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The archaeological site of Taibeh located south of Wadi Musa, Jordan, incorporates at least two, maybe even five, successive layers associated with the Late Ahmarian, also known as Masraqan, technocomplex. The Masraqan is elsewhere connected with the beginning of the intensive use of plant food and with permanent settlements. Taibeh could be the first site to present as much as 5 successive layers of this cultural unit. The Masraqan is relatively well constrained in time, usually dated between 18 and 25 ka BP. A series of heated flints was collected at Taibeh to be dated using TL. Two informations are required for the estimation of a TL age: the equivalent dose ( D e ) which is the dose accumulated in the flint since it had been heated, and the dose rate ( D ˙ ) to which the flint is exposed during the burial time. The D e estimation was done applying two different protocols, and both produced consistent results. The D ˙ estimation was realised using a modified version of DRAC (Durcan et al., 2015) which allows to use different radio-element concentrations for the flints and the surrounding sediment.

Simplified procedures were introduced in OSL dating of young samples with dim and poorly bleached quartz grains. Standardized growth curve (SGC) has been established with quartz OSL dating with the single-aliquot regenerative-dose (SAR) protocol. OSL dating is achieved by measuring the natural OSL signal (LN) and the luminescence (TN) response to a test dose, and then projecting onto the SGC. Large data sets of aliquots enable to have statistical analysis and application of age models for poorly bleached samples. Finite mixture model (FMM) was applied to the data sets. Only aliquots meeting the objective selecting criteria are analyzed further for determining the equivalent dose (De) values. As a result, reliable De estimates were obtained using the proposed simplified procedures, with the advantage of saving substantial machine time. Single grain measurements have been effectively achieved with the single aliquots for the dim samples.

Standardised growth curves (SGCs) were established for extracts of potassium feldspar (K-feldspar), plagioclase and polymineral grains from various geological settings (deserts, loess, lake or fluvial deposits) from Northern China. Single-aliquot regenerative-dose (SAR) protocol was used with the measurements of multiple elevated temperature post-IR IRSL (MET-pIRIR) signals from 50 °C to 250 °C with an interval of 50 °C. Regenerative-dose normalisation was applied for the SGC construction. The shapes of the SGCs of K-feldspar vary between IRSL signals measured at different temperatures. For coarse grains (63–180 μm), the SGCs of the K-feldspar, plagioclase and polymineral fractions are close to each other. However, the polymineral fine grains (4–11 μm) have a distinct SGC from the coarse-grain fractions. It may be caused by the difference in alpha irradiation. Two test doses (145 Gy and 72.5 Gy) were applied to construct the SGCs for K-feldspar. The SGC built with the larger test dose has a larger characteristic saturation dose (D0). Test dose used for equivalent dose (De) measurements need to be the same as the test dose used for SGC construction, otherwise the SGC De may not be estimated accurately. With the same test dose used, the De values estimated from SGCs are identical with the De values generated from individual dose response curves.

The upper limit of optically stimulated luminescence (OSL) dating technique is usually defined by signal saturation. In nature the OSL signal saturates even faster than in the laboratory. Here we present a study on natural saturation of OSL and thermally transferred OSL (TT-OSL) signals of quartz grains from Nilotic origin. Quartz samples from two representative sections from the coastal plain of Israel, and which span approximately similar time frames, were used to construct semi-natural dose response curves (DRC) for OSL and TT-OSL by plotting the natural signal of samples against their depth and equivalent dose (De). Samples from these two sections, as well as from other sites, define typical OSL and TT-OSL DRC's for Nilotic quartz that was transported to the eastern shores of the Mediterranean Sea. The constructed semi-natural OSL DRC is unique to the quartz of Nilotic origin and indicates the upper limit for reliable OSL dating of this quartz at 140 Gy due to signal saturation. The natural TT-OSL luminescence grows linearly up to 400 Gy, and is constant for 400–600 Gy. Steady-state between TT-OSL trap-filling, due to ionizing radiation, and concurrent thermal emptying of these traps is achieved at 600 Gy. TT-OSL dating of the Nilotic quartz is expected to underestimate ages over ∼120 ka due to the low thermal stability of the signal.

A large range of equivalent dose (De) values was observed by applying the single-aliquot regenerative-dose (SAR) procedure to the optically stimulated luminescence (OSL) signal of single grains of quartz extracted from sediments at the Yujiagou site in the Nihewan Basin, north China. Many quartz grains yielded De values close to zero, which results in severe age underestimation when compared with the results of potassium-rich feldspar grains measured using post-infrared infrared stimulated luminescence (pIRIR) procedure. Dose recovery tests suggest that the SAR protocol is suitable for De determination. However, a large grain-to-grain variation in thermal stability was identified based on single-grain pulse-annealing measurements. We found that most of the zero-dose or low-dose grains are associated with thermally unstable OSL signals, which explains the large dispersion of the quartz OSL De distribution. This is further confirmed by the short lifetime of the unstable OSL signals obtained using single-aliquot pulse-annealing test.

