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Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: the case of a missing LGM expansion
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Department of Physics, Purdue Rare Isotope Measurement Laboratory, Purdue University.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined 10Be apparent exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Apparent exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in ages for individual sites and within the recognised four morphostratigraphical groups. The age disparity is inexplicable as arising from differences in inheritance without the application of unrealistic assumptions but it can be explained as arising from differences in post-glacial shielding, yielding exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40-65 ka. More extensive glaciations occurred before 60-100 ka and 95-165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Har Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is supported by high-resolution glacier modelling experiments.

National Category
Physical Geography Geology
Research subject
Physical Geography; Quarternary Geology
Identifiers
URN: urn:nbn:se:su:diva-38688OAI: oai:DiVA.org:su-38688DiVA: diva2:312533
Note
9 authorsAvailable from: 2010-04-26 Created: 2010-04-26 Last updated: 2010-10-07Bibliographically approved
In thesis
1. Palaeoglaciology of the northeastern Tibetan Plateau
Open this publication in new window or tab >>Palaeoglaciology of the northeastern Tibetan Plateau
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study concerns the palaeoglaciation of the northeastern Tibetan Plateau, with emphasis on the Bayan Har Shan (Shan = Mountain) in the headwaters of Huang He (Yellow River). To reconstruct past glacier development multiple techniques, including remote sensing, field investigations, cosmogenic exposure dating, and numerical modelling have been employed. Analysis of the large-scale geomorphology indicates that glacial erosion has been dominant in the elevated mountain areas on the low-relief plateau, whereas fluvial erosion outpaces glacial erosion along the plateau margin. Landform and sediment records yield evidence for multiple local glaciations, restricted to the highest mountain areas, and a maximum glaciation beyond the mountain front. Absence of data supporting the former presence of proposed ice sheets, plateau-wide or regional, tentatively indicates that no ice sheet glaciation occurred on the northeastern Tibetan Plateau. Cosmogenic exposure dating of boulders, surface pebbles, and sediment sections in central Bayan Har Shan indicates that its record of past glaciations predates the global Last Glacial Maximum (LGM). Based on a world-wide analysis, yielding that wide age disparity within apparent exposure age datasets is most likely caused by post-glacial shielding processes, the Bayan Har Shan exposure ages constrain four periods of glaciation with minimum ages of 40-65 ka, 60-100 ka, 95-165 ka, and undetermined oldest stage. Similar to Bayan Har Shan, the plateau-wide distribution of boulders with pre-LGM exposure ages close to present-day glaciers shows that its LGM glaciers were generally not much larger than today. The results of a high resolution glacier model applied to nine regions across the plateau indicates that temperature depressions of 2-4 K are enough to expand glaciers beyond their global LGM extent, implying that during periods of Northern Hemisphere glaciation the Tibetan Plateau was not much colder than today or became exceedingly dry.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2010. 15 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 21
Keyword
Tibetan Plateau, palaeoglaciology
National Category
Physical Geography Geology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-38689 (URN)978-91-7447-074-1 (ISBN)
Public defence
2010-06-02, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of doctoral defence the following publications were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.Available from: 2010-05-11 Created: 2010-04-26 Last updated: 2010-05-13Bibliographically approved

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