| 1. |
- Alexanderson, Helena, et al.
(author)
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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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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 6:3-4, s. 326-340
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Journal article (peer-reviewed)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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| 2. |
- Alexanderson, Helena, et al.
(author)
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A short-lived aeolian event during the Early Holocene in southeastern Norway
- 2015
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 30, s. 175-180
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Journal article (peer-reviewed)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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| 3. |
- Alexanderson, Helena, et al.
(author)
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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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In: Quaternary Geochronology. - 1871-1014. ; 80
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Journal article (peer-reviewed)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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| 4. |
- Alexanderson, Helena
(author)
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Luminescence characteristics of Scandinavian quartz, their connection to bedrock provenance and influence on dating results
- 2022
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 69
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Journal article (peer-reviewed)abstract
- The success of optically stimulated luminescence (OSL) dating relies to a large extent on suitable characteristics of the analysed mineral, in this case quartz. Previous OSL dating of Quaternary sediments in Scandinavia has shown that quartz characteristics vary widely across the region, resulting in dating studies with varied success. The aim of this study is to provide an overview of quartz luminescence characteristics in Sweden and Norway, evaluate their effect on dating results and discuss the underlying causes of their variability. A qualitative assessment of luminescence signal characteristics of quartz from Late Quaternary sediment deposits, from a range of geological and geographical settings, has been made by re-analysing data from samples previously dated at the Lund Luminescence Laboratory, Sweden. This allowed a general characterisation of signals and a study of the relationship of these properties to dating result ‘quality’. To quantify the results, selected samples were further analysed with single-grain measurements and with small aliquots. The results show that the average luminescence signal from quartz is fairly dim but dominated by a fast signal component and changes little during measurement. Dose determination precision is ∼4% for 8-mm aliquots and ∼6% for 2-mm aliquots. However, the luminescence signal characteristics have a spatial variation across Sweden and Norway, which appears to correlate with large-scale bedrock units. In areas of sedimentary bedrock outside the Scandinavian mountains and within the Blekinge-Bornholm province, the quartz is brighter and has a stronger fast signal component, while in the Caledonian orogenic belt, the signal is very weak and lacks a fast component. These differences lead to a range in precision of doses, from ∼2% to >40% (for doses in the order of 5–400 Gy), and in the number of rejected aliquots (0–100%) depending on location, but also implies that quartz luminescence can be used as a provenance indicator in part of Sweden and Norway.
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| 5. |
- Alexanderson, Helena, et al.
(author)
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Luminescence signals from modern sediments in a glaciated bay, NW Svalbard
- 2012
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 10, s. 250-256
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Journal article (peer-reviewed)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 degrees C) the ice-proximal sample showed relatively high doses (similar to 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 degrees C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 degrees C) doses were overall much higher (similar to 20-55 Gy), which partly is due to a significant (similar to 12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 degrees C) signal. In this Arctic environment it appears that bleaching is limited in the first similar to 100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 degrees 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 degrees C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin. (C) 2012 Elsevier B.V. All rights reserved.
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| 6. |
- Alexanderson, Helena, et al.
(author)
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Was southern Sweden ice free at 19–25 ka, or were the post LGM glacifluvial sediments incompletely bleached?
- 2007
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 2:1-4, s. 229-236
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Journal article (pop. science, debate, etc.)abstract
- Glacifluvial deposits along an ice-marginal zone in Småland, southern Sweden, have been dated using post-IR blue OSL. To test for incomplete bleaching, we adopted two strategies: analysis of modern analogues and small-aliquot dose distributions. Samples of modern fluvial sediments show no significant incomplete bleaching; they yield equivalent doses of only 0.5-2 Gy (~0.25-4% of our glacifluvial sediment doses). Small-aliquot dose distributions do not provide any evidence for incomplete bleaching. The sediments are believed to have been deposited during deglaciation and appear to fall into two age groups: 19-25 ka (mainly sandur sediments) and 33-73 ka (mainly deltaic sediments). Compared to the expected ages (13-15 ka), even the younger glacifluvial OSL ages appear up to 10 000 years (~25 Gy) too old. The ages are nevertheless stratigraphically consistent and correspond between sites; we deduce that the 19-25 ka ages are true deposition ages. For glacifluvial sedimentation to take place on the South Swedish Upland at this time either a very early deglaciation is required, or alternatively ice-free conditions just prior to the LGM. The deltaic sediments (33-73 ka) were most likely not significantly bleached during deposition and thus they date events prior to the latest ice advance.
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| 7. |
- Allington, Megan L., et al.
