Submarine Slope Erosion along Permian Bank Margin, West Texas: ASBTRACT

Abstract

Recent sea floor investigations, such as those of the western Atlantic-Blake Plateau region by Heezen and Stetson and coworkers, indicate extensive erosion by deep ocean currents on flat surfaces and on steeper submarine slopes. Evidence of small-scale submarine erosion of lithified crusts or skeletal material is increasingly being recognized, but few examples of ancient unconformities are known that represent appreciable erosion in a deep marine environment. Forming the 2 major unconformities of the Leonardian and Guadalupian strata of the Guadalupe Mountains of Texas required extensive erosion; that this erosion and the creation of numerous small channels and diastems in associated strata occurred in a continually submerged, relatively deep, marine environment best fits the present geologic data. The 2 unconformities are roughly parallel. They form the upper and lower boundaries of the dark basinal carbonates of the Cutoff Formation. The lower unconformity, disconformable shelfward, steepens basinward to 5-10° and truncates over 200 m of essentially flat-lying Victorio Peak bank margin carbonates before flattening basinward. This unconformity probably inherited the relief of a gentler bank margin depositional profile. Erosion steepened and caused bankward slope retreat for possibly hundreds of meters. The upper unconformity locally intersects the lower and is onlapped by about 300 m of the Brushy Canyon Formation, composed largely of deep water sandstones. These unconformities and associated diastems are generally smooth, sharp surfaces, showing scant evidence of the environment of erosion, but broad gentle undulations, and spoon-shaped, possibly closed depressions, some with tens of meters of relief, appear characteristic of both unconformities. Several V- to U-shaped basin-trending channels are present locally. The mid-Permian bank margin of the classic Guadalupe Mountain area appears to furnish an outcrop analog for some of the processes of both deposition and erosion along deep submarine slopes. The possibility that deep marine erosion created many unconformities of the geologic record should be considered seriously. End_of_Article - Last_Page 358------------