Helena Alexanderson | Lund University (original) (raw)

Papers by Helena Alexanderson

Research paper thumbnail of Pilgrimstad revisited–a multi‐proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden

Boreas, Apr 1, 2011

The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ... more The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice-free/ice-covered intervals during the Early and Middle Weichselian. Multi-proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between $80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and 14C dating, and macrofossil, siliceous microfossil and chironomid analyses shows:(i) a lower succession of glaciofluvial/fluvial, lacustrine ...

Research paper thumbnail of Sedimentary features reveal transport paths for Holocene sediments on the Kristianstad coastal plain, SE Sweden

Research paper thumbnail of Luminescence dating of aeolian–coastal events on the Kristianstad plain, SE Sweden

Research paper thumbnail of The Taimyr Peninsula and the Severnaya Zemlya archipelago, Arctic Russia: a synthesis of glacial history and palaeo-environmental change during the Last Glacial cycle (MIS 5e–2)

Quaternary Science Reviews, 2015

ABSTRACT We reconstruct the Last Glacial cycle glacial history of the Taimyr Peninsula area.•The ... more ABSTRACT We reconstruct the Last Glacial cycle glacial history of the Taimyr Peninsula area.•The reconstruction is based on 39 described stratigraphies.•Three ice sheets advances of successively smaller dimensions are recorded.•We record major isostatic imprint, resulting in high-level marine environments.•During LGM minor parts of Taimyr was glaciated, instead being a terrestrial tundra.

Research paper thumbnail of A short-lived aeolian event during the Early Holocene in southeastern Norway

Quaternary Geochronology, 2015

ABSTRACT The Starmoen dune field is part of a larger aeolian system in the Jømna and Glomma river... more ABSTRACT The Starmoen dune field is part of a larger aeolian system in the Jømna 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 ∼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.

Research paper thumbnail of The Late Weichselian Kongsfjorden ice stream, NW Svalbard: surface exposure age constraints on ice dynamics and retreat

Research paper thumbnail of Using cosmogenic isotopes to reconcile two contrasting hypotheses for ice extent in East Greenland during the last glaciation

Research paper thumbnail of Sol, sand och strålning: ett recept för att åldersbestämma istiden

Research paper thumbnail of Securing transferable skills training in geology education

Research paper thumbnail of Shallow hydrostratigraphy in an arsenic affected region of Bengal Basin: Implication for targeting safe aquifers for drinking water supply

Science of The Total Environment, 2014

To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigate... more To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigated the shallow hydrostratigraphic framework over an area of 100 km(2) at Chakdaha Block of Nadia District, West Bengal. Drilling of 29 boreholes and subsequent hydrostratigraphic modeling has identified three types of aquifer within 50 m below ground level (bgl). Aquifer-1 represents a thick paleochannel sequence, deposited parallel to the River Hooghly and Ichamati. Aquifer-2 is formed locally within the overbank deposits in the central floodplain area and its vertical extension is strictly limited to 25 m bgl. Aquifer-3 is distributed underneath the overbank deposits and represents an interfluvial aquifer of the area. Aquifer-3 is of Pleistocene age (~70 ka), while aquifer-1 and 2 represent the Holocene deposits (age <9.51 ka), indicating that there was a major hiatus in the sediment deposition after depositing the aquifer-3. Over the area, aquifer-3 is markedly separated from the overlying Holocene deposits by successive upward sequences of brown and olive to pale blue impervious clay layers. The groundwater quality is very much similar in aquifer-1 and 2, where the concentration of As and Fe very commonly exceeds 10 μg/L and 5 mg/L, respectively. Based on similar sediment color, these two aquifers have jointly been designated as the gray sand aquifer (GSA), which constitutes 40% (1.84×10(9) m(3)) of the total drilled volume (4.65×10(9) m(3)). In aquifer-3, the concentration of As and Fe is very low, mostly <2 μg/L and 1mg/L, respectively. This aquifer has been designated as the brown sand aquifer (BSA) according to color of the aquifer materials and represents 10% (4.8×10(8) m(3)) of the total drilled volume. This study further documents that though the concentration of As is very low at BSA, the concentration of Mn often exceeds the drinking water guidelines.

Research paper thumbnail of An Arctic perspective on dating Mid-Late Pleistocene environmental history

Quaternary Science Reviews, 2014

Research paper thumbnail of Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard

Quaternary Science Reviews, 2014

Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsf... more Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsfjordhallet 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.

Research paper thumbnail of Landscape imprints of changing glacial regimes during ice-sheet build-up and decay: a conceptual model from Svalbard

Quaternary Science Reviews, 2014

The behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted. ... more The behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted. Fjords, which were temporarily occupied by fast flowing ice-streams during major glaciations, and inter-fjord areas, which were covered by less active ice, show different signatures of past glaciations. The land and marine records of glaciations over the western Svalbard fjord region have been extensively studied during the last few decades. We have re-examined ice-flow records from stratigraphic and geomorphic settings, and propose a succession of ice-flow events that occurred repeatedly over glacial cycles: the maximum, the transitional, and the local flow style. The differently topographically constrained segments of the ice-sheet switched behaviour as glacial dynamics developed through each glacial cycle. These segments, as well as the different flow styles, are reflected differently in the offshore stratigraphic record. We propose that the glacial geomorphological signatures in the inter ice-stream areas mostly developed under warm-based conditions during a late phase of the glaciations, and that the overall glacial imprints in the landscape are strongly biased towards the youngest events.

Research paper thumbnail of Late Quaternary ice sheet history of northern Eurasia

Quaternary Science Reviews, 2004

The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1... more The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100-80 ka), (3) the Middle Weichselian (60-50 ka) and (4) the Late Weichselian (25-15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic-and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90-80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60-50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the ARTICLE IN PRESS

Research paper thumbnail of The DeKalb mounds of northeastern Illinois as archives of deglacial history and postglacial environments

Quaternary Research, 2010

... A second variety occurs in areas underlain by finer-grained silty clay diamicton. These mound... more ... A second variety occurs in areas underlain by finer-grained silty clay diamicton. These mounds are formed in part by diamicton that was squeezed (“pressed”) into the void formed by glacialkarst; any lake sediment is thin (< 3 m), and fossil preservation sporadic. Methods. ...

Research paper thumbnail of Was southern Sweden ice free at 19–25ka, or were the post LGM glacifluvial sediments incompletely bleached?

Quaternary Geochronology, 2007

ABSTRACT

Research paper thumbnail of Timing of the deglaciation in southern Patagonia: Testing the applicability of K-Feldspar IRSL

Quaternary Geochronology, 2012

ABSTRACT The timing of the ice margin retreat of the Late Glacial Patagonian Ice Sheet (PIS) in s... more ABSTRACT The timing of the ice margin retreat of the Late Glacial Patagonian Ice Sheet (PIS) in southern Patagonia has been the object of discussion for many years. In order to resolve questions about the complex response of the PIS to past climate change, any geological interpretation and data modelling need evaluation against an absolute chronology. The aim of this project is to investigate the applicability of OSL dating to sediments from southern Patagonia; in particular, we examine the dating potential of K-feldspar IRSL signals. Samples were collected from landforms interpreted as being deposited during deglaciation of the PIS, with an expected age range of 17 and 22 ka, and from recently deposited sediment. We measure small aliquots and single grain distributions using an IR50 SAR protocol with IRSL stimulation at 50 °C following a preheat at 250 °C (held for 60 s). Uncertainties are assigned to our individual dose estimates based on the over-dispersion (OD) observed in laboratory gamma dose recovery experiments (22% for small aliquots and 18% for single grains). Then the possible effects of incomplete bleaching and differential fading are examined. For our natural samples we observe environmental ODs between 30 and 130% and mean residual doses between ∼30 and 80 Gy. Minimum age models are used to identify the part of the dose population that is most likely to have been well-bleached and results from these models are compared. The models give ages that are consistent with each other; this may imply that they successfully identified the fully-bleached grains in the distributions, although there are some discrepancies between our small aliquot and single grain data. We observe large fading rates (on average 7.9 ± 0.6%/decade for large aliquots) but nevertheless a comparison of our fading corrected ages with the expected age range shows that 2 out of 3 ages are consistent with geological interpretation and an established radiocarbon and cosmogenic nuclide chronology. We conclude that these investigations suggest that fading corrections can be based on laboratory average small aliquot/single grain fading rates. The third age is supported by an alternative geological interpretation, and the two ages consistent with the existing chronology imply that in the Strait of the Magellan the hills of the Brunswick peninsula (&gt;70 m.a.s.l) were deglaciated at around 22 ka.

