Abstract: Modes of Emplacement of Prospective Hydrocarbon Reservoir Rocks of Outer Continental Margin Environments

Joseph R. Curray

Potential hydrocarbon reservoir rocks of the outer continental margin may be emplaced by at least four different mechanisms. (1) Crustal thinning and block faulting are common during early rifting stages of formation of intraplate continental margins, followed by subsidence of porous and permeable continental, shore zone, and shallow-marine sediments to abyssal depths, where they may be covered by pelagic sediments and/or prograding wedges of normal continental margin facies. (2) The process of subduction may be accompanied by transfer of sediments from the underthrusting plate to the leading edge of the overriding plate, followed by uplift in imbricate thrust sheets to the crest of a nonvolcanic ridge or the edge of a marginal plateau lying outboard of a volcanic arc or ndean-type continental margin. These sediments may be of reservoir potential only if they represent facies which otherwise would be favorable before the offscraping and if they are not deformed to melange. (3) Normal processes of distribution of sediments are reasonably well understood from studies of the modern oceans, but the lesson of these studies cannot be applied indiscriminately to interpretation of pre-Quaternary sediments and continental margins because of the profound effects of Quaternary sea-level fluctuations. The same principles of sediment distribution apply to the various depositional environments of all tectonic settings, including intraplate, subduction-plate edge, and transform-plate edge continental margins. (4) Sediment accumulations of outer shelf or slope environme ts may be displaced into deeper water base-of-slope environments by submarine sliding. Such slides or olistostromes may occur on either intraplate or plate-edge margins. Slope instability may result from either depositional or tectonic oversteepening and may be triggered by either oceanographic or tectonic disturbance.

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