Out of Sequence Thrusting along the Frontal Ouachitas-Arkoma Basin Transition Zone, Southeastern Oklahoma

Cemen, Ibrahim¹, Surinder Sahai¹, Wiiliam Parker², Wahab Sadeqi¹, Marline Collins¹, Steve Hadaway¹, Osman Kaldirim¹ (1) Oklahoma State University, Stillwater, OK (2) Oklahoma State University, Stillwater,

The Frontal Ouachitas-Arkoma Basin transition zone in southeastern Oklahoma contains several gas fields producing from the lower Atokan Spiro/Wapanucka and the middle Atokan Red Oak reservoirs. The Choctaw fault is the leading edge thrust that separates highly deformed frontal Ouachitas from the mildly deformed Arkoma foreland basin. The hanging wall of the Choctaw contains a well developed imbricate fan formed in a break-forward sequence of thrusting. The footwall of the Choctaw contains a duplex structure with varying number of horses along the transition zone, containing all the structural traps of the Spiro/Wapanucka reservoirs. The duplex contains, in general, break forward hinterland dipping thrusts.

Recently acquired 3-D seismic data suggest that the horses within the duplex structure contain backthrusts which cause structural thickening of the Spiro/Wapanucka reservoirs. The backthrusts explain the rapid thickness changes in the Spiro/Wapanucka reservoir which was usually attributed to facies changes. The duplex structure is overlain by a thick section of the lower to middle Atoka flysch sequence containing several broad folds. The seismic data also suggest the presence of a branch of the Choctaw fault which produced a large box fold containing two oppositely dipping thrust faults at its core. The south-dipping thrust is listric and joins the Choctaw fault as it flattens. The north dipping thrust is a backthrust branching from the south dipping thrust. The transition zone also contains a large backthrust system, the Carbon fault zone, which is locally exposed at the surface but is mostly imaged in the seismic data as blind thrust. We interpret all the backthrusts in the transition zone as foreland dipping out-of-sequence thrust faults formed during the north to northwest directed Pennsylvanian thrusting.