| 1. |
- Alexanderson, Helena, et al.
(författare)
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200 ka of glacial events in NW Svalbard: an emergence cycle facies model and regional correlations
- 2018
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Ingår i: arktos. - : Springer Science and Business Media LLC. - 2364-9461 .- 2364-9453. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- Late Quaternary sedimentary units at Kongsfjordhallet, NW Svalbard, represent five cycles of glaciations and subsequent deglaciations during high relative sea levels. The high sea level events are interpreted as glacioisostatically induced and imply preceding regional glaciations, which we constrain in time by luminescence and radiocarbon ages to just prior to ~ 195, ~ 130, ~ 85, ~ 60, and ~ 15 ka. Combined with the stratigraphical record from nearby Leinstranda we identify six, possibly seven, major glacial advances during the last 200 ka in the Kongsfjorden region. Two of these occurred during the Saalian and at least four during the Weichselian. The results are based on detailed sedimentological, stratigraphical and chronological investigations of the uppermost 15 m of the 40-m-high Kongsfjordhallet coastal sections. The succession is dominated by sediments of marine and littoral origin, representing partial shallowing-upward sequences due to isostatic rebound. Only one subglacial till was recognised. Interestingly, alluvial and periglacial deposits, not commonly recognised in this type of setting, occur in the sequence. These include weathered coarse alluvium, sandy channel fills as well as cryoturbated sediments and solifluction deposits, which are positive evidence of a non-glacial environment. The sequence of sediments that represents an emergence cycle has been formalised in a facies model.
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| 2. |
- Alexanderson, Helena, et al.
(författare)
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A 200 ka glaciation history from NW Svalbard
- 2018
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Konferensbidrag (refereegranskat)abstract
- Late Quaternary sedimentary units at Kongsfjordhallet, NW Svalbard, represent five cycles of glaciations and subsequent deglaciations during high relative sea levels. The high sea-level events are interpreted as glacioisostatically induced and imply preceding regional glaciations, which we constrain in time by luminescence and radiocarbon ages to just prior to ~195 ka, ~130 ka, ~85 ka, ~60 ka and ~14 ka. Combined with the stratigraphical record from nearby Leinstranda (Alexanderson et al. 2011) we identify six, possibly seven, major glacial advances during the last 200 ka in the Kongsfjorden region. Two of these occurred during the Saalian and at least four during the Weichselian. The results are based on detailed sedimentological, stratigraphical and chronological investigations of the uppermost 15 m of the 40-m-high Kongsfjordhallet coastal sections. The succession is dominated by sediments of marine and littoral origin, representing partial shallowing-upward sequences due to isostatic rebound. Only one subglacial till was recognized. Interestingly, alluvial and periglacial deposits, not commonly recognized in this type of setting, occur in the sequence. These include weathered coarse alluvium, sandy channel fills as well as cryoturbated sediments and solifluction deposits. The sedimentary succession has been summarised in a facies model for an emergence cycle following deglaciation. Our study encompasses only the upper 15 m of the coastal cliff sections at Kongsfjordhallet (succession A of Houmark-Nielsen and Funder 1999), and there is an additional ~20 m of sediments below our Unit 1, which is promising for future studies aiming to go further back in time.Alexanderson, H., Landvik, J. Y. and Ryen, H. T. 2011. Chronology and styles of glaciation in an inter-fjord setting, northwestern Svalbard. Boreas 40, 175-197.Houmark-Nielsen, M. and Funder, S. 1999. Pleistocene stratigraphy of Kongsfjordhallet, Spitsbergen, Svalbard. Polar Research 18, 39-49.
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| 3. |
- Alexanderson, Helena, et al.
(författare)
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A 200 ka glaciation history from NW Svalbard
- 2017
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Ingår i: ; , s. 6-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the Kongsfjorden area in NW Svalbard, there are several stratigraphic sites containing information on Quaternary environmental change, and which can be used to reconstruct local depositional conditions, regional events such as large-scale glaciations and relative sea-level change. Here, we present results from an investigation of one of these sites, the Kongsfjordhallet coastal sections, which are located on the northern shore of Kongsfjorden. The sedimentary units at Kongsfjordhallet represent five high relative sea level events, which imply preceding regional glaciations (Henriksen et al., this volume). Together with the record from nearby Leinstranda (Alexanderson et al. 2011) we can thus identify six, possibly seven, large glacial advances during the last 200 ka in the Kongsfjorden region. Two of these occurred during the Saalian and at least four during the Weichselian. The glaciations are constrained in time by the ages of the high relative sea level events to just prior to ~190 ka, ~130 ka, ~100-85 ka (possibly two events), ~60 ka, ~35 ka and ~14 ka. Our study encompasses only the upper 15 m of the coastal cliff sections at Kongsfjordhallet (corresponding to succession A of Houmark-Nielsen and Funder 1999), and there is an additional ~20 m of sediments below our Unit 1, which is promising for future studies aiming to go further back in time. ReferencesAlexanderson, H., Landvik, J. Y. and Ryen, H. T. 2011. Chronology and styles of glaciation in an inter-fjord setting, northwestern Svalbard. Boreas 40, 175-197.Henriksen, M., Alexanderson, H., Ryen, H.T., Landvik, J.Y. & Peterson, G. this volume: Non-glacial deposits key to the late Quaternary history of NW Svalbard.Houmark-Nielsen, M. and Funder, S. 1999. Pleistocene stratigraphy of Kongsfjordhallet, Spitsbergen, Svalbard. Polar Research 18, 39-49.
