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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 50 (2000), Pages 751-753

Variable Lowstand Deposition and Tectonic Implications Along the Louisiana Continental Margin During Quaternary and Neogene

Susan Moffett, Allen Lowrie, John Milliman


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 during 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 catchments. 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 Fan Fold 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.

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