‘Cold’ stage formation of calcrete nodules in the Chinese Loess Plateau: evidence from U-series dating and stable isotope analysis

This pilot study shows that some calcrete nodules from the base of palaeosols in the Chinese loess sequences can be dated by U-series isochron methods. The ages obtained suggest that the nodules did not form during interglacial climate stages; rather, they formed either during interglacial/glacial transitions or glacial climate stages. Thus, the nodules appear not to have formed contemporaneously with the soils beneath which they immediately lie but significantly post-date them. Post-pedogenic injection of carbonate into stratigraphically lower horizons is therefore identified. This finding contradicts previous assumptions regarding the timing of nodule formation. Carbon and oxygen isotope analyses of the nodules identify isotopic compositions which independently suggest that climatic conditions cooler and possibly drier than at present prevailed at the time of nodule formation.