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State of Florida
Department of Natural Resources
Tom Gardner, Executive Director




Division of Resource Management
Jeremy Craft, Director




Florida Geological Survey
Walt Schmidt, State Geologist and Chief









Open File Report 24


The Geology of Flagler County, Florida


by

Jonathan D. Arthur


Florida Geological Survey
Tallahassee, Florida
1988

























3 1262 04545 4229




'/




LIBRARY









State of Florida
Department of Natural Resources
Tom Gardner, Executive Director

Division of.Resource Management
:Jeremy Craft, Director

Florida Geological Survey
Walt Schmidt, State Geologist



Open File Report 24

The Geology of Flagler County, Florida

by

Jonathan D. Arthur


Geo\ot 8
f a903 estOenasr S3ee
'te nesse e 304










Florida Geological Survey
Tallahassee, Florida
1988





FLAGLER COUNTY


GEOMORPHOLOGY

Flagler County is located within the Atlantic Coastal Lowlands

physiographic zone. White (1970) has delineated six geomorphic

features within Flagler County (Figure 1). The following

discussion is primarily a summary of his observations.

The largest geomorphic feature in Flagler County is the

Eastern Valley, which covers the western two-thirds of the

county. This valley is approximately 20 miles wide and contains

most of the low lying wetlands of Flagler County. Elevations in

this region range from 5 to 28 feet above mean sea-level (MSL).

SCrescent Lake is the major drainage basin in the western half of

the county. Tributaries flowing into the lake include Salt Creek,

Haw Creek, Black Branch and Hunter Branch. Lake Diston, located

in the southwest corner of the county, receives drainage from

surrounding wetlands and Little Haw Creek.

Espanola Hill, a topographic high within the Eastern Valley,

is an elongate feature that parallels the Atlantic coastline and

has a maximum elevation of 59 feet above MSL. The orientation of

Espanola Hill and its location proximal to the Atlantic Coastal

Ridge suggests that the feature may be a relict beach ridge

(White, 1970).

Four narrow, linear geomorphic provinces are located within

the eastern third of Flagler County, all of which parallel the







Atlantic coastline. These features include the Atlantic Coastal

Ridge, the Atlantic Coastal Lagoons, the Atlantic Barrier Chain

and the Atlantic Beach Ridges. During Pamlico sea-level stands,

about 340,000 years ago (Stringfield, 1966), the shoreline known

as the Atlantic Coastal Ridge was developed. Oscillating

regression of the Pamlico seas produced linear coastal deposits

which are components of the Atlantic Barrier Chain. The Atlantic

Beach Ridges and Coastal Lagoons are products of Holocene

shoreline sedimentation.




STRATIGRAPHY


Flagler County is underlain by several thousand feet of

sedimentary rocks which overlie upper Pre-Cambrian Lower

Cambrian crystalline basement, beginning at approximately 5000

feet in depth (Barnett, 1975). The oldest geologic formation

penetrated by water wells in the county is the Avon Park

Formation of Middle Eocene age. Overlying this formation are the

limestones of the Ocala Group and the phosphatic clays, sands and

limestone of the Hawthorn Group. These units underlie

Pleistocene and Recent undifferentiated sand, shell and clay

deposits, which are exposed at the surface. Figure 1 shows

geologic cross-section locations and Figures 2 and 3 show the

geologic formations that are penetrated by wells in Flagler

County.


K Y
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ST. JOHNS COUNTY
-


al 4 5 M I W-5039
1, 4 ,0, 1
4 8 8 Km. B'

SLAKE
'OISSTON |
DISSTON FLAGLER COUNTY ,
VOLUSIA COUNTY
EXPLANATION
Atlantic Beach Ridges

' Atlantic Coastal Lagoons
W Atlantic Barrier Chain

SAtlantic Coastal Ridge

D Eastern Valley

Espanola Hill

Figure 1. Geomorphology of Flagler County
and Cross-section location map.


