Single-aliquot Regenerative-dose Research Articles

Multi-method luminescence dating of young aeolian dunes in the central Tibetan plateau

The environment of the Tibetan Plateau (TP) is extremely sensitive to global climate change, and the frequent aeolian activity on the central TP generates large amounts of dust with the result that the region has a major impact on regional and global environmental change. The extensive aeolian dunes on the central TP provide a direct and valuable archive of aeolian activity; however, the age and sediment deposition processes of these dunes are still poorly understood. Optically stimulated luminescence (OSL) dating, an effective method for dating aeolian sediments, has been used sparingly in the region. In this study, we applied quartz single-aliquot regenerative-dose (SAR) OSL, K-feldspar post-infrared infrared-stimulated luminescence (pIRIR), and single-grain K-feldspar pIRIR methods to determine the ages of two well-preserved sand dunes in the Lunpola (LD) and Tuotuohe (TTH) river basins in the central TP. Our results showed that the quartz OSL signal of the TTH dune was dim, while the LD dune quartz exhibited a higher OSL sensitivity than that of the TTH dune. The high recuperation observed could be attributed to the low signal-to-noise ratio of the OSL signals. The K-feldspar signal was bright and the pIR50IR170 signal could be used to date young dune samples in the central TP, whereas it could be affected by the residual dose, or incomplete bleaching in the TTH profile, resulting in age overestimation. The single-grain K-feldspar protocol had a good potential for dating the young TP dunes. Multi-method luminescence dating is recommended for the cross-checking of young dune samples with low OSL sensitivity in the TP. Our luminescence dating reveals that aeolian dunes in the central TP formed approximately 385 to 330 a and persisted to the present, possibly in response to climate change since the late stage of Little Ice Age (1400−1850 CE).

Quantitative radiation dosimetry by measuring thermoluminescence of resistors in electronic personal dosimeters

A study on retrospective dosimetry was performed using electronic personal dosimeters (EPDs) for reconstructing doses received by radiographic testing workers. The dosimetric properties of the thermoluminescence (TL) peak in the temperature range of 100–200 °C were investigated by measuring the TL of the resistors extracted from the EPDs in a darkroom environment. Results showed that this TL peak exhibited optimal dosimetric properties, with a minimum detectable dose as low as 13 mGy. To calculate the absorbed dose using the resistors, a simplified single aliquot regenerative (SAR) dose method using the TL peak was employed. The zero dose of the commercial EPD (model CLOVER) was determined to be 58 ± 72 mGy through the random selection of six EPDs. Additionally, a dose overestimation correction factor for compensating rapid sensitivity changes after TL measurement of the natural sample was calculated as 1.73 ± 0.09. Furthermore, it was observed that the TL signal faded exponentially to approximately 60% over a period of 12 weeks. Subsequently, retrospective dosimetry was performed by irradiating EPDs with a standard gamma ray dose of 1 Gy. The radiation exposure dose calculated from the TL peak of the resistors was found to be approximately 10% lower. These findings showed that the retrospective dosimetry with EPD can be utilized for accurately estimating the radiation exposure dose.

New chronology of K-feldspar isochron optical dating (iIRSL) in the late Pleistocene coastal aeolian deposits of Southeast China

Old red sand (ORS), which developed during the late Pleistocene, is widely distributed along the coasts of the western Pacific and Indian Ocean. Recently, advancements in the Optically Stimulated Luminescence (OSL) dating technology have primarily determined its sedimentary age. However, in tropical and subtropical regions, chemical weathering can impact the calculation of environmental dose rates, potentially leading to age biases whose magnitude remains uncertain. The new K-feldspar isochron dating method (iIRSL) has the potential to address this issue. This approach effectively enhances the accuracy of age data by accounting for variations in past dose rates caused by chemical weathering and changes in water content during sample burial. This study used the iIRSL method to conduct infrared stimulated luminescence signal tests on ORS samples from the Haitan Island, south China. Five grain sizes of K-feldspar grains were extracted from each sample during experimentation. The single aliquot regenerative dose method (SAR) was utilized to determine the equivalent dose for each grain size and calculate age using the isochron method (iIRSL). Furthermore, it compared the iIRSL ages with quartz age (SAR). The results indicate that: (1) This study obtained four iIRSL ages, which are consistent with the ages obtained from quartz (SAR) within a reasonable range, ranging from 62.13 ± 4.85 to 39.44 ± 4.85 ka BP. (2) Comparison of the simulation results of different weathering degrees using the iIRSL method and K-feldspar two-step IRIR methods indicates that the iIRSL method can effectively mitigate the impact of chemical weathering on age determination, giving more reliable iIRSL ages. (3) The ORS along the southern coast of China mainly deposited during Marine Isotope Stages 5, 4, and 3, exhibiting relatively higher deposition rates during MIS 5 and MIS 3 at approximately 30 cm/ka and 15 cm/ka respectively. This suggests that the ORS was predominantly deposited during periods of elevated sea levels. However, it is important to note that the data from MIS 5 may have been influenced by the absence of samples from this particular stage and limitations in dating methods, resulting in a lower frequency-density of deposition ages during MIS 5 and creating an “illusion” of sediment interruption.

Correlations between quartz OSL dose-response curve and TL glow curve characteristics, and their implications for equivalent dose estimation

Optically stimulated luminescence (OSL) dating of quartz using the single-aliquot regenerative-dose (SAR) procedure requires construction of dose-response curves (DRCs). The shapes of DRCs and their characteristic saturation doses (D0 values) are well-known to be highly variable between samples and among individual grains from the same sample, but the factors that control DRC characteristics are imperfectly understood. Here we report correlations between OSL DRC shapes and thermoluminescence (TL) glow curve characteristics for a sample of quartz from northern Australia. Individual grains were measured using the SAR procedure and one of two preheat temperatures (160 °C and 260 °C), and grouped according to similarities in their DRC shapes. Grains from each DRC group were then physically transferred onto a separate disc for TL measurement as a multi-grain aliquot. A strong correlation was observed between DRC group and laboratory-irradiated TL glow curve shapes, along with some differences between the two preheats. Irrespective of the selected preheat, earlier saturating DRC groups are associated with the most intense 110 °C TL signal, and the least intense 325 °C TL signal, which corresponds to the main OSL trap. Later saturating DRC groups generally show the opposite trend. There are also trends within other regions of the glow curve and DRC group, such as prominent TL responses at 140–160 °C, 220–240 °C and 390–410 °C. We assessed the effect on the accuracy of equivalent dose (De) estimation using an associated radiocarbon age as an independent cross-check of the OSL ages for the DRC groups. De over- and under-estimates were obtained for some DRC groups. Most notably, grains preheated to 160 °C displayed a pattern of De values which decreased with an increase in D0. We relate this to variable concentrations of charge at the ∼230 °C TL trap prior to regenerative dose OSL measurements. OSL ages for most DRC groups preheated to 260 °C are close to the radiocarbon age, as are those of later saturating DRC groups preheated to 160 °C; the latter DRC groups have the smallest TL signals at ∼230 °C relative to the TL peak at 325 °C. The results of this study suggest that correlations between single-grain De and D0 values can occur due to underlying differences in the TL characteristics of grains with different DRC shapes. In the absence of independent age control and prior to measuring multi-grain aliquots of quartz, we recommend that OSL dating practitioners screen their samples for any single-grain patterns of De as a function of DRC shape, to determine the optimal SAR measurement conditions and data-analysis procedures for De estimation.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Alluvial-lacustrine record of Mid- to Late-Holocene moisture variations trend verified by multiple proxies in the middle and lower reaches of the Hutubi River, northwest China

