Jakob Wallinga

Optically stimulated luminescence (OSL or optical) dating can be used to determine the time of deposition of sediments. Application of the method for young fluvial deposits is difficult due to incomplete zeroing of the luminescence clock, resulting in overestimation of the burial age. Here we present new optical dating methods and ages obtained on two sites in embanked floodplains of the River Waal. Results are in correct stratigraphical order and agree favourably with available age constraints

ABSTRACT One of the major dilemmas in feldspar luminescence dating is that the infra-red stimulated luminescence (IRSL) signals are either stable and difficult to bleach when measured at elevated temperatures, or unstable and easy to bleach when measured at low temperatures. To identify a signal for sediment dating that is both stable and easy to bleach, we investigate the potential of an optically and thermally transferred IRSL (T-IRSL) signal. Based on the mechanisms described in Wang et al. (2014), we develop a T-IRSL single-aliquot regenerative-dose (SAR) measurement protocol. We investigate the a-thermal stability of six different T-IRSL signals from a sample of infinite age using fading experiments, and by comparing field and laboratory saturation levels. The T-IRSL signal measured at 125 °C (T-IRSL125) following a preheat of 280 °C, is found to be as stable as the post-IR IRSL 290 °C signal (pIRIR290). Furthermore, laboratory bleaching experiments show that the T-IRSL125 signal bleaches faster than the pIRIR290 signal, and that the corresponding residual doses are more than 40% lower. This indicates that T-IRSL signals may be superior to pIRIR methods for dating young and/or insufficiently bleached deposits. However, a SAR protocol performance test of the T-IRSL125 signal yielded a systematic underestimation of 8 ± 2%. This is possibly caused by a sensitivity change during the first preheat and requires further investigation.

ABSTRACT Optically stimulated luminescence (OSL) dating is widely accepted as a cornerstone dating method for sediments. The method is particularly suitable for aeolian sediments formed between 10 and 100 ka, but is also widely applied to non-ideal deposits. Where light exposure prior to burial is insufficient for complete resetting of the OSL signal in all grains, additional processing is needed to determine accurate burial ages. The Minimum Age Model (MAM; Galbraith et al., 1999) has proven to be very powerful for such analysis, but results on sequences of poorly-bleached samples indicate that MAM uncertainty estimates are too optimistic. We have recently proposed a method to improve MAM uncertainty estimates (Cunningham & Wallinga, 2012). This method involves repeated calculation of the MAM result, with slightly changing input data and model parameters. Resulting uncertainty ranges are wider and more realistic than those of the standard MAM. Moreover, the approach allows construction of probability density distributions of age which can be used for Bayesian modelling (e.g. Oxcal) to combine data of different samples and/or data obtained using other methods. Here we explore the possibilities of the bootstrapped MAM approach combined with Bayesian analysis by detailed investigation of a 2-m thick sequence of aeolian deposits formed during the past 150 years. Processed OSL results on ten samples taken in a vertical sequence compare favourably with dendrochronological age constraints on stem discs taken from buried sections of the tree.

The reliability of equivalent-dose determinations on quartz made with the single-aliquot regenerative-dose (SAR) protocol is examined using a suite of sedimentary samples for which the equivalent dose is expected to be >200 Gy. Experiments on one sample were used to evaluate the precision obtained using the standard measurement procedure with (a) a range of pre-heat temperatures, and (b) a single pre-heat temperature. The precision is compared with that achieved using SAR for a repeated dose point after an initial pre-heat, and for a known dose given before the initial pre-heat. It is concluded that, at least for this sample, the scatter in OSL measurements dominates the spread in the estimates of De.

The electron-trapping probability in OSL traps as a function of irradiation temperature is investigated for sedimentary quartz and feldspar. A dependency was found for both minerals; this phenomenon could give rise to errors in dose estimation when the irradiation temperature used in laboratory procedures is different from that in the natural environment. No evidence was found for the existence of shallow trap saturation effects that could give rise to a dose-rate dependency of electron trapping.

The occurrence and effect of optical absorption of the infrared stimulated luminescence (IRSL) signal and the thermoluminescence (TL) signal from potassium-rich feldspar is investigated for two samples. If optical absorption of the luminescence signal occurs, it is expected that this will cause an age underestimation that will be most severe for coarser grain sizes. Of the two samples under study here, one sample is shown to be affected by optical absorption, whereas the other is not. There is a significant decline in luminescence age with increasing grain size for the sample which exhibits optical absorption, but not for the other sample. However, both samples show a severe IRSL age underestimation for all grain sizes, compared to the age obtained by optical stimulation of quartz from the same samples. We conclude that, although there is an effect of optical absorption on the IRSL age, there must be additional reasons for the underestimation of the IRSL age.

Shallow marine and intertidal shell rich sediments from the low coastal plain of Dubai were dated by optically stimulated luminescence. Combined high-resolution gamma spectrometry and ICP–MS analyses revealed significant disequilibria in the 238U decay series. Time dependent dose rates were modelled for two scenarios including a closed system and an open system with linear U and Ra uptake. OSL ages that were calculated using the linear uptake model are in good agreement with archaeological evidence and radiocarbon datings on shells and wood. The presented results illustrate that luminescence-dating techniques are suitable to set up a chronostratigraphic frame for calcareous coastal environments if an appropriate model is applied to consider the influence of radioactive disequilibria and time dependent dose rates. A comprehensive radionuclide analysis of the sediments is thought necessary to perform geochemically supported dose rate simulations.

