THE RELATIONSHIP AMONG CLUMPED AND STABLE (C AND O) ISOTOPES IN INCIPIENT PEDOGENIC CARBONATES AND IMPLICATIONS FOR THEIR POTENTIAL TO REFLECT THE ANCIENT ENVIRONMENTAL CONDITIONS ASSOCIATED WITH PALEOSOL FORMATION

The stable carbon (δ13C), oxygen (δ18O), and "clumped" isotopic compositions of terrestrial carbonates have been used to reconstruct ecological, hydroclimatic, and thermal conditions, respectively, throughout the late Quaternary as well as earlier segments of geologic history, in different locales worldwide. Quantitative reconstruction of past variations in moisture source, seasonal temperature, and variations among C3, CAM, and C4 plants from pedogenic carbonates formed under semi-arid and arid climatic regimes is predicated on examination of the modern soil isotopic system. Incipient accumulations of pedogenic carbonates in mid-Holocene and younger deposits around the globe have, in fact, been examined for their isotopic composition as have, in some cases, components of the modern/recent soil and vegetation systems governing their isotopic composition. Such attempts to better understand the timing (i.e., hourly and longer timescales) and mechanisms of pedogenic carbonate formation have served as calibrations enabling reconstructions of past ecological, hydroclimatic, and thermal conditions from paleosol carbonates. However, the temporal and spatial variability of conditions influencing the carbonate formation precludes confident reconstruction of changes in the d18O of ancient precipitation, composition (C3 vs. C4) and variability in ancient vegetation, and seasonality/temperature of formation across large areas and timescales. Although there is no substitute for rigorous calibration work, the strength of the relationship between d18O and d13C in soil carbonates may inform us about important aspects of ancient soils and their hydrology and ecology, in turn serving as a tool for screening and/or more accurately interpreting ancient environmental conditions from either/both isotopic component(s). Toward assessing this potential, the relationship among stable C and O isotopes, and clumped isotopes, in young soils formed in climatically and ecologically disparate regions will be presented and discussed.