Abstract: Debris Flow Outrunner Blocks, Glide Tracks, and Pressure Ridges Identified on the Continental Slope of West Africa Using 3-D Seismic Coherency

NISSEN, SUSAN E., NORMAN L. HASKELL, CRAIG T. STEINER and KATRINA L. COTERILL

A 3-D seismic coherency horizon slice 144 ms below the water bottom on the continental slope of West Africa shows numerous linear features which are not readily apparent on conventional seismic amplitude slices. These features are up to 12 km in length and 100-200 m in width. Morphologically, they are analogous to smaller scale (less than 1 km in length and 125 m in width) glide tracks formed by the down slope movement of outrunner blocks during a recent debris flow in the Kitimat fjord of British Columbia, Canada. A low-coherency-bounded area with dimensions of 100 m X 250 m at the downdip end of a selected glide track on the 144 ms coherency slice is interpreted to be an outrunner block. Vertical seismic sections and dip/azimuth displays show that the glide tracks and outrunner blocks exhibit topographic relief.

The coherency slice, associated dip/azimuth displays, and vertical seismic sections also suggest the presence of pressure ridges on the West African continental slope. These pressure ridges occur both within a proposed debris flow and in front of a selected outrunner block. Pressure ridges have been identified at similar locations in the Kitimat debris flow.

The identification of glide tracks, outrunner blocks, and pressure ridges on the West African continental slope using 3-D seismic coherency plots confirms that debris flows have been the predominant depositional processes active on this continental slope during the Holocene.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria