Analysis of the evolution of the Cenozoic ecological environment and process of plateau surface uplift in the Wenquan areain the interior of the Qinghai-Tibet Plateau

Abstract：The data of sporopollen assemblages collected from Cenozoic strata in the Wenquan area in the interior of the Qinghai-Tibet Plateau indicate that: from the Paleocene to early Miocene, paleovegetation evolved from mixed needleleaf and broadleaf forests-forest grassland vegetation in the early stage to veld vegetation in the late stage and the paleoclimate also evolved from the warm-wet subtropical climate to warm-cool one; from Pliocene to early Pleistocene, broadleaf trees were obviously reduced, while herbaceous plants increased markedly, reflecting that the climate began to evolve towards the dry-cold climate; and since the late part of the middle Pleistocene, the evolution from veld vegetation to desert grassland vegetation appeared, which finally molded an environment of modern desert grassland vegetation represented mainly by Chenopodiaceae and Artemisia. The change of the ecological environment in the interior of the Qinghai-Tibet Plateau reveals that the Qinghai-Tibet Plateau has undergone at least three uplift events with ecological-environmental significance since the Paleocene. Fanglomerate sediments and sporopollen assemblages in the Paleocene-early Oligocene Tuotuo River Formation indicate that: the Qinghai-Tibet Plateau had been uplifted to the altitudes of 1000-1500 m above sea level by the terminal Cretaceous-early Paleocene and the plateau landform might have a framework of alternating high mountains and basins; the noticeable increase in subtropical components in the vegetation of the early Miocene Wudaoliang Formation might be related to the climatic wetness caused by plateau monsoons induced by the plateau surface uplift and it is inferred that the plateau had uplifted to 2000-2500 m above sea level. In the late part of the middle Pleistocene, herbaceous plants predominated, indicating that the type of plateau vegetation had changed and that the plateau has been uplifted to an altitude of more than 3000 m above sea level.