Electron spin resonance dating of optically bleached quartz grains from the Middle Palaeolithic site of Cuesta de la Bajada (Spain) using the multiple centres approach

Electron spin resonance (ESR) dating of optically bleached quartz grains was performed on three sediment samples collected from the Middle Palaeolithic site of Cuesta de la Bajada (Spain). A standard multiple grain and multiple aliquot additive dose procedure was employed, and both the Al and Ti centres were measured as part of the multiple centres approach.ESR age estimates obtained for the three samples indicate that the Al centre provides a maximum possible chronology, as the Ti centres show that the Al signal was likely not systematically reset to its residual level during sediment transport. A direct comparison between ESR ages based on the Ti centres and single grain optically stimulated luminescence (OSL) ages from samples collected nearby shows broadly consistent results. The Ti-H centre also appears to provide suitable chronologies for at least two of the three Middle Pleistocene samples studied here. Surprisingly, the only sample showing consistent ESR ages between the Al and Ti centres appears to be overestimated in comparison with the Ti-centre and OSL ages derived from the other two samples. This indicates either incomplete bleaching of both the Al and Ti centres for this sample, or unexpected impacts of other sources of D_e uncertainty, such as multi-grain averaging effects. The ESR dating results overall indicate that the archaeological sequence of Cuesta de la Bajada CB-3 is most likely correlated to either MIS 7 or 9.     

A combined luminescence and radiocarbon dating study of the Ili loess,Central Asia

Similar to the loess in the Chinese Loess Plateau (CLP), the loess deposits in the Ili basin of Central Asia arid area play an important role in understanding the climate and environmental changes. However, in contrast to the intensively investigated loess deposits in the CLP, the Ili loess is still insufficiently known and poorly understood. The geochronology study of the Ili loess remains controversial. In order to examine the potential of optically stimulated luminescence (OSL) dating for the Ili loess, we carry out a combined luminescence and radiocarbon dating study on a 6.9 m loess section in the south margin of the Ili basin. Polymineral fine grains were investigated by post infrared (IR) OSL using a Multiple-Aliquot Regenerative-dose (MAR) protocol. Radiocarbon dating of organic carbon were carried in a 3 Megavolt (MV) multi-element Accelerator Mass Spectrometry (AMS). The results indicate that the OSL ages are in agreement with the observed stratigraphy in the field, which is well correlated with that of the CLP, but the AMS ¹⁴C ages are much younger than the OSL and assumed stratigraphical ages. Thus, the OSL dating technique may provide an absolute chronology in this loess section. Further methodological approaches and more samples analysis will lead to the improvement of this chronology for high-resolution paleoclimatic interpretation.     

Investigating the amount of zeroing in modern sediments of River Danube, Austria

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.     

ESR and OSL dating of fossil-bearing deposits from Naracoorte Cave Complex palaeontological sites,south Australia

Little work has been undertaken on combined dating of sedimentary quartz grains using electron spin resonance (ESR) and optically stimulated luminescence (OSL) techniques in Australia. This study aims to assess the suitability of a combined ESR and OSL dating approach for establishing improved chronologies of Middle-Late Pleistocene deposits within the Naracoorte Cave Complex (NCC), South Australia. Here, we apply ESR and OSL dating in tandem to a series of samples collected from three different NCC sites: Whale Bone, Specimen and Alexandra cave. ESR quartz dating focuses on the multi-centre (MC) approach, which involves comparative evaluations of Al and Ti centre signals, while paired luminescence dating focuses on single-grain OSL analysis and includes examination of multi-grain averaging effects. The comparative ESR-OSL dating results exhibit broad agreement for deposits spanning 50–150 thousand years, with either the Ti–H or Al centre ages overlapping with paired OSL ages at 2σ in nearly all cases. MC ESR evaluations (Al v Ti–Li v Ti–H age assessments) indicate incomplete resetting of the bleachable Al centre signal for a small number of samples. Two-thirds of samples exhibit Ti–Li ages that are significantly older than corresponding Al centre ages, which is unexpected from a bleaching kinetics perspective and may indicate a broader reliability issue for Ti–Li palaeodose evaluation with these particular samples. Our findings: (i) support the applicability of both palaeodosimetric dating methods in this depositional setting; (ii) highlight the merits of applying combined ESR-OSL analyses in tandem, and; (iii) provide one of the first reliable evaluations of quartz ESR MC dating for samples with natural dose ranges as low as only a few tens of Gy. These results show that the Whale Bone, Specimen and Alexandra cave sites are temporally related and can be used to derive multi-site reconstructions of faunal assemblages and palaeoenvironmental history.     

