Abstract:
In the southern part of the Appalachian thrust belt, the thrust system is buried by Gulf Coastal Plain sediments; thus, directly studying this Paleozoic thrust belt is impossible. However, multi-channel seismic data and well log data are used to explore this thrust belt. In this region, Gulf Coastal Plain sediments cover the Paleozoic thrust belt that formed during the Ouachita and Alleghenian orogeny. Due to a lack of well control and limited availability of proprietary quality seismic reflection profiles, only a few other studies interpret subsurface structures beneath the Gulf Coastal Plain (Thomas, 1973; Thomas, 1989; Bally, 1983; Hale-Erlich and Coleman, 1993). Stratigraphic thicknesses in the thrust belt were derived from the Ethel M. Koch #1 well and in the Black Warrior Basin from the James W. Sterling 17-14 well. Two additional wells, the Willis #1 and Dollarhide #1 were used to identify the depth to formation tops within the interpretation. An 84 kilometer long seismic profile was depth-converted using a sonic log from the Koch well and then projected onto a straight line perpendicular to the Appalachian thrust belt which shortened the length of the line to 78 kilometers. Five main horizons were interpreted in two way travel time and depth-converted using interval velocities derived from synthetic seismograms and the sonic log in the Koch well. A 14 kilometer zone of poorly imaged seismic data within line segment 691-1 A may be the result of high velocity material juxtaposed with the base of the Coastal Plain sediments. Two interpretations, both incorporating forward-propagating sequences, were made. The depth of the upper detachment altered the structural style of the ramp anticline on thrust 1 from a fault bend fold in interpretation #1 to a fault propagation fold in interpretation #2. Consequently, the depth of the detachment along with the fault trace of thrust 2 effected the thickness of units incorporated in thrust 2 and the thickness and number of units incorporated in thrust 3. The lengths of the units are quantitative, while the actual positions are speculative. The flexural slip method and line length balancing was used to balance the cross sections. Shortening estimates range from 23 kilometers or 29% shortening in interpretation # 1 to 19 kilometers or 26% shortening in interpretation #2.
