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1.
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2.
  • Blaauw, Maarten, 1974-, et al. (författare)
  • Were last glacial climate events simultaneous between Greenland and western Europe?
  • 2008
  • Ingår i: Climate of the Past Discussions. - 1814-9359. ; 4, s. 1203-1217
  • 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)
  • Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany
  • 2011
  • Ingår i: Quaternary Geochronology. - 1871-1014 .- 1878-0350.
  • 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)
  • Constraining the chronology of Pleistocene glaciations on Svalbard: Kapp Ekholm re-visited
  • 2016
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45:4, s. 790-803
  • 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)
  • Eastern Beringia and beyond : Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada
  • 2012
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 319, s. 28-45
  • 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)
  • Exploring the potential of luminescence methods for dating Alpine rock glaciers
  • 2013
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 18, s. 17-33
  • 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)
  • Luminescence dating of mammoth remains from Northern Switzerland
  • 2012
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 10:SI, s. 257-263
  • 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)
  • PERFORMANCE OF DIFFERENT LUMINESCENCE APPROACHES FOR THE DATING OF KNOWN-AGE GLACIOFLUVIAL DEPOSITS FROM NORTHERN SWITZERLAND
  • 2014
  • Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 41:1, s. 65-80
  • 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)
  • Faunal evidence of a Holocene pluvial phase in Southern Arabia with remarks on the morphological variability of Helenina anderseni
  • 2011
  • Ingår i: Journal of Foraminiferal Research. - 0096-1191 .- 1943-264X. ; 41, s. 248-259
  • 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)
  • Single-grain dose-distribution measurements by optically stimulated luminescence using an integrated EMCCD-based system
  • 2015
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 29, s. 70-79
  • 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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11.
  • Gribenski, Natacha, 1986- (författare)
  • Comparison of dating methods for paleoglacial reconstruction in Central Asia
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Reconstruction of former Central Asian glaciers extents can provide valuable information about past atmospheric circulation variations. These extents, often marked by terminal moraines, need to be chronologically constrained. Cosmogenic nuclide exposure (CNE) dating is widely used to directly date moraines. In addition, there is increasing interest on using optically stimulated luminescence (OSL) techniques for dating glacial landforms. This thesis focuses on the methodological aspects of directly dating glacial landforms to perform paleoglacial reconstructions in Central Asia, with an emphasis on OSL dating.For OSL dating of sediments from glacial settings, it is important to measure the luminescence signal at the single grain scale, because the sediments are likely affected by partial bleaching due to short light exposure during glacial or glaciofluvial transport. The use of an Electron Multiplying Charges Coupled Device (EMCCD)-based imaging system for single grain OSL measurements would offer larger flexibility in light stimulation and sediment type, compared to the current Single Grain Risø reader. An automated image processing procedure has been developed to compensate for sample carrier displacement over repeated measurements and for attributing pixels to each grain for signal integration when using this imaging system. However, significant cross talk contamination, demonstrated by laboratory and simulation experiments, prohibits accurate single grain luminescence measurements. Preliminary experiments using a basic image processing algorithm show good potential for software correction solutions.Paleoglacial reconstructions conducted in the Altai Mountains, Central Asia, using both CNE and OSL dating demonstrate that luminescence measurements of glaciofluvial sediments performed at the multi-grain scale result in large age overestimates, and that single grain measurements allow for more accurate dating of glacial landforms. However, uncertainties remain that are related to the model used for extracting equivalent doses for well-bleached grains and to fading corrections when using feldspar minerals. The timing of glaciation can be inferred from scattered CNE moraine boulder ages if most of the ages are concentrated within a few thousand years, with only few ages clearly older or younger. Overall, combining CNE and OSL techniques for dating a glacial landform is a powerful approach for producing robust glacial chronologies, despite uncertainties inherent to each technique.Paleoglacial reconstructions from the Altai Mountains indicate Marine Isotope Stage (MIS) 2 and MIS 4/late MIS 5 local Last Glacial Maximums. In Central Asia, in addition to a regional MIS 2 glaciation, previous studies indicate a period of major glacial advances during MIS 3 that is out of phase with global ice volume records. However, most MIS 3 glacial chronologies from Central Asia are based on too few or too heavily scattered CNE data sets, or on OSL or Electron Spin Resonance (ESR) ages for which partial bleaching has not been properly investigated. Hence, at this stage, chronological evidence is insufficient to demonstrate a regional MIS 3 glaciation in Central Asia.Surge-related glacial features identified in the Russian Altai also highlight the importance of conducting detailed geomorphology and sedimentology studies to understand former ice dynamics, which is essential for inferring appropriate paleoclimate information from paleoglacial reconstructions.
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12.
  • Gribenski, Natacha, et al. (författare)
  • Investigation of cross talk in single grain luminescence measurements using an EMCCD camera
  • 2015
  • Ingår i: Radiation Measurements. - : Elsevier BV. - 1350-4487 .- 1879-0925. ; 81, s. 163-170
  • Tidskriftsartikel (refereegranskat)abstract
    • Highly sensitive electron multiplying charges coupled devices (EMCCD) enable the spatial detection of luminescence emissions from samples and have a high potential in single grain luminescence dating. However, the main challenge of this approach is the potential effect of cross talk, i.e. the influence of signal emitted by neighbouring grains, which will bias the information recorded from individual grains. Here, we present the first investigations into this phenomenon when performing single grain luminescence measurements of quartz grains spread over the flat surface of a sample carrier. Dose recovery tests using mixed populations show an important effect of cross talk, even when some distance is kept between grains. This issue is further investigated by focusing just on two grains and complemented by simulated experiments. Creation of an additional rejection criteria based on the brightness properties of the grains is inefficient in selecting grains unaffected by their surroundings. Therefore, the use of physical approaches or image processing algorithms to directly counteract cross talk is essential to allow routine single grain luminescence dating using EMCCD cameras.
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13.
  • Gribenski, Natacha, 1986-, et al. (författare)
  • Major glaciation in Central Asia during MIS 3: reality or dating artefact?
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Previous investigations have concluded that a period of major glacial advances occurred during Marine Isotope Stage (MIS) 3 (57-29 ka) in Central Asia, out of phase with global ice volume records. We have re-examined the Kanas moraine complex in the Altai Mountains, where an MIS 3 glaciation has been previously inferred. New cosmogenic exposure and single grain luminescence ages indicate that the Kanas complex was formed during MIS 2 (29-12 ka); we regard the initial MIS 3 interpretation as a result of dating artefacts. Building on this example, we reanalyze chronological data associated with proposed major MIS 3 glacial advances in Central Asia (24 sites). We find that chronological data do not allow glaciation timing inferences for most of the sites, and that chronological evidence for major MIS 3 glacial advance only exists at one site.
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14.
  • Guralnik, B., et al. (författare)
  • OSL-thermochronometry using bedrock quartz : A note of caution
  • 2015
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 25, s. 37-48
  • Tidskriftsartikel (refereegranskat)abstract
    • Optically stimulated luminescence (OSL) thermochronometry is an emerging application, whose capability to record sub-Million-year thermal histories is of increasing interest to a growing number of subdisciplines of Quaternary research. However, several recent studies have encountered difficulties both in extraction of OSL signals from bedrock quartz, and in their thermochronometric interpretation, thus highlighting the need for a methodological benchmark. Here, we investigate the characteristic OSL signals from quartz samples across all major types of bedrock and covering a wide range of chemical purities. High ratios of infrared to blue stimulated luminescence (IRSL/BLSL), an insensitive 'fast' OSL component, and anomalously short recombination lifetimes seen in time-resolved luminescence (TROSL), are often encountered in quartz from crystalline (magmatic and metamorphic) bedrock, and may hamper successful OSL dating. Furthermore, even when the desirable signal is present, its concentration might be indistinguishable from its environmental steady-state prediction, thus preventing its conversion to a cooling or heating history. We explore the saturation properties and the thermal activation parameters of various OSL signals in quartz to outline the capabilities and limitations for their use in low-temperature thermochronometry.
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15.
  • Heiri, Oliver, et al. (författare)
  • Palaeoclimate records 60-8 ka in the Austrian and Swiss Alps and their forelands
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 106, s. 186-205
  • Tidskriftsartikel (refereegranskat)abstract
    • The European Alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60-8 thousand years (ka) ago. We review quantitative and semi-quantitative approaches for reconstructing climatic variables in the Austrian and Swiss sector of the Alpine region within this time interval. Available quantitative to semi-quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids, cladocerans, co-leopterans, diatoms and pollen preserved in lake sediments and peat, the analysis of oxygen isotopes in speleothems and lake sediment records, the reconstruction of past variations in treeline altitude, the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence, and the interpretation of past soil formation processes, dust deposition and permafrost as apparent in loess-palaeosol sequences. Palaeoclimate reconstructions in the Alpine region are affected by dating uncertainties increasing with age, the fragmentary nature of most of the available records, which typically only incorporate a fraction of the time interval of interest, and the limited replication of records within and between regions. Furthermore, there have been few attempts to cross-validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence. Based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60-8 ka in the Alps and their forelands. These include (1) the compilation of individual, fragmentary records to longer and continuous reconstructions, (2) replication of climate records and the development of regional reconstructions for different parts of the Alps, (3) the cross-validation of different proxy-types and approaches, and (4) the reconstruction of past variations in climate gradients across the Alps and their forelands. Furthermore, the development of downscaled climate model runs for the Alpine region 60-8 ka, and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in Europe within this time-interval.
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16.
  • Hoffmann, Gösta, et al. (författare)
  • Fluvio-lacustrine deposits reveal precipitation pattern in SE Arabia during early MIS 3
  • 2015
  • Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 382, s. 145-153
  • Tidskriftsartikel (refereegranskat)abstract
    • On a global scale, Marine Isotope Stage (MIS) 3 (ca. 55-30 ka) was characterised by frequent and abrupt changes in climate. At the same time, humans may have dispersed out of Africa and populated the planet. For the Arabian Peninsula, a key region in both contexts, the paucity of suitable terrestrial records leaves our knowledge of the environmental conditions during this important period enigmatic. Here, we elucidate the environmental history for part of the Oman Mountains by analysing luminescence-dated fine-grained playa-like sediments from Wadi Mistal that formed in a landslide-dammed ephemeral lake. We identified 112 individual fining-upward sequences in the distal facies of the lake that are interpreted to represent major precipitation events during early MIS 3. The nature of sedimentation together with the presence of desiccation cracks and the absence of any faunal remains imply that the lakes had a temporary nature. It appears that the time of deposition was characterised by strong short-lived precipitation events, rather than continuous rainfall under a monsoonal regime. This points towards a climatic situation during early MIS 3 that was not so different from that of the present, at least in this part of Arabia.
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17.
  • Hoffmann, Gösta, et al. (författare)
  • Geo-archaeological evidence for a Holocene extreme flooding event within the Arabian Sea (Ras al Hadd, Oman)
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 113, s. 123-133
  • Tidskriftsartikel (refereegranskat)abstract
    • The Arabian Sea is regarded as one of the least studied regions in terms of coastal hazards such as tropical cyclones and tsunamis. Parts of the coastline are developing rapidly, especially in Oman. This calls for a proper understanding of the natural processes that act on and affect it. This can be done by investigating the magnitude and impact of past events, in particular on human settlements. By doing this, future risks may not only be scientifically predicted and evaluated, but the damage caused by future events might even be mitigated. Evidence of past extreme wave events is preserved in the onshore stratigraphic record. In addition to this, the coastal zone of Oman is rich in archaeological remains. Presented here are the results of comprehensive mapping and analysis of extreme wave deposits of an archaeological site near Ras al-Hadd, suggesting that the Early Bronze Age site HD-6 was inundated at 4450 cal. BP. An event layer is identified between two settlement phases within the archaeological excavation. A contemporaneous sand bed with a maximum thickness of 0.4 m was mapped in the vicinity of the settlement. Ground penetrating radar surveys allow measurement of the thickness as well as identification of the internal facies architecture of the deposit. A high resolution digital elevation model reveals the coastal geomorphology. It is concluded that the causative event must have been a tsunami that was most likely generated within the Makran Subduction Zone. This interpretation does however, remain tentative at the moment Archaeological evidence indicates that the site was immediately re-occupied after the event, which attests to a certain resiliences of the Early Bronze Age coastal communities in the region.
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18.
  • Juschus, Olaf, et al. (författare)
  • Late Quaternary Lake-Level Changes of Lake El´gygytgyn, NE Siberia
  • 2011
  • Ingår i: Quaternary Research. - 0033-5894 .- 1096-0287. ; 76, s. 411-451
  • Tidskriftsartikel (refereegranskat)abstract
    • Lake El'gygytgyn is situated in a 3.6 Ma old impact crater in northeastern Siberia. Presented here is areconstruction of the Quaternary lake-level history as derived from sediment cores from the southern lakeshelf. There, a cliff-like bench 10 m below the modern water level has been investigated. Deep-watersediments on the shelf indicate high lake levels during a warm Mid-Pleistocene period. One period with lowlake level prior to Marine Oxygen Isotope Stage (MIS) 3 has been identified, followed by a period of high lakelevel (10 m above present). In the course of MIS 2 the lake level dropped to −10 m. At the end of MIS 2 thebench was formed and coarse beach sedimentation occurred. Subsequently, the lake level rose rapidly to theHolocene level. Changes in water level are likely linked to climate variability. During relatively temperateperiods the lake becomes free of ice in summer. Strong wave actions transport sediment parallel to the coastand towards the outlet, where the material tends to accumulate, resulting in lake level rise. During coldperiods the perennial lake ice cover hampers any wave activity and pebble-transport, keeping the outlet openand causing the lake level to drop.
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19.
  • Kleman, Johan, et al. (författare)
  • Age and duration of a MIS 3 interstadial in the Fennoscandian Ice Sheet core area-Implications for ice sheet dynamics
  • 2021
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 264
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous assumptions of continuous ice cover of the core area of the Fennoscandian Ice Sheet, from Marine Isotope Stage 4 (ca. 70 ka) to the end of MIS 2 (ca. 12 ka), have been challenged by the discovery of several sites in central and northern Scandinavia with interstadial sediments of assumed MIS 3 age. The sequences have often been dated by Optically Stimulated Luminescence (OSL) and dates of around 55 ka are present at most sites, indicating ice-free conditions at this time. There is less consensus about the timing of the build-up and advance of the last (Late Weichselian) ice sheet after this ice-free stage. To address the duration of MIS 3 ice-free conditions in central Scandinavia, we reviewed available dating evidence. At the few sites where multiple OSL dates are available, ages indicate around 15 ka of ice-free conditions. Two studies employing cosmogenic nuclide dating of preserved interstadial ground surfaces both indicate a 20 ka long period of ice-free conditions during the last ice-free period before the Holocene. Our interpretation is that central Scandinavia became ice-free around 55 ka and remained so until c. 35 ka, when the Scandinavian Ice Sheet started to expand once again. Expansion started from a small-sized remnant ice sheet, or from separate remnant ice caps in Norway. Available data limits the size of any Scandinavian ice sheet remnant surviving the MIS 3 interstadial to less than 1 m of global sea-level equivalent.
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20.
  • Lomax, Johanna, et al. (författare)
  • Luminescence based loess chronostratigraphy of the Upper Palaeolithic site Krems-Wachtberg, Austria
  • 2014
  • Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 351, s. 88-97
  • Tidskriftsartikel (refereegranskat)abstract
    • The loess section Krems-Wachtberg (Lower Austria) is well known for its Upper Palaeolithic find layer, which contains a double and a single infant burial. The layer containing the grave (archaeological horizon AH 4.4) was dated to 26,580 +/- 160 C-14 BP (Einwogerer et al., 2006), corresponding to ca. 31 ka cal BP and is embedded in an 8 m thick loess sequence. In order to provide a chronostratigraphy of the entire section, 38 samples for luminescence dating were taken at high resolution from below and above the find layer. The samples were dated using the quartz coarse grain fraction, the quartz fine grain fraction and/or the polymineral fine grain fraction. The resulting ages are in correct chronostratigraphic order and, in case samples were measured with different protocols, agree within errors with each other and with the radiocarbon age of the find layer. The polymineral fine grain ages are systematically slightly lower than the quartz ages, although no fading could be detected in laboratory experiments. Loess deposition at the site commenced ca. 40 ka ago and reaches up to ca. 22 ka. The ages indicate nearly continuous loess sedimentation throughout this time span. Short breaks in sedimentation probably exist but cannot be resolved due to the uncertainties of luminescence ages.
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21.
  • Lowick, Sally E., et al. (författare)
  • Testing the application of post IR-IRSL dating to fine grain waterlain sediments
  • 2012
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 8, s. 33-40
  • Tidskriftsartikel (refereegranskat)abstract
    • The polymineral fine grain fraction of a set of ten known age samples were used to test the suitability of elevated temperature post-IR infrared stimulated luminescence (pIRIR) to date waterlain sediments in Switzerland. Equivalent Dose (De) values were obtained using elevated temperatures of 225 °C (pIRIR225) and 290 °C (pIRIR290) and IRSL50/225 (preceding measurement of pIRIR225), and these displayed a systematic increase with increasing stimulation temperature, which brought those derived from the pIRIR protocols into saturation for the older half of the samples (>100 ka). Significant residuals were recorded for the pIRIR signals, and these were found to further increase following attenuation of the bleaching source confirming that these signals are harder to bleach than the IRSL measured at 50 °C. Fading tests recorded g-values of between 1 and 4%, and displayed no obvious decrease with increasing stimulation temperature. For the younger half of the samples, fading corrected ages for all protocols resulted in overestimation compared to robust independent dating for all samples, and draw into question the relationship of fading measured in a laboratory generated signal to that which is naturally generated. Uncorrected IRSL50/225 ages for all samples were in good agreement with independent dating, but still displayed a general overestimation using pIRIR signals. These overestimations may largely be due to the significant residual doses resulting from the harder to bleach nature of the elevated temperature signal, and present a considerable problem when dating waterlain sediments. A considerable challenge when using the pIRIR signal is to be able to separate the effects of both residual doses and fading and confirm that one is not masking the other. Despite this, the pIRIR protocols were successful at one site, although they offered no benefit compared to dating with more conventional luminescence signals. A comparison of De values derived from a standard IRSL signal to that from IRSL50/225, suggest that the latter overestimates by ∼10% due to a decrease in sensitivity of the sample prior to measurement of the test dose.
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22.
  • Lowick, Sally, et al. (författare)
  • Investigating age underestimation in the high dose region of optically stimulated luminescence using fine grain quartz
  • 2011
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 6, s. 33-41
  • Tidskriftsartikel (refereegranskat)abstract
    • The age range of the single-aliquot regenerative-dose (SAR) protocol applied to quartz optically stimulatedluminescence (OSL) has become the subject of debate as age underestimations for samples ofEemian age (ca. 125 ka) and older are increasingly reported. In order to investigate the origin of the ageunderestimation, the behaviour of fine grain quartz samples taken from two sites was compared.Sediment from both sites originates in the Alps, with those from Azzano Decimo, northeastern Italy,already displaying a significant age underestimation before reaching the Eemian, while ages for samplesfrom Niederweningen, northern Switzerland, agree with expected ages well beyond the Eemian. Estimateddose (De) values for both sets of samples are up to around 400 Gy, and all meet the usualperformance criteria for testing the reliability of the SAR protocol. De values determined using a sensitivity-corrected multiple aliquot regenerative-dose (MAR) protocol were within 10% of those determinedusing a SAR protocol for both sites, and so could not overcome the significant underestimation seen atAzzano Decimo. Lifetime calculations confirmed the stability of the signal well beyond the age rangerequired at both sites, for both the initial integral as well as that used for an early backgroundsubtraction. The relative percentage contribution of the fast and medium OSL components to the initialintegral remained constant in both the natural signal and similar sized laboratory generated doses. Thequartz OSL from both sites displayed similar characteristics under all analyses and no indication wasfound for the possible origin of the age underestimation seen at Azzano Decimo. In the comparisonsmade between the doseeresponse of both laboratory and naturally generated signals in these samples,no evidence was found to suggest that the presence of the high dose linear region is restricted to thelaboratory. The reliability of quartz OSL ages derived from this part of the curve however, remain inquestion, and require the support of independent age control until a performance criterion can be foundwith which to test it.
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23.
  • Lüthgens, Christopher, et al. (författare)
  • Age of the Pomeranian ice-marginal position in northeastern Germanydetermined by Optically Stimulated Luminescence (OSL) dating ofglaciofluvial sediments
  • 2011
  • Ingår i: Boreas. - 0300-9483 .- 1502-3885. ; 40, s. 598-615
  • Tidskriftsartikel (refereegranskat)abstract
    • The Pomeranian ice margin is one of the most prominent ice-marginal features of the Weichselian glaciation innorthern Europe. Previous results of surface-exposure dating (SED) of this ice margin disagree with establishedchronologies and ice retreat patterns, i.e. are much younger than previously expected. We crosscheck the age of thePomeranian ice-marginal position in northeastern Germany using single-grain quartz Optically Stimulated Luminescence(OSL) dating of glaciofluvial sediments. OSL dating indicates an active ice margin between 20.11.6 kaand 19.42.4 ka forming outwash plains attributed to the Pomeranian ice-marginal position. On the basis of theseresults, we suggest a critical reassessment of previous SED data available for the Pomeranian ice-marginal positionwithin their respective regional geomorphological contexts. From a process-based point of view, SED ages derivedfrom glacigenic boulders document the stabilization of the landscape after melting of dead ice and landscapetransformation under periglacial conditions rather than the presence of an ice margin. SED indicates a firstphase of boulder stabilization at around 16.40.7 ka, followed by landscape stabilization within the area attributedto the recessional Gerswalder subphase around 15.20.5 ka. A final phase of accumulation of glaciolacustrine andglaciofluvial sediments at around 14.71.0 ka documents the melting of buried dead ice at that time.
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24.
  • Madritsch, Herfried, et al. (författare)
  • Climatic and tectonic controls on the development of the River Ognon terrace system (eastern France)
  • 2012
  • Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 151, s. 126-138
  • Tidskriftsartikel (refereegranskat)abstract
    • The River Ognon in eastern France is the principal drainage of the southwestern Vosges Mountains. Its lowermost valley reach is oriented parallel to the northwestern front of the Alpine collision zone and is characterized by a well-developed terrace system. Geomorphological, sedimentological, and geochronological analyses were performed on this terrace system and associated deposits. The results allow for reconstructing the Pleistocene evolution of the river valley and for concluding on the processes that led to the formation of the terrace system. The lithological characterization of the terrace deposits by means of heavy mineral analyses indicates pronounced modifications of the river's drainage area. Optically stimulated luminescence dating suggests that the last significant catchment modification and associated sediment accumulation correlates with the last glacial advance in the Vosges Mountains. Despite the apparently strong impact of climatic processes on the evolution of the River Ognon, our investigation also indicates a mild tectonic influence on presently observed terrace distribution.
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25.
  • Margold, Martin, et al. (författare)
  • Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum
  • 2016
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 132, s. 161-174
  • Tidskriftsartikel (refereegranskat)abstract
    • Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic Be-10 exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.
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26.
  • Margold, Martin, et al. (författare)
  • Repeated megafloods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000 years
  • 2018
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 187, s. 41-61
  • Tidskriftsartikel (refereegranskat)abstract
    • Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km(3) megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0-6.5 million m(3)s(-1), mean flow depths of 120-150 m, and average flow velocities up to 21 ms(-1)
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27.
  • Massuanganhe, Elidio A., 1982-, et al. (författare)
  • Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique
  • 2018
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 489, s. 64-73
  • Tidskriftsartikel (refereegranskat)abstract
    • Many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation fromriver inflows. In this paper we use the example of the Save River delta to assess the palaeogeographic distributionof mangrove wetlands and to analyze their dynamics. To track past occurrences of mangrove wetlands in thestudy area we have integrated sedimentological data with siliceous microfossil analysis combined with AMSradiocarbon and OSL dating. The results show a fine-grained deposit with an approximate thickness of 2 m,present at different sampling sites. In the upper deltaic plain, the deposit is interbedded between sand layers,while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position. In most of thesampling sites the deposit shows a succession with brackish-marine diatoms at the bottom of the sequence whilethe upper part shows only scattered occurrences. Based on sedimentological and microfossil characteristics wehave interpreted the layer to represent a mangrove wetland deposit. The development of the deposit in the studyarea is suggested to have been initiated around 3100 cal. yr BP, induced by sea-level rise. Thereafter, the developmentfollowed the combined effect of a sea-level fall and delta progradation processes. In some areas,particularly in the proximal part of the delta, the mangrove deposit has developed progressively on top of thedelta-front. From around 1300 years ago (OSL) onwards, massive alluvial sedimentation impacted the mangroveecosystem. However, the retreat of mangrove wetland coincided with a regional fall of sea level. At the edges ofthe alluvial deposit, the current mangrove ecosystem has reclaimed the habitat in some sectors where gullyerosion has exposed the once extinct mangrove habitat.
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28.
  • Massuanganhe, Elidio, 1982-, et al. (författare)
  • Geomorphology and landscape evolution of Save River delta, South-central Mozambique
  • Annan publikation (populärvet., debatt m.m.)abstract
    • The Save River delta has well-preserved geomorphological and sedimentological features with potential to reveal its evolution as well as past regional environmental changes, which are anticipated to integrate into other data at a global scale. In this study we mapped and integrated these features to understand the environmental processes that drove the late evolution of the delta. The results suggest that the present configuration of the delta was primarily dominated by a delta-front protruding into the sea, in a faulted coast section that may have favoured the formation of the depocenter. The development of the delta-front was initiated prior to c. 3100 cal. yrs BP, and around this age, fine-grained sediments started to accumulate on it forming a mangrove wetland deposit that expanded from the proximal sector of the delta to the current position shown in a geomorphological map. The results show successive dune ridges in the southern sector of the delta which indicate a series of consecutive shorelines over time as the delta prograded towards the current position. These dunes have created favourable conditions for accumulation of fine-grained sediments in the back-barrier sectors, contributing to the development of the mangrove wetland. An alluvial floodplain developed during the last millennium, probably a result of high precipitation the catchment area.
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29.
  • Matter, Albert, et al. (författare)
  • Palaeo-environmental implications derived from lake and sabkha deposits of the southern Rub' al-Khali, Saudi Arabia and Oman
  • 2015
  • Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 382, s. 120-131
  • Tidskriftsartikel (refereegranskat)abstract
    • Shallow lakes and sabkha deposits are evidence of past periods of higher groundwater table than today, and hence reflect increased humidity in the Rub' al-Khali, the large desert in the southern part of the Arabian Peninsula. Reported here are the observations made during four expeditions into this remote area in combination with luminescence dating constraining the age of the deposits. The results presented extend the spatial coverage of evidence and show that most of the deposits correlate to MIS 5 (ca. 130-70 ka) and the Early/Mid Holocene (ca. 11-5.5 ka). A single sample points towards potentially more humid conditions during the transition MIS 4/3 (ca. 65-55 ka). The presence of the mussel Unio in some of the deposits attributed to MIS 5 is indirect evidence for the presence of fish in the lakes, which must have supported a rich and diverse fauna (and probably also flora). Together with other evidence, this demonstrates that a number of small persistent lakes were spread across the Rub' al-Khali for at least some of the time. These lakes would not only have been a potential source of freshwater but could also have provided an additional and easy accessible food source via the fish for humans migrating through the area. The presented palaeoenvironmental data underlines that parts of MIS 5 represent a time window of opportunity for a potential expansion of modern humans across Arabia.
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30.
  • May, Jan-Henrik, et al. (författare)
  • Reconstruction of a complex late Quaternary glacial landscape in the Cordillera de Cochabamba (Bolivia) based on a morphostratigraphic and multiple dating approach.
  • 2011
  • Ingår i: Quaternary Research. - 0033-5894 .- 1096-0287. ; 76, s. 106-118
  • Tidskriftsartikel (refereegranskat)abstract
    • Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations inthe Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results fromdetailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulatedluminescence (OSL), and radiocarbon dating (14C) from the Huara Loma Valley, Cordillera de Cochabamba(Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solidgeomorphic framework. We identified two major glaciations. The older is not well constrained by theavailable data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regardingthe latter, a first advance dated to ~29–25 ka occurred roughly contemporaneous with the onset of the globallast glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20–18 ka. The locallast glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~17–16 ka,followed by several smaller readvances until ~10–11 ka, and complete deglaciation at the end of the EarlyHolocene.
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31.
  • May, Jan-Hendrik, et al. (författare)
  • Refining late Quaternary plunge pool chronologies in Australia's monsoonal 'Top End'
  • 2015
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 30, s. 328-333
  • Tidskriftsartikel (refereegranskat)abstract
    • Plunge pool deposits from Australia's 'Top End' are considered as important archives of past monsoonal activity in the region. The available chronology of these deposits was so far based on thermoluminescence (TL) dating and indicated maximum flood magnitudes during the Last Glacial Maximum in contrast with more arid conditions as deduced from other archives of the region. This study revisits plunge pool deposits at Wangi Falls by applying multiple and single-grain Optically Stimulated Luminescence (OSL) dating of quartz and high-resolution gamma spectrometry, supported by radiocarbon dating of organic material. The aim is to reappraise the existing chronology and investigate if the deposits are affected by partial bleaching, post-depositional mixing and/or problems related to annual dose determination. The latter seems to have a minor impact on the ages at most. Equivalent Dose (D-e) distributions are broad, in particular for single grains, but apparently hot result from partial bleaching or post-depositional mixing. Rather, microdosimetry caused by radiation hotspots in the sediment and zircon inclusions in the quartz grains is considered problematic for these sediments. The results presented here imply that the previous TL chronology overestimated the real deposition age of the sediments.
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32.
  • Muru, Merle, et al. (författare)
  • Reconstructing Holocene shore displacement and Stone Age palaeogeography from a foredune sequence on Ruhnu Island, Gulf of Riga, Baltic Sea
  • 2018
  • Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 303, s. 434-445
  • Tidskriftsartikel (refereegranskat)abstract
    • Holocene shore displacement and the palaeogeography of Late Mesolithic and Late Neolithic settlements on Ruhnu Island, Gulf of Riga, were reconstructed using foredune sequence luminescence dating, sedimentological data supported by ground-penetrating radar analysis, and GIS-based landscape modelling. The foredune ridges consist of very well to well sorted fine-to medium-grained aeolian sand and are underlain by seaward dipping foreshore sediments. The studied sequence of 38 ridges was formed between 6.91 +/- 0.58 ka and 2.54 +/- 0.19 ka ago, and represents a period of falling relative sea level. Foredune plain progradation, with average rates of 0.3-0.6 m per year, was controlled by isostatic land uplift, which caused a continuous withdrawal of shorelines to lower elevations. The dated foredune succession was used to reconstruct the coastal palaeogeography of the island. Palaeogeographical reconstructions show that during two phases of Late Mesolithic habitation, at ca. 7.2 cal. ka BP and 6.2 cal. ka BP, seal hunters settled the coastal zone of Ruhnu Island. Based on tool material and pottery type they could have originated from Saaremaa Island, which according to palaeoreconstruction of the Gulf of Riga, was located approximately 70 km northwest of Ruhnu Island during the Late Mesolithic. Later signs of human occupation, radiocarbon dated to ca. 4.7 cal. ka BP, were from the centre of the island, hundreds of metres away from the shore at about 8 m above its contemporary sea level. This Late Neolithic habitation shows a clearly different pattern than earlier coastal settlement, and suggests a shift in subsistence strategy towards agriculture and animal husbandry.
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33.
  • Plotzki, A., et al. (författare)
  • Geomorphological and sedimentary evidence for late Pleistocene to Holocene hydrological change along the Rio Mamore, Bolivian Amazon
  • 2013
  • Ingår i: Journal of South American Earth Sciences. - : Elsevier BV. - 0895-9811 .- 1873-0647. ; 47, s. 230-242
  • Tidskriftsartikel (refereegranskat)abstract
    • Aerial photography and satellite imagery reveal manifold geomorphological evidence of a dynamic evolution of past and present rivers in the Bolivian Amazon. Comparison of oxbow lake and meander scar dimensions along an inactive meander belt of the Rio Mamore (Llanos de Moxos, north-eastern Bolivia) and its modern counterpart suggests significant regional paleohydrological variability. We used these features as geomorphological and sedimentary archives to enhance our understanding of longer-term variations of the fluvial system. Late Pleistocene to Holocene hydrological changes of the Rio Mamore are inferred from: (i) the analysis of satellite imagery, (ii) discharge estimates from meander morphology, (iii) stratigraphic, and (iv) chronological information based on luminescence and radiocarbon dating. The combined data from three oxbows indicate that the now abandoned meander belt - the paleo-Mamore - continued to be active at least until similar to 5 ka, and likely even postdating 3 ka. An up to threefold increase in discharge is estimated for the modern Rio Mamore versus the paleo-Mamore. The altered runoff regime may have triggered an avulsive shift towards the currently active Rio Mamore. The preceding increase in discharge in turn, was possibly related to a shift in climatic conditions, which changed markedly between the mid- and late Holocene in tropical South America. In addition, it may have been the indirect result of capturing the avulsive Rio Grande system to the east of the Rio Mamore. Alternative explanations for the differences in dimensions of the paleo versus the modern Rio Mamore, i.e. contemporaneous activity of both rivers or alteration of site factors such as the channel/floodplain relationship, are considered to be unlikely.
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34.
  • Plotzki, A., et al. (författare)
  • Geomorphology and evolution of the late Pleistocene to Holocene fluvial system in the south-eastern Llanos de Moxos, Bolivian Amazon
  • 2015
  • Ingår i: Catena (Cremlingen. Print). - : Elsevier BV. - 0341-8162 .- 1872-6887. ; 127, s. 102-115
  • Tidskriftsartikel (refereegranskat)abstract
    • In the Bolivian Amazon several paleochannel generations are preserved. Their wide spectrum of morphologies clearly provides crucial information on the type and magnitude of geomorphic and hydrological changes within the drainage network of the Andean foreland. Therefore, in this study we mapped geomorphological characteristics of paleochannels, and applied radiocarbon and optically stimulated luminescence dating. Seven paleochannel generations are identified. Significant changes in sinuosity, channel widths and river pattern are observed for the successive paleochannel generations. Our results clearly reflect at least three different geomorphic and hydrological periods in the evolution of the fluvial system since the late Pleistocene. Changes in discharge and sediment load may be controlled by combinations of two interrelated mechanisms: (i) spatial changes and re-organizations of the drainage network in the upper catchment, and/or (ii) climate changes with their associated local to catchment-scale modifications in vegetation cover, and changes in discharge, inundation frequencies and magnitudes, which have likely affected the evolution of the fluvial system in the Llanos de Moxos. In summary, our study has revealed the enormous potential which geomorphic mapping and analysis combined with luminescence based chronologies hold for the reconstruction of the late Pleistocene to recent fluvial system in a large portion of Amazonia.
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35.
  • Preusser, Frank, et al. (författare)
  • Comparing different post-IR IRSL approaches for the dating of Holocene coastal foredunes from Ruhnu Island, Estonia
  • 2014
  • Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 41:4, s. 342-351
  • Tidskriftsartikel (refereegranskat)abstract
    • Different post-IR Infrared Stimulated Luminescence (IRSL) approaches are applied to sediments from a Holocene coastal foredune sequence on Ruhnu Island in the eastern Baltic Sea. The comparison of D (e)-values and ages determined by the different approaches is complimented by fading and bleaching experiments. The fading experiments imply strong fading of IRSL (50A degrees C) signals and no fading of any of the post-IR IRSL signals, but this is not confirmed by the determined D (e)-values. In fact, post-IR IRSL (150A degrees C) D (e)-values agree within errors with those calculated for IRSL (50A degrees C). From the bleaching experiments it is inferred that the higher values observed for post-IR IRSL at more elevated stimulation temperatures (225A degrees C/290A degrees C) are likely related to either thermal transfer and/or slow-to-bleach components within the signal. For the dating of the Holocene foredune sequence of Ruhnu Island, the post-IR IRSL (150A degrees C) approach is preferred and these agree with the limited independent age control available from radiocarbon dating. Accordingly, the sequence formed between ca. 7.0 ka and 2.5 ka ago.
