Geochemical Characteristics And Provenance Indicating Significance Of Loess Deposit In Eastern Monsoon Since The Pleistocene

Loess-paleosol recorded a wealth of information about ancient climate change.The geochemical characteristics of loess is a good indicator for material source,it restores ancient geological history of climate evolution and is an important part of the current research of loess.Chifeng is a monsoon fringe city in the east China,controlled by high altitude westerly circulation and the low East Asian monsoon,it deposited with different thickness loess-paleosol strata,from north to south.It is an important significance to analysis the geochemical characteristics of Chifeng region and infer the material sources of Chifeng region loess.In this thesis,we measured and analyzed macro elements,trace elements,within loess and paleosol of different periods,which are from Keshiketengqi,Wengniute,Kala Qin flag in Chifeng and Hunshandake sand,black springs river terraces in north Chifeng.Combined with the age sample test results and by comparison with other regions,we analysis the material source of Chifeng Loess,preliminarily,and get the following conclusions:1.the method test results of chronology show that the HGZC sectional bottom boundary Age?OSL?dating to 66.85±8.13ka,DWP sectional bottom boundary Age?ESR?dating of 236ka,SSJZ ectional bottom boundary brick Age ESR dating to 903±119ka.2.The constant elements of Loess in Chifeng region is similar to Loess Plateau:SiO₂?mean 71.38%?,Al203?mean 13.58%?,it is constant elements in descending order:SiO₂>Al₂O₃>Fe₂O₃>CaO>K₂O>MgO>Na₂O>Ti O₂.It indicates that the loess material in Chifeng band,the eastern fringe of the monsoon comes from the upper crust.It is the product of mix sediments which was heighly mixed at the upper air.3.The distribution patterns of REE similar to the Loess Plateau which was formed by wind action:it enriched of LREE,lost of HREE,negative anomalies of Eu.This provide evidence for the genesis aeolian of Chifeng loess again.?REE,LREE,HREE and LREE/HREE values of Chifeng were lower than Lingtai loess,and had greater distribution of?Eu,more focused range of?Ce.The scope of?Ce has the biggest difference from deserts,river terraces sample.Means of rare earth elements in Pleistocene samples are generally higher than the Last Glacial sample.By inference,the loess provenance in Pleistocene was relatively stable throughout the Chifeng region.However,the provenance changed unstable since the late Pleistocene,and was different from middle pleistocene.4.The test results of trace elements show that:Sc,Nb,Ta,Pb,Th in Chifeng has lower element values than Lingtai loess,and higher values of Sr.The differences of Ta,Th element content value are obvious.The trace elements in loess strata were lower than ancient formations.At the same time,the stabilizing elements:Hf/Nd-La/Nd,Zr/Hf-Ba/Rb,Th/Nd-La/Th range projection area in Chifeng is different from the Loess Plateau.The Hf/Nb projected range of Chifeng loess is between 0.5 to 0.9,and Ba/Rb is different 4.5 to 7.0,significantly higher than the Loess Plateau.Meanwhile,the content of trace elements in Malan loess are although most agree with Lishi loess,But there is a huge difference in Sc,V,Co,Ni elements.Speculated that the Pleistocene loess in Chifeng region may be formed with the similar wind power with Xinjiang loess,and was affected by westerlies more apparent in the Pleistocene.But the changes of geochemical characteristics since the late Pleistocene loess showed the difference between the late and middle pleistocene provenance in Chifeng area.In this paper,we made a preliminary order for the spatial and temporal distribution of loess deposition in Chifeng,And then described and analyzed the detailed geochemical characteristics of Chifeng loess.It provides a basic reference for the loess paleoclimate research Chifeng region.We discussed the source matter of Chifeng since thePleistocene loess,and it is important for the future of the region depth AGCM.