Evolution Of Terminal Lakes Of Inland Rivers During Late Quaternary In Alxa Plateau,NW China Based On Quartz And K-feldspar Luminescence Dating Of Paleolake Shoreline

The Alxa Plateau(AP),located in the modern monsoon-westerlies transitional region,has arid climate and on which the inland-rivers and closed lakes with extremely sensitivity to the climate and environment change are distributed.The Shiyang River and the Heihe River are the main river systems and distribute in the eastern and western AP respectively.Series of well-preserved paleoshorelines are in the terminal-lake basin of two rivers(e.g,Ejina basin of Heihe River,and Baijian Lake Basin of Shiyang River),providing a robust record for studies of spatio-temporal evolution of lakes during the late Quaternary.In this study,accurate elevation of the paleoshorelines in the study area were measured by using the differential GPS system(DGPS).The lithology of the sections trenched at shorelines at different elevation were descripted and luminescence dating samples were collected at different depth of the section for chronology determination.Quartz OSL dating and K-feldspar pIRIR dating were used to these samples for age estimation and reliability of quartz OSL ages and K-feldspar pIRIR ages are monitored by internal checks of luminescence characterstics and using comparing of quartz and K-feldspar ages.Based on modern DEM data,spatio-temporal evolution process of the two terminal lakes were reconstructed using the robust chronology and sedimentology of shoreline sequence.Our results suggest:(1)quartz OSL dating and K-feldspar pIRIR dating are in good agreement with each other when the sample ages younger than 10 ka,that is to say,the two kinds of dating data are reliable.However,when the sample older than 60 ka,the quartz OSL ages have shown a systematic smaller comparing to their K-feldspar pIRIR ages,which is possibly caused by saturated or near saturation of quartz OSL signal,while K-feldspar pIRIR age has an uplimit of ~ 300 ka in the Alex Plateau,as a result,quartz OSL age less than 10 ka and K-feldspar pIRIR ages large than 60 ka are used for chronology of these shoreline deposit.(2)Lakes at Ejina Basin and Baijian Lake basin have experienced high-stand lake levels during MIS 5 and Holocene,however,the water level evolution process of lakes at Ejina Basin of western Alxa and Baijian Lake Basin of eastern Alxa is asynchronous: Lake high stand appeared at Baijian Lake Basin at ~ 125-97 ka(corresponding to MIS 5e-5c)with maximum water-level elevation of ~ 1317 m a.s.l.,corresponding to ~ 25 m water depth.During the Holocene,lake high stand appeared at Baijian Lake Basin at at ~ 9-7 ka with maximum water-level elevation of ~ 1313 m a.s.l.,corresponding to ~ 21 m water depth.In contrast,Lake high stand appeared at Ejina Basin at ~ 98-77 ka(corresponding to MIS 5c-5a)and ~ 4-3 ka,respectively,during which water depth reached to its maximum of ~ 25 m and ~ 26 m,respectively.(3)The comparison of lake level changes at eastern and western Alxa Plateau to the records of intensities of East Asian summer monsoon indicate that lake level changes in the eastern AP is consistent to the East Asian summer monsoon intensity changes,while lake level changes in the western A.P.were asynchronous to to the East Asian summer monsoon intensity changes,but consisting to moisture changes in arid central Asia.Thus,we suggest that the precipitation and lake level changes in eastern AP is mainly controlled by East Asian summer monsoon intensities and the precipitation and lake level changes in western AP is possibly related to climatic changes in arid central Asia.