Alluvial-lacustrine deposits are important carriers for studying paleo-hydrological information and the evolution of paleo-environments. In this study, a total of 6 optically stimulated luminescence (OSL) samples from 2 profiles in the lower and middle reaches of the Hutubi River in the North Tianshan Mountains were dated, and a comprehensive analysis was conducted by integrating sedimentary structures, grain sizes, and magnetic susceptibility characteristics to explore the sedimentary environment patterns and regional evolution processes during the Mid to late Holocene. The results revealed the following findings: (1) The OSL signal of quartz samples indicates the predominance of fast components, allowing reliable dating of regional fluvial sediments using the appropriate condition-tested coarse-grained quartz single-aliquot regenerative dose (SAR) protocol within the 90–125 μm range. (2) Analysis of sedimentary structures, grain sizes, and magnetic susceptibility characteristics reveals lithofacies of heterotopic synchronous or homotopic asynchronous in exposed profiles, with predominantly poorly sorted fine and very fine sand. Magnetic susceptibility is primarily controlled by the content of magnetic minerals in the coarse particles, while also being influenced by the combined effects of provenance input and depositional environment, indicating a complex regional sedimentary environment influenced by variable hydrodynamic conditions driven by fluvial processes. (3) Based on OSL dating results and the analysis of various environmental proxy indicators, it is determined that the climatic environment in the Middle and Late-Holocene in the downstream areas of the northern piedmonts of the Tianshan Mountains demonstrates a fluctuating pattern of wet and dry alternations. The sedimentary environment shifted from a stable state in the Mid-Holocene to an unstable state in the Late-Holocene. The intermittent appearance of wet records may be associated with increased river activity caused presumably by the release of high-altitude ice due to rising temperatures and warming conditions.

Combined optically stimulated luminescence and radiocarbon dating of aeolian dunes in Arctic Sweden

AbstractMultiple parabolic sand dune fields formed in Arctic Sweden after the last deglaciation, facilitated by an abundance of loose glaciofluvial sediment, limited vegetation cover and strong winds. Following initial stabilisation, these dunes underwent repeated reworking after fire events, as evidenced by the presence of buried soils, charcoal layers and redeposited sands in the dune stratigraphy. These reworking events may be driven by wider climate forcing; however, to date, no chronological framework exists for this activity in Sweden. As such, here, we apply quartz optically stimulated luminescence (OSL) dating of Arctic Swedish sand dunes using two dunes at the sites of Vastakielinen and Jorggástat. Resultant double‐SAR (single aliquot regenerative dose) quartz OSL ages are in good agreement with independent ages provided by 14C dating of charcoal fragments recovered from charcoal layers within the dunes, and we conclude that the chosen protocol is generally well suited for dating aeolian reworking of dune sediments in Arctic Sweden. While feldspar contamination limits precise age assignment for initial dune movement, our results nonetheless suggest repeated and long‐lasting aeolian activity in Arctic Sweden throughout the Holocene and, although there are differences in detail, further suggest some general trends in terms of dune stability and reworking over Arctic Fennoscandia.

Thermoluminescence dating of gypsum in loess deposits

Gypsum deposits within loess deposits are an important indicator of weathering processes and climate change. We conducted a thermoluminescence (TL) dating study of the gypsum from loess deposits of the Jiuzhoutai section in the western Chinese Loess Plateau. Determination of the equivalent doses (De) of gypsum samples was conducted using several protocols, including single-aliquot regenerative-dose (SAR-TL), multiple-aliquot additive dose (MAAD-TL), and Isothermal TL of SAR (SAR-ITL). The TL glow peak at 280 °C was targeted because of its reported stable signals. The test dose check, estimation of sensitivity changes, and the dose recovery test were applied to assess the applicability of the different protocols, and the characteristics of the thermoluminescence signals for gypsum were evaluated. The De results for the SAR-TL, MAAD-TL, and SAR-ITL protocols were within the error ranges. Among the three protocols, SAR-ITL did not involve high-temperature heating and it provided a more accurate De value, and thus it was used for De determinations for gypsum dating. With a dose rate of 1.74 ± 0.07 Gy/ka, the minimum TL age of the gypsum veins was ∼182 ± 7 ka. U-series dating was also applied to the same samples for comparison. However, the extremely low ratio of 230Th/232Th (≤4 × 10−6) of the gypsum veins deposited within the loess resulted in a large error of the U-series dates. We conclude that TL dating is more appropriate for the dating of gypsum in loess deposits.

