Hypogene Evaporite Karst of the Greater Delaware Basin

Abstract

The Permian Basin of west Texas and southeastern New Mexico is host to extensive karst development in carbonate and evaporite strata. The Delaware Basin and associated Northwestern Shelf include both Guadalupian and Ochoan evaporites with diverse hypogene karst features of four general types: fluvial-induced; pressure gradient-dominated; density convection-dominated; and hydrocarbon-enhanced. Although many classic definitions of hypogene speleogenesis emphasize confined or semi-confined hydrogeologic conditions, analyses of Permian evaporites of this region show that hypogene karst can develop in near-unconfined conditions as long as local meteoric influences are minimal. Since the early Paleogene, eastern migration of the Pecos River in New Mexico has created a persistent potentiometric low as a target for upward migration of fluids, producing multi-story rectilinear maze caves as well as large cenote-like collapse structures in the Seven Rivers Formation, with less dramatic examples also common throughout the back-reef facies. Within the Castile Formation, evidence of hypogene speleogenesis is common, ranging from isolated rise structures nearly 100 m deep to multi-story maze caves and intrastratal brecciation. Evaporite calcitization and associated sulfur ores are common as the result of sulfate reduction in the presence of ascending hydrocarbon-rich fluids. Overlying strata of Salado and Rustler formations also host hypogene karst, but to a much lower documented degree and largely associated only with cross-formational breccia pipes and intrastratal brecciation.