Quaternary Glacial Landforms Evolution And Geochronology In The Kanas River Valley,Altai Mountains,China

Glacier is widely considered as "the thermometer for the landmass",which is extremely sensitive to climate changes.While since the Quaternary Glacier was formed relatively late,the general configuration and sediments of glacier are well-preserved and become a top choice and attract many researchers.The exploration on the global effect of Quaternary glacier based on its timing and style promotes the research and development significantly and more progress are already made.The Altai Mountain locates inside of the Euasian,far away from the inland orogen of plate collision boundary,and the north of the modern glacier in high Asia.Based on its beneficial latitudinal and geographical conditions,it developments of several large-scale glaciation during the Quaternary with the help of abundant westerly precipitation.Recognizing the glacial scales and geomorphologic characters in the Altai Mountains can help to understand the relationship between climate and tectonicsthe,changes of the westerlies.However,the researches on glacial chronology in the Altai area are lagged behind due to the Cosmic nuclide,¹⁰Be surface exposure dating is still a giant scientific gap to be filled in.In this paper,we utilized all types of scientific techniques,including field trips for glacial general configuration,tracking and locating the spatial distribution of glacial boulders,the ¹⁰Be surface exposure dating,and collecting and screening of sediment grain size.Aiming at the Kanas River valley of the Altai Mountains at the Quaternary Glacier,we did a series of studies on the properties of glacial formation,estimation of glacial age,glacial scale at different stages,and reconstruction of Equilibrium line Altitude?ELA?.Besides,we further explored and compared the glacial formation differences between the Altai Mountains and other Central Asia glaciers in terms of the spatial-temporal variations and causes of the formation.There are plenty of typical Quaternary glacier landforms which preserved in the Kanas River valley of the Altai Mountains.The glacial erosion landscapes is featured with layering cirques,horn,arete,roche moutonnee,glacial polish,glacial valley and glacial erosion lake.The glacial erosion landscapes is featured with glacial moraine,hummocky moraine,glaciofluvial landform and widely distributed glacial boulders.The twenty-five ¹⁰Be surface exposure ages can be divided into five clusters:151.3 ±14.8?182.3 ± 17.9 ka,107.5 ± 10.4 ka,64.1 ± 6.1?69.8 ± 6.6 ka,39.1 ± 3.7?48.5 ± 4.6 ka,18.4 ± 1.8?22.2 ± 2.1 ka.Seven glacial advances in the Kanas River valley of the Altai Mountains have been identified,which are equivalent in age to the marine oxygen isotope stage?MIS?6.MIS 5d,MIS 4,MIS 3b,global Last Glacial Maximum?LGM?.Neoglaciation and Little Ice Age?LIA?.The properties of the grain size of twenty-two sediment samples demonstrated that hummocky moraine including three groups of moraines at Kanas Lake outlet formed in the LGM,consistent with the ¹⁰Be surface exposure ages,which is slightly different from previous outcomes by optically stimulated luminescence?OSL?age results.Besides,the grain size of hummocky moraine at Kanas Lake outlet,and its surrounding glaciofluvial landform,as well as its third stage moraine terraces on the east varies significantly,which can also confirm the result from ¹⁰Be surface exposure ages.Using the space distribution of glacial boulders to reconstruct the extent of the development of each glacier event.We concluded that the extent of glaciers decreased with time.The thickness of the glacier decreased from 787 m to 111 m and the width decreased from 5300 m to 700 m between the Glacial Station and the glacier terminus during MIS 6.The length and width are also the largest during MIS 6.The thickness of the glacier was 66?500 m and the width of the glacier was 350?4450 m.Similar to Tian Shan and Pamir of the Central Asia,the largest local last glacial maximum occurred during MIS 4 in the Altai Mountains,instead of the MIS 3 stage in Tibet Plateau or global Last Glacial Maximum.By the comparison of glaciation sequences between with Tian Shan and Pamir Alai Mountains of the Central Asia,we concluded that glacial advances occurred universality in MIS 6,MIS 4.MIS 2 and LIA in the Central Asia mountains.It is not popular for the warm stages like MIS 5 and MIS 3,or rapid climatic event like Younger Dry as?YD??8.2 ka BP Cold Event to happen in this area.ELA depressions and glacial retreat distances between every glacial events in the Central Asia mountains illustrates the reasons that there are not many tall mountains standing on the west of Altai Mountains,and its location is by more north,low temperature and precipitation are more beneficial compared with these in Tian Shan,which also explained the great glacial scale and high activity in Altai Mountains.The climatic condition for glacial formation in Altai Mountains are favorable to these in Tian Shan,but the tectonic condition,namely the altitude,is relatively inferior,so the starting times of the oldest glacial period for these two mountains are both at MIS 6 stage based on the ¹⁰Be surface exposure ages.