Abstract: Seismic Recognition of Depositional Facies on Slopes and Rises

P. R. Vail

Slopes and rises of continental shelves are characterized by (1) foundered shallow-water shelf deposits, (2) deltaic sediments carried to the slope by gravity-slide faults, and (3) deep-marine deposits consisting of marine cones, slumps, turbidites, and hemipelagic drape deposits. The distribution and seismic recognition of these depositional facies is highly dependent on tectonic setting, rate of sediment supply, and sea-level changes.

Slopes and rises of pull-apart margins with intermediate to low rates of sediment supply relative to rates of subsidence are characterized by foundered-shelf deposits that still may be drillable, locally restricted deltas with gravity-slide faults, and marine cones. Marine cones and widespread submarine erosional surfaces are characteristically initiated by lowering of sea level.

Slopes and rises of pull-apart margins with high rates of sediment supply relative to rates of subsidence are characterized by foundered-shelf deposits commonly too deep to be drilled, delta deposits carried to the slope by gravity-slide faults, turbidites associated with prograding delta lobes and slope basins. Canyon cutting and slope-basin turbidites commonly are initiated by lowering of sea level.

Slopes and rises of compressional margins are characterized by uplifted abyssal sediments overlain by slope sediments. Submarine unconformities overlying uplifted sediments are common at low stands of sea level.

Slopes and rises of strike-slip margins are characterized by fault-block basins and highs. Depositional facies are highly dependent on rate of deposition and type of sediments filling basins and the rock type within the faulted blocks.

Seismic examples from each tectonic setting show depositional facies, rate of sediment supply, and sea-level changes.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC