--> Abstract: Influence of Sediment Supply and Slope Stability on Depositional Style of Present-Day Mississippi Margin Turbidite Systems, by C. H. Nelson, D. C. Twichel, and W. C. Schwab; #90987 (1993).

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NELSON, C. HANS, U. S. Geological Survey, Menlo Park, CA; D. C. TWICHELL and W. C. SCHWAB, U. S. Geological Survey, Woods Hole, MA

ABSTRACT: Influence of Sediment Supply and Slope Stability on Depositional Style of Present-Day Mississippi Margin Turbidite Systems

The Mississippi margin is characterized by a large mud-rich sediment source, rapid progradation, and extensive sediment instability. The depositional systems of the associated intraslope basins and adjacent Mississippi Fan exhibit an equal interplay of non-channelized, mass-transport aprons with debris-flow deposits and channelized fans with turbidites. This contrasts with other margins that have relatively greater sediment stability and a sandier but lower sediment supply. Their associated turbidite systems are dominated by channelized fans, such as Astoria Fan, or turbidite systems may be compartmentalized along the margin so that localities of greater sediment stability develop channelized turbidite systems and unstable areas develop mud-rich mass-transport aprons, such as along th Ebro margin. Ubiquitous instability of the Mississippi slope results in coeval development and intermixing of mass-transport aprons and channelized turbidite systems on floors of intraslope basins. Massive retrograde failure along the prograding Mississippi slope apparently causes the large-scale intermingling of mass transport aprons and channelized fanlobes noted by others in Mississippi Fan. This influence of marginin stability and equal deposition of chaotic debris flow silt beds with graded sand beds continues down to the finest scale in outer fan depositional lobes. The silt beds appear to be derived from a high periodicity of local sediment failures from muddy canyon walls; whereas, the graded sand turbidites appear to be deposited from sand that is flushed from canyon heads by t rbidity currents.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.