A luminescence dating study of loess deposits from the Yili River basin in western China

The loess deposits surrounding the high mountainous regions of Central Asia play an important role in understanding environmental changes in Eurasia on orbital and sub-orbital timescales. However, problems with dating Central Asian loess have limited the interpretation of climatic and environmental data, especially on sub-orbital timescales. We selected a controversial loess section, Zeketai (ZKT, with a thickness of 23 m), in the Yili basin in Xinjiang Province in western China, to establish a detailed and systematic Optically Stimulated Luminescence (OSL) chronology. Quartz grains of 38–63 μm were isolated from 15 samples and the single-aliquot regenerative-dose (SAR) protocol was employed for D_e determination. OSL ages are in stratigraphic order and range from 13.8 ± 1 to 72 ± 6 ka, suggesting continuous loess accumulation during the last glaciation. We compared these dating results with that of the previously published fine-grain sized quartz (4–11 μm) using simplified multiple aliquot regenerative-dose (SMAR) protocol, and with the previous published radiocarbon dating (¹⁴C) ages on snail shells. With the exception of three young samples from the upper 6 m of the section, the SMAR dating results are basically consistent with the results using the SAR protocol. Both the SMAR and SAR OSL ages are consistently older than the ¹⁴C ages, and the radiocarbon date results should be used with caution since they appear to have been underestimated.     

Application of OSL dating to middle to late Holocene arroyo sediments in Kanab Creek,southern Utah,USA

Middle to late Holocene alluvium, identified as Quaternary alluvial unit 4 (Qa4), along Kanab Creek in southern Utah, USA was dated using optically stimulated luminescence (OSL) on quartz sand, and by radiocarbon dating of detrital charcoal. Entrenchment beginning in 1882 AD created arroyo walls that expose up to 35 m of the Qa4 alluvium. The stratigraphy and sedimentology suggest that fluvial aggradation along the study reach occurred rapidly. Due to the high sediment supply, short transport distances and semi-arid climate with flashy discharge, partial bleaching (zeroing) of the luminescence signal was expected to be a problem for OSL dating. We approached this problem by first using small-aliquot (∼20 grains) and single-grain dating of quartz sand to reduce the number of grains contributing to the OSL signal. Second, we used statistical parameters based on single-grain and small-aliquot equivalent dose (De) distributions of bleached sediment to help identify partial bleaching and to inform if a minimum age model (MAM) should be used for age calculation. Comparison of results with radiocarbon ages demonstrates the success of OSL dating on Kanab Creek arroyo-fill deposits, although careful attention should be paid to the sedimentary facies and stratigraphy of the targeted sample horizon to minimize the effects of partial bleaching. Thin, decimeter-scale plane-bedded and ripple cross-bedded sandy lithofacies were found to be the best target for OSL dating, as these sediments showed minimal evidence for incomplete solar resetting. Additionally, results generally indicate that better-bleached sediments are found in downstream reaches. Age control from these arroyo-fill deposits was acquired in order to fulfill larger research goals of understanding regional arroyo incision and aggradation cycles.     

