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FLRD GEOLOSk ( IC SUfRiW
[year of publication as printed] Florida Geological Survey [source text]
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State of Florida
Department of Natural Resources
Elton J. Gissendanner, Executive Director
Division of Resource Management
Charles W. Hendry, Jr., Director
Florida Geological Survey
Steve R. Windham, Chief
Open File Report 8
St. Vincent Island
(St. Vincent National Wildlife Refuge)
Kenneth M. Campbell
Florida Geological Survey
3 1262 04545 4386
fPC I i i
OFR 8 Cce
St. Vincent Island
(St. Vincent National Wildlife Refuge)
Kenneth M. Campbell
Florida Geological Survey
St. Vincent Island is a Holocene barrier island located in Franklin
County, Florida, west-southwest of Apalachicola, Florida (figure 1). The
island is located on the Apalachicola Sheet topographic quadrangle (U.S G.S.,
1:250,000) and on the Indian Pass and West Pass 7.5 minute quadrangle maps
St. Vincent Island is accessible only by boat. To obtain current access
information, contact the Refuge Manager:
St. Vincent National Wildlife Refuge
Post Office Box 347
Apalachicola, Florida 32320
Significance of site
St. Vincent Island consists of an extensive, virtually undisturbed beach
ridge plain of late Holocene age. The system of 12 beach ridge sets
(approximately 180 individual ridges) provides a detailed window into late
Holocene coastal and sea level history.
Florida Bureau of Geology Library
903 W. Tennessee St.
Tallahesee, FL 32304
The dominant structure in the St. Vincent Island area is most commonly
called the Apalachicola Embayment. The embayment is narrowest to the
northeast, and opens to the south and southwest along an axis which plunges to
the south-southwest (Schmidt, 1984). The embayment is bounded by the
Chattahoochee Anticline to the northwest and the Ocala Arch to the southeast.
The adjacent highs bring Eocene and Oligocene sediments to the surface.
Neogene and Quaternary sediments pinch out or are truncated against the
flanks of the high (Schmidt, 1984).
St. Marks Formation
The St. Marks Formation was named by Puri and Vernon (1964).
Lithologically, the St. Marks is a dolomitio,-calcarenitic limestone, ranging
to a packed biomicrite to wackestone, very pale orange to light gray to white
Ln color, moderately to well indurated and fossiliferous. The St. Marks is
often quartz sandy and may contain occasional greenish clay blebs (Schmidt,
The St. Marks dips to the southwest and ranges in thickness from zero at
the east edge of the Apalachicola Embayment to over 200 feet near the
embayment axis just west of St. Vincent Island (Cameron and Mory, 1977). In
the St. Vincent Island area, the St. Marks Formation becomes indistinguishable
from the overlying Bruce Creek Limestone (figures 2 and 3) (Schmidt, 1984).
Bruce Creek Limestone
The Bruce Creek Limestone was named by Huddlestun (1976a) for Alum Bluff
equivalent carbonate rocks in the coastal portion of Walton County and
vicinity. More recently other authors have mapped this unit to both the east
and west of Walton County. Schmidt et al (1982) and Bolling (1982) have shown
that the eastern extent of the Bruce Creek coincides with the eastern boundary
of the Neogene Apalachicola Embayment where the Bruce Creek and the underlying
St. marks Formation are indistinguishable (Schmidt, 1984).
Lithologically, the Bruce Creek in the St. Vincent Island area is a white
to light yellowish-gray, moderately indurated, macro-moldic, calcarenitic
limestone with some dolomite (Schmidt, 1984). Common accessary minerals
include quartz sand (up to 20%), with pyrite, phosphorite, mica, clay and
glauconite in trace amounts. Common microfossils include planktonic and
benthic foraminiEera, ostracods, bryozoans and calcareous nannofossils
The Bruce Creek dips gently to the south-southwest at approximately 12
feet per mile (Schmidt, 1984). Several workers (Huddlestun, 1976a; Schmidt
and Clark, 1980; Clark and Schmidt, 1982; Bolling, 1982) have dated the Bruce
Creek as Middle Miocene based on planktonic foraminifera.
