SURFACE DENUDATION OF THE GYPSUM PLAIN

The Castile Formation crops out in Eddy County, New Mexico and Culberson County, Texas, covering more than 1500 square kilometers. The region contains more than ten thousand reported surficial karst features, including closed depressions, sinking streams and caves, with surficial karren dominating exposed rock surfaces.

A standard gypsum tablet study was conducted over the region for two years to delineate the rate of surface denudation across the Castile outcrops of the Gypsum Plain. Fifty five sites were monitored with triplicate gypsum tabs that were deployed for four month intervals. Rates of surface denudation were calculated based on mass loss of the gypsum tabs and compared with weather data collected at three control locations within the study area. Surface denudation rates exceeded 50 cm/ka in some areas with an average denudation rate of more than 30 cm/ka. Greatest rates of denudation occurred during the late summer and fall, in association with the monsoon season, while the lowest rates occurred during the late spring and early summer.

The Castile Formation is bounded by the Guadalupe Mountains to the northwest, the Delaware Mountains and Apache Mountains to the west and southwest, the Glass Mountains to the southeast and the Rustler Hills to the east; the orographic effects of these features contribute to a complex pattern of surface denudation associated with shifting seasonal climate patterns. True denudation within the gypsum plain varies from models developed from standard tablet studies due to variations in soil thickness and alluvial deposits; however, standard tablet studies provide a quantitative measurement of the rate at which the gypsum plain is evolving.