PENNSYLVANIAN STRUCTURAL EVOLUTION OF THE ARKOMA FORELAND BASIN, SOUTHERN OKLAHOMA

The Arkoma Basin, an arcuate structural feature located in southern Oklahoma and western Arkansas, is a foreland basin of the Ouachita fold-thrust belt. It contains about 5,000 feet thick Middle Cambrian to Late Mississippian miogeoclinal rocks, overlain by about 20,000 feet thick Pennsylvanian flysch and molasse deposits.

In the Potato Hills area of the Central Ouachitas, the Middle Ordovician to Mississippian rock units are exposed at the surface on the hanging wall of the Winding Stairs fault. In the subsurface, the Choctaw Detachment is the roof thrust of an antiformal stack structure which involves Pennsylvanian rock units. From the central Ouachitas to the leading edge of the frontal Ouachitas, strain partitioning is accommodated by imbricate fan thrusts on the hanging wall of the Choctaw Detachment. The strain partitioning is accommodated primarily by a triangle zone and associated duplex structure in the frontal Ouachitas-Arkoma Basin transition zone where the Atokan turbiditic sequence is well exposed in both hanging wall and footwall of the Choctaw Detachment. The duplex structure is located between Springer Detachment (the floor thrust) and the Lower Atokan Detachment (the roof thrust) in the footwall of the Choctaw Detachment. The triangle zone is floored by the Lower Atokan Detachment and flanked by the Choctaw Detachment to the south and the Carbon fault to the north. When restored to their original position prior to lower Atokan, our balanced structural cross-sections indicate about 60% shortening from the Central Ouachitas to the Arkoma Basin. The shortening is, however, only about 25% in the Arkoma Basin in the footwall of the Choctaw Detachment.

The Arkoma Basin contains over 4 Trillion Cubic Feet undiscovered natural gas, mostly within shallow marine to deltaic Pennsylvanian sandstones of the Atoka Formation. Since the Late-1990s, the lower Atokan Spiro/Wapanucka reservoir has been a major exploration target.