| 1. |
|
|
| 2. |
|
|
| 3. |
- Blomdin, Robin, et al.
(författare)
-
Evaluating the timing of former glacier expansions in the Tian Shan : A key step towards robust spatial correlations
- 2016
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 78-96
-
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.
|
|
| 4. |
- Blomdin, Robin, 1986-, et al.
(författare)
-
Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia
- 2016
-
Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 12:1, s. 123-136
-
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.
|
|
| 5. |
- Blomdin, Robin, 1986-, et al.
(författare)
-
Paleoglaciation on opposite flanks of the Ikh-Turgen Mountains, Central Asia : Importance of style of moraine deposition for 10-Be surface exposure dating
-
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.
|
|
| 6. |
- Blomdin, Robin, 1986-
(författare)
-
Paleoglaciology of the Tian Shan and Altai Mountains, Central Asia
- 2016
-
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.
|
|
| 7. |
- Blomdin, Robin, et al.
(författare)
-
Timing and dynamics of glaciation in the Ikh Turgen Mountains, Altai region, High Asia
- 2018
-
Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 47, s. 54-71
-
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.
|
|
| 8. |
- Blomdin, Robin, et al.
(författare)
-
Topographic and climatic controls on paleoglaciation patterns across the Tian Shan and Altai Mountains, Central Asia
-
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.
|
|
| 9. |
- Bonow, Johan M., 1969-
(författare)
-
Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins : reference forms for conclusions on uplift and erosion
- 2004
-
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.
|
|
| 10. |
- Ebert, Karin, 1976-
(författare)
-
Cenozoic landscape evolution in northern Sweden : Geomorphological interpretation within a GIS-framework
- 2009
-
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.
|
|
| 11. |
- Ebert, Karin, 1976-, et al.
(författare)
-
DEM-analysis of palaeosurface remnants in the mountain zone of northern Sweden
-
Annan publikation (refereegranskat)abstract
- Palaeosurface remnants are parts of old planation surfaces that have been elevated and partly down-cut by subsequent erosion. Such surfaces constitute an important landscape element when reconstructing the evolution of a landscape’s tong term development, although their morphological identification may be uncertain. In this study we examine to which degree palaeosurface remnants and surface generations can be identified objectively by GIS-analyses. A combination of fieldwork and GIS-analysis of digital elevation models (DEMs) was used to investigate palaeosurface remnants in two study areas, Ätnajåkki valley and Tjeuralako plateau in the northern Scandes of Sweden. Our results indicate that surfaces with an inclination of less than 11 °, and that were not affected by glacial erosion, correspond well with palaeosurface remnants as mapped subjectively in the DEM, air photos and in the field. Peaks in the hypsographic curves, at similar elevation intervals for both areas, show the altitudinal distribution of several palaeosurface generations that were identified in the field. The DEM analysis is shown to be a useful tool, but subjective mapping of glacially eroded areas is necessary to exclude glacially eroded areas, some of which may otherwise be misinterpreted as palaeosurface remnants, in the DEM. Hence, the combination of field observations and GIS-analyses is important when mapping and analysing palaeosurface remnants and their distribution correctly in a DEM. The method shown is nonetheless straightforward and reproducible.
|
|
| 12. |
- Ebert, Karin, et al.
(författare)
-
DEM identification of macroscale stepped relief in arctic northern Sweden
- 2011
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 132:3-4, s. 339-350
-
Tidskriftsartikel (refereegranskat)abstract
- Stepped relief is a characteristic feature of many upland areas on Earth. In this study, we examine if stepped relief can be identified objectively by GIS-analysis of digital elevation models (DEMs). We specifically study the stepped relief landscapes of northern Sweden, comprising areas of contrasting topography in the mountainous northern Scandes and on the inselberg plains of the Precambrian basement east of the Caledonides.We mainly use hypsographic curves to examine the elevation distribution of the study areas and to identify palaeosurfaces. Peaks in the hypsographic curves are interpreted as palaeosurfaces, while hypsographic minima are interpreted as breaks in slope, separating these surfaces. In the northern Scandes, where only patchy remnants of palaeosurfaces remain, we use empirical cutoff values of slope angles to restrict palaeosurface areas to those identified in thefield and in air photos. In addition, air photo andfield mapping of glacially eroded areas is necessary to exclude glacially formed low relief surfaces, such as valley floors. These latter procedures introduce an unavoidable degree of subjectivity to the study. Our results indicate that in the northern Scandes, surfaces with an inclination of 11°, after glacially formed features are abstracted, correspond well with palaeosurface remnants. Breaks in slope separating the surface generations in themountains are centred around 860, 1320, and 1520 masl (above sea level), respectively. On the plains east of the northern Scandes, hypsographic data were filtered to remove inselbergs in order to analyse only the plains. Hypsographic curves of both the filtered and the unfiltered data of the inselberg plains show minima at elevations that correspond to steps separating multiple palaeosurfaces at elevations of 190, 250, and 400 masl. The steps separating the different palaeosurfaces are, in places, aligned with known geological discontinuities, but extensive remnants also transect structure. The presence of stepped relief is consistent with existing models of phased Cenozoic uplift and incision in northern Fennoscandia.
