Potential of establishing a ‘global standardised growth curve’ (gSGC) for optical dating of quartz from sediments

We report investigations of the optically stimulated luminescence (OSL) signals of sedimentary quartz from different regions of Asia, Africa, Europe and North America using a single-aliquot regenerative-dose (SAR) procedure. We show that variations in the shape of dose response curves (DRCs), or growth curves, of the test dose sensitivity-corrected OSL signals among single aliquots composed of multiple grains can be greatly reduced by normalising the DRCs using one of the regenerative dose OSL signals. We refer to this regenerative-dose normalisation procedure as ‘re-normalisation’. We find a common re-normalised DRC extends to doses of ∼250 Gy for samples that differ significantly in terms of geological provenance, sedimentary context and depositional age. This feature permits the development of a ‘global standardised growth curve’ (gSGC) for OSL signals from single aliquots of quartz. The equivalent dose (D_e) of an aliquot can be estimated from the natural signal, one regenerative dose signal and their corresponding test dose signals. For the variety of samples investigated, we find that D_e estimates obtained from the gSGC are consistent with those obtained using full SAR procedures for doses of up to ∼250 Gy. Use of the gSGC for single aliquots would greatly reduce the time required to estimate the D_e values of older samples and for a large number of aliquots.     

Variability in quartz OSL signals caused by measurement uncertainties: Problems and solutions

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 (D_e) 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 D_e distribution, with D_e 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 (L_n/T_n) from all measured grains is projected on to the corresponding SGCs to determine D_e. Our simulation results show that this method can produce reliable D_e estimates up to 5D₀, which is far beyond the conventional limit of ∼2D₀ using the standard SAR procedure.     

Effects of the size of the test dose on the SAR protocol for quartz optically stimulated luminescence dating of loess in the eastern Tibetan Plateau

Dating of quartz by optically stimulated luminescence (OSL) has been revolutionized with introduction of the test dose (TD) in development of a measurement sequence known as the single-aliquot regenerative-dose (SAR), whereby a valid sensitivity correction for the luminescence signal is provided in the measurement cycle. However, the size of the TD used in the SAR protocol remains controversial. Previous studies show that the TD has little effect on the equivalent dose (D_e) for young samples in luminescence dating in which the applicability of different deposits varies greatly in different regions. However, detailed studies are lacking on how TD size affects SAR–OSL results of samples with a relatively high D_e range. In this study, typical loess samples with high D_e values (∼60 Gy–∼250 Gy) from the eastern Tibetan Plateau were selected to investigate the effects of variation in TD size on the quartz SAR–OSL protocol. Dose recovery tests show that a known dose could be recovered successfully by applying different TDs. Test dose size has an effect on shapes of regenerated dose–response curves (DRCs) and has different influences on D_es and characteristic saturation doses for quartz samples with a high dose range. A TD size of 20%–30% D_e is a good compromise for Tibetan loess with D_e of ∼60–120 Gy in the quartz SAR protocol, and a TD size larger than 30% should be considered for samples with a larger D_e. The results of this study highlight the importance of TD size in the SAR–OSL protocol for quartz samples with a high dose range.     

Investigation of the applicability of standardised growth curves for OSL dating of quartz from Haua Fteah cave,Libya

The establishment of standardised growth curve (SGC) for equivalent dose (D_e) 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 (L_x/T_x), 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 L_x/T_x signals for two sensitivity-corrected regenerative dose points. Equivalent dose (D_e) 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 (L_n), one regenerative dose signal (L_x1) and their corresponding test dose signals (T_n, T_x1). For the samples investigated from Haua Fteah, we found that D_e 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 D_e 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 D_e values based only on those grains or aliquots that have relatively high saturation levels.     

Underestimation of fine grain quartz OSL dating towards the Eemian: Comparison with palynostratigraphy from Azzano Decimo,northeastern Italy

Palynostratigraphical records have been used to understand the response of vegetation to climate change, and benefit from independent dating to ensure a robust correlation with global climate and sea-level change. In order to constrain the pollen chronology of a long sedimentary core taken at Azzano Decimo in the Friulian foreland of northeastern Italy, optically stimulated luminescence (OSL) has been applied to fine grain quartz. The samples meet all the standard performance criteria set to test the reliability of the single-aliquot regenerative-dose (SAR) protocol, and still show increasing dose response at 500 Gy. OSL ages are in good agreement with radiocarbon dating and the pollen interpretation down to 70 ka, and with D_e values of ～140 Gy, but below this point, they display an increasing age underestimation towards the Eemian and beyond. The comparison of D_e values measured using both a SAR and single-aliquot regeneration and added-dose (SARA) protocol, confirmed that both were successfully correcting for sensitivity changes in the quartz during measurement of the burial dose, and this was not the reason for the age underestimation. The quartz OSL dose response curve for all samples is best described by a saturating exponential plus linear (SEPL) function. Although all underestimated ages are derived from D_e values that fall on the high dose linear region of this curve, it is unclear if this is the cause of the underestimation.     

Testing the applicability of a standardized growth curve (SGC) for quartz OSL dating: Kalahari dunes,South African coastal dunes and Florida dune cordons

Standardized growth curves (SGCs) have recently been developed as a means to reduce measurement times when determining palaeodoses in the standardized luminescence (OSL) dating of quartz, but this approach is not without its critics. We test the performance of SGCs derived from samples from a range of environments in southern Africa and Florida (United States of America). Data presented here suggest that the method performed well when determining low (<50 Gy) equivalent dose (D_e) values from samples with different geological provenances within South Africa. However, the application of an SGC built from South African data performed poorly when used to estimate the palaeodoses of samples from Florida, with seven out of ten samples failing to replicate the single aliquot regenerative (SAR)-derived D_e value to within ±10%. We thus advocate the use only of regionally based SGCs for full D_e determination, although SGCs can also be utilized as a way of quickly generating SAR ‘range finders’ irrespective of sample origin. Furthermore, one sample from the Florida site did not show regenerative growth in accordance with any samples from either the South Africa or Florida data, resulting in significant D_e underestimation when using the SGC. Although the reasons for such behaviour are not yet understood, this re-iterates the recommendation of Burbidge et al. [2006. D_e determination for young samples using the standardised OSL response of coarse-grain quartz. Radiation Measurements 41(3), 278], to incorporate a single regenerative step in SGC protocols in order to check consistency.     

OSL and IRSL dating of raised beach sand deposits along the southeastern coast of Norway

Raised beach sand deposits along the southeastern coast of Norway were dated by optical (OSL) and infrared stimulated luminescence (IRSL) and the quartz and K-feldspar luminescence characteristics were described. Due to the poor quartz luminescence characteristics, only a limited number of samples were suitable for OSL dating. More promising are the K-feldspar extracts, with typical K-feldspar luminescence characteristics and no sign of fading. For equivalent dose (D_e) determination, sand-size quartz and feldspar extracts were used, applying a single aliquot regenerative (SAR) protocol. Both, OSL and IRSL D_e estimates show a wide distribution, unexpected for beach deposits. The calculated OSL and IRSL age estimates were generally in good agreement and the correctness of the ages was confirmed by independent age control. Because only a limited number of the quartz samples were suitable for OSL dating, IRSL dating of the K-feldspar represents an alternative to OSL quartz dating.     

Optical dating of young deltaic deposits on a decadal time scale

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_es of sandy quartz obtained with the early background subtraction method.     

Test of high sampling density OSL dating of aeolian samples from the south margin of the Tengger Desert using the global standardised growth curve (gSGC) method

Chronostratigraphic records in the drylands of north China provide basic archives to reveal the dynamic connections between climate changes and the behaviour of aeolian systems. However, the interpretation of aeolian chronostratigraphy is not straightforward and may be associated with significant uncertainty due to a number of external and localised forces. Taking into account this complexity of aeolian systems, excluding preservation and sampling bias from palaeoclimatic signals requires that the interpretation of chronostratigraphic records be based on as many dates from as many sites as possible. Optically stimulated luminescence (OSL) dating provides a direct way to date aeolian sediments. However, the determination of equivalent dose (D_e) using the commonly applied single-aliquot regenerative dose (SAR) protocol is relatively time-consuming for samples with burial doses exceeding 50 or 100 Gy.In this study, the global standardised growth curve (gSGC) method is applied to multi-grain aliquots of coarse quartz from various sites covering a wide region of the south margin of the Tengger Desert in north China to rapidly determine D_e for a large number of aliquots and samples. The large between-aliquot variability in the shape of the dose response curve (DRC) is significantly reduced using a least-squares normalisation procedure. The results of a leave-one-out cross-validation (LOOCV) protocol demonstrates that D_e values determined using the gSGC and SAR methods are very consistent with each other up to at least 200 Gy and 400 Gy, for the 90–150 μm and 63–90 μm fractions, respectively. It suggests that the gSGC protocol can be used as an efficient procedure for D_e determination of a large number of aeolian samples from multiple sites. This in turn provides a better constraint for the interpretation of Late Quaternary aeolian chronostratigraphic records in drylands of north China.     