The Intracoastal was named by Huddlestun (1976a,b) in the Walton County,
Florida area. Schmidt and Clark (1980) and Schmidt (1982) extended the for-
mation eastward to eastern-most Franklin County (east of St. Vincent Island).
Schmidt and Clark (1980) describe the Intracoastal as a "very sandy,
highly micro-fossiliferous, poorly consolidated, argillaceous, calcarenitic
limestone." The dominant lithologic components include quartz sand, clay,
calcilutite, phosphorite and abundant microfossils. Accessory minerals
Include mica, glauconite, pyrite and heavy minerals, generally in trace
amounts (Schmidt, 1984).
The Intracoastal dips very gently to the west and west-southwest in the
viLcLnty of St. Vincent Island. The dip in this area is less than three feet
per mile (Schmidt, 1984). The formation thickens from the eastward margin of
the Apalachicola Bmbayment and ranges from 100 to 200 feet thick in the
vincinLty of St. Vincent Island (Schmidt, 1984). The top of the Intracoastal
has been dated as Late Pliocene in Bay County, to the west of St. Vincent
Island (Schmidt and Clark, 1980).
Chipola and Jackson Bluff Formations
The Chipola Formation and the overlying Jackson Bluff Formation are
undiferentiated in the vicinity of St. Vincent Island. Both formations are
predominantly molluscan rich, argillaceous, quartz sandy shell beds (Schmidt,
1984). The Jackson Bluff, where it is differentiated from the Chipola,
generally contains more quartz sand and clay, is more poorly indurated, with
pelecypods dominant over gastropods. Where the Chipola is not identified,
the entire shell bed thickness is considered to be Jackson Bluff (Schmidt,
1984). In the St. Vincent Island area, the base of the undifferentiated
Chipola Jackson Bluff contains a shell barren clayey sand unit (Schmidt,
the dip of the Jackson Bluff in the St. Vincent Island area is variable
however the regional dip is to the south-southwest at about three feet per
mile (Schmidt, 1984). The Jackson Bluff in the vicinity of St. Vincent Island
has been dated as Late Pliocene to possibly Early Pleistocene (Schmidt, 1984).
Schnable and Goodell (1968) discussed the Pleistocene and Holocene
geology of the coastal area of the Apalachicola coast, including St. Vincent
Island. Pleistocene sediments vary in thickness from approximately 120 feet
at Cape San Bias (west of St. Vincent Island) to less than 10 feet to the east
(Schnable and Goodell, 1968). Two of Sohnable and Goodell's borings are
located along the western portion of the lagoon side of St. Vincent Island.
These borings show 22-25 feet of Holocene sediment, but do not reach the base
of Pleistocene sediment. Limestone is encountered in local water wells at
100-110 feet below mean sea level (Schnable and Goodell, 1968). This would
indicate approximately 75 to 90 feet of Pleistocene sediment at St. Vincent
Schnable and Goodell (1968) utilize a two part breakdown of Pleistocene
sediments-and suggest that two depositional cycles are represented. Each
depositional cycle is represented by a fining upward sediment package
separated from overlying and underlying units by unconformities.
The lower Pleistocene unit of Schnable and Goodell (1968) at St. Vincent
Island consists of a coarse sand, overlain by silty clay and clay, in turn
overlain by very clean fine quartz sand. The uppermost portion of the lower
unit consists of gray silty, clayey quartz sand or dark gray, quartz sandy,
silty clay. Clays within the lower Pleistocene unit consist primarily of
kaolinite with smaller quantities of montmorillonite (Schnable and Goodell,
--The .upper Pleistocene sequence (Schnable and Goodell, 1968) consists of a
silty, fine to coarse quartz sand which grades upward to fine grained sands
and silty sands. The fine sands and silty sands are overlain by clayey sand
and sandy clay.
