Abstract: Regional Extent and Characteristics of Mesozoic Evaporite in Western Trans-Pecos Texas and Adjacent Northern Chihuahua

Donald F. Reaser

Mesozoic evaporite underlies a major part of the Chihuahua trough, a NW-trending negative tectonic element in NE Mexico and adjoining United States. The evaporite basin, as depicted by DeFord and Haenggi (1970), extends from El Paso/Juarez on the north to the Rio Conchos on the south and encompasses more than 20,000 mi². The evaporite sequence ranges up to an estimated 3,000 feet thick and consists mostly of massive, white to gray gypsum/anhydrite with lesser amounts of halite and limestone.

Surface exposures of evaporite occur at several places in northern Chihuahua. At Sierra de la Alcaparra, along the western edge of the evaporite basin, gypsum has been mined commercially. The former presence of salt in the Lower Cretaceous Navarrete Formation at Sierra del Alambre (NE Chihuahua) is indicated by large cubic pseudomorphs after halite ("hopper crystals") preserved in clay.

Some deep wells have also penetrated evaporite sequences in the region. The Texaco, Inc. Emmett Unit #1, located along the Rio Grande in southern Hudspeth County, Texas, was drilled in 1982 to a total depth of 18,500 feet. The test topped evaporite at a well depth of 13,412 feet and cut nearly 2,848 feet of white to light gray anhydrite with some intervals of limestone, dolomite, quart sandstone and minor variegated shale.

The age and maximum thickness of the evaporite is uncertain; however, faunal evidence and stratigraphic position suggest that the age of the evaporite is probably late J to early K.

AAPG Search and Discovery Article #90960©1995 AAPG Southwest Section Meeting, Dallas, Texas