A STRUCTURAL ANALYSIS OF THE WASHITA VALLEY FAULT IN THE SOUTHEAST ANADARKO BASIN

We propose that the Washita Valley Fault in the southeast Anadarko Basin originated when Precambrian-Cambrian pre-existing rift-related faults became reactivated as a rotational stress field reached a favorable orientation for strike-slip displacement. During the Early to Middle Pennsylvanian, contractional deformation dominated as a Precambrian-Cambrian failed rift underwent structural inversion along a northeast directed stress field. Structures that developed in the basin consisted primarily of thin-skinned fold-thrust structures resulting from slip along two main detachment levels. By the Late Pennsylvanian, stress rotated towards the east-northeast causing left-lateral strike-slip displacement along east-west oriented structures. During this time the Washita Valley Fault originated from an east-west oriented pre-existing basement fault. The Washita Valley Fault formed as a near-vertical segment cutting through the earlier fold-thrust structures. Movement was accompanied by oblique normal slip allowing grabens to develop that were subsequently filled with Virgilian age sediment. A left-step of the Washita Valley Fault allowed for a significant graben to develop near the east end of the study area resulting in a thick Virgilian age growth section validating the timing of fault movement. The Wichita Mountain Fault also underwent a component left-lateral strike-slip displacement during the Late Pennsylvanian highlighting its continuous movement and deformation history in a rotating stress field. While much of the published literature on the Washita Valley Fault is limited to the Arbuckle Uplift, our study documents its subsurface architecture, timing, and structural history in the southeast Anadarko Basin using a modern 3D seismic dataset in relation to evolving Pennsylvanian tectonics.