Research paper thumbnail of Luminescence signals from modern sediments in a glaciated bay, NW Svalbard

Quaternary Geochronology, 2012

ABSTRACT Landforming processes are highly active in the Arctic, and luminescence dating can be us... more ABSTRACT Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores.Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 °C) the ice-proximal sample showed relatively high doses (∼12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 °C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 °C) doses were overall much higher (∼20–55 Gy), which partly is due to a significant (∼12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 °C) signal.In this Arctic environment it appears that bleaching is limited in the first ∼100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 °C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 °C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin.

Research paper thumbnail of Coastal glaciers advanced onto Jameson Land, East Greenland during the late glacial–early Holocene Milne Land Stade

Research paper thumbnail of Sub-till glaciofluvial sediments at Hultsfred, South Swedish Upland

GFF, 2010

... 508134 Helena Alexanderson a * pages 153-159. ... Clastic dykes with sorted and laminated sed... more ... 508134 Helena Alexanderson a * pages 153-159. ... Clastic dykes with sorted and laminated sediments are by Larsen &amp; Mangerud (199225. Larsen, E. and Mangerud, J. 1992. Subglacially formed clastic dikes. ... (200828. Lindén, M., Möller, P. and Adrielsson, L. 2008. ...

Research paper thumbnail of Pilgrimstad revisited–a multi‐proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden

Boreas, Apr 1, 2011

The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ... more The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice-free/ice-covered intervals during the Early and Middle Weichselian. Multi-proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between $80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and 14C dating, and macrofossil, siliceous microfossil and chironomid analyses shows:(i) a lower succession of glaciofluvial/fluvial, lacustrine ...

Research paper thumbnail of Sedimentary features reveal transport paths for Holocene sediments on the Kristianstad coastal plain, SE Sweden

Research paper thumbnail of Luminescence dating of aeolian–coastal events on the Kristianstad plain, SE Sweden

Research paper thumbnail of The Taimyr Peninsula and the Severnaya Zemlya archipelago, Arctic Russia: a synthesis of glacial history and palaeo-environmental change during the Last Glacial cycle (MIS 5e–2)

Quaternary Science Reviews, 2015

ABSTRACT We reconstruct the Last Glacial cycle glacial history of the Taimyr Peninsula area.•The ... more ABSTRACT We reconstruct the Last Glacial cycle glacial history of the Taimyr Peninsula area.•The reconstruction is based on 39 described stratigraphies.•Three ice sheets advances of successively smaller dimensions are recorded.•We record major isostatic imprint, resulting in high-level marine environments.•During LGM minor parts of Taimyr was glaciated, instead being a terrestrial tundra.

Research paper thumbnail of A short-lived aeolian event during the Early Holocene in southeastern Norway

Quaternary Geochronology, 2015

ABSTRACT The Starmoen dune field is part of a larger aeolian system in the Jømna and Glomma river... more ABSTRACT The Starmoen dune field is part of a larger aeolian system in the Jømna 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 ∼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.