Evaluation of the modified single-aliquot regenerative-dose procedure for equivalent dose determination

A common optically stimulated luminescence (OSL) method for dating sediments is the single-aliquot regenerative-dose (SAR) protocol, which is widely applied to measure the equivalent dose (De) in various sedimentary samples. The modified SAR protocol is distinguished from the conventional SAR protocol by the application of additional high-temperature (e.g. 280 °C) optical stimulation at the end of the procedure. In this study, we performed a dose recovery test using fine-grained (4–11 μm) quartz sample derived from coastal sediments and found that the De values recovered using the modified SAR protocol were significantly overestimated by ∼30% compared with the given dose, except for a preheating temperature of 160 °C. In contrast, De values recovered using the conventional SAR protocol showed good agreement with the given dose (within ±10%) over a large preheating temperature range (160–260 °C). Differences in the dose-response curves between the conventional and modified SAR protocols may have led to the overestimation of De values recovered using the latter approach. The lack of proportionality between Lx and Tx in the modified SAR protocol complicated the construction of the SAR dose-response curve and dose recovery. To avoid these phenomena, which may be highly sample dependent, modified SAR for OSL dating should be applied only to samples dominated by the slow OSL component and with high recuperation levels.

A new analytical model to fit both fine and coarse grained quartz luminescence dose response curves

We address two issues: (a) the choice of suitable analytic forms for curve fitting quartz OSL-SAR dose response data and (b) possible physical interpretations of the difference between fine (4–11 μm) and coarse (63–90 μm) grain samples. We start with a phenomenological model with three levels: an OSL-active trap, a deep trap, and a radiative center. This model yields a simple analytic form for the dose response under the optically stimulated luminescence-single-aliquot regenerative dose (OSL-SAR) protocol. By comparing with experimental data from nine quartz samples, we show that this form provides excellent agreement and may, in some cases, be better than the commonly-used double-saturating-exponential form despite this form having fewer adjustable constants. Further, because this analytic form is derived from a model, physical parameters can be inferred from the curve fits. In particular, concentrations for the OSL-active and deep electron traps can be computed and the variation in concentrations of these traps between samples is discussed. Within this model, the difference between fine and coarse grain samples is consistent with the OSL-active trap being a surface trap as opposed to a volume trap.

Post-violet infrared stimulated luminescence (pVIRSL) dating protocol for potassium feldspar

Devi et al. (2022) suggested that post-violet infrared stimulated luminescence (pVIRSL; IRSL at 100 °C after a violet bleach at 50 °C) of K-feldspars, generally has a near zero athermal fading rate. This study explores the mechanism and suitability of the pVIRSL signal for dating applications. The results suggest that pVIRSL is a recuperated signal, arising from the eviction of charges in deep traps by violet stimulation followed by their recapture to the IR traps. A post-violet IR single aliquot regenerative dose (pVIR-SAR) protocol worked well for seven K-feldspar samples from varied depositional environments with ages ranging from 6 to 286 ka. The pVIRSL paleodoses of most samples, accorded with paleodoses computed using the published ages and their environmental dose rates.

Surface mount multilayer ceramic capacitors as optically stimulated luminescent dosimeters

The choice of dosimetric materials for precise retrospective dose assessment in case of any emergencies is very challenging. Since few decades, electronic components like ceramic resistors, inductors, IC chips, surface mount resistors and inductors have been proven to be suitable candidates for dose estimation using thermoluminesce (TL)/optically stimulated luminescence (OSL) techniques. In this work, OSL technique is applied to study dosimetric properties of surface mount multilayer ceramic capacitors (SM MLCC) available in commonly used instruments like printer, computer mouse, USB flash drive and personal gadgets like mobile phone etc. To understand the OSL process involved, the elemental composition and crystallinity of the SM MLCCs were analyzed using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) techniques. It is found that the main constituent is barium titanate with aluminium silicate as major impurity along with some trace elements and is responsible for the origin of the radiation induced OSL signal. Some important dosimetric characteristics like OSL sensitivity, repeatability, OSL dose response, and OSL signal stability upon storage were studied. The stimulation time was optimized as 50 s and used for all OSL measurements. The dose response was found to be linear from 500 mGy to 15 Gy and simply increased (up to 40 Gy). Fading analysis showed that the OSL signal decreases by ∼ 25 % in 1 day, ∼ 50 % in 4 days, and remained stable after that at least up to 8 days. The dose was recovered using single aliquot regenerative-dose (SAR) technique with very good accuracy. These results of dosimetric studies and validation study suggest that surface mount multilayer ceramic capacitors have potential use as retrospective dosimeters.

Early Holocene dust activity variation in the southern Tibetan Plateau and its response to solar irradiance

The Tibetan Plateau (TP) is an important source for long-range-transported Asian dust, however, the past variation of dust activity in the TP is poorly understood. In this study, we analyzed a ∼ 4.8-m aeolian loess-sand sequence from the Yarlung Tsangpo Valley in the southern TP. A closely spaced sampling strategy was used for optically stimulated luminescence (OSL) dating. With single-aliquot regenerative-dose (SAR) OSL and post-infrared (post-IR) OSL protocols, the medium-grained (38–63 μm) quartz fraction was selected to establish a detailed chronology. The two most popular OSL readers (Lexsyg and Risø) were applied to all samples for equivalent dose measurement, and the corresponding comparison shows very good reproducibility of ages derived from the two independent reader systems. A total of 23 luminescence ages were obtained ranging from 6.7 ± 0.3 ka to 11.6 ± 0.7 ka in stratigraphical order. Aeolian sands accumulated during cold-dry Younger Dryas period, and the overlying loess deposited during Early Holocene. Frequency-dependent susceptibility is used to infer pedogenesis intensity or vegetation cover, and coarse grain size fraction is used to reflect the dust activity frequency during Early Holocene. The reconstructed variation of dust activity frequency in the southern TP shows strong cyclicity of ∼ 1 ka, ∼ 0.7 ka and ∼ 0.5 ka with confidence level of >95%, probably indicating that the regional dust activities on centennial and millennium scales are closely related to the changes of the North-Atlantic Oscillation (NAO) phase as response to solar irradiance forcing.

A new chronological framework for Chuandong Cave and its implications for the appearance of modern humans in southern China

Chuandong Cave is an important Late Paleolithic site because it documents the early appearance of bone tools in southern China. We used the single-aliquot regenerative-dose protocol for optically stimulated luminescence dating to improve the precision of the chronology for the Chuandong Cave sedimentary sequence. The age of each layer was determined using a Bayesian modeling approach which combined optically stimulated luminescence ages with published AMS 14C dates. The results showed that Layer 10 began accumulating since 56 ± 14 ka and provides the upper age limit for all artifacts from the sequence. Bone awl tools from Layer 8, the earliest grinding bone tools in this site, were recovered within sediments between 40 ± 7 ka and 30 ± 4 ka. Layer 8 also indicates the appearance of modern humans in the Chuandong Cave sequence. Layers 4–2, ranging from 15 ± 3 ka until 11 ± 1 ka and including the Younger Dryas period, contain a few bone awls and an eyed bone needle. The shift from bone awls to eyed bone needles in the Chuandong Cave sequence indicates that modern humans adapted to the changing climate of southern China. We conclude that modern human behavior in bone tools appeared in southern China as early as 40 ± 7 ka, became more sophisticated during the Last Glacial Maximum, and spread more widely across southern China during the Younger Dryas.

