A NEW POLLEN RECORD OF THE LAST 2.8 MA FROM THE CO NGOIN, CENTRAL QINGHAI-XIZANG (TIBETAN) PLATEAU

A new pollen record from the lake of Co Ngoin in the central Qinghai-Xizang (Tibetan) Plateau provides information on the vegetation and climate changes during the last 2.8 Ma. Seven major significant changes in pollen associations indicate the processes of vegetation change and possible tectonic uplifts. The seven changes in vegetation succession include a temperate montane conifer and broad-leaved mixed forest, cold temperate montane dark conifer forest, alpine shrub-meadow and alpine desert, montane dark coniferous forest and alpine shrub meadow, montane dark coniferous forest and alpine meadow, alpine desert and meadow. The pollen record provides the evidence at least five times tectonic uplifts occurred at about 2.58 Ma, 1.87 Ma , 1.17 Ma , 0.83 Ma, and 0.3 Ma ago, respectively. Before 0.8 Ma, this region maintained the altitude below 4,000 m a. s. l. The larger amplitude of uplift occurring at about 0.8 Ma ago enforced the plateau rising into cryosphere, shaping the basic topographic pattern of modern plateau. The major successions in vegetation of this area were largely controlled by the stepwise uplift of the Tibetan Plateau.