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Abstract: Inner Shelf Sediment Distribution and Thickness Patterns in a Mixed Carbonate/Siliciclastic Depositional Setting

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

A regional overview of geophysical data (high-resolution seismic and side-scan sonar) from the west Florida shelf reveals an inner continental shelf dominated by a Cenozoic limestone bedrock unconformity supporting a thin, mixed siliciclastic and carbonate sedimentary veneer. The study area covers 6000 km2 extending approximately 40 km offshore from a 175 km stretch of coastline centered on Tampa Bay.

Delineation of shelf sedimentary provinces reflects a first order control by bedrock geology which is dominated by large-scale warping or shelf-valley systems several kilometers in scale. Superimposed on this framework are sinkholes, bedrock highs, and channels. A prominent flat unconformity truncates many of these structures and often marks the base of Holocene sand deposits offshore. Estuarine retreat paths, shallow channel systems, and thicker surficial sediment deposits tend to associate with the valley systems.

Recent sediments are thin and discontinuous away from the influence of the Tampa Bay ebb-tidal delta where accumulations can be over 10 m in thickness. Other Holocene sediment accumulations include (1) sand ridges ranging (.5 to 4 m's of relief, 10 to 100 m's in width, 100's m's of spacing, and km's in length), (2) broad, very thin sheets, or (3) active ebb-tidal deltas located just off tidal inlets. More than 50% of the seafloor extending out to 40 km distance is characterized by hardground exposures or a thin coarse sediment veneer less than .05 m thick. The trend of offshore deposits suggests patterns controlled by a non-steady sea-level rise.

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