Luminescence dating of marine sediments from the Sea of Japan using quartz OSL and polymineral pIRIR signals of fine grains

Luminescence dating has long been used for chronological constraints on marine sediments due to the ubiquitous dating materials (quartz and feldspar grains) and its applicability over a relatively long time range. However, one of the main difficulties in luminescence dating on marine sediments is partial bleaching, which causes age overestimations. Especially, partial bleaching is typically difficult to be detected in the fine grain fraction (FG) of marine sediments. The recently developed feldspar post-IR IRSL (pIRIR) protocol can detect non-fading signals and thus avoid feldspar signal instability. In the current study, fine grains were extracted from a gravity core in the northern Sea of Japan, and the aim is to test the feasibility of using different luminescence signals with various bleaching rates to explore the bleaching conditions of fine grain fraction in marine sediments. The results suggest that the quartz OSL signal and polymineral pIRIR signals at stimulation temperatures of 150 °C and 225 °C (pIRIR₁₅₀ and pIRIR₂₂₅) of FG were well bleached prior to deposition. The OSL ages were used to establish a chronology for this sedimentary core and the resulting age-depth relationship is self-consistent and comparable with radiocarbon dates. We conclude that different luminescence signals with various bleaching rates can be used to test the bleaching conditions of fine grain fraction in marine sediments; and the luminescence dating can be applied to marine sediments with great potential.     

Luminescence chronology of the upper part of the Stari Slankamen loess sequence (Vojvodina,Serbia)

A thick Middle and Late Pleistocene loess-palaeosol sequence is exposed at the Stari Slankamen section in the Vojvodina region situated in the south-eastern part of the Pannonian basin, Serbia. The profile exposes an about 45 m thick series of loess intercalated by at least eight pedocomplexes. Ten samples were dated by luminescence methods using a modified single aliquot regenerative dose (SAR) protocol for polymineral fine grains and for quartz extracts from the upper part of the Stari Slankamen loess sequence. The infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (OSL) signals from all polymineral samples showed anomalous fading, suggesting that the post-IR OSL signal is still dominated by feldspar OSL. The ages ranging from 4.6 to 193 ka were obtained after fading correction. These ages indicate that the loess unit V-L1L1, the weakly developed soil complex V-L1S1 and the loess unit V-L1L2 were deposited during marine isotope stage (MIS) 2, 3, and 4, respectively, and also indicate that the loess unit V-L2 is of the penultimate glacial age.     

Optically stimulated luminescence dating of single and multiple grains of quartz from perennially frozen loess in western Yukon Territory, Canada: Comparison with radiocarbon chronologies for the late Pleistocene Dawson tephra

Optically stimulated luminescence (OSL) dating of perennially frozen loess was tested on quartz grains extracted from deposits associated with the late Pleistocene Dawson tephra in western Yukon Territory, Canada. OSL samples were obtained from ice-rich loess bracketing the Dawson tephra, while radiocarbon (¹⁴C) samples were collected from the bulk sediments directly underlying the tephra and from a ground-squirrel burrow 2.7 m below the tephra. Here we report the OSL characteristics and ages of the extracted quartz grains, as well as additional radiocarbon ages for samples described in Froese [2002. Age and significance of the late Pleistocene Dawson tephra in eastern Beringia. Quaternary Science Reviews 21, 2137–2142; 2006. Seasonality of the late Pleistocene Dawson tephra and exceptional preservation of a buried riparian surface in central Yukon Territory, Canada. Quaternary Science Reviews 25, 1542–1551]. We refine the time of Dawson tephra deposition to between 25,420±70 and 25,290±80 ¹⁴C a BP. Bayesian analysis of constraining radiocarbon ages places the deposition of the Dawson tephra at between 30,433 and 30,032 cal a BP. Linear modulation (LM) OSL analysis of multi-grain aliquots of quartz showed that the initial part of the decay curve is dominated by a rapidly bleached (‘fast’) component; these samples, however, had relatively dim continuous wave (CW) OSL signals at the multi-grain aliquot (each composed of 80 grains) and single-grain scales of analysis. The single-aliquot regenerative-dose protocol was applied to multi-grain aliquots and single grains to obtain equivalent dose (D_e) values for samples collected from below and above the Dawson tephra. The D_e values were examined graphically and numerically, the latter using the central age, minimum age, and finite mixture models. For multi-grain aliquots, the central age model gave weighted mean D_e values between 30 and 50 Gy, which greatly underestimated the expected D_e of 74–81 Gy for both samples studied. Possible reasons for these underestimations are discussed, and a solution proposed based on single-grain analysis. Measurements of single grains produced D_e values in agreement with the expected D_e, and yielded OSL ages of 28±5 and 30±4 ka for the samples taken from above and below the Dawson tephra, respectively. Examination of individual grains with differing luminescence behaviors showed that a significant number of the measured quartz grains exhibited anomalous luminescence properties that would have compromised the results obtained from multi-grain aliquots. We therefore recommend analysis of individual grains to overcome the age-shortfall from multi-grain analysis of these and similar samples of quartz.     

