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Fort Thompson Formation
Stratigraphic range: Pleistocene
Type	Geological formation
Lithology
Primary	Sand, marl, animal shell marl
Location
Region	South Florida
Country	United States
Type section
Named for	Fort Thompson fossil beds
Named by	E. H. Sellards

The Fort Thompson Formation is a Pleistocene geologic formation underlying Florida's Everglades.

Age

Era : Neogene
Period: Miocene
Faunal stage: Chattian through early Blancan ~28.4 to ~2.588 mya, calculates to a period of 25.512 million years

Lithology

Fort Thompson formation is of fresh-water marine origin and composed of sand, marl, shell marl, sandstone, and limestone. Marl and sand are the two main components with limestone related to fluctuation in the water table and calcium carbonate cementation.

The alternating fresh-water and marine marls and limestones exposed at Fort Thompson were initially named the Fort Thompson beds by Sellards (1919, p. 71-72). Cooke and Mossom (1929, p. 211-215) later named this sequence the Fort Thompson formation and indicated that the beds lie unconformably on the Caloosahatchee marl and are overlain by the Lake Flirt marl of Pleistocene and Recent age.

Development. --The Fort Thompson formation at the type locality is about 6 feet thick. In the Miami area it attains a maximum thickness of 80 feet and constitutes the major part of the Biscayne aquifer as described by Parker (1951, p. 820-823). The southern 18 miles of the line of test wells is approximately the western boundary of the Biscayne aquifer. In this area the Fort Thompson formation ranges from 3 to 9 feet in thickness. The strata of Pleistocene age between wells 10 and 33 possibly are transitional beds between the Fort Thompson and Anastasia formations.

Lithology. --The

Age. --Parker and Cooke (1944, p. 94-96) correlated the beds at old Fort Thompson with the inferred fluctuations of sea level during the Pleistocene epoch. Fresh-water beds have not been reported in the Pliocene of the Atlantic Coastal Plain, and they do not occur in the Caloosahatchee marl (Pliocene) in the outcrop area, although fresh-water shells are found, in places, mixed with the marine forms. Any sequence of marine and fresh-water beds, or fresh-water beds, older than the Lake Flirt marl is considered as representing the Fort Thompson formation.

http://sofia.usgs.gov/publications/circular/314/pleistocene.html http://www.chnep.org/info/Symposium97/9802-5.pdf

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Florida Pleistocene coastal terraces

Florida Pleistocene coastal terraces are part of remaining Pleistocene marine terraces and shorelines along the Atlantic seaboard.

Defined, these terraces are the former bottoms of shallow seas usually flooded with deposits of sand, clay, silt, and shells bounded along their inner margins by shoreline features such as relect beaches, swales, inner lagoons, seaward facing wave cut scarps or sea cliffs, offshore and bay bars. They are found along the Atlantic seaboard to the Gulf of Mexico and south of any area which was subject to glaciation.

Terrace names

• Hazelhurst
• Okefenokee
• Coharie
• Wicomico
• Penholoway
• Talbot
• Pamlico
• Silver Bluff

In 1988, P. F. Huddlestun renamed all of the higher terraces, using local place names from Georgia and subdividing Cooke's Sunderland terrace into three separate discontinuous remnants (Argyle, Waycross, and Okefenokee.

Hazelhurst Terrace

The Hazelhurst Terrace was originally known as the Brandywine Terrace, named by W. B. Clark in 1915 for deposits in Prince George's County, Maryland. In Florida, the Hazelhurst Terrace existed in the northern reaches of the counties of Escambia, Santa Rosa, Okaloosa, and Walton. The counties of Washington, Calhoun, and Jackson had groups of small islands. Further east, almost the entire county of Gadsden was dry land. Jefferson and Madison had four small islands while a single oblong island was shared by Bradford and Clay counties. Polk County had the isolated southern most islands.

Elevation

The Hazelhurst Terrace is set at 215-320 feet above mean sea level.

Coharie Terrace

The Coharie Terrace is named for the Great Coharie Creek, a tributary of the Black River in North Carolina. The Coharie represents the second interglacial sea level rise. Northwest Florida experienced the greatest amount of deposition from both fluvial and wave action.