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36.
  • Preusser, Frank, et al. (författare)
  • Direct dating of Quaternary phreatic maar eruptions by luminescence methods
  • 2011
  • Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 39:12, s. 1135-1138
  • Tidskriftsartikel (refereegranskat)abstract
    • The suitability of quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) for the direct dating of phreatic eruptions was tested on examples from the Eifel Volcanic Field, Germany. The mean IRSL age of 11.6 +/- 0.5 ka for Ulmener Maar Tephra is in excellent agreement with the independent age control (11 +/- 0.1 ka), but the mean OSL age of 14.2 +/- 0.6 ka overestimates the known age by 3 ka. For Meerfelder Maar Tephra, consistent IRSL (mean 74.9 +/- 5.0 ka) and OSL ages (74.9 +/- 5.5 ka) have been observed. The consistent results from Meerfelder Maar imply that the overestimation observed for Ulmener Maar quartz OSL might not be relative to the eruption age, but rather represents a small absolute offset. In samples taken from deposits of the eruption of Laacher See Volcano, no resetting of the OSL signal and highly scattered IRSL estimates were found. This implies that phreatomagmatic eruptions are less well suited for this dating approach compared to pure phreatic maar eruptions, where the effect of high-pressure shock waves probably dominates the process of resetting the luminescence signal.
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37.
  • Preusser, Frank, 1967-, et al. (författare)
  • Quaternary glaciation history of northern Switzerland
  • 2011
  • Ingår i: E&G Quaternary Science Journal. - 0424-7116. ; 60, s. 282-305
  • Tidskriftsartikel (refereegranskat)abstract
    • A revised glaciation history of the northern foreland of the Swiss Alps is presented by summarising field evidence and chronologicaldata for different key sites and regions. The oldest Quaternary sediments of Switzerland are multiphase gravels intercalated bytill and overbank deposits (‘Deckenschotter’). Important differences in the base level within the gravel deposits allows the distinguishingof two complex units (‘Höhere Deckenschotter’, ‘Tiefere Deckenschotter’), separated by a period of substantial incision.Mammal remains place the older unit (‘Höhere Deckenschotter’) into zone MN 17 (2.6–1.8 Ma). Each of the complexes containsevidence for at least two, but probably up-to four, individual glaciations. In summary, up-to eight Early Pleistocene glaciations ofthe Swiss alpine foreland are proposed. The Early Pleistocene ‘Deckenschotter’ are separated from Middle Pleistocene depositionby a time of important erosion, likely related to tectonic movements and/or re-direction of the Alpine Rhine (Middle PleistoceneReorganisation – MPR). The Middle-Late Pleistocene comprises four or five glaciations, named Möhlin, Habsburg, Hagenholz(uncertain, inadequately documented), Beringen, and Birrfeld after their key regions. The Möhlin Glaciation represents the mostextensive glaciation of the Swiss alpine foreland while the Beringen Glaciation had a slightly lesser extent. The last glacial cycle(Birrfeld Glaciation) probably comprises three independent glacial advances dated to ca. 105 ka, 65 ka, and 25 ka. For the last glacialadvance, a detailed radiocarbon chronology for ice build-up and meltdown is presented.
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38.
  • Rodrigues, Leonor, et al. (författare)
  • Pre-Columbian agriculture in the Bolivian Lowlands : Construction history and management of raised fields in Bermeo
  • 2015
  • Ingår i: Catena (Cremlingen. Print). - : Elsevier BV. - 0341-8162 .- 1872-6887. ; 132, s. 126-138
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent archaeological research suggests that some parts of the Amazon Basin were significantly modified by pre-Columbian populations. One of the most impressive examples of such transformations is the raised fields of south-western Amazonia, in the Llanos de Moxos in the Bolivian Lowlands. Despite a growing interest in raised field agriculture, due to the important role it seems to have played in the development of pre-Columbian complex societies, very few field-based investigations have been performed in the Amazon Basin. As a result, there is limited knowledge of how these fields were constructed, managed and within which time-frame they were in use. This study provides a new interpretation of how pre-Columbian raised fields were managed and a chronological sequence of their utilisation and eventual abandonment. Fieldwork was carried out in the indigenous community of Bermeo, in the vicinity of San Ignacio de Moxos, where some of the best preserved fields in the Llanos Moxos are found. Magnetic susceptibility and the geochemistry of the sediments, combined with radiocarbon and optically stimulated luminescence dating, show that the raised fields were in intermittent use since as early as AD 570-770. The original surface on which the fields were built and distinct periods of construction and use have been identified. The data suggests that raised fields were built during a few separate construction events, probably linked to periods of more frequent and severe floods. The study challenges the most widely accepted theory that suggests that pre-Columbians were able to cultivate these fields on a continuous basis by transferring nutrient-rich sediments from the canals to the fields. We conclude that pre-Columbians built raised fields to overcome periods of increased flooding, with the main objective of improving drainage.
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39.
  • Rosenberg, Thomas M., et al. (författare)
  • A comparison of single and multiple aliquot TT-OSL data sets for sand-sized quartzfrom the Arabian Peninsula
  • 2011
  • Ingår i: Radiation Measurements. - : Elsevier BV. - 1350-4487 .- 1879-0925. ; 46:6-7, s. 573-579
  • Tidskriftsartikel (refereegranskat)abstract
    • The quartz OSL signal from dune sands from Saudi Arabia and Oman start to saturate at doses of about100 Gy. In order to try to date dune sands with greater expected doses, a previously published,single-aliquot, regenerative-dose protocol (SAR) for thermally-transferred optically stimulatedluminescence (TT-OSL) was tested. Dose recovery tests, recycling and recuperation ratios showed robustfunctioning and dose response curves demonstrated the potential to extend the dose range to beyond600 Gy. Multiple aliquot additive dose (MAAD) TT-OSL protocols were used to test for sensitivity changesin the SAR TT-OSL protocol up to doses of 1200 Gy. A strong dose dependent deviation of the SAR TT-OSLrelative to the MAAD TT-OSL dose response is observed. Comparison of the TT-OSL and OSL sensitivitydata obtained from the MAAD and SAR data sets shows a lack of proportionality between TT-OSL and OSLfor the SAR data which will result in a problem when SAR dose response curves are constructed usingmany regeneration points with doses above 300 Gy.
  •  
40.
  • Rosenberg, T. M., et al. (författare)
  • Humid periods in southern Arabia : Windows of opportunity for modern human dispersal
  • 2011
  • Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 39:12, s. 1115-1118
  • Tidskriftsartikel (refereegranskat)abstract
    • Arabia is a key area for the dispersal of anatomically modern humans (AMH, Homo sapiens) out of Africa. Given its modern hostile environment, the question of the timing of dispersal is also a question of climatic conditions. Fresh water and food were crucial factors facilitating AMH expansions into Arabia. By dating relict lake deposits, four periods of lake formation were identified: one during the early Holocene and three during the late Pleistocene centered ca. 80, ca. 100, and ca. 125 ka. Favorable environmental conditions during these periods allowed AMH to migrate across southern Arabia. Between ca. 75 and 10.5 ka, arid conditions prevailed and turned southern Arabia into a natural barrier for human dispersal. Thus, expansion of AMH through the southern corridor into Asia must have taken place before 75 ka, possibly in multiple dispersals.
  •  
41.
  • Rosenberg, Thomas M., et al. (författare)
  • Middle and Late Pleistocene humid periods recorded in palaeolake deposits of the Nafud desert, Saudi Arabia
  • 2013
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 70, s. 109-123
  • Tidskriftsartikel (refereegranskat)abstract
    • Present climate in the Nafud desert of northern Saudi Arabia is hyper-arid and moisture brought by north-westerly winds scarcely reaches the region. The existence of abundant palaeolake sediments provides evidence for a considerably wetter climate in the past. However, the existing chronological framework of these deposits is solely based on radiocarbon dating of questionable reliability, due to potential post-depositional contamination with younger C-14. By using luminescence dating, we show that the lake deposits were not formed between 40 and 20 ka as suggested previously, but approximately ca 410 ka, 320 ka, 200 ka, 125 ka, and 100 ka ago. All of these humid phases are in good agreement with those recorded in lake sediments and speleothems from southern Arabia. Surprisingly, no Holocene lake deposits were identified. Geological characteristics of the deposits and diatom analysis suggest that a single, perennial lake covered the entire south-western Nafud ca 320 ka ago. In contrast, lakes of the 200 ka, 125 ka, and 100 ka humid intervals were smaller and restricted to interdune depressions of a preexisting dune relief. The concurrent occurrence of humid phases in the Nafud, southern Arabia and the eastern Mediterranean suggests that moisture in northern Arabia originated either from the Mediterranean due to more frequent frontal depression systems or from stronger Indian monsoon circulation, respectively. However, based on previously published climate model simulations and palaecolimate evidence from central Arabia and the Negev desert, we argue that humid climate conditions in the Nafud were probably caused by a stronger African monsoon and a distinct change in zonal atmospheric circulation.
  •  
42.
  • Rosentau, Alar, et al. (författare)
  • Holocene relative shore level changes and Stone Age hunter-gatherers in Hiiumaa Island, eastern Baltic Sea
  • 2020
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 49:4, s. 783-798
  • Tidskriftsartikel (refereegranskat)abstract
    • Holocene relative shore level (RSL) changes and Stone Age palaeogeography of Hiiumaa Island are reconstructed using airborne LiDARelevation data, sedimentological and archaeological proxies as well asGIS-based landscape modelling. Altogether, 38RSLindex and limiting points are used in modelling and presented in the current paper. The highest raised shorelines of the Ancylus Lake and Litorina Sea, mapped at the elevations of 47 and 26 m a.s.l., formed around 10.3 and 7.4 cal. kaBP, respectively. The reconstructedRSLcurve reveals a 20-m drainage of Ancylus Lake followed by a land-uplift-driven 3-m regression during the Initial Litorina Sea period.RSLrise during the Litorina Sea transgression remained below 4 m and its maximum was reached later than proposed previously, discarding therefore the idea of highly diachronous Litorina culmination in the eastern Baltic Sea. During the period 7.4-6.0 cal. kaBP,RSLfall was about 4.3 mm a(-1), and afterwards in average at about 1 mm(-1)less suggesting deceleration in isostatic rebound. suggesting deceleration in isostatic rebound. Palaeogeographical reconstructions show that during its earliest occupation at about 7.6 cal. kaBPless than 1% of the terrain of Hiiumaa was above the sea level and that wind-protectedSEexposed shores were the most preferred campsite locations of Late Mesolithic and Neolithic settlers. These campsites are located successively at lower elevations following the shoreline retreat and show repeated use of this coastal area between 7.6 and 4.6 cal. kaBP. Due to the spread of the Corded Ware culture around 4.8-4.0 cal. kaBPthe settlements of Hiiumaa Island and many other coastal areas of the eastern Baltic moved from the coast to more suitable places for agriculture and animal husbandry.
  •  
43.
  • Rufer, Daniel, et al. (författare)
  • Late Quaternary history of the Vakinankaratra volcanic field (central Madagascar) : insights from luminescence dating of phreatomagmatic eruption deposits
  • 2014
  • Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 76:5, s. 817-
  • Tidskriftsartikel (refereegranskat)abstract
    • The Quaternary Vakinankaratra volcanic field in the central Madagascar highlands consists of scoria cones, lava flows, tuff rings, and maars. These volcanic landforms are the result of processes triggered by intracontinental rifting and overlie Precambrian basement orNeogene volcanic rocks. Infrared-stimulated luminescence (IRSL) dating was applied to 13 samples taken from phreatomagmatic eruption deposits in the Antsirabe-Betafo region with the aim of constraining the chronology of the volcanic activity. Establishing such a chronology is important for evaluating volcanic hazards in this densely populated area. Stratigraphic correlations of eruption deposits and IRSL ages suggest at least five phreatomagmatic eruption events in Late Pleistocene times. In the Lake Andraikiba region, two such eruption layers can be clearly distinguished. The older one yields ages between 109 +/- 15 and 90 +/- 11 ka and is possibly related to an eruption at the Amboniloha volcanic complex to the north. The younger one gives ages between 58 +/- 4 and 47 +/- 7 ka and is clearly related to the phreatomagmatic eruption that formed Lake Andraikiba. IRSL ages of a similar eruption deposit directly overlying basement laterite in the vicinity of the Fizinana and Ampasamihaiky volcanic complexes yield coherent ages of 68 +/- 7 and 65 +/- 8 ka. These ages provide the upper age limit for the subsequently developed Iavoko, Antsifotra, and Fizinana scoria cones and their associated lava flows. Two phreatomagmatic deposits, identified near Lake Tritrivakely, yield the youngest IRSL ages in the region, with respective ages of 32 +/- 3 and 19 +/- 2 ka. The reported K-feldspar IRSL ages are the first recorded numerical ages of phreatomagmatic eruption deposits in Madagascar, and our results confirm the huge potential of this dating approach for reconstructing the volcanic activity of Late Pleistocene to Holocene volcanic provinces.
  •  
44.
  • Rufer, Daniel, et al. (författare)
  • Proposing new approaches for dating young volcanic eruptions by luminescence methods
  • 2012
  • Ingår i: Geochronometria. - : Walter de Gruyter GmbH. - 1733-8387 .- 1897-1695. ; 39:1, s. 48-56
  • Tidskriftsartikel (refereegranskat)abstract
    • The application of luminescence dating to young volcanic sediments has been first investigated over three decades ago, but it was only with the technical innovations of the last decade that such analyses became viable. While current analytical procedures show promise for dating late Quaternary volcanic events, most efforts have been aimed at unconsolidated volcanic tephra. Investigations into direct dating of lava flows or of non-heated volcanoclastics like phreatic explosion layers, however, remain scarce. These volcanic deposits are of common occurrence and represent important chrono- and volcanostratigraphic markers. Their age determination is therefore of great importance in volcanologic, tectonic, geomorphological and climate studies. In this article, we propose the use of phreatic explosion deposits and xenolithic inclusions in lava flows as target materials for luminescence dating applications. The main focus is on the crucial criterion whether it is probable that such materials experience complete luminescence signal resetting during the volcanic event to be dated. This is argued based on the findings from existing literature, model calculations and laboratory tests.
  •  
45.
