Selection Of Integration Time Intervals And Standardized Growth Curve For Quartz OSL Of Loess In The Eastern Tibetan Plateau

Aeolian loess,widely distributed in the eastern margin of the Tibetan Plateau(ETP),is one of the most important archives for past environmental changes.Well-established stratigraphic chronologies of loess sequences would contribute to the better understanding of the paleoclimate information lay behind the loess.As a promising dating method,the reliability of optically stimulated luminescence(OSL)in dating loess sediments has been proven.However,studies about OSL chronologies of the loess in the ETP is few.In order to promote the application of OSL dating in the ETP,we need to make better sense of the characteristics of the OSL signals and explore a more sophisticated way to measure and calculate the equivalent dose(D_e).In this study,we analyzed the characteristics of quartz OSL signals,the background integral subtraction and the standardized growth curve(SGC)of typical loess samples in the ETP.The characteristics of quartz OSL signals were analyzed by the preheat test,the dose recovery test,decay curves,growth curves and components of OSL signals.By comparing the‘early-background’approach with the widely used‘late-background’approach,we evaluated the influence of different integration time intervals of quartz OSL decay curves on D_e values of the loess samples in the ETP.Furthermore,we used the single aliquot regenerative dose(SAR)protocol,the standardized growth curve(SGC)and the global quartz OSL standardized growth curve(gSGC)to analyze the D_e values of all samples,examining the reliability of different analytical methods.The main conclusions are as follows:1)Quartz OSL signals of the loess in the ETP are most dominated by the fast OSL component,which is suitable for the SAR procedure.The results illustrate that the quartz OSL signals decay very fast,and the proportions of fast component of all samples are more than 84%,decaying to the background value within 4 s.Quartz OSL signals have obvious preheat plateau between 240℃and 260℃,in which the results of dose recovery are between 0.9 and 1.0.2)Different integration time intervals(early-background subtraction and late-background subtraction)has different effects on the calculation of D_e values for the loess samples in the ETP.For those samples of<10 Gy,the D_e values used for the early-background subtraction are consistent,within the error range,with the counterparts of late-background.For samples>10 Gy,the influence of different background time intervals subtraction on D_e is significant,about 10%-38%for the average D_e used for the late-background subtraction.It seems that the difference increases with growing values of D_e.3)Comparison of the SAR method,SGC method and gSGC method shows that D_e values and consequent ages obtained by the three methods are consistent within the error range.For those samples with D_e values of>200 Gy,there is a significant overestimate for D_e when using the SGC method.However,we find that D_e estimates obtained from the gSGC are consistent with those obtained using full SAR procedures,without significant error when D_e values become greater than 200 Gy.Our results are of great significance for the comprehensive understanding of the characteristics of quartz OSL signals.We proposed a new dating strategy would facilitate the efficiency and accuracy of D_e measurement for the loess samples in the ETP.