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STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Virginia B. Wetherell, Secretary




DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director



FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief




Open File Report 59


The geomorphology and geology of
Escambia County, Florida

by

Frank R. Rupert


Florida Geological Survey
Tallahassee, Florida
1993


ISSN 1058-1391




UNIVERSITY OF FLOIDA L2RARIES











The geomorphology and geology
of Escambla County, Florida

Frank R. Rupert, P.G. 149


GEOMORPHOLOGY
Escambia County is situated at the western
end of the Northern or Proximal geomorphic
zone of White (1970). This zone includes the
northernmost Florida peninsula, and all of the
panhandle. Locally, the Northern Zone is
subdivided into two geomorphic provinces: the
Western Highlands and the Gulf Coastal
Lowlands (Figure 1).

Western Highlands
The Western Highlands comprise the
northern three-quarters of Escambia County.
They are the western extension of the series of
topographic highlands which span northern


ALABAMA
3-- .-~


Figure 1. Geomorphic and cross
section location map.


- Florida. These highlands are thought to be the
stream-dissected remnants of an extensive delta
plain that covered southern Alabama, southern
Georgia, and northern Florida. The terrain is
characteristically comprised of gently rolling
clayey-sand hills and ridges, punctuated by a
series of deeply-incised dendritic streams. Land
surface elevations range from 280 feet above
mean sealevel (MSL) in northern Escambia
County, near the Florida Alabama state line, to
approximately 100 feet above MSL at the
southern edge of the highlands.
Large surface water bodies are rare in the
Western Highlands. A number of small ponds
are perched on low-permeability layers with the
clayey sand sediments comprising the highlands.
As with most of Florida, the Western
Highlands have been modified by marine
erosion. Healy (1976) identified three marine
terrace elevation zones in the Western
Highlands:theSunderland/OkeefenokeeTerrace,
which extends from the southern edge of the
zone (approximately 100 feet MSL) to 170 feet
above MSL; the Coharie Terrace (170 to 215 feet
above MSL); and the Hazelhurst Terrace (215 to
320 feet above MSL), which includes the highest
elevations in Escambia County.

Gulf Coastal Lowlands
The Gulf Coastal Lowlands zone covers the
southern one-quarter of Escambia County. It
extends from the base of the Western Highlands
southward to the present coastline, and includes
the Escambia River Valley and the modem
coastal barrier islands. The boundary between
the Gulf Coastal Lowlands and the uplands to
the north is marked by a relict marine
escarpment, lying at an elevation of
approximately 100 to 120 feet above MSL
_ The terrain in the Gulf Coastal Lowlands is
generally flat and sandy, reflecting erosion and
subsequent deposition by high-standing
Pleistocene seas. Healy (1976) recognized four
marine terrace elevation zones comprising
portions of the Gulf Coastal Lowlands: the Silver
Bluff Terrace (0 to 10 feet above MSL), the











Pamlico Terrace (10 to 25 feet above MSL), the
Talbot Terrace (25 to 42 feet above MSL), the
Penholoway Terrace (42 to 70 feet above MSL),
and the Wicomico Terrace (70 to 100 feet above
MSL).
The land surface in the Gulf Coastal
Lowlands slopes gently from an elevation of
about 100 feet above MSL at the northern edge
of the lowlands to 0 feet MSL near the coast.
Much of the land adjacent to Perdido Bay and
landward of the Gulf coastal barrier islands is
swampy, and is drained by small sluggish
creeks. Relict Pleistocene sand beach ridges
and dunes are situated on the mainland and the
landward edge of Perdido Key, just west of Big
Lagoon.
Perdido Key and Santa Rosa Island are
Holocene barrier islands, comprised of quartz
sand and shell beds, and supporting a series of
coast-parallel sand dune and beach ridge
systems. The larger of these dunes attain
elevations of up to 45 feet above MSL, but are
continually vulnerable to erosion by storm
surges. Low swales positioned between the
dunes may contain standing fresh water, and
commonly accumulate organic.

Escambla Valley
The valley of the Escambia River forms a
broad extension of the Gulf Coastal Lowlands
which straddles the river northward to the
Florida-Alabama state line (White et al., 1964). It
begins at sea level where the river enters the
northwestern edge of Escambia Bay through a 4-
mile-wide swampy delta. From here it extends
northward to the Alabama state line, following
the 1.5 to 2 mile wide floodplain of the Escambia
River. The elevation in the valley gradually rises
to an elevation of about 50 feet above MSL at
the point where it enters Alabama.

