IRSL Signal Research Articles

Luminescence Dating of Lacustrine Sediments from Cuoe Lake on the Central Tibetan Plateau

Luminescence dating technology has been used for chronological constraints on lacustrine sediments due to the ubiquitous materials (e.g., quartz and feldspar) as dosimeters, and a relatively long dating range, compared with the commonly used radiocarbon dating method. However, quartz dating on the Tibetan Plateau may suffer from dim and unstable luminescence signals. In the current study, we investigate a lake-related outcrop from the shore of Cuoe Lake on the central Tibetan Plateau. Both coarse-grained quartz and K-feldspar fractions were extracted, and OSL and post-IR IRSL signals were measured from these fractions, respectively. Combining the stratigraphy analysis and dating results, this study shows that: (1) quartz appears to be unsuitable for dating because of very dim natural signals and even anomalous fading (average <i>g</i>-value: 4.30 ± 2.51 %/decade). The suitability of the applied pIRIR protocol measured at 150°C (pIRIR<sub>150</sub>) for K-feldspar samples was confirmed by a set of luminescence tests; (2) compared with the luminescence-based chronology, the <sup>14</sup>C age of shells from the same sediment layer yielded older age by ∼7 ka, which is likely attributed to hard water reservoir effect in Cuoe Lake; (3) the lake level reached its peak and maintained high-stand during the early Holocene (∼9.4–7.1 ka). This study highlights the applicability of K-feldspar luminescence dating when the counterpart quartz OSL is insensitive and encounters anomalous fading.

Optimization of OSL/IRSL experimental measurement parameters on various types of naturally occurring CaSO4 samples; sensitization pattern versus temperature, bleaching properties and slurry zeroing effect

Calcium sulphate (CaSO4) geological material is the main constituent of art objects and geological formations, mostly in the form of gypsum. Nevertheless, investigations of either optically or infrared stimulated luminescence (OSL or IRSL respectively) properties are scarce for this material towards age assessment applications. The present work studies for both IRSL and OSL signals of CaSO4 (a) the effect of the preheating to the sensitivity, towards selecting the optimum preheating conditions, (b) the bleaching ability of both signals via the corresponding residual TL signal levels, towards selecting the appropriate stimulation duration and (c) whether mixing with water acts as a zeroing mechanism for these signals. IRSL and OSL yield different sensitization threshold temperatures, being 250 °C or 300 °C, depending on the water content of the mineral (hemihydrate, anhydrous and the most usual dihydrate). However, for the cases of protocols involving either a single IRSL measurement or post IRSL OSL measurements, preheating temperature should not exceed 225 °C. The optimum stimulation duration is 100 s for the blue OSL and 60 s for the IRSL. Finally, mixing with water affects (i) insignificantly the zeroing of IRSL signal in anhydrites, (ii) partially the zeroing of OSL in all groups and (iii) substantially the zeroing of IRSL signal in gypsum and bassanite.

The effect of residual signal on dose measurements using MET-pIRIR signals from K-feldspar

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.

The suitability of a low temperature post-IR IRSL signal for dating alluvial and colluvial “cut and fill” sequences in the Great Karoo, South Africa

Abstract Alluvial and colluvial “cut and fill” deposits preserved in valleys of the Karoo, South Africa, reflect basin-scale adjustments in fluvial process-regime. Such deposits in the Wilgerbosch catchment have previously proven difficult to date using radiocarbon (14C) and optically stimulated luminescence (OSL) methods. In this paper, we test the suitability of K-feldspar post-IR infrared (pIRIR) methods on 19 samples from Africanders Kloof, a low-order tributary of the Sundays River. Using three carefully screened quartz OSL ages, radiocarbon dating and site stratigraphic considerations we argue that the pIRIR170 protocol can be used to produce reliable age estimates. Fading rates for the pIRIR170 signal are consistently low (average g2days: 0.81 ± 0.58). The pIRIR170 residuals are dose dependent (r2 = 0.58); but are consistently low as a proportion (e.g. 1–4%) of sample equivalent dose (De). Despite the water-lain depositional context, single aliquot De distributions tend toward normality (for 11/19 samples) irrespective of aliquot size (2 mm or micro-aliquots containing 2–30 grains) with only a few statistical outliers per sample (max. n = 3) and overdispersion (OD) ranging from 1.6 to 30% excluding the two youngest (late Holocene) samples (OD: 37–87%). The resulting pIRIR170 ages are in the correct stratigraphic order and illustrate the potential of pIRIR170 luminescence dating to investigate the timing, processes and drivers of fluvial system adjustments across the Karoo.

