Characteristics of element and Sr-Nd isotope composition of the Songnen sandy land and their indications of regional dust material sources
The Songnen sandy land is located in the easternmost part of the Eurasian loess belt,and the study of its material composition is beneficial to reconstruct the glacial-interglacial dust transport pathways in the Songnen Plain.To this end,123 fluvial and eolian sand samples from the Songnen sandy land were systematically collected,geochemically analyzed for major,trace and rare earth elements and Sr-Nd isotopic compositions in different grain size fractions,and quantitatively reconstructed from the eolian dust material sources using the Frequentist model,to explore the contribution of the components of different grain size fractions in different regions of the Songnen sandy land to the loess in the Harbin and the transport paths.The results show that the Songnen sandy land has experienced a primary chemical weathering process(the mean CIA values of＜63 μm,＜30 μm,and＜10 μm fractions were 55.20,57.46,and 57.51),with a low recirculation history(the mean values of the CIA/WIP ratios for the＜63 μm,＜30 μm,and＜10 μm fractions were 0.98,1.08,and 1.04).Based on the elemental geochemistry and Sr-Nd isotope composition of the different grain size fractions,the Songnen sandy land was divided into two geochemical subzones,the northwestern and southwestern parts.The quantitative reconstruction results of the geochemical compositions of different grain size fractions showed that the contributions of different grain size fractions(＜63 μm,＜30 μm and＜10 μm)to the Harbin loess in these two subzones were 75.7%～88.5%,73.4%～84.9%and 61.0%～89.7%(southwestern part)and 11.5%～24.3%,15.1%～26.6%and 10.3%～39%(northwestern part).This study reveals that the dust transport path in the Songnen Plain since the Last Glacial Period has been dominated by the south-west direction,which differs from the circulation pattern dominated by the north-west wind during the glacial period.
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