Sand-loess sequences in the desert-loess transition zone are sensitive terrestrial archives for recording past climatic changes and atmospheric dust activities. However, a high-resolution chronology for relative long-term sand-loess sequences is still rare. In this study, we used quartz SAR OSL and K-feldspar pIRIR (pIRIR290) methods to date a 16.8 m sand-loess sequence at Zhenbeitai in Yulin (North-Central China). The quartz is sensitive, fast component dominated but saturates at ∼150 Gy. The measured K-feldspar pIRIR290 De showed no dependency on the first IR stimulation temperature between 50 °C and 260 °C. Dose recovery results were consistent with unity up to ∼800 Gy for a test dose of approximately 30% of the equivalent dose to be measured. The resulting pIRIR290 ages are consistent with the stratigraphy up to ∼121 ka. Thus, a high-resolution chronology up to the last interglacial could be established for the Zhenbeitai sand-loess section. Derived mass accumulation rates show sedimentation rates of ∼10–80 cm/ka for the upper loess (

The application of a regeneration procedure for optically stimulated luminescence (OSL) dating requires that the dose-response curve (DRC) of a natural sample is the same as that of a laboratory-generated one. However, the build-up of the laboratory-generated DRCs of quartz has been widely reported in the literature, i.e., the laboratory-generated DRCs are significantly higher than the natural counterparts in the high dose region (above 150 or 200 Gy). This results in severe underestimation of equivalent dose (De) for quartz OSL in the high dose region during the application of a single-aliquot regenerative-dose (SAR) protocol. However, the potential mechanism governing the build-up of the laboratory-generated DRC is still unclear. In this study, we performed a comprehensive investigation of the natural and laboratory-generated OSL signals and DRCs using a kinetic model for quartz. We compared the differences in charge concentrations between natural and laboratory-irradiated aliquots following irradiation and monitored the competition for holes and electrons during preheat and stimulation, for the natural, regenerative, and test dose cycles. In the course of the modelling, we could see the build-up of laboratory-generated DRCs, the underestimation of De, and a double exponential saturation characteristic of the DRCs. We demonstrated a discrepancy in competition for electrons in the deep electron trap and recombination centres during stimulation between the natural, regenerative, and test dose cycles. The simulation results are directly relevant to quartz OSL De determination using the SAR protocol and reveal the mechanisms responsible for the experimentally observed different behaviours between natural and laboratory-generated DRCs.

We simulated the variability in measured quartz optically stimulated luminescence (OSL) signals and dose response curves (DRCs) caused by measurement uncertainties, including counting statistics and instrumental irreproducibility. We find that these measurement errors can give rise to large variations in the observed luminescence signal and contribute to among-aliquot or among-grain scatter in DRCs and equivalent dose (De) values. Different measurement systems (i.e., luminescence readers) may have different counting statistics properties and, hence, may exhibit differing extents of variation in the observed OSL signal, even for the same sample. Our simulation shows that the random measurement uncertainties may result in some grains or aliquots being ‘saturated’ (that is, the measured natural signal is consistent with, or lies above, the saturation level of the measured DRC) and that the rejection of these ‘saturated’ grains may result in a truncated De distribution, with De underestimation for samples with natural doses close to saturation (e.g., twice the characteristic saturation dose, D0). We propose a new method to deal with this underestimation problem, in which standardised growth curves (SGCs) are established and the weighted-mean natural signal (Ln/Tn) from all measured grains is projected on to the corresponding SGCs to determine De. Our simulation results show that this method can produce reliable De estimates up to 5D0, which is far beyond the conventional limit of ∼2D0 using the standard SAR procedure.

Optically Stimulated Luminescence (OSL) dating on quartz is well established following the introduction of the Single-Aliquot Regenerative-dose (SAR) protocol. Despite its widespread use, it has a major drawback in frequently underestimating the age of samples with equivalent dose (De) larger than ~120 Gy. In this study, we investigate fine-grained quartz extracted from Chinese loess with fairly well known ages. For these samples, we determined that the Des obtained using the standard SAR protocol (i.e., with preheat and cut-heat temperatures of 260 °C and 220 °C respectively) significantly underestimated the expected burial doses larger than 100 Gy. The dependence of OSL intensity on preheating conditions was investigated using both natural and bleached aliquots. Both the natural and regenerative OSL intensities increase with the preheat temperature to a maximum at ~260 °C and decrease afterwards. However, the regenerated OSL intensity demonstrates a greater variability compared to the natural one. This difference in variability could not be corrected by the test dose OSL responses when a standard SAR protocol was used. A simple multiple-aliquot regenerative-dose (MAR) protocol with a carefully selected preheating condition can resolve the problem of inadequate sensitivity correction between the natural and subsequent regenerative cycles. The growth of the MAR dose-response curve (DRC) was in good agreement with the sensitivity-corrected natural OSL signals up to ~340 Gy, which extends the upper age limit of quartz OSL samples of Chinese loess back to at least 110 ka.

The establishment of standardised growth curve (SGC) for equivalent dose (De) determination can substantially reduce the amount of instrument time required for OSL measurements. In this study, we investigated the applicability of SGC for the optically stimulated luminescence (OSL) signal from single grains and small aliquots of sedimentary quartz from Haua Fteah cave, in Libya. The samples exhibit large inter-grain and inter-aliquot variation in the shape of their single grain and small aliquot dose response curves (DRCs) constructed from a range of sensitivity-corrected regenerative dose signals (Lx/Tx), which prevents the establishment of a single common SGC among different grains or small aliquots. Instead, the DRCs for the small aliquots can be divided into a minimum of three groups using the Finite Mixture Model, with the DRC saturating at a different dose level for each group. In order to establish a common DRC, or SGC, for each group, we propose a new normalisation method, the so-called least-squares normalisation procedure (‘LS-normalisation’), which largely reduces the variation between aliquots within the same group and allows the establishment of a common DRC, or SGC, for each group. In order to apply the SGC method for these samples, two regenerative dose points are needed for each aliquot to attribute it to one of the groups based on the ratio of the Lx/Tx signals for two sensitivity-corrected regenerative dose points. Equivalent dose (De) values for each aliquot can be estimated using the fitting parameters calculated for the SGC of the relevant group to which it belongs, together with measurements of the natural signal (Ln), one regenerative dose signal (Lx1) and their corresponding test dose signals (Tn, Tx1). For the samples investigated from Haua Fteah, we found that De estimates obtained from the SGCs are consistent with those obtained using a full SAR procedure. Our results suggest that small single-aliquot and single-grain De values obtained from application of the SGC may be underestimated if there is a significant proportion of early-saturating grains present in the sample; such grains or aliquots are mostly rejected due to saturation when analysed using the full SAR procedure. In this case, it is necessary to calculate the De values based only on those grains or aliquots that have relatively high saturation levels.

Optically stimulated luminescence (OSL) dating has recently been applied to crystalline (i.e. igneous and metamorphic) rock surfaces. With the advent of this technique, early studies can guide improvements to the methodology that will lead to more robust age constraints. Low OSL sensitivity, poor measurement reliability, and equivalent dose scatter are common problems with dating quartz from crystalline rock surfaces. We investigate OSL characteristics of quartz extracted from crystalline Antarctic beach cobbles. Comparison of OSL behavior with cathodoluminescene characteristics and mineral composition and texture does not show a distinct relationship, suggesting luminescence behavior results from the natural radiation environment and post-crystallization transport history, rather than provenance source and the nature of crystal defects. Elemental composition of processed samples used for OSL measurements indicates standard methods of chemical preparation are not always suitable to extract pure quartz samples. Additionally, heterogeneous radiation production and attenuation poses a problem for estimating dose rates, in particular regarding beta contributions that dominate effective dose rates. We determine the sensitivity of effective dose rates to water content parameters and crystal size needed to calculate dose rates for crystalline rock surfaces. An increase in the value of all modelled parameters serves to reduce effective dose rates and, thus increase OSL ages. Dose rates are most sensitive to crystal size, which can introduce large uncertainty in burial ages from crystalline rocks due to heterogeneous crystal morphology (i.e. size and shape). This study provides a step forward in understanding the challenges and improving the methodology of luminescence dating of quartz from crystalline rock surfaces.

Dose saturation represents a fundamental limitation for obtaining finite optically stimulated luminescence (OSL) quartz ages over Middle Pleistocene timescales. Single-grain OSL studies typically reveal significant intra- and inter-sample variability in quartz dose saturation properties at the individual grain level. This enhanced variability may offer the potential to obtain extended-range chronologies exceeding the traditional upper age limits of multiple-grain OSL dating. However, there have been relatively few detailed assessments of single-grain OSL properties over high dose ranges. In this study we investigate extended-range single-grain OSL dating potential at Cuesta de la Bajada, one of the most important Ancient Middle Palaeolithic sites in the Iberian Peninsula. The quartz samples from this site exhibit exceptional dose saturation properties and contain significant populations of individual ‘supergrains’ with bright OSL signals, very high characteristic saturation dose (D0) limits of 200 to >600 Gy, and dose-response curves that closely conform to single saturating exponential functions. Assessments of OSL signal composition and the ability to successfully recover a known laboratory dose of 470 Gy support the potential for obtaining high equivalent dose (De) values with reasonable fitting uncertainties. A series of novel sensitivity tests are used to assess potential biases in supergrain De estimation over high dose ranges related to (i) thermally transferred signal contributions, (ii) choice of dose-response curve fitting function, and (iii) insufficient dose saturation properties of individual grains. The single-grain De values obtained using the standard quality assurance criteria and novel sensitivity tests are consistent at 2σ, and are in agreement with quartz Ti-centre ages obtained on two of three paired electron spin resonance (ESR) samples collected from Cuesta de la Bajada. These comparisons support the suitability of our single-grain OSL results and suggest there may be good potential for using quartz supergrains to establish extended-range chronologies at some Middle Pleistocene sites. Comparisons with other single-grain OSL studies across the Iberian central plains suggest that favourable dose saturation properties may be influenced by regional-scale geological controls. The importance of undertaking single-grain OSL dating at Cuesta de la Bajada is also demonstrated by the results of synthetic aliquot experiments, which reveal multiple-grain age offsets of 60–170 ka when unsuitable grain types are inadvertently included in the final age calculations. The single-grain OSL results indicate that the main archaeological horizon at Cuesta de la Bajada (unit CB3) accumulated between 264 ± 22 and 293 ± 24 ka. These ages are consistent with the chronologies of other key early Middle Palaeolithic sites in the region (Ambrona AS6 and Gran Dolina TD10) and indicate that the Ancient Middle Palaeolithic techno-complex likely spread across Iberia from at least Marine Isotope Stage 9 onwards.

We performed dose recovery tests on proto-historic enamel samples that were dosed to approximately 200 Gy to present equivalents of Middle to Late Pleistocene fossil teeth. The experimental results confirmed that the ESR dose response of fossil tooth enamel can be best described by a double saturating exponential (DSE) function. When using a DSE for dose evaluation, it is necessary to irradiate samples to very high doses (at least 20 kGy, ideally up to 50 kGy) and use at least 15 additive dose steps. In past studies, dose estimations were mostly carried out using a single saturating exponential (SSE) function and maximum doses (D max ) in the range of around five to ten times the equivalent dose, usually less than 5 kGy. To address the question whether older dose estimations have to be disregarded as unreliable, we carried out computer simulations using DSE dose response curves which were then fitted with SSEs. Artificial data sets were generated for a wide range of preset dose values between 10 and 5000 Gy. The results indicate a strong correlation between the magnitude of the D E value with systematic and random errors. Reliable doses can be obtained with SSEs for preset dose values of E value. Higher preset doses (>1 kGy) require modified D max values. Although here the application of DSEs is preferable, the use of SSEs can nevertheless provide reliable results with reasonably small systematic errors for doses of up to 2000 Gy, provided D max is adjusted to about 1*D set and measurement precision is better than 0.3%. The overall uncertainty remains acceptable (∼10%) using DSEs for D E values of up to 5000 Gy, provided the measurement precision is better than 0.5% and up to 20 dose steps are used. 5000 Gy is apparently the maximum dose than can be reliably assessed with ESR. Finally, we provide some detailed recommendations to ensure reliable dose evaluations with either the SSE or DSE functions. These recommendations can also be used to evaluate the reliability of previously published ESR dose assessments.