|
|
| 13. |
- Ebert, Karin, 1976-, et al.
(författare)
-
Meteoric Be-10 concentrations from saprolite and till in northern Sweden : Implications for glacial erosion and age
- 2012
-
Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 12, s. 11-22
-
Tidskriftsartikel (refereegranskat)abstract
- We examine Be-10 concentration in two pit profiles in the Parkajoki area at similar to 67 degrees N on the northern Fennoscandian shield in northern Sweden. Due to repeated cover by cold-based, non-erosive ice sheets, the area retains many relict non-glacial features, including tors and saprolites. In the examined pit profiles, gruss-type saprolite developed from weathering of intermediate igneous rocks is overlain unconformably by Weichselian till.Our results show that Be-10 concentrations found in the till greatly exceed the levels of Be-10 that can have accumulated since deglaciation at similar to 11 ka and are comparable to those reported from Pliocene and Early Pleistocene tills in North America. Old tills with grussified boulders at depth were excavated in the Parkajoki area and correlations with neighbouring parts of Finland indicate a Middle Pleistocene or older age. Evidence from pit excavations and geochemistry shows that the underlying saprolites have been truncated by glacial erosion and that previously weathered material has been incorporated into the till sequence. Hence, Be-10 inventories in the tills are dominated by material recycled from Middle Pleistocene or older soils, near-surface sediments and saprolite, and cannot be used to date the periods of till deposition. The retention of relict Be-10 in the tills nonetheless confirms minimal glacial erosion.Concentrations of meteoric Be-10 in the saprolites are lower than any reported saprolite concentrations measured in other settings. Uncertainty in the pre-glaciation Be-10 concentrations in the saprolites makes age determinations difficult. One possibility is that that the saprolite had higher Be-10 concentrations in the past but that saprolite formation ended after glaciation and burial by till and that the Be-10 has substantially decayed. Modelling of the meteoric Be-10 depth profiles in this case suggests that the saprolites in the Parkajoki area were formed at a minimum of 2 Ma. Erosion of the saprolite allows an older age of up to similar to 5 Ma, with up to 250 cm of material removed and incorporated into later tills. A second possibility is that concentrations of meteoric Be-10 in the saprolite were originally lower, with formation of the saprolite in a period or periods of ice- and permafrost-free conditions before 0.8 Ma.
|
|
| 14. |
- Ebert, Karin, 1976-, et al.
(författare)
-
Multi-phase development of a glaciated inselberg landscape
-
Annan publikation (refereegranskat)abstract
- We investigate the evolution of a glaciated inselberg landscape in northern Sweden since the late Mesozoic, c. 65 million years ago. The study area is part of the Fennoscandian shield and has been stripped of cover rocks and also largely of weathering mantles by preglacial and glacial erosion to leave low relief inselberg plains, with a thin cover of Quaternary deposits. We use these inselbergs as the basis for study of the impact of glacial and preglacial erosion on the shield landscape. GIS-analyses of digital elevation models (DEMs) enable us to identify the morphometry of the inselbergs. Field mapping and mechanical excavations of inselberg margins allow links to be explored between dome-like granite inselbergs and sheet structures and to examine till and saprolite mantles. Very low glacial erosion in the Parkajoki area allows the final stages of preglacial relief development to be reconstructed for the Late Neogene. The hypsometry of the study area, in combination with inselberg elevation and distribution, allows four palaeosurfaces to be identified. The effects of glacial erosion on the bedrock forms of the inselbergs of the study area were generally restricted to inselberg streamlining by steepening of inselberg flanks. The inselberg landscape relief was enhanced by the removal of saprolite mantles during the Quaternary glaciations. The saprolites formed during the late Neogene, thin or absent close to the inselberg summits and of 10-20 m thickness at the inselberg feet and on the plains. The inselbergs are much older features, however, and deep kaolinization and soft ores are evidence for development by etching from a Mesozoic base level surface. Eocene marine clays on the continuation of the inselberg plains in northern Finland at around 260 m a.s.l. indicate that the inselberg plains above the Pakko palaeosurface generation predate the Paleogene-Eocene thermal maximum. Erosion rates, calculated for two reconstructed summit envelope surfaces, range between 1.5m/Myr and 4.8m/Myr since the late Mesozoic. The inselberg plains of northern Sweden are therefore directly comparable to other shield landscapes in extra-glacial areas that have experienced episodes of deposition of thin cover rocks, long periods of weathering and very low long term rates of erosion.
|
|
| 15. |
- Ebert, Karin, 1976-, et al.
(författare)
-
Pre-glacial landforms on a glaciated shield : the inselberg plains of northern Sweden
- 2012
-
Ingår i: Norsk Geologisk Tidsskrift. - 0029-196X. ; 92:1, s. 1-17
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the long-term geomorphological evolution of the inselberg plains on the glaciated northern Fennoscandian shield. The shield surface has been largely stripped of pre-Quaternary correlative sediments and saprolites by non-glacial and glacial erosion, which makes investigations of pre-Quaternary landscape development a challenge. The relief of the study area, covering 33,000 km3 in the centre of the shield in northern Sweden, includes an abundance of inselbergs that provide the basis for the study. We examine the relief of the inselberg plains, integrated with glacial-geomorphologic features, geology, and weathering remnants, by using GIS-analysis and fieldwork. Several key areas are used to demonstrate the impact of glaciations on the large scale relief, and the influence of geology, structure and deep weathering on relief formation.Glacial erosion had only a minor impact on the large-scale bedrock morphology of northern Sweden. Based on excavations and observations in the Parkajoki area, an area largely preserved under cold-based ice during Quaternary glaciations, we infer that grus weathering, resulting in saprolite covers of up to 10-20 m thickness, occurred in the Neogene. However, inselbergs are considerably higher than that, and must therefore be the result of older deep weathering and erosional events. Narrow fracture zones associated with deep kaolins found in northern Fennoscandia may represent the roots of older generations of deep weathering covers but their age and formation is yet unclear. The geology of the area has greatly influenced the present surface relief. The positions and footprints of the inselbergs are often closely controlled by bedrock type and fracturing. Granite inselbergs generally have dome forms where dome shape and slopes are determined by joint patterns. Steps between palaeosurfaces locally coincide with lithological boundaries and major faults. These links indicate the fundamental importance of etch processes in shaping the relief through multiple cycles of deep weathering and stripping. Palaeosurfaces have been extended and lowered through time, with isolation of small inselbergs during erosion of higher palaeosurfaces. The timescales for relief generation remain uncertain and there is a pressing need to understand the significance of and to date the sediments, saprolites and weathered ore bodies that rest on the surface of the northern Fennoscandian shield.
|
|
| 16. |
- Ebert, Karin, 1976-, et al.
(författare)
-
The impact of Quaternary glaciations on inselbergs in northern Sweden
- 2010
-
Ingår i: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 115:1-2, s. 56-66
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the glacial modification of inselbergs (large, isolated bedrock hills) in northern Sweden. Inselbergs are generally regarded as products of deep weathering (etching) and stripping under warm and humid climates. Unlike inselbergs found in the tropics, the inselbergs in northern Sweden were exposed to ice sheet glaciation for long periods of the Quaternary. We used DEMs to examine 794 inselbergs in our study area and they were classified according to their degree of glacial modification. Bedrock structural control was assessed using GIS data on the regional geology. Clusters of inselbergs were mapped in the field for features indicative of glacial erosion, such as glacial cliffs and stripped bedrock surfaces, and for features indicative of limited erosion, such as tors and blockfields. The results of the study indicate that inselbergs in the area were mostly modified by Quaternary ice sheets only to a low or moderate extent and that the degree of glacial erosion is dependent on their relief and location. Inselbergs with a relative relief of < 100 m and in areas of lower absolute relief experienced the strongest glacial modification, where the strongest glacial modification can result in lateral erosion of the inselberg flanks. Inselberg summits often display signs of minimal glacial erosion, such as tor-like bedrock outcrops with signs of strong weathering. In summary, we argue that inselbergs in northern Sweden have largely retained their pre-Quaternary shape despite long periods of ice sheet cover.
|
|
| 17. |
- Fabel, D., et al.
(författare)
-
Retreat rate of the northern Fennoscandian Ice Sheet margin
- 2007
-
Ingår i: Geophysical Research Abstracts.
-
Konferensbidrag (refereegranskat)abstract
- The deglaciation chronologies of the northern and north-eastern margins of the Fennoscandian Ice Sheet are relatively poorly constrained. This is because the principal methodological tool to trace and date the deglaciation pattern, the occurrence of deglaciation varves, does not apply in the northernmost regions of Fennoscandia. Moreover, a paucity of radiocarbon dates allows for only a most generalised pattern for the post-Younger Dryas shrinkage of the ice sheet to its final deglaciation configuration in the northern Swedish mountains. We are tracing the deglaciation of the Fennoscandian Ice Sheet from its Younger Dryas terminal moraines in northern Norway and eastern Finland towards the northern Swedish mountains, using cosmogenic nuclide apparent exposure ages of depositional and erosional features related to the former ice sheet margin. Because the ice sheet had initially warm-based conditions close to its margin, the dominant morphology is one of eskers and aligned lineation systems such as crag-and-tails. Abundant meltwater has locally eroded bedrock to considerable depth and deposited fans or deltas perched above current local base levels. Subglacial conditions during final deglaciation close to the mountain range were cold-based, thus inhibiting the formation of eskers and lineation systems. However, there is a ubiquity of meltwater erosional imprints and occasional plucking scars where, locally, pressure-melting conditions were reached. Surface exposure ages from these different geomorphological settings should yield true deglaciation ages provided the following conditions are met, (i) erosion on crags of crag-and-tails, across transverse erosional scarps, and in meltwater channels has exposed bedrock surfaces without a prior exposure history, and (ii) depositional features contain exposed boulders without a prior exposure history. Results show that transverse erosional scarps and erratics yield reliable deglaciation ages, but that bedrock samples from meltwater channels and crag-and-tails and sediment samples from eskers occasionally yield unreliable deglaciation ages due to cosmogenic nuclide inheritance and potential shielding by snow. Apparent deglaciation ages range from _14 ka at the Younger Dryas moraine to _8 ka approximately 500 km to the south in the northern Swedish Mountains. The spread of ages do not deviate from what would be expected for a regular uninterrupted retreat by the ice margin
|
|
| 18. |
- Fredin, Ola, 1972-
(författare)
-
Mountain centered icefields in northern Scandinavia
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range.Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden.The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.
|
|
| 19. |
- Fredin, Ola, et al.
(författare)
-
Relict lateral moraines in northern Sweden : evidence for an early mountain centered ice sheet
- 2002
-
Ingår i: Sedimentary Geology. - 0037-0738 .- 1879-0968. ; 149:1-3, s. 145-156
-
Tidskriftsartikel (refereegranskat)abstract
- Glacial geomorphology along the eastern rim of the Scandinavian mountain range includes glacial landforms from the last deglaciation as well as from earlier glacial stages. One of the most prominent landform groups from earlier glacial stages, and the most diagnostic for ice sheet reconstruction, is a set of lateral moraines. In this paper, we describe these lateral moraines within a key area around Kvikkjokk, northern Sweden. Position of these lateral moraines in relation to the last deglaciation patterns indicates that they were formed before the last glacial maximum (LGM). The location and morphology of moraines show that they were deposited by a mountain centred ice sheet with outlet glaciers along major valleys, emanating from the highlands west of the Kvikkjokk area. This ice sheet was likely less than 170-km wide and no more than 600-m thick. Climatologically and glaciologically, we expect the relict lateral moraines to have been deposited before 75 ka BP (marine oxygen isotope stage 4). Their preservation is a consequence of subsequent overriding of nonerosive cold-based ice. Ice-marginal landforms and deposits from mountain centred ice sheet configurations in Fennoscandia are scarce. Therefore, the relict lateral moraines are important tools for reconstructing these elusive early glacial stages, possibly correlated to the ice sheet inception.
|
|
| 20. |
- Fu, Ping, 1982-, et al.
