The Material Compositions Of The Harbin Loess Deposits And Their Implications For Eolian Dust Provenances

Loess,as a typical representative of Quaternary sediments is widely distributed,continuous and sensitive to explain the evolution information of Quaternary paleodeposit environment.In recent years,the study of the origin and origin of the Eurasian loess belt is the key to understand the coupling relationship between dust accumulation and regional tectonic-geomorphology and climate change.Harbin loess is located at the easternmost end of Eurasian loess belt.As a typical loess accumulation in northeast China,the study on the chemical composition of the sphere has not been carried out,the nature and material origin of the loess are not uniform.In order to carry on the new research we take the Harbin loess as the research object,through the loess sample geochemistry characteristic and the grain size characteristic carries on the qualitative and the quantitative analysis,has discussed this section loess sedimentary environment,the climate evolution and the material source information in depth.The first mode of loess particle size in Harbin is 36-40?m,the second mode is8-10?m,which is mainly close to the clay,and the extremely fine-grained component?<1?m?shows the third mode?0.8?m?.It is suggested that the loess sediment source in this section is mainly low-altitude near-source sediment,supplemented by high-altitude far-source sediment,suggesting that the climate of this section is dry and cold.In element composition,the main oxides of constant elements are mainly SiO₂,Al₂O₃,Fe₂O₃,and the sum of the three accounts for 85.23%of the total.The CaO and MgO content in XWP loess is obviously higher than that in Harbin loess,while the Na₂O?K₂O,Al₂O₃ and Fe₂O₃ content of Harbin loess is slightly higher than that of both.XWP loess has the lowest Na₂O and K₂O content,and KLG loess has the lowest content.The trace elements have higher Rb,Nb,Ba and lower Co,Ni,Zr compared with Chinese loess.REE showed that the relative enrichment of LREE Eu showed obvious negative abnormalities.the geochemical composition of the Harbin loess in the barren mountain profile shows spatial homogeneity.The low chemical alteration index CIA?58-60?and the A-CN-K map all indicated that the Harbin loess suffered only low-grade chemical weathering degree.The values of SiO₂/Al₂O₃ and ICV indicate that the sediment contains certain clay minerals,reflecting the low maturity of the sediment and showing the characteristics of the initial cycle deposition.Based on the source discriminant diagram of inactivity element ratio and Sr-Nd isotopic ratio,the relationship between Harbin barren mountain and adjacent Songnen Sandy Land,Horqin Sandy Land and Hunshandak Sandy Land is obtained.The Sr-Nd isotopic composition characteristics of Harbin loess show that the ratio of ⁸77 Sr/⁸⁶Sr changes very little but?Nd?0?worth changing greatly.Compared with the Plateau Loess and the northern border desert of China,the ⁸77 Sr/⁸⁶Srr ratio of Harbin loess is obviously higher than that of Loess Plateau and slightly higher than that of Northern Border Desert,but the?Nd?0?value is slightly lower than that of Northern Border Desert and slightly higher than that of the Plateau Loess.The geochemical method cannot determine the source of Harbin loess well,so the integrated method?including particle size,elemental and isotopic composition,MDS and PCA statistical methods and natural geographical elements,etc.?is used to determine more accurately that there is a mixed source of Harbin loess,and the Songnen Sandy Land provides the main dust material for the Harbin loess deposits,and that the Hunshandake Sand Land and the Horqin Sand Land may also provide a small amount of fine dust for the Harbin loess deposits and however,the Hulunbuir Sand Land cannot be the source of the Harbin loess deposits.