LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
A Chronological Study of the Loess Deposits Over – and Underlying the Eltville Tephra Using the Newest Luminescence Techniques Applied to Sand-Sized Quartz: Results for Two Late Weichselian Type Localities
Vandenberghe, D.A.G.1, De Meester, E.1, Velghe, G.1, Zöller, L.2,
Van den haute, P.1
1Laboratory of Mineralogy and Petrology (Luminescence Research Group), Department of Geology and Soil Science, Ghent University, Krijgslaan 281 (S8), B-9000 Ghent, Belgium
2LS Geomorphologie, University of Bayreuth, D-95440 Bayreuth, Germany
The Eltville tephra is a widespread tephra layer in Germany, the Netherlands and Belgium. Especially in loess sections, it has been widely used as a tephrostratigraphical marker. The age of the tephra has been established by luminescence dating of over- and underlying loess units, and is now generally accepted to be very close to ~20ka. The majority (if not all) of the dates has been obtained by applying thermoluminescence (TL) and/or infrared-stimulated luminescence (IRSL) techniques to polymineral fine (4-11μm) grains. However, luminescence dating has undergone major methodological developments in the past ten years. At present, the preferred dating methodology involves the application of the single-aliquot regenerative- dose (SAR) protocol to optically stimulated luminescence (OSL) signals from quartz; this approach has been proven to yield accurate and precise dates for sediments from a wide variety of sedimentary environments and age.
In this paper, we reinvestigate the age of the Eltville tephra in the Late Weichselian type sections at Lixhe (Belgium) and Mainz-Weisenau (Germany). A stateof- the-art optical dating technology is used, in which the ages are obtained by applying the SAR-OSL protocol to fine-sandy (63-90μm) quartz grains.
We investigate the luminescence characteristics to some extent. In general, the samples behave well in the SAR-protocol: recycling ratios are close to unity, growth curves pass very close to the origin, and a laboratory dose given prior to any heat treatment can be measured accurately. Examination of the linearly modulated OSL (LM-OSL) signals demonstrates that the samples are dominated by a fast component. The equivalent dose is independent of preheat temperature, and a pulse anneal experiment is used to further confirm that the dosimetric signal is thermally stable.
Within analytical uncertainty, the optical ages are consistent with the stratigraphic position of the samples. The dates obtained for over- and underlying loess units bracket the age of the Eltville tefra at Lixhe between 33±4ka and 30±1ka, and at Mainz-Weisenau between 31±4ka and 36±4ka; these age constraints are significantly older than the ~20ka age that was previously established for this marker horizon.
Ongoing investigations aim at resolving this discrepancy; these involve application of the “classic” TL and IRSL protocols to the polymineral fine grains, SAR-OSL dating of fine-grained quartz, and quartz-based OSL dating of samples bracketing the Eltville tephra at the intensively-investigated exposure near Nussloch (Germany).