Miocene vegetation and climatic changes reconstructed from a sporopollen record of the Tianshui Basin, NE Tibetan Plateau

Abstract: The Miocene vegetation and climate history of western China remains unclear. However, widely-distributed Miocene sediments of the Tianshui Basin in the NE Tibetan Plateau provide a great potential for deciphering the Miocene vegetation and climate history of this region. This paper presents first sporopollen record from these sediments, covering the period from 17.1 to 6.1Ma. Sporopollen data reveal that temperate, warm-temperate broad-leaved forest of Quercus, Ulmus and Betula dominated the Tianshui region between 17.1 and 14.7Ma, which was replaced by forest or forest-steppe of Ulmus, Artemisia and Betula between 14.7 and 11.7Ma. After a return to a broad-leaved forest of Betula and Quercus during 11.7–8.5Ma, the forest decreased rapidly and was replaced mostly by steppe vegetation (mainly composed of Artemisia, Chenopodiaceae and Poaceae) after 8.5Ma. We interpret the observed vegetation changes as a result of global climate change, which is characterized by global cooling, development of Arctic ice-sheets and permanent El Niño state after the Middle Miocene Climatic Optimum. The rapid development of steppe at about 8.5Ma suggested a permanent drying of the Asian interior at this time, coinciding with the onset of the well-known Hipparion red clay deposition in North China. [Copyright &y& Elsevier]