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Ouachita-Appalachian Juncture: A Paleozoic Transpressional Zone

W. S. Hale-Erlich, J. L. Coleman, J. A. Lopez, M. S. Lober

The late Paleozoic collision of the Gondwana supercontinent with the trailing southern margin of North America created the Ouachita and Appalachian orogenic belts. Transecting these belts are several transpressional or wrench fault zones, including the Val Verde basin-Texas lineament system, the Ardmore-Anadarko basin trend, and the Reelfoot rift complex. Vertical movement within these wrench zones resulted in the emplacement of pop-block or flower structures. In Texas and Oklahoma these features are major structural traps for oil and gas. In this work, we propose that the (buried) juncture between the Ouachita and Appalachian foldbelts in Mississippi is a similar transpressional fault zone.

Recent reconstructions of the collision between Gondwana and North America indicate a relative closure direction of southeast to northwest. Normal decollement thrusting occurred in the Appalachian and Ouachita foldbelts, where the structural grain of the North American margin was nearly perpendicular to the closure direction. Where the structural grain was oblique to closure direction, wrench faulting and high-angle thrust faulting occurred, due to the combined effect of both translational and compressional stress fields.

In southwestern Alabama and Mississippi the trailing North American plate margin consisted of Mississippian and Pennsylvanian clastics draped over a thick Cambro-Ordovician carbonate shelf. This shelf trends northeast-southwest in Alabama but turns sharply to trend north-northwest in Mississippi, possibly reflecting changes in Precambrian basement relief. Transpressional stresses would have been generated near this sharp bend during the collision. This study identifies one such transpressional fault zone, on the basis of seismic data and well control, in east-central Mississippi.

The shear zone trends north-south just west of the Alabama-Mississippi state line and lies between the normal northwest-verging overthrusts of the buried Alabama Appalachians and the less-organized structures in the Paleozoic section of central Mississippi. A number of pop-block structures have been identified within this system, and two have been drilled. The results of these wells support the interpretation presented here.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.