Abstract: Alabama/West Florida Shelf Margin Deltas: Importance of Fluvial Incision as an Initiator of Slope Canyons

BART, PHILIP J.
Louisiana State University, Baton Rouge, LA;
JOHN B. ANDERSON
Rice University, Houston, TX;
RUSSELL V. RICHMOND
Louisiana State University, Baton Rouge, LA

Undoubtedly, bypass of fluvial sediments through canyonindented slopes is an important contributor to lowstand depositional systems. However, due to complex interactions with other mechanisms (sediment supply, antecedent topography, salt tectonics, etc.) the question of how the process of sediment bypass of the shelf margin-delta system is initiated has not been resolved. In this seismic-stratigraphic study of near-surface stratigraphy of the Alabama/west Florida shelf (an area with low subsidence, no faulting and no salt tectonics) the isolated effect of fluvial response to relative-sea-level fall is investigated. In the study area, shelf-margin-delta depositional units are primarily composed of discrete prograding wedges. Based on available age constraints, we infer that these depositional cycles are associated with failing limbs of 100 ka glacioeustatic relative-sea-level cycles of the Pleistocene. Seismic-stratigraphic analysis, contour mapping and paleogeographic reconstruction of shelf -margin-delta environments indicate that slope-canyon connections between the shelf margin delta and upper slope did not develop in spite of frequent and widespread subaerial exposure of the shelf. Slope canyons may be lacking in the study area due to the absence of salt tectonics and growth faulting. Another possibility is that the sandy nature of surface sediments offshore Alabama/west Florida inhibits organized drainage from the subaerially-exposed continental shelf during relative lyshort Pleistocene lowstands. Nonetheless, based on the absence of shelf-to-slope connections in the study area, we propose that, acting alone, lowstand fluvial incision of the shelf edge is not an important initiator of slope canyons and fluvial bypass to to the basin.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas