Pedogenic carbonate isotope record of vegetational evolution since late Miocene in Loess Plateau

lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai (35°N), the Loess Plateau. Stable carbon isotopic composition indicates that ( ⅰ ) Cplants might be present at least by7.0 Ma; ( ⅱ ) Cplants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of Cvegetation since ～2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. Cplant expansion at Lingtai cannot be fully understood with the "global Cexpansion" model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C/Cshift except changes in atmospheric COconcentrations and temperature. The latitudinal zone for C/Ctransition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal boundary