Study On OSL Dating And Stratigraphic Age Of Loess In The Upper Reaches Of Hanjiang River

Since the last glacial climate change research has always been a research hot spot,and the loess is also one of the three major carrier that climate change research,recorded a lot of environmental evolution information,therefore the loess in-depth research has important significance.Upper Hanjiang region is located in the south Qinling,north subtropical and temperate zone transition region.This region is sensitive to climate change,and a large number of eolian loess distributed in this region.It is of great significance to study eolian loess in this area for researching upper Hanjiang river climate change and Global climate evolution rule.Based on the Tuojiawan loess-paleosol profile in the upper Hanjiang river,yun county as the research object.After careful observation,eleven samples were taken from an eolian loess-soil section in the Tuojiawan profile for optically stimulated luminescence(OSL)dating and took 345 samples for analysing its physical and chemical properties at the same time.According to the requirements of experimental technology,water content,radioactive elements U,Th,K and the measurement of environmental dose rate,equivalent dose selection of test conditions samples of leg degree analysis,and the determination of equivalent dose(De)and so on in different experimental.Magnetic susceptibility and grain size of sediment samples,elements and chromaticity climate proxy data test in detail.For organizing data analysis,and discusses the since the loess-paleosol profiles in the upper Hanjiang river terrace recorded a number of important climate change events and interpretation the significance of the optical dating.The main conclusions are as follows:(1)Through the recycle ratio,dose recovery and thermal transfer experiment,determine equivalent dose temperature condition for TJW profile optical dating samples.The test conditions in 220?260 ?.(2)Through the bleaching curve method of the OSL samples,the discrete degree analysis method of equivalent dose and the frequency distribution histogram in equivalent dose of the OSL sample were analyzed.And found that the bleaching curve was good for loess deposits on the surface of the upper Hanjiang river terrace.It is suitable for optical dating.(3)OSL ages were measured by using the quartz single aliquot regenerative-dose(SAR)protocol.The OSL results show that:the optical ages of these samples ranged from(55.11+5.20)?(13.57+1.33)ka BP,showing a good relation with the depth in the TJW profile,it was indicated that the profile formed by loess weathering and accumulation.This section contains the period of late pleistocene and complete holocene loess layer.(4)Through analysising the physical and chemical indicators in the TJW profile found a warmer climate events in the period of late pleistocene.Combined with the OSL dating data determine the climate events happened in 27.5?21,5 ka B.P.before and after.The warmer climate events is closely related with a event founded in MIS3 period,it can be a good comparison.(5)TJW profile layer is integrity,recorded the regular of climate change from 55 ka B.P.In the late pleistocene,the upper Hanjiang river region climate was dry and cold,the winter wind was strong,but the values of magnetic susceptibility and grain size parameters and the change of constant element content reflects during 27.5?21.5 ka B.P.the climate was warm and wet.In the early holocene,from the cold and dry to warm and humid climate change.In the middle the climate attain the most warm and moist stage,abundant precipitation,the summer wind is strong.In the late holocene,the climate change from warm and wet to dry and cold.