| Loess-paleosol sediment is a good vehicle for research the global climate variation and its driving mechanism as widely distributed aeolian sediments all around the world.Loess sediment in NE China also shows the characteristics of the alternation of loess and paleosol sediments with the alternating cycles of glacial and inter-glacial period.Althrough the study of loess-paleosoil sediments from NE China have obtained some understandings on the variation about the inland dryness and humidity of Asian,the desertification process of the nearby desert,the vegetation succession of NE China,and the evolution of atmospheric circulation systems of the Northern Hemisphere.Relatively little is known about the regional comparative studies and the mechanism for the difference through using several reliable proxies.In this paper,the NYZ section,which is located in Chifeng City,Inner Mongolia is selected,and its age,magnetic parameters,grain size parameters,and chromaticity parameters are measured.The purpose is to excavate the paleoclimate information,improve the understanding of the evolution of the East Asian monsoon,and clarify the region’s response to the global climate.The preliminary conclusions of this study are as follows:(1)Based on the optical luminescence dating,the paleomagnetic dating,and 10 correspondingly divided peaks and valleys of the magnetic susceptibility curve and the deep-sea oxygen isotope curve of glacial-interglacial cycle,21 age control points were obtained.Combined with the extrapolation of the deposition rate,the basic age framework of the NYZ section was established,indicated that the deposition of loess in this area began at least since early Pleistocene.(2)Through the analysis of the magnetic parameters of the NYZ section,we found that the magnetic parameters also show low values in the loess sediments,but high values in the paleosol deposits.The main magnetic-carrying mineral of loess-paleosol sediment in NE China is magnetite,and its magnetic enhancement mechanism conforms to the "pedogenesis theory" model,which means that the variation of magnetic susceptibility and other magnetic parameters is mainly dominated by ultra-fine ferromagnetic minerals produced by pedogenesis.The fluctuation of the magnetic susceptibility can reflect the evolution characteristics of the East Asian summer monsoon.(3)Based on the understanding of the magnetic enhancement mechanism of NE loess-paleosol sediment,this study selected magnetic parameters,grain size parameters and chromaticity parameters to reconstruct the climate evolution history of the NYZ section since MIS 21.According to the fluctuation degree and trend of climate variation,three climate evolution stages were divided :(I)From MIS 21 to MIS 15,characterized by a relatively stable climate condition.All of the magnetic parameters,grain size parameters and chromaticity parameters are well consist with the glacial-interglacial alternation.And the difference in characteristics between glacial sediments and interglacial sediments is relatively small,means that the climate fluctuations are not large.(II)From MIS 14 to MIS 13,the climatic conditions changed drastically.Firstly,an extremely dry and cold glacial period was appeared,and then a warmer interglacial period,that is,the MIS 13 stage happened.(III)From MIS 12 to the present,after experiencing dramatic changes in the paleoenvironmental conditions between MIS 14 and MIS 13,the local climate recorded by the loess-paleosol deposits has not recovered as warm and humid as it was before MIS14.Both the grain size parameter and the chromaticity parameter indicated an obvious trend of increasing inland aridification since MIS 12,and accompanied by the intensification of the glacial-interglacial cycle oscillation amplitude.Such a phenomenon is attributed to a regional response to the MBE.(4)Based on a recent research,the seasonal climate information of the three climate evolution stages in NE China was extracted.By comparison,it is found that the East Asian summer monsoon force since MIS 12 was significantly weaker than before,implying that the weakening of summer monsoon and the strengthening of winter monsoon are consistent with the intensification of inland aridification.(5)Different loess-paleosol depositional profiles in Northeast China show relatively obvious regional differences in lithology and sediment accumulation rate,which may be caused by differences in depositional environments of different profiles,such as topographic differences,distances from material sources differences and possible local erosion effects,etc.But in general,the climate evolution process recorded by the three sedimentary profiles is still strongly consistent,and the magnetic susceptibility values of the SBH profile,SSJZ profile and NYZ profile all show a decreasing trend since the Pleistocene,suggesting that the global ice The climate evolution characteristics of the increase in the amount of water and the intensified degree of aridification in inland Asia.(6)By comparing with the typical section located in Chinese Loess Plateau,we found that the response of the Northeast region in global climate change has a good consistency with the XF section in the central of Chinese Loess Plateau.The consistency of this climate evolution is also particularly prominent in the MIS 13,characterized by an abnormally high magnetic susceptibility values,indicated an abnormally warm and humid interglacial period.The emergence of this climate change feature is the performance of the regional response of the Northeast to the global climate variation.It may be that the East Asian monsoon was affected by the weaker Western Pacific Subtropical High,and retreated to the northeast,caused the soil sediments in the western Chinese Loess Plateau produce little amount of strong magnetic mineral during the MIS 13 period. |
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