ORIGIN AND MANIFESTATIONS OF EVAPORITE KARST GEOHAZARDS OF THE DELAWARE BASIN, SOUTHEASTERN NEW MEXICO

The prolific expansion of petroleum exploration and resulting increased development of infrastructure in the Delaware Basin has led to widespread concern for significant concentrations of karst geohazards within gypsum strata of the Castile Formation, present along the western margin of the basin. Hypogene karst manifestations ranging from extensive, complex maze caves to isolated mega-vugs have formed at depth due to dissolution by migrating fluids originating in the Bell Canyon Formation. Fractures and joint sets within the Castile have allowed continued dissolution and formation of upward stoping solutional breccias, secondary calcitization and precipitation of native sulfur. Over time, surface denudation leading to significant thinning of areas of the Castile has exposed previously confined hypogene formations, allowing for reactivation of dissolution, breach by surface precipitation and epigenic overprinting. Episodes of increased precipitation have allowed pure epigene karst development within near surface strata in the form of laterally limited gypsum caves, sinks, suffusion caves, gypsite and karren.

Current models attribute the speleogenetic origin of karst geohazards in the Castile to have been initiated by uplift, tilting and increased geothermal gradients throughout the Miocene, encouraging the development of hypogene porosity, dissolution, brecciation and evaporite calcitization. The latest Miocene allowed for surface denudation of the western margin of the Castile, beginning epigene karst development. Epigenic processes increased with the wetter climate of the Pliocene and Pleistocene, followed by the migration of the Pecos River across the basin through the late Eocene. Hypogene and epigene processes continued at a slower rate with the shift to a more arid climate during the Holocene while formation of gypsic soils and infilling of exposed void space increased. Each manifestation poses significant risk due to difficulty of detection of shallow features and increased instability leading to the possibility of catastrophic collapse of infrastructure, as well as increasing the complexity of infiltration regimes and associated hydrogeologic system.