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November 18th, 2020 12:00 PM - 1:00 PM

A Structural Analysis of the Wichita Uplift & Structures in the SE Anadarko Basin, Part 2: The Washita Valley Fault, A Smoking Gun to Evolving Pennsylvanian Tectonics?

Dr. Molly Turko

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In a previous talk, Dr. Turko described the structural evolution of the Wichita Uplift and proposed that pre-existing normal faults of Precambrian-Cambrian age were either reactivated or controlled the location of the Pennsylvanian age structures in the Anadarko Basin. She also showed that a progressive rotation in regional stresses from NE-SW to a more ENE-WSW direction during the Pennsylvanian uplift resulted in strike-slip deformation along the more E-W oriented structures, including the Washita Valley Fault (WVF). In this talk, we will take a closer look at the WVF within a 3D seismic survey through the SE Anadarko Basin.

It is proposed that the WVF in the southeast Anadarko Basin originated when 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 NE 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 ENE causing left-lateral strike-slip displacement along E-W oriented structures. During this time the WVF originated from E-W oriented pre-existing basement faults. This 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 WVF 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 of 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 WVF is limited to the Arbuckle Uplift, this study documents its subsurface architecture, timing, and structural history in the SE Anadarko Basin using a modern 3D seismic dataset in relation to evolving Pennsylvanian tectonics.



Dr. Molly Turko has over 10 years of experience in the oil and gas industry and is a subject matter expert in structural geology. She has had the opportunity to work in multiple basins in the U.S including the Anadarko, Ardmore, Powder River, Appalachian, Onshore Gulf Coast, and Rocky Mountain Basins. She received both a B.Sc. (2009) and a M.Sc. (2011) in geology from the University of Tulsa followed by a Ph.D. (2019) from the University of Oklahoma where she studied under Dr. Shankar Mitra. Some of her favorite projects include numerical modeling of fractured reservoirs and interpreting seismic data in complex geologic settings where structural models are a must! Molly’s passion is mentoring and teaching, but her favorite role is leading structural geology field courses in Nevada and Southern Oklahoma. Molly is currently a team member of Applied Stratigraphix as their Structural Geology Expert along with consulting for Turko Tectonics and Structural Geology.