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Florida Pleistocene coastal terraces and shorelines were the geologic result of interglacial (warming) and glacial (cooling) periods over what is now the Florida peninsula during the Pleistocene epoch giving the state its final distinct shape.
Overview[edit]
Florida emerged out of the late Pliocene's cooler and drier climate, somewhat close to today's climate, and into the Pleistocene's increasing cold climate. Florida's size east to west was enormous compared to today.
During the Pleistocene, repeated advancement and retreat of the North American glacial sheet resulted in fluctuations of sea level over several thousand years with the Florida peninsula either below or above the surrounding seas leaving behind distinct established terraces and shorelines assigned by mineral deposits and maximum sea level relative to the current mean sea level. Tidal activity, river systems, and currents were also a factor in erosion and deposition.
These marine terraces and shorelines were named by various geologists, verified and mapped by the USGS. Each glacial retreat caused sea level to rise less than the previous retreat, giving an extremely accurate depiction of the physical appearance of Florida during a particular interglacial.
Hazelhurst[edit]
The Hazelhurst terrace and shoreline (formerly the Brandywine) was assigned by C. W. Cooke[1]. The Hazelhurst is associated with the Gelasian, the first warming of the Early Pleistocene, 2.5 to 1.8 million years ago. It includes Vernon's Coastwise delta plain[2] and MacNeil's high Pliocene terrace. Deposits are found between 97 to 65.5 meters (320—215 feet) above mean average sea level.
The largest areas in land mass of the Hazelhurst in Florida are in the counties of Santa Rosa, Escambia, Walton, and Gadsden. It is these counties which have the bulk of sediments associated with the Hazelhurst. Deposits are also found to a lesser degree in Washington, Calhoun, and Jackson in the panhandle as well as Jefferson, Bradford, and Clay County, Florida to the east. South of these locales was underwater.
Coharie[edit]
The Coharie terrace and shoreline was applied by C. W. Cook in 1931 and was named for the Great Coharie Creek, a tributary of the Black River in North Carolina. It is associated with a Pre-Illinoian interglacial, most probably the disused Yarmouthian interglacial[3] and was the second rise in sea level during the Early Pleistocene glacial retreat. The Coharie is defined by sediments at 65 to 52 meters (215—170 feet) above current mean sea level. In Florida the Coharie is included with the Sunderland terrace in USGS mapping.
The Coharie is an overlaying of deposits on the Hazelhurst. It can best be described as increasing of land mass compared to the Hazelhurst
Sunderland[edit]
The Sunderland terrace and shoreline was assigned and named after a small town in Calvert County, Maryland. It is associated with a Pre-Illinoian interglacial, most probably the disused Yarmouthian interglacial and was the fourth rise in sea level during the Early Pleistocene glacial retreat. The Sunderland is defined by sediments at 52 to 30.5 meters (170—100 feet) above current mean sea level. In Florida the Sunderland is iCncluded with the Okefenokee terrace in USGS mapping. This terrace is found in the northern parts of the counties of Okaloosa and Walton. The Sunderland is also found in the northern counties of Gadsden, Jefferson, Madison, Suwanee, Bradford, Alachua, and Columbia.
Okefenokee[edit]
The Okefenokee terrace and shoreline was assigned by MacNeil in 1950 and named after Okefenokee Swamp. It includes deposits of the Sunderland terrace assigned by Cooke. It is associated with a Pre-Illinoian interglacial (Yarmouthian) and was the third rise in sea level during the Early Pleistocene glacial retreat. The Okefenokee is defined by sediments at 52 to 30.5 meters (170—100 feet) above current mean sea level. The dry land mass left behind can best be described as
Wicomico[edit]
The Wicomico terrace and shoreline was assigned by Cooke and is named for the Wicomico River in St. Mary's County, Maryland and Charles County, Maryland. The Wicomico is associated with the Sangamonian interglacial between 75,000 to 180,000 years ago (T. Lodge), (Kurtén & Anderson)[4][5] The Wicomico is defined by sediments located at 30.5 to 21 meters (100—70 feet) above current mean sea level.
Penholoway[edit]
The Penholoway terrace and shoreline was assigned by Cooke and named after Penholoway Creek in Wayne County, Georgia and associated with the Sangamonian interglacial. The Penholoway is defined by sediments located at 21 to 13 meters (70—42 feet) above current mean sea level. The seaward boundary is generally better defined than the landward boundary.[6]
Talbot[edit]
The Talbot terrace and shoreline was assigned by Cooke and named for Talbot County, Maryland. The Talbot is associated with the Sangamonian interglacial. The Talbot is defined by sediments located at 12 to 7.5 meters (42—25 feet) above current mean sea level.[7]
Pamlico[edit]
The Pamlico terrace and shoreline was assigned by Cooke and named for Pamlico County, North Carolina. The Pamlico is associated with the Sangamonian interglacial.[8] The Talbot is defined by sediments located at 7.6 to 2.4 meters (25—8 feet) above current mean sea level. It is the best developed formation in Florida due to the least modification by erosion.
Silver Bluff[edit]
The Silver Bluff terrace and shoreline was assigned by Cooke and named for Pamlico County, North Carolina. The Silver Bluff, according to MacNeil, is probably associated with the Holocene climatic optimum of ~4000 to 5000 BP.[9] and is defined by sediments located at 3.0 to 0.3 meters (10—1 feet) above current mean sea level composed of beach sand.[10]
The Silver Bluff does not include any well developed land features except in Franklin County and Gulf County in the north as well as Monroe County and Dade County. In other parts of Florida, the Silver Bluff established what are now barrier islands, all of the beach front on the east coast, and inland deposits. One outstanding feature would be Cape Canaveral.
Notes[edit]
The maps associated with this article originated with the United States Geological Survey and were created using a manual map overlay.
References[edit]
- Most information provided by: Fkorida Geological Survey, Terraces and Shorelines
- ^ Cooke, C. W., Seven coastal terraces in the Southeastern states, Washington Academy of Science Journal, v. 21, number 21, p. 503-515
- ^ Vernon, R. O., Geology of Holmes and Washington Counties, Florida; Department of Conservation, Florida Geologic Survey, Bulletin 21
- ^ Miller, James J., An environmental history of northeast Florida, University Press of Florida, 1st edition, 1998, ISBN 0813016002
- ^ Kurtén, Bjorn, Anderson, Elaine. Pleistocene mammals of North America, Columbia University Press, October 15, 1980, ISBN 0231037333
- ^ GeoScience World, Rates and possible causes of neotectonic vertical crustal movements of the emerged southeastern United States Atlantic Coastal Plain, Thomas M. Cronin, U.S. Geological Survey, M.S. 970
- ^ Volusuia County, Florida Natural History
- ^ Solution To The "Two-Talbot" Problem of Marine Pleistocene Terrace in South Carolina
- ^ Lodge, Thomas E., The Everglades handbook: understanding the ecosystem. CRC Press; 2 edition, July 26, 2004 ISBN 1566706149
- ^ Lodge, Thomas E., The Everglades handbook: understanding the ecosystem. CRC Press; 2 edition, July 26, 2004 ISBN 1566706149
- ^ http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=FLHh%3B0 USGS Florida geologic map data, Holocene sediments.