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| 4. |
- Alexanderson, Helena, et al.
(författare)
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A sedimentary model for transverse inland dunes in central Scandinavia
- 2018
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Konferensbidrag (refereegranskat)abstract
- The largest dune fields in Sweden and Norway are small in international comparison but still form distinct parts of this previously glaciated landscape. The dunes formed c.10.5-9 ka ago, shortly after the last deglaciation, when winds close to the ice sheet were strong and vegetation was largely absent [1-4]. Since then they have been more or less stable and today they are covered by forest. Most of the dunes are curvi-linear in shape and formed transverse to the wind [5]. Here we present a sedimentary model for these transverse inland dunes, based on geophysical and sedimentological investigations of dunes at Skattungheden, Bonäsheden and Starmoen in central Sweden and south-eastern Norway. Ground-penetrating radar profiles reveal the main architectural elements of the dunes, while logging of sediment exposures in the dunes provide information on sedimentary structures. Grain-size analysis and scanning electron microscope studies of individual grains give us more detail on sediment characteristics.The main dune body, consisting of cross beds generally dipping 25-30°, makes up the largest part of the dunes; minor elements include windward side cover, dune-crest superimposed features and dune-toe apron (Fig. 1). The dominating sediment structures are planar parallel lamination, massive to vaguely stratified beds and a few types of secondary structures, such as bioturbation or physical disturbances. Few large erosional discordances are seen, and the dominating depositional processes are wind-ripple migration and some grain fall on the sloping lee sides. The sediments are well-sorted fine-to-medium sand, dominated by quartz, but with significant amounts of feldspar as well as some lithic fragments, micas and heavy minerals. Most grains are angular to subrounded and their surfaces display few traces of aeolian transport. Overall, the dune sands show large similarities to their source material (glacifluvial deposits), which suggests only short transport and brief reworking by aeolian processes.References[1] Alexanderson, H. and M. Bernhardson, OSL dating and luminescence characteristics of aeolian deposits and their source material in Dalarna, central Sweden Boreas, 2016. 45: p. 876-893.[2] Alexanderson, H. and M. Henriksen, A short-lived aeolian event during the Early Holocene in southeastern Norway. Quaternary Geochronology, 2015. 30: p. 175-180.[3] Bernhardson, M. and H. Alexanderson, Early Holocene NW-W winds reconstructed from small dune fields, central Sweden. Boreas, 2018.[4] Alexanderson, H. and D. Fabel, Holocene chronology of the Brattforsheden delta and inland dune field, SW Sweden. Geochronometria, 2015. 42: p. 1-16.[5] Bernhardson, M. and H. Alexanderson, Early Holocene dune field development in Dalarna, central Sweden: A geomorphological and geophysical case study. Earth Surface Processes and Landforms, 2017. 42: p. 1847-1859.
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| 5. |
- Alexanderson, Helena, et al.
(författare)
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A short-lived aeolian event during the Early Holocene in southeastern Norway
- 2015
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 30, s. 175-180
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Tidskriftsartikel (refereegranskat)abstract
- The Starmoen dune field is part of a larger aeolian system in the Jomna and Glomma river valleys in southeastern Norway. It is believed to have formed just after the last deglaciation in the area, but no absolute ages have been available to support this. Here, we present a set of quartz optically stimulated luminescence (OSL) ages from the aeolian sediments and the underlying glacifluvial deposits. The results show that the main dune-building phase was a short-lived event similar to 10 ka ago, likely with a duration less than a few hundred years. This suggests a rapid stabilisation of an initially unstable environment in newly deglaciated terrain. A much younger event with limited and surficial reworking of sand is dated to 770 +/- 110 years ago, and the modern age of an active dune provide additional OSL quality control. Age overestimation is found for glacifluvial sediments, probably due to incomplete bleaching as indicated by e.g. scattered dose distributions from small aliquots. OSL measurements were conducted using coarse quartz grains (180-250 m), which show a dominance of a fast signal component. (C) 2015 Elsevier B.V. All rights reserved.
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| 6. |
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| 7. |
- Alexanderson, Helena, et al.