FGS 030988






0
~50


-50


-100


-150


-200


-250


-300


DCL

-N -p -


SAND AND CLAY



l AWrTHORN GROUP
I-


OCALA GROUP


(UNDIFFERENTIATED)


--350
TD 540'


NW


TD


VERTICAL EXAGGERATION 211X


IL


MSL -


410'


AVON PARK FORMATION


(UNDIFFERENTIATED)
SAND AND SHiLL. -
S (UNDIFFERENTIATED)

(UNDIFFERENTIATED)


INDICATES NO SAMPLES
AVAILABLE


0 1 2 3 4 S MILES

0 2 4 6 8 KILOMETERS


FIGURE 2. GEOLOGIC CROSS-SECTION A A'


FPS 010988


Ii


ItF


IL















4~
o
a
U
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MSL--- 0


SAO ND*.. -


PD -S

:--^,HORN
s S -


CLAY


. -

GROUP


(UNDIFFERENTIATED)

(UNDIFFERENTIATED)

(UNDIFFERENTIATED)

- -


INDICATES NO SAMPLES
AVAILABLE


0 1 2 3 4 5 MILES
I I v a I I "
0 2 4 6 8 KILOMETERS


VERTICAL EXAGGERATION = 211X


OCALA GROUP
(UNDIFFERENTIATED)








AVON PARK
FORMATION



TD 410'


FIGURE 3. GEOLOGIC CROSS-SECTION B B'


FGS 020988


- 50


--50



--100



--150



- -200



- -250



-300


S-350







EOCENE SERIES


Avon Park Formation


The Avon Park Formation (Miller, 1986) in this region contains

a variable lithology, both vertically and laterally. In general,

it consists of a dense, reddish brown to buff, organic-rich,

seamed limestone and brown to gray, crystalline dolomitic

limestone near the base, grading upward to an interbedded gray to

white chalky limestone and hard, crystalline dolomite near the

top (Bermes et al., 1963). Some of these limestone beds contain

abundant foraminifera and echinoids. The top of the Avon Park

Formation is found at depths ranging from 205 feet to 370 feet

below MSL. This formation is a component of the Floridan aquifer

system.



Ocala Group

The Ocala Group (?uri, 1957) consists of three formations. In

ascending order, these are the Inglis Formation, the Williston

Formation and the Crystal River Formation. Lithology of the

Ocala Group generally consists of tan to buff, coarsely granular

limestone of the Inglis Formation at the base, becoming more

indurated within the Williston Formation and white to cream,

chalky massive marine limestone in the Crystal River Formation.

The fossil content of these formations includes a variety of

foraminifera, bryzoans, mollusks and echinoids. Delineation of

the Ocala Group into formations was based upon these fossils, as
K)^







well as lithology. Ocala Group sediments range from 50 feet thick

in southern Flagler County (Bermes et al., 1963) t-o approximately

200 feet thick in northwest Flagler County. Depth to the top of

the Ocala Group averages 100 feet below MSL. Also a component of

the Floridan aquifer system, the Ocala Group is the principle

source of water in the area (Bermes et al., 1963).


MIOCENE SERIES


Hawthorn Group

The Hawthorn Group (Scott, 1988) unconformably..overlies the

Ocala Group beneath Flagler County. Three formations are

recognized within the Hawthorn Group in northern Florida. In

ascending order, these are the Penney Farms Formation, an inter-

bedded phosphatic sand, clay and carbonate; the Marks Head

Formation, a complexly interbedded phosphatic clay, sand and

carbonate; and the Coosawatchee Formation, which consists of

green to tan phosphatic quartz sand with variable amounts of clay

and dolomite. These formations have been described separately

in one core (W-15282) located in northeastern Flagler County.

Lithologic descriptions of this well show 9 feet of the Penney

Farms Formation overlain by 33 feet of the Coosawatchee Formation

with an absence of the Marks Head Formation (T. Scott in Johnson,

1986). The Hawthorn Group averages approximately 35 feet in

thickness and thins toward the south and east portions of Flagler

County. Depth to the top of the Hawthorn Group sediments ranges

from 60 to 80 feet below MSL. The clayey Hawthorn Group






sediments serve as confining beds for the Floridan aquifer

system. Small sand bodies within the Hawthorn are a component of

a near surface aquifer in the area (Bermes et al., 1963).




