Early Pleistocene deposits and paleoclimatic and paleoenvironmental changes in the Zanda basin, Ngari area, Tibet

Abstract：The paper analyzes various geological records closely related to the earliest Pleistocene climatic and environmental changes in the Zanda basin, Ngari, Tibet. The analytic results indicate that the earliest Pleistocene deposits in the study area may be divided into three sedimentary facies and four lithozones and that the paleoclimatic and paleoenvironmental changes may be divided into four stages: ① the 2.68-2.45 Ma stage, which is marked by alluvial and diluvial deposits, when freeze-and-thaw folds started to appear and the vegetations were dominated by arbores, mainly including Pinus, Chenopodiaceae and Artemisia, indicating a cool-temperate alpine climate; ② the 2.45-2.11 Ma stage, which is also marked by alluvial and diluvial deposits, when most freeze-and-thaw folds in strata were contorted, herbaceous plants increased rapidly, showing the features of the shrub-grassland climate, and the climate became cool and dry; ③ the 2.11-1.49 Ma stage, which is marked by alluvial-diluvial and periglacial deposits (mainly periglacial deposits), when the freeze-and-thaw folds increased, there appeared cryophilic ostracods, and the quantity and varieties of herbaceous plants reached a maximum and the shrubs also increased relatively, showing that the climate became more and more arid; and ④ the 1.49-1.36 Ma stage, which is marked by glaciolacustrine deposits, when the freeze-and-thaw folds appeared extensively in the strata, the abundance of cryophilic ostracods was very high and the herbaceous plants decreased slightly but pteridophytes increased significantly, showing the features of the cold-dry grassland climate.