) and the potentiometric surface is high,
surficial waters are unable to infiltrate into the
ground thus sustaining wetland conditions.


MINERAL AND ENERGY RESOURCES


Lafayette County has several potential
geological resources, however, no commercial
development of these resources currently is
taking place (Spencer, 1989; Spencer, personal
communication, 1991). Surficial deposits In the
county Include clayey sand, limestone, and peat.
In the deep subsurface, test wells have been
drilled in search for oil and gas.

Sand and Clay

Surficial sediment deposits in the county
are largely comprised of clayey sands (Knapp,
1978a, 1978b; Figure 4). No commercial deposits
of sand or clay are reported or mined. Small,
localized borrow pits scattered throughout the
county have likely been used for road fill. Bell
(1924) notes that the underlying sediments (i.e.
the Hawthorn Group) may contain thin localized
layers of clay, however none are suitable for
mining.

Limestone and Dolostone

Knapp (1978a, 1978b) shows surface
exposures of limestone along the Suwannee
River, and limestone and dolostone in the
southwest corner of the county near the
Steinhatchee River (Figure 4). Five limestone
quarries are known to have been in operation in
the county, however, none are active as of the
writing of this report. The Dowling Pit, the most
recently active, is located in the northeast corner
of the county, adjacent to the Suwannee River
(Schmidt, et al. 1979). The remaining quarry sites
are also located along the Suwannee River and
were probably developing product from the Ocala
Limestone.

Peat

Localized peat deposits are associated
with wetland regions of Lafayette County. In a
statewide investigation of peat deposits, Davis
(1946) collected peat from swamps in south-
central Lafayette County (Mallory Swamp) and
about 2 miles south-southwest of Mayo in Bear
Bay. Griffin et al. (1982) report that no data is
available for Lafayette County with respect to the
occurrence of fuel grade peat deposits.








the unit include gastropods, pelecypods,
echinolds (e.g. Rhyncholampusgouldii), abundant
milliolids and other benthic foraminifera such as
Dictyoconus sp. The top of the Suwannee
Limestone Is found between 30 and 80 feet bis.
Thickness of the unit ranges from 0 to 25 feet.
The formation eroslonally pinches out to the
northeast against the Ocala Limestone where the
Ocala occurs as a stratigraphic high, cropping out
In a band paralleling the Suwannee River (Figures
2 and 4). Toward the west-central part of the
county, as evidenced by W-15954 (Figure 3), the
formation is also absent. Existing data suggest
that the extent of the Suwannee Limestone is
limited to the central portion of the county.

Miocene Series

Hawthorn Group

Hawthorn Group sediments (Scott, 1988)
are Miocene in age (approximately 25 to 5 mya)
and generally consist of phosphatic siliciclastics
(sands, silts and clays) and carbonates. In
Lafayette County, the Hawthorn Group sediments
are noticeably less fossiliferous than the
underlying Eocene and Oligocene carbonates.
Samples of Hawthorn in Lafayette County include
lithologies of white sandy, phosphatic carbonate
and very pale orange to light gray phosphatic
clay. Some of the clayey lithologies could be
considered "hard rock" phosphate. The
subsurface extent of Hawthorn sediments
approximately coincides with that of the
underlying Suwannee Limestone. In limited areas,
the Hawthorn Group may lie unconformably
above the Ocala Limestone (Figure 2). Depth to
the top of the Hawthorn Group, where present,
ranges from 5 to 45 feet bls. Available data
indicate that all of this unit is overlain by Post-
Miocene sediments. Figure 4 shows three
locations where Hawthorn Group sediments lie
within 20 feet of land surface in the Northern
geomorphic zone. The Hawthorn Group averages
20 feet thick and ranges from 0 to 40 feet thick in
the subsurface of Lafayette County.

Post-Miocene Series

Undifferentiated Sands and Clays

The distribution of post-Miocene series
(younger than 5 mya) clayey sands is shown in
Figure 4. Deposits greater than 20 feet thick are


limited to the central and western portions of the
county. These sediments lie above either
Hawthorn Group sediments, Suwannee
Limestone, or Ocala Limestone (Figure 2 and 3)
and are generally moderate yellowish brown to
brown in color with variable amounts of organic
material. Thicknesses range from 0 to 45 feet and
average about 25 feet.

