238 research outputs found
Dating Pleistocene deltaic deposits using in-situ 26Al and 10Be cosmogenic nuclides
No full textThe present study aims at testing the possibility of using the in-situ cosmogenic burial dating technique on deltaic deposits. The sequence analyzed is exposed along the Ligurian coast (north-west Italy) and is made of proximal marine and continental deposits previously considered Pliocene or Plio-Quaternary in age. In the study area two allostratigraphic units were recognized. The lower unit represents the evolution of a small coarse-grained delta developed in a fjord or embayment environment. The coarsening/shallowing upward trend observed within the sections, from bottom to top, suggests that the delta prograded rapidly in the landward portion of the canyon placed opposite to the paleo-river outlet. Within the deltaic sequence the transgressive and highstand system tracts were recognized. The unit 2 is composed by several alluvial fan systems deposited in small incised valleys developed within the previously, uplifted deltaic deposits and successively incised by a braided river system. In-situ produced cosmogenic nuclides were used in order to date the age of the deposition of the deltaic deposits. Results suggest that the studied deltaic sediments belonging to the unit 1 were deposited between 1,300,000 and 200,000 year ago thus during the Lower to Middle Pleistocene, whereas the unit 2 was deposited during the Middle Pleistocene as a consequence of a tectonically driven uplift phase. Furthermore samples collected within the prograding part of the delta show the higher denudation rates. The obtained results demonstrate that burial ages and related erosion rates inferred from cosmogenic nuclides concentrations can be considered as a very useful tool to reconstruct the sea level changes over the past 1 million year
Response to Bromley et al. "Comment on 'Was Scotland deglaciated during the Younger Dryas By Small and Fabel (2016)
No full textNo abstract available
Cosmogenic dating
No full textProgress Code: completedStatement: The downloadable dataset only contains sampling locations. The cosmogenic data have not been archived, and given the length of time that has passed, it is unlikely that they will be archived (2019-06-20).The data set consists of cosmogenic exposure ages for samples collected by Research School of Earth Sciences in the Prince Charles Mountains and vicinity.<br/><br/>Thus far work has been carried out in the 2001/2002, 2002/2003, 2003/2004 and 2004/2005 field seasons.<br/><br/>Currently, the only data publicly available is an excel spreadsheet detailing sampling locations.<br/><br/>The objectives of this project were:<br/><br/>To develop a comprehensive understanding of the Lambert Glacier of East Antarctica, from the time of the last maximum glaciation to the present, through an integrated and interdisciplinary study combining new field evidence - ice retreat history from cosmogenic exposure dating, geodetic measurements of crustal rebound, satellite measurements of present ice heights and changes therein - with other geological and glaciological data and numerical geophysical modelling advances. The project contributes to the quantitative characterisation of the complex interactions between ice-sheets, oceans and solid earth within the climate system. Outcomes have implications for geophysics, glaciology, geomorphology, climate, and past and future sea-level change.<br/><br/>This work was completed as part of ASAC projects 2502 and 2516 (ASAC_2502 and ASAC_2516).<br/><br/>The fields in this dataset are:<br/><br/>Sample<br/>Date<br/>Collector<br/>Type<br/>Lithology<br/>Location<br/>Elevation<br/>Latitude<br/>Longitud
Wolf und Lamm. Ein Dialog über eine äsopische Fabel (= Phaedrus 1, 1)
No full textDer vorliegende Dialog zwischen den vier Autoren behandelt Phaedrus‘ Fabel über den Wolf und das Lamm (1, 1). Im Gespräch wird Fragen nachgegangen wie „Warum ist dieses Gedicht eine Fabel?“, „Was ist das Thema des Gedichts?“, „Was wollte der Autor vermitteln?“, „Was soll man als Leser lernen?“, „Welche Rolle spielt der Dialog in der Auseinandersetzung?“, „Worin besteht der Konflikt?“, „In welchen Situationen kann ein ähnlicher Konflikt vorkommen?“.The present dialogue deals with Phaedrus‘ fable about the wolf and the lamb (1, 1). In this discussion the four authors address questions like “Why is this poem a fable?”, “What is the subject matter of the poem?”, “What did the author want to tell us?”, “What should we learn from the scene?”, “What should we make of the fact that the two protagonists talk with one another?”, “What are the main features of the confrontation?”, “In which situations might a similar confrontation occur?”.Le dialogue qui suit, entre les quatre auteurs, porte sur la fable „le Loup et l’Agneau“ (1.1), reprise d’Esope. Plusieurs questions sont abordées dans la discussion comme : „en quoi ce poème est-il une fable?“, „quel est le véritable thème du poème“, „que veut communiquer l’auteur?“, „que peut-on apprendre de cette scène?“, „quel rôle joue le dialogue dans cette altercation?“, „quel est l’enjeu de ce conflit?“, „dans quelles situations un semblable conflit peut-il surgir?“
