Mid-Permian Shelf Margin Erosion Surfaces, Western Escarpment, Guadalupe Mountains, Texas: ABSTRACT

Abstract

Three basin-sloping erosion surfaces, interpreted as submarine seismic sequence boundaries, are spectacularly exposed along the Guadalupe Mountains' western escarpment. Each surface has about 300 m of basin margin relief over 2 to 3 km and displays 30 to 80 m of local channeling and/or listric-shaped relief. The upper (post-Grayburg) and lower (post-Victorio Peak) surfaces truncate predominantly flat-bedded, shoaling-upward bank (or low-angle ramp) dolomite strata. The middle surface (post-Cutoff) locally cuts through the deep marine drape of 300 m relief of the 75-m thick Cutoff formation. The post-Grayburg surface is listric-shaped and truncates about 140 m of Grayburg in a basinward distance of 1.5 km. This post-Grayburg erosion surface marks a major change in Permian carbonate sedimentation from earlier bank strata to the steep foreslopes of 400 + relief of the Goat Seep-Capitan reef complex. Erosional retreat of the Grayburg and Victorio Peak bank margin may have been 100 m to 1 km or more. Evidence of submarine erosion includes deep marine facies directly overlying the erosion surfaces, the regional improbability of hundreds of meters of sea level lowering, and the lack of recognition of subaerial or coastal features. The erosion processes remain uncertain. Retrograde slumping is favored for the listric-shapedmore » post-Grayburg surface. Bottom-hugging density currents were likely important for the lower two surfaces and perhaps for all three surfaces. Bare and eroded slopes are increasingly being recognized in modern submarine environments. They are likely more abundant and important in the geologic record than has been recognized to date.« less