The palaeoenvironmental evolution of the Yellow River headwater basin in Qinghai Province since Early Pleistocene

The Yellow River headwater basin located in the northeast Tibetan Plateau is the source of the Yellow River. This basin is very sensitive to the change of environment and climate. In this paper, the authors analyzed the pollen in the fluvial and lacustrine facies sediments in the Yellow River headwater basin. The pollen assemblage includes herbaceous pollen (Asteraceae, Artemisia families, Chenopodiaceae, Gramineae) and woody pollen (pine, birch). An analysis of characteristics of various kinds of plant pollen revealed the evolution and change of the palaeovegetation and palaeoclimate in Yellow River headwater basin since the Early Pliocene. The evolution has gone through four stages: the first phase from 2239 ka BP to 901 ka BP was a forest-steppe environment, reflecting a warm and humid climate; the second phase from 901 ka BP to 350 ka BP was a shrub steppe environment, suggesting a cold and dry climate; the third stage from 350 ka BP to 28 ka BP was a grass savanna-meadow grassland environment, implying a cold- humid climate; the fourth stage from 28 ka BP to 8 ka BP was a desert steppe environment, indicating a cold and dry climate.