Schmidt (1984) breaks Quarternary sediments into two lithologic packages,
but did not attempt to differentiate between Pleistocene and Holooene
sediments. The lower unit of Schmidt, onshore in the vicinity of St. Vincent
Island consists of massive clays with interspersed quartz sands which grade
and thin northward into graded sands with some massive clays. Schmidt's upper
unit consists of clean sands and clayey sands (Schmidt, 1984).
Holocene sediments in the vicinity of St. Vincent Island consist
primarily of the present day barrier islands, spits and shoals and sediments
filling the old entrenched Apalaohicola River Valley. Holocene sediments
attain their greatest thickness (74 feet) in the entrenched river valley.
Outside the old Apalachicola River Valley, Holocene sediments range from
approximately 10-25 feet thick (Schnable and Goodell, 1968).
St. Vincent Island rests on basal Holocene sediments which consist of
clayey, fine grained quartz sands, quartz sandy muds and poorly sorted quartz
sands. These Holocene sediments are deposited on an oxidized Pleistocene sur-
face (Otvos, 1984). The island itself is constructed of well to very well
sorted quartz sands, deposited under littoral or supratidal conditions. Many
of the beach ridge swales and some of the ridges are blanketed with silts and
clays. The first two ridges behind the present beach, and those immediately
adjacent to Indian Pass are dune decorated (Stapor, 1973).
Beach Ridge Development
Beach ridges are linear sand ridges which were deposited along the beach
face in areas with a gentle offshore slope, low wave energy, and an abundant
sand supply. Beach ridges form only on accreting beaches. Because they form
on the beach face they indicate the location and orientation of the coastline
at the time they were formed.
Beach ridges are constructed by wave run-up in the swash zone by waves
which fall in the long term "maximum wave energy" category (Tanner and
Stapor, 1972). The internal structure of beach ridges indicates that all or
almost all of the ridge is constructed by wave run-up, with very little
washover (Tanner and Stapor, 1972). Internal bedding is almost exclusively
composed of planar, seaward dipping cross beds. The ridge grows upward and
seaward as material is deposited. Smaller ridges may be constructed by "fair
weather waves" but will be destroyed when wave energy increases.
Beach Ridge Plain Development
Stapor (1973), describes several basic types of beach ridge patterns,
each of which is indicative of specific depositional environments. Stapor's
categories are: (1) Ridges convex seaward, occurring at the distal prograding
tip of spits; (2) Ridges concave seaward which are being actively eroded per-
pendicular to their ridge and swale orientation; (3) Ridges concave seaward
deposited in embayed sections of the coast; and (4) Ridges convex seaward which
represent net seaward growth, not lateral extention.
Beach ridges of category (3) are predominant on St. Vincent Island (sets
A-G and set K) (figure 4). Category (3) ridges which are essentially parallel
indicate that sediment was transported from offshore without significant
longshore transport. On St. Vincent, beach ridge sets A, B, C, F, G, H, J
and K are indicative of these conditions. Sets D and E are splayed to the
east (increasing ridge crest spacing), a condition which indicates that west-
ward Longshore drift supplied the sand for their construction (Stapor, 1973).
Beach ridges of set I, although indistinct, appear to splay to the west,
indicating a temporary reversal of drift direction (to the east).
Beach ridge sets H, I, J & L were deposited in large part due to the
migration of the West Pass lunate bar across the inlet (Stapor, 1973).
The youngest ridge set (L) is of category (4). The sediment source for these
ridges was sand delivered by easterly (primary) and southerly (secondary)
transporting drift systems (Stapor, 1973).