In optical dating, incomplete and heterogeneous resetting (“bleaching”) of the luminescence signal measured from mineral grains since the last episode of transport and deposition is commonly observed for sedimentary samples. As a result, different grains could have different equivalent dose (De) values at the time of deposition. For such samples, statistical treatment of the De distribution is required to estimate the burial dose. This study aims to assess the reliability of burial dose determination for heterogeneously bleached samples using the minimum age model (MAM). We modeled heterogeneous bleaching processes under various bleaching scenarios and simulated the resulting single-grain De distributions using a Monte Carlo method. Various factors that could potentially affect the reliability of burial dose estimates are investigated, including the distribution of residual dose, proportion of fully bleached grains, baseline dose, sample size, and unaccounted between-grain standard deviation. The simulation results reveal that the performance of the model depends primarily on the residual dose distribution. The proportion of fully bleached grains has the most influence on the reliability of MAM burial dose estimates.

Overestimation in dose recovery results was observed at high doses (>1000 Gy) when a single-aliquot regenerative-dose (SAR) procedure is applied to the multiple-elevated-temperature post-IR IRSL (MET-pIRIR) signals from potassium-rich feldspar (K-feldspar) grains from the Nihewan Basin. Such overestimation results from the non-bleachable (residual) signals that were not appropriately corrected for. A signal-subtraction method was proposed to solve this problem, which involves building growth curves for the bleachable and non-bleachable signals. Here we modelled the effect of residual signal on equivalent dose (De) and found that even a small amount of residual signal may give rise to large overestimation at high doses. Our results highlight that residual signals may not only affect young samples but may lead to erroneous results for old samples. Our study also suggests that although residual signals may result in significant error in the dose recovery, they may have a very small effect on natural samples because their residual signals seem to be relatively small.

In optical dating, equivalent dose (De) values for a sample are commonly obtained from measurement of the luminescence signals of individual mineral grains or aliquots and projection of the natural signals onto the corresponding regenerative-dose response curves. A final De estimate is calculated by using a statistical model to combine the individual De values. This method can be problematic for samples that contain large numbers of ‘saturated’ grains, which may result in underestimation of the final De value due to truncation of the full De distribution at high doses. To circumvent this problem, Li et al. (2017) proposed a new method—the so-called LnTn method—in which the re-normalised sensitivity-corrected natural signals (Ln/Tn) are analysed for all measured grains from a particular sample, and the weighted mean re-normalised Ln/Tn value is projected onto a standardised growth curve to estimate the final sample De. As no grains or aliquots are rejected because they are ‘saturated’, a full (untruncated) distribution of re-normalised Ln/Tn ratios is obtained. In this study, we use numerical simulations of ‘samples’ with a variety of assigned burial dose (palaeodose) distributions to systematically investigate the shape of the resulting Ln/Tn distributions. We test application of the central age, minimum age and finite mixture models to Ln/Tn ratios (rather than to De values) for well-bleached, insufficiently bleached and post-depositionally mixed samples. Our results show that application of statistical models to Ln/Tn ratios from single grains or aliquots is reliable, and that the LnTn method can be used to date samples with De values up to 4 times the characteristic saturation dose (D0), which is well above the conservative upper limit of 2D0.

In luminescence dating of feldspar, laboratory induced luminescence necessary to assess the naturally acquired dose in the environment suffers from a poorly understood instability over time, known as anomalous fading (AF). AF is the source of commonly observed age underestimation in optical dating of feldspar. Approaches to circumvent AF include correction methods as well as attempts to measure directly an unfading component of feldspar luminescence, e.g. post-IR IRSL protocols. The former has the advantage of measuring the easily bleachable traps but requires extrapolations of fading rates. Post-IR IRSL methods can be limited by the use of more difficult-to-bleach traps and hence by potential age overestimations. In this paper, we show how post-isothermal laboratory induced luminescence (pIt-IR) allows measuring an equivalent dose (De) that is not dependent on time elapsed since irradiation. In this procedure, one measures two IRSL signals, first from an IR stimulation at low temperature (i.e. IR50) followed by a second one, at a higher temperature (i.e. IR225). Since both signals fade at different rates, De from IR50 is lower than that of IR225. In pIt-IR, a succession of thermal treatments is carried out before the measurement of laboratory-induced IR50 and IR225 luminescence. The dependence of De on thermal annealing is different for each IR signal so one can find which thermal treatment will yield the same De for both signals. This De is assumed to be the true total radiation dose received by the feldspar minerals in nature, more properly known as the paleodose (P). This new methodology is herein applied to three samples of different ages and different geological contexts. Post-isothermal luminescence is thus proposed as a way to circumvent AF, even though extended isothermal annealing treatment is not shown to eradicate AF.

Single-grain dating of quartz near saturation is shown to have the potential of under-estimating equivalent dose. Experimental work shows that dose recoveries can be under-estimated when the administered dose approaches saturation, an observation also seen by Duller (2012). Duller (2012) found that by calculating the ratio between the fast and medium bleaching components, the “fast ratio”, for each grain, the under-estimation can be corrected by removing those grains with low fast ratios. Similar results are shown for samples from archaeological sites in South Africa and South Carolina. To understand why grains with low fast ratios might lead to equivalent dose under-estimation, simulations using a comprehensive quartz model was employed. It was found that large grain-to-grain variation in the decay constants for the fast and medium components can cause this effect.

