Stable oxygen and carbon isotopes of pedogenic carbonate as indicators of Plio-Pleistocene paleoclimate in the southern Rio Grande Rift, south-central New Mexico

Abstract

Stable oxygen and carbon isotopes of pedogenic carbonate provide a detailed record of paleoclimatic changes from late Pliocene through early Pleistocene in the Rio Grande rift of south-central New Mexico. A total of 30 calcic paleosols were sampled at three stratigraphic sections of the fluvial lithofacies of the Camp Rice Formation, and one calcic paleosol was sampled from fluvial sediment inset against the Camp Rice Formation. Three paleoclimatic stages are indicated by the carbon and oxygen isotopic data from south-central New Mexico. The initial stage, from 3.1 to 2.5 Ma, was characterized by the overall lowest values of ∂18O and ∂13C and by an increase in values with decreasing age, suggesting high effective moisture and abundant winter precipitation. The second stage (2.5-1.4 Ma) displays an increase in ∂18O with decreasing age but no significant change in ∂13C with time, suggesting that the effective moisture was nearly constant, but that temperature and/or summer precipitation may have increased through time. The final stage (1.4-0.7 Ma) shows an overall increase in both ∂18O and ∂13C with decreasing age corresponding to less effective moisture, higher temperature, and/or greater summer precipitation through time. -from Authors