Glacial Geomorphologic Process And Its Response To The Southwest Monsoon In The Taniantaweng Shan During The Quaternary

Glaciation in Tibetan Plateau responds sensitively to global climate changes and provides a proxy for quantifying regional and global climate change.There are successions of multiple moraines that record glacial recessions in Tibetan Plateau during the Quaternary glacial-interglacial cycles,playing a crucial role in reconstructing the Quaternary glacial history,exploring the evolution of global climate system and the law of the glacier development.Situated to the west of the Hengduan Mountains,the middle section of the Taniantaweng Shan is at the transition zone of the southeastern Tibet Plateau and the Yunnan–Guizhou Plateau.Since the Quaternary glacial period,numerous glacial actions have occurred in the region.Glacial erosion can also be mapped using the accumulation landforms,in particular the well-preserved glacial deposits.Maritime in nature and sustained by precipitation from the Southwest monsoon,the advance and retreat of the Quaternary glaciers in this region thus directly reflect fluctuations in the Southwest monsoon.This special geographical location gives particular importance to the evolutionary process of Quaternary glacial research,especially absolute dating of the oldest remnants of glaciation in the Taniantaweng Shan.It is of great significance to enrich the glacial evolution time series since the late Quaternary in the Southeast of Tibetan Plateau,verify the Quaternary glaciations evolution mechanisms in the middle or lower latitude areas which are influences of both tectonic uplift and climate change.The methods employed are field investigation,¹⁰Be,OSL and ESR dating method.We ascertained the basic geomorphology features of the Quaternary glaciers,the glacial sequences and the glacier extent of variations over the glaciation in the study area.Many methods are combined to reconstruct the ELA and climatic conditions in different glacial periods.Based on the other indicators,the response in glacier development in the area during the Quaternary glacial period to the evolution of Southwestern Monsoon is also examined.Contrast the other Quaternary glaciation areas in Southeast and East of Tibet plateau,results show that:The glacial erosive landforms mainly embody as“U”shaped valleys,a large number of cirques,typical r?che moutonnées?sheepback?,comb-shaped arêtes,and pyramid-shaped horns,and also include a large number of polished surfaces and scratches.Glacial erosion lakes can be identified at some glacial valley headstream.Glacial deposits landforms include arc-shaped moraines and lateral moraines,four groups of moraines developed in the Quzha Valley,Juequ Valley and Ruqu Valley,and three groups of moraines in Qinggulong Valley.Furthermore,glacial deposits landforms also include interlayer glacifluvial deposits,a large number of boulders and moraines.The dating results show that during the Late Quaternary,glaciers occurred in the Taniantaweng Shan at least four times.These glacial advances can be assigned to the Penultimate glaciation?MIS 6,MIS=Marine Oxygen Isotope Stage?during the Middle Pleistocene,the middle stage of the last glacial cycle?MIS3?,the Last Glacial Maximum?LGM?during the Last Pleistocene,and the early Holocene.Different dating results can testify each other.The timing of the glacial advance by the ¹⁰Be exposure ages is:90.73±8.71 ka,30.99±2.97 ka,15.43±1.46 ka²1.26±2.04 ka,8.18±0.78ka⁸.54±0.82ka.Since the MIS 6,the glacier extent progressively decreases.The largest glacier extensive during the last glacial is not LGM but the MIS 3.The glacier of early Holocene was preserved in the form of terminal moraine at a location which ranged from the contemporary glacier terminus to the rock step at the cirque mouth.The types of glacier evolved from the compound valley glaciers to the cirques glaciers or hanging glaciers.Comparing the Quaternary glacial in different periods with other surrounding mountains,we suggest that this diversity of glaciation time among different mountain glacial periods,the closer to the interior of the plateau,the older the mountain glacier age is,the more frequent and complete the series is,and the more it goes to the periphery of the plateau,in the eastern margin of the plateau with only Last Glacial evidences.Before the penultimate glacial was the biggest in the Tibetan Plateau,glacial landforms distributed in the central part,the penultimate glacial maximum moved to further eastern areas and the Last Glacial landforms distributed only in the eastern margins.All the results verify the new theory about the coupling of glaciation and tectonic uplift.The result show that,since the MIS 6,the equilibrium-line altitude?ELA?are 4674 m,4930 m,5131 m and 5320 m,respectively.The?ELA are 751 m,495 m,294 m and 112 m,respectively.The temperature fell down 10.13?,7.86?,6.35?and 6.28?during the MIS6,MIS 3,LGM and the early Holocene.The glacier reached their maximum extent during the Penultimate glaciation and responded dominantly and directly to changes millennial-scale monsoon events superimposed on orbital timescales and high global ice volume,with increased monsoon precipitation and that these glaciers also responded to lower temperatures.The two glacier events during the last glaciation?MIS 3 and LGM?may respond the fluctuations of Southwest monsoon driven by the abrupt changes in the North Atlantic climate?Heinrich Event 3 and 2?at the millennial-scale.The timings of Early Holocene glacial advances are synchronous with the8.2 ka event in the Northern Hemisphere.The result suggest that the Atlantic Meridional OverturningCirculation?AMOC?transporttheclimaticunstablesignal in middle and high latitude of Northern Hemisphere to the low latitude and may induce the Early Holocene glacial advances.In addition,water vapor transported by the Southwest Monsoonwas obstructed the topographical condition and had a significant impact on the Quaternary glacier in Taniantaweng Shan.