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sur le développement des zones arides et semi-arides

Titre : The End Member Characteristics of Loess Grain Size and Environmental Evolution since S5 in Section Jinding of the Desert-loess Transitional Zone

Auteur : 韩玉希

Grade : Master 2022

Université : Hebei GEO University

Résumé
The desert-loess border zone in northern China is located in the arid-semi-arid region,which is under the joint control of the East Asian monsoon and westerly winds,with severe soil erosion and fragile ecological environment,and is particularly sensitive to environmental changes ;therefore,this region has become a hot spot in the study of Quaternary environmental evolution in recent years.This research work attempts to study the environmental evolution of the Late Pleistocene stratigraphy in this region.In this paper,we use the photoluminescence dating method and orbital tuning dating method and climate proxy index to determine the eolian deposits since S5 at 0-17 m in the Jinding section of the desert-loess transitional zone.On this basis,the end member analysis method was used to separate the end member components of the sedimentary stratigraphy of the Jinding profile in the desert-loess transitional zone,and the OSL dating and interpolation methods were combined to date this profile,and the comparative analysis was carried out with the magnetization rate index to explore the information of the paleoenvironmental evolution of the profile since S5,and the following insights were obtained.The section Jinding developed a loess-paleosol sedimentary sequence,which is different from the loess-paleosol-wind-formed sand sequence in other typical profiles of the desert-loess transitional zone,and there is no wind-formed sand deposition in its sedimentary stratigraphy,indicating that the Mawwusu Desert has not expanded to the Jinding area since S5,providing a new scientific evidence for the boundary study of the desert-loess transitional zone.The four particle size end-member fractions occupy different dominant positions in the cold and warm periods of the section Jinding since S5,among which:EM1（8.93 μm）represents dust transported in high altitude and long-distance suspension ;EM2（22.44 μm and 4 μm）represents near-source material transported at low altitude during strong winter winds and dust normally present in the upper part of the region ;EM3（20 μm）is homologous with EM1 fraction and carried by EM3（20 μm）is a finer particle fraction carried by the westerly winds with the EM1 fraction ;EM4（28.25 μm）represents the coarser particles carried by the spring dust storms dominated by the East Asian winter winds in short suspension.Overall,the warm-period end-member EM1 and EM3 components account for a high proportion of the deposited finer-grained paleosol layer,while the cold-period end-member EM2 and EM4 components account for a high proportion of the deposited coarser-grained loess layer.The changes of grain size and magnetization rate curves of the section are basically consistent,and each end-member component has a good correspondence with the grain size characteristics,reflecting the sensitive response to the cold and warm climate changes during the deposition of the desert-loess transitional zone,further revealing the close relationship between the section Jinding and global changes during the accumulation process

Mots clés : Jinding ;desert-loess transitional zone ;paleoclimate;particle size end member ;magnetization rate ;

Présentation (CNKI)