and Van den Haute, P. 2007. Late Weichselian fluvio-aeolian sands and coversands of the type locality Grubbenvorst (southern Netherlands): sedimentary environments, climate record and age.ABSTRACT: The Weichselian Late Pleniglacial and Lateglacial aeolian stratigraphy (Older Coversand I, Beuningen Gravel Bed, Older Coversand II, Younger Coversand I, Usselo Soil, Younger Coversand II) in the southern Netherlands has been reinvestigated in its type locality (Grubbenvorst). Sedimentary environments have been reconstructed and related to their climatic evolution based on periglacial structures. In addition, 22 optically stimulated luminescence (OSL) ages have been determined that provide an absolute chronology for the climatic evolution and environmental changes of the coversand area.From this work it appears that, prior to 25 ka fluvial deposition by the Maas dominated. After 25 ka fluvial activity reduced and deposition occurred in a fluvio-aeolian environment with continuous permafrost (Older Coversand I). This depositional phase was dated between 25.2 AE 2.0 and 17.2 AE 1.2 ka. The upward increase of aeolian activity and cryogenic structures in this unit is related to an increase of climatic aridity and a decrease in sedimentation rate during the Last Glacial Maximum (LGM). The Beuningen Gravel Bed, that results from deflation with polar desert conditions and that represents a stratigraphic marker in northwestern Europe, was bracketed between 17.2 AE 1.2 and 15.3 AE 1.0 ka. Based on this age result a correlation with Heinrich event H1 is suggested. Permafrost degradation occurred at the end of this period. Optical ages for the Older Coversand II unit directly overlying the Beuningen Gravel Bed range from 15.3 AE 1.0 ka at the base to 12.7 AE 0.9 ka at the top. Thus this regionally important Older Coversand II unit started at the end of the Late Pleniglacial and continued throughout the early Lateglacial. Its formation after the Late Pleniglacial (LP) maximum cold and its preservation are related to rapid climatic warming around 14.7 ka cal. BP. The Allerød age of the Usselo Soil was confirmed by the optical ages.

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Using a set of modern/young (0 to about 200 years old) dust samples collected from the Chinese Loess Plateau the bleachability of IRSL measured at 50°C (IR 50 ) and post-IR 50 elevated temperature IRSL (measured at 225°C and at 290°C) is investigated by measuring the apparent (residual) doses recorded by these signals. Doses recorded by quartz OSL are used as a reference. Allowing for differences in dose rates it seems that both IRSL and post-IR IRSL signals yield residual doses that are significantly larger than the doses measured in quartz. These residual doses can be largely explained by thermal transfer caused by preheating. Nevertheless, we advise against the use of a low temperature preheat (<200°C) with IR 50 to date loess samples because, as has been reported before, the signal appears to be thermally unstable. In general, we conclude that it may not be advisable to apply post-IR IRSL dating to Chinese loess samples where residuals of up to ~20 Gy are a significant fraction of the total dose. However, these residuals quickly become unimportant when dating older samples, and this is the age range in which post-IR IRSL dating is likely to be most useful.

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Floodplain deposition is an essential part of the Holocene sediment dynamics of many catchments and a thorough dating control of these floodplain deposits is therefore essential to understand the driving forces of these sediment dynamics. In this paper we date floodplain and colluvial deposition in the Belgian Dijle catchment using accelerator mass spectrometric radiocarbon and optical stimulated luminescence dating. Relative mass accumulation curves for the Holocene were constructed for three colluvial sites and 12 alluvial sites. A database was constructed of all available radiocarbon ages of the catchment and this database was analysed using relative sediment mass accumulation rates and cumulative probability functions of ages and site-specific sedimentation curves. Cumulative probability functions of ages were split into different depositional environments representing stable phases and phases of accelerated clastic deposition. The results indicate that there is an important variation between the different dated sites. After an initial stable early and middle Holocene phase with mainly peat growth in the floodplains, clastic sedimentation rates increased from 4000 BC on. This first phase was more pronounced and started somewhat earlier for colluvial deposits then for alluvial deposits. The main part of the Holocene deposits, both in colluvial and alluvial valleys, was deposited during the last 1 ka. The sedimentation pattern of the individual dated sites and the catchment-wide pattern indicate that land use changes are responsible for the main variations in the Holocene sediment dynamics of this catchment, while the field data do not provide indications for a climatological influence on the sediment dynamics.

A study was made of the applicability of three different techniques for equivalent dose (D e ) determination in the optical dating of quartz: the single-aliquot regenerative-dose technique (SAR), the single-aliquot additive-dose technique (SAAD) and the multiple-aliquot additive-dose technique (MAAD). For this purpose, quartz grains were extracted from a sequence of Upper Pleniglacial to Late-glacial coversands exposed at the locality of Ossendrecht in the southwestern Netherlands, a site for which both radiocarbon and earlier luminescence dates are available, providing independent age control.Upon testing the different assumptions underlying each of the three OSL techniques investigated, the SAR protocol was found to be the technique of choice. The optical ages obtained with this protocol were in good agreement with the chronostratigraphical position of the sediments investigated and with the available chronostratigraphical information on the same and equivalent deposits. This confirms the suitability of the SAR technique for dating coversands. Furthermore, a small laboratory intercomparison of SAR-based D e determinations yielded results that were in fair overall agreement.