An analysis of the components of the luminescence signals of selected polymineral and quartz samples from loess in western China and southern Tajikistan,and their suitability for optical dating

Previous luminescence dating studies on loess from China and Tajikistan have focused on the establishment of the regional chronology of the loess sequences. In order to improve the precision and accuracy of optical ages derived from the loess of the last glacial period in these regions, we have examined the components of luminescence signals in three loess samples from western China and southern Tajikistan. Our results show that the polymineral IRSL and post-IR OSL, and quartz OSL signals from loess of the two regions are represented by three components, which display different bleaching and growth characteristics. While the composition of the polymineral IRSL signals is similar between samples with the same age from the two regions, in the case of quartz there is significant discrepancy in the proportion of the fast and medium components of the OSL signals. Greater difference is observed in the composition of the polymineral post-IR OSL signals for the loess from the two regions. The three components of polymineral IRSL signals yield almost identical equivalent dose values as that derived from the total IRSL signal. An apparent agreement in equivalent dose is observed between the fast component of the polymineral post-IR OSL and the quartz OSL for the loess of western China but not in the loess of the same age from southern Tajikistan. The fast component of the quartz OSL yields an equivalent dose 25% higher than that based on the total signal for the sample from the base of the Late Pleistocene loess in southern Tajikistan. This demonstrates the importance of signal selection for an accurate luminescence dating of Central Asian loess.     

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.     

OSL dating of loess deposits bracketing Sheep Creek tephra beds,northwest Canada: Dim and problematic single-grain OSL characteristics and their effect on multi-grain age estimates

Geochemically-fingerprinted tephra beds provide unique chronostratigraphic markers for comparing Quaternary sedimentary records across eastern Beringia (Alaska and Yukon Territory). Establishing reliable numerical age control on these tephra horizons enables them to be placed within firm temporal frameworks and increases their potential as correlative tools for regional palaeoenvironmental reconstructions. To this end we present new single-grain and multi-grain quartz optically stimulated luminescence (OSL) chronologies for loess deposits bracketing three well-documented and regionally significant variants of the Sheep Creek tephra (SCt) at two sites in west-central Yukon Territory (Ash Bend and Quartz Creek). Single-grain OSL ages bracketing the SCt-A and SCt-K reveal that these tephras were deposited during late Marine Isotope Stage (MIS) 5 or early MIS 4. The SCt-C variant and associated organic-rich bed at Ash Bend were likely deposited during late MIS 5, based on a single-grain OSL age of ∼81 ka for the overlying sediments. The single-grain OSL ages obtained for these deposits are in stratigraphic order and in broad agreement with a fission track age estimate of ∼77 ka for the SCt-K. In contrast, comparative chronologies obtained using multi-grain aliquots are stratigraphically inconsistent and unexpectedly young when compared with the independent SCt-K age. Detailed examination of the single-grain OSL datasets reveal a range of unfavourable luminescent properties that could have contributed to the multi-grain aliquot age discrepancies; including, very low yields of luminescent grains, weak OSL signal sensitivities and large populations of aberrant grains (particularly 0 Gy grains and ‘dim’ grains with a tendency to sensitise during the equivalent dose (D_e) measurement sequence) that have similarly sized OSL signals as grains used for D_e analysis. Synthetic aliquot D_e datasets constructed from single-grain OSL measurements reveal that the large proportional light sum contributions of 0 Gy and dim grains could possibly account for multi-grain age underestimations in some of the Ash Bend samples. In light of these potentially problematic averaging effects, we do not consider the multi-grain OSL ages to be reliable and suggest that single-grain approaches may be preferable for dating sediments with similar quartz luminescence behaviours across this region.     

Luminescence and ESR dating of the sedimentary infill from the multi-level cave system of Alkerdi-Zelaieta (Navarre,N Spain)

The finding of Upper Paleolithic engravings in 2016 triggered a multidisciplinary investigation of the Alkerdi cave system (Urdazubi, N Spain). The study of the speleogenetic processes led to the identification of at least 6 paragenetic cave levels with associated sedimentary infill. In order to unravel the timing of changes in the karst dynamics and to get some insights about sediment origin, two sediment samples were collected from cave levels 4 and 1 for numerical dating purpose, using both Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) methods. One additional modern-age sample was also taken from the entrance of the karst to evaluate the magnitude of the optical bleaching achieved by the quartz grains before entering the cave system. Last, one sample was collected from a flowstone for U-series dating, providing independent age control.OSL measurements were carried out using small quartz multi-grain (MG) and single-grain (SG) Single Aliquot Regenerative-dose (SAR) protocol. Initial Equivalent Dose (D_e) results show evidence of saturated OSL signal for the sample of the higher level (with ∼60% of saturated aliquots). Unlike SA data, SG analyses do not meet the usual quality criteria (e.g., relatively high recuperation ratios, only a few grains with useable signal), suggesting that corresponding dating results should be treated with caution.Hence, both MG and SG TT-OSL and MG ESR methods were subsequently employed, as the corresponding signals are known to have higher saturation levels than OSL ones. ESR analyses were based on the Multiple Centre (MC) approach using the standard multi-grain multi-aliquot additive (MAA) dose method, while TT-OSL measurements were performed following Demuro et al. (2020). The latter, however, did not return any useful results for both samples. MC ESR data show the usual D_e pattern (D_e(Al)>D_e(Ti op. D)>D_e(Ti–H)) indicating that among the three ESR signals analyzed, the Ti–H most likely provides the closest estimate to the true burial age. However, low measurement repeatability and goodness-of-of fit indicate that the reliability of the ESR results may be reasonably questioned.Results derived from this multi-technique dating approach provide the first chronological constraints for the sedimentary infill of the Alkerdi cave system. In particular, they suggest that sediment deposition in Cave Level 4 (ALK-OSL01) occurred around 130 ka, which is in good agreement with the minimum age constraint given by the speleothem (80.5 ± 9.0 ka). In comparison, the young age obtained for sample ALK-OSL02 (5.0 ± 0.9 ka) suggests recent Holocene formation of the lowest cave level 1.Finally, the MG De value obtained for the modern sample is close to zero (<1 Gy), indicating that the OSL signal is almost fully reset at a multi-grain level before entering the cave. Additionally, despite the large De overdispersion measured in this modern sample, the De values are one to two order of magnitude lower than those obtained with the same model in the other two samples. Therefore, the large OSL D_e overdispersion (OD) values of up to 64% obtained for the two samples from Cave Level 4 and 1 are most likely related to re-sedimentation processes inside the cave system.     

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.     