  • Rupnik, Petra Jamsek, et al. (författare)
  • Geomorphic evidence of recent activity along the Vodice thrust fault in the Ljubljana Basin (Slovenia) - a preliminary study
  • 2013
  • Ingår i: Annals of Geophysics. - : Instituto Nazionale di Geofisica e Vulcanologia, INGV. - 1593-5213 .- 2037-416X. ; 56:6, s. S0680-
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated two prominent, E-W trending scarps in Quaternary sediments, located close to the town of Vodice in the Ljubljana Basin (central Slovenia). By using detailed geomorphological analysis of the scarps, field surveying, and structural observations of deformed Quaternary sediments, we conclude that the scarps are the surface expression of a N-dipping thrust fault that has been active during the Quaternary. From Optically Stimulated Luminescence and Infrared Stimulated Luminescence dating of deformed Quaternary sediments we estimate a slip rate of 0.1 to 0.3 mm a(-1) in the last 133 ka. Using the published empirical fault-scaling relationships, we estimate that an earthquake of magnitude 5.9 to 6.5 may be expected on the Vodice thrust fault. The fault may, therefore, present a major seismic hazard for the densely populated and urbanised region of central Slovenia.
  •  
46.
  • Schmidt, Christoph, et al. (författare)
  • Quantification and spatial distribution of dose rate relevant elements in silex used for luminescence dating
  • 2012
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 12, s. 65-73
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermoluminescence (TL) is routinely used to date heated lithic artefacts which mostly consist of silex (a mixture of amorphous opal and microcrystalline chalcedony). Analytical investigations of bulk samples confirmed that these materials contain considerable concentrations of radioactive elements, generating an internal dose rate contribution. Common dosimetric models assume the latter to be homogeneous throughout the sample. If this assumption would prove invalid, this will result in systematic errors in the calculated age, especially in the course of so called 'hot spots' of alpha-emitters (and associated local changes in a-sensitivity) and the dose response characteristics of alpha-radiation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of 22 silex samples are presented here, quantifying element concentrations at several tens analytical spots per sample. Along with radioactive elements (K, Rb, U, Th), another 21 major, minor and trace elements were measured in order to allow characterization of the impurities present in most of the samples. The dataset provides a detailed picture of the spatial distribution of radionuclides and hence of the uniformity of the internal alpha- and beta-dose rate. It is shown that the silex itself mostly contains low amounts of K (<0.1 wt.%), U (<1.0 mu g g(-1)) and Th (<0.4 mu g g(-1)), and dosimetrically negligible Rb concentrations. Systematically higher concentrations are obtained by ICP-MS measurements of the bulk samples. This matches with the finding that impurities (veins, inclusions) often yield significantly elevated radionuclide concentrations, up to two orders of magnitude higher than the silex values. These veins and inclusions, for example Ca or Mg carbonates and Fe-Mn-oxy-hydroxides, lead to steep gradients mainly in the internal alpha-radiation field. Alternative approaches are required to account for the non-uniform internal dose rate and improve the reliability of TL dates of problematic samples.
  •  
47.
  • Schmidt, C., et al. (författare)
  • THE ASSESSMENT OF RADIONUCLIDE DISTRIBUTION IN SILEX BY AUTORADIOGRAPHY IN THE CONTEXT OF DOSE RATE DETERMINATION FOR THERMOLUMINESCENCE DATING
  • 2013
  • Ingår i: Archaeometry. - : Wiley. - 0003-813X .- 1475-4754. ; 55, s. 407-422
  • Tidskriftsartikel (refereegranskat)abstract
    • A combination of two autoradiography methods was applied to investigate the radionuclide distribution patterns in a range of different silices. We obtained greyscale images (-radiation) and -track patterns for qualitative assessment, and used a statistical approach to quantify the degree of uniformity of the radiation fields. It was found that almost all samples are poor in potassium, thorium and uranium, and that locally high concentrations are present only in dark-coloured veins and inclusions. Statistical analyses reveal evidence of radionuclide clustering in more than half of the 21 specimens. Concerning thermoluminescence dating of burnt lithics, such gradients should be taken into account to improve precision and accuracy in cases where the external radiation is not strongly dominating for the sample under consideration.
  •  
48.
  • Stokes, Chris R., et al. (författare)
  • On the reconstruction of palaeo-ice sheets : Recent advances and future challenges
  • 2015
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 125, s. 15-49
  • Forskningsöversikt (refereegranskat)abstract
    • Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.
  •  
49.
  • Trauerstein, Mareike, et al. (författare)
  • Climatic imprint on landscape morphology in the western escarpment of the Andes
  • 2013
  • Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 194, s. 76-83
  • Tidskriftsartikel (refereegranskat)abstract
    • Because of competing forces and variations through time, the relative importance of geomorphic processes responsible for the long-term topographic evolution of a mountain range is not always obvious. Here we perform a space-for-time substitution with the western escarpment of the Andes between 10 and 20 degrees S to identify the mechanisms of plateau destruction over geological timescales. We use this setting to propose that variations in the precipitation rate play a primary role in setting hillslope relief in uplifted mountainous landscapes. We find that in dry climates local topographic relief grows with increasing precipitation, independent of the underlying lithology and given an overall uniform rock uplift history. We proceed by differentiating Andean landscapes with generally low precipitation rates (80-500 mm a(-1), Peruvian Andes 10-20 degrees S) where local relief correlates positively with precipitation, from those with higher precipitation rates (400-1400 mm a(-1), Chilean Andes 35-40 degrees S) where increases in precipitation lead to topographic decay. We suggest that these trends result from dominant bottom-up control (channel incision is faster than hillslope response) giving way to an increasing top-down control (hillslope lowering is faster than channel incision). With low precipitation, relief growth is controlled by stream incision and knickzone retreat into a largely undissected plateau. With higher precipitation rates, relief is set by the steepness of graded streams and the rates of sediment production and transport on hillslopes. Trends of topography can also be interpreted in temporal terms in which the higher precipitation results in shorter response times, such that the Peruvian Andes between 10 and 20 degrees S are still responding to Miocene uplift, while in the Chilean Andes between 35 and 40 degrees S, these knickzones have already propagated through the entire fluvial network. We anticipate that such changes also operate during the formation and destruction of other mountainous plateau landscapes.
  •  
50.
  • Trauerstein, Mareike, et al. (författare)
  • Exploring fading in single grain feldspar irsl measurements
  • 2012
  • Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 10, s. 327-333
  • Tidskriftsartikel (refereegranskat)abstract
    • IR laser stimulated luminescence was used to determine the equivalent dose (De) for about 150 luminescent K-feldspar grains of two well-bleached aeolian sand samples, previously dated using quartz optically stimulated luminescence (OSL) and thermally-transferred OSL (TT-OSL). Fading tests were performed both on the entire single grain disc, using stimulation by IR LEDs, and on each grain individually, by stimulation with an IR laser. The single grain De distributions are highly over dispersed, even after applying rejection criteria, such as recycling ratio and recuperation. Fading rates determined with the IR LED stimulation do not represent the fading behavior of the IR laser stimulated signal and are therefore considered inappropriate for the fading correction of single grain D-e values. Fading rates of individual grains exhibit a wide range of values (0%-10% per decade) and plotting the single grain fading rates against the single grain De values reveals a negative relationship. Different approaches were taken to correct for fading, but the resulting ages tend to underestimate the reference ages.
  •  
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