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| 3. |
- Blomdin, Robin, et al.
(författare)
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Evaluating the timing of former glacier expansions in the Tian Shan : A key step towards robust spatial correlations
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 78-96
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Tidskriftsartikel (refereegranskat)abstract
- The timing of past glaciation across the Tian Shan provides a proxy for past climate change in this critical area. Correlating glacial stages across the region is difficult but cosmogenic exposure ages have considerable potential. A drawback is the large observed scatter in Be-10 surface exposure data. To quantify the robustness of the dating, we compile, recalculate, and perform statistical analyses on sets of 10Be surface exposure ages from 25 moraines, consisting of 114 new and previously published ages. We assess boulder age scatter by dividing boulder groups into quality classes and rejecting boulder groups of poor quality. This allows us to distinguish and correlate robustly dated glacier limits, resulting in a more conservative chronology than advanced in previous publications. Our analysis shows that only one regional glacial stage can be reliably correlated across the Tian Shan, with glacier expansions occurring between 15 and 281 a during marine oxygen isotope stage (MIS) 2. However, there are examples of older more extensive indicators of glacial stages between MIS 3 and MIS 6. Paleoglacier extent during MIS 2 was mainly restricted to valley glaciation. Local deviations occur: in the central Kyrgyz Tian Shan paleoglaciers were more extensive and we propose that the topographic context explains this pattern. Correlation between glacial stages prior to late MIS 2 is less reliable, because of the low number of samples and/or the poor resolution of the dating. With the current resolution and spatial coverage of robustly-dated glacier limits we advise that paleoclimatic implications for the Tian Shan glacial chronology beyond MIS 2 are speculative and that continued work toward robust glacial chronologies is needed to resolve questions regarding drivers of past glaciation in the Tian Shan and Central Asia.
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| 4. |
- Blomdin, Robin, 1986-, et al.
(författare)
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Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia
- 2016
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Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 12:1, s. 123-136
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a map of the glacial geomorphology of the Altai andWestern Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 mresolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.
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| 5. |
- Blomdin, Robin, 1986-, et al.
(författare)
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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
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Blomdin, Robin, 1986-
(författare)
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Paleoglaciology of the Tian Shan and Altai Mountains, Central Asia
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Blomdin, Robin, et al.
(författare)
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Timing and dynamics of glaciation in the Ikh Turgen Mountains, Altai region, High Asia
- 2018
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 47, s. 54-71
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Tidskriftsartikel (refereegranskat)abstract
- Spanning the northern sector of High Asia, the Altai region contains a rich landform record of glaciation. We report the extent, chronologies, and dynamics of two paleoglaciers on opposite flanks of the Ikh Turgen mountains (In Russian: Chikhacheva Range), straddling the border between Russia and Mongolia, using a combination of remote sensing-based glacial geomorphological mapping, 10Be surface exposure dating, and geomorphometric analysis. On the eastern side (Mongolia), the Turgen-Asgat paleoglacier, with its potential for developing a large accumulation area (∼257 km2), expanded 40 km down valley, and mean ages from a latero-frontal moraine indicate deglaciation during marine oxygen isotope stage (MIS) 3 (45.1 ± 1.8 ka, n = 4) and MIS 2 (22.8 ± 3.3 ka, n = 5). These minimum age constraints are consistent with other 10Be glacial chronologies and paleoclimate records from the region, which indicates glacier culmination during cold and wet conditions coinciding with MIS 3 (piedmont-style glaciation; inferred for a few sites across the region) and glacier culmination during cold and dry conditions coinciding with MIS 2 (mainly valley-style glaciation; inferred from several sites across the region). On the western side (Russia), the Boguty paleoglacier had a smaller accumulation area (∼222 km2), and advanced 30 km down valley across a low gradient forefield. Surface exposure ages from two moraine complexes on this side of the mountains exhibit wide scatter (∼14–53 ka, n = 8), making paleoclimate inferences and comparison to other proxies difficult. Ice surface profile reconstructions imply that the two paleoglaciers likely shared an ice divide. © 2018 Elsevier B.V.
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| 8. |
- Blomdin, Robin, et al.
(författare)
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Topographic and climatic controls on paleoglaciation patterns across the Tian Shan and Altai Mountains, Central Asia
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Reconstructing spatial patterns of the extents and dynamics of paleoglaciers across Central Asia is key in understanding the mechanisms of global environmental change. The Tian Shan and Altai Mountains are located in the continental interior of Eurasia, at the confluence of several major climate systems. In order to test hypothesized patterns in paleoglacier extent, and to test the role of paleoclimate and mountain topography in modulating the evolution of these glacial systems, we perform a domain-wide terrain analysis. We first divide the Tian Shan and the Altai Mountains into six physiographic regions delineated by major drainage divides and outlining generalised climate zones. Thereafter we mine published datasets on the distribution of glaciers and glacial landforms, calculate their area-elevation distributions (hypsometry), and extract present-day regional equilibrium line altitudes (ELAs) and long-term average ELAs (paleo-ELAs). We show that the use of glacial landform hypsometry is an effective tool to quantify broad-scale paleoglaciation patterns and find that there is a regional variability in glacier extents across the Tian Shan and Altai Mountains. Reconstructed ELAs show pronounced spatial gradients; increasing ELAs from northern to southern Tian Shan, and increasing ELAs from the northern to both the southeastern and southwestern Altai Mountains. In contrast, maximum paleoglaciation patterns and paleo-ELAs were more uniform across the two mountain systems, with inter-regional topographic variability influencing moraine distributions and thus complicating regional paleo-ELA determinations. Because estimated paleo-ELAs were relatively uniform across the Tian Shan and Altai Mountains, the paleo-ELA lowering were most pronounced in the more continental southern and eastern regions. Our current data is insufficient to explain whether this observation is the result of a different regional paleoclimatic regime than today, or if paleoglaciers responded dynamically different to a paleoclimate forcing of the same magnitude. Our ELA reconstructions also lack temporal constraints, so we furthermore propose that future studies systematically compare hypsometry-derived ELA reconstructions with those stemming from surface energy mass balance models, other proxy records (i.e. lake- and ice core records), and from chronologically constrained ice-marginal moraines.
