Optically Stimulated Luminescence Dating Of Aeolian Sand Sediment In The Central Tibetan Plateau

The Tibetan Plateau(TP)is highly sensitive to global changes and is currently experiencing extensive desertification.Studying the history and influencing factors of aeolian sand activity in the TP is of great significance for the ecological protection of the TP and the prediction of environmental changes in the future.At present,little is known about the age and change process of aeolian sand activity in the central TP(CTP).Optically stimulated luminescence(OSL)dating is an effective method for dating aeolian sediments.However,this method has not been widely applied to study the history of sandstorms in the CTP.In this study,quartz SAR-OSL,K-feldspar postinfrared infrared stimulated luminescence(p IRIR),and single-grain K-feldspar postIRIR methods were used to date five aeolian sediment profiles in the Tuotuo River Basin,Lunpola Basin,and Kumukuli Basin of the CTP.The factors leading to the uncertainty in the dating results were analyzed,and their significance was discussed.The findings are beneficial for understanding the OSL dates of aeolian sand sediments,the history of aeolian activity,and environmental changes in the CTP.The key findings can be summarized as follows:(1)OSL dating revealed significant differences in the luminescence characteristics of quartz and K-feldspar in the aeolian sand sediments of the CTP.In the Tuotuo River Basin,the quartz OSL and K-feldspar p IR-IRSL luminescence signal intensities of the TTH-1 profile were moderate,the quartz recycling ratio was relatively high,and the overdispersion of the equivalent dose in single-grain dating was large(approaching60%);thus,K-feldspar could be effectively dated.The TTH-2 profile exhibited a weak quartz OSL luminescence signal,high recycling ratio and recuperation,and moderate K-feldspar p IR-IRSL luminescence signal intensities.Although the high recuperation presented a challenge,K-feldspar could still be effectively dated.In the Lunpola Basin,the LD profile exhibited moderate quartz OSL and K-feldspar p IR-IRSL luminescence signals,stronger than in the TTH-2 profile.The problem of high recuperation arose for both the quartz and K-feldspar samples,and the fast component of quartz was relatively small.Only the K-feldspar samples could be effectively dated.In the Kumukuli Basin,the quartz OSL and K-feldspar p IR-IRSL luminescence signals had high intensity in the KM-I and KM-II profiles,and the dating results were good for both quartz and Kfeldspar.The results indicate that the K-feldspar was older than the quartz.(2)The level of recuperation was high for young aeolian sand samples during the OSL dating of CTP samples.The recuperation(the zero dose as a percentage of the natural dose)for the TTH-2 and LD profiles was outside the acceptable range(5%).This is primarily attributed to the young samples in these two profiles(a few hundred years old)and the weak luminescence signal intensity.Consequently,the natural dose was close to the zero dose,resulting in high recuperation.In the OSL dating of young samples,this high recuperation can be ignored on the determination of the equivalent dose.(3)The applicability of OSL dating to aeolian sand sediment profiles in the CTP depends on the region.The obtained dating results were not completely consistent among the different dating techniques;the TTH-1,TTH-2,and LD profiles were dominated by the K-feldspar dating results,whereas the KM-I and KM-II profiles were dominated by the quartz dating results.The age and stratigraphic order in each profile were not entirely consistent,and multiple methods were required to cross-verify and analyze the specific aeolian sedimentation process and reliably date aeolian sediment formation.(4)Strong aeolian sand activity in the CTP can be traced back at least to the early Holocene.The periods of high aeolian sand activity were mainly the early to middle Holocene(6.37–8.65 ka B.P.)and the Little Ice Age.The comprehensive dating results show that the TTH-1 profile was formed approximately 6.73 ± 0.33 ka ago,the TTH-2profile was formed at least 0.59 ± 0.08 ka ago,the LD profile was formed at least 0.40± 0.03 ka ago,the KM-I profile was formed at least 6.72 ± 0.42 ka ago,and the KM-II profile was formed at least 8.65 ± 0.50 ka ago.The dating results indicate that global environmental changes have important effects on aeolian sand activity in the TP.Our findings are of great significance for understanding the OSL dates of aeolian sand sediments in the CTP along with the past process of aeolian sand activity and its relationship with environmental changes.