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ABSTRACT: Variable Lowstand Deposition and Tectonic Implications along the Louisiana Continental Margin during QuaternaryNeogene

MOFFETT, SUSAN, Consultant, Picayune, MS; ALLEN LOWRIE, Consultant, Picayune, MS; and JOHN MILLIMAN, VIMS, College of William and Mary, Gloucester Point, VA

Recent data, although still fragmentary, suggest that fluvial discharge to coastal oceans was significantly reduced during the last glacial maximum (LGM) and the corresponding sea-level lowstand. Post-glacial floods and debris outbursts (which presumably gradually migrated northward with deglaciation) may have increased local sediment fluxes and sedimentation by one to three orders of magnitude. Such discharge events, particularly at low latitudes as is the Mississippi River, would have occurred the early stages of sea-level regression, such that they might be interpreted as lowstand features. These short-lived events also may have resulted in short-term, compressive tectonic forces impacting underlying sedimentary wedges.

Much lowstand deposition occurs along the continental slope and rise. Once intra-slope basins are initiated, they become sediment catchment. Loci of deposition are the loci of compression. Thus, the entire slope could act as a periodic and non-uniform. compressor to the sub-salt province. The Mississippi Fanfold Belt may be, in part, the result of compressive oscillations during lowstands. These short-term "forces" can serve as "drivers" of salt and supra- and sub-salt tectonics. Migrating salt carries these intra-slope, compressive loci, changing compressive zones through time.

Zones of weakness within the slope and sub-salt can be augmented or diminished by the sedimentary outbursts. Rapid deposition increases geo-pressuring, and associated stresses increase sedimentary fracturing, thus enhancing fluid-flow and dewatering of sediments, and an uneven extrusion of sediments over a rugged basement.



AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas