POLYGENETIC EVAPORITE KARST OF THE CASTILE FORMATION OF THE WESTERN DELAWARE BASIN

Evaporite karst development within the Castile Formation of the Gypsum Plain, Culberson Co., TX and Eddy Co., NM, exhibits evidence of polygenetic speleogenesis. Numerous small-scale cave and karst features exist within the region that reflect modern, epigenic processes; however, intensely karsted areas contain features that exhibit complex morphologies and extensive secondary sediments.

Epigenic karst development is characterized by extensive karren development on exposed bedrock surfaces, shallow filled sinkholes and incised arroyos with open drains. Cave development is strongly controlled by brittle deformation but is generally limited spatially, with rapid decreases in aperture width away from insurgence points as a result of the high dissolution kinetics of calcium sulphate. Variations in lithologic fabric exhibit a strong influence on epigenic karst. Massive, sucrosic gypsum more commonly develops epigenic karst, while dissolution in laminated fabrics is more limited, likely as a result of the solubility differences between calcite and gypsum laminae.

Regions of intense karst development exhibit large, closely-spaced, closed depressions with limited drainage areas, which are often associated with caves that can be laterally extensive and morphologically complex. Large cave passages are not supported by the limited drainage basins associated with closely-spaced sinkholes. Numerous ceiling cupolas and smooth, scallop-free walls in caves suggest hypogenic dissolution, while incised, scalloped floors suggest overprinting by modern epigenic processes. Clay and fine-grained sand commonly fills solutionally widened fractures and ceiling channels, indicating partial infilling of previous dissolution paths.

Extensive epigenetic karst and regions of polygenetic karst development suggest a complex hydrologic history for the evaporite karst of the Western Delaware Basin. Current fieldwork suggests at least two episodes of karst development and possibly more.