HYDROGEOLOGY

Ground water is water within the pore
spaces of rocks and sediments in the subsurface.
When these pore spaces are interconnected
(permeable), ground water is free to flow under
the influence of gravity or pressure. If the pore
spaces are not present or not interconnected,
such as in clay-rich strata, the flow of the ground
water is restricted. These physical parameters of
rocks as they relate to ground water movement
and storage have given rise to a classification of
hydrogeologic units in Florida (Southeastern
Geological Society Ad Hoc Committee, 1986). In
Lafayette County, the pertinent units include the
surficial aquifer system, the intermediate confining
unit and the Floridan aquifer system. An aquifer
system is "a heterogeneous body of intercalated
permeable and poorly permeable material that
functions regionally as a water-yielding hydraulic
unit" (Poland, et al., 1972).

The extent of the surficial aquifer system
in the county has not been well defined. This
aquifer system is a water-table aquifer
(unconfined) within post-Miocene clayey sands of
the central and western part of the county. In the
San Pedro Bay area of adjacent Taylor County, a
surficial (water table) aquifer system reaching
maximum thicknesses of 50 feet has been
reported (Burnson, 1982).

The intermediate confining unit, where
present, is comprised of clayey Miocene
(Hawthorn Group) sediments and in some cases
the relatively clay-rich post-Miocene sediments.
A map showing general hydrogeologic conditions
of the region (Burnson, 1982) delineates a "Class
II semiconfined Floridan aquifer" which roughly
corresponds to the distribution of clayey sands
shown in Figure 4. Burnson's "Class II" area
includes the central and western parts of
Lafayette County and presumably the surficial
aquifer system, which may in places lie above the
confining unit. He also reports a thin (less than 5









feet thick) Miocene confining unit beneath the
surficial aquifer system in the San Pedro Bay area
of Taylor County.

As noted earlier, the Floridan aquifer
system is the major source of drinking water In
Lafayette County. The Floridan aquifer system
underlies the entire county and is between
approximately 1250 and 1475 feet thick (Miller,
1986). Depths to this aquifer system range from
0 to about 60 feet bis. Along the Suwannee River
and the southern border of the county, the
Floridan aquifer system is unconfined (Burnson,
1982; see also the extent of the Ocala Limestone,
Figure 4). The uppermost geologic formations of
this system include either the Suwannee
Limestone (where present) or the Ocala
Limestone.

The potentiometric surface of an aquifer
system reflects the surface (or elevation) to which
the ground water would rise due to hydrostatic
pressure. When an aquifer system is confined by
overlying impermeable beds, the potentiometric
surface may be situated above land surface.
Under such (artesian) conditions, if an unconfined
path exists between the aquifer system and the
surface, ground water will flow freely at land
surface in the form of seeps and springs. As
noted in the GEOMORPHOLOGY section and
shown in Figure 1, numerous springs occur along
the Suwannee and Steinhatchee Rivers, indicating
that those ground waters are under some amount
of pressure from within the Floridan aquifer
system with respect to the river stage.

In addition to the presence of springs, the
potentlometric surface is also one of the variables
influencing the location and extent of wetlands in
the county. Figure 4 shows that carbonates of
the Floridan aquifer system comprise the majority
of the bedrock in the region. Approximately half
of the county lacks a significant aquifer confining
unit (Burnson, 1982) and the potentiometric
surface of the Floridan aquifer system is at or
near land-surface elevation (Barr, 1987). These
combined factors cause standing water conditions
(i.e. wetlands) when drainage and evaporation do
not counter the effect. In areas where wetlands
lie above the intermediate confining unit clayeyy
sands) and the potentiometric surface is high,
surficial waters are unable to infiltrate into the
ground thus sustaining wetland conditions.


MINERAL AND ENERGY RESOURCES


Lafayette County has several potential
geological resources, however, no commercial
development of these resources currently is
taking place (Spencer, 1989; Spencer, personal
communication, 1991). Surficial deposits In the
county Include clayey sand, limestone, and peat.
In the deep subsurface, test wells have been
drilled in search for oil and gas.

Sand and Clay

Surficial sediment deposits in the county
are largely comprised of clayey sands (Knapp,
1978a, 1978b; Figure 4). No commercial deposits
of sand or clay are reported or mined. Small,
localized borrow pits scattered throughout the
county have likely been used for road fill. Bell
(1924) notes that the underlying sediments (i.e.
the Hawthorn Group) may contain thin localized
layers of clay, however none are suitable for
mining.

