Abstract: Atoka Formation (Pennsylvanian) Depositional Environment and Growth Faulting, Southwestern Arkoma Basin, Oklahoma

Bruce E. Archinal

The Atoka Formation along the southwestern margin of the Arkoma basin in Coal and Pontotoc Counties, Oklahoma, is a shale and mudstone unit interbedded with thin sandstones and thin sandy limestones. Detailed surface mapping and measured stratigraphic sections show that the Atoka was deposited on a marine shelf that received only minor amounts of medium clastic sediments. The sandstones present are lower foreshore beach, submerged barrier bars, or longshore bars and were deposited during brief stillstands or minor regressions that occurred intermittently during a general transgression.

The Clarita anticline was a positive structural feature and the Clarita fault was an active down-to-the-north growth fault during Atoka deposition. A thickened Atoka sequence, deposited just north of these features, thins onto and across them. This relation was unrecognized by previous workers who thought that Fusulinella was present 200 ft (60 m) above the top of the Morrowan and only 100 ft (30 m) above Profusulinella, when the actual stratigraphic separation might be more than 1,000 ft (300 m).

Petroleum explorationists need to be aware of the possibility of growth faulting in the subsurface along the Clarita and Phillips faults. Multiple reservoirs could be present if closure exists and the downthrown block contains an expanded section with numerous sandstone beds. Hydrocarbon accumulations are possible on the high side of faults, where deposition kept pace with fault growth and sands were deposited on the upthrown block.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma