Optically Stimulated Luminescence Chronology And Palaeoenvironmental Implications Of Aeolian Sediment And The Nalinggele River Terraces In The Tibetan Plateau

Global climate change has aroused widespread curiosity in the international community.The uplift of the Qinghai-Tibet Plateau(QTP)plays an important role in the formation and evolution of the East Asian systems.The QTP lies at a critical and sensitive junction of four climatic systems: the Westerlies,the East Asian monsoon,the Siberian High and the Indian monsoon.The QTP is rich in a large number of Aeolian deposits and river landscapes,both of which are sensitive to these climate systems and can provide past valuable environmental conditions.This paper focuses on the scientific problems such as the formation,evolution and paleoclimate significance of Aeolian sediments along the Xining-Lhasa line through the entire QTP and the Nalinggele River terraces in the Qaidam Basin since the late Quaternary.Optically Stimulated Luminescence(OSL)dating and 14 C dating,comprehensive use of stratigraphy,geomorphology and climatic index to reconstruct the history of the Late Quaternary environment.The thesis mainly comprises two parts:In the first part the Aeolian sediments along the Xining-Lhasa line through the QTP is regarded.Aeolian sediments can reflect the temperature,humidity,wind field,vegetation and other factors while accumulating.In this paper,the Aeolian sediments are sampled throughout the Xining-Lhasa line in the QTP,including but not limited to the Qinghai Lake,the Qaidam Basin and the Gonghe Basin,which are studied by the predecessors.From northeast to southwest,the Xiala profile,the Maqin profile,the Qumalai profile and the Yalungtsangpo profile are mainly dissected.121 OSL samples and 13 14 C samples are obtained in total.Application of the magnetic susceptibility,grain size analyses and previous research data,better understanding of this Aeolian sediments issue in the QTP has been achieved.The main results are as follows:(1)The comparison of OSL and 14 C dating results of Aeolian sediments shows that Holocene samples are consistent within the error range.(2)Since the late Pleistocene in the QTP,Aeolian deposition has occurred and continues to this day.(3)Loess,which is concentrated deposit at 82 ~ 70 ka,35 ~ 26 ka and 17 ka,started to accumulated at least 82 ka,which indicates that the accumulation of loess is prior to accumulate during the transition from warm period to cold period.(4)Accumulation of Aeolian deposits in MIS4,MIS2 and LGM stages has undetected so far,may be attribute to poor vegetation in dry and cold climatic conditions,so that dust cannot be trapped.(5)The history of sedimentary environment represented by Aeolian sediments can compare with the history of ice core of Guliya and lake sediments recorded in the QTP well.So Aeolian sediment can be used as independent climate index.The second part is regarding the OSL-dated river terrace sediments from the Nalinggele River in the Qaidam Basin.The Nalinggele River is derived from the Kunlun Mountains,flowing through the alluvial fan,and finally empties into the threelake area(Dongtaiji Nair Lake,Xitaiji Nair Lake and Yiliping),known for its rich lithium.The research work of the Nalinggele river valley landforms evolution is less,if any,is also a lack of exact age,which make the history of the Nalinggele River is not very clear,and there is almost no link with the three salt lakes.In this paper,the history and driving factors of the terraces in the upper reaches of the Nalinggele River has been reconstructed through the OSL dating,and further analyzes the relationship between its formation and salt lake evolution.The main results are as follows:(1)Ages of the four terraces in the upper reaches of the Nalinggele River is 13.1 ± 1.0 ka(T4),11.3 ± 1.0 ka(T3),9.9 ± 1.7 ka(T2)and 7.5 ± 0.5 ka(T1).(2)According to the terrace formation age and tug of war height,the incision rate of the Nalinggele River is 0.84 mm / a.(3)Based on the ages,the incision rate,the sedimentary characteristics of the terraces,also compare with the climatic events,the Nalinggele terraces may attribute to the climatic change,and no evidence of the tectonic causes has been found yet.And further infer that the three lakes has a lithium element enrichment period since the early Holocene.