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

查看全文 作　　者：Shiling [1]Yang;Zhongli [1]Ding;Zhaoyan [1]Gu;Jimin [1]Sun;Shangfa [1]Xiong 机构地区：[1]Chinese Acad Sci, Inst Geol, Beijing 100029, Peoples R China 出　　处：《Chinese Science Bulletin》索引1999年第44卷第11期,共5页 摘　　要：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 ) C₄ plants might be present at least by7.0 Ma; ( ⅱ ) C₄ plants expanded gradually between ~4.0 and ~3.2 Ma, and their biomass fraction was up to 50%; and ( ⅲ ) the biomass of C₄ vegetation since ~2.0 Ma seems to have been decreased to the level (about 20%) before 4.0 Ma. C₄ plant expansion at Lingtai cannot be fully understood with the 'global C₄ expansion' 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 C₃/C₄ shift except changes in atmospheric CO₂ concentrations and temperature. The latitudinal zone for C₃/C₄ transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal 关 键 词：pedogenic CARBONATE PALAEOVEGETATION shift atmospheric CO2 concentrations.