(author)
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Constraining the eruption history of Rangitoto volcano, New Zealand, using palaeomagnetic data
- 2023
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In: Quaternary Geochronology. - : Elsevier. - 1871-1014 .- 1878-0350. ; 78
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Journal article (peer-reviewed)abstract
- New Zealand's largest city, Auckland, is situated within the basaltic Auckland Volcanic Field (AVF). Therefore, understanding the eruption history of the local volcanoes in the field is of great importance in order to assess future hazards that they may pose. Rangitoto is the youngest and largest volcano in the AVF, although the timing of the first eruption and the duration of the volcanic activity are still uncertain. Here, we use palaeomagnetic methods to provide additional constraints to the duration of the main shield-building phase of Rangitoto, previously estimated to have lasted either less than 100 years or approximately 1000 years. Lava flow samples from an -140 m length vertically oriented drill core produced 203 palaeoinclinations and 74 palaeointensity estimates. Our results show significant variation in both inclination (up to 30 degrees) and intensities (which fall between 25 and 60 & mu;T; present day field values for Auckland are -55 & mu;T). Potential non-geomagnetic explanations for these variations, including thermochemical processes and rheological deformation are discussed. A statistical model was created to determine the minimum duration for the construction of Rangitoto that is compatible with the variations in the palaeomagnetic data, using prior information about the rate of change of the geomagnetic field. We conclude that the palaeomagnetic data are incompatible with the previously suggested short duration (under 100 years) of the shield-building phase and suggest instead a range of 150-450 years, when also accounting for the available radiocarbon ages. Given these results, this has implications for the timing, and thus impact of possible future eruptions in the AVF.
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| 8. |
- Barsanti, M., et al.
(author)
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Challenges and limitations of the Pb-210 sediment dating method : Results from an IAEA modelling interlaboratory comparison exercise
- 2020
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In: Quaternary Geochronology. - : Elsevier. - 1871-1014 .- 1878-0350. ; 59
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Journal article (peer-reviewed)abstract
- The Pb-210 sediment dating is the most widely used method to determine recent (similar to 100-150 years) chronologies and sediment accumulation rates in aquatic environments and has been used effectively for reconstruction of diverse environmental processes associated with global change. Owing to the relative accessibility of the Pb-210 methodology, many environmental chronologies have been produced, but not always critically assessed. Sometimes, sedimentary processes such as compaction, local mixing, erosion, or episodic sedimentation are not taken into account, nor the validity of the fundamental premises and proper estimation of uncertainties assessed. A Pb-210 dating interlaboratory comparison modelling exercise was designed within the framework of the IAEA (International Atomic Energy Agency) Coordinated Research Project "Study of temporal trends of pollution in selected coastal areas by the application of isotopic and nuclear tools" (CRP K41016), to identify potential problems associated with the use of Pb-210 dating models and to suggest best practices to obtain reliable reconstructions. The exercise involved 14 laboratories worldwide with different levels of expertise in the application of the Pb-210 dating methods. The dating exercise was performed using Pb-210, Ra-226 and Cs-137 activity data from two sediment cores (coastal and lacustrine sediments), and the participants were requested to provide their Pb-210 chronologies based on dating models. This modelling exercise evidenced the limitations and constraints of Pb-210 method when supplementary and validation information is not available. The exercise highlighted the relevance of solid understanding of the fundamentals, assumptions and limitations of the Pb-210 dating method and its validation, and allowed identifying key aspects to improve the reliability of Pb-210 dating process, including: a critical examination and interpretation of the Pb-210 activity depth profile; an appropriate selection of the Pb-210 dating model according to the characteristics of the Pb-210 activity profile and the environmental setting taking into account sediment compaction in the calculations; a sound identification of the Pb-210 equilibrium depth and the estimation of the Pb-210 inventory ensuring the best possible estimation of interpolated Pb-210 values when needed; and the use of independent markers to corroborate the age models.
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| 9. |
- Blomdin, Robin, et al.
(author)
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Timing and dynamics of glaciation in the Ikh Turgen Mountains, Altai region, High Asia
- 2018
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 47, s. 54-71
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Journal article (peer-reviewed)abstract
- Spanning the northern sector of High Asia, the Altai region contains a rich landform record of glaciation. We report the extent, chronologies, and dynamics of two paleoglaciers on opposite flanks of the Ikh Turgen mountains (In Russian: Chikhacheva Range), straddling the border between Russia and Mongolia, using a combination of remote sensing-based glacial geomorphological mapping, 10Be surface exposure dating, and geomorphometric analysis. On the eastern side (Mongolia), the Turgen-Asgat paleoglacier, with its potential for developing a large accumulation area (∼257 km2), expanded 40 km down valley, and mean ages from a latero-frontal moraine indicate deglaciation during marine oxygen isotope stage (MIS) 3 (45.1 ± 1.8 ka, n = 4) and MIS 2 (22.8 ± 3.3 ka, n = 5). These minimum age constraints are consistent with other 10Be glacial chronologies and paleoclimate records from the region, which indicates glacier culmination during cold and wet conditions coinciding with MIS 3 (piedmont-style glaciation; inferred for a few sites across the region) and glacier culmination during cold and dry conditions coinciding with MIS 2 (mainly valley-style glaciation; inferred from several sites across the region). On the western side (Russia), the Boguty paleoglacier had a smaller accumulation area (∼222 km2), and advanced 30 km down valley across a low gradient forefield. Surface exposure ages from two moraine complexes on this side of the mountains exhibit wide scatter (∼14–53 ka, n = 8), making paleoclimate inferences and comparison to other proxies difficult. Ice surface profile reconstructions imply that the two paleoglaciers likely shared an ice divide. © 2018 Elsevier B.V.
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| 10. |
- Blomdin, Robin, et al.
(author)
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Timing of the deglaciation in Southern Patagonia : testing the applicability of k feldspar irsl
- 2012
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 10, s. 264-272
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Journal article (peer-reviewed)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 degrees C following a preheat at 250 degrees 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 similar to 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 (>70 m.a.s.l) were deglaciated at around 22 ka.
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