STRATIGRAPHY
Escambia County is underlain by thousands
of feet of Mesozoic and Cenozoic sedimentary
rocks. The oldest known sediments encountered
by drilling, consisting of Jurassic quartzitic
sandstone and gray shale, were penetrated at a
depth of 17,950 feet in an oil test well in the
north-central part of the county. These
sediments are part of the Smackover Formation,
which yields petroleum in wells situated in the
Jay field in adjacent Santa Rosa County. The
youngest sediments are Pleistocene and


Holocene undifferentiated sands, clayey sands,
and alluvium. Figure 1 shows the locations of
the shallow geologic cross sections illustrated in
Figures 2 and 3.
The rock strata underlying Escambia County
dip and thicken gently to the southwest in a
homoclinal structure. This structure is produced
by the thickening and downwarping of sediments
as they dip into the large sedimentary basins of
the Gulf of Mexico sedimentary basin and the
Mississippi Embayment, situated west and south
of the county respectively (Marsh, 1966). The
majority of the vast thickness of Tertiary
sediments underlying the county are continental
siliciclastics and marginal marine units.
Locally, the thick sequence of Miocene and
younger siliciclastic rock units function as fresh
water aquifer systems, and are a source of non-
petroleum economic mineral commodities. The
following discussion of the geology of Escambia
County is therefore restricted to the Middle
Miocene and younger strata. All stratigraphic
nomenclature follows Braunstein et al.(1988),
and the areal extent of units is taken from Scott
(1993).

Middle and Upper Miocene Series
Pensacola Clay
The Pensacola Clay (Marsh, 1966) is a dark
to light gray to brownish-gray, silty, variably
sandy clay and quartz sand unit underlying
central and southern Escambia County. This
formation characteristically contains a prolific
benthic foraminifera assemblage, as well as
marine molluscs and ostracods. The Pensacola
Clay consists of three members in this area a
lower clay member, a thin sand member named
the Escambia Sand, and an upper clay member.
The formation ranges from approximately 380
feet thick in the east-central part of the county to
over 1000 feet thick just north of Pensacola and
under Perdido Bay. It unconformably overlies
Oligocene carbonates of the Chickasawhay
Formation.
The Pensacola Clay is generally absent in the
northern portion of the county. Here it grades
into the Coarse Clastics or is truncated by the
overlying Citronelle Formation. The top of the
formation varies in depth from approximately 250
feet below land surface (bls) near Cantonment,
to nearly 800 feet bls under Perdido Bay in
southwestern Escambia County.













A

60-200
40-
40100
20
0 0 ..


-40 -100 CITF
-60 -200
-80.
300
-100
-120 -400
-1401
-160 -500 PEN
-180-600
-200.
-700
-220-
-240 -800
-260
-20 -900
-300 1
-1000

TD=3025 1. TO
VERTICAL EXAGGI
APPROXIMATELY


,-A'
I-.
o, l
UI 02

E F





IONELLE
IFM.I


4---


ACOLA 1
TD=550 It.
CLAY MILES
0 1 2 3 4 5
KILOMETER
KILOMETERS


S"To=1524 It.
1=5048 ft.
ERATION IS
175 TIMES TRUE SCALE


I B
300
80
60 200
40
100
20
0 0
-20-
-100
-40
-60- -200
-80


-120 -.400
-140
-500
-160
-180 .600
-200
-220-
-240
-260
-280 .-900
-300
-1000


MILES
o0 1 2 3 4 5
=130011. KILOMETERS TD=3025 I
VERTICAL EXAGGERATION IS APPROXIMATELY 175 TIMES TRUE SCALE


Figure 2. Cross section A A'.


Figure 3. Cross section B B'.


Mlocene-Pliocene Series
Coarse Clastics
Marsh (1966) coined the name Miocene
Coarse Clastics for the extensive beds of light-
brown to light-gray, poorly sorted fine to very
coarse sand, granules, and small quartz pebbles
and mollusc shells underlying the wester-most
Florida panhandle. These beds most likely
transgress the Miocene-Pliocene age boundary,
and the general name Coarse Clastics has been
adopted (Braunstein et al., 1988). The mineral
muscovite is common as an accessory
throughout the unit. Perhaps the most distinctive
feature of the Coarse Clastics, and that which
differentiates them form the overlying Citronelle
Formation, is the presence of abundant small
marine molluscs. In some well samples, these
fossils comprise 5 to 50 percent of the sample.
Thickness of the Coarse Clastics is variable.
It is about 70 feet thick in north-central Escambia
County, from where it generally thickens to the
southeast and southwest, attaining a maximum
thickness of nearly 500 feet just southeast of
Cantonment. Depth to the top of the unit varies
from approximately 280 feet bls beneath


Pensacola Bay, to nearly 650 feet bls in
northwestern Escambia County near the Florida-
Alabama state line.
The Coarse Clastics interfinger with the
Pensacola Clay in south central Escambia
County, and are in turn unconformably overlain
by the Pleistocene age Citronelle Formation and
undifferentiated terrace deposits.

