--> Analog for Shelf-Margin (Lowstand) Deltas: Seismic Stratigraphy of Fraser Delta, Canada, by B. S. Hart; #90986 (1994).

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Abstract: Analog for Shelf-Margin (Lowstand) Deltas: Seismic Stratigraphy of Fraser Delta, Canada

Bruce S. Hart

The Fraser Delta has formed following a post-glacial relative sea level drop of about 120 m, and is prograding into water locally over 300 m deep. Like other deep-water deltas (e.g., lowstand shelf-margin deltas), the Fraser Delta is characterized by a mud-dominated delta slope which typically dips at 2-3° seaward. Sedimentation rates exceeding 10 cm per year have been measured on the delta slope. Submarine channel and failure complexes have developed seaward of fluvial distributaries. Failure in these settings is promoted by rapid deposition of sandy sediments near the river mouth. Submarine failures are funneled downslope through channel systems as density currents. The channels are 10s of meters deep, several 100's of meters wide, lack well-developed levee systems and extend s veral km offshore into water depths of over 200 m. Fine and medium sands issue from the downslope terminus of a submarine channel and form debris accumulations and turbidites. Failure-derived fine and medium sands form an apron along the base of the delta slope. These base of slope deposits and upper slope river-mouth sands form potential reservoir units. Two large (over 40 sq km) failure complexes appear to be the consequence of rapid deposition, the presence of abundant interstitial (biogenic) gas, and possibly to regional tectonic activity. The Holocene deltaic and prodeltaic sediments form an offshore-thinning wedge which is locally over 200 m thick. Delta slope clinoforms downlap onto a surface formed during maximum post-glacial inundation. Isopachs of the Holocene section show the nfluence of underlying structural relief.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994