Evaluating OSL-SAR protocols for dating quartz grains from the loess in Ili Basin,Central Asia

Late Pleistocene records of loess deposition are a critical archive for understanding terrestrial paleoenvironment changes in Central Asia. The age of loess is not well known for the deserts regions and surrounding high plateaus in Central Asia. Previous studies have shown that there remains a disparity between ages for loess deposition by luminescence and ¹⁴C dating. This study evaluates the potential of optically stimulated luminescence (OSL) to date a loess sequence resting on fluvial sands in the east Ili Basin, Central Asia. The single-aliquot regenerative-dose (SAR) protocol on coarse grain quartz was employed for equivalent dose determinations. The basal fluvial sand returned a secure OSL age, with low overdispersion value in equivalent doses (19 ± 2%) of ca. 36 ka and provides a close, but maximum age estimate (within 5 ka) on the initiation of loess deposition. However, the loess yielded high overdispersion values for equivalent doses and age reversals, coincident with diffuse paleosols; indicating that pedoturbation with loess deposition may be a dominant process. OSL ages between ca. 45 and 14 ka calculated using a maximum age model and OSL ages from other sites in the Basin suggests that the latest major period of loess deposition was between 70 and 10 ka ago. A future hypothesis to test based on these analyses is that there may be three periods of heightened loess deposition at ca. 45, 35 to 19 and 14 ka, when desert source areas to the west were particularly dry.     

Construction ages of the Upton Stone Chamber: Preliminary findings and suggestions for future luminescence research

The Upton Chamber in Massachusetts, an earth-covered stone structure 3.4 meters (m) in diameter, with a corbelled stone dome, and a 4.3 m long entrance passageway, is studied with the aim of determining whether optically stimulated luminescence (OSL) dating methods can be used to establish the approximate construction date of the entranceway. Three samples, taken from soil behind the lowest stones in the wall of the entrance passageway, returned OSL ages between 385 and 660 years ago (or from 1625 A.D. to 1350 A.D.; using the year 2011 as the 0 year). One sample, taken below the bottom of the artifact layers in an archeological test pit in front of the chamber entrance, returned OSL ages between 650 and 880 years ago. A modern sample collected from a nearby fluvial channel returned an age between 55 and 175 years. The Upton Chamber OSL sampling results are challenging to interpret because there are mixtures in the samples of both younger and older grains that likely result from human modification, root or soil processes, animal bioturbation (i.e. ants and worms), and/or partial bleaching. The ages were determined using the lowest component of the finite mixture model as applied to a distribution of quartz grains. Further research may enable us to determine whether older components are of anthropomorphic or geological origin.     

Investigating the components of the optically stimulated luminescence signals of quartz grains from sand dunes in China

The optically stimulated luminescence (OSL) signals from quartz consist of several physically distinct components, which are commonly referred to as fast, medium and slow components. In this study, the OSL components of quartz from the Taklimakan Desert and the Hunshandake sandy land in north China are investigated. Our results show that the relative contributions of OSL components to the bulk OSL signal can be significantly different among quartz grains from both deserts. Laboratory dosing, optical bleaching and heating experiments are used to test their effects on the relative contributions of quartz OSL components. It is found that cycles of dosing and optical bleaching have insignificant impact on the relative contributions of quartz OSL components, while heating to high temperature (500 °C) can significantly enhance the contribution of the fast component to the bulk OSL signals, especially for quartz samples from the Taklimakan Desert. Such results suggest that the different heating history of natural quartz grains plays an important role in controlling OSL components. Additionally, the quartz grains from the Hunshandake sandy land can easily be distinguished from those of the Taklimakan Desert, by using a ternary plot of fast-medium-slow components. The quartz grains from the Hunshandake sandy land exhibit a much stronger fast component than those from the Taklimakan Desert. This can be explained by that the quartz grains from the Hunshandake sandy land are mainly of igneous origin, while most of the quartz grains from the Taklimakan Desert are of low grade metamorphic origin.     