PLIOCENE TO HOLOCENE SERIES (UNDIFFERENTIATED)


In the subsurface of coastal northeast Florida, Pliocene and

Pleistocene formations have been delineated on a regional basis,

however, within Flagler County, these sands, shells and clays at

or near the surface have not been assigned to specific

formations. Therefore, these surficial and coastal lithologies

are termed Pliocene to Holocene (undifferentiated) sediments.


The Pliocene component of this undifferentiated package is the

Nashua Formation. This formation represents a near shore marine

depositional environment and was named by Matson and Clapp

(1909). The Nashua Formation consists of a quartz sand with

variable amounts of clay and carbonate matrix and common mollusk

shells.


The remaining overlying sands, shells and clays are either

part of the Pleistocene Anastasia Formation or are categorized as

Pleistocene to Holocene undifferentiated deposits. Variably

cemented shell beds (coquina) as well as unconsolidated sands and

shells comprise the Anastasia Formation (Sellards, 1912), which

is found only near the coast in Flagler County. Shell-bearing

lithologies vary from over 100 feet thick near the coast,

thinning to zero thickness towards western Flagler County







(Florida Geological Survey well file data). The total Pliocene

to Holocene deposits range from 50 to 140 feet thick in the area.




MINERAL RESOURCES


The mineral resources of Flagler County include sand, clay and

coquina. The following discussion provides an overview of the

occurrence and commercial use of these resources.



Sand


Sand accumulations cover approximately three quarters of

Flagler County. Maximum sand thickness occurs in the northwest

part of the county, reaching depths of 140 feet. The sand ranges

in grain size from medium sand to silt and commonly contains

small shell fragments and localized clay lenses. Recent tests by

the Florida Geological Survey (Hoenstine et al., 1988) indicate

that the sands are suitable for brick masonry, sand-cement

riprap, sand-asphalt hot mix and sand seal coat. Due to a large

percentage of impurities, the sands are probably not suitable for

manufacturing glass. Although economic heavy mineral deposits

occur in north-central and northeast Florida, no public

information exists regarding the abundance or distribution of

heavy minerals in Flagler County sand bodies.






Clay


Few relatively pure clay deposits occur near the surface in

Flagler County. Most of the clay is found as a clayey-sand

lithology. Calver (1949) reports pure clay deposits are located

near Black Point and Haw Creek. He states that the clays are

suitable for manufacturing common brick, hollow block and drain

tile. Bell (1924) reports an eight foot thick unit of clay, at a

depth of three feet in the vicinity of Shell Bluff which borders

Crescent Lake. This clay is thought to underlie an extensive

portion of western Flagler County. Physical properties suggest

that the Shell Bluff clay may also be used for brick, tile and

hollow block ware (Bell, 1924). Bell (1924) also reports clay

beds exposed near St. Johns Park, located on the north shore of

Dead Lake.


Coquina


Coquina is a plastic sedimentary rock composed of shells and

shell fragments cemented by calcium carbonate. The source of

coquina in Flagler County is the Anastasia Formation. Cooke

(1945) reports two coquina pits exposed on either side of the

brick road to Bunnell, 2.6 miles west of Flagler Beach. The

brick road is now known as Highway 100 and the pits are currently

in operation. Well cemented coquina is suitable for building

material. Less consolidated varieties are useful as concrete mix

and road surfacing material.






HYDROGEOLOGY


Groundwater is defined as the water in the saturated zone

within the subsurface where water is free to move within the

interstices of the rocks and sediment under the influence of

gravity or pressure. A physical characteristic of rocks and

sediment which defines their ability to transmit water (or other

fluids) is known as permeability. The degree of permeability

generally depends on the size, shape and extent of pore spaces

and their interconnections. For example, clay has low

permeability whereas sand has high permeability.


