A stable isotope record from paleosols and groundwater carbonate of the Plio-Pleistocene Camp Rice Formation, Hatch-Rincon Basin, southern New Mexico

A bstrAct — Stable oxygen and carbon isotope data from paleosols and shallow groundwater carbonates of the Plio-Pleistocene Camp Rice Formation in the western Hatch-Rincon Basin supplement an existing dataset from Neogene basin-fill in southern New Mexico and southeastern Arizona. In addition to their utility as proxies for paleoclimate and paleoenvironment, these data highlight local controls on the isotope chemistry of authigenic carbonate, such as depositional setting and hydrology. Oxygen isotope values for carbonates from Camp Rice piedmont deposits are higher on average (-6.8‰) than those from axial-fluvial parent material (-7.4‰), but mean carbon isotope values are identical (-4.3‰). The high carbon isotope values of soil carbonates formed in the ancestral Rio Grande floodplain differ from landscape mosaicism of C 3 versus C 4 plants observed in the Mangas Basin of southwestern New Mexico. This could be due to the influence of a shal- low and perhaps saline water table. Mean δ 18 O values increase from -7.6‰ for >3.1 Ma to -6.7‰ for <3.1 Ma samples and mean δ 13 C values increase from -4.9‰ to -3.8‰. Our data generally support a latest Pliocene-early Pleistocene transition to a warmer, drier climate with increased summer precipitation. This interpretation is consistent with stable isotope records from correlative deposits in the neighboring Palomas and eastern Hatch-Rincon Basins as well as southeastern Arizona.