Quartz luminescence dating and its application tosediments from Manas Lake in northwestern China

by Tse Yuen-yeung ;

Institution: University of Hong Kong
Year: 2017
Keywords: Sediments (Geology) - China, Northwest; Optically stimulated luminescence dating
Posted: 02/01/2018
Record ID: 2155151
Full text PDF: http://hdl.handle.net/10722/239983


Optically stimulated luminescence (OSL) dating hasbeen a powerful tool in dating late Quaternary sediments depositedin a wide variety of environments. This study focuses on OSL datingof quartz grains extracted from sediments. Methodological aspectsabout different components of quartz OSL are studied. The datingmethod has been applied to lacustrine and paleoshoreline sedimentsfrom Manas Lake in northwestern China. Quartz OSL signal consistsof fast, medium and slow components. In conventional datingprotocol, the initial OSL signal, which is usually dominated byfast component, is used to evaluate the equivalent dose (De).However, erroneous results can be obtained if the initial OSLsignal contains significant proportions of the medium and slowcomponents. Three samples were used to demonstrate suchmethodological aspect. The De values of these samples were found todecrease significantly with stimulation time. This is attributed toincreasing influence of thermally unstable medium and slowcomponents in the later part of OSL signals. The De values of fastand medium components were obtained by fitting the De(t) plots(i.e. apparent De against stimulation time). The fast component Devalues obtained for the three samples range from 330 to 390 Gy,while the medium component gave significantly lower De values of 40Gy. The apparent De values obtained from the initial OSL signals(~210-250 Gy) were underestimated by more than 100 Gy relative tothe fast component De, which is a result of significantcontribution of medium components (~20%) in the initial signals.OSL dating has been applied to sediments from the lake beaches ofManas Lake. The lake is a closed lake basin in an arid region innorthern Xinjiang Province of China, with its current lake bed at244 m a.s.l. Samples from Manas Lake gave flat De(t) plots and thusno fitting is required for corrections of other componentcontributions. The dating results show that lacustrine episodesdated at ~80-73 ka ago were recorded in the northwestern side ofthe lake at 270 m a.s.l., while paleoshoreline to near-shoreenvironments during ~80-90 ka ago were recorded in the oppositeside of the lake at 262 m a.s.l. The ~80 ka old sedimentary layersin the southeastern side are overlain by paleoshoreline sedimentsformed within the last ~1 ka, separated by a large age gap.Combining the results with previous studies, it is concluded thatbreaks in sedimentary records are common in the lake area atelevation > 260 m a.s.l. When comparing sedimentary environmentsat different time from different sites, it is suggested that asmall amount of uplift of the northwestern side of Manas Lakerelative to the southeastern side have occurred during the last 80ka. published_or_final_version Earth Sciences Master Master of Philosophy