Circumvention of anomalous fading in feldspar luminescence dating using Post-Isothermal IRSL

Abstract 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.

Testing the upper limit of luminescence dating based on standardised growth curves for MET-pIRIR signals of K-feldspar grains from northern China

The standardised growth curve (SGC) method has been applied to potassium-rich feldspar (K-feldspar) from samples at the Nihewan Basin, northern China. It was observed that the shapes of SGCs obtained from multiple-aliquot regenerative-dose (MAR) and single-aliquot regenerative-dose (SAR) procedures are different at high doses (>900 Gy) for the multiple-elevated-temperature post-IR IRSL (MET-pIRIR) signals observed at high temperatures (e.g., 290 °C) This difference can be attributed to the presence of residual signals in the MAR SGCs due to solar bleaching involved in the MAR procedure. Similar shapes of the SAR and MAR SGCs were obtained after correcting for the residual signals. Comparing the De estimates for both methods suggests that the SAR SGCs yield more reliable results. We tested the SAR SGCs for sediments from the Dadaopo section in the Nihewan Basin, including materials from the Brunhes/Matuyama (B/M) boundary (~780 ka). By interpolating the central re-normalised Ln/Tn ratios onto the corresponding SAR SGCs, the 290 °C MET-pIRIR signals yielded ages in stratigraphic order, and the sample from the B/M boundary yielded an age estimate broadly consistent with the expected age. Our results suggest that the MET-pIRIR SAR SGC method has the potential to date samples up to ~700–800 ka in this region.

Constraining the transgression history in the Bohai Coast China since the Middle Pleistocene by luminescence dating

Three phases of transgression have been identified in the Middle to Late Pleistocene sedimentary succession in the Bohai Sea, northern China, which is considered to be key information for understanding environmental evolution and marine-terrestrial interaction in the East Asia. However, the timing of these transgressions still remains controversial. In this study, luminescence dating was performed on a core drilled in the North Bohai Coast to establish a reliable chronological framework of the transgression-regression cycles. After validating the applicability of luminescence dating for the Bohai sediments, quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared (IR) IRSL (pIRIR) signals with elevated temperatures at 150, 225 and 290 °C were employed for dating the sediment core. The quartz OSL signal used for the upper 25 m of the sediment core was well-bleached, yielding finite ages within ca. 50 ka, whilst the K-feldspar pIRIR225 signal was also well-bleached for the Pleistocene samples with an extended dating limit to ca. 300 ka. The luminescence ages of ca. 200 ka and ca. 7.0–0.2 ka indicated that the lowermost and uppermost of three transgression units likely represent sea-level highstand during Marine Isotope Stages (MIS) 7 and 1, respectively, which were also evidenced by the consistency between the reconstructed palaeo-topography elevation and the contemporaneous global mean sea-level. Our luminescence ages of the second transgressive unit suggest it has a MIS 3 origin, being consistent with previous studies, but this appears to be unlikely as the level of the unit is significantly above the interstadial sea-level in the MIS 3. Further high-resolution luminescence dating of the second transgression is thus required.

