A cool, arid climate featuring steppe vegetation characterizes the modern day temperate zone of northwestern China. In contrast, palynofloras indicate that the paleoclimate there was warmer and wetter during the Pleistocene than during the Holocene. To document vegetational and climatic changes during the Quaternary, fossil pollen and spores were systematically studied in sediments from the Qaidam Basin in the Qinghai Province at the northeastern margin of the Tibetan (Qinghai–Xizang) Plateau.
Pollen and spores in four cores from the Quaternary lacustrine deposits in the Qaidam Basin showed four distinctive pollen zones. The basal assemblage, Zone Q1, is dominated by taxa having tropical or subtropical warm, wet climatic affinity and is probably Early Pleistocene in age. The overlying assemblage, Zone Q2, is dominated by taxa having warm–temperate and semi–wet climatic affinity and is probably Middle Pleistocene in age. Zone Q3 is dominated by taxa having temperate and semiarid climatic affinity and is probably Late Pleistocene in age. The uppermost assemblage, Zone Q1, is dominated by taxa having cool–temperate, arid climatic affinity and is Holocene in age.
The modern vegetation of the high plateau is dominated by xerophytic and halophytic herbs and shrubs. The palynofloral assemblages show that this modern vegetation became established during the Holocene, when cool, dry conditions prevailed following Pleistocene deglaciation. This climatic cooling is interpreted as the result of continued Himalayan–Tibetan Plateau uplift in the Holocene. Modern vegetation zones are used as a basis for comparison with the fossil assemblages and suggest that the Qaidam Basin might have been elevated at least 2,000 to 3,000 m since the Early Pleistocene. Dabuxun Lake in the basin may have been elevated about 700 m in the past half million years. The pollen data therefore allow more precise dating of Himalayan–Tibetan uplift. Intense uplift at the end of Early Pleistocene is indicated and further uplift probably occurred in the middle substage of the Middle Pleistocene. The results of this study contribute to understanding Himalayan–Tibetan Plateau evolution, regional Quaternary correlations, and climatic changes around the globe.