ZENG, HONGLIU
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Abstract: Some 3-D Seismic Examples of Line-Sourced, Highly Linearized, Siliciclastic Slope and Base-of-Slope Depositional Systems

Stratal slices have been generated from several 3-D seismic volumes that survey the Tertiary siliciclastic strata in the offshore Gulf of Mexico, offshore West Africa, and North Sea. Like modern depositional systems on satellite pictures, high-horizontal- (<30 m) seismic images reveal in detail complicated morphology of ancient submarine turbidite deposits.

Of special interest are the line-sourced, highly linearized turbidite systems developed in slope and base-of-slope environments. Derived from the ancient shelf break, multiple feeder channels are mostly arranged in dip direction, with individual channels almost straight and increasing in size downdip. Levee/lobe deposits are nondetectable in heavily channeled systems and well defined in the others. Channel branching/merging/cutting ranges from rare in a well-defined channel/lobe complex to common in channel-dominant systems. Destructive processes are not evident, although one of the systems was heavily faulted in the base-of-slope portion by strike-oriented gravity faults after deposition. Hydrocarbons were directly detected in one system by recognizing brightened channel-levee segments trapped by faults.

These systems are interpreted as lowstand, shelf-fed aprons, with some of the systems sitting beneath clinoform/progradational sequences and accompanying submarine canyons. There is no evidence of direct delta-feeding. The size of these systems is generally large, ranging from 100 to 500 km². The thickness, measured from seismic section, ranges from single event (<50 m) to 200 ms (200 to 300 m).

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas