Physical And Chemical Properties And Provenance Analysis Of Surface Sediments In In Gobi And Deserts Of The Mongolian Plateau

The changes of sediments in the Mongolian Plateau have an important impact on the aeolian environment in Northwest and North China.The resolution of sediment source problems is of great significance for the identification of provenance and transmission paths.In this paper,178 surface sediment samples were collected through two field investigations in the Mongolian Plateau.Using the analysis methods of particle size and geochemistry,the characteristics,properties and composition of the sediments in Hobq Desert,Ulan Buh Desert,Mu Us Sandy Land and South Gobi were obtained.The main purpose is to clarify the physicochemical characteristics of sediments in the study area.To find the similarities and differences between the inner and outer Mongolian sands in terms of grain size components,sedimentary environment,migration process and weathering conditions.And to further reveal the provenance relationship between the deserts and the Gobi Altai.Then,explore the"near-source"and"far-source"issues of the deserts and the sandy land in the western Inner Mongolia.?1?Particle size analysis shows:the study aera is mainly medium sand and fine sand?65%?,containing a small amount of coarse sand?15%?and extremely fine sand?10%?,clay and silt?7%?,and none gravel.The sediments in the Hobq Desert and the Gobi Altai are good sorting,with medium sorting in the Ulan Buh desert and poor sorting in the Mu Us Sandy Land.The skewness of sediments in the study area is mainly symmetrical distribution or positive.Due to the complex distribution of sedimentary environment,the grain size grading and parameter characteristics in different areas and of different sediment types vary greatly.?2?Geochemical analysis shows:in the study area,the highest content of7 kinds of constant oxides?SiO₂,Al₂O₃,CaO,Fe₂O₃,K₂O,MgO and Na₂O?is SiO₂?70%?,followed by Al₂O₃?11%?.Among the 10 microelements,the highest content is Ba?580?g/g?,followed by Sr?230?g/g?.Compared with UCC,only SiO₂,K₂O,Zr and Rb showed slight enrichment,and the remaining macro-and microelements all showed varying degrees of loss.In different sand areas,except for the large variation of CaO content,the other elements have the same trend of enrichment and loss.The weathering index and the A-CN-K model show that the sediments as a whole is in the de-Na and K stage with CIA value between 49.88⁶3.85 when continental chemical weathering is weak,and develop in the dry and cold environment.In addition,the weathering degree in the South Gobi is higher than it in Hobq Desert,Ulan Buh Desert and Mu Us Sandy Land.Geochemical evidence indicates that the sediments in the inner and outer Mongolia study area have significantly different element compositions and weathering degrees.?3?Source tracing indicate:the sediments in study aera has not undergone strong sorting and re-cycling,that is,they did not undergone a sediments mixing in wide range.What's more,the factor analysis results indicate that the contribution rate of the first factor?K₂O,CaO,MgO and SiO₂?and the second factor?Al₂O₃?of the major oxides to the sediments is 64.83%and 16.53%,respectively.And the contribution rate of the first factor?Ti,Mn,Rb and Sr?and second factor?P,Ba,Ce,Zr and Co?of microelements can reach 64.47%and 21.55%respectively.The factor scores of macro-and microelements show that there are great differences in the mineral composition and weathering process of the inner and outer Mongolia study area.From the analysis of provenance,the compositions of the sediments in the above two aeras are very complicated,both similarities and differences,but the differences are the main feature.?4?The results of analysis indicate:the grain size with the highest sediment content in the study area is between 100³00?m,and it is a saltatin load,which is difficult to transport over long distances.The Mongolian Plateau as a whole geographical unit,although there is similarity on the long-time scale,on the short time scale,the surface sediments that reflect the modern pr ocess are very different.In addition,in the surface sediments,it is difficult to establish a clear source connection with the South Gobi sediments because the content of silt?including distant dust?is less than 7%.To sum up,the sediments in the western Inner Mongolia study area are mainly"in-situ sand accumulation",and the source of sand is the activation of ancient sands from locally dried lake and river sediments.In addition,different types of sediments in the study aera are formed by combination of different near-source supplies.If the underlying sediment formed on the basis of long-term evolution or fine-grained suspended dust,its possible source contribution needs to be further explored.