The Stable Isotope Chemistry of Pedogenic Carbonates at Kyle Canyon, Nevada

Abstract

Abstract The C and O isotopic composition and radiometric ages of laminar pedogenic CaCO 3 coatings were examined in limestone‐derived alluvium along an elevational and climatic transect of the Mojave Desert of Nevada. The δ 13 C of the soil CO 2 decreased with increasing elevation and was related to plant density and available soil moisture. Laminar pedogenic carbonate coats which formed on the bottoms of clasts were separated into inner and outer laminae. The δ 13 C of carbonates in the outer laminae decreased with increasing elevation as a result of a decrease in the percentage of detrital carbonate in the sample and a decrease in the δ 13 C of the soil CO 2 . The δ 18 O of the outer laminae also decreased with elevation and, after correcting for contamination by detrital carbonate, appeared to correspond to changes in the isotopic composition of the precipitation. The δ 13 C of the carbonate in the inner laminae also decreased with increasing elevation; however, carbonate in the inner laminae was much purer than the outer laminae and appeared to be predominantly pedogenic in origin. The δ 13 C of these layers reflects the δ 13 C of soil CO 2 and, for most samples, corresponded to expected values for modern carbonate. Based on uncertainties in dating techniques and the estimated range in isotopic composition of pedogenic carbonate, however, it was not possible to determine if some of the inner laminae formed in the latest pluvial period and reflect past pedogenic conditions.