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Strata of the lower and middle Atoka Formation in the Arkoma Basin comprise submarine-fan and marine-slope facies that display a variety of primary and secondary sedimentary structures, formed by sediment gravity-flow depositional processes and dewatering, respectively. Primary sedimentary structures are most common in beds deposited by unconfined sediment gravity flows on submarine-fan lobes, whereas secondary sedimentary structures are most common in beds deposited by channelized sediment gravity flows in fan channels and slope channels. Primary sedimentary structures display horizontal fabrics, whereas secondary sedimentary structures display deformed and vertical fabrics. Abundance and distribution of clay minerals in Atoka sandstones are related to sedimentary structures. Beds that display primary sedimentary structures contain little detrital clay that is sparsely disseminated through the sandstone. In contrast, beds that display secondary sedimentary structures contain more detrital clay that forms pervasive grain coatings, bridges between grains, and consolidation laminae. Other beds lack sedimentary structures and display abundant detrital clay that forms a matrix-supported fabric.

The abundance and distribution of detrital-clay minerals exerted significant influences on diagenesis and reservoir quality of Atoka sandstones. Among sandstones with grain-supported fabrics, those that display primary sedimentary structures and contain little detrita) clay were pervasively cemented by quartz overgrowths and are characterized by poor reservoir quality. Those that display secondary sedimentary structures and contain more abundant detrital clay retained primary porosity because quartz-overgrowth nucleation was inhibited by clay coatings on detrital grains. Porosity was enhanced in these sandstones by dissolution of framework grains, and the sandstones are characterized by good reservoir quality. Sandstones with matrix-supported fabrics apparently had little original porosity, which was reduced by compaction of the pervasive matrix; they are characterized by poor reservoir quality. These observations suggest that channelized turbidite facies have greater potential to retain good reservoir quality than unconfined turbidite facies, because the former have detrital-clay minerals emplaced within sand during dewatering and those clay minerals inhibit destruction of porosity by quartz cementation.

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