Abstract

The Potrero de Padilla is the southeastern part of the bilobate Berrendo-Padilla anticline which makes up Sierra de Padilla in central Coahuila. The Potrero, a huge natural corral, occupies the breached axial area of the mountain-forming anticline. The bedrock is of Cretaceous age, listed in ascending order from the anticlinal core outward: Patula? arkose, 50 m. thick; Padilla limestone, 125 m.; La Mula? shale, 150 m.; Cuchillo-Taraises formation, 650 m.; Cupido limestone, the upper unit of the Coahuilan series, 310 m.; La Pena formation, 58 m., and Aurora limestone, 350 m., of the Comanchean series; and 500 m. of undifferentiated Cretaceous sediments containing Washitan, Woodbinean, and Austinian equivalents. The Berrendo-Padilla anticline is a relatively symmetrical, doubly plunging, bilobate fold trending about N.10 degrees W. Dips on the flanks range from about 30 degrees in the ridge-forming Aurora limestone to about 75 degrees in the relatively nonresistant beds near the axis. Faults are common, especially bedding-plane faults. Drag folding was mapped in the northern part of the Potrero and with associated fractures localized the high-grade lead carbonate ores found in the Cuchillo-Taraises formation.

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