Comparing the accuracy and precision of luminescence ages for partially-bleached sediments using single grains of K-feldspar and quartz

Glacial settings are considered to be the most challenging context for the application of luminescence dating. The optically stimulated luminescence (OSL) signal of quartz is often preferred for luminescence dating in partially-bleached settings as it resets (or bleaches) more rapidly in response to sunlight than the post-IR IRSL (pIRIR) signal of K-feldspar, and can therefore better characterise the well-bleached part of the partially-bleached De distribution. However, the relative bleaching extents of single grains of quartz and K-feldspar have not yet been compared for sedimentary samples from the natural environment. Here we compare the De distributions and accuracy and precision of ages determined using single grains of quartz and K-feldspar from sedimentary samples deposited in a proglacial setting with independent age control. We found that the extent of bleaching of the OSL signal of quartz and pIRIR225 signal of K-feldspar was similar (with similar over-dispersion), and therefore the pIRIR225 signal bleached to similarly low levels as the OSL signal of quartz in this partially-bleached setting. We also observed a consistent offset in over-dispersion between quartz and K-feldspar of ∼10% that can be linked to scatter arising from internal dose-rates of K-feldspar and should be included when applying age models. The results here demonstrate that the accuracy and precision of ages determined using the pIRIR225 signal of single grains of K-feldspar were similar to the OSL signal of quartz. However, K-feldspars were 5–18 times more efficient than quartz at determining the population of interest for age calculation as a larger proportion of K-feldspar grains emitted a detectable luminescence signal in comparison to quartz. These findings contradict our current understanding of the bleaching of K-feldspar and quartz grains in the natural environment, and are likely applicable to other partially-bleached settings (e.g. fluvial, alluvial).

Component-resolved bleaching correlation between OSL and IRSL signals in various geological materials

The primary aim of the present study includes establishing a qualitative as well as quantitative correlation between OSL and IRSL signals in various materials of geological origin, by investigating the influence of the IR stimulation to the OSL signal. The materials which are the subject of the present study include one K-feldspar belonging to the group of microcline, two different grain size fractions of Durango apatite at the edge of the nano-scale and gypsum. A two-step stimulation protocol was applied, including an exposure of the irradiated sample to infrared stimulation for various time and a subsequent continuous wave OSL using blue light. In the framework of a component-resolved analysis, the IRSL decay curves were fitted using analytical equations describing the localized tunneling recombination model; the subsequent OSL decay curves were also fitted using a linear superposition of analytical expressions describing both delocalized and localized recombination processes. The selection of number and type of components in the latter case is also elaborated, based on the physical meaningfulness of the de-convolution results.

First luminescence-depth profiles from boulders from moraine deposits: Insights into glaciation chronology and transport dynamics in Malta valley, Austria

In this study, we investigate the potential of rock surfaces to provide luminescence burial ages for boulders from moraine deposits. We sampled four boulders from a terminal moraine at the Malta Valley, Austria, all deposited ∼2 m below the present ground surface, and measured the IRSL signal as a function of depth into the boulder surfaces. It is clear from these profiles that all four boulders were exposed to at least some daylight prior to final deposition, and in one boulder, there is evidence for multiple exposure/burial events. The profiles show that the luminescence signal at the surface of two boulders must have been completely zeroed before burial. The burial doses derived from these two well-reset surfaces can thus be safely used to calculate burial ages, which may be the same as the depositional age of the terminal moraine. The IRSL signals from both boulders seem to suffer from anomalous fading with g-values of up to 15% decade−1. The younger fading-corrected age of ∼14 ka is in agreement with the deposition of the terminal moraine and coincides with the assumed Gschnitz stadial, while the older age of ∼39 ka most likely represents an earlier event during which this boulder was exposed to light.Our results suggest that there is a high probability of sampling light-exposed and even well-bleached boulders from moraine deposits. We thus conclude that rock surface luminescence dating offers the possibility of obtaining reliable ages for moraine deposition. Even boulders which are partially bleached and thus not suitable for dating can provide insight into transportation pathways as well as depositional processes in glacial environments leading to a better understanding of the dynamics of glaciers.