Characteristics of the quartz isothermal thermoluminescence (ITL) signal from the 375 °C peak and its potential for extending the age limit of quartz dating

The quartz isothermal thermoluminescence (ITL) signal measured at 330 °C (ITL330) has been proposed as a method to measure deep traps in quartz, i.e., 375 °C TL peak, therefore offering the potential to extend the dating limit of quartz. However, little is known about the applicability of this signal for dating. We therefore investigate the characteristics of the ITL330 signal, in terms of the origin of the signal, thermal stability, and bleachability. Since the trapping sensitivity changes induced by high temperature treatments undermine the application of the single aliquot regenerative dose (SAR) protocol, here we evaluate the reliability and applicability of the multiple aliquot methods, i.e., multiple aliquot additive dose (MAAD) and multiple aliquot regenerative dose (MAR) protocols, using samples from the Luochuan section on the Chinese Loess Plateau with the independent age control. Results indicate that the ITL330 signal is closely associated with the 375 °C peak of the glow curve, originating from a deep trap at about 1.8 eV with a thermal lifetime of ∼1010 years at 10 °C. The natural ITL330 dose response curve (DRC) indicates the signal has a theoretical dating range up to ∼800 Gy, equivalent to ∼230 ka. When the natural DRC is compared with the laboratory generated DRCs using MAR and MAAD protocols, they start to diverge in shape after ∼200 Gy, resulting in significant ITL330 age underestimation beyond ∼70 ka. However, application of the pulsed-irradiation (PI) method for the MAAD protocol reveals that the shape of the natural DRC can mostly be reproduced with the PI-MAAD protocol and thus it can provide reliable ages up to natural saturation at ∼230 ka. While further investigations are required to assess the impact of the repeated pulse irradiation and heating on the signal and determine the optimal pulsed irradiation conditions, it appears that this approach can be a promising step forward to provide a better simulation of the trapping conditions in nature.

Multi dating approach of long marine core sediments from the south-eastern continental shelf of Korea: Comparison of SAR OSL, TT-OSL and pIRIR dates

Marine sediments constitute important archives of past oceanic, climate, and sea-level changes. However, it is difficult to derive accurate chronological models due to the absence of long sediment cores and limitations of dating methods. To investigate the feasibility of applying optically stimulated luminescence (OSL) ages to establish high-resolution chronologies in the East Sea of Korea, we obtained three cores with lengths up to 120 m from the eastern continental shelf of Korea. Most of the core sediments were homogeneous or crudely laminated mud, with some sand and gravel bed. Multiple dating methods, including fine-grained quartz single-aliquot regenerative-dose (SAR) OSL, thermally transferred OSL (TT-OSL) from fine-grained quartz, and single-grain K-feldspar post-infrared (IR) infrared stimulated luminescence (IRSL) (pIRIR), following the above description, were applied to overcome the age limitation and create an accurate age model through cross-checking among the different dating methods. We also investigated the applicability of the standardised growth curve (SGC) to TT-OSL signals in continental shelf environments. The equivalent dose (D e ) values from the SGC were consistent with those from the SAR TT-OSL procedure, which suggests that the SGC is valid for long core sediments on the continental shelf. A detailed chronology derived from the radiocarbon, U/Th, and multiple OSL age dating methods was compared. Especially, in core 19ESDP-101, a comparison between TT-OSL ages from fine-grained quartz and pIRIR ages from coarse K-feldspar showed agreement to within 10% at most depths for which ages were measured. We demonstrated that OSL dating from long marine core sediments in a continental shelf margin environment can provide an accurate and precise chronology in undatable regions.

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.

