A Preliminary Study On The Evolution Of Gobi In Northwest China During Late Quaternary

Badan Jilin Desert and Kumtag Desert are typical regions with arid environment to the north of Qilian Mountain and north of Altun Mountain in northwest of China.However,the formation,evaluation of Gobi in this region and its relation with climate and tectonic movement have not been considered sofar.Therefore,the study of the Gobi in north Qilian Mountain and north Altun Mountain is not only of great importance for understanding of the regional environment,but also has great significance for the study of desert,loess sedimentary evolution and dust release.This work pays attention to the study on the evolution of Gobi in northwest China during Late Quaternary-a case study from the Gobi in north Qilian Mountain and north Altun Mountain.Through collecting the existed research data and combining with field investigations,we get surface sediment samples and sedimentary sequence samples of Gobi and carry on the analysis of the age and deposition.The work is organized as follows.We collect the existed Gobi's age records in previous publications and get the ages of Gobi samples by optical stimulated luminescence(OSL)technique.Then we obtain the time frame of the Gobi's formation and evolution from the late pleistocene and LGM to the Holocene Megathermal and to the modern time.By measuring size of ravel,shape of Gobi gravels and the magnetic susceptibility,we deduce level space,vertical space and temporal depositing characteristics of the Gobi in the study area.According to the Gobi's surface outcrop and its relation with the regional tectonic movement,we conclude the relation between Gobi's formation and evolution and the climate characteristics.Finally,we summarize the similarities and differences in the evolution of the Gobi in north Qilian Mountain and north Altun Mountain.Based on the above research,we reveal the formation and evolution of Late Quaternary in Gobi.The tectonic movement is the geological foundation of Gobi.In addition,we note that the gravel sediment is an important factor which affects the formation of Gobi.Hydrodynamic force and climatic are the main influences of average particle size of gravel,psephicity and permeability of gravel.We summarize the similarities and differences in the evolution of the Gobi in north of Qilian Mountain and Altun Mountain.The characteristics are as follows.The average particle size distribution and sorting of gravel in Gobi samples of north Qilian Mountain have a north-south differentiation:the average particle size becomes smaller and the sorting is enhanced from south to north.The average particle size distribution and sorting of gravel in Gobi samples of north Altun Mountain have a same differentiation from east to west.Eroded Gobi and cumulated Gobi show different deposition characteristics in the stratigraphic cross section.For eroded Gobi,the average particle size and its range of the upper part are larger than those of the lower part.However,the average particle size of cumulated Gobi is basically uniform and the distribution range is small.For the two kinds of Gobi sections,gravel roundness of the upper part is stronger than the lower one,but the sorting of the upper part is weaker than the lower part.From glacial to interglacial,for eroded Gobi,gravel content becomes smaller,average particle size becomes larger,sorting is worse and roundness is stronger.For cumulated Gobi,the characteristics are opposite from glacial to interglacial.Overall,the characteristics of grain size of Gobi surface sediment,morphological characteristics,sedimentary formation,and climate evolution are different for the Gobi in north of Qilian Mountain and Altun Mountain.