The Role of Hypogene Processes In Sulfate Reduction and Speleogenesis In the Castile Formation: Eddy County, New Mexico and Culberson County, Texas

The Castile Formation outcrops over ~1800 km² in Eddy County, New Mexico and Culberson County, Texas. GIS-analysis has indicated that over 9,000 karst features are likely to exist in this area. Many of these features are epigenic in origin. However, evidence of hypogene processes is widespread throughout the area. Dense clusters of hypogenic caves are typically associated with calcitized evaporites and selenite masses, suggesting a genetic relationship. Within these caves, specific morphologic forms (i.e. risers, cupolas, and half-tubes) provide evidence of their hypogenic origin.

Brecciation is common throughout the Castile Formation, indicating subsurface dissolution and collapse. Blanket breccias and subsidence troughs are suggestive of confined horizontal flow, while breccia pipes have been formed from upward stoping of subsurface voids. Calcitized evaporites are extensive throughout the region and are frequently associated with zones of brecciation. Deposits of native sulfur have also been observed in association with zones of brecciation, calcitized evaporites, and selenite masses.

The close proximity of hypogene caves, breccias, native sulfur, selenite masses, and calcitization suggests that hypogene processes have dominated sulfate diagenesis in the Castile Formation. Hypogene processes have provided pathways through which hydrocarbons from the underlying Bell Canyon formation have migrated upward and contributed to the calcitization of the Castile Evaporites. Hydrogen sulfide or native sulfur produced in this process has continued to migrate upward or laterally into oxic regions where selenite has been deposited. Significant overprinting due to surface denudation and epigenic processes has resulted in complex speleogenetic evolution within the Castile Formation.