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Abstract: Stratigraphic Framework of a Mixed Carbonate/Siliciclastic Inner Shelf Sand Ridge System

EDWARDS, JAMES H., ALBERT C. HINE, STANLEY D. LOCKER, Department of Marine Science, University of South Florida; GREGG R. BROOKS, Department of Marine Science, Eckerd College

The West-Central Florida inner shelf has recently been the focus of extensive high resolution seismic, side scan sonar and vibracore surveys. The various surveys have identified that the bedrock of the inner shelf is dominated by a Cenozoic limestone with karst topography. Superimposed on the bedrock is a thin sediment veneer of mixed siliciclastics and carbonates. The sediment cover is commonly sequestered into linear sand ridges obliquely oriented to the shoreline, possessing relief from 1-4 meters and widths from 100-300 meters.

Twenty-four vibracores extracted from a ridge field off the coast of Indian Rocks Beach have identified seven different Holocene lithofacies within the sand ridges. The vibracores' stratigraphy represents the evolution of the sand ridges through the Holocene transgression, demonstrating a shift from a back-barrier depositional environment to an open marine regime. The major ridge facies consists of sediments deposited in the nearshore. It appears to be a combination of fine to medium quartz sands with intermittent lenses of carbonates. Other common facies identified include back-barrier deposited sediments, lithoclasts constituents of the underlying bedrock that may represent a ravinement surface and sediments that are the result of limestone bedrock alteration.

Genesis of the sand ridges appear to be a result of the present day hydraulic regime. It is inferred that storm induced flow in combination with sea-level rise and shoreface erosion have carved and sequestered the siliciclastic/carbonate sands into these linear features.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah