Assessing the applicability of isotopic analysis of pedogenic gypsum as a paleoclimate indicator, Southern New Mexico

A lack of well preserved paleoclimate indicators coupled with the abundance of gypsic soils in arid and semi-arid regions has stimulated research on using δ18O and δD isotopic analysis of the hydration water of gypsum to interpret paleoclimate. This study stresses the importance of establishing a pedogenic origin for gypsum crystals prior to isotopic analysis and evaluates the dominant processes controlling the formation of pedogenic gypsum. Isotopic analyses were conducted on the hydration water of pedogenic gypsum (23 samples) and local precipitation and river water (5 samples) in southern New Mexico. The isotopic signature of the hydration water indicates significant enrichment compared to local meteoric water. Evaporation is the driving mechanism by which gypsum accumulates in soils, and it is the dominant process controlling the isotopic fractionation of the hydration water of gypsum. Because the amount of isotopic fractionation during each episode of evaporation through time cannot be quantified, this technique is not suitable as a method to interpret paleoclimate.