Impact of phased uplift of Tibetan Plateau on environmental changes since late Middle Pleistocene: Palynological records in the three terraces of Middle Shiquan River

Three fluvial terraces in Porougong River in the middle reach of Shiquan River were identified, and the palynological records were investigated to decipher the paleoenvironmental changes in the west inland of the Tibetan Plateau. Three phases of uplift in the west inland of the Tibetan Plateau are suggested to be associated with the third, second, and first fluvial terraces (T₃, T₂, and T₁) being formed at ca.126-25.1 ka B.P., 25.1-4.5 ka B.P., and 4.5-1.3 ka B.P., respectively. The differentiated uplift rate infers that the inland Tibetan Plateau shows an earlier uplift than the surroundings. Coincident with the phased uplift, three episodes of the changes in paleovegetation and paleoclimate since late Middle Pleistocene could be identified by the spore-pollen records, including the forests under the warm-wet climate featured by the assemblage of Picea + Pinus-Betula-Ulmus-Chenopodiaceae-Epheara in the third terrace, the forest-grassy vegetation under the semi-arid and semi-wet climate as shown by the Picea + Pinus-Chenopodiaceae-Epheara assemblage in the second terrace, and the grassland under the cold-dry climate indicated by the Chenopodiaceae-Artemisia-Ephedra assemblage in the first terrace. The association of the paleovegetation and paleoclimate changes with the phased uplift of the fluvial terraces has revealed the important impact of the Plateau uplift.