Limestone and Dolostone

Knapp (1978a, 1978b) shows surface
exposures of limestone along the Suwannee
River, and limestone and dolostone in the
southwest corner of the county near the
Steinhatchee River (Figure 4). Five limestone
quarries are known to have been in operation in
the county, however, none are active as of the
writing of this report. The Dowling Pit, the most
recently active, is located in the northeast corner
of the county, adjacent to the Suwannee River
(Schmidt, et al. 1979). The remaining quarry sites
are also located along the Suwannee River and
were probably developing product from the Ocala
Limestone.

Peat

Localized peat deposits are associated
with wetland regions of Lafayette County. In a
statewide investigation of peat deposits, Davis
(1946) collected peat from swamps in south-
central Lafayette County (Mallory Swamp) and
about 2 miles south-southwest of Mayo in Bear
Bay. Griffin et al. (1982) report that no data is
available for Lafayette County with respect to the
occurrence of fuel grade peat deposits.









Oil and Gas

During the 1940's, the first oil and gas
exploration wells wildcatss) were drilled in
Lafayette County. To date, a total of eight
wildcats have been drilled to depths ranging from
3507 to 10,077 feet bis. All of these wells were
dry holes and were subsequently plugged. As
our nation's energy resources and needs are
reassessed, a renewed Interest in the Paleozoic
sediments beneath Lafayette County may lead to
future drilling. In the near future, however, no
drilling for oil and gas is proposed.



REFERENCES


Applin, P. L., 1951, Preliminary report on buried
pre-Mesozoic rocks in Florida and
adjacent states: USGS Circular 91, 28 p.

Barr, G. L., 1987, Potentiometric surface of the
Upper Floridan aquifer in Florida, May
1985: Florida Geological Survey Map
Series 119, scale 1:2,000,000.

Bell, O. G., 1924, A preliminary report on clays of
Florida: Florida Geological Survey
Fifteenth Annual Report, 266 p.

Burnson, T., 1982, Hydrogeologic overview of
Suwannee River Water Management
District: Suwannee River Water
Management District Technical Report
82-3, 19 p.


Cooke, C. W., and
Suwannee
Geological
Proceedings,


Mansfield, W. C., 1936,
Limestone of Florida:
Society of America
p. 71-72.


Dall, W. H. and Harris G. D., 1892, Correlation
papers-Neocene: U.S. Geological Survey
Bulletin 84, 349 p.

Davis, J. H., 1946, The peat deposits of Florida,
their occurence, development and uses:
Florida Geological Survey Bulletin 30, 247
P.


Griffin, G., Wieland, C. C., Hood, L. Q., Goode, III,
R.W., Sawyer, R. K., and McNeill, D. F.,
1982, Assessment of the peat resources
of Florida, with a detailed survey of the
northern Everglades: State of Florida,
Governor's Energy Office, Tallahassee,
Florida, 190 p.

Healy, H. G., 1975, Terraces and shorelines of
Florida: Florida Geological Survey Map
Series 71, scale 1:2,000,000.

Knapp, M. S., 1978a, Environmental Geology
Series Gainesville Sheet: Florida
Geological Survey Map Series 79, scale
1:250,000.

1978b, Environmental Geology
Series Valdosta Sheet: Florida Geological
Survey Map Series 88, scale 1:250,000.

Uoyd, J. M. and Campbell, K. M., 1986,
(Unpublished) geologic map of Lafayette
County, in Scott, T. M. and Campbell, K.
M., Geologic map of Florida, Florida
Geological Survey Map Series (in
preparation).

Miller, J. A., 1986, Hydrogeologic framework of
the Floridan aquifer system in Florida and
parts of Georgia, Alabama and South
Carolina: U.S. Geological Survey
Professional Paper 1403-B, 91 p.

Poland, J. F., Lofgren, B. E., and Riley, F. S.,
1972, Glossary of selected terms useful in
studies of the mechanics of aquifer
systems and land subsidence due to fluid
withdrawal: U.S. Geological Survey Water-
Supply Paper 2025, 9 p.

Puri, H. S., Yon, J. W., Jr., and Oglesby, W. R.,
1967, Geology of Dixie and Gilchrist
Counties, Florida: Florida
Geological Survey Bulletin 49, 155 p.

Rosenau, J. C., Fualkner, G. L., Hendry, C. W.,
Jr., and Hull, R. W., 1977, Springs of
Florida: Florida Geological Survey Bulletin
31, 461 p.









