| 1. |
- Alexanderson, Helena, et al.
(författare)
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Coupled luminescence and cosmogenic nuclide dating of postglacial deflation surfaces and sand drift on a raised ice-contact delta at Veinge, SW Sweden
- 2024
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Ingår i: Quaternary Geochronology. - 1871-1014. ; 80
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Tidskriftsartikel (refereegranskat)abstract
- Wind-abraded cobbles (ventifacts) and aeolian sand are known from the sandy-gravelly coastal areas of south-western Sweden, especially in association with raised deltas. Ventifacts are recorded on at least two different stratigraphic levels, at some sites atop glaciofluvial sediment, at other sites atop littoral deposits, and in some places at both levels, while aeolian sand usually forms a surficial cover. The formation of ventifacts has usually been coupled to abrasion due to katabatic winds from the retreating ice sheet or with periglacial climate during the Younger Dryas stadial (12.8–11.7 ka).To determine the timing of these deflation events, we have applied a combination of dating methods to ventifacts and associated sediments on top of an ice-contact delta at Veinge, south-western Sweden. Quartz and feldspar luminescence dating as well as portable luminescence profiling has been used for littoral and aeolian sediments over- and underlying deflation surfaces, while rock surface luminescence burial dating and paired 14C–10Be cosmogenic nuclide dating were conducted on ventifacts. The results show that a first deflation event occurred c. 16.5 ka, just after deglaciation and prior to a regional transgression that peaked around 15.7 ka. At 12.4–11.4 ka, during the Younger Dryas stadial, a new set of ventifacts formed on the surface of the exposed littoral sands and gravels. Some wind abrasion also occurred in the early Holocene, but at c. 8.5 ka the surface was covered by aeolian sand, up to 2.5 m thick.The combination of different dating methods have allowed us to draw more informed conclusions on the timing and duration of these wind abrasion/transport events than would have been possible from the use of only single-method dating. It has also made it possible to infer some environmental conditions during deposition. For example, both glaciofluvial and littoral deposits show evidence of incomplete bleaching of the luminescence signal. This suggests short subaerial transport and brief reworking by waves, respectively, though bleaching conditions improved during shore regression. Rock surface burial luminescence profiles reveal that some ventifacts were repeatedly exposed, but that later event(s) were shorter in duration as indicated by quartz-feldspar age comparisons.
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| 2. |
- Alexanderson, Helena, et al.
(författare)
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Late glacial to Early Holocene deflation events and aeolian deposition on a raised ice-contact delta at Veinge, SW Sweden
- 2024
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Wind-abraded cobbles (ventifacts) and aeolian sand are known from the sandy-gravelly coastal areas of south-western Sweden, especially in association with raised deltas. Ventifacts are recorded on at least two different stratigraphic levels, on top of glaciofluvial sediment and/or on top of littoral deposits, while aeolian sand usually forms a surficial cover. The formation of ventifacts has usually been coupled to abrasion due to katabatic winds from the retreating ice sheet or with periglacial climate during the Younger Dryas stadial (12.8-11.6 ka). However, there are very few absolute ages, and the timing of wind deflation has recently been challenged and proposed to be much older (110-70 ka). To determine the timing of these deflation events, we have applied a combination of dating methods to ventifacts and associated sediments on top of an ice-contact delta at Veinge, south-western Sweden. Quartz and feldspar luminescence dating as well as portable luminescence profiling has been used for the over- and underlying sediments, while rock surface luminescence burial dating and paired 14C10Be cosmogenic nuclide dating were done on ventifacts. The results show that a first deflation event occurred c. 16.5 ka, just after deglaciation and prior to a regional transgression that peaked around 15.7 ka. At 12.4-11.4 ka, during and just after the Younger Dryas stadial, a new set of ventifacts formed on the surface of the exposed littoral sands and gravels. Some wind abrasion also occurred in the early Holocene, but at c. 8.5 ka the surface was covered by aeolian sand, up to 2.5 m thick. The combination of dating methods allowed us to extract more information about the timing and duration of these wind abrasion/transport events than we would have if only a single method had been used, and it is also possible to infer some environmental conditions. For example, both glaciofluvial and littoral deposits show evidence of incomplete bleaching of the luminescence signal. This suggests short subaerial transport and brief reworking by waves, respectively, though bleaching conditions improved during shore regression. Rock surface burial luminescence profiles reveal that some ventifacts were repeatedly exposed, but that later event(s) were shorter in duration as indicated by quartz-feldspar age comparisons.
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| 3. |
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| 4. |
- Anjar, Johanna, et al.
(författare)
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MIS 3 marine and lacustrine sediments at Kriegers Flak, southwestern Baltic Sea
- 2010
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 39:2, s. 360-366
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Tidskriftsartikel (refereegranskat)abstract
- Sediment cores from the Kriegers Flak area in the southwestern Baltic Sea show a distinct lithological succession, starting with a lower diamict that is overlain by a c. 10 m thick clay unit that contains peat, gyttja and other organic remains. On top follows an upper diamict that is inter-layered with sorted sediments and overlain by an upward-coarsening sequence with molluscs. In this paper we focus on the clay unit, which has been subdivided into three subunits: (A) lower clay with benthic foraminifera and with diamict beds in the lower part; (B) thin beds of gyttja and peat, which have been radiocarbon-dated to 31-35 14C kyr BP (c. 36-41 cal. kyr BP); and (C) upper clay unit. Based on the preliminary results we suggest the following depositional model: fine-grained sediments interbedded with diamict in the lower part (subunit A) were deposited in a brackish basin during a retreat of the Scandinavian Ice Sheet, probably during the Middle Weichselian. Around 40 kyr BP the area turned into a wetland with small ponds (subunit B). A transgression, possibly caused by the damming of the Baltic Basin during the Kattegat advance at 29 kyr BP, led to the deposition of massive clay (subunit C). The data presented here provide new information about the paleoenvironmental changes occurring in the Baltic Basin following the Middle Weichselian glaciation.
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| 5. |
- Knudsen, Karen Luise, et al.
(författare)
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Marine glacial and interglacial stratigraphy in Vendsyssel, northern Denmark: foraminifera and stable isotopes
- 2009
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 38:4, s. 787-810
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Forskningsöversikt (refereegranskat)abstract
- The marine Quaternary of Vendsyssel has been studied in a series of new boreholes in the area, and the climatic development is discussed on the basis of foraminiferal assemblages and stable isotopes. The foraminiferal zones are correlated with previously published records from northern Denmark, and the spatial local and regional distribution is discussed in details based on the new evidence. The new data show that the marine sedimentation in Vendsyssel was not continuous from the Late Saalian to the Middle Weichselian, as previously thought. For example, there is indication of a hiatus at our key site, Asted Vest in the central part of Vendsyssel, at the transition between regional foraminiferal zones N4 and N3, i.e. at the Late Saalian (MIS 6) - Eemian (MIS 5e) transition. The hitherto most complete Early Weichselian succession (zone N2) in Vendsyssel is presented from Asted Vest. Deposits from the Early Weichselian sea-level lowstands (MIS 5d and 5b) may, however, be missing in parts of the area. Two major breaks in the marine deposition during the Middle Weichselian represent glacial advances into northern Denmark. The first event occurred just after deposition of the regional foraminiferal zone N2 (late MIS 4), and the second event in the middle part of zone N1 (early MIS 3). Zone N1 is succeeded by a series of non-marine units deposited during the sea-level lowstand of the Weichselian maximum glaciation (late MIS 3 and MIS 2), including deeply incised tunnel valleys, which have been refilled with non-marine sediments during the Late Weichselian. Vendsyssel was inundated by the sea again during the Late Weichselian, at c. 18 kyr BP. Subsequently, the marine conditions were gradually changed by forced regression caused by local isostatic uplift, and around the Weichselian-Holocene transition most of Vendsyssel was above sea level. A continuous deposition across the Late Weichselian-Holocene boundary only occurred at relatively deep sites such as Skagen. The environmental and climatic indications for Vendsyssel are in accordance with the global sea-level curve, and the Quaternary record is correlated with the oxygen isotope record from the NorthGRIP ice core, as well as the marine isotope stages.
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| 6. |
- Knudsen, Karen Luise, et al.
(författare)
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Quaternary of Vendsyssel, northern Denmark - Introduction
- 2009
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 38:4, s. 730-731
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Tidskriftsartikel (refereegranskat)abstract
- Knudsen, K. L. & Larsen, N. K. 2009: Quaternary of Vendsyssel, northern Denmark - Introduction. Boreas, 10.1111/j.1502-3885.2009.00100.x. ISSN 0300-9483.
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| 7. |
- Krohn, Charlotte Fog, et al.
(författare)
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Litho- and chronostratigraphy of the Late Weichselian in Vendsyssel, northern Denmark, with special emphasis on tunnel-valley infill in relation to a receding ice margin
- 2009
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 38:4, s. 811-833
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Tidskriftsartikel (refereegranskat)abstract
- Lithostratigraphy and chronostratigraphy of samples from 18 deep boreholes in Vendsyssel have resulted in new insight into the Late Weichselian glaciation history of northern Denmark. Prior to the Late Weichselian Main advance c. 23-21 kyr BP, Vendsyssel was part of an ice-dammed lake where the Ribjerg Formation was deposited c. 27-23 kyr BP. The timing of the Late Weichselian deglaciation is well constrained by the Main advance and the Lateglacial marine inundation c. 18 kyr BP, and thus spans only a few millennia. Rapid deposition of more than 200 m of sediments took place mainly in a highly dynamic proglacial and ice-marginal environment during the overall ice recession. Mean retreat rates have been estimated as 45-50 m/yr in Vendsyssel with significantly higher retreat rates between periods of standstill and re-advance. The deglaciation commenced in Vendsyssel c. 20 kyr BP, and the Troldbjerg Formation was deposited c. 20-19 kyr BP in a large ice-dammed lake in front of the receding ice sheet, partly as glaciolacustrine sediments and partly as rapid and focused sedimentation in prominent ice-contact fans, which make up the Jyske As and Hammer Bakker moraines. In the northern part of central Vendsyssel, at least four generations of north-south orientated tunnel valleys are identified, each generation related to a recessional ice margin. This initial deglaciation was interrupted by a major re-advance from the east c. 19 kyr BP, which covered most of Vendsyssel. An ice-dammed lake formed in front of the ice sheet as it retreated towards the east; the Morild Formation was deposited here c. 19-18 kyr BP. Related to this stage of deglaciation, eight ice-marginal positions have been identified based on the distribution of large tunnel-valley systems and pronounced recessional moraines. The Morild Formation consists of glaciolacustrine sediments, including the sediment infill of more than 190 m deep tunnel valleys, as well as the sediments in recessional moraines, which were formed as ice-contact sedimentary ridges, possibly in combination with glaciotectonic deformation. The character of the tunnel-valley infill sediments was determined by proximity to the ice margin. During episodes of rapid retreat of the ice margin, tunnel valleys were quickly abandoned and filled with fine-grained sediments in a distal setting. During slow retreat of the ice margin, tunnel valleys were filled in an ice-proximal environment, and the infill consists of alternating layers of fine- to coarse-grained sediments. At c. 18 kyr BP, Vendsyssel was inundated by the sea, when the Norwegian Channel Ice Stream broke up, and a succession of marine sediments (Vendsyssel Formation) was deposited during a forced regression.
