Environmental Proxiex In The Laohushan Loess-paleosol Sequence Of Nanjing And Paleoclimate Significance

Global change study is one of the frontier fields in current sciences of the world. Loess is a good information carrier for paleo-environmental change. The focus issue of pole-climatic and paleosol study is to extract factor which affects environment change from loess- paleosol. Xiashu loess, as marginal eolian sediments,holds the regional signals of variations in the East Asian Monsoon. So from the study of Xiashu loess ,we can reveal paleo-climatic fluctuations for the south of the lower Yangtze Basin.In this paper , Laohu Shan loess-paleosol profile ,located in Nanjing and has 10.5 meters depth, was selected. Through systematical study of grain size distribution , magnetic susceptibility and concentration of clay mineral , major elements( Fe, Al, Si, Ti) and REE, the following conclusions can be drawn:1.Laohu Shan loess-paleosol profile was composed of eolian, and receiving physical weathering and chemical weathing;2.Xiashu loess has the same eolian from loess in North China. Each sample has double peaking distribution of grain size,and the major value of size is 32~16 m and 0.5~2 m respectively .The grain size concentration of >8 m and <8 m can indicate winter monsoon and summer monsoon and western circulation respectively. But the concentration of >45 m grain size maybe indicate strong winter monsoon or storm;3. The concentration variation of iron oxide and aluminum oxide can be serve as proxy recorder for paleo-climatic fluctuations. At the same time,their ratios between them can be also useful ones;4.Each grain size has own different magnetic susceptibility and every one can be erve as proxy recorder for paleo-climatic fluctuations respectively. However, the magnetic susceptibility of the <2 m size fraction is greater than of the larger fractions and the bulk sample, and the resolution as a proxy of this fraction is also better than the other fractions. But from this paper ,we also find when considering the contribution ratio to bulk sample y of various grain sizes, the >2 m fraction can not be ignored;5. Clay mineral of each horizon from Laohu Shan sequence has the samecharacter, and consist of quartz , illite , chlorite and kaolinite mostly. The concentrations of quartz and kaolinite,as same as chlorite and magnetic susceptibility have relationship in same degree. Diffraction peak value of major clay minerals can reflect paleo-climatic change.One of the illite index, weaver index, can also reflect weathering degree for Xiashu loess;6.From this paper, the REE concentration of the acetic-acid insoluble residues from Laohushan loess-paleosol sequence were tested. The results indicated the acetic-acid insoluble residues appears to be a resistant fraction of inherited aerosol. After weathering, the REE concentration of paleosol is little larger than the one of loess. Different fraction has different concentration REE, and the REE original value of eolian may be affected by wind choice.