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Lanzhou University (2019)

Environmental Significance of the Chemical Composition of Surface Aeolian Sediments in the Badain Jaran Desert, NW China


Titre : Environmental Significance of the Chemical Composition of Surface Aeolian Sediments in the Badain Jaran Desert, NW China

Auteur : 陈秋洁;

Grade : Master’s Theses 2019

Université : Lanzhou University

Résumé partiel
Surface aeolian sediments in deserts include aeolian sands,as well as lake surface sediments in the hinterland of desert.This is because lakes in desert hinterlands that are not recharged by river runoff,sediment is input solely by wind transport.Those surface aeolian sediments are regarded as indispensable archives for the study of global and regional environmental evolution.However,the weathering,erosion,transport and deposition processes in hyper arid desert regions are different from those in other arid and semi-arid areas,therefore,the paleoenvironmental signifances and modern processes of aeolian transportation and deposition of aeolian sediment are particular.Among them :(1)the mechanisms controlling the spatial variability of chemical elements in the aeolian sands and lake surface sediment ;(2)the environmental significance revealed by elemental proxies in aeolian sand and lake surface sediments ;(3)how to extract and separate reliable elemental proxie from lake sediments in lakes in the hinterland of desert for paleoenvironmental reconstruction ?At present,further research is needed.Solutions to the above-mentioned issues can provide reliable elemental proxie with clear environmental indicators for the internal links between regional and global environmental changes,and provide new evidence for the hot issue of the process and mechanism of the interaction of the earth’s surface layer.In this study,a total of 115 samples of aeolian sand,lacustrine sediment,and exposed bedrock were collected across the entire Badain Jaran Desert in the hyperarid region of northwestern China and analyzed for major elements and trace elements by X-ray fluorescence spectrometry.Meanwhile,100 surface sediment samples were collected from five lakes in the hinterland of the Badain Jaran Desert,NW China,and examined for their major,trace and rare earth element(REE)contents and mineral assemblages.XRF results of aeolian sediments showed that significant differences in the chemical compositions of aeolian sediments were observed among different grain size fractions.The concentrations of most measured elements were higher in the fine(<250μm)than coarse fractions.The enrichment of CaO,Fe2O3,MgO,Cr,Ni,Ti,and Zn in fine aeolian sands showed that elemental composition was highly dependent on grain size.Compared with the average chemical composition of the upper continental crust(UCC),the aeolian sands in the Badain Jaran Desert were enriched in SiO2,while other major elements(i.e.,Al2O3,Fe2O3,MgO,CaO,Na2O,K2O,and Ti)showed significant depletion and possible leaching characteristics,This result indicates that the aeolian sands have not been subjected to intense weathering and recycling.The CIA values of aeolian sediments in the Badain Jaran Desert were all below 50,varying between 41.2 and 49.9,which were significantly lower than those of shale but close to those of unaltered granitic rocks.Badain Jaran Desert can be divided into four different zones from north to south(A–D),based on differences in the principle component scores.

Mots clés : Aeolian sediments; Hyperarid region; Desert; Groundwater-recharged lakes; Major and trace elements; Rare earth element; Lake sediment;

Présentation (CNKI)

Page publiée le 8 novembre 2019