Cenozoic Palaeoclimate Evolution Based On The Records Of Sediment Elements In The Jiuquan Basin

A series of major global changes have taken place in the Cenozoic: the rapid stepwise climate cooling,Asia inland aridification,episodic tectonic uplifts of Tibetan Plateau and the formation and evolution of Asian monsoon.The Tibet uplift and global cooling are important factors influencing the evolution of climate in Asia.By studying the response of the important regional climate change to global cooling and the uplift of the Tibet can provide the informations for the study of climate evolution history and evolution mechanism in Asia.The Jiuquan Basin is located at the western edge of the Hexi Corridor on the northern margin of the Tibetan plateau,developing continuous Cenozoic sediments,which completely record the processes of the climate evolution and the deformation and uplift of the northeastern plateau.This study selected Huoshaogou section,Ciyaokou section,Shiyangjuan section and Laojunmiao section as the study objects,which have continuous and precise stratigraphic sediments.We restored the history of the Cenozoic climate evolution,based on the analysis of sediment elements content,chemical weathering records and climatic proxy records of the sediments,combined with previous research results,and comparison with the records of the global climate change and the uplift of the Tibetan Plateau.We get the following conclusions:The elements sequence of sediment(<2?m)was builded since the 40 Ma in Jiuquan basin.The source area of the Jiuquan basin is the primary weathering stage since Cenozoic.Jiuquan basin have experienced five stages of climate evolution.From 40?34Ma,the climate is semi-arid,although the chemical weathering is relatively strong(showing a weakening trend),it is controled by source in Altun Mountain.From 34?26Ma,the climate is dry,chemical weathering intensity is significantly weakened relative to the previous period.From26?14Ma,the climate is semi-humid,chemical weathering enhanced.From14?8Ma,the climate is humid,chemical weathering strength is further increased relative to the previous period.From8?0Ma,the climate is drought,chemical weathering intensity decreased.Based on the comprehensive analysis of chemical weathering index and various climatic proxy records,and compared with the uplift of the Tibetan Plateau and global oxygen isotope curve,it is concluded that 40?14Ma climate evolution process is mainly controlled by the global cooling,and 14?0Ma may be controlled by the Tibetan Plateau uplift and global cooling.