| 1. |
- Kjaer, Kurt, et al.
(author)
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The first independent chronology for Middle and Late Weichselian sediments from southern Sweden and the Island of Bornholm
- 2006
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In: GFF. - 2000-0863. ; 128:3, s. 209-220
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Journal article (peer-reviewed)abstract
- Conventional Optically Stimulated Luminescence (OSL) dating using the equivalent dose distributions of 8 mm aliquots have been extended to key stratigraphical sites in southernmost Sweden and the island of Bornholm. The objective has been to bridge the lack of an independent chronology, which might catalyze a new understanding of the ice flow patterns related to the initiation of the Last Glacial Maximum, and the stratigraphical development during the deglaciation sequence. Sediments from proximal environments are usually 10-15 kyr older than expected from regional stratigraphical correlations and radiocarbon dates of mammoth tusks. We propose that OSL signals are inherited from reworked sediments that were sufficiently bleached prior to glacial or glaciofluvial transportation and deposition. Sediments from distal and beach environments seem to indicate proper depositional ages. Thus, the main Weichselian stadial was preceded by almost 20 kyr of ice free conditions, succeeded by an ice advance from south-southeast before northeasterly ice flow predominated. Major inconsistencies still exists for the final deglaciation. Two distinct environmental reconstructions of the uppermost diamict at two separate sites, both superimposed on a periglacial surface, predict either deposition during subaquatic conditions associated with drifting icebergs after 16 kyr or subglacial sedimentation associated with an ice advance in Oresund. It remains unsolved whether the periglacial surface at the two sites can be correlated or if they represent two different stratigraphical levels. In perspective, the introduction of OSL dates in Skane has identified the periglacial marker horizon or horizons as targets for future intensive dating.
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| 2. |
- Nathan, RP, et al.
(author)
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Environmental dose rate heterogeneity of beta radiation and its implications for luminescence dating: Monte Carlo modelling and experimental validation
- 2003
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In: Radiation Measurements. - 1879-0925. ; 37:4-5, s. 305-313
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Journal article (peer-reviewed)abstract
- The recent development of rapid single sand-sized grain analyses in luminescence dating has necessitated the accurate interpretation of D-e distributions to recover a representative D-e acquired since the last bleaching event. Beta heterogeneity may adversely affect the variance and symmetry of D-e distributions and it is important to characterise this effect, both to ensure that dose distributions are not misinterpreted, and that an accurate beta dose rate is employed in dating calculations. In this study, we make a first attempt providing a description of potential problems in heterogeneous environments and identify the likely size of these effects on D-e distributions. The study employs the MCNP 4C Monte Carlo electron/photon transport model, supported by an experimental validation of the code in several case studies. We find good agreement between the experimental measurements and the Monte Carlo simulations. It is concluded that the effect of beta, heterogeneity in complex environments for luminescence dating is two fold: (i) the infinite matrix dose rate is not universally applicable; its accuracy depends on the scale of the heterogeneity, and (ii) the interpretation of D-e distributions is complex and techniques which reject part of the D-e distribution may lead to inaccurate dates in some circumstances. (C) 2003 Elsevier Science Ltd. All rights reserved.
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