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Abstract: Post-Miocene Stratigraphy and Depositional Environments of Valley-Fill Sequences at the Mouth of Tampa Bay, Florida

FERGUSON, THOMAS W., KEMRON Environmental Services, Inc.; RICHARD A. DAVIS, JR., University of South Florida

Post-Miocene sea-level lowstands allowed rivers and karst processes to incise the exposed carbonate platform along the Gulf Coast of Florida. Since their formation, the resulting valleys have been filled and incised multiple times in response to high-frequency, sea-level changes. Little Pliocene to mid-Pleistocene deposits survived erosion along the present coast except within these valleys. The sedimentary sequences within the incised valley underlying the mouth of Tampa Bay have potentially recorded numerous sea-level incursions and excursions during the Pliocene and Pleistocene.

Sediment analysis of cores from a north-south transect across the mouth of Tampa Bay has enabled the identification of lithofacies, ranging from well-sorted, quartz sand to dense, fossiliferous, phosphatic grainstone. Interpreted depositional environments represented by the lithofacies include freshwater to open marine. Channel development and migration within the paleovalley does not allow correlation of the lithofacies across the transect. Fining-upward sequences truncated by tidal ravinement surfaces extending throughout the paleovalley can be identified, however.

Seismic lines collected across the study area permit the correlation of identified lithofacies with discernable, seismically distinct units. Five units, representing Oligocene to Miocene limestones to Holocene sediments, are bounded by four sequence boundaries representing significant sea-level regressions. Lowstand and Transgressive System Tracts can be identified revealing the landward migration of facies during subsequent sea-level transgressions. Absolute dates and extant faunal assemblages constrain the age of the units to Late Pleistocene. These data indicate that Late Pleistocene sediments immediately overly the Miocene bedrock in the cores and suggest that no Pliocene sediments remain within the study area.

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