Abstract

Guadalupian siliciclastic rocks and bioclastic limestones crop out near Shafter, Presidio County, Texas. The upper part of the Wordian Ross Mine Formation consists of a low-stand clastic wedge succeeded by sandstones, shales and carbonate mudstones, representing a rise of sea level onto a nearby carbonate platform. The Ross Mine Formation is overlain in turn by prograding carbonate foresets of the Capitanian Mina Grande Formation. The stereographic rotation of these beds to their original orientation reveals that the Mina Grande Formation prograded westward as far as this area from a carbonate platform on the eastern edge of the Marfa Basin. Subsurface cores from east and west of the study area suggest the same orientation. To the west, dark basinal shales and mudstones are succeeded by thick, basin-filling evaporites, while to the east lie platform edge carbonate mudstones (possible mud mounds).