OSL DATING OF HOLOCENE SEQUENCE AND PALAEOCLIMATE CHANGE RECORD IN SOUTHEASTEARN MARGIN OF MU US DESERT,NORTH CHINA
毛乌素沙漠东南缘全新世剖面光释光年代及古气候意义

Dune fields with several palaeosoil layers are common in marginal desert in Northern China and potentially reflect drought-moist variability in the Late Quaternary.A Holocene profile of aeolian deposits with alternating units of dune sands and sandy palaeosoils record dune building and stabilization at least three times in the Jinjie area(southeastern margin of Mu Us desert in China),which is specially located in loess-desert transitional region in response to East Asian monsoon alternation so as to likely archive millennial-scale patterns of palaeoenvironmental variability.Jinjie section (38.74°N,110.15°E; 1181m a.s.l),30km northwest of Shenmu County, is a ca.5-m-thick aeolian sandy profile (overlying layers of 2.5m modern dune and did not see bottom) with 3 layers of black or dark brown palaeosoils which correspond to three considerable dune fixations. In order to establish reliable timing of dune development,this study applied optically stimulated luminescence(OSL)dating techniques to the aeolian sediments features.10 luminescence samples obtained from this profile were dated using the quartz single aliquot regeneration(SAR)protocol.Combining with palaeoclimate proxies(e.g. ,grain sizes and magnetic susceptibilities),the records revealed as many as seven periods of significant rapid climate changes during the time intervals the palaeosoil layers deposited.The spatial and temporal extent of the data have allowed for correlations to be made with evidence from global climate changes.The first arid episode occurred before 7.5ka in the early Holocene,with widespread aeolian sand mobilization and sparse vegetation.During 7.5~3.9ka,climate turned to be warmer and more humid with the occurrence of thick palaeosoil layers in the lowest,at the same time with Holocene Optimum.When it comes to 3.9~2.9ka,the dune rebounded to reactive with strong winter monsoon,and the climate became arid again.The timing of widespread dune reactivation coincided with well-known 4ka event.The climate became warm and humid during 2.9~1.7ka,with lower magnetic susceptibility than the upper palaeosoil layer.Although the summer monsoon is weakened,the winter monsoon failed to become predominant.Climate fluctuated more frequently after 1.7ka with a warm climate episode during 1.0~0.5ka and an arid one around 0.2ka.It also revealed that the human significance of Holocene climate variability since 1ka ago.More importantly,the Holocene climate changes and evolution records from the Jinjie section could be correlated with the worldwide millennial-scale climate shifts,suggesting that the activity of East Asia monsoon in the Holocene may have directly been controlled or affected by global climate system.Several intervals coincide with major disruptions of civilization,revealing the human significance of Holocene climate variability at times.