Rapid sample preparation and measurement protocols for optically stimulated luminescence (OSL) dating have been investigated as a method of increasing the throughput of samples (e.g. Roberts et al. 2009). Here, we investigate the potential of dating samples treated using only hydrochloric acid (HCl) for providing accurate range-finder ages for quartz. The equivalent dose (De) is underestimated for older samples using a standard single-aliquot regenerative-dose (SAR) protocol, but measurement of the post-IR OSL signal (e.g. Roberts and Wintle, 2003) provides De estimates within 15% of the ‘target fully prepared De’ for two-thirds of samples. The application of a standardised growth curve (SGC) is also investigated. For these dune samples, the most efficient preparation and measurement procedure from which accurate De estimates can be obtained is treatment with HCl-only, measurement of the natural and regenerative post-IR OSL signal, and calculation using a region-independent SGC. A slightly longer protocol incorporating an additional preparation stage of heavy liquid density separation can be used to improve De estimates in samples where feldspar-contamination is thought to be particularly problematic. In practice, these time savings of days to weeks in the preparation and measurement protocols mean that a large number of samples can first be rapidly treated with HCl, the post-IR blue OSL signal measured using a shortened double-SAR protocol, and De calculated by applying an independent SGC before then deciding which samples require full preparation and measurement, rather than the inefficiency of committing time and resources to all samples if this is unnecessary for the context of a particular suite of samples. The potential of this rapid preparation and measurement protocol is discussed in relation to sand dune dating studies.

The optically stimulated luminescence (OSL) signals from quartz have been widely used to estimate the equivalent dose ( D e ) of environment radiation after the deposition of mineral grains. However, the usage of quartz is often limited due to the lower saturation behavior compared with feldspar. Saturation limits among quartz (defining the upper dating range) vary significantly. It is important to better understand the reason for various dose saturation behaviors of the quartz OSL signals. In this study, coarse quartz grains were extracted from the Taklimakan Desert and the Hunshandake sandy land in north China and the dose saturation behavior of quartz OSL signals were studied. Our results suggest that the quartz grains produce very different aliquot-specific dose response curves, showing the significant variability in dose saturation characteristics for OSL signals. Laboratory dosing, optical bleaching and heating experiments were designed to simulate their effects on the dose saturation behavior for the quartz OSL. The results demonstrate that cycles of dosing and optical bleaching have insignificant impact on the OSL dose growth curves, while the heating to high temperature (above 400 °C) can significantly change the dose saturation characteristics for the quartz OSL. Such results suggest that the different heating history of quartz might be an important factor for the variability in dose saturation characteristics for OSL signals. Additionally, the quartz grains from the Hunshandake sandy land exhibit lower dose saturation level for OSL signals, compared with that from the Taklimakan Desert. This can be explained that the quartz grains from Hunshandake sandy land are mainly of igneous origin, while the quartz grains from Taklimakan Desert are mainly of metamorphic origin.

Portable optically stimulated luminescence (OSL) readers are robust devices that allow rapid determination of luminescence signals of polymineralic coarse-grained samples. To date, however, the utility of portable OSL readers has largely been confined to the construction of luminescence profiles that depict variations of luminescence signal intensities with depth. Because the luminescence signals used to construct such profiles are uncalibrated, it is neither practical to quantitatively compare portable OSL data from different sites nor is it possible to approximate sample ages. Such comparisons could be facilitated by converting portable OSL signals into equivalent doses ( D e ). However, determining D e requires the construction of unique growth curves for each sample; a laborious procedure that negates the rapidity associated with portable measurements. To circumvent that limitation, we construct standardised growth curves (SGCs) using normalized regeneration dose signals obtained using a portable OSL reader from the feldspar component of polymineralic sands from five disparate eolian dune sites in Alberta, Canada. Comparison of SGCs from different samples indicates general congruence and we merge these to construct a regionally applicable curve which we test by comparing the D e obtained from given samples with that obtained using conventional OSL dating protocols. Results show that, though the uncertainties associated with the portable OSL data are high, the D e values from the two approaches are linearly proportional. This direct variation enables portable OSL SGC D e values to be used independently in reconnaissance studies that aim to screen samples for more detailed analysis using standard OSL methods. The affordability of portable OSL readers suggests that the approach could be attractive to researchers who do not have ready access to conventional OSL readers.

The infrared (IR) stimulated luminescence (IRSL) and post-IR IRSL (pIRIR) signals from K-feldspar can, for convenience, be divided into two components, bleachable and ‘non-bleachable’, where the latter corresponds to the ‘residual’ signal observed in sunlight-bleached samples. In this paper, we examine the non-bleachable component of IRSL of K-feldspar for several sedimentary samples from across Eurasia. We observed a large variability in the residual doses among these samples after prolonged exposure to sunlight. By employing multiple elevated temperature (MET) IR stimulations at 50–300 °C, we show that the residual dose increases systematically with stimulation temperature, attaining values as high as ∼50 Gy at 300 °C, even after several hours to tens of hours of exposure to unfiltered sunlight. We examined two samples in detail and found that the bleachable and non-bleachable components produced different dose response curves. Pulse annealing studies showed that the non-bleachable component is more stable than the bleachable component, suggesting that a preheat procedure cannot eliminate the non-bleachable component. Additional experiments revealed that the non-bleachable component is dose dependent. Owing to this dose dependency, we demonstrate mathematically and empirically that the simple subtraction of a residual dose from the measured equivalent dose ( D e ) – which is the most common approach employed (if any residual dose is subtracted at all) – will result in underestimation of the actual D e . We present a method to correct for the dose dependency of the residual dose, which can improve the accuracy of either MET-pIRIR or pIRIR age estimates for samples in which the non-bleachable component represents a significant fraction of the measured signals.

