Seismic Characteristics of Pleistocene Glacial Cycles near Shelf Edge, Offshore Louisiana, Gulf of Mexico

Joel S. Watkins, Louis Schneider, Fred Hilterman

Seismic stratigraphic studies of the shelf edge and the upper slope basins in the southern parts of the South Marsh Island, Eugene Island, Ship Shoal, and Green Canyon areas of the Louisiana outer continental shelf reveal at least four Pleistocene seismic stratigraphic cycles. These apparently reflect cyclic depositional patterns associated with glacially driven highstands and lowstands of sea level during this time.

In the upper slope basins, a strong continuous reflector probably of turbiditic origin marks the base of each cycle. This reflector is thought caused by initial slumping occurring as sea level begins to fall. Overlying this reflector is a zone of chaotic-to-hummocky reflectors thought caused by slumping associated with knick-point erosion and channel-cutting during falling sea level. The upper portion of the cycle is largely reflectorless or weakly reflective punctuated with occasional strong, continuous turbidite reflectors. The reflectorless portion of the cycles is thought to represent homogeneous hemipelagic sedimentation during highstands.

Shelf reflectors are usually moderately strong and continuous. A strong reflection(s), identified in some instances with gas sands, marks several sea level lowstands. Erosion is locally evident during lowstands. Otherwise, shelf reflectors are relatively uniform and show few characteristics associated with rising, falling, or highstanding parts of the sea level cycle.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.