Distribution Patterns and Accumulation Rates of Fine-Grained Sediments in Upper Tampa Bay, Florida

BROOKS, GREGG R., and LARRY J. DOYLE, University of South Florida, St. Petersburg, FL, ROGER JOHANSSON, Bay Study Group, City of Tampa, FL, ANDY SQUIRES, King Engineering Association, Tampa, FL, and HEPSI D. ZSOLDOS and ROBERT H. BYRNE, University of South Florida, St. Petersburg, FL

Tampa Bay, a drowned river valley, is the largest estuary on Florida's west coast and is almost completely surrounded by heavy urban development. A series of eleven sediment cores and high-resolution seismic reflection data were collected in Hillsborough Bay, the northeast lobe of Tampa Bay, in order to determine the processes controlling sediment distribution patterns and accumulation rates throughout the recent geologic past.

Surface sediments consist of a mixture of carbonate and terrigenous clastic sands and muds. Mud-size sediments in the open bay are concentrated in low-energy bathymetric depressions. Accumulation rates determined by carbon 14 methods for the past several thousand years average 31-49 cm/1000 years. Rates for approximately the past 100 years, determined by lead 210 and cesium 137 methods, range from 0.13 to 0.42 cm/year. Sediment texture, gross mineralogy, and organic content show no major variations, but a weak tendency toward increasing organic and carbonate contents and an accompanying decrease in grain size in the upper 20-30 cm of some cores suggests that there may have been an alteration in sedimentation patterns beginning approximately 100 years ago.

Results indicate a major control on the distribution of fine-grained sediments in Hillsborough Bay is bathymetry, as broad, shallow depressions have acted as fine-grained sediment sinks for the past several thousand years. The apparent recent increase in accumulation rate, as well as observed alterations in sedimentation patterns beginning approximately 100 years ago, is consistent with early urban development of the Tampa Bay area.

AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)