We report here the results of a feasibility study of luminescence dating of polymineralic volcanic ash. Of the several possible protocols that used different emission bands and different IR stimulation regimes, the post infrared-infrared stimulated luminescence (pIR-IRSL) signal (detected using a violet-blue emission window with stimulation temperature in the region 260–320 °C) provided the most stable signal. This involved, i) identification of the most suitable temperature for pIR-IRSL read out, ii) determination of alpha efficiency and, iii) estimation of anomalous (athermal) fading rate. Anomalous fading rate (g-value in %/decade) of pIR-IRSL signal at 300 °C was 0.0–1.6%/decade and it ranged from 2.4 to 5.2%/decade for IRSL at 50 °C, both preheated to 320 °C. Thus, though more stable, pIR-IRSL signals may fade in nature, and even during laboratory extended irradiation. Of the models for fading correction by Huntley and Lamothe (2001) and Kars et al. (2008) , the Kars et al. (2008) model performed better as the natural luminescence intensity was closer to the onset of saturation in the luminescence dose response curve. Our measurements suggest that alpha efficiencies of the pIR-IRSL signals are higher than that of IRSL. Fading corrected pIR-IRSL single aliquot regeneration (SAR) protocol based ages on three of the five volcanic ash beds are in agreement with the expected ages of ∼74 ka, based on geochemical association of the present samples to be the Youngest Toba Tuff (YTT). Other ash samples that gave ages of D 0 ) was ∼330 Gy and this implied a maximum measurable equivalent dose of 660 Gy. The minimum detectable dose was ∼5 Gy. These dose limits correspond to a typical age range of 1–150 ka using the pIR-IRSL signal for volcanic ashes.

We report an investigation of the effect of different single grain OSL behaviours on multiple-grain (single aliquot) De estimates. This was done by creating ‘synthetic aliquots’ in which signals are summed from collections of individual grains. The samples used were taken from aeolian linear dune sediments, from sites located in the Kalahari. We note this is a type of sample for which single multiple-grain aliquots are routinely used for dating. Several grain behavioural types were identified in our samples but the only grain type that systematically affected multiple-grain De estimates was the ‘over-saturating’ type (the case where the natural signal (Ln/Tn) is significantly greater than the regenerated Lx/Tx signal at saturation), the presence of which lead to higher estimates of De. The magnitude of this effect is controlled by the contribution of ‘over-saturating’ grains to the total light sum of the multiple-grain aliquot and the maximum increase observed in this study was w15 Gy. Of the four samples investigated here, interaliquot variations in the signal contribution of ‘over-saturating’ grains led to a significant increase in dispersion in just one of the samples. More generally, the presence/absence of these grains is considered to be a likely source of significant ‘intrinsic’ scatter in single aliquot dating and likely to broaden multiple-grain De distributions. We suggest all samples are screened for this behaviour before single aliquot dating is attempted.

Modern Mississippi Delta sediments were analyzed to investigate quartz OSL signal resetting in large river deltas and test the accuracy of OSL dating on a decadal time scale with the early background subtraction and a recently proposed burial dose estimation procedure. Both fine silt-sized and sand-sized quartz were measured with a modified single-aliquot regenerative dose (SAR) protocol and equivalent dose ( D e ) was calculated using different background subtraction methods. Evidence of insufficient bleaching was observed, but the residual signal is equivalent to ∼100 a on average for both sandy quartz and fine silt-sized quartz. It is shown that dose distributions of sandy quartz are affected by the background subtraction. The proportion of aliquots that have D e in agreement with expectation is significantly larger when an early background is subtracted compared to the late background subtraction. This is, in contrast, not observed for fine silt-sized quartz. Accurate OSL ages were obtained by employing the unlogged minimum age model to D e s of sandy quartz obtained with the early background subtraction method.

The 12 May 2008, Ms 8.0 Wenchuan earthquake provided an excellent opportunity to test zeroing assumptions for optical dating of different types of earthquake-related sediments. Using OSL, we investigate the residual dose of the Wenchuan earthquake-related samples in four different depositional settings (flood, earthquake-dammed lake, sand volcanoes, pre-earthquake surface soils). The residual equivalent dose ( De ) varies with grain size, mineralogy, and the methods used in the De determination. All the samples, except the pre-earthquake surface samples, were poorly bleached with a maximum individual residual dose up to 356 Gy. Despite the poor sensitivity of the coarse-grain quartz samples, the small aliquot results using probability plot method ( Jain et al., 2004 ) overestimate the De when compared to the single grain De from the same sample. Ages from optical dating of paleoearthquakes with short recurrence intervals should be interpreted with caution, and we recommend using the single grain approach in dim, poorly-bleached samples related to paleoearthquakes.

IR laser stimulated luminescence was used to determine the equivalent dose (D e ) for about 150 luminescent K-feldspar grains of two well-bleached aeolian sand samples, previously dated using quartz optically stimulated luminescence (OSL) and thermally-transferred OSL (TT-OSL). Fading tests were performed both on the entire single grain disc, using stimulation by IR LEDs, and on each grain individually, by stimulation with an IR laser. The single grain D e distributions are highly over dispersed, even after applying rejection criteria, such as recycling ratio and recuperation. Fading rates determined with the IR LED stimulation do not represent the fading behavior of the IR laser stimulated signal and are therefore considered inappropriate for the fading correction of single grain D e values. Fading rates of individual grains exhibit a wide range of values (0%–10% per decade) and plotting the single grain fading rates against the single grain D e values reveals a negative relationship. Different approaches were taken to correct for fading, but the resulting ages tend to underestimate the reference ages.

