CHARACTERIZATION OF PLAYA LAKES IN THE GYPSUM KARST OF SOUTHEASTERN NEW MEXICO AND WEST TEXAS, USA

The Delaware Basin and backreef facies of the Guadalupe Reef are currently undergoing an unprecedented infrastructure build-up as petroleum exploration, discovery, and exploitation escalate. The Bureau of Land Management – Carlsbad Field Office currently requires performance of surface karst inventories prior to the start of any construction. Any karst features located have a buffer assigned to them depending on the type of feature and the likelihood of rapidly conducting runoff into the subsurface. The New Mexico State Land Office is currently considering a plan to require these surface inventories as well. Many karst feature types are already known in the region including caves, swallets, cover-collapse sinkholes, caprock-collapse sinkholes, solution tubes, and springs. Playa lakes are shallow depressions found on gypsum bedrock in southeastern New Mexico and west Texas, and as far north as Vaughn and Santa Rosa, New Mexico, and even on Quaternary alluvial gravels in eastern New Mexico. These depressions are curious in that some of them are obviously linked to underground conduits (caves) via surface openings, while others have no such features. These features could be cover-collapse sinkholes that have filled in with Quaternary windblown alluvium and soil, or they could be solutionally formed via pooling of rainwater, dissolution of the gypsum and re-precipitation as the water evaporates, and subsequent deflation of the unconsolidated gypsum by wind. It is not known how the playa lakes are linked to the other karst features and why they are so closely associated. In this study we use field observations and three complimentary geophysical methods (ground penetrating radar, electrical resistivity imaging, and near-surface seismic) to make inferences about the subsurface structure of these depressions and their relationship to the karst features located in and around them. If it is found that these playa lakes should be considered karst features, rather than surface hydrologic features, they should be treated the same way as other karst features in the region when determining the routing of linear infrastructure and the placement of infrastructure pads and ponds.