Page 1. Optically stimulated luminescence dating of uvial deposits: a review JAKOB WALLINGA Wallinga, J. 2002 (December): Optically stimulated luminescence dating of uvial deposits: a review. Boreas, Vol. 31, pp. 303–322. Oslo. ISSN 0300-9483. ...

ABSTRACT Landscape response to alternations of climate induces periods of enhanced sediment supply to rivers during cold climate, promoting valley widening and strath formation while incision rate is reduced. During these periods, rivers are aggrading and usually show a braided pattern. The transition from valley widening to downcutting leads to formation of the climatic-aggradation fluvial terraces observed along most rivers. Age and height of such terraces are commonly used for estimating mean fluvial incision rates. However these rates must be taken with caution when one wants to detail the dynamics of river incision into the bedrock because of its climatically-induced punctuated nature. Numerical simulations actually suggest that incision rates are not linear between the formation of two successive climatic-aggradation fluvial terraces. The Rangitikei River (New Zealand) is actively downcutting in an uplifting Plio-Pleistocene sedimentary basement. Entrenchment is punctuated by climatic terraces. The more recent one formed from 30 to 15 ka, spanning the Last Glacial Maximum. Since the LGM, the Rangitikei River incised 75-meter deep gorges into the LGM terrace deposits (max 15 meters) and the underlying bedrock, at a mean rate of ~4.1 to 5.6 mm.a-1 assuming a linear dynamics. We investigate here this post-LGM entrenchment dynamics using optical dating (IRSL of feldspar) of 17 post-LGM autocyclic strath terraces cut into the bedrock. All the IRSL calculated ages using Multiple Aliquots or Single Aliquot Regenerative protocols are older than the LGM, implying a systematic overestimation of the ages. Overestimation is confirmed by measurements of the luminescence signal of present-day river sediments and of 2004' flood deposits, whose calculated IRSL ages are of 37.4 +/- 3.1 and 55.1 +/- 3.5 ka. Age overestimation may occur when dating fluvial deposits using luminescence methods because of insufficient exposure of minerals to daylight before their settlement in the deposits to be dated. In fluvial settings, the solar resetting of the luminescence signal of particles is limited by turbidity because of attenuation of light through the water column and by mode and distance of particle transportation. Overestimation also likely depends on magnitude and frequency of input of non-bleached particles from hillsides and river banks. Here, using additional luminescence measurements on single-grains and/or very-small aliquots (3-5 grains), we show that IRSL age overestimate depends on the proportion of mixing between grains that have been bleached during their fluvial transportation and unbleached ones, coming from the bedrock. Our data set is consistent with a non-linear incision rate since the LGM and we show that the proportion of mixing between bleached and unbleached grains is intimately linked to variations in the rate of bedrock erosion and related supply of unbleached grains to the river. Our study consequently suggests that the shape and width of IRSL age distributions obtained through single-grain measurements could illuminate the past dynamics of rivers.

... Luminescence dating has been widely applied to establish the timing of coversand deposition in ... plaggen agri-culture was the dominant land use system in the Pleistocene coversand area ... IRSL dating results for the Boxtel core penetrating Middle and Late Quaternary deposits ...

Abstract: Abstract: Optically stimulated luminescence (OSL) dating is a quantitative dating method to determine the time of last exposure of sand and silt to (sun) light. However, insufficient resetting of the optically stimulated luminescence signal prior to sediment deposition can result in ...

Botanical microfossils, macroremains and oribatid mites of a Weichselian interstadial deposit in the central Netherlands point to a temporary, sub-arctic wetland in a treeless landscape. Radiocarbon dates and OSL dates show an age between ca. 54.6 and 46.6 ka cal BP. The vegetation succession, starting as a peat-forming wetland that developed into a lake, might well be linked with a

An almost 50-m-deep core from the Weichselian Rhine-Meuse palaeovalley, near the present Dutch coast, reveals new insights into how this continental-scale fluvial system responded to relative sea-level fluctuations associated with the last Quaternary glaciations. A multidisciplinary study of this core included sedimentological and stratigraphic analysis aug- mented with data on shell, diatom and pollen content to infer depositional environments. Optically

ABSTRACT We present a multiple luminescence signal measurement procedure that simultaneously measures six different luminescence signals from a single polymineral aliquot (i.e. multiple-signal, short MS-SAR approach). The six signals show different bleaching rates in bleaching experiments, ranging from rapid bleaching for the quartz dominated blue stimulated luminescence signal (measured at 125 °C, BSL-125), to the slow-bleaching polymineral thermoluminescence signal. The bleaching rate of the infrared stimulated luminescence (IRSL) measured at room temperature (IR-25) and elevated temperature post-IR IRSL (pIRIR-90, pIRIR-155, pIRIR-225) signals decrease with increasing measurement temperature. Owing to these different bleaching rates, the MS-SAR approach allows inference of the degree of bleaching, and thereby information on the transport history of sediments. We test this approach by applying the MS-SAR to four coastal samples from a well-monitored sand-nourishment site at the Dutch coast. Our results show that the proposed MS-SAR approach can be utilised to construct bleaching plateaus which provide an independent and time-effective measure of the degree of poor bleaching in a sediment sample based on the measurement of only a few large aliquots. We propose that the MS-SAR protocol can be used to profile the age, luminescence properties and degree of bleaching of minimal prepared polymineral. This pre-profiling will allow the selection of suitable samples for full luminescence dating analysis in a target-orientated and time-effective manner.