A high-resolution quartz OSL chronology of the Talede loess over the past ∼30 ka and its implications for dust accumulation in the Ili Basin,Central Asia

Similar to the loess deposits on the Chinese Loess Plateau (CLP), a reliable chronology plays also an important role in revisiting past climate and environment changes recorded by the loess in Central Asia. Previously, a few luminescence and ¹⁴C ages, mainly covering the last glacial, were obtained for several loess sections in Central Asia, which are often controversial. Until now, there is still a lack of reliable high-resolution chronologies covering the late Pleistocene, especially the Holocene. Here, the fine-grained (4–11 μm) quartz single-aliquot regenerative-dose (SAR) optically stimulated luminescence (OSL) dating protocol is used to establish a detailed chronology of the uppermost part (∼5 m) of Talede loess in the Ili Basin Central Asia. Conventional tests of the SAR protocol and the general luminescence characteristics indicate that this protocol is suitable for dating the Talede loess. Finally, 15 closely-spaced quartz OSL ages, ranging from 0.72 ± 0.05 to 28.9 ± 2.12 ka and with no reversals, were obtained. Consistent with previous studies in the Ili Basin, two of the three ¹⁴C ages show discrepancy when compared with quartz OSL ages for the Talede loess section. The constructed OSL chronology of the Talede loess reveals that the dust accumulation is rapid during marine isotope stage (MIS) 2, especially during the Last Glacial Maximum (LGM), and is also continuous during the Holocene, with the dust accumulation rate exhibiting a relatively low level and an increasing trend. Comparison of the dust accumulation at Talede with that at other sites in the Ili Basin indicates that the rapid dust accumulation during the LGM is not universal, and the slow dust accumulation during the Holocene is probably true for the entire Ili Basin. Comparison of different grain sized quartz OSL ages from Central Asian loess show characteristics of both consistency and inconsistency, which needs to be further investigated.     

Optical dating of aeolian and fluvial sediments in north Tian Shan range,China: Luminescence characteristics and methodological aspects

Loess and fluvial sand are important materials for dating river terraces and alluvial fans. This study focuses on the methodological aspects of dating loess and fluvial deposits from the northern flank of the Tian Shan range, China, using sand-sized quartz and potassium (K) feldspar. Luminescence characteristics of quartz and K-feldspar were studied for searching suitable dating procedures. Our results indicate that 1) most quartz aliquots were contaminated by feldspar, and were dated using a post-infrared optically stimulated luminescence (post-IR OSL) procedure. A Fast ratio acceptance threshold of 15 can be applied to select these aliquots with post-IR OSL signals dominated by quartz OSL; 2) the multi-elevated-temperature post-IR IR stimulated luminescence (MET-pIRIR) procedures are applicable for K-feldspar. A test dose of ∼30% of the natural dose is appropriate for dating of older (>10 ka) samples. An Age (T, t) plateau test can be used to evaluate the dating results; 3) for the loess samples, both quartz and K-feldspar were well bleached and are suitable for dating. Dating using K-feldspar is preferred for its higher efficiency; 4) for the fluvial sand samples, only the quartz grains were fully bleached. Single-aliquot dating of quartz gives reliable ages.     

Single grain optically stimulated luminescence dating of glacial sediments from the Baiyu Valley,southeastern Tibet

The Qinghai-Tibetan Plateau is an important area for the study of Quaternary glaciation. Optically stimulated luminescence (OSL) dating has the potential to contribute to the chronology of glaciation in this region, but it is important to assess the accuracy of OSL dating of these glacial sediments. In this study, single grain quartz OSL signals are examined for five glacial samples collected from the moraines outside the Baiyu Valley, southeastern Tibet. The quartz grains exhibit poor luminescence characteristics, with a small proportion of grains passing the screening criteria. Grains which pass the screening criteria have relatively low signal intensity, leading to D_e values with large uncertainties. MAM and CAM were used to determine D_e values for these samples. The OSL ages are consistent with the sequence of events derived from the geomorphological relationship of the samples, and also with previous published radiocarbon ages. However, it is more difficult to reconcile the OSL ages and the terrestrial cosmogenic nuclide (TCN) ¹⁰Be ages. Analysis of both single grain quartz OSL data and TCN ¹⁰Be data is complex in this area. Further work is required to increase confidence in the OSL ages generated for the glacial sediments from this region.