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FLRD GEOLOSk ( IC SUfRiW


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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)

by

Kenneth M. Campbell


Florida Geological Survey
Tallahassee, Florida
1984
































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St. Vincent Island

(St. Vincent National Wildlife Refuge)


Kenneth M. Campbell

Florida Geological Survey

1984


Location

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

(U.S.G.S., 1:24,000).


Access

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
(904) 653-8808

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







Site Information

Regional Geology

Structure

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).

Aeogene Stratigraphy

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,

1984).

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

(Schmidt, 1984).

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.

Intracoastal Formation

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,

1984).

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).








Quaternary Stratigraphy


Undifferentiated Pleistocene

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

Island.

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,

1968).

--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

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

level reversals.

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,

1977).

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.








Bibliography


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

Dept.


,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,

146 p.







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,

pp. 224-234.


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,

pp. 393-399.








Figure 1: Location Map


Figure 2:


Figure 3:


Figure 4:






















Figure 5:


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.













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