HYPOGENE DIAGENESIS OF THE CASTILE FORMATION, DELAWARE BASIN, WEST TEXAS

Hypogene processes have dominated the diagenetic evolution of the Castile evaporites throughout the Delaware Basin, including: 1) development of cavernous porosity and intrastratal brecciation; 2) emplacement of economic secondary minerals; and 3) calcitization of evaporites. Upward and lateral migration of hypogene fluids, driven by mixed free and forced convection from the underlying Bell Canyon and Cherry Canyon formations into the overlying Ochoan evaporites, has driven diagenetic alterations, including permeability enhancement through the creation of complex hypogenic caves, laterally extensive breccia sheets and vertical breccia pipes. Secondary fluid migration through these high permeability flow paths enabled hydrocarbon-rich fluids to pass through the Castile Formation, promoting sulfate reduction with intense evaporite calcitization along the lower surface of the Castile Formation and throughout strata with established preferential flow routes. Sulfate reduction appears to be coupled with thermal fluids, with most documented zones of calicitization also exhibiting proximal selenitic masses, suggesting that thermal sulfate reduction likely dominated. Native sulfur is found infilling pore space in some calcitized regions, where late phase hypergenic fluids have not removed mineralization. Currently the outcrops of the Castile Formation are rapidly denuding with rates averaging 50 centimeters per thousand years, which is causing hypergene overprinting throughout surficial exposures of the Castile Formation.