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Heather E. Anderson and Philip J. Bart
Louisiana State University, Howe-Russell E-235, Baton Rouge, LA, 70803
Results from ongoing regional seismic stratigraphic studies, conducted along the northwestern and north-central Gulf of Mexico, suggest that allocyclic controls (tectonics, base-level, and climate) are not constants and have significant effect on the nature of sediment influx and development of sand bodies on the shelf (Banfield, et al., 1997 and Snow, 1998). This study represents the eastern most extension of this ongoing project attempting to relate drainage basin dynamics and resultant shelf strata. The studies are being conducted to determine the response of different systems to changes in sea level, climate, and fluvial geomorphology during the last glacial eustatic cycle. In particular, the Apalachicola system is unique for its ramp-type margin, relatively low subsidence, and drainage basin characteristics. The drainage basin of the Apalachicola system has significant relief with numerous perennial tributaries and a minimal distance separating Pleistocene uplands from the coast, compared with the Colorado and Brazos fluvial systems of Texas. As a result, the alluvial valley is deeply incised and sediment delivered to the shelf is dominated by sands.
During the summer of 1998, approximately 500 kilometers of high-resolution seismic data was collected on the middle and outer shelf of west Florida. Seismic facies analysis shows large (up to 500 square and 70 meters thick), sand-dominated delta lobes on the shelf. Delta lobes have been mapped along the shelf with relative ages tentatively constrained by comparison with the oxygen isotope/sea-level curve. Delta lobes appear to occur within highstand, lowstand, and transgressive systems tracts. Progressive seaward shifts in the delta suggest a continuous sediment supply to the shelf during the falling limb of sea level. Conversely, sediment supply may have been more episodic during the transgression. A more precise history of delta evolution is currently under investigation.
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