--> Along Strike Structural Variations in the Frontal Ouachitas-Arkoma Foreland Basin Transition Zone


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Along Strike Structural Variations in the Frontal Ouachitas-Arkoma Foreland Basin Transition Zone


The Arkoma Foreland Basin was formed by the northeast directed Pennsylvanian compressional stress field during the Ouachita Orogeny. We have constructed many balanced structural cross-sections along the frontal Ouachitas–Arkoma Basin transition zone between the Hartshorne Gas Field area in Oklahoma and the Mansfield Gas Field area in Arkansas, based upon available 2D and 3D seismic data and well logs. The cross-sections reveal strike oriented structural variations to accommodate the east-west strain partitioning within the basin.

In the Hartshorne and Wilburton Gas Field areas, our structural cross-sections and structural contour maps of the Lower Atokan Spiro/Wapanucka gas reservoirs suggest the presence of a duplex structure that may have been laterally displaced by tear faults (i.e., strike-slip faults) that are not mappable at the surface. This suggests that the tear faults may be dying out upsection, into the Atokan shale units. In the duplex structure, there are foreland-dipping out-of-sequence backthrusts in addition to the break-forward in-sequence hinterland-dipping thrusts. The backthrusts cause structural thickening of the Spiro/Wapanucka reservoirs and appear to be younger than the in-sequence thrusts. The roof thrust of the duplex joins the north-dipping Carbon Fault on the surface, and serves as the northern boundary of the triangle zone with a zero-displacement point below the syncline. Eastward, the Carbon Fault becomes a blind backthrust and the duplex structure contains fewer horses and no detectable backthrusts.

In the Mansfield Gas Field area in western Arkansas, a triangle zone is present in the subsurface between the Choctaw and Ross Creek faults and within the accommodation zone area. The triangle zone is composed of three stacked wedges that share a roof thrust, which meets the south-dipping Stanley Detachment at a tip-line below the Poteau Syncline. In this area, a duplex structure is present with only two horse structures. The Stanley Detachment is the floor thrust of the duplex structure and utilizes the Devonian shale beds. The Lower Atokan Detachment is the roof thrust and uses the Atokan shales. In summary, our structural cross-sections demonstrate substantial structural variations along strike of the frontal Ouachitas–Arkoma Basin transition zone. This variation is very important for gas exploration in the Pennsylvanian sandstone gas reservoirs in the Arkoma Basin.