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Regional Stratigraphy and Geologic History of Barrier Islands, West-Central Coast of Florida

West-Central Florida Coastal Studies Home
Open File Report: Second West-Central Florida Coastal Studies Workshop
Introduction
Agenda
Processes
Framework
Morphodynamics
Attendees
Contact:
Chief Scientist
Kristin E. Yale , Department of Geology, University of South Florida, Tampa, FL
Richard A. Davis, Jr., Department of Geology, University of South Florida, Tampa, FL

Barrier island complexes typically consist of elongate and drumstick shore parallel islands, which are bounded by tidal inlets. The dynamics of barrier coasts rely on processes which interact to produce a specific type of barrier. The barrier island complex on the west coast of Florida extends for about 300 km from Anclote Key in the north to Cape Romano in the south. All types and sizes of barrier islands occur along this low energy coastline, which has low tidal ranges and wave heights. It is considered to have a complicated mixing of both wave- and tide-dominated conditions.

Stratigraphic analyses of barrier islands can provide insight into the long-term morphodynamics and geologic history of the west-central Florida Gulf coast barrier system. Stratigraphic cross-sections can be used to categorize each island into the wave-dominated, aggradational type or the drumstick, transgressive/progradational type. Wave-dominated barriers display a 'layer cake' stratigraphy, commonly with a nearshore, foreshore, back beach, and dune sequence (Crowe, 1983). Examples of this stratigraphy in wave-dominated barriers are provided in Anclote Key, Bunces Key, and Three Rooker Bar (Kuhn, 1983; Crowe, 1983; Gibbs, 1991). Drumstick barriers are commonly characterized by a transgressive stratigraphy where the barrier is thin and a progradational stratigraphy where the barrier is wide. The transgressive sequence contains back barrier facies overlain by washover and capped by salt marsh, beach and dune facies, while the progradational sequence contains offshore deposits overlain by nearshore sands, capped by bach and dune deposits. Examples of this stratigraphy are found in Anna Maria Island and Caladesi Island (Pekala, 1995; Brame, 1976). These are the stratigraphic models that will be used to characterize the west-central Florida coast.
map

Figure 1: Map of study area showing locations of nine transects.

The study area ranges from Anclote Key to Venice and includes transects through 9 of these barrier islands (Figure 1). These transects have been located to provide coverage of each expected geologic set of conditions. More specifically, the first transect is through Anclote Key, the second through Caladesi Island, then two through Sand Key, and one through Treasure Island, all located in Pinellas county. The transects continue in Manatee and Sarasota Counties through Anna Maria Island, Longboat Key, Siesta Key, and finally through Casey Key. Of these, it is known that Anclote Key, Sand Key, and Casey Key are wave-dominated, long, narrow linear barriers, and Caladesi Island, Anna Maria Island, and Siesta Key are mixed-energy, short, drumstick barriers (Davis, 1988). All nine transects will be investigated in order to confirm or determine each barrier's stratigraphy, construct a stratigraphic model, and to ascertain the aspects in which they differ.

Stratigraphic studies allow for changes in island morphology to be traced through more time than is represented in historical records. Relatively long-term trends in shoreline erosion and accretion can be identified by constructing geologic histories for the barrier islands. The identification of these trends are useful in predicting future trends in morphological changes, as well as predicting the future migration and stability of the barrier island chain. Stratigraphic studies of modern barrier islands will allow coastal planners and managers to more easily understand such a dynamic system.

References

  • Brame, J.W., 1976. The Stratigraphy and Geologic History of Caladesi Island, Pinellas County, Florida. Unpublished master's thesis, University of South Florida, 109p.
  • Crowe, Douglas E., 1983. Stratigraphy and Geologic History, Bunces Key, Pinellas County, Florida. Unpublished master's thesis, University of South Florida, 101p.
  • Davis, R.A., Jr., 1988. Morphodynamics of the West-Central Florida Barrier System: The Delicate Balance Between Wave- and Tide-Domination. Proceedings of the KNGMG Symposium 'Coastal Lowlands, Geology and Geotechnology' p. 225-235.
  • Gibbs, Ann E., 1991. Stratigraphy and Geologic History of Three Rooker Bar: A Recently Emergent Barrier Island on the West-Central Coast of Florida. Unpublished master's thesis, University of South Florida, 131p.
  • Kuhn, B.J., 1983. Stratigraphy and Geologic Evolution of Anclote Key, Pinellas County, Florida. Unpublished master's thesis, University of South Florida, 108p.
  • Pekala, John M., 1995. Stratigraphy and Geologic History of Anna Maria Island, Manatee County, Florida. Unpublished master's thesis, University of South Florida, 144p.

Coastal & Marine Geology Program > St. Petersburg Coastal and Marine Science Center > West-Central Florida Coastal Studies Project > Second West-Central Florida Coastal Studies Workshop > Morphodynamics > Regional Stratigraphy and Geologic History of Barrier Islands, West-Central Coast of Florida


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