| 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 multi-method approach to dating middle and late Quaternary high relative sea-level events on NW Svalbard - A case study
- 2011
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 6:3-4, s. 326-340
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Tidskriftsartikel (refereegranskat)abstract
- Waxing and waning ice sheets and changing sea levels have been interpreted from the Quaternary stratigraphic record at Leinstranda, Broggerhalvoya in NW Svalbard. We have identified seven high relative sea-level events, related to glacio-isostatic loading, and separated by at least four glacial events. To establish a chronology for the high sea-level events (interstadials and interglacials) and the intervening glaciations, we have used three different absolute dating methods: optically stimulated luminescence (OSL) of shallow marine deposits, and electron spin resonance (ESR) and radiocarbon (AMS-C-14) dating of fossils contained in these sediments. Of the absolute dating methods, OSL has provided the stratigraphically most consistent dataset and which also matches a biostratigraphically inferred interglacial. The ESR ages of mollusc shells suffer from low precision due to unusually large uranium content in most dated shell samples, which in turn is most likely a result of significant recent uranium enrichment of the sediments. Most radiocarbon ages are non-finite. The results show that the high relative sea-level events range in age from the Saalian sensu lato (>= Marine Isotope Stage, MIS, 6) to the early Holocene (MIS 1), and include events OSL-dated to 185 +/- 8 ka, 129 +/- 10 ka, 99 +/- 8 ka and 36 +/- 3 ka. The methods used by us and by previous investigators of the same site are compared and assessed, and sources of error, accuracy and precision of ages are discussed. (C) 2011 Elsevier B.V. All rights reserved.
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| 5. |
- Alexanderson, Helena, et al.
(författare)
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An Arctic perspective on dating Mid-Late Pleistocene environmental history
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 9-31
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Forskningsöversikt (refereegranskat)abstract
- To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.
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| 6. |
- 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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| 7. |
- Alexanderson, Helena, et al.
(författare)
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Chronology and styles of glaciation in an inter-fjord setting, northwestern Svalbard
- 2011
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 40:1, s. 175-197
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Tidskriftsartikel (refereegranskat)abstract
- A 30-m-thick sedimentary succession at Leinstranda on the southwestern coast of Brøggerhalvøya, northwestern Svalbard, spans the two last glacial–interglacial cycles and reveals information on glacial dynamics, sea-level changes and the timing of these events. We investigated the deposits using standard stratigraphical and sedimentological techniques, together with ground-penetrating radar, and established an absolute chronology based mainly on optically stimulated luminescence dating. We identi?ed facies associations that represent depositional settings related to advancing, overriding and retreating glaciers, marine and littoral conditions and periglacial surfaces. The environmental changes show an approximate cyclicity and reflect glaciations followed by high sea levels and later regression. The luminescence chronology places sea-level highstands at 185±8 ka, 129±10 ka,99±8 ka and 36±3 ka. These ages constrain the timing of recorded glaciations at Leinstranda to prior to c. 190 ka, between c. 170 and c. 140 ka (Late Saalian) and between c. 120 ka and c. 110 ka (Early Weichselian). The glaciations include phases with glaciers from three different source areas. There is no positive evidence for either Middle or Late Weichselian glaciations covering the site, but there are hiatuses at those stratigraphic levels. A high bedrock ridge separates Leinstranda from the palaeo-ice stream in Kongsfjorden, and the deposits at Leinstranda reflect ice-dynamic conditions related to ice-sheet evolution in an inter-fjord area. The environmental information and theabsolute chronology derived from our data allow for an improved correlation with the marine record, and for inferences to be made about the interaction between land, ocean and ice during the last glacial–interglacial cycles.
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| 8. |
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| 9. |
- Alexanderson, Helena, et al.
(författare)
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Sediments of MIS 5e age suggested by new OSL dates from the Skilvika section, west Svalbard
- 2018
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 37:1
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Tidskriftsartikel (refereegranskat)abstract
- The sediment succession at Skilvika, west Svalbard, represents one of the key stratigraphic records of the Late Quaternary palaeoenvironments and glaciation history of the Svalbard/Barents Sea area. A formation of raised marine sediments, interfingering with and capped by glacial deposits of local origin, have previously been assumed to be of an Early Weichselian age, likely marine isotope stage (MIS) 5c. Here we present a new series of optically stimulated luminescence (OSL) ages that suggest the events took place in MIS 5e. This advocates a revision of the correlation with other key stratigraphic sites on Svalbard.
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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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