The Parras basin, in southern Coahuila and western Nuevo Leon, Mexico, contains 4,500-6,000 meters of Upper Cretaceous and lower Tertiary terrigenous sedimentary rocks. Approximately 1,500-2,100 meters of Lower Cretaceous carbonate rocks and 2,000-3,000 meters of Triassic and (or) Jurassic evaporites, carbonates, and terrigenous rocks flank parts of the basin and underlie large areas within the basin. The Triassic and (or) Jurassic sedimentary rocks exhibit complex facies relations. Lower Cretaceous carbonate rocks are remarkably uniform in large areas of northeastern Mexico. Most of the Upper Cretaceous and lower Tertiary sediments were deposited in a boot-shaped, shallow, subsiding basin between the present-day Sierra Madre Oriental and Coahuila platform.

The Upper Cretaceous-lower Tertiary Difunta Group displays intertonguing relations between two distinct lithic types: red, non-marine to brackish-water sandstone and shale alternate with gray to black, brackish-water to marine, calcareous sandstone and shale. Regionally the red strata pinch out or change facies toward the north and east in the basin where marine deposition was continuous from Late Cretaceous to early Tertiary time. Some redbeds change facies down depositional dip into gray marine strata. Red strata also have been discovered in the Upper Cretaceous Parras Shale, which normally is gray to black, calcareous shale, 1,200-1,500 meters thick.

During Paleocene or Eocene time, the sediments of the Parras basin were deformed contemporaneously with the adjacent Sierra Madre Oriental structural belt. Deformational intensity in the Upper Jurassic and Lower Cretaceous carbonate rocks of the nearby Sierra Madre appears to be related to the distribution and thickness of the "Minas Viejas" (Triassic and [or] Jurassic) evaporites. The type and degree of deformation within the Parras basin are not uniform as indicated by three factors. (1) Overturned folds and imbricate thrusts, which probably do not extend below the Parras Shale, characterize the constricted western part of the basin; (2) broad, elongate, open folds in the southeastern part extend downward to folds in Lower Cretaceous strata; and (3) broad, open, domal folds in the n rtheast are related to Lower Cretaceous uplifts on the surface and at depth.