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Paleoglaciation on opposite flanks of the Ikh-Turgen Mountains, Central Asia: Importance of style of moraine deposition for 10-Be surface exposure dating
Stockholm University, Faculty of Science, Department of Physical Geography.ORCID iD: 0000-0003-0306-5291
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The ages of marginal moraines that record extensive glacier expansions across the Altai Mountains of Central Asia are poorly documented. We present 18 10Be exposure ages from moraines in valleys on opposite flanks of the Ikh-Turgen Mountains. On the eastern side, exposure ages from a latero-frontal moraine indicate deglaciation during MIS 3 (45.3±2.7 ka) and MIS 2 (22.8±3.5 ka). Corresponding exposure ages, from the western side, indicate a more complex story with large scatter (~14-53 ka). Owing to their close proximity, the paleoglaciers should have responded similarly to climate forcing, yet they exhibited a distinctly different behavior. We propose that differences in glacier dynamics caused differences in ice-marginal depositional environments, explaining the scatter in exposure ages on the western side. This study shows the importance of style of deposition in chronological studies of glacial landforms and demonstrates that certain moraine types can be difficult to use as paleoclimate proxies.

National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-134739OAI: oai:DiVA.org:su-134739DiVA: diva2:1037705
Projects
Central Asia Paleoglaciology Project (CAPP)
Funder
Swedish Research Council, No. 2011-4892
Available from: 2016-10-17 Created: 2016-10-17 Last updated: 2016-10-24Bibliographically approved
In thesis
1. Paleoglaciology of the Tian Shan and Altai Mountains, Central Asia
Open this publication in new window or tab >>Paleoglaciology of the Tian Shan and Altai Mountains, Central Asia
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The mountain-systems of Central Asia, act as barriers to atmospheric circulation patterns, which in turn impose striking climate gradients across the region. Glaciers are sensitive indicators of climate change and respond to changes in climate gradients over time by advancing during cold and wet periods and receding during warm and dry periods. The aim of this thesis is to investigate whether there are large-scale patterns in how past glaciers in the Tian Shan and the Altai Mountains of Central Asia responded to climate change. Multiple methods have been used, including: remote sensing, terrain analysis, field investigations, and cosmogenic nuclide (CN) dating. The glacial landform records indicate that the region experienced mainly alpine-style glaciations in the past. Large complexes of ice-marginal moraines in high elevation basins are evidence of outlet glaciers sourced from large valley glaciers, ice caps and ice-fields, and these moraine sequences, record the maximum extent of paleoglaciation. In the Ikh-Turgen Mountains, located in the continental, eastern Altai Mountains, deglaciation of these moraines occurred during marine oxygen isotope stage (MIS) 3 at ~45 ka. This is consistent with a colder and wetter climate during this time, inferred from ice core and lake level proxies. Another deglacial phase occurred during MIS 2 at ~23 ka, synchronous with the global Last Glacial Maximum. In the Russian Altai Mountains, lobate moraines in the Chuya Basin indicate deglaciation at ~19 ka, by a highly dynamic paleoglacier in the Chagan-Uzun catchment, which experienced surge-like behaviour. Furthermore, across the Tian Shan, an evaluation of new and existing CN glacial chronologies (25 dated moraines) indicates that only one regional glacial stage, between 15 and 28 ka (MIS 2), can be defined and spatially correlated across the region. These paleoglaciers were mainly restricted to valleys as a result of arid conditions during this time and variation in their extents is interpreted to reflect topographic modulation on regional climate. The ages of the oldest evidence for robust local glacial stages in the Tian Shan are not yet well constrained, however, moraines in the central Kyrgyz Tian Shan and the eastern Chinese Tian Shan have apparent minimum ages overlapping with MIS 5 and MIS 3 (with missing MIS 4 and 6 stages). However, different geological processes, such as inheritance and post-depositional shielding (e.g. deposition by surging glaciers or hummocky terrain deposition), have influenced the dating resolution, making several moraine ages inappropriate for regional comparison. Finally, to quantify regional patterns of paleoglaciation, the hypsometry (area-elevation distribution) of glacial landforms is used to estimate average paleo equilibrium line altitudes for the region. This analysis shows that while present-day ELAs mirror strong climate gradients, paleoglaciation patterns were characterised by more gentle ELA gradients. The paleo-ELA depressions across Central Asia were most prominent in the continental southern and eastern regions (500–700 m). Finally, the results from this thesis, show that Central Asia was repeatedly glaciated in the past, but underscore the importance of considering 1) catchment characteristics and styles of glaciation and 2) other non-climatic factors controlling glacier dynamics when interpreting CN chronologies to make paleoclimate inference.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2016. 34 p.
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 59
Keyword
Paleoglaciology, glacial geomorphological mapping, cosmogenic nuclide dating, Tian Shan, Altai Mountains
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-134748 (URN)978-91-7649-567-4 (ISBN)978-91-7649-568-1 (ISBN)
Public defence
2016-12-09, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Central Asia Paleoglaciology Project (CAPP)
Funder
Swedish Research Council, No. 2011-4892
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Accepted. Paper 5: Manuscript.

Available from: 2016-11-16 Created: 2016-10-17 Last updated: 2016-11-04Bibliographically approved

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