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