Testing the applicability of standardised growth curves (SGCs) for OSL signals of quartz grains from the Yangtze Delta,China

The standardised growth curve (SGC) technique has the potential to save instrument time for equivalent dose (D_e) determination when applying single-aliquot regenerative-dose (SAR) protocol during optically stimulated luminescence (OSL) measurements. In this study, we test the applicability of two commonly used SGC procedures for OSL signals of quartz grains from aqueous deposits of the Yangtze Delta in China, which have been reported for weak luminescence signals and suffering from partial bleaching. Multiple silt-sized and sand-sized fractions of quartz samples from eight cores are used to construct SGCs by test dose standardisation (TD-SGC) and least-squares normalisation (LS-SGC), respectively. Three strategies, i.e. region-specific (SGC_R), region with core-specific (SGC_R + C) and core-specific (SGC_C), are adopted to categorise these normalised data into different SGC datasets. The large variability of dose response signals is substantially reduced by the SGC procedures for most of these datasets. Hence, common SGCs for a variety of samples from the Yangtze Delta can be established, irrespective of their distinctive particle sizes and luminescence characteristics. The D_e values are then estimated using both TD-SGC and LS-SGC procedures for samples from a specific core. Comparing to the full SAR protocol, the TD-SGC procedure roughly gives reproducible D_e estimates lower than ∼100 Gy while the LS-SGC procedure derives generally consistent D_e estimates of up to ∼230 Gy. Although LS-SGC_C and LS-SGC_R + C procedures replicate the most consistent D_e values, the LS-SGC_R procedure performs better in efficiency with a slightly less accuracy. In addition to careful comparison of LS-SGC and full SAR procedures, we suggest that a synchronous ratio derived by the chosen regenerative dose and its response signal for re-normalisation can be used to predict the LS-SGC D_e reliability on samples from similar sedimentary environments.     

Construction of a ‘global standardised growth curve’ (gSGC) for infrared stimulated luminescence dating of K-feldspar

We investigated the infrared stimulated luminescence (IRSL) and post-infrared IRSL (pIRIR) signals emitted by K-feldspars from sedimentary samples from Asia, Europe and Africa using a single-aliquot multiple elevated temperature (MET) stimulation procedure. For separate aliquots of the same sample, we show that variation among the dose response curves (DRCs), or growth curves, constructed from the regenerative dose signal (L_x), the test dose signal (T_x, an indicator of luminescence sensitivity) and the sensitivity-corrected signal (L_x/T_x) can be largely eliminated by normalising the DRCs using one of the regenerative dose signals; we call this procedure ‘regenerative-dose normalisation’ or re-normalisation. Furthermore, for the MET-pIRIR signals measured at 250 °C, we find that different samples have re-normalised DRCs that follow the same growth function, despite the samples differing significantly in terms of their geological provenance, sedimentary context, equivalent dose (D_e) and luminescence sensitivity. This common feature offers the potential to establish a ‘global standardised growth curve’ (gSGC) for different samples of K-feldspar, and thereby enable D_e values to be estimated for a large number of single aliquots by projecting the re-normalised natural signals on to the gSGC. For the 18 samples investigated in this study, we find that D_e estimates obtained from the gSGC are consistent with those obtained using full single-aliquot regenerative dose (SAR) procedures for doses of up to ∼1600 Gy. The establishment of a gSGC would greatly reduce the time required to date older samples using K-feldspar, as regenerative doses of several hundreds to a few thousands of Gy are typically delivered to each aliquot in each SAR cycle.     

Optical dating of perennially frozen deposits associated with preserved ancient plant and animal DNA in north-central Siberia

We present chronological constraints on a suite of permanently frozen fluvial deposits which contain ancient DNA (aDNA) from the Taimyr Peninsula of north-central Siberia. The luminescence phenomenology of these samples is first discussed, focusing on the optically stimulated luminescence (OSL) decay curve characteristics, thermoluminescence (TL) properties, and signal compositions of quartz from these previously unstudied deposits. Secondly, we assess the suitability of these samples for OSL dating and present the OSL chronologies obtained using both single-grain and multi-grain equivalent dose (D_e) measurements. The results of our analyses reveal a large amount of inter-aliquot variability in OSL decay curve shape that is directly related to differences in the size of the 280 °C TL peak and the associated slowly bleached ‘S2’ OSL component. Longer OSL stimulation durations are adopted in the D_e measurement procedure to prevent the progressive build-up of slowly bleached signal components throughout successive single-aliquot regenerative-dose (SAR) measurement cycles. The use of low preheat temperatures in the SAR procedure also reduces the deleterious effects of these slowly bleached signal components. The resultant single-grain and multi-grain OSL chronologies obtained using this approach are stratigraphically consistent and are in close agreement with independently established ¹⁴C ages at our sites. The findings of this research reveal the potential of OSL dating as a means of providing a reliable chronometric framework for sedimentary aDNA records in permafrost environments.     

A comparative study of sand- and silt-sized quartz fractions for MAR-VSL dating using loess-palaeosol deposits in southern Germany

Multiple-aliquot regenerative-dose violet stimulated luminescence (MAR-VSL) dating studies of the Chinese loess-palaeosol sequence in Luochuan using sand- and silt-sized quartz have previously produced inconsistent results; the VSL ages were in agreement with their independent ages up to ∼900 ka for sand-sized quartz, whereas the silt-sized VSL ages underestimated the independent chronology beyond ∼100 ka. Here we therefore evaluate the VSL dose response pattern of sand- (63–100 μm) and silt-sized (4–11 μm) quartz grains from the loess-palaeosol sequence in southern Germany in high resolution but with a limited age range up to ∼160 ka. All the samples studied benefit from good age control provided by reliable quartz optically stimulated luminescence (OSL) ages and fading corrected feldspar post-infrared infrared stimulated luminescence at 225 °C (pIRIR₂₂₅) ages, which can be used for assessing the validity of the estimated VSL ages. The comparison of the MAR standardised dose response curve (DRC) using regeneration doses up to ∼1000 Gy for both grain size fractions demonstrates that they are almost similar in shape with comparable characteristic saturation doses. The comparison of the natural and laboratory generated DRCs of each grain size reveals that they broadly overlap in the low dose range for both fractions, while in the high dose range the deviation between natural and laboratory DRCs is higher for the silt-sized quartz fraction. It is also shown that the magnitude of the characteristic saturation dose is dependent upon the size of the maximum given dose, especially for the silt-sized quartz. The constructed laboratory standardised DRCs to very high doses (up to ∼6000 Gy) showed continuous signal growth at high doses, particularly in the case of silt-sized quartz grains, thereby confirming our previous observation. The sand-sized quartz has a much less pronounced linear growth component and can therefore be considered more suitable for dating samples with equivalent doses falling on the high dose region of the DRC.     

Investigating the potential of HCl-only treated samples using range-finder OSL dating

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 (D_e) 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 D_e estimates within 15% of the ‘target fully prepared D_e’ 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 D_e 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 D_e 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 D_e 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.     

Quartz luminescence dating of Anglian Stage (MIS 12) fluvial sediments: Comparison of SAR age estimates to the terrace chronology of the Middle Thames valley,UK

Quartz optically stimulated luminescence (OSL) is increasingly being used to constrain the depositional age of fluvial and glaciofluvial sequences over orbital (Milankovitch) timescales within the British Isles. Few of these previous studies have had any age control; however there is some evidence that OSL ages based on the single aliquot regenerative dose (SAR) protocol may be subject to systematic age underestimation as samples approach saturation. In this study, the age of 12 luminescence samples from a chronologically well-constrained site dating to 450 ka from the Thames terrace sequence, southern Britain, was measured using SAR in order to test the performance of the method close to its upper age limit. The characteristics, dose response and thermal stability of the OSL signal in these samples were assessed by investigating equivalent dose (D_e) as a function of stimulation time and component-resolved pulse annealing. Despite the fact that the samples are dominated by the quartz fast component, these results showed that both the medium and slow components have lower stabilities than the fast component, but with the unstable medium component most affecting the initial part of the OSL signal used in dating. Based on isolating the fast component either through curve fitting or eliminating the medium component using the early background subtraction method, OSL ages up to 450 Gy were found to compare well with the expected age of the site of 450 ± 23 ka. In contrast, a systematic age underestimation of 10% was manifested at lower doses when using the initial part of the OSL signal, contaminated by the medium component. These results suggest that the early background subtraction method should be used when dating in the non-linear part of the growth curve as it provides a better separation of thermally unstable signals and represents a more convenient approach than curve fitting in well-behaved samples.     