Holocene Sea Level History
Stapor and Tanner (1977) present a Holocene sea level history developed
from evidence preserved on St. Vincent Island and the adjacent mainland. The
evidence utilized includes: 1) "average elevations of erosional scarps and
beach ridge sets" 2) "elevation and distribution of cultural components of
archeological sites" 3) "elevation of silt and clay beds containing marine
shells" and 4) carbon 14 dating. Stapor and Tanner find evidence for 4 sea
Following a long period of sea level rise beginning approximately 20,000
years before present (BP), and continuing thru the early Holocene, sea level
reached the highest Holocene sea level stand approximately 5,000 BP (Stapor
and Tanner, 1977). This sea level stand is at approximately 5.0 feet above
present sea level. The evidence for this high Holooene sea level stand
consists of a wave cut scarp cut into unconsolidated pre-Holocene sands on the
mainland shoreward of the present location of St. Vincent Island (figure 5).
This appears to be the Silver Bluff position (Stapor and Tanner, 1977).
The first sea level reversal documented by Stapor and Tanner (1977)
occurred approximately 6000-4000 BP when sea level rise changed to fall. The
evidence consists of the topographically low silt and clay covered beach
ridges on St. Vincent Island (figure 4 sets A D, figure 5) located offshore
of the topographically high (+ 5.0 feet) scarp found on the mainland. St.
Vincent Island beach ridge sets A D were deposited at sea levels
approximately 5.0 feet lower than present, a sea level fall of approximately
10 feet. Archeological information provides the only present information
regarding the time of formation of the mainland scarp, the St. Vincent beach
ridges and the sea level reversal. Norwood occupation sites are present on
both the mainland scarp and at sites 60 & 64 on St. Vincent Island (figure 2).
This indicates that they were formed prior to 4000-3000 BP (Stapor and Tanner,
The second reversal (from fall to rise) occurred after the deposition of
beach ridge sets A-D and prior to deposition of the marine shell bed which
overlies the silts and clays which blanket set D. The marine shells are C-14
dated at 2100 130 BP (figure 4). The marine shells are exposed
approximately 1.6 feet above present sea level, indicating a rise of about 6.5
feet (Stapor and Tanner, 1977).
The third reversal (from rise to fall) occurred after deposition of the
dated marine shells (2110 130 BP), but prior to the early Swift Creek
(1800-1500 BP) occupation of archeological site 71 (figure 2). This site is a
midden which rests on silt and clay material. The contact is located in the
middle of the present day intertidal zone (Stapor & Tanner, 1977). The magni-
tude of sea level fall is 6.5 8.2 feet (Stapor and Tanner, 1977).
The last sea level reversal documented by Stapor and Tanner (1977)
occurred after the Weeden Island (1500-800 BP) occupation of site 72
(figure 4). The base of the shell midden at site 72 rests on silt and clay
substrate 3.9 feet below present sea level. Sea level rise to the present
poeLtion is 3.9 feet.
Based on elevation, there are two major groups of beach ridge sets on St.
Vincent Island. Sets A D (figure 2) have crest elevations of about 1m. Sets
E L (figure 4) have crest elevations of approximately 8.2 feet (excluding
dune ridges and dune decorated beach ridges which have elevations up to 16.4
feet). Tanner and Stapor (1972) related beach ridge height to wave height and
concluded that fair weather waves are not responsible for beach ridge
formation. Stapor and Tanner (1977) state that most of the beach ridges on
St. Vincent Island could be constructed by modern day storm waves (3.3 4.9
feet). The 3.3 foot crest ridges (sets A D) would require either less wave
energy, or lower sea level. As these ridges are blanketed with silt and clay,
the tower sea level accounts for the difference in elevation.
Secondary deposits of alluvial silt and clay, marsh deposits and shell beds
have tilled or partially filled many of the beach ridge swales. If these
secondary deposits were removed, St. Vincent would be several islands as the
original surfaces of the swales are often below present day sea level. This
supports Stapor and Tanner's (1977) conclusion that mean sea level has for the
past approximately 4,000 years fluctuated around a mean value which is less
than 4.9 feet below present mean sea level position.
Bolling, Sharon, 1982, Neogene Stratigraphy of Gulf County, Florida,
unpublished M.S. thesis, Florida State University Geology Dept., 146 p.
