Pollen-based Reconstructions of Late Pleistocene and Holocene Vegetation and Climatic Changes of Yang Lake Area, Tibet

In order to research the late Quaternary palaeoclimate evolution in the Yang Lake area, northern Tibet, we drilled the shallow well and surveyed the profile sections (ZK₁ and IP₁₆) in the periphery of the lake and exposed its river facies sedimentary strata. Abundant sporopollen fossils were discovered in the 48 samples. According to sporopollen types and contents, from bottom to top, they were divided into five assemblages: (1) Chenopodiaceae high content assemblage. (2) Ephedra-Quercus-Chenopodiaceae-Artemisia assemblage. (3) Ephedra-Chenopodiaceae-Artemisia assemblage. (4) Betulaceae-Quercus-Chenopodiaceae assemblage. (5) Ephedra-Chenopodiaceae-Artemisia assemblage. The palaeovegetation reconstructed by a great amount of pollen records displays five changes: steppe → poor-forest grassland → steppe → poor-forest grassland → steppe. A synthesis of pollen records, total organic carbon and element content from ZK₁ and IP₁₆ showed the history of climate cycle changes during late Pleistocene and Holocene. During 11 220 a.B.P or so, the first climate cycle was characterized by warm and dry climate to semi-dry and semi-humid climate. During 8 970 a.B.P or so, the second climate cycle was characterized by warm and dry climate to semi-dry and semi-humid climate. The last climate cycle is symmetry to the fifth pollen assemblage, was characterized by warm and dry climate. By the climate cycle periodicity, we presume that the area climate would be semi-dry and semi-humid in the future.