Attenuation of light in different rock types and implications for rock surface luminescence dating

There is growing interest in rock surface burial and exposure luminescence dating for use in Quaternary science and in archaeology. Such methods have enormous potential both in increasing the range of sedimentary contexts that can be dated, and improving the accuracy and the precision of dating within those contexts. Bleaching of the luminescence signal with depth into the rock surface is likely to vary with lithology. However, previous work on rock surface dating has not systematically studied the differences in light attenuation for rocks of different lithologies, or directly quantified the attenuation of light in different rock surfaces. This study investigates the attenuation of light in different rock types (greywacke, sandstone, two granites and quartzite) using two different approaches: 1) sunlight bleaching experiments, to assess the residual infrared stimulated luminescence signal measured at 50 °C (IRSL50) and the post-IR IRSL signal measured at 225 °C (post-IR IRSL225) at different depths within the rocks after different durations of exposure to daylight; and, 2) direct measurement of light attenuation in rock slices using a spectrometer. Data from the spectrometer shows that for all rocks, attenuation is greater for shorter wavelengths (∼400 nm) than longer ones. A consistent difference in attenuation coefficient is seen when comparing the IRSL50 and the post-IR IRSL225 signals; this is thought to reflect the different sensitivity of these two signals to infrared and visible light. Direct measurement using a spectrometer is much more rapid than undertaking a bleaching experiment, and also provides wavelength-resolved attenuation data. Comparison of the numerical values from the two approaches is complex, but they yield consistent results. For the samples analysed here, the rocks that appear lightest in colour show the least attenuation of light and the luminescence signals are bleached to the greatest depths, and are thus the most suitable for dating using luminescence.

Constructions of standardised growth curves (SGCs) for IRSL signals from K-feldspar, plagioclase and polymineral fractions

Abstract 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.

Single-grain dating of potassium-rich feldspar grains: Towards a global standardised growth curve for the post-IR IRSL signal

Abstract Potassium-rich feldspar (K-feldspar) grains were extracted from 28 sediment samples from sites in Asia, Europe and Africa and the dose response curves — or growth curves — were constructed from the post-infrared infrared stimulated luminescence (pIRIR) signals emitted by individual grains. The samples exhibit large between-grain variation in both pIRIR signal intensity and the shape of the corresponding growth curves; the latter can be largely explained as a result of measurement uncertainties, including counting statistics and instrumental irreproducibility. This between-grain variation can be reduced by applying a least-squares normalisation (LS-normalisation) procedure, which allows a common growth curve — or global standardised growth curve (gSGC) — to be established for individual K-feldspar grains from the range of samples investigated. Equivalent dose (De) values for single grains can be estimated using the fitting parameters of the gSGC, together with measurements of the natural signal (Ln), one regenerative-dose signal (Lx) and their corresponding test-dose signals (Tn, Tx). The De values obtained using the gSGC approach are consistent at 2σ with those obtained from the individual growth curves constructed for each of the grains. The establishment of a gSGC greatly reduces the time required to measure a large number of grains for old samples, and it also overcomes the problem of De underestimation that can occur using a full single-aliquot (or single-grain) regenerative-dose (SAR) procedure when a large number of grains are rejected due to issues of ‘saturation’. The construction of a gSGC may, therefore, potentially extend the dating range of pIRIR signals beyond the reliable limit of De estimation using the standard SAR method.

Luminescence dating of Holocene beach-ridge sands on the Yumigahama Peninsula, western Japan

Abstract We applied infrared stimulated luminescence (IRSL50) and post-infrared (post-IR) IRSL150 dating to K-feldspar sand obtained from Holocene beach ridges on the Yumigahama Peninsula, Japan, to investigate the rate of progradation of the beach, which has been affected by 17–18th century iron mining in a local river catchment. All samples showed higher equivalent doses for the post-IR IRSL signal. Fading tests indicated that IRSL yielded relatively high g-values (11–13%/decade), while post-IR IRSL yielded negative g-values (–5 to –8%/decade). The corrected IRSL age of the oldest sample, 8.1 ± 1.3 ka, was slightly overestimated with respect to its expected age of 5–6.7 ka. The corrected age is highly dependent on the g-value, which if slightly inaccurate would have caused the overestimate. The uncorrected post-IR IRSL ages were underestimated, and we consider that the post-IR IRSL signal faded. However, given the negative g-values, application of an appropriate fading correction was not feasible. The corrected IRSL ages of the younger samples, coupled with an assumption of residual dose, roughly agreed with the historical shoreline changes, indicating that the rate of shoreline progradation increased markedly during the recent period of mining-related enhanced sediment discharge.

