Structure of the Alleghanian Thrust Belt under the Gulf Coastal Plain of Alabama

Delores M. Robinson¹, Ryan M. Bailey², and Andrew M. Goodliffe¹
¹Department of Geological Sciences, University of Alabama, P.O. Box 870338, Tuscaloosa, Alabama 35487–0338, U.S.A.
²Anadarko Petroleum Corporation, 1201 Lake Robbins Dr., The Woodlands, Texas 77380, U.S.A.

Mesozoic and Tertiary sedimentary rock of the Gulf coastal plain covers the Paleozoic Appalachian orogen in central Alabama, obscuring the intersection of the northwest-trending Ouachita thrust belt and the northeast-trending Alleghanian thrust belt. Direct observation of the thrust belt system is not possible, and few studies exist because of the lack of well control and limited public availability of seismic reflection profiles. This study uses existing multichannel seismic reflection data and well log data to clarify the subsurface structures and estimate the amount of shortening in the Alleghanian thrust belt in westcentral Alabama under the Gulf coastal plain.

The seismic line extends 34.2 mi in a nearly north-south direction, perpendicular to the thrust belt, from the Black Warrior basin in the north to near the Talladega slate belt in the south. To correct the two-way travel times of the seismic sections to depth, we built a synthetic seismogram from a nearby deep well, constructed two velocity models, and interpreted and balanced two cross sections. In west-central Alabama, the thrust belt is forward propagating and hinterland dipping, with thrust sheets that range in length from ~5–17 mi and have thicknesses between 11,000–14,500 ft. Depth to basement is between 23,500– 26,000 ft. Estimates of shortening from the balanced cross section are between 26–33%. No indication of interference structures exists between the northeast-trending Alleghanian thrust belt and northwest-trending Ouachita thrust belt. These structural data, in addition to gravity and magnetic data, indicate that the Alleghanian thrust belt continues along a similar northeast- southwest trend toward the Suwannee-Wiggins suture, which marks the boundary between Laurentian and Gondwanan (African origin) crust, and does not sharply curve toward the Ouachita thrust belt.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012