ABSTRACT

The Southern Oklahoma Aulacogen (SOA) is a classic area of structural study; however, the style and timing of late Paleozoic deformation remains highly controversial. The westernmost surface exposure of the NW-trending Washita Valley Fault (WVF) and associated structures along the northern margin of the SOA were mapped at a scale of 1:3000 to investigate style and timing of faulting. West-northwest fold orientations, W-NW trending thrust faults, and conjugate joint sets suggest compression along a bearing of approximately N 34 E during the early stages of the Pennsylvania orogeny. However, the dominantly vertical surface orientation of the WVF and associated secondary faults suggests that this fault is the result of a later and more easterly-bearing greatest principal stress which produced left-lateral transpression. The secondary faults offset the W-NW trending folds, thus revealing that the folding and thrusting was followed by transpressive left-lateral movement and subsequently by pure left-lateral motion during Late Pennsylvanian. This chronology may reflect multi-plate collisions during the late Paleozoic deformation of the SOA.

Modern valley constrictions, alluvium ponding, buried scarps, displaced terrace, and apparent left-lateral deflections in stream courses occur along the Washita Valley Fault. These geomorphic features suggest Quaternary down-to-the-south and left-lateral fault motion.