The use of in-situ produced cosmogenic radionuclides in glaciology and glacial geomorphology
No full textThe usefulness of in-situ produced cosmogenic radionuclides in constraining glacial chronologies through exposure-age dating has been demonstrated in numerous studies. However, an understanding of cosmogenic radionuclide techniques and their uncertainties opens up a wide range of other potential applications in glaciology and glacial geomorphology. Recently developed applications include: estimation of spatial and temporal variations in the depth of glacial erosion from cosmogenic radionuclide inheritance, which provides important constraints on process-based erosion models; and burial dating, which can provide chronological control for glacial advances and the onset of till deposition. An interesting new application, currently at the level of theoretical model development, concerns the unraveling of complex exposure and burial histories. Overall, in-situ produced cosmogenic radionuclide techniques provide a means with which to constrain a wide range of ice-sheet and glacial models over time-scales of a thousand to a few million years
A Lateglacial 10Be production rate from glacial lake shorelines in Scotland
No full textThe identification of tephra within varved deposits of a former ice-dammed lake that existed in Scotland during the Younger Dryas provides an opportunity to calibrate 10Be production rates using previously published 10Be concentrations from the lake shoreline and independently derived ages for the tephra’s derived from the Greenland Ice Core records. The best-estimate ages of the tephras yield indistinguishable 10Be production rate values for spallation with an average value of 4.26 ± 0.21 atoms g-1 a-1 using the ‘Lm’ scaling scheme. These values are in best agreement with the most proximal reference 10Be production rate from Norway
Was Scotland deglaciated during the Younger Dryas?
No full textRecent work has produced data that challenges the canonical view that the Younger Dryas (c.12.9–11.7 ka) was a time of glacier expansion across the North Atlantic. Boulders on moraines located within the inner sector of the Scottish Loch Lomond Stadial (≈Younger Dryas) ice cap yield cosmogenic exposure ages 12.8–11.3 ka with a best estimate moraine age of 11.5 ± 0.6 ka. This age contradicts the interpretation that Scotland was completely deglaciated as early as 12,580 cal yr BP and no later than 12,200 cal yr BP. Our data supports the previously accepted scenario, supported by a wide variety of data, that final deglaciation of Scotland did not occur until late in the Loch Lomond Stadial or the early Holocene
The use of in-situ produced cosmogenic radionuclides in glaciology and glacial geomorphology
No full textThe usefulness of in-situ produced cosmogenic radionuclides in constraining glacial chronologies through exposure-age dating has been demonstrated in numerous studies. However, an understanding of cosmogenic radionuclide techniques and their uncertainties opens up a wide range of other potential applications in glaciology and glacial geomorphology. Recently developed applications include: estimation of spatial and temporal variations in the depth of glacial erosion from cosmogenic radionuclide inheritance, which provides important constraints on process-based erosion models; and burial dating, which can provide chronological control for glacial advances and the onset of till deposition. An interesting new application, currently at the level of theoretical model development, concerns the unraveling of complex exposure and burial histories. Overall, in-situ produced cosmogenic radionuclide techniques provide a means with which to constrain a wide range of ice-sheet and glacial models over time-scales of a thousand to a few million years
Exposure-age dating of rock avalanche debris at Raven Crag (Pasture Beck valley, Hartsop) using cosmogenic 10Be
