STRUCTURE OF THE APPALACHIAN THRUST BELT UNDER THE GULF COASTAL PLAIN SEDIMENTS

Gulf Coastal Plain sediments cover the Paleozoic Appalachian thrust belt in west-central Alabama. Located at the intersection of the Ouachita and Appalachian orogenies, this region is integral in understanding the dynamics between the two corresponding thrust belts. Because direct observation of the thrust belt is impossible, researchers depend upon other means to study the subsurface structures. However, few studies exist in this region because of the lack of well control and limited availability of proprietary seismic reflection profiles. In this study, existing multichannel seismic and well log data are used to clarify the subsurface structures and estimate the amount of shortening in the Appalachian thrust belt.

The profile lines extend 78 kilometers in a nearly north-south direction, perpendicular to the thrust belt from the Black Warrior Basin to the Talledga Slate Belt. After a synthetic seismogram and velocity model were developed, cross sections were interpreted from the lines. Because the thrust belt is covered by Gulf Coastal Plain sediments, these cross sections provide unparalleled insight into the geometry of the subsurface thrust belt. In west-central Alabama, the thrust belt is forward propagating and hinterland dipping with thrust sheets that vary in length from 8-27 kilometers and have a thickness of 3.4-4.4 kilometers. Depth to basement is between 7-8 kilometers. In this cross section, no region of incoherency exists; thus, a ductile duplex is not present this far to the southwest in the Appalachian thrust belt. Estimates of shortening from the balanced cross section are between 26-29%.