Depositional History of the Morrowan Succession (lower Pennsylvanian) in the Permian Basin
نویسنده
چکیده
Morrowan-age units in the Permian Basin appear to show a “second-order” transgression from siliciclastic fluvial-deltaic to shallow-marine and subsequently to carbonate deposition. In general, Morrowan-age siliciclastics dominate deposition in the west of the Permian Basin, while carbonate deposition dominates in the east. The predominance of carbonate facies in the east is due to a lack of siliciclastic supply to that part of the basin. Morrowan siliciclastic deposition is interpreted to have developed in a large incisedvalley-fill system. An updip-to-downdip transition from fluvial and deltaic to estuarine and openmarine facies is interpreted. Excellent reservoir potential is noted in amalgamated, stacked channel systems and bayhead deltas. Significantly, these incising valleys may have served as conduits for shelf-margin bypass during periods of lowstand. It is proposed that such bypass channels may have fed sediment into the deeper basin, developing lowstand basin-floor-fan deposits. The Morrowan of the Permian Basin needs to be reassessed in terms of such a new play type, as basin-floor fans are known for their excellent reservoir potential. This succession is overlain by Upper Morrowan carbonates. The deposition of the Upper Morrowan carbonate unit in the Permian Basin area probably indicates a switch from local tectonic to regional eustatic control as tectonism diminished in the hinterland and sediment supply from the north/northwest shut off. Overall, it appears that carbonate deposition occurred over a much larger area in the Permian Basin (Eastern Shelf and Delaware Basin) than previously documented. The presence of algally dominated bioherms and higher energy facies (ooid grainstones), augmented by fracture porosity, indicate potentially overlooked reservoir intervals. With the current explosion of interest in the shale gas systems (primarily the Barnett
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Depositional History of the Atokan Succession (lower Pennsylvanian) in the Permian Basin
Atokan-age units in the Permian Basin record a 2-order transgression, with aerially restricted, lower Atokan fluvial to shallow-marine siliciclastics followed by pervasive carbonate deposition. In general, Atokan-age siliciclastics dominated deposition in the west of the Permian Basin while carbonate deposition dominated throughout the rest of the basin. Predominance of carbonate facies across ...
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