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Seismic Models of Late Quaternary Fluvial Facies, Louisiana Continental Shelf

John R. Suter, Henry R. Berryhill

More than 20,000 km of interpreted high-resolution seismic profiles allowed us to identify and map facies in late Quaternary deposits of the Louisiana continental shelf, based on seismic reflection characteristics. Extensive fluvial facies, comprising about 30% of the stratigraphic section, were deposited from the shoreline to the shelf break during the last two glacio-eustatic regressions. Drainage patterns have a consistent northeast-southwest orientation, modified by the effects of growth faults and diapirism. Major fluvial drainages have shifted eastward through time from offshore the Texas-Louisiana border to the position of the modern Mississippi River.

Fluvial facies range from entire courses of extrabasinal streams as much as 40 km wide and 50 m thick, to single buried channels representing coastal plain rivers. Stream courses are broad, dip-oriented lenses marked by high-angle clinoforms in most orientations, indicating multilateral sand bodies deposited by point-bar migration. Platform borings show thick sections of coarse to fine sand in these deposits. Individual channels may show lateral accretion, have reflections parallel or subparallel to the channel perimeter (indicating vertical aggradation), or be composites. Subparallel to parallel, closely spaced horizontal reflections in strike-parallel lenses are interpreted as estuarine deposits, with high-amplitude mounded reflectors representing oyster reef and bank deposits. Over ank sediments are recognized by low-angle clinoforms that diverge from buried channels. Overbank deposits are thickest near the present shoreline and thin offshore, reflecting both lesser aggradation during lowstand periods and truncation of deposits by shoreface erosion during transgression.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.