(författare)
-
Complex erosion patterns produced by the Haizishan paleo-ice cap
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Determining patterns and rates of glacial erosion is important in understanding landscape evolution, topographic relief production, geochemical cycles, climate change, and glacial thermal regimes of paleo glaciers and ice sheets. Combining in situ $^{10}$Be and $^{26}$Al apparent exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4 000 km$^2$ Haizishan paleo-ice cap on the southeastern Tibetan Plateau. Our results show that ice caps developed several times on the low relief Haizishan Plateau and produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with last deglaciation, complete resetting of the cosmogenic exposure age clock indicates that more than 2 m of glacial erosion occurred during the last major glaciation (which in this area correlates with the global Last Glacial Maximum (gLGM)). However, older apparent exposure ages on bedrock and in saprolites profiles in areas known to have been covered by the paleo ice cap during gLGM indicate inheritance and thus limited or no erosion by the last ice cap in several areas, including the central zone of the paleo ice cap and at the head of an outlet glacier. Similarly, cosmogenic radionuclide depth profiles in saprolites show erosion of $>$2 m in an outlet valley bottom and in the mountains that make up the northern border of the paleo ice cap, while samples from saprolites in areas of otherwise scoured terrain have a large nuclide inheritance indicating limited erosion. As patterns of glacial erosion intensity are largely driven by basal thermal regime, our results are consistent with a hypothesis of complex thermal regimes for the paleo Haizishan ice cap during gLGM that was proposed previously on the basis of landform patterns. Future work, including glaciological modeling, is required to fully understand the implications and mechanisms of the complex thermal regime of this paleo ice cap.
|
|
| 21. |
- Fu, Ping, 1982-, et al.
(författare)
-
Glacial geomorphology and paleoglaciation patterns in Shaluli Shan, the southeastern Tibetan Plateau — Evidence for polythermal ice cap glaciation
- 2013
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 182, s. 66-78
-
Tidskriftsartikel (refereegranskat)abstract
- Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area on the southeastern TibetanPlateau. Our studies provide evidence for multiple glaciations, including the formation of regional ice caps andvalley glaciers. The low-relief topographywithin the Shaluli Shan, the Haizishan Plateau, and Xinlong Plateau displayzonal distributions of glacial landforms that is similar to those imprinted by Northern Hemisphere ice sheetsduring the last glacial cycle, indicating the presence of regional, polythermal ice caps. Abundant alpine glaciallandforms occur on high mountain ranges. The pattern of glaciated valleys centered on high mountain rangesand ice-scoured low relief granite plateaus with distinctive patterns of glacial lineations indicate a strong topographiccontrol on erosional and depositional patterns by glaciers and ice caps. In contrast to the Shaluli Shan,areas farther north and west on the Tibetan Plateau have not yielded similar landform evidence for regionalice capswith complex thermal basal conditions. Such spatial differences across the Tibetan Plateau are the resultof variations in climate and topography that control the extent and style of glaciations and that reinforce the importanceof detailed geomorphological mapping for understanding paleoclimate variations and characteristics offormer glaciations.
|
|
| 22. |
- Fu, Ping, et al.
(författare)
-
Glacial geomorphology of the Haizi Shan area, SE Tibetan Plateau
- 2009
-
Konferensbidrag (refereegranskat)abstract
- The Haizi Shan area on the SE Tibetan Plateau is characterized by an elliptical relatively low relief plateau surrounded by steeper fluvial valleys. Glacial deposits and erosive imprints are widely distributed indicating former glacier expansions of varying extents in a presently ice-free area. We have initiated a project on the glacial history of the Haizi Shan area and we here present some initial mapping results. Glacial landforms have been mapped based on remote sensing (SRTM digital elevation model, Landsat ETM+ satellite imagery, and Google Earth) and one short reconnaissance field season. Well-preserved moraines from different stages and distinctive U-shaped glacial valleys are abundant (Fig. 1). In the Daocheng Valley southwest of the Haizi Shan Plateau we have mapped glacial deposits in the form of discontinued moraine ridges at Sangdui village. This line, which might be the maximum Quaternary glacial extent, can be traced for several kilometers along the western side of the valley as dispersed erratic boulders. This implies that during the maximum glaciation, ice from the Haizi Shan Plateau crossed the valley and reached up to the piedmont of the opposite mountain. Smaller in extent than the former, numerous large moraine ridges reach down towards valley floors along the edges of the Haizi Shan Plateau. In several locations these valleys lack cirque heads indicating former outlet glaciers emanating from a Haizi Shan ice cap. We will use TCN and OSL dates of samples collected from numerous ice marginal moraines of the Haizi Shan Plateau to determine a glacial chronology. Hence, using remote sensing, field investigations and numerical dating techniques for the Haizi Shan we aim to advance our knowledge on Quaternary glaciations of the SE Tibetan Plateau.
|
|
| 23. |
- Fu, Ping, 1982-, et al.