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| 8. |
- Larsen, Nicolaj Krog, et al.
(författare)
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Debris entrainment by basal freeze-on and thrusting during the 1995-1998 surge of Kuannersuit Glacier on Disko Island, west Greenland
- 2010
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Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 35:5, s. 561-574
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Tidskriftsartikel (refereegranskat)abstract
- Kuannersuit Glacier, a valley glacier on Disko Island in west Greenland, experienced a major surge from 1995 to 1998 where the glacier advanced 10.5 km and produced a similar to 65 m thick stacked sequence of debris-rich basal ice and meteoric glacier ice. The aim of this study is to describe the tectonic evolution of large englacial thrusts and the processes of basal ice formation using a multiproxy approach including structural glaciology, stable isotope composition (delta O-18 and delta D), sedimentology and ground-penetrating radar. We argue that the major debris layers that can be traced in the terminal zone represent englacial thrusts that were formed early during the surge. Thrust overthrow was at least 200-300 m and this lead to a 30 m thick repetition of basal ice at the ice margin. It is assumed that the englacial thrusting was initiated at the transition between warm ice from the interior and the cold snout. The basal debris-rich ice was mainly formed after the thrusting phase. Two sub-facies of stratified basal ice have been identified; a lower massive ice facies (S-M) composed of frozen diamict enriched with heavy stable isotopes overlain by laminated ice facies (S-L) consisting of millimetre thick lamina of alternating debris-poor and debris-rich ice. We interpret the stratified basal ice as a continuum formed mainly by freeze-on processes and localized regelation. First laminated basal ice is formed and as meltwater is depleted more sediment is entrained and finally the glacier freezes to the base and massive diamict is frozen-on. The increased ability to entrain sediments may partly be associated with higher basal freezing rates enhanced by loss of frictional heat from cessation of fast flow and conductive cooling through a thin heavily crevassed ice during the final phase of the glacier surge. The dispersed basal ice facies (D) was mainly formed by secondary processes where fine-grained sediment is mobilized in the vein system of ice. Our results have important implications for understanding the significance of basal ice formation and englacial thrusting beneath fast-flowing glaciers and it provides new information about the development of landforms during a glacier surge. Copyright (C) 2010 John Wiley & Sons, Ltd.
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| 9. |
- Larsen, Nicolaj Krog, et al.
(författare)
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Investigating the last deglaciation of the Scandinavian Ice Sheet in southwest Sweden with Be-10 exposure dating
- 2012
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 27:2, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- In this study we have obtained 17 cosmogenic exposure ages from three well-developed moraine systems - Halland Coastal Moraines (HCM), Goteborg Moraine (GM) and Levene Moraine (LM) - which were formed during the last deglaciation in southwest Sweden by the Scandinavian Ice Sheet (SIS). The inferred ages of the inner HCM, GM and LM are 16.7 +/- 1.6, 16.1 +/- 1.4 and 13.6 +/- 1.4 ka, respectively, which is slightly older than previous estimates of the deglaciation based on the minimum limiting radiocarbon ages and pollen stratigraphy. During this short interval from 16.7 +/- 1.6 to 13.6 +/- 1.4 ka a large part (100-125 km) of the marine-based sector of the SIS in southwest Sweden was deglaciated, giving an average ice margin retreat between 20 to 50 m a(-1). The inception of the deglaciation pre-dated the Bolling/Allerod warming, the rapid sea level rise at 14.6 cal. ka BP and the first inflow of warm Atlantic waters into Skagerrak. We suggest that ice retreat in southwest Sweden is mainly a dynamical response governed by the disintegration of the Norwegian Channel Ice Stream and not primarily driven by climatic changes. Copyright (c) 2011 John Wiley & Sons, Ltd.
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| 10. |
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