Loess sedimentation in Tibet: provenance,processes, and link with Quaternary glaciations |
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| Institution: | 1. British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;2. Earth Sciences and Geography, Keele University, Staffordshire ST5 5BG, UK;3. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;1. Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain;2. Departamento de Geoquímica, Petrología y Prospección Geológica, Universidad de Barcelona, Martí i Franquès, s/n, 08028 Barcelona, Spain;3. Instituto Geológico y Minero de España (IGME), Manuel Lasala 44, 50006 Zaragoza, Spain;1. Cold and Arid Regions Environmental and Engineering Research Institute, Key Laboratory of Desert and Desertification, Chinese Academy of Sciences, 260 Donggang West Road, Lanzhou, Gansu Province, China;2. School of Energy and Power Engineering, Lanzhou University of Technology, 287 Langongping Road, Lanzhou, Gansu Province, China;3. University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, China |
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| Abstract: | Well-preserved loess deposits are found on the foothills of mountains along the middle reaches of the Yarlung Zangbo River in southern Tibet. Optically stimulated luminescence (OSL) dating is used to determine loess ages by applying the single-aliquot regeneration technique. Geochemical, mineralogical, and granulometric measurements were carried out to allow a comparison between loess from Tibet and the Chinese Loess Plateau. Our results demonstrate that (i) the loess deposits have a basal age of 13–11 ka, suggesting they accumulated after the last deglaciation, (ii) loess in southern Tibet has a “glacial” origin, resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near-surface winds, and (iii) the present loess in the interior of Tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt. The lack of full-glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial. Such processes would have been repeated during each glacial–interglacial cycle of the Quaternary. |
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