Refining the OSL age of the last earthquake on the Dheshir fault,Central Iran

In Central Iran there are several cities along the Dehshir fault, which have similar geological conditions to that of the city of Bam prior to the 2003 earthquake (Mw 6.5), during which more than 30,000 lives were lost. Optical stimulated luminescence (OSL) samples were collected from the Dehshir fault in order to place constraints on its seismic history. The single aliquot regenerative (SAR) dose measurement protocol on coarse grained quartz extracts was used for this study. This SAR protocol had to be optimized for the low OSL sensitivity by varying both the preheat temperatures and test doses used. Dose recovery tests showed that given laboratory dose could be successfully recovered. However, replicate palaeodose (D_e) data were scattered and consequently ages based on mean D_e's had large uncertainties. As this is thought to largely reflect poor bleaching conditions prior to sediment burial at the site, various statistical procedures were employed in conjunction with the stratigraphic knowledge of the site to try and extract more refined burial ages from the samples. From this the timing of the last earthquake was estimated around 2.0 ± 0.2 kyr. This refined age suggests that the earthquake catalogue of Iran is incomplete and more paleoseismological investigation is required to recognize and date the previous events of Dheshir fault.     

Establishing a luminescence chronology for a palaeosol-loess profile at Tokaj (Hungary): A comparison of quartz OSL and polymineral IRSL signals

We present a comparative study of quartz OSL, polymineral IRSL at low temperature (50 °C, IR₅₀) and post-IR elevated temperature (290 °C) IRSL (pIRIR₂₉₀) feldspar dating on nine samples from the Tokaj loess section in NE Hungary (SE Europe). Preheat plateau tests show a drop in quartz OSL D_e between 160 and 240 °C but above 240 °C a clear D_e plateau is present. Quartz OSL SAR is shown to be generally appropriate to these samples (recycling, recuperation) but a satisfactory dose recovery result was only obtained when a dose was added to a sample without any prior optical or thermal pre-treatment; this gave a dose recovery ratio of 1.04 ± 0.05 after subtracting the natural dose from the measured dose. The pIRIR₂₉₀ SAR protocol also results in acceptable dose recovery results for the pIRIR₂₉₀ signal (1.08 ± 0.01) when a large dose is added to the natural dose. Bleaching experiments suggest a detectable non-bleachable residual pIRIR₂₉₀ dose of 10 ± 4 Gy. Agreement with quartz OSL ages is best achieved by correcting the IR₅₀ ages for fading; however this is not necessary when using the pIRIR₂₉₀ signal. With respect to Hungarian Late Quaternary geology our results indicate that the major part of the Tokaj loess has been deposited during MIS 3 (60–24 ka), with periods of soil formation occurring during the onset of MIS 3 (≥58 ka) and between about 35 and 25 ka. Our results also indicate episodic deposition of loess and varying, non-linear sedimentation rates during MIS 3. Proxy analyses in the literature are based on the traditional concept of continuous deposition; in the light of our new data the use of such simple assumptions must be reconsidered.     

Investigating the optically stimulated luminescence dose saturation behavior for quartz grains from dune sands in China

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.     

Potential of quartz OSL dating on moraine deposits from eastern Tibetan Plateau using SAR protocol

Optically stimulated luminescence (OSL) dating methods have been widely applied in Quaternary glaciology. However, glacigenic deposits are considered in general as problematic for OSL dating, mainly because they are transported shorter distances prior to burial and are usually partially bleached. Thus, most researchers choose glaciofluvial and glaciolacustrine sediments (with relatively longer transportation times) for OSL dating when constraining the age of glaciation. In this study, four samples were collected from a lateral moraine series at Zhuqing Village, northern margin of Queer Shan Mountain, eastern Tibetan Plateau, in order to investigate the applicability of OSL dating for morainic deposits. Quartz grains (38–63 μm) were extracted and measured using single aliquot regenerative-dose (SAR) protocol. Internal checks and dose recovery test show that the SAR protocol is appropriate for equivalent dose (D_e) determination. The effect of thermal transfer is small for all samples and the recycling ratio for each individual sample is close to unity. The symmetry in the D_e distributions indicates that quartz grains were well-bleached prior to burial. OSL ages show good agreement with geomorphological and field investigations, and are also concordant with an independent ESR age. It is concluded that: (a) the morainic deposits in Zhuqing were well-bleached and suitable for OSL dating; (b) SAR protocol can be applied to morainic deposits for samples under study.