A Preliminary Study On Depositional Characteristics And Evolution Process Of Gobi Desert From North Altun Mountains Since Late Quaternary

Gobi desert covers a large area in the northwestern China,but few studies have been undertaken to investigate its depositional characteristics and formation process.Sand storm and dust emission from the Gobi desert have an impact on the regional even global environment.Study on the evolution of the Gobi desert would help us understand the local environment,and help to guide practical campaign such as resource development and ecological construction in Gobi region.This paper is researched on Gobi desert from North Altun Mountains,and we analyzed the sediments from Gobi surface and the typical section.On the spatial scale,we investigate the sediments from different parts of the Gobi desert,including bedrock residue?alluvial fan-in?alluvial fan-side and found that sorting of the sediment decreases together with the increasing roundness from the top part of Gobi to alluvial fan-side with the change of topography and carrying distance.On the time scale,palaeoenvironmental changes of the Gobi deserts in front of Northern Altun Mountains are also investigated by a typical alluvial section.Based on optically stimulated luminescence(OSL)dating the Shanshuigou section which is close to the Nan Hu oasis of Dunhuang in Gansu province,as well as investigations such as grain size,magnetic susceptibility and organic carbon isotopic composition,the Gobi depositional environment variation since 5 ka was examined.Results show that the evolution of the Gobi deserts are of fluctuation.Sediment transport capacity was higher during 5.24-3.57 ka because of increased river discharge and wet climate condition,and thus the Gobi desert was expanded.Then the transported processes were reduced as a result of trend of dry and warm climate during3.57-1.15 ka,togetherwith the shrunk Gobi accretion process.During 1.15-0 ka,the climate is in a moderate condition,as well as the flow velocity.The sedimentary dynamics are affected by climatic change at centennial to millennial time scales,and the alluvial fan margin of northern Alhun Mountains is in a steady accretion process basically.