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Structural Evolution of Triangle Zones and Duplex Structures Along the Frontal Ouachitas-Arkoma Basin Transition Zone in Oklahoma and Western Arkansas


We have studied the structural evolution of the Frontal Ouachitas-Arkoma Basin transition zone between the Wilburton gas field and Wister Lake areas in Oklahoma and Mansfield gas field area in Western Arkansas based on available 3D and 2D seismic data and well logs. The Choctaw fault is the leading edge thrust of Ouachitas in Oklahoma. Its displacement is transferred onto the Ross Creek fault in western Arkansas within an accommodation zone. In the Wilburton gas field area, the horses within the duplex structure contain backthrusts which cause structural thickening. Our structural cross-sections and structural contour maps of the Lower Atokan Spiro/ Wapanucka reservoir suggest that the transition zone also contains tear faults that are not mappable in the surface. The faults have caused strike-slip displacement of the duplex structure in the subsurface. The backthrusts are formed as foreland dipping out of sequence faults within the break-forward sequence of thrusting which produced hinterland dipping duplex structure in the northeast directed Pennsylvanian compressional stress field during the Ouachita Orogeny. The roof thrust joins a north-dipping backthrust that bounds the San Bois Syncline to the south, and serves as the northern boundary of the triangle zone. Eastward along the strike of the transition zone, the backthrust becomes a blind backthrust and the duplex structure contains fewer horses. In the Wister lake area, the backthrust is probably located in the subsurface at the core of the Heavener Anticline. In western Arkansas, a triangle zone is present in the footfall the Choctaw and Ross Creek faults. The triangle zone is composed of three stacked wedges that share a roof thrust which meets a floor thrust at a tip line below the Poteau Syncline. This geometry suggests that accommodation zones on the surface may suggest the presence of a triangle zone in the subsurface. The geometric relationships summarized above demonstrate a duplex structure and associated triangle zone is present along the strike of the frontal Ouachitas-Arkoma Basin transition zone from Wilburton gas field area in Oklahoma to the Mansfield gas field area in Arkansas about 160 km (100 miles) although details of the triangle zone geometry and internal structures of the duplex differs substantially along the strike of the transition zone.