Pliocene Series
Cltronelle Formation
The Citronelle Formation (Matson, 1916) is
predominantly a lightyellowish-brown to reddish-
brown to light-gray to white quartz sand unit,
containing lenses and beds of clay and chert
and quartz gravel. It forms the stream-incised
hills of the Westem Highlands Zone, and forms
a distinct bluff at Bay Bluff, along the western
shore of Escambia Bay. Analyses by Coe (1979)
suggest that the Citronelle Formation sediments
are largely deltaic in origin. Clay beds within the
Citronelle Formation may reach 60 feet in
thickness, and a few, such as one at Molino, are
of suitable economic grade for brick making
(Marsh, 1966). Fossils are generally rare, but











scattered molluscs,foraminifera, shrimp burrows,
fossil pollen and wood remains have been
reported from Citronelle sediments in various
parts of Escambia County (Marsh, 1966).
The abundant iron oxide in the Citronelle
Formation lends a reddish color to many of the
sediments, and may concentrate in sand beds
forming hardpan layers. These hardpan layers
vary from less than an inch to several feet thick.
Owing to their resistant nature and low
permeability, small ponds may form over
hardpan layers as well as over clay beds.
Ground water percolating downward through the
sediments will commonly reach a hardpan layer,
and be diverted laterally. When this lateral flow
intersects a surface stream gully, bluff, or
hillside, the exiting flow may undermine the
overlying sediments, causing a semicircular
collapse feature called a steephead. As erosion
continues, the steephead migrates away from the
water seepage point, cutting a stream gully as it
progresses. Steepheads are most common in
the deeply-incised terrain of the Western
Highlands.
The thickness of the Citronelle Formation
varies considerably. Because of the difficulty in
differentiating Citronelle sediments from the
overlying terrace deposits, there is some
uncertainty in the overall thickness range.
However, the Citronelle Formation generally
varies from about 200 feet thick at the southern
edge of the county to almost 800 feet thick in the
northwestern comer of Escambia County (Marsh,
1966).

Pleistocene and Holocene Series
Undifferentiated sand and clay
A series of undifferentiated, commonly
unconsolidated quartz sands and clays overlie
the Citronelle Formation in much of Escambia
County. These sediments are deposited in a
series of elevational marine terraces. The
younger terraces near the modem coast contain
still-discemable relict shoreline features, such as
clean quartz sand dunes and beach ridges. In
many areas, particularly in the central and
northern portions of the county, these sediments
are difficult to differentiate from the underlying
Citronelle Formation. They cap the hills of the
Westem Highlands, and accumulate as alluvium
in stream channels. These sediments consist
primarily of clean to slightly clayey quartz sands,
generally containing less clay and quartz
pebbles than the older Citronelle sediments.


The unconsolidated sediments, along with
Holocene alluvium and shoreline sands, are
grouped into the undifferentiated sand and clay
unit. Because of the difficultly in differentiating
them from the underlying Citronelle Formation
sediments, the undifferentiated sediments are not
depicted on the geologic cross sections (Figures
2 and 3).

GROUND WATER
Ground water, or water that fills the pore
spaces in subsurface rocks and sediments, is
the principal source of potable water in
Escambia County. It is derived primarily from
precipitation within Escambia and neighboring
counties.
The primary aquifer systems present under
Escambia County are the surficial aquifer, also
called the Sand and Gravel Aquifer, and the
deeper Floridan aquifer system. These units are
separated by an aquiclude, commonly
containing water-bearing units, named the
intermediate aquifer/confining unit. Data on the
extent and thickness of each aquifer system is
taken from Musgrove et al. (1961, 1965), Marsh
(1966), and Scott et al. (1991).

Sand and Gravel Aquifer
The majority of water wells in Escambia
County draw water from the Sand and Gravel
Aquifer. This aquifer is formed in the porous
siliciclastic sediments of the Coarse Clastics, the
Citronelle Formation, and the surficial
undifferentiated sand and clay units. It extends
under the entire county, overlying Oligocene
carbonate in the northern part of the county, and
overlying the Pensacola Clay in the southern
portion of the county. It is variable in thickness,
ranging from the surface down to depths of 200
to 500 feet bls. Unlike the carbonate aquifer
system in much of Florida, water from the Sand
and Gravel Aquifer is low in mineral content due
to the predominantly insoluble quartz sand and
gravel composition of the water-bearing
sediments. As such, it makes an economical
industrial water source for manufacturing
processes requiring low mineral content water:

Intermediate aquifer/confining unit
Locally, the Sand and Gravel Aquifer is
separated from the underlying Floridan aquifer
system by an intermediate confining unit
comprised of the Pensacola Clay. This low-
permeability unit is variable in thickness,










generally ranging from 380 to 1000 feet thick. It
acts as an aquiclude and effectively isolates the
two aquifer systems. The Escambia Sand
member, situated within the Pensacola Clay, may
contain freshwater but is not utilized as a water
source in Escambia County.