Regional hydrogeologic units in Florida have been established

on the basis of varying permeabilities within stratigraphic units

(Southeastern Geological Society, 1986). Pertinent to Flagler

County, the hydrogeologic units include the surficial aquifer

system, the intermediate aquifer system and the Floridan aquifer

system.


The surficial aquifer system in Flagler County contains

permeable sands and shells ranging from Pliocene to Holocene in

age. This aquifer system is non-artesian (non-flowing) and is

primarily replenished by local rainfall. The extensive wetlands

in northern Flagler County are probably not the result of

impermeable beds impeding the infiltration of rain but rather a

result of the surficial aquifer system being filled to capacity

(Bermes et al., 1963). The surficial aquifer system reaches

depths of 100 feet below MSL.


The intermediate aquifer system occurs primarily within the






Hawthorn Group sediments. Impermeable clay-rich lithologies of

the Hawthorn Group serve as confining layers within this system.

However, localized permeable sand and limestone lenses within the
Hawthorn yield moderate amounts of artesian (flowing) water to

some domestic wells in the county (Bermes et al.,1963). In

Flagler County, thickness of the intermediate aquifer system,

which in some cases may be more appropriately termed the

intermediate confining unit, ranges from approximately five to

80 feet. Upper impermeable portions of the intermediate system

serve as the base of the surficial aquifer system. The Floridan

aquifer system is capped by the impermeable sediments of.the...

lower Hawthorn. Permeable portions of the Hawthorn Group, such

as basal carbonates, may be an upper component of the Floridan.

The Floridan aquifer system in Flagler County is the major

source of water for irrigation, public supply and industry. In

general, Eocene limestones and dolomites of the Avon Park
Formation and the Ocala Group comprise a majority of this

aquifer. Depth to the Floridan aquifer system in the area ranges

from 75 to 190 feet below MSL. Recharge to the system occurs

where the Hawthorn Group is thin enough (or absent) to allow

downward leakage from the intermediate and primarily the

surficial aquifer system as pressure conditions allow.






REFERENCES


Bell, O. G., 1924, A preliminary report on clays of Florida:

Florida Geological Survey Fifteenth Annual Report, 266 p.

Barnett, R. S., 1975, Basement structure of Florida and its

tectonic implications: Gulf Coast Association of Geological

Societies Transactions, v.25, p. 122-142.

Bermes, B. J., 1963, Geology and ground-water resources of

Flagler, Putnam, and St. Johns Counties, Florida: Florida

Geological Survey Report of Investigation 32, 97 p.

Calver, J. L., 1949, Florida kaolins and clays: Florida

Geological Survey Information Circular 2, 59 p.

Cooke, C. W., 1945, Geology of Florida: Florida Geological Survey

Bulletin 29, 339 p.

Hoenstine, R., Yon, B., Lane, E., Spencer, S. and Bond, P., 1988,

Mineral Resources of Flagler County: Florida Geological Survey

(in preparation).

Johnson, R., 1986, Shallow stratigraphic core tests on file at

the Florida Geological Survey: Florida Geological Survey

Information Circular 103, 431 p.

Matson, G. C. and Clapp, F. G., 1909, Florida Geological Survey

Second Annual Report, 299 p.

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, p.

25-27.

Puri, H. S., 1957, Stratigraphy and zonation of the Ocala Group:

Florida Geological Survey Bulletin 38, 248 p.







Scott, T. M., 1988, The lithostratigraphy of the Hawthorn Group

(Miocene) of Florida: Florida Geological Survey Bulletin 59,

148 p.

Sellards, E. H., 1912, Florida Geological Survey Fourth Annual

Report, 175 p.

Southeastern Geological Society Ad Hoc Committee on Florida

hydrostratigraphic unit definition, 1986, Hydrogeologic units of

Florida, Florida Geological Survey Special Publication 28, 9 p.


Stringfield, V. T., 1966, Artesian water in Tertiary limestone in

the southeastern United States: U. S. Geological Survey

Professional Paper 517, 226 p.

White, W. A., 1970, Geomorphology of the Florida Peninsula:

Florida Geological Survey Bulletin 51, 164 p.