Late Cenozoic environmental evolution of the Qinghai-Tibet Plateau as indicated by the evolution of sporopollen assemblages

Abstract：Sporopollen was analyzed for samples from Neogene lacustrine sediments of the Tuotuohe, Tongtianhe, Nagqu, East Wenquan and Oiyug basins and Late Quaternary lacustrine sediments of Bas Co, Co Ngoin and Nam Co on the Tibetan Plateau. According to these data together with the sporopollen assemblage data from the Xining-Minhe basin, Lunpola basin, Namlin basin and Weihe basin, the authors analyzed the evolution of the Late Cenozoic paleovegetations and paleoenvironment on the Qinghai-Tibet Plateau and in its adjacent regions and found that vegetation and environment differentiation occurred in the Late Oligocene-Early Miocene in the Qinghai-Tibet region and its surrounding regions, resulting in rapid decrease and gradual disappearance of tropical-subtropical plants in the Qinghai-Tibet region. Such a change of vegetation did not coincide with the global warm climate and lower paleolatitudes of the Qinghai-Tibet region in the Late Oligocene-Early Miocene, and the extinction of tropical-subtropical plants indicates that the Qinghai-Tibet Plateau was uplifted in the Early Miocene. The broad-leaf and needle-leaf plants on the plateau showed a trend of general decrease and quasi-periodical fluctuations from the Early Miocene to Late Quaternary, which corresponded well with the global climate changes. In the Late Quaternary herbaceous plants increased gradually, leading to the appearance of the vegetation landscape of mixed needle-leaf plants, broad-leaf plants, shrubs and herbaceous plants dominated by Artemisia, Pinus and Betula on the Tibetan Plateau in the Late Pleistocene and Early Holocene.