Evolution Of Sedimentary Environment In Linfen Basin Since Middle Quaternary

Middle Plesitocene is an important period of Quaternary.For knowing the environmental changes now and predict the climate in the future,it is essential for studying Quaternary of environmental evolution.Chinese research is concentrated in the late Pleistocene(Q3) and Holocene(Q4).At present,there are few studies on the Middle Pleistocene(Q2),especially the Middle Quaternary.The following works had been done in this thesis:one is determined the division of loess time,another is that due to reconstruct the paleoclimate,the correlation between magnetic susceptibility and grain sizes should be analyzed depend on sedimental environment.(1)According to drilling cores of the seismic station section (DZT),the <4μm clay content and magnetic susceptibility of the Linfen Guojiazhuang Dizhentai,we will transform the section between the depth and age based on the previous achievement. between the depth and age based on the previous achievement. Though getting the control point between the profile depth and the age of deep sea oxygen isotope at Dizhentai, we conclude the section’s upper bound of the late Pleistocene is130ka B.P.,and the bottom of section is715ka B.P..(2) We find different processing methods have great influence on the content of coarse and fine particles during the process of measurement, when measuring the sample size and magnetic susceptibility. The general siphon method will reduce the ultrafine particle. The prticle size was divided into <4μm、4-16μm16-63μm、>63μm and the median particle size(Md) by Udden-Wentworth. We get the following results by measuring the high frequency, low frequency and the frequency of magnetic susceptibility derived from the low and high frequency of magnetic susceptibility. When the climate is in warm and wet period, the fine particles of <4μm and4-16μm in loess deposits will increase; when in the dry and cold climate period, coarse loess deposition of16-63μm and>63μm will add, and the magnetic susceptibility is also corresponding changes. As the deposition is in warm period, the temperature is high with heavy rain and more content of coarse particles, low magnetic susceptibility, and when is in cold and dry period, all is the contrary. The sedimentary environment of Linfen basin in the late Middle Pleistocene of715-130ka B.P. Has beenthrough5times of cold period and5times of warm periods. In theperiod of425-370ka B.P.,the Fenhe River incised down to form theterrace and then in cold period, formed the lake sediments, whichmade the Linfen basin’s DZT profile loess deposition in the latePleistocene, and the middle period is fluvio-lacustrine deposits.In order to know about the environment changes in Linfen basinbetter,we compare the magnetic susceptibility and particle size ofthe Guojiazhuang profile and the Xifeng, Changwu, the two typicalsections, finding that climate changes of Xifeng, Changwu andGuojiazhuang profiles basically follow the warm-cold-warm rules,which shows global climate change. Because of the difference ofthe profile lithology and the regional environment,the climatefluctuations of Linfen Guojiazhuang profile is not the same with thetypical profile.