OSL chronological evidence reveals one of the earliest island-type Neolithic sites in the coastal area of South China

Many prehistoric sites are preserved in the southeast China coastal area; however, it is still unclear when ancient human activity occurred owing to a lack of chronological evidence, which is unfavourable for research on the coupling of prehistoric man-earth relationships. In this study, we present an optically stimulated luminescence (OSL) chronology analysis of two profiles (T1 and T4) collected from the Neolithic Jianhu (JH) site on Haitan Island, South China. The single-aliquot regenerative-dose (SAR) protocol for coarse silt (38–63 μm) quartz was used to determine the equivalent dose (De). The results showed that the OSL technology is reliable and of great value for archaeochronology in coastal aeolian regions. The results suggest that the JH site is one of the earliest Neolithic sites in the coastal area of Fujian. The ages of cultural layers with ancient human activities at the JH site varied from 7.4 ± 1.13 to 5.77 ± 0.35 ka, thereby making the JH site the earliest Neolithic site in the coastal area of Fujian. The sand-tempered pottery unearthed from the JH site can be used as direct evidence of ancient human survival, and its age is 6.33 ± 0.21 ka with a high precision, which presents the earliest OSL data on pottery in South China. We also discuss the regional environmental background of ancient human activity. The Keqiutou culture corresponds to a period of relatively high sea level and a superior natural environment on Haitan Island. The sea retreat 5.7 ka ago was a crucial factor driving prehistoric human migration to the Fuzhou Basin and Taiwan Island.

Critical role of the deep electron trap in explaining the inconsistency of sensitivity-corrected natural and regenerative growth curves of quartz OSL at high irradiation doses

Natural quartz minerals that contain impurities, complex defect structures, and multiple trap levels within their crystals have been widely used for optically stimulated luminescence (OSL) dosimetry. Accurate application of the single-aliquot regenerative-dose (SAR) protocol requires an equivalence between the sensitivity-corrected natural and regenerative growth curves. In this work, the sensitivity-corrected natural and regenerative growth curves of quartz OSL are modelled using a comprehensive kinetic model based on the band theory of solids. We demonstrate that the trapping behaviour of the deep electron trap exerts a critical influence on the inconsistency of the sensitivity-corrected natural and regenerative growth curves at high irradiation doses. A delay in saturation of the deep electron trap at high irradiation doses leads to a substantial increase in electron competition in the recombination centres during the irradiation of the test dose and a decrease in electron competition in the centres during the subsequent stimulation of the test dose OSL. As a consequence, the test dose OSL responses as functions of irradiation doses are inconsistent (incompatible) between natural and regenerative aliquots, and the sensitivity-corrected regenerative growth curve tends to be higher than the natural one in the high-dose region. There may be substantial deep electron traps within the crystal of natural quartz that cause their delayed saturation at high irradiation doses.

Chronology of Last Glacial Maximum sediments in the coast of Fujian, South China

The coast in South China is an important area for the coupling of terrestrial, marine, and atmospheric processes. Widespread loose sediments in the area likely recorded regional climatic and geomorphic processes since the Late Pleistocene, and these that can be deciphered through geochronology. In the present study, eighteen samples prepared from the FN1 core retrieved from the Funing Bay in the coast of Fujian were used for OSL dating. The single-aliquot regenerative-dose (SAR) approach was employed for dating using three grain-size fractions of quartz, while coarse-grained K-feldspars were used for post-infrared infrared stimulated luminescence (pIRIR) dating of the core. Seven samples were also dated using the AMS 14C dating technique to establish the reliable chronology. The results reveal the following: 1) Minerals and grain size variations directly affect the accuracy of the luminescence dating. The present study demonstrates that cross-validation of the OSL dating data is an effective way to enhance their reliability. 2) Dating results from the three grain-size fractions of quartz in the upper section of the core are consistent within the error range, and these agree with ages from the AMS 14C method for the corresponding horizon. However, the OSL ages based on the three grain-size fractions of quartz and the coarse-grain K-feldspar differed for the lower section of the core (10.6–14.7 m). 3) Samples produced ages ranging from 25.4 to 0.8 ka based on the OSL dating method. According to a chronological framework starting from the Last Glacial Maximum and a palaeoenvironmental index, the sedimentation rate is partitioned into three main periods. Sedimentation rates during the periods between 25 and 21 ka and < 7 ka are higher than those for the period between 21 and 7 ka. These results suggest that the sedimentation rate was probably linked to the regional transgression events.