Constraints on the late Quaternary glaciations in Tibet from cosmogenic exposure ages of moraine surfaces |
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| Authors: | Marie-Luce Chevalier George Hilley Paul Tapponnier Jérôme Van Der Woerd Jing Liu-Zeng Robert C Finkel Frederick J Ryerson Haibing Li Xiaohan Liu |
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| Institution: | 1. Key laboratory for Continental Dynamics, Institute of Geology, CAGS, 26, Baiwanzhuang Road, Beijing 100037, China;2. Department of Geological and Environmental Sciences, 450 Serra Mall, Braun Hall, Stanford University, Stanford, CA 94305, USA;3. Earth Observatory of Singapore, 50 Nanyang Ave, N2-01a-09, Singapore 639798;4. Institut de Physique du Globe de Strasbourg, UMR 7516 CNRS/ Université de Strasbourg, 5 rue Descartes, 67084 Strasbourg, France;5. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, P.O. Box 2871, 18 Shuang Qing Road, 100085 Beijing, China;6. Earth and Planetary Science Department, University of California, Berkeley, 371 McCone Hall, Berkeley, CA 94720-4767, USA;7. L-231, Atmospheric Earth and Energy Division, Physical and Life Sciences directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA;1. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, USA;2. Department of Physics and Astronomy, and Purdue Rare Isotope Measurement Laboratory (PRIME Lab), Purdue University, West Lafayette, USA;3. Department of Physical Geography and Quaternary Geology, and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden;4. German Research Centre for Geosciences, Potsdam, Germany;5. Department of Geological Sciences, California State University, Northridge, USA;6. Department of Earth and Planetary Sciences, University of California, Davis, USA;7. Department of Earth Science, University of California, Santa Barbara, USA;8. Faculty of Geography, Lomonosov Moscow State University, Moscow, Russia;9. Department of Geography, University of Tennessee, Knoxville, USA;10. Central Asian Institute of Applied Geosciences, Bishkek, Kyrgyzstan;11. School of Earth and Environmental Sciences, University of Wollongong, Wollongong, Australia;12. College of Urban and Environmental Sciences, Peking University, Beijing, China;1. Department of Earth Sciences, University of Gothenburg, Sweden;2. Earth and Environmental Sciences Institute, Pennsylvania State University, USA;3. Geomorphology and Glaciology, Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Sweden;4. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, USA;1. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, CAS, Beijing, China;2. Graduate University of Chinese Academy of Sciences, Beijing, China;1. Department of Geography, University of Tennessee, Knoxville, TN 37996, USA;2. College of Urban and Environmental Sciences, Peking University, Beijing 100871, China;3. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA;4. Bolin Centre for Climate Research, Department of Physical Geography and Quaternary Geology, Stockholm University, S-106 91 Stockholm, Sweden;5. Department of Physics, Purdue Rare Isotope Measurement Laboratory, Purdue University, West Lafayette, IN 47907, USA;1. Department of Geography, South Dakota State University, Brookings, SD 57007, USA;2. Department of Geography, The University of Tennessee, Knoxville, TN 37996, USA;3. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA;4. College of Urban and Environmental Sciences, Peking University, Beijing 100871, China;5. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100085, China;6. Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA |
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| Abstract: | This contribution provides new constraints on the timing of Tibetan glacial recessions recorded by the abandonment of moraines. We present cosmogenic radionuclide 10Be inventories at 17 sites in southern and western Tibet (32 crests, 249 samples) and infer the range of permissible emplacement ages based on these analyses. Individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10Be abundance. We consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages: 1) Erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age; and 2) Erosion progressively exposes large boulders with little prior exposure, and so the oldest sample age records the minimum moraine emplacement age. We found that depending on the scenario chosen, the moraine emplacement age can vary by > 50% for ～100 ka-old samples. We consider two scaling models for estimating the production rates of 10Be in Tibet, which has an important, although lesser, effect on inferred moraine ages. While the data presented herein effectively increase the database of sample exposure ages from Tibet by ～20%, we find that uncertainties related to the interpretation of the 10Be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies. A reanalysis of published data from moraines throughout Tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the Tibetan moraine age database. Thus, when viewed in a similar way with other samples collected from this area, uncertainties within moraine exposure ages obscure attribution of Tibetan glacial advances to temperature minima or precipitation maxima. Our work suggests that more reliable chronologies of Tibetan glaciations will come from improvements in production rate models for this portion of the world, as well as a better understanding of the processes that form and modify these geomorphic surfaces. |
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