A Comparative Study On Luminescence Dating Methods Of Loess In The Eastern Margin Of Tibetan Plateau

Loess,deep-sea sediments and ice cores are three ideal materials for the study of global climate change,which are important contents for the study of Quaternary environmental change.Loess deposits are widely distributed in the eastern margin of the Tibetan Plateau,which well records the evolution of palaeo-environment in the plateau area.At present,scholars mainly focus on its origin,material source,sedimentary characteristics and environmental significance,while chronology research is relatively weak.The establishment of a reliable chronological framework is an important prerequisite for the study of loess deposition process and environmental significance in the Plateau.The rapid development and application of luminescence technology provide a good opportunity for the study of the chronology of the plateau loess.In this paper,the typical loess sequences located in the eastern margin of the Tibetan Plateau were selected as the object,a comparative study was carried out between the quartz single aliquot regenerative dose(SAR)method,quartz standardized growth curve(SGC and LS-SGC)method and the potassium feldspar two-step method(Post-IRIR).The aim is to discuss the interpretation of the optical dating at the eastern edge of the Tibetan Plateau loess in the applicability and reliability.The research is helpful to understand the sediment process and its environmental significance of the plateau loess.Based on the above research work,the following understandings are obtained:(1)The quartz OSL analysis of loess in the eastern margin of the Tibetan Plateau shows that there is a temperature plateau between 200?and 260?,and the parameter results are satisfactory;Quartz signal of loess in the eastern margin of the plateau is dominated by fast components,and the equivalent dose can be measured by SAR method.The frequency histogram of De value and the dispersion of OSL signal were analyzed to verify that the signal is fully bleached before the sample is buried in this area.The growth curve shapes and saturation dose shows that the signal of quartz samples in this region reached saturation at 200?230 Gy(?50 ka),and the quartz age is underestimated.The De obtained by the SGC method is consistent with the SAR De in the range of 0?100 Gy,while the LS-SGC De shows good agreement with SAR De in the range of 100?200 Gy.(2)The prior-IR stimulation plateau test,dose recovery,recycling ratio and recuperation indicated that pIR₂₀₀IR₂₉₀ could be used for the equivalent dose test of potassium feldspar in the eastern plateau.By analyzing the decay curves of potassium feldspar IRSL₂₀₀ and pIR₂₀₀IR₂₉₀ signals,it finds that the initial photon counts can reach more than n×10⁴ at two temperatures,and the OSL signals are strong enough.By comparing the signals at two temperatures,it can be seen that the pIRIR₂₉₀ signal is more stable than IRSL₂₀₀ and can obtain a reliable De value.The analysis of De value distribution,over dispersion and residual dose of potassium feldspar shows that the pIRIR₂₉₀ signal of potassium feldspar in this area was well bleached and the residual dose was less than 8 Gy.The growth curve shape and potassium feldspar saturation dose indicated that the potassium feldspar signal in this study was in the unsaturated region,and the age test results are reliable.(3)The comprehensive comparison of quartz OSL dating and potassium feldspar pIRIR dating shows that within the upper limit of quartz dating,the pIRIR₂₉₀ age of potassium feldspar is consistent with that of quartz in the error range,which verifies the reliability of potassium feldspar dating.The age of quartz and potassium feldspar can be used as the plateau loess dating.The quartz age of the samples older than?50 ka is underestimated,and the pIRIR₂₉₀ age of potassium feldspar can be selected to establish the loess age framework.The 160 ka old age frame of the loess in the eastern plateau has been established by using quartz and potassium feldspar luminescence dating.The comprehensive dating results of Machang loess profile show that the loess accumulation rate in the eastern margin of the Tibetan Plateau is lower than that in the Loess Plateau region.The loess accumulation rate in the eastern margin of the Loess Plateau during the last glacial age is higher than that of the palaeosol during the last interglacial age,which is consistent with the pattern of the Loess Plateau.