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Heather E. Anderson1, Philip J. Bart1, John B. Anderson2
(1) Louisiana State University, Baton Rouge, LA
(2) Department of Geology and Geophysics, Rice University, Houston, TX

Abstract: High-resolution sequence-stratigraphic architecture of a Late Quaternary depositional system: Apalachicola margin, Florida

Previous studies conducted along the northern Gulf of Mexico shelf demonstrate major along-strike variations in stratal-stacking patterns. Clearly, these variations reflect differences in shelf morphology, subsidence, climate, tectonics, and drainage-basin characteristics. In an effort to evaluate the influence of these different factors on stratal-stacking patterns, end-member type settings are being studied using high-resolution seismic data. In this study, we report results from an investigation of the Apalachicola fluvial/deltaic system. This system is unique because of its overall ramp-type morphology; absence of growth faulting and salt tectonics; deeply incised tributaries; and narrow coastal plain. The drainage basin is large (60,000 km2) compared to adjacent coastal plain drainage systems in the northeast Gulf of Mexico.

Approximately 540 kilometers of high-resolution single-channel seismic data were collected during the summer of 1998. This data allows for detailed seismic-facies analysis and mapping of depositional systems associated with the highstand, lowstand, and transgressive systems tracts of the last three glacial cycles. Seismic-stratigraphic analysis shows large deltas (up to 500 km2 and 70 m thick) deposited on the middle to outer shelf during the late highstand. In spite of the dramatic falls in sea level during the previous glacial cycles, lowstand deposition in deep-water was minimal with an absence of lowstand fans, slope canyons, and gullies. During the lowstand, fluvial incision dominated the inner and middle shelf. Fluvial valleys mimic those of the modern highstand. The transgressive systems tract is heterogeneous, characterized by backstepping shorelines, barriers, and deltas. Mechanisms controlling variations in deposition are currently under investigation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana