The Palaeogene deserts and their implications for the origin of monsoons on the eastern margin of the Qinghai-Xizang Plateau,SW China

The desert deposits as a kind of unusual deposits developed under specific climatic conditions in the geologic history play a particular role in the approaches to global climatic changes and atmospheric circulation patterns. Numerous studies show that although gypsum and other salt deposits indicating xerothermal climates once occurred over a wide area of the eastern margin of the Qinghai-Xizang Plateau within the arid zone prior to the establishment of the modern Eastern Asian monsoon systems, especially during the early-middle Palaeogene, the presence or absence of deserts remain to be uncertain up to now. The recent results obtained in the research of the early-middle Palaeogene red strata in the sedimentary basins on the eastern margin of the Qinghai-Xizang Plateau with the aid of the integration of sedimentology, palaeoclimatology and palaeogeography have disclosed that there was indeed an enrichment zone of aeolian dunes with stable thickness on the eastern margin of the Qinghai-Xizang Plateau during the early-middle Palaeogene. This implies that the basin-range type desert depositional systems might be present in the study area during the Palaeogene on the basis of palaeogeographic and sedimentary model and palaeoclimatic proxy index analysis. The sedimentary facies and palaeocurrent analysis indicates that the presence of a transitional boundary from arid to humid and from planetary wind circulation to monsoon circulation in the study area may mark the occurrence of Eastern Asian monsoon events. For this reason, the results of research in the present paper may provide not only new sedimentological data for the approaches to the evolution of the Cenozoic arid zones in China and global climatic changes but also significant atmospheric circulation evidence for the uplift of the Qinghai-Xizang Plateau and the origin of the Eastern Asian monsoons.