(författare)
-
Glacial geomorphology of the Shaluli Shan area, southeastern Tibetan Plateau
- 2012
-
Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 8:1, s. 48-55
-
Tidskriftsartikel (refereegranskat)abstract
- We present a glacial geomorphological map covering 1.04 x 10(5) km(2) of the Shaluli Shan (Shan Mountain), southeastern Tibetan Plateau. Using a 90 m digital elevation model from the Shuttle Radar Topography Mission and 15/30 m Landsat Enhanced Thematic Mapper Plus satellite imagery, we have mapped glacial valleys, marginal moraines, hummocky terrain, glacial lineations and ice-scoured terrain. Lineations and scoured areas largely overlap on the low relief granite plateau of the Shaluli Shan and relate to former ice cap glaciation. These landscape features indicate that past ice cap glaciation included basal sliding conditions, and thus warm-based ice. Glacial valleys and marginal moraines are dominant landforms in the high mountain ranges of Shaluli Shan and occur on and fringing the plateau. This glacial geomorphological map forms the basis for paleoglaciological reconstructions of this southeastern Tibetan Plateau region and indicates the former presence of multiple glaciations involving valley glaciers and ice caps. The map is presented at a scale of 1:630,000.
|
|
| 24. |
- Fu, Ping, et al.
(författare)
-
Ice cap erosion patterns from bedrock Be-10 and Al-26, southeastern Tibetan Plateau
- 2019
-
Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 44:4, s. 918-932
-
Tidskriftsartikel (refereegranskat)abstract
- Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ Be-10 and Al-26 analysis of bedrock, boulder, and river sand samples, geomorphological mapping, and field investigations, we examine glacial erosion patterns of former ice caps in the Shaluli Shan of the southeastern Tibetan Plateau. The general landform pattern shows a zonal pattern of landscape modification produced by ice caps of up to 4000 km(2) during pre-LGM (Last Glacial Maximum) glaciations, while the dating results and landforms on the plateau surface imply that the LGM ice cap further modified the scoured terrain into different zones. Modeled glacial erosion depth of 0-0.38 m per 100 ka bedrock sample located close to the western margin of the LGM ice cap, indicates limited erosion prior to LGM and Late Glacial moraine deposition. A strong erosion zone exists proximal to the LGM ice cap marginal zone, indicated by modeled glacial erosion depth >2.23 m per 100 ka from bedrock samples. Modeled glacial erosion depths of 0-1.77 m per 100 ka from samples collected along the edge of a central upland, confirm the presence of a zone of intermediate erosion in-between the central upland and the strong erosion zone. Significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate restricted glacial erosion during the last glaciation. Our study, for the first time, shows clear evidence for preservation of glacial landforms formed during previous glaciations under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the Haizishan ice cap during the LGM.
|
|
| 25. |
- Fu, Ping, 1982-, et al.
(författare)
-
Paleoglaciation of Shaluli Shan, southeastern Tibetan Plateau
- 2013
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 64, s. 121-135
-
Tidskriftsartikel (refereegranskat)abstract
- Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes, and here we focus on the glacial history of the Shaluli Shan, an area of the southeastern Tibetan Plateau that receives much of its precipitation from monsoon flow. Based on field investigation, geomorphological mapping, and Be-10 exposure dating of moraines, we identify glacial deposits from the Late Glacial, with minimum ages at 13.0 +/- 1.2 -17.1 +/- 1.6 ka, global Last Glacial Maximum (gLGM) at 21.6 +/- 2.0 ka, and pre-gLGM at 102.3 +/- 10.0-183.6 +/- 17.0 ka. These ages are consistent with and significantly extend the known range from most prior chronological work using terrestrial cosmogenic nuclides in this area, and include a set of dates for the Kuzhaori moraine that raise questions about prior chronologies based on the electron spin resonance technique. Ice caps about 4000 km(2) in size covered the Haizishan Plateau and the Xinlong Plateau during the global LGM, with large glaciers extending far down outlet valleys. The presence of ice cap glaciation, here, contrasts strongly to glaciation elsewhere in the Shaluli Shan and more central regions of the Tibetan Plateau where ice expansion remained constricted to valleys. This work provides important insights into the paleoclimate pattern and monsoon evolution of the Tibetan Plateau over past glacial cycles and indicates that the Shaluli Shan has a glacial chronology more consistent with the Northern Hemisphere paleo-ice sheets than other areas of the Tibetan Plateau.
|
|
