DEPOSITIONAL DELIVERY SYSTEMS FOR THE ATOKA FORMATION (MIDDLE PENNSYLVANIAN), SOUTHERN MIDCONTINENT, UNITED STATES

The Atoka Formation (Middle Pennsylvanian) comprises three separate terrigenous clastic delivery systems along the southern margin of the North American midcontinent (Arkansas and Oklahoma). These systems consistently reflect system input to the east, along the present Mississippi Embayment, but petrographic data indicate sources in both the southern Appalachians and eastern craton. Thus, there are three coeval, homotaxial, but discrete systems that delivered terrigenous clastics to the southern Ozark shelf, the Arkoma basin, and the Ouachita orogen respectively. The Atoka Formation of the Ozark shelf is characterized by cyclic, shallow, epeiric marine conditions, with a predominance of tidal to tidally-influenced sequences. Fluvial systems combined sediments derived from the eastern midcontinent and southern Appalachians. They entered the northern Arkoma shelf along what is now the Mississippi Embayment, where the clastics were distributed by east-west longshore currents. These delivery systems may have produced barrier islands high on the Arkoma shelf, but are mostly represented by a series of constructive and tidal delta systems oriented east-west along the axis of the Arkoma foreland basin. Fluvial systems feeding the Ouachita trough combined sediments derived from both the southern Appalachians and the active Ouachita Orogen producing turbidite sequences. The Ozark and Arkoma successions exhibit a change from open marine in the lower portion of the formation to more restricted conditions in the middle and upper Atoka. All three successions exhibit a flooding of MRFs in the middle and upper Atoka interval, indicating the proximity of a high rank metamorphic source produced by compressional tectonics in the southern Appalachians that were initiated in middle Atokan time.