Research paper thumbnail of The Late Weichselian Kongsfjorden ice stream, NW Svalbard: surface exposure age constraints on ice dynamics and retreat

Research paper thumbnail of Using cosmogenic isotopes to reconcile two contrasting hypotheses for ice extent in East Greenland during the last glaciation

Research paper thumbnail of Sol, sand och strålning: ett recept för att åldersbestämma istiden

Research paper thumbnail of Securing transferable skills training in geology education

Research paper thumbnail of Shallow hydrostratigraphy in an arsenic affected region of Bengal Basin: Implication for targeting safe aquifers for drinking water supply

Science of The Total Environment, 2014

To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigate... more To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigated the shallow hydrostratigraphic framework over an area of 100 km(2) at Chakdaha Block of Nadia District, West Bengal. Drilling of 29 boreholes and subsequent hydrostratigraphic modeling has identified three types of aquifer within 50 m below ground level (bgl). Aquifer-1 represents a thick paleochannel sequence, deposited parallel to the River Hooghly and Ichamati. Aquifer-2 is formed locally within the overbank deposits in the central floodplain area and its vertical extension is strictly limited to 25 m bgl. Aquifer-3 is distributed underneath the overbank deposits and represents an interfluvial aquifer of the area. Aquifer-3 is of Pleistocene age (~70 ka), while aquifer-1 and 2 represent the Holocene deposits (age &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;9.51 ka), indicating that there was a major hiatus in the sediment deposition after depositing the aquifer-3. Over the area, aquifer-3 is markedly separated from the overlying Holocene deposits by successive upward sequences of brown and olive to pale blue impervious clay layers. The groundwater quality is very much similar in aquifer-1 and 2, where the concentration of As and Fe very commonly exceeds 10 μg/L and 5 mg/L, respectively. Based on similar sediment color, these two aquifers have jointly been designated as the gray sand aquifer (GSA), which constitutes 40% (1.84×10(9) m(3)) of the total drilled volume (4.65×10(9) m(3)). In aquifer-3, the concentration of As and Fe is very low, mostly &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;2 μg/L and 1mg/L, respectively. This aquifer has been designated as the brown sand aquifer (BSA) according to color of the aquifer materials and represents 10% (4.8×10(8) m(3)) of the total drilled volume. This study further documents that though the concentration of As is very low at BSA, the concentration of Mn often exceeds the drinking water guidelines.

Research paper thumbnail of An Arctic perspective on dating Mid-Late Pleistocene environmental history

Quaternary Science Reviews, 2014

Research paper thumbnail of Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard

Quaternary Science Reviews, 2014

Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsf... more Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsfjordhallet 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.

Research paper thumbnail of Landscape imprints of changing glacial regimes during ice-sheet build-up and decay: a conceptual model from Svalbard

Quaternary Science Reviews, 2014

The behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted. ... more The behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted. Fjords, which were temporarily occupied by fast flowing ice-streams during major glaciations, and inter-fjord areas, which were covered by less active ice, show different signatures of past glaciations. The land and marine records of glaciations over the western Svalbard fjord region have been extensively studied during the last few decades. We have re-examined ice-flow records from stratigraphic and geomorphic settings, and propose a succession of ice-flow events that occurred repeatedly over glacial cycles: the maximum, the transitional, and the local flow style. The differently topographically constrained segments of the ice-sheet switched behaviour as glacial dynamics developed through each glacial cycle. These segments, as well as the different flow styles, are reflected differently in the offshore stratigraphic record. We propose that the glacial geomorphological signatures in the inter ice-stream areas mostly developed under warm-based conditions during a late phase of the glaciations, and that the overall glacial imprints in the landscape are strongly biased towards the youngest events.

Research paper thumbnail of Late Quaternary ice sheet history of northern Eurasia

Quaternary Science Reviews, 2004

The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1... more The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100-80 ka), (3) the Middle Weichselian (60-50 ka) and (4) the Late Weichselian (25-15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic-and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90-80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60-50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the ARTICLE IN PRESS

Research paper thumbnail of The DeKalb mounds of northeastern Illinois as archives of deglacial history and postglacial environments

Quaternary Research, 2010

... A second variety occurs in areas underlain by finer-grained silty clay diamicton. These mound... more ... A second variety occurs in areas underlain by finer-grained silty clay diamicton. These mounds are formed in part by diamicton that was squeezed (“pressed”) into the void formed by glacialkarst; any lake sediment is thin (< 3 m), and fossil preservation sporadic. Methods. ...

