Subsurface correlation of Permian strata and analysis of the depositional environments of the Marfa Basin at the Shafter Mine, Presidio County, Texas.

摘要

The Marfa Basin at Shafter, Texas, is the southwestern extent of the Permian Basin. Over 327 cores at the Shafter Mine were drilled, logged and stored by Silver Standard Company in Shafter. The lithology of the strata suggests that this locality was part of a basin margin/deep basin environment. This study focused specifically on identifying, dating, and correlating the Permian portions of these cores, correlating individual turbidites and debris flows when possible and dating these events. During the Middle Permian, the Ross Mine and Mina Grande Formations are equivalent to similar formations in the Glass Mountains, the Apache Mountain and the Guadalupe Mountains. The Ross Mine consists mostly of shale, silty shale, mudstones, wackestones and packstones, while the Mina Grande consists mostly of mudstones, wackestones and packstones. Cycles of turbidity currents and debris flows occur repeatedly in the Wordian Ross Mine Formation and continue through the Capitanian Mina Grande Formation and are overlain by spar-cemented and intraclast dolopackstone similar to that of the Tessey and Rustler Formations. The presence of these Ochoan evaporite-related rocks indicates that the Marfa Basin did not have an unrestricted connection to the Permian ocean at that time. The main source of carbonate debris is from a shelf edge deposit, possibly the Capitan.