| Global deserts/sands cover about one-third of the Earth's land surface,and their evolution are related to the ecological environment of the whole Earth and the survival and development of human society.As aeolian sediments,deserts/sands are sensitive to climate change,and especially desert/sand spatial changes are direct performance of regional environmental evolution.The Last Glacial Maximum(LGM)and the Holocene Optimum(HO)are representative climatic periods in 30,000 years,and the spatial pattern of sands in the two periods has been an important element in the study of paleoenvironmental evolution.During the ?2 ka,the increased intensity of human activities has affected the regional ecological environment,leading to another change in the spatial pattern of sandy areas,but related studies are scarce.The Gonghe Basin,located in the northeastern Qinghai-Tibet Plateau,the transition zone of arid/semi-arid region,controlled alternately by the westerlies and Asian monsoons,and is exceptionally sensitive to environmental response,and has been a hot research area for reconstructing paleoenvironmental changes.However,it is not fully understood that the spatial evolution process of the Gonghe Basin tune fields in LGM,HO and since ?2 ka.Therefore,in this paper,we take the Gonghe Basin tune fields as the research object and analyze the palaeoenvironmental significance of stratigraphic ages and locations of profile points since LGM,HO,and ?2 ka,based on the collected aeolian profiles and published aeolian sequences and ages to reconstruct the boundaries of the Gonghe Basin tune fields during the characteristic periods.In addition,the high-resolution profiles and previously published stratigraphic ages are used to obtain the history of aeolian activity in the basin,to explore the response of the spatial pattern of the tune fields to environmental evolution and to analyze its factors.Based on the 58 years obtained from the experimental analysis and the published190 ages,it has been reconstructed that the boundaries of the Gonghe Basin tune field in the three characteristic periods: compared with the modern sand land boundary,the Gonghe Basin tune field was expanded in the LGM period,in which the Mugetan tune field was far away from the west,North and south,and was about 10?20 km away from the modern boundary and expanding about 20-30% relative to the modern sands area,and the mobile dunes of Talatan tune fields expanded to the south,expanding to the foothills of the Heka Mountains about 20?30 km from the southwest of the modern boundary,with an area expanded by about 20?30%;during the HO,the sands were fixed,thicker sandy paleosol developed,and the mobile dunes of Talatan contracted to the southeast,contracting to the neighborhoods of Tiegai village about20?30 km from the modern boundary,with an area contracted by about 30?40%compared to the modern sands.Since ?2 ka,the Gonghe Basin tune fields have expanded outward again,and the northern boundary of the Mugetan tune fields had expanded the farthest,reaching near the Duoshizuigou;the eastern and southwestern expanded closer,about 5 km from the modern boundary,and the total area has expanded by about 20%.In addition,combining environmental proxies analysis of 265 samples,such as grain size,magnetic susceptibility,element geochemistry and soil organic carbon,and probability density functions based on all ages,we have discussed the coupling mechanism between the spatial change of the Gonghe Basin tune fields and aeolian activity history in the basin since LGM: From the LGM to the last deglaciation period,aeolian sand was widely distributed in the basin,with a large area of quicksand,which was mainly related to the expanded global continental ice sheet and the enhanced winter monsoon;From the last deglaciation to early Holocene,the distribution of loess was more than in the previous stage,and the area of quicksand was reduced,which was related to the strong winter monsoon;12?9 ka,the climate was relatively dry and cold,the vegetation coverage was low,the sand flowed and activated,and the sand area expands,which was related to the strong winter wind;9?5 ka,the climate gradually turned humid,vegetation coverage got higher,aeolian activity weakened,some tune fields were fixed,and quicksand range shrinks.Aeolian activity at 7?5 ka was the weakest,and the quicksand area was the smallest,which was related to the strong summer monsoon;5?2 ka was in the stage of rapid change,the aeolian activity was enhanced,and the tune fields were expanded again,which was related to the weaken summer monsoon.Since ?2 ka,the enhanced human activities had stimulated the activation of aeolian activities,causing expansion of tune fields.The environmental changes in the basin were affected by both natural and human factors. |
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