Behavior of the electron trapping probability change in IRSL dating of K-feldspar: A dose recovery study

Abstract Dose recovery tests were performed on potassium feldspar using the single-aliquot regenerative-dose (SAR) multi-elevated-temperature post-IR IRSL (MET-pIRIR) dating protocol with a large number of samples from various backgrounds. The dose recovery ratios were always smaller than unity for the 50 °C IRSL signal, but the ratios increased with signals from elevated temperatures. For the pIRIR signal at 250 °C, the recovery ratios were within the range of 1.0 ± 0.1. Underestimations of the recovery ratios for low-temperature IRSL signals resulted from the increase of the electron trapping probability during the first preheat treatment. The electron trapping probability can be reset by solar bleaching. The modified SAR protocol with solar bleaching behind each cycle or the MAR protocol is recommended if the low-temperature IRSL signals are applied to obtain ages. Solar simulator with the xenon arc lamp is more efficient in reducing the electron trapping probability compared to the sunlight. Bleaching duration with the solar simulator should be chosen with caution.

Exploring the behaviour of luminescence signals from feldspars: Implications for the single aliquot regenerative dose protocol

A series of dose recovery experiments are undertaken on grains of potassium-rich feldspar using a single aliquot regenerative dose (SAR) protocol, measuring the post-infrared infrared stimulated luminescence (post-IR IRSL) signal. The ability to successfully recover a laboratory dose depends upon the size of the test dose used. It is shown that using current SAR protocols, the magnitude of the luminescence response (Tx) to the test dose is dependent upon the size of the luminescence signal (Lx) from the prior regeneration dose because the post-IR IRSL signal is not reduced to a low level at the end of measuring Lx. Charge originating from the regeneration dose is carried over into measurement of Tx. When the test dose is small (i.e. 1%–15% of the given dose) this carry-over of charge dominates the signal arising from the test dose. In such situations, Tx is not an accurate measure of sensitivity change. Unfortunately, because the carry-over of charge is so tightly coupled to the size of the signal arising from the regeneration dose, standard tests such as recycling will not identify this failure of the sensitivity correction. The carry-over of charge is due to the difficulty of removing the post-IR IRSL signal from feldspars during measurement, and is in stark contrast with the fast component of the optically stimulated luminescence (OSL) signal from quartz for which the SAR protocol was originally designed.

Variations in luminescence properties of quartz and feldspar from modern fluvial sediments in three rivers

Abstract Studies of modern sediments, their sedimentology and depositional processes are important for understanding the behaviour of the luminescence characteristics of quartz and feldspar in fluvial settings. Previous studies have shown large variations in OSL characteristics of quartz from different fluvial systems, while the IRSL and pIRIR signals from K-feldspar have been understudied. We test the effects of fluvial setting on luminescence characteristics by collecting modern (

Pulsed IRSL: A stable and fast bleaching luminescence signal from feldspar for dating Quaternary sediments

