Polyphase Deformation in Marathon Basin, West Texas

Darrell Sims, Alan Morris

Marathon basin, Texas, is the westernmost window into the Ouachita orogene. Interpreted as the result of northwest-southeast compression, intermittent orogenic pulses began in the Mississippian and continued into the Early Permian (Wolfcampian). However, the northeastern portion of the basin contains structures that could not have resulted from a single compression orientation and indicate that deformation continued to affect Wolfcampian and Leonardian rocks. Our work confirms the protracted nature of upper Paleozoic deformation and indicates that late-and postorogenic events were not related to the northwest-southeast compression manifest throughout the Marathon basin.

The northeastern part of the basin exposes Morrowan(?)-Desmoinesian rocks. We recognize a duplex thrust system, traceable for 10 km, rooted in the uppermost Morrowan(?) Tesnus Formation and creating a double thickness of (Morrowan-Atokan) Dimple Limestone. The duplex is folded by 50 to 2,000-m half-wavelength northwest-verging folds which plunge gently southwestward. Dimple thickness is further increased by a large number of contraction faults, each with up to 2 m of stratigraphic throw. Superimposed upon these structures are southeast-plunging, 10-20-m half-wavelength open kinks with vergence sympathetic with the regional trend variation apparent in this part of the basin. The superimposed structures are the result of a northeast-southwest compressive event. North of the Ouachita exp sure, rocks containing lower Leonardian fusulinids are deformed into gentle eastwest-trending 500-m half-wavelength folds which are likely the result of another distinct compression orientation trending north-south. Pervasive east-west extension in all Pennsylvanian-age rocks is indicated by subvertical, calcite-filled veins.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.