Oil and Gas

During the 1940's, the first oil and gas
exploration wells wildcatss) were drilled in
Lafayette County. To date, a total of eight
wildcats have been drilled to depths ranging from
3507 to 10,077 feet bis. All of these wells were
dry holes and were subsequently plugged. As
our nation's energy resources and needs are
reassessed, a renewed Interest in the Paleozoic
sediments beneath Lafayette County may lead to
future drilling. In the near future, however, no
drilling for oil and gas is proposed.



REFERENCES


Applin, P. L., 1951, Preliminary report on buried
pre-Mesozoic rocks in Florida and
adjacent states: USGS Circular 91, 28 p.

Barr, G. L., 1987, Potentiometric surface of the
Upper Floridan aquifer in Florida, May
1985: Florida Geological Survey Map
Series 119, scale 1:2,000,000.

Bell, O. G., 1924, A preliminary report on clays of
Florida: Florida Geological Survey
Fifteenth Annual Report, 266 p.

Burnson, T., 1982, Hydrogeologic overview of
Suwannee River Water Management
District: Suwannee River Water
Management District Technical Report
82-3, 19 p.


Cooke, C. W., and
Suwannee
Geological
Proceedings,


Mansfield, W. C., 1936,
Limestone of Florida:
Society of America
p. 71-72.


Dall, W. H. and Harris G. D., 1892, Correlation
papers-Neocene: U.S. Geological Survey
Bulletin 84, 349 p.

Davis, J. H., 1946, The peat deposits of Florida,
their occurence, development and uses:
Florida Geological Survey Bulletin 30, 247
P.


Griffin, G., Wieland, C. C., Hood, L. Q., Goode, III,
R.W., Sawyer, R. K., and McNeill, D. F.,
1982, Assessment of the peat resources
of Florida, with a detailed survey of the
northern Everglades: State of Florida,
Governor's Energy Office, Tallahassee,
Florida, 190 p.

Healy, H. G., 1975, Terraces and shorelines of
Florida: Florida Geological Survey Map
Series 71, scale 1:2,000,000.

Knapp, M. S., 1978a, Environmental Geology
Series Gainesville Sheet: Florida
Geological Survey Map Series 79, scale
1:250,000.

1978b, Environmental Geology
Series Valdosta Sheet: Florida Geological
Survey Map Series 88, scale 1:250,000.

Uoyd, J. M. and Campbell, K. M., 1986,
(Unpublished) geologic map of Lafayette
County, in Scott, T. M. and Campbell, K.
M., Geologic map of Florida, Florida
Geological Survey Map Series (in
preparation).

Miller, J. A., 1986, Hydrogeologic framework of
the Floridan aquifer system in Florida and
parts of Georgia, Alabama and South
Carolina: U.S. Geological Survey
Professional Paper 1403-B, 91 p.

Poland, J. F., Lofgren, B. E., and Riley, F. S.,
1972, Glossary of selected terms useful in
studies of the mechanics of aquifer
systems and land subsidence due to fluid
withdrawal: U.S. Geological Survey Water-
Supply Paper 2025, 9 p.

Puri, H. S., Yon, J. W., Jr., and Oglesby, W. R.,
1967, Geology of Dixie and Gilchrist
Counties, Florida: Florida
Geological Survey Bulletin 49, 155 p.

Rosenau, J. C., Fualkner, G. L., Hendry, C. W.,
Jr., and Hull, R. W., 1977, Springs of
Florida: Florida Geological Survey Bulletin
31, 461 p.










REFERENCES (continued)


Schmidt, W., Hoenstlne, R. W., Knapp, M. S.,
Lane, E., Ogden, G. M., Jr., and Scott, T.
M., 1979, The limestone, dolomite and
coquina resources of Florida: Florida
Bureau of Geology Report of Investigation
No. 88, 54 p.

Scott, T. M., 1988, The Ilthostratlgraphy of the
Hawthorn Group (Miocene) of Florida:
Florida Geological Survey Bulletin 59, 148
p.

Southeastern Geological Society Ad Hoc
Committee on Florida hydrostratigraphic
unit definition, 1986, Hydrogeologlcal
Units of Florida: Florida Geological
Survey Special Publication 28, 8 p.

Spencer, S. M., 1989, The industrial minerals
Industry directory of Florida, Part 1:
Florida Geological Survey Information
Circular 105, 35 p.

White, W. A., 1970, The geomorphology of the
Florida Peninsula: Florida Geological
Survey Bulletin 51, 164 p.










FLRD GEOLOSk ( IC SUfRiW


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