Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
American Association of Petroleum Geologists Annual Meeting, Dallas, April 18-21, 2004
An Example of Slope-Parallel Shale Ridge Triggered by Thin-Skinned Lateral Extension, South Texas
Ramón H. Treviño, Bruno C. Vendeville, Robert G. Loucks, L. Frank Brown, Ursula Hammes, Patricia Montoya, and Randy L. Remington
An area, located near Corpus Christi, Texas, comprises two large, coast-parallel, listric, normal growth faults detached on Oligocene deep-water shale. Similar to most large Gulf Coast growth faults, the fault planes dip basinward, have accommodated large amounts of extension, and link along strike with other faults. Less characteristically, the hanging wall of the growth fault system contains an elongate shale ridge whose strike is slope-parallel and, hence, perpendicular to the growth faults. The roof of the shale ridge is affected by a steep, younger normal fault rooted on the ridges crest. 3-D seismic-reflection data show that the oldest strata above the shale ridge underwent early uplift and folding (recorded by lateral changes in stratal thickness) soon after the onset of slip along the main growth faults. The shale ridge may have formed in response to local lateral (slope-perpendicular) extension or shortening related to either early divergent or convergent movement in the hanging wall of the growth-fault system. Slight divergence may have formed a detached graben within the hanging wall and associated reactive rise of a shale ridge beneath it. Alternatively, slight convergence may have formed a shale-cored anticline. Both scenarios would have allowed for a shale ridge trending perpendicular to the main growth faults. Later, slight divergent movement within the hanging wall of the main growth faults reactivated the shale ridge in extension and formed the perpendicular normal fault above the ridges crest.