| 1. |
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| 2. |
- Blaauw, Maarten, 1974-, et al.
(författare)
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Were last glacial climate events simultaneous between Greenland and western Europe?
- 2008
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Ingår i: Climate of the Past Discussions. - 1814-9359. ; 4, s. 1203-1217
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Tidskriftsartikel (refereegranskat)abstract
- During the last glacial period, several large abrupt climate fluctuations took place on the Greenland ice cap and elsewhere. Often these Dansgaard/Oeschger events are assumed to have been synchronous, and then used as tie-points to link chronologies between the proxy archives. However, if temporally separate events are lumped into one illusionary event, climatic interpretations of the tuned events will obviously be flawed. Here, we compare Dansgaard/Oeschger-type events in a well-dated record from south-eastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, tuning of proxy archives should be avoided.
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| 3. |
- Dehnert, Andreas, et al.
(författare)
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Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany
- 2011
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Ingår i: Quaternary Geochronology. - 1871-1014 .- 1878-0350.
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Tidskriftsartikel (refereegranskat)abstract
- Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to PlioePleistocene fluvial successionsfrom the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1)measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrationsbased on a first-order conceptualisation of the geological context and the principal succession ofdepositions and subsequent erosional and burial phases, and (3) using parameter estimation to identifyvalues for the a priori unknown model parameters (burial age, initial nuclide concentrations, terraceerosion rates) that result in minimal disagreement between hypothetical and measured nuclideconcentrations.
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| 4. |
- Eccleshall, Sarah V., et al.
(författare)
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Constraining the chronology of Pleistocene glaciations on Svalbard: Kapp Ekholm re-visited
- 2016
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45:4, s. 790-803
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Collegium Boreas. Published by John Wiley & Sons LtdThe Kapp Ekholm site, in central Spitsbergen, shows alternating units of glaciomarine sandy silt and diamicton representing three glacial cycles and is key in reconstructing the Late Pleistocene glacial history of Svalbard. Part of the site is reinvestigated here by focusing on re-dating two units (B and F) interpreted as interglacial/interstadial glaciomarine deposits, in order to constrain the controversial chronology. A combination of Optical Stimulated Luminescence (OSL) on quartz, infrared stimulated luminescence with a 50°C readout temperature (IRSL50) and post infrared-infrared stimulated luminescence (pIR), both on feldspar, was applied. While Formation B was beyond the dateable range of OSL, IRSL50 and pIR ages lead to the conclusion that this unit represents the Last Interglacial, Marine Isotope Stage (MIS) 5e, and the underlying diamicton the MIS 6 glacial. Formation F yielded ages implying that the formation represents the MIS 5a interstadial and the underlying diamicton is interpreted to represent the MIS 5b stadial. This agrees with conclusions drawn concerning the Pleistocene glaciations elsewhere on Svalbard.
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| 5. |
- Fritz, Michael, et al.
(författare)
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Eastern Beringia and beyond : Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada
- 2012
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 319, s. 28-45
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry. and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2 cal ka BP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean delta O-18 of -29.1 parts per thousand); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial. and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until similar to 11 cal ka BP during a period of low glacio-eustatic sea level. The late glacial-Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2 cal ka BP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table. reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet. ocean, and permafrost that have existed since the Late Wisconsinan.
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| 6. |
- Fuchs, Margret C., et al.
(författare)
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Exploring the potential of luminescence methods for dating Alpine rock glaciers
- 2013
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 18, s. 17-33
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Tidskriftsartikel (refereegranskat)abstract
- Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 ka and 8 ka for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.
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| 7. |
- Gaar, Dorian, et al.
(författare)
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Luminescence dating of mammoth remains from Northern Switzerland
- 2012
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 10:SI, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- Remains of at least two individuals of woolly mammoths (Mammuthus primigenius) were discovered after blastings in a limestone quarry located on the southern slope of the Jura Mountains, northern Switzerland. During the subsequent excavation two blocks were taken for luminescence dating from the sediment surrounding the remains; the deposits are interpreted to represent the filling of a karst hole. Luminescence dates on the polymineral and purified quartz fine grain fraction are compared to those obtained for single grains of quartz and small aliquots of quartz as well as feldspar coarse grains. All approaches give ages consistent within the dating uncertainties and are interpreted to prove the robustness of the dating results. The age of the sediment of ca. 63 ka indicates deposition during Marine Isotope Stage (MIS) 4, thus, during a time when Switzerland experienced rather cold climatic conditions. These are some of the oldest numerically dated woolly mammoth remains of Europe.
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| 8. |
- Gaar, Dorian, et al.
(författare)
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PERFORMANCE OF DIFFERENT LUMINESCENCE APPROACHES FOR THE DATING OF KNOWN-AGE GLACIOFLUVIAL DEPOSITS FROM NORTHERN SWITZERLAND
- 2014
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 41:1, s. 65-80
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Tidskriftsartikel (refereegranskat)abstract
- Luminescence properties of two samples taken from sand lenses in proglacial outwash deposits of a piedmont glacier that reached the Swiss midlands during the Last Glacial Maximum are investigated in detail. Deconvolution of CW-OSL decay curves shows that the fast component dominates the OSL signal of quartz. The chemistry of single feldspar grains, in particular the K content in different grains, is determined using wavelength dispersive spectrometry (electron microprobe), revealing an average 12.9 wt.% K of the grains contributing to the IRSL signal. D-e distributions are investigated in order to gain insights into partial bleaching, and agreement is found for quartz OSL and feldspar IR50 and pIRIR(225) ages for small aliquots and single grains when applying the Minimum Age Model. These ages are also consistent with independent age control. For one sample, ages determined using the Central Age Model result in highly overestimated ages for both feldspar and quartz.
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| 9. |
- Gennari, Giordana, et al.
(författare)
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Faunal evidence of a Holocene pluvial phase in Southern Arabia with remarks on the morphological variability of Helenina anderseni
- 2011
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Ingår i: Journal of Foraminiferal Research. - 0096-1191 .- 1943-264X. ; 41, s. 248-259
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Tidskriftsartikel (refereegranskat)abstract
- Although foraminifera have been found living in inlandsaline lakes isolated from the sea, this phenomenon has rarelybeen recognized in the fossil record. This study documents theoccurrence of benthic foraminifera in Holocene lake sedimentslocated nearly 500 km inland from the Red Sea, in theAl-Mundafan region of southern Saudi Arabia. The lakeformed during a regional pluvial period, 10,500–6000 yr BP.The presence of foraminifera and brackish charophytes in thestudied section represent an interval when the lake wasslightly brackish due to high evaporation. The studiedsediments yielded a bispecific benthic foraminiferal faunacomprised of Helenina anderseni and Trichohyalus aguayoi,as well as the brackish charophyte genus Lamprothamnium.The benthic foraminifera are species characteristic ofmangrove swamps, salt marshes, and lagoons, which areenvironments currently widespread along the Red Sea coasts.Because the Al Mundafan area was never connected to the seaduring the Quaternary, wading birds must have been thevector that transported the foraminifera to the paleolake
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| 10. |
- Greilich, S., et al.
(författare)
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Single-grain dose-distribution measurements by optically stimulated luminescence using an integrated EMCCD-based system
- 2015
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 29, s. 70-79
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Tidskriftsartikel (refereegranskat)abstract
- We report on the feasibility of assessing single-grain dose-distributions by using an EMCCD-based imaging system with complementary analysis software. Automated image-processing was successfully applied to compensate sample motion and for grain identification. Following a dose recovery test, 74% of the grains were recognized successfully, and 44% exhibited a suitable OSL dose response behavior to interpolate an equivalent dose value, and a central dose recovery ratio of 1.038 was obtained.
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