Comparative study of the sedimentology and provenance of the Atoka Formation in the Frontal Ouachita Thrust Belt, Oklahoma

Most depositional models for the Pennsylvanian deepwater Atoka Formation of Oklahoma indicate that Atokan sediments were derived from the southeast extension of the Ouachita Mountains, the Appalachian Mountains, and the craton of Laurentia. However, it is difficult to reconcile sediment transport from these sources with the northeast-directed paleocurrent indicators that dominate Atokan strata in the Choctaw thrust sheet south of Wilburton, Oklahoma. Before this study little was known about the provenance of the northeastward-deposited Atokan sandstones.; The sedimentology, petrography, and detrital zircons of deposits from two opposing submarine fan systems were examined in this study. Detrital zircon characteristics studied include cathodoluminescence image, U/Pb age, Th/U ratio, and grain elongation.; Detrital zircon samples were collected from five sandstones with northeast-directed paleocurrent indicators, and five sandstones with west- to south-directed paleocurrent indicators. Grenville-age (∼1.1 Ga) zircons dominated all samples. 600--800 Ma zircons, found only in northeastward-deposited Atokan turbidites, are probably from the Sabine Plate, which had collided with Texas by Atokan time. A Wichita Igneous Complex zircon, found in a northeastward-deposited Spiro sandstone bed, indicates that sub-regional northeastward transport of sediments in the Ouachita Trough had begun by earliest Atokan.; Unroofing of a feldspathic terrane, southwest of the Wilburton area, led to northeastward-deposition of arkosic sandstones which now have enhanced porosity due to dissolution of feldspars.; Field observations indicate that the Spiro sandstone of the Choctaw thrust sheet was deposited in an offshore shelf environment. All other Atokan strata in the Choctaw thrust sheet were deposited in a deepwater environment. All Atokan strata in the Ti Valley thrust sheet, including the Spiro, were deposited in a deepwater environment. Lithofacies associations indicative of lower-fan and middle-fan deposition were observed in both thrust sheets. Intervals of predominantly Ta sandstones and shale were deposited in a proximal-lobe/lower-fan environment. Ta sandstones, with erosive lower-bed contacts, and thin ripple-laminated Tc sandstones were deposited in and around channels in a middle-fan environment. Lower-fan to middle-fan facies successions in both thrust sheets indicate progradation of two opposing submarine fan systems in this area during early Atokan.