A protocol for optical dating of potassium-rich feldspar (K-feldspar) is proposed. It utilizes the infrared stimulated luminescence (IRSL) signal measured by progressively increasing the stimulation temperature from 50 to 250 °C in step of 50 °C, so-called multi-elevated-temperature post-IR IRSL (MET-pIRIR) measurements. Negligible anomalous fading was observed for the MET-pIRIR signals obtained at 200 and 250 °C. This was supported by equivalent dose (De) measurements using the IRSL and MET-pIRIR signals. The De values increase progressively from 50 °C to 200 °C, but similar De values were obtained for the MET-pIRIR signal at 200 and 250 °C. Measurement of modern samples and bleached samples indicates that the MET-pIRIR signals have small residual doses less than 5 Gy equivalent to about 1–2 ka. We have tested the protocol using various sedimentary samples with different ages from different regions of China. The MET-pIR IRSL ages obtained at 200 and 250 °C are consistent with independent and/or quartz OSL ages.

The possibility of dating basalt using luminescence was tested on four samples with independent age control from Cima volcanic field, California, with the ultimate aim of assessing whether the technique could be used to date sediments on the surface of Mars. Previous analysis of these samples had demonstrated that the infrared stimulated luminescence (IRSL) signal is most suitable for dating as it showed the lowest fading rate among various luminescence signals. In this study, changes in equivalent dose as a function of preheat are described. The ages for the two youngest Cima samples agree with the independent ages based on cosmogenic nuclide measurements (12.0 ± 0.8 ka). In the two older samples (dated to 320 and 580 ka by K–Ar), the luminescence behaviour is more complex and the form of the IRSL decay curve is seen to vary with dose. Mathematical fitting is used to isolate two components and their intensities are used to produce dose response curves. The slower component yields a larger equivalent dose. However, even using this component and after correction for fading, the ages obtained for the older samples are younger than the K–Ar ages.

The usual practice in optical dating is to derive an equivalent dose ( D e ) (and hence age) from integration of the initial part of the measured optically stimulated luminescence (OSL) signal. This ‘bulk’ OSL signal is known to comprise several semi-independent components, each of which decays at different rates during measurement, and thus contributes a different proportion to the bulk signal as measurement time progresses. Data are presented here which show a strong dependence of D e on the bulk signal integration interval, with reduced D e for later signal integration intervals resulting from lower medium component D e values. This dependence leads to two problems: (i) deciding which signal integral to choose, and (ii) the possibility that all bulk signals will provide systematic age underestimation due to medium component signal contributions. Isolating the fast component of the bulk OSL signal provides a solution to both problems and several methods of achieving this are assessed; an efficient new method is described which is incorporated in to standard single-aliquot regenerative-dose measurement sequences. This method involves the direct measurement of the fast-component signal using infrared (830 nm) stimulation of quartz at 160 °C, prior to the standard bulk OSL measurement with 470 nm stimulation. It is shown that the measured quartz infrared stimulated luminescence signals resolve pure fast-component signals and provide D e estimates consistent with those from signal deconvolution. This approach can only be applied to samples with relatively bright luminescence emissions, but in these cases is expected to provide a more robust estimate of palaeodose.

Equivalent dose (De) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different rela- tionships between De values and grain sizes of these five samples. The first relationship is that the De values obtained from various grain sizes are in agreement within 1 delta errors. The second rela- tionship is that De values are similar to each other for fractions between 125 and 300 mm, while the De value of the 63-90 mm fraction is 40w55% smaller than others. For example, the De values obtained for sample #3 are 20.15 � 1.19 Gy, 19.80 � 0.83 Gy and 20.93 � 1.06 Gy for fractions of 90-125, 125-150 and 250-300 mm respectively, but are 10.79 � 0.84 Gy for the 63-90 mm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (

Geochemical alteration processes in archaeological sites may affect the environmental dose rate during the burial history and cause inaccuracy in age determination by palaeodosimetric dating methods, such as luminescence or ESR. In Arago Cave (Tautavel, France), the original composition of the sandy aeolian sediments of palaeoanthropological level G, where the Homo heidelbergensis Arago XXI skull was found, has been modified by both carbonation and phosphatization processes. Eight fossil teeth were collected from different geochemically affected parts of level G and analyzed by the ESR–U-series method. All the teeth are presumably contemporaneous. The results show that the samples from the phosphated area agree within error with those from the carbonated area. Surprisingly, the samples from the non-altered area show ages 100–150 ka younger. This difference is mainly due to the remarkable changes in the gamma dose rate over time. The measured in situ dose rate accounts for more than 50% of the total dose rate for all the samples. We observed that the samples' equivalent dose ( D E ) were generally 20% lower in the non-altered area than in the carbonated and phosphated ones. These results show the crucial effect of the geochemical processes affecting the age calculation by ESR–U-series method in comparison with independent chronological data.

A newly developed range-finder luminescence dating method is applied to samples from the eastern Punjab region of Pakistan. Overbank sediments from this area are the subject of an ongoing project into the demise of the Harappan civilization about 4.2 ka and the range-finder technique was used to ascertain whether samples from three pits are from this part of the Holocene. Luminescence measurements of raw sample gave a signal dominated by feldspars, even when using a [post-IR] optically stimulated luminescence (OSL) signal. Following etching in hydrofluoric acid samples gave OSL signals characteristic of quartz and these were used to calculate the equivalent dose. The total dose rate was estimated from beta counting. Eight range-finder OSL ages extend from 4000 to 6600 years ago and are consistent with two radiocarbon ages from the same pits demonstrating that these sediments do straddle the period of interest for this project. The range-finder approach provides a rapid means of informing future field sampling campaigns.