Cameron, C. C. and P. C. Mory, 1977, Mineral Resources of the Bradwell Bay
Wilderness and the Sopchoppy River Study Area, Wakulla County, Florida,
U. S. Geol. Survey Bull. 1431, 37 p.
Clark, Murlene Wiggs, and W Schmidt, 1982, Shallow Stratigraphy of
Okaloosa County and Vicinity, Florida, Fla. Bureau of Geology, Rept. of
Invest. 92, 51 p.
Huddlestun, Paul F 1976a, The Neogene Stratigraphy of the Central Florida
Panhandle, unsubmitted dissertation Florida State University, Geology
,1976b, The Neogene Stratigraphy of the Central Florida Panhandle, Geol.
Soc. America Section Meeting, V. 8, N. 2, p. 203 (abstract).
Otvos, E. G., 1984, Alternate Interpretations-of Barrier Island Evolution,
Apalachicola Coast, Northwest Florida, Litoralia, vol. 1 #1, pp. 9-21.
Puri, Harbans S., and R. O. Vernon, 1964, Summary of the Geology of Florida
and a Guidebook to the Classic Exposures, Fla. Geol. Survey, Special
Publication 5, Revised, 312 p.
Schmidt, Walter, 1984, Neogene Stratigraphy and Geologic History of the
Apalachicola Embayment, Florida, Florida Geological Survey, Bulletin 58,
and M. W. Clark, 1980, Geology of Bay County, Florida, Fla. Bureau of
Geology Bull. 57, 76 p.
__ M. W. Clark, and S. Bolling, 1982, Neogene Carbonates of the Florida
Panhandle, in Fla. Bureau of Geology, Special Publication No. 25,
Miocene of the Southeastern United States, Proceedings of the Symposium,
Schnable, Jon E., and H. G. Goodell, 1968, Pleistocene-Recent Stratiqraphy,
Evolution, and Development of the Apalachicola Coast, Florida, Geol. Soc.
of America, Special Paper 112, 72 p.
Stapor, F W. 1973, Coastal Sand Budgets and Holocene Beach Ridge Plain
Development, Northwest Florida, Ph.D. Dissertation, Florida State
University, Tallahassee, Florida, 221 p.
and W F. Tanner, 1977, Late Rolocene-Mpan Sea Level Data From
St. Vincent Island and the Shape of the Late Holocene Mean Sea Level Curve,
Proceedings, Coastal Sedimentology Symposium, Florida State University,
Department of Geology, publishers, pp. 35-68.
Tanner, W. F. and F W. Stapor, 1972, Precise Control of Wave Run-up in Beach
Ridge Construction, Zeitschrift Fur Geomorphologie, vol. 16, #4,
Figure 1: Location Map
North-South Geologic Cross-Section, modified from Schmidt, 1984.
East-West Geologic Cross Section, modified from Schmidt, 1984.
Diagrammatic sketch map of St. Vincent Island, Franklin County,
Florida showing the different sets of beach ridges (A, B, C,..., L)
which comprise this Holocene island. The number 60, 64, 71 and 72
locate critical Indian middenst these sit number should begin with
8Fr to correspond with the site survey files of the Department of
Anthropology, Florida State University. The C-14 data of 2110 BP
locates the marine shell bed exposure; this shell bed stra-
tigraphically overlies the clay/silt deposits which blanket beach
ridge set D. The open arrows indicate directions of present-day
net long shore transport. Modified from Stapor and Tanner, 1977.
A detailed interpretation of the Holocene history of St. Vincent
Island Florida. Modified from Stapor, 1973.
0 5 MILES
0 5 KILOMETERS
ST. MARKS LIMESTON
-120 -L- 400
0 10 20 MILES
0 10 20
OFFSHORE SAND DIRECTLY TO BEACH *
LONGSHORE DRIFT 0
MAINLAND ,, *'"
-- ---- ST. VINi
/ LITTLE ST. GEORGE
ST. LUNATE %,,
ST VINCENT SOUND
1 o ..... 2 11 BPL 130
G f Z 0S T G E O R G E