Research paper thumbnail of Was southern Sweden ice free at 19–25ka, or were the post LGM glacifluvial sediments incompletely bleached?

Quaternary Geochronology, 2007

ABSTRACT

Research paper thumbnail of Timing of the deglaciation in southern Patagonia: Testing the applicability of K-Feldspar IRSL

Quaternary Geochronology, 2012

ABSTRACT The timing of the ice margin retreat of the Late Glacial Patagonian Ice Sheet (PIS) in s... more ABSTRACT The timing of the ice margin retreat of the Late Glacial Patagonian Ice Sheet (PIS) in southern Patagonia has been the object of discussion for many years. In order to resolve questions about the complex response of the PIS to past climate change, any geological interpretation and data modelling need evaluation against an absolute chronology. The aim of this project is to investigate the applicability of OSL dating to sediments from southern Patagonia; in particular, we examine the dating potential of K-feldspar IRSL signals. Samples were collected from landforms interpreted as being deposited during deglaciation of the PIS, with an expected age range of 17 and 22 ka, and from recently deposited sediment. We measure small aliquots and single grain distributions using an IR50 SAR protocol with IRSL stimulation at 50 °C following a preheat at 250 °C (held for 60 s). Uncertainties are assigned to our individual dose estimates based on the over-dispersion (OD) observed in laboratory gamma dose recovery experiments (22% for small aliquots and 18% for single grains). Then the possible effects of incomplete bleaching and differential fading are examined. For our natural samples we observe environmental ODs between 30 and 130% and mean residual doses between ∼30 and 80 Gy. Minimum age models are used to identify the part of the dose population that is most likely to have been well-bleached and results from these models are compared. The models give ages that are consistent with each other; this may imply that they successfully identified the fully-bleached grains in the distributions, although there are some discrepancies between our small aliquot and single grain data. We observe large fading rates (on average 7.9 ± 0.6%/decade for large aliquots) but nevertheless a comparison of our fading corrected ages with the expected age range shows that 2 out of 3 ages are consistent with geological interpretation and an established radiocarbon and cosmogenic nuclide chronology. We conclude that these investigations suggest that fading corrections can be based on laboratory average small aliquot/single grain fading rates. The third age is supported by an alternative geological interpretation, and the two ages consistent with the existing chronology imply that in the Strait of the Magellan the hills of the Brunswick peninsula (&gt;70 m.a.s.l) were deglaciated at around 22 ka.

Research paper thumbnail of Luminescence signals from modern sediments in a glaciated bay, NW Svalbard

Quaternary Geochronology, 2012

ABSTRACT Landforming processes are highly active in the Arctic, and luminescence dating can be us... more ABSTRACT Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores.Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 °C) the ice-proximal sample showed relatively high doses (∼12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 °C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 °C) doses were overall much higher (∼20–55 Gy), which partly is due to a significant (∼12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 °C) signal.In this Arctic environment it appears that bleaching is limited in the first ∼100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 °C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 °C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin.

Research paper thumbnail of Coastal glaciers advanced onto Jameson Land, East Greenland during the late glacial–early Holocene Milne Land Stade

Research paper thumbnail of Sub-till glaciofluvial sediments at Hultsfred, South Swedish Upland

GFF, 2010

... 508134 Helena Alexanderson a * pages 153-159. ... Clastic dykes with sorted and laminated sed... more ... 508134 Helena Alexanderson a * pages 153-159. ... Clastic dykes with sorted and laminated sediments are by Larsen &amp; Mangerud (199225. Larsen, E. and Mangerud, J. 1992. Subglacially formed clastic dikes. ... (200828. Lindén, M., Möller, P. and Adrielsson, L. 2008. ...