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| 9. |
- Bonow, Johan M., 1969-
(författare)
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Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins : reference forms for conclusions on uplift and erosion
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Palaeosurfaces and palaeovalleys are landforms under destruction in the present climate and/or tectonic regime, and thus mainly reflect processes not active today. Uplifted palaeosurfaces exist along the formerly glaciated passive continental margins around the North Atlantic. Large-scale landform development has recently become a matter of interest also for geologists and geophysicists as the result of an increasing awareness that a thorough knowledge of uplift, erosion, deposition and development of landforms along continental margins can only be accomplished by combined studies using independent data from different scientific disciplines. The present study focuses on one of these above data sets; the landform record. Two uplifted areas, southern Norway and central West Greenland, were selected for landform analysis of high resolution digital elevation models, aerial photographs, relation between landforms in basement and cover rocks, offshore seismic lines and X-ray diffraction of clay minerals in saprolites. In southern Norway, analysis of slope angles within the range of pediment slopes was combined with analysis of main valley incision. This resulted in the identification of three main planation surfaces in a stepped sequence formed along the main valleys as a consequence of tectonic uplift events, maybe in the Palaeogene, (in total >1000 m). Two phases of late uplift (~900 m), probably in the Neogene, triggered incision of deep fluvial valleys, later reshaped by glacial erosion (up to 300 m). In central West Greenland palaeosurfaces were analysed in relation to cover rock of different age. An exhumed etch surface, characterized by a typical hilly relief, occurs on Disko and south of Disko Bugt, and are by the presence of cover rocks shown to be sub-Palaeocene in origin. To the north, a post-Eocene erosion surface on Nuussuaq, cuts across basement and basalt and was probably formed close to sea level. Uplift in two phases elevated this surface up to 2000 m above present sea level and broke it in differently tilted tectonic blocks. South of Disko Bugt, a planation surface, of probably the same age as the one on Nuussuaq, cuts the tilted etch surface, and also cuts across different bedrock types. The planation surface rises towards the south and splits in two surfaces, separated in altitude up to 300 m, within two highly elevated areas. The separation into two surfaces indicate two uplift events: A first minor event of a few hundred metres in the uplift centres resulted in incision of the lower planation surface. This event was later followed by a major uplift event amounting to >1000 m. Correlation with the offshore sedimentary record suggests that both uplift events occurred in the Neogene. The erosion pattern calculated from one reconstructed palaeosurface to present topography shows large spatial variations. This is interpreted as an effect of differential bedrock resistance and local variations of glacial erosion (400–1300 m in low areas). The results presented in this thesis demonstrate the usefulness of palaeosurfaces and palaeovalleys as tools for deciphering magnitude of uplift events, establishing relative event chronologies and for calculation of erosion. Moreover integrated studies of palaeolandforms, offshore geology and thermal chronologies, are shown to be invaluable when used to solve the spatial and temporal patterns of uplift, erosion and deposition.
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| 10. |
- Ebert, Karin, 1976-
(författare)
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Cenozoic landscape evolution in northern Sweden : Geomorphological interpretation within a GIS-framework
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The large-scale bedrock landscape in northern Sweden has a complex evolution history of planation, uplift, transgression, burial, weathering, and erosion. The aim of this thesis is to examine the long-term development of the area. Terms for base-level surfaces in the area are defined. A combination of GIS-analyses of digital elevation models and field work is used to explore landform characteristics and formation. Inselbergs east of the northern Scandes in northern Sweden are used as a basis for describing landscape development. In total, 794 inselbergs are identified in the study area. The inselbergs are classified according to their degree of glacial erosion. The Parkajoki area, with low glacially modified inselbergs, tors, boulder fields and saprolites, has been shown to have largely escaped Quaternary glacial erosion and is taken as a type area to describe the late-Neogene landscape development prior to glaciation. The removal of Neogene saprolite mantles at the inselberg feet in areas of glacial erosion increased inselberg relief during the Quaternary by 10-20 m. For landscape evolution further back in time, beyond the Neogene, the hypsography of the study areas shows at least two palaeosurface generations in the northern Scandes and at least four palaeosurface generations on the inselberg plains. The distribution of inselbergs in relation to palaeosurface generations in the same elevation intervals suggests land uplift with a tilt towards the SE-ESE. Eocene marine diatom findings at 260 m a.s.l. in Finland, 200 km east of the study area, indicate a pre-Eocene age of the inselberg plains above this elevation. The development of today’s inselberg plains likely started in the late Mesozoic, with a sub-Mesozic etch surface that was subjected to land uplift at the late Mesozoic-Paleocene transition during breakup of the Atlantic. The great antiquity of the northern Swedish bedrock landscape stands as an analogy for shield areas in for example Australia and Africa.
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