| 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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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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| 5. |
- 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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