The presence of genuinely zero-age or near-zero-age grains in modern-age and very young samples poses a problem for many existing burial dose estimation procedures used in optical (optically stimulated luminescence, OSL) dating. This difficulty currently necessitates consideration of relatively simplistic and statistically inferior age models. In this study, we investigate the potential for using modified versions of the statistical age models of Galbraith et al. [Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., Olley, J.M., 1999. Optical dating of single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part I, experimental design and statistical models. Archaeometry 41, 339–364.] to provide reliable equivalent dose (D e ) estimates for young and modern-age samples that display negative, zero or near-zero D e estimates. For this purpose, we have revised the original versions of the central and minimum age models, which are based on log-transformed D e values, so that they can be applied to un-logged D e estimates and their associated absolute standard errors. The suitability of these ‘un-logged’ age models is tested using a series of known-age fluvial samples deposited within two arroyo systems from the American Southwest. The un-logged age models provide accurate burial doses and final OSL ages for roughly three-quarters of the total number of samples considered in this study. Sensitivity tests reveal that the un-logged versions of the central and minimum age models are capable of producing accurate burial dose estimates for modern-age and very young ( e distributions, or (ii) smaller sub-populations of well-bleached grains for which the D e values are known with high precision. Our results indicate that the original (log-transformed) versions of the central and minimum age models are still preferable for most routine dating applications, since these age models are better suited to the statistical properties of typical single-grain and multi-grain single-aliquot D e datasets. However, the unique error properties of modern-age samples, combined with the problems of calculating natural logarithms of negative or zero-Gy D e values, mean that the un-logged versions of the central and minimum age models currently offer the most suitable means of deriving accurate burial dose estimates for very young and modern-age samples.

A number of recent optically stimulated luminescence (OSL) studies have cited post-depositional mixing as a dominant source of equivalent dose (De) scatter across a range of sedimentary environments, including those previously considered ‘best suited’ for OSL dating. The potentially insidious nature of sediment mixing means that this problem may often only be identifiable by careful statistical analysis of De data sets. This study aims to address some of the important issues associated with the characterisation and statistical treatment of mixed De distributions at the multi-grain scale of analysis, using simulated De data sets produced with a simple stochastic model. Using this Monte Carlo approach we were able to generate theoretical distributions of single-grain De values, which were then randomly mixed together to simulate multi-grain aliquot De distributions containing a known number of mixing components and known corresponding burial doses. A range of sensitivity tests were undertaken using sediment mixtures with different aged dose components, different numbers of mixing components, and different types of dose component distributions (fully bleached, heterogeneously bleached and significantly overdispersed De distributions). The results of our modelling simulations reveal the inherent problems encountered when dating mixed sedimentary samples with multi-grain De estimation techniques. ‘Phantom’ dose components (i.e. discrete dose populations that do not correspond to the original single-grain mixing components) are an inevitable consequence of the ‘averaging’ effects of multi-grain De analysis, and prevent the correct number of mixing components being identified with the finite mixture model (FMM) for all of the multi-grain mixtures tested. Our findings caution against use of the FMM for multi-grain aliquot De data sets, even when the aliquots consist of only a few grains.

In this study we report on optical stimulated luminescence (OSL) ages of quartz extracted from a sedimentary record in the N-Oman mountain range. Equivalent dose ( D E ) distributions derived from single aliquot measurements (SAR) of small aliquots (ca. 200 grains) were investigated to test whether the skewness and broadness of the dose distribution can be used as criteria for the identification of insufficient bleaching. Furthermore, the methods proposed by Lepper and McKeever [2002 An objective methodology for dose distribution analysis. Radiation Protection Dosimetry 101 (1–4), 349-352]. Singhvi [Juyal, N., Chamyal, L.S., Bhandari, S., Bushan, R., Singhvi, A.K., in press. Continental record of the southwest monsoon during the last 130 ka: evidence from the southern margin of the Thar Desert, India. Quaternary Science Review] and Fuchs and Lang [2001 Fuchs, M., Lang, A., 2001. OSL dating of coarse-grain fluvial quartz using single-aliquot protocols on sediments from NE Peloponnese, Greece. Quaternary Science Review 20, 783–787.] to derive D E 's from insufficiently bleached sediments were compared. At first, the investigations were carried out on artificially bleached, irradiated and mixed quartz material from the Oman study area to simulate insufficiently bleached sediments. Then, the various statistical methods for identifying insufficient bleaching and D E derivation were applied to the natural samples from the study area, where 18 samples were measured. For the identification of insufficient bleaching the preferential parameter is the broadness of a distribution. For D E calculation, both the Singhvi method and the Fuchs and Lang method produce similar results, which are consistent with the stratigraphic order. A drawback of both methods is their sensitivity to low outliers. The Lepper and McKeever method was not applied to the natural samples, due to limitations in its application to a small number of aliquots and due to the ambiguous identification of the rising limb of the dose distributions.

Aeolian samples from deserts in northern China were studied using the optically stimulated luminescence (OSL) of quartz and potassium (K) feldspar separates. K-feldspar has shown advantages over quartz for dating samples younger than 100 years, due to its more homogeneous equivalent dose ( D e ) values, higher internal dose rate and higher luminescence sensitivity to dose. Without additional measurements, the luminescence characteristics of quartz obtained in D e determination procedures can be used to reveal the source material and/or quartz thermal history for the deserts in northern China. The results indicated that the duration of paleosol formation in desert areas reflects regional paleoenvironments.

Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past.