High-Resolution Seismic Stratigraphic Analysis of the Late Quaternary Upper Slope and Shelf Edge: Main Pass-Viosca Knoll Area, Gulf of Mexico

MCMILLEN, K. J., Marathon Oil Co., Houston TX, R. D. WINN, JR., Marathon Oil Co., Littleton, CO, J. E. DAMUTH, Mobil Oil Co., Dallas, TX, and P. WEIMER, University of Colorado, Boulder, CO

High-resolution (800 Hz) sparker data from the Main Pass-Viosca Knoll area, offshore Louisiana, show shelf-edge deltas with oblique progradational clinoforms, parallel, and channel-fill reflections in the near-surface, latest Quaternary section of the upper slope. Sequence boundaries are indicated by onlap of slope facies onto older outer-shelf deltas and shelf margins, erosional truncation, and minor channel erosion on the top of progradational units and on the slope. We tentatively identify these sequence boundaries as Type I. Each depositional sequence consists of two seismic units: (1) a lower unit consisting of parallel, seaward-dipping reflections; (2) an upper unit consisting of parallel reflections and progradational clinoforms that converge or downlap downslope on top of the ower parallel unit. The lower unit may represent part of a thin (approximately 10 to 30 ms) transgressive systems tract and the upper unit a highstand systems tract, or both units may be part of a prograding wedge or shelf margin systems tract. Precise correlation to absolute time and sea level awaits analysis and integration of shallow cores taken in the area by an industry consortium.

Facies and isochron mapping of each sequence indicates an overall back-stepping of the shelf-edge deltas and shelf margins during the latest Quaternary. The Quaternary shelf edges are an area of isochron thicks and thins resulting from erosion and redeposition. Major channels commonly cross salt diapirs and may occupy the same site during successive lowstands.

Comparison with multichannel seismic profiles shows that each shelf-edge delta seen on the high resolution profiles is represented by a single reflection on multichannel data. Steep clinoforms, downlap surfaces, and individual sequences are not seen on the multichannel data.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)