No full textA recent paper (Wilson & Jarman, 2022) documented 84 rock slope failures (RSFs) in the Lake District and the adjacent Howgill Fells. The definition adopted for a RSF was that used by Jarman & Harrison (2019, p.202):any substantial rockmass exposed to slope gravitational processes which has lost structural integrity, regardless of its degree of disintegration or distance travelled.A minimum threshold size of 0.01 km2 (100x100 m) was applied by Wilson & Jarman (2022) in order to exclude small-scale rockfalls, which are abundant in the fells of Lakeland. To determine RSF size, source ‘cavity’, travel path and debris accumulation areas were combined. Although a tripartite system of RSF classification was employed - i.e. (1) rock slope deformations of both extensional and compressional modes, (2) rockslides of typically arrested translational form, and (3) rock avalanches of cataclasmic and sub-cataclasmic types - in reality RSFs may be complex in that they can display characteristics of more than one of these categories. Thus in some circumstances classification may be difficult.In the inventory compiled by Wilson & Jarman (2022) 12 RSFs were assigned to the sub-cataclasmic rock avalanche category. These comprise failures that have largely evacuated their source areas and have disintegrated but the leading edge of the debris has only just reached the slopefoot, with the bulk of the debris aligned along the travel path. Failures of this type are invariably at the lower end of the RSF size range (0.01-0.3 km2 in the Lake District).Age assessment of Lake District RSFs has so far relied on a consideration of their morphology along with evaluation of their relationship to Late Devensian (32-11.7 ka) glacier margins. This has resulted in a small number of failures being inferred to pre-date Late Devensian glaciation. These failures, or parts thereof, are likely to have been reactivated during or following ice wastage. A few other failures are of undoubted Holocene (11.7 ka-present day) age because they either occurred in recent centuries or they occupy locations that were buried beneath glacier ice during restricted glaciation of the Younger Dryas Stadial (12.9-11.7 ka). Therefore the majority of the failures are likely to have occurred during wastage of the Lake District’s Late Devensian ice dome (~20-14.7 ka) and/or in the Lateglacial period (14.7-11.7 ka). However, numerical ages have not yet been obtained for any of the 84 documented failures.In this paper we report two cosmogenic nuclide (10Be) ages for boulders from the debris of the sub-cataclasmic rock avalanche at Raven Crag (Pasture Beck valley, Hartsop). These are the first numerical ages to be reported for a Lake District RSF, although cosmogenic ages for RSFs in other mountain areas of Britain have been available for several years. The rock avalanche debris is located within Younger Dryas ice limits and it displays a downslope rather than down-valley configuration – i.e. debris alignment does not indicate any overriding and down-valley transport by glacier ice. Together these factors support a Holocene age for the rock avalanche. <br/
Holocene Chronology of the Brattforsheden Delta and Inland Dune Field, SW Sweden
No full textBrattforsheden is a large glacifluvial deposit in southwestern Sweden and associated with it is one of Sweden's largest inland dune fields. Although the relative ages of the Brattforsheden deposits are well known, absolute ages from the area are few. In this study we have used optically stimulated luminescence (OSL), surface exposure (Be-10) and radiocarbon (C-14) dating to provide an absolute chronology for the deglaciation and for the Holocene development of the aeolian dunes. Our data show that the deglaciation took place just before 11 ka (11.5 +/- 0.6 ka OSL, 11.3 +/- 0.8 ka Be-10), in line with the C-14-based regional deglaciation age. Aeolian dunes started forming immediately after deglaciation and were active for at least 2000 years, well after vegetation had established. Renewed aeolian activity occurred 270-180 years ago, resulting in the deposition of sand sheets. Comparison between dating methods and studies of OSL dose distributions show that glacial, glacifluvial and littoral sediments suffer from incomplete bleaching and thus that mean OSL ages from such deposits overestimate the true depositional age. By using small aliquots and statistical age models, this effect can partly be countered. Also, some of the Be-10 ages appear too old, which may be due to previous exposure
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