STRUCTURAL GEOMETRY OF THE FRONTAL OUACHITAS-ARKOMA FORELAND BASIN TRANSITION ZONE, IN OKLAHOMA AND WESTERN ARKANSAS

The Arkoma Basin is located between the Ozark Mountains to the north and the Ouachita Mountains to the south. The basin experienced high subsidence and sedimentation rates during Ouachita Orogeny thrusting in late Mississippian and Pennsylvanian when the northern margin of the basin was the North American continent passive margin and the southern margin was the prograding thrust sheets for the Ouachita fold-thrust belt. Thrust loading and sediment loading during the orogeny formed and ultimately incorporated synorogenic sediment into the northward-propagating Ouachita fold-thrust belt

We have studied the structural evolution of the Frontal Ouachitas-Arkoma Basin transition zone between the Hartshorne gas field and Wister Lake area, Oklahoma and Mansfield gas field in Western Arkansas. The Choctaw fault serves as the leading edge thrust in Oklahoma. Its displacement is transferred onto the Ross Creek fault in western Arkansas within an accommodation zone. The footwall structures of the two faults contain structural features, such as duplex structures and triangle zones that resulted from the strain partitioning along the transition zone. In the Hartshorne gas field area, the horses within the duplex structure contain backthrusts which were formed as foreland dipping out of sequence faults within the break-forward sequence of thrusting that produced hinterland dipping duplex structure in the northeast directed Pennsylvanian compressional stress field. The roof thrust of the duplex structure 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, the transition zone exhibits the geometry of a triangle zone with multistory series of duplex structures. The footwall of the leading edge thrust, the Ross Creek Fault, consists of a zone of ductile duplex of incompetent shales of the Pennsylvanian Atoka Formation. The ductile duplex is bounded to the north by a north-dipping backthrust below the Waldron Syncline.