Geology of the Sierra de la Parra area, Northeast Chihuahua, Mexico

The Sierra de la Parra area includes about 660 square miles in northeast Chihuahua, Mexico. The area is on the eastern margin of the Chihuahua Trough, a relatively narrow, northwest-southeast trending negative feature flanked by the Aldama and Diablo Platforms. During the Late Jurassic and Cretaceous 12,000 to 21,000 feet of basal evaporites, limestone, marl, shale and sandstone accumulated in the trough. In contrast, on the Diablo Platform, 15 miles to the east, less than 2,800 feet of sediments, devoid of evaporites, were deposited. A zone of recurrent faulting along the western margin of the Diablo Platform marks the eastern limit of the Chihuahua Tectonic Belt. This zone separates the predominantly block faulted platform rocks to the north and east from the intensely and complexly deformed rocks of the flanking basin. Laramide movement along this boundary fault zone tilted the Mesozoic basin rocks eastward producing a décollement on the evaporite section and producing subsequent folding and thrusting immediately east of the evaporite basin. Complex disharmonic folding caused by evaporite, shale, and marl flowage is present in thrust plates at all scales up to fold amplitudes of 10,000 feet. Normal faulting of Cretaceous rocks in the upper plate was caused by evaporite flowage into anticliines from adjacent areas. The La Parra and Cipress faults trend N. 40° W. and are anomalous to Laramide structures in the area. These faults probably lie along older Paleozoic fault trends which were reactivated in the Laramide orogeny and late Tertiary. The Palo Pegado, Cipress, and associated boundary faults of the Presidio graben represent Tertiary reactivation along the platform edge fault zone. Although faulting commenced with the advent of volcanic activity, most displacement on the Tertiary faults took place after most of the volcanic related deposition ceased. Several thousand feet of regional uplift probably took place during this faulting. Although block faulting occurred in the intensely deformed area, it is questionable whether it resulted from basement displacement or further flow of evaporites. Bolson fill was deposited over downfaulted blocks during Late Tertiary and Quaternary. Small Quaternary fault scarps indicate continued tectonic activity.