Elevation

• The Coharie Terrace is set at 170-215 feet above sea level.

Okefenokee Terrace

The Okefenokee Terrace represents the third interglacial rise in sea level and includes the Sunderland Terrace named by Cooke in 1939.

Elevation

• The Okefenokee Terrace is set at 100-170 feet above sea level.

Wicomico Terrace

The Wicomico Terrace is associated with the Wicomico Sea and a period of time during the Aftonian interglacial (Pre-Illinoian) ~1.5 million years ago.

Penholoway Terrace

1 million

Pamlico Terrace

The Pamlico Terrace 500,000 to 100,000 ka

Talbot Terrace

marine oxygen isotope stage 3 (OIS 11, 15)

Silver Bluff Terrace

less than 10,000 years ago.

Correlation of terraces and shorelines

Initial geological observations.

• G. C. Matson and S. Sanford, Escambia, Citrus, & Alachua counties: Newberry 70-100 feet correlates with the Wicomico. Tsala Apopka 40-60 feet correlates with the Penholoway, Pensacola 0-40 feet, no correlation.
• C. W. Cooke, 1939 and 1945 statewide observations: Hazelhurst with an elevation of 215-270 feet. Coharie Terrace at 170-215 feet. Sunderland Terrace 100-170 feet. Wicomico Terrace at 70-100 feet. Penholoway Terrace at 42-70 feet. Talbot Terrace at 25-42 feet. Pamlico Terrace at 5-25 feet. Silver Bluff at 9-10 feet.
• R. O. Vernon, Holmes and Washington counties (1942). Coastwise fluvial delta plain at 250-320 feet correlates with the Hazelhurst. Coastwise surface marine terrace at 170-220 feet correlates with the Coharie. Coastwise marine terrace at 60-105 feet correlating with the Wicomico. Coastwise marine terrace at 115-150 correlates with the Okefenokee. Coastwise marine terrace 5-30 feet correlates with the Pamlico.
• R. O. Vernon, Citrus and Levy Counties (1951): Coharie at 220 feet. Okefenokee at 150 feet. Wicomico at 100 feet. Pamlico at 25 feet.
• F. S. MacNeil, Statewide observations (1950): High Pliocene terrace at 150-280 feet correlates with the Hazelhurst. Okefenokee at 150 feet. Wicomico at 100 feet. Pamlico at 25-35 feet. Silver Bluff at 8-10 feet.
• O. T. Marsh, Escambia and Santa Rosa counties (1966): High level or upland surface marine terrace 60-280 feet correlates with the Hazelhurst. Offshore bar at 190-200 feet correlates with the Coharie. Penholoway at 70-80 feet. Pamlico at 30 feet.
• C. W. Hendry and C. Sproul, Leon County observations (1966). Miocene-Pliocene fluvial delta plain at 260 feet correlates with the Hazelhurst. Okefenokee Dunes correlates with the Coharie. Okefenokee marine terrace at 150 feet. Wicomico marine terrace at 100 feet. Pamlico marine terrace at 25-35 feet.
• W. J. Yon, Jr., Jefferson County observations: Miocene fluvial delta plain to 260 feet correlates with the Hazelhurst. Wicomico marine terrace at 40-45 feet. Pamlico marine terrace at 26-40 feet. Silver Bluff marine at 10 feet.
• B. J. Bermes, G. W. Leve, and G. R. Tarver, Flagler, Putnam, and St. Johns counties observations: Coharie (marine) at 170-215 feet. Sunderland (marine) at 100-170 feet. Wicomico (marine) at 100-70 feet. Penholoway (marine) at 42-70 feet. Talbot (marine) 25-42 feet. Pamlico (marine) at 10-25 feet. Silver Bluff (marine) at 10 feet.

References

• Voldosta State University [1]

Clark, W. B., The Brandywine formation of the middle Atlantic coastal plain, American Journal of Science, p. 499-506. http://publicfiles.dep.state.fl.us/FGS/WEB/terraces_300dpi20.pdf