(författare)
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Chronologies of the glacial history of Svalbard – a review
- 2010
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Ingår i: Arctic Palaeoclimate and its Extremes (APEX) abstract volume. ; , s. 21-21
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The basis of the glacial history of Svalbard lies in stratigraphic studies of terrestrial and marine geological records. Classic litho- and biostratigraphy give us local relative chronologies of events but to compare with other areas and records we are dependent on absolute age control. This presentation will focus on the Middle to Late Quaternary terrestrial record to which a range of different absolute dating techniques have been applied; these techniques all have their pros and cons regarding materials, resolution, age range, etc. Amino acid chronology, although not a strictly absolute dating method, may provide some age inferences. Radiocarbon dating of organic material such as shell and bone is still the most common technique and one that is generally considered reliable. It is however limited by its age range to the last ~50 ka, and our interest goes further back than so. Various versions of luminescence dating, particularly optically stimulated luminescence (OSL), have therefore become strong contenders during the recent decade, mainly due to their longer age range and applicability to a wider range of deposits than radiocarbon dating. Luminescence dating nevertheless has its drawbacks too, for Svalbard these are mainly related to the risk of incomplete bleaching (leading to age overestimation) and poor resolution (leading to large uncertainties for final ages). Other techniques that have been used on fossil material include electron spin resonance (ESR) and uranium-thorium (U/Th) dating. In common for most techniques is that we cannot date glacial events, but the intervening non-glacial (interstadial, interglacial) episodes. Cosmogenic exposure dating is an exception, which is also able to provide information on the thickness of ice sheets through time. From a geologist’s point of view we will discuss these different techniques, their usefulness and what we can expect of them. Do the dating methods meet our wishes regarding resolution? Are results from different methods comparable? The discussion will be based on our experience from the ongoing SciencePub project (www.ngu.no/sciencepub) and on literature and we will show examples of method applications and comparisons.
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| 8. |
- Alexanderson, Helena, et al.
(författare)
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Inland dunes and cover sand in southern Sweden and Norway – evidence of late glacial and historical aeolian activity
- 2014
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Ingår i: ; , s. 148-148
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Konferensbidrag (refereegranskat)abstract
- Aeolian deposits in Sweden and Norway are poorly explored as environmental records. Many, mainly small, occurrences of windblown sand have been mapped, but few have been investigated in any detail and even fewer have been absolutely dated. Here we present results from a project aiming to determine the timing and magnitude of wind activity in inland settings in southern Sweden and Norway and to better understand the aeolian impact on the landscape. By the end of this year, four areas will have been investigated: three inland dune fields (Bonäsheden, Brattforsheden, Starmoen) and one cover sand site (Blentarp). Our work includes geomorphological mapping, sedimentological and stratigraphic studies, ground penetrating radar investigations, and luminescence and radiocarbon dating. Aeolian sand is in most areas found on top of glaciofluvial sediments that were deposited during deglaciation. Cover sand is generally thin, but can reach 1-2 m thickness in depressions and may contain palaeosols. Most dunes are transverse, and can be used to infer palaeowind directions. Luminescence dating shows that the first aeolian deposition took place during or right after deglaciation, and that the main part of the sand was deposited within a few thousand years after deglaciation. This confirms the supposed deglaciation age of the oldest aeolian deposits based mainly on their geomorphological context. In at least two of the areas (Brattforsheden and Blentarp), aeolian sand has been reactivated at least once during historical times (<500 years ago). This is likely mainly due to human impact, such as expansion of agriculture or mining.
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| 9. |
- Farnsworth, Wesley R., et al.
(författare)
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Dynamic Holocene glacial history of St. Jonsfjorden, Svalbard
- 2017
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Ingår i: Boreas. - : Wiley. - 0300-9483. ; 46:3, s. 585-603
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Tidskriftsartikel (refereegranskat)abstract
- Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord-system on the west coast of Spitsbergen, Svalbard. High-resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord-system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and 14C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0±0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial-Little Ice Age in inner St. Jonsfjorden. The present-day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up-fjord from its Neoglacial maximum extent. Cross-cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break-up of Osbornebreen. Glacial deposits, landforms and their cross-cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.
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| 10. |
- Henriksen, Mona, et al.
(författare)
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Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 92, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsf-jordhallet area, NW Svalbard, have provided new insight on configuration, dynamics, and deglaciation of the Late Weichselian Kongsfjorden ice stream. The minimum Late Weichselian ice surface elevation in Kongsfjorden was >449 m a.s.l. indicating considerably thicker ice and a steeper surface gradient than earlier suggested. For the adjacent inter-ice stream area an even steeper surface slope is reconstructed. The glacial landforms, as well as the surface exposure ages of erratic boulders at different elevations, suggest a gradual lowering of the ice surface. Deglaciation of the higher elevations was probably underway by 20.0 ka. At ca 16.6 ka a large moraine complex ('the Kongsfjorden moraine') was deposited close to the fjord mouth. The shape of the moraines, the steep ice surface gradient, as well as the correlation to fine laminated clay lacking ice rafted debris deposited in the trough beyond the moraine suggest that ice dynamics switched from ice-stream behaviour to a slower flowing outlet (tidewater) glacier. A Younger Dryas or Early Holocene advance of local valley glaciers is shown by moraine lobes cross-cutting the Late Weichselian lateral moraines. (C) 2013 Elsevier Ltd. All rights reserved.
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