Abstract Elevated temperature post-infrared infrared stimulated luminescence (post-IR IRSL; pIRIR) dating method using feldspar has led to a significant advancement in dating Quaternary sediments, as this signal has been shown to be stable on geological time scales. In comparison to the conventional IRSL, the pIRIR signal is nearly free from anomalous fading, but it is more difficult to reset during daylight exposure; the latter characteristic may give rise to age over-estimation in some environments because of partial bleaching. The pulsed IRSL signal has also been known to be less affected by anomalous fading, when the signal is recorded during the off-time of LED stimulation pulses. In this study, we compare the signal bleachability, thermal and athermal stability, and age estimates derived using different measurement methods, i.e., pulsed IRSL measured at 50 °C (pulsed IR 50 ; subscripts refers to measurement temperature), continuous wave (CW) pIRIR 225 and pIRIR 290 signals, as well as the two IR 50 signals measured as a part of the pIRIR protocols. This comparison is carried out for 3 samples taken from Late Quaternary fluvial sediments, which have independent age estimates from radiocarbon dating and tephrochronology. We observe that under exposure to solar simulator, the pulsed IR 50 signal bleaches as rapidly as the CW IR 50 , and much more rapidly than the pIRIR signals. Furthermore, the pulsed IR 50 signal is also as stable as the pIRIR signals, especially when the middle part of the decay curve is used for signal intensity calculation.

Thermally assisted OSL application for equivalent dose estimation; comparison of multiple equivalent dose values as well as saturation levels determined by luminescence and ESR techniques for a sedimentary sample collected from a fault gouge

Equivalent dose estimation (De) constitutes the most important part of either trap-charge dating techniques or dosimetry applications. In the present work, multiple, independent equivalent dose estimation approaches were adopted, using both luminescence and ESR techniques; two different minerals were studied, namely quartz as well as feldspathic polymineral samples. The work is divided into three independent parts, depending on the type of signal employed. Firstly, different De estimation approaches were carried out on both polymineral and contaminated quartz, using single aliquot regenerative dose protocols employing conventional OSL and IRSL signals, acquired at different temperatures. Secondly, ESR equivalent dose estimations using the additive dose procedure both at room temperature and at 90K were discussed. Lastly, for the first time in the literature, a single aliquot regenerative protocol employing a thermally assisted OSL signal originating from Very Deep Traps was applied for natural minerals. Rejection criteria such as recycling and recovery ratios are also presented. The SAR protocol, whenever applied, provided with compatible De estimations with great accuracy, independent on either the type of mineral or the stimulation temperature. Low temperature ESR signals resulting from Al and Ti centers indicate very large De values due to bleaching in-ability, associated with large uncertainty values. Additionally, dose saturation of different approaches was investigated. For the signal arising from Very Deep Traps in quartz saturation is extended almost by one order of magnitude. It is interesting that most of De values yielded using different luminescence signals agree with each other and ESR Ge center has very large D0 values. The results presented above highly support the argument that the stability and the initial ESR signal of the Ge center is highly sample-dependent, without any instability problems for the cases of quartz resulting from fault gouge.

Bleaching of the post-IR IRSL signal from individual grains of K-feldspar: Implications for single-grain dating

Post-IR IRSL (pIRIR) signals from K-feldspar grains measured at elevated temperatures are increasingly being used for dating sediments. Unfortunately the pIRIR signal from K-feldspars bleaches more slowly than other signals (e.g. OSL from quartz) upon exposure to daylight, leading to concerns about residual signals remaining at deposition. However, earlier studies have not assessed whether the pIRIR signal bleaches at the same rate in all feldspar grains. In this study laboratory bleaching experiments have been conducted and for the first time the results show that the rate at which the pIRIR signal from individual K-feldspar grains bleach varies. To determine whether grain-to-grain variability in bleaching rate has a dominant control on equivalent dose (De) distributions determined using single grains, analysis was undertaken on three samples with independent age control from different depositional environments (two aeolian and one glaciofluvial). The De value determined from each grain was compared with the rate at which the pIRIR225 signal from the grain bleaches. The bleaching rate of each grain was assessed by giving a 52 Gy dose and measuring the residual De after bleaching for an hour in a solar simulator. There is no clear relationship between the rate at which the pIRIR225 signal of an individual grain bleaches and the magnitude of its De. It is concluded that variability in the bleaching rate of the pIRIR225 signal from one grain to another does not appear to be a dominant control on single grain De distributions.