Floridan aquifer system
The Floridan aquifer system is composed of
porous carbonate rocks of Miocene and Eocene
age. The top of the unit lies at depths generally
in excess of 600 feet under Escambia County.
Water within the Floridan aquifer system is
harder, with a higher dissolved mineral content
than the overlying Sand and Gravel Aquifer
water. The chloride content increases
substantially downdip, under the Perdido Bay
area in southwestern Escambia County.
Although the Floridan aquifer system is the
primary fresh water source in much of Florida, it
is not used extensively in the western panhandle.
The availability of high quality water at shallower
depths in the Sand and Gravel Aquifer precludes
the need to drill deeper wells to reach the
Floridan aquifer system.

MINERAL RESOURCES
The principal near-surface, non-energy
mineral resources occurring in Escambia County
are quartz sand, gravel and clay. These
commodities are mined from open pits in the
shallowundifferentiated sediments and Citronelle
Formation. The following discussion summarizes
the current mining status and potential for each
commodity in Escambia County.

Sand and Gravel
Quartz sand and gravel are mined by three
companies in Escambia County. Information on
each operation is from Spencer (1993).
Campbell Sand & Gravel Company operates the
Century Mine, situated in section 4 of Township
5N, Range 30W, near Century. Sand and a
range of gravel sizes for masonry and concrete
mixes are the primary products from this
operation. Clark Sand Company produces
masonry sand from the Pensacola Mine, located
in multiple sections of Township 2S, Range 30W.
American Clay and Shell Company operates the
Belview Pit in Township 1S, Range 39W, section
39, which provides local fill material.
Several other small commercial operations
and numerous private pits are worked for various
mixtures of sand and clay. This material is used


locally for fill. Sand is an abundant resource
throughout Escambia County, and future
exploitation will be largely dependent upon local
market demand.

Clay
Refractory clay, used in making brick
products, has been mined in the county for
many years. The Taylor Brick Company,
followed later by Bickerstaff, operated a large pit
located near the town of Molino. Although
currently inactive, these companies mined brick
clay from a 50 feet thick bed in the Citronelle
Formation.
In the central and northern parts of the
county, the Citronelle Formation contains clay
beds ranging from a few inches up to tens of
feet in thickness. These beds extend from a few
feet to several miles in length (Musgrove et al.,
1961). The presence of these deposits suggests
that economic quantities of clay are readily
available in Escambia County. However,
resumption of the mining at Molino, or
development of other clay mines within the
county will depend largely on the local demand
for clay products.

References

Braunstein, J., Huddlestun, P.F., and Biel, R.,
1988, Gulf Coast Region, Correlation of
Stratigraphic Units of North America
(COSUNA) Project: American Association of
Petroleum Geologists, Tulsa, OK.

Coe, C.J., 1979, Geology of the Plio-Pleistocene
sediments in Escambia and Santa Rosa
Counties, Florida: MS Thesis, Florida
State University, 115 p.

Healy, H.G., 1975, Terraces and shorelines:
Florida Bureau of Geology Map Series 71.

Marsh, O.T., 1966, Geology of Escambia and
Santa Rosa Counties, Western Florida
Panhandle: Florida Geological Survey Bulletin
no. 46, 140 p.

Matson, G.C., 1916, The Pliocene Citronelle
Formation of the Gulf Coastal Plain: U.S.
Geological Survey Professional Paper 98,
p. 167-192.









Musgrove, R.H., Barraclough, J.T., and Marsh,
O.T., 1961, Interim Report on the water
resources of Escambia and Santa Rosa
Counties, Florida: Florida Geological Survey
Information Circular no. 30, 89 p.

Musgrove, R.H., Barraclough, J.T., and
Grantham, R.G., 1965, Water Resources of
Escambia and Santa Rosa Counties, Florida:
Florida Geological Survey Report of
Investigations no. 40, 102 p.

Scott, T.M., Lloyd, J.M., and Maddox, G., 1991,
Florida's ground water quality monitoring
program hydrogeologic framework: Florida
Geological Survey Special Publication 32, p.
95.

Scott, T.M., 1993, Geologic map of Escambia
County, Florida: Florida Geological Survey
Open File Map Series 14.

Spencer, S.M., 1993, The Industrial Minerals
Industry Directory of Florida: Florida
Geological Survey Information Circular 109,
30 p.

White, W., Puri, H., and Vernon, R., 1964,
Unpublished manuscript cited in: Puri, H. and
Vernon, R., 1964, Summary of the geology of
Florida and a guidebook to the classic
exposures: Florida Geological Survey Special
Publication no. 5 (revised), 312 p.

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