OSL dating of sediments from deserts in northern China

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

Optical dating of young tidal sediments in the Danish Wadden Sea

We have tested the applicability of optically stimulated luminescence (OSL) to the dating of young estuarine sediments (<1000 years) to determine whether this method can be used to complement and support existing techniques, such as ²¹⁰Pb dating. The degree of bleaching before deposition is investigated by examining the age trend in various sediment cores, and where possible, by comparison with independent age control provided by ²¹⁰Pb dating. The consistency between optical ages and ²¹⁰Pb ages is shown to be satisfactory on a time-scale down to only a few years.

We conclude that OSL provides reliable and reproducible results in cores from sub-, inter- and supra-tidal sediments, ranging from only a few years up to 1000 years old, confirming its value in the estimation of estuarine accretion rates. With OSL it is, for the first time, possible to date sediment cores from silty and sandy tidal flats, providing a new approach to the problem of evaluation of stability and calculation of sediment budgets for estuaries and coastal lagoons.     

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.     

Dating of lower terrace sediments from the Middle Rhine area, Germany

Modern and known-age Pleistocene fluvial sediments were investigated by optical dating of quartz to test the suitability of the approach for dating deposits from the deeply incised Middle Rhine Valley. Samples from modern flood sediments revealed skewed distributions indicating different residual levels of equivalent dose (D_e) within the different aliquots. Nevertheless, a substantial number of aliquots from the modern deposits reflect D_e values close to zero. For the Pleistocene samples, optical ages are in general consistent with age control given by the presence of the Laacher See Tephra and radiocarbon dating. However, some samples overestimate the known age by a few thousand years when using the arithmetic mean. This is apparently explained by including aliquots in the determination of mean D_e where the optical signal was incompletely bleached at deposition. The most difficult issue in this context is identifying a suitable approach that can distinguish between the variability of D_e due to partial bleaching and microdosimetry. However, even when considering these limitations it appears that optical dating will by a quite suitable method to date Pleistocene sediments from such a complex fluvial environment, especially when focusing on a precision scale beyond a few thousand years.     

Chronostratigraphy of a sediment record from the Hajar mountain range in north Oman: Implications for optical dating of insufficiently bleached sediments

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

Testing the use of OSL from quartz grains for dating debris flows in Miyun,northeast Beijing,China

Extreme seasonal summer rain storms are common in the mountains to the north east of Beijing and these often result in mass movement of sediment slurries transported for up to a few km. These debris flows can be deadly and are very destructive to infrastructure and agriculture. This project tests the application of luminescence dating to determining the return frequency of such extreme events. The high sediment concentration and the very short flow duration gives very little opportunity for daylight resetting during transport and only a small fraction of the total mass is likely to be reset before transport begins. Here we examine the quartz single-grain dose distribution from a recent known-age (<25 years) debris flow from a small (∼3.9 km²) catchment ∼140 km north of Beijing and compare it with those from three samples from a sedimentary sequence containing the evidence of multiple flow events.Multi-grain quartz OSL signals are dominated by the fast component and <1% of the 150–200 μm grains give a detectable test dose (4.5 Gy) response. Single-grain beta dose recovery gave a ratio of 0.97 ± 0.06 (n = 30) with an over-dispersion of 23 ± 8% (CAM). Both the recent known age and the palaeo-distributions are highly dispersed with over-dispersions greater than 50%. The average weighted doses range between ∼3 mGy and ∼6.5 Gy, indicating that all deposits are no more than a few thousand years. Minimum age modelling give an age estimate for the youngest sample consistent with the known age, and minimum ages for the older palaeo-deposits suggest that there have been at least 3 major debris flows in this small catchment in the last 1000 years.     

Luminescence dating of glaciolacustrine silt in overdeepened basin fills beyond the last interglacial

OSL and IRSL dating are applied to samples from a 152 m-long drill core to constrain the timing of three glaciolacustrine depositional periods within the infill of an overdeepened bedrock trough in the Lower Glatt valley, N Switzerland. The characterisation of the dose-response suggests that the polymineral IRSL₅₀ and pIRIR_180/225 signals are close to saturation, while quartz OSL ages are within the range of reliable dating. The demarcation of the upper quartz OSL dating limit, however, remains challenging. Dose-recovery tests performed with long storage periods were used to investigate the reliability of the high region of the dose-response curve. They suggest an upper limit for reliable dating of ∼400 Gy for these samples, which was considerably lower than the commonly used 2D₀ criterion. Lifetimes were calculated for the quartz OSL and the thermal stability of the signal is not considered as problematic for the determined ages. Allowing for a contribution from inherited dose due to partial bleaching, places the infill of the overdeepened valley within the penultimate glacial cycle (MIS6).     

Single-grain quartz OSL dating of debris flow deposits from Men Tou Gou,south west Beijing,China

Debris flows in the mountainous regions south west of Beijing, China occur frequently and often result in considerable mass movements with disastrous consequences for human life, infrastructure and agriculture. Obtaining chronological information on such events is important for the prediction of the return frequency of these debris flows, risk assessment and climate change research. In this project, we use quartz single-grain optically stimulated luminescence (OSL) methods to determine the burial ages of five debris flow samples from the Zhai Tang region ∼60 km west of Beijing. OSL characteristics were found to be acceptable despite the low inherent brightness of quartz extracted from these samples. Single-grain thermal transfer was determined to be negligible and beta dose recovery experiments were satisfactory. The quartz single-grain dose distributions strongly indicate that the samples were poorly bleached prior to deposition; relative over-dispersions are larger than 60%. Minimum age modelling indicates that all five samples were deposited within the past few hundred years, indicating that catastrophic debris flows are occurring under the historically-recent land-use pattern.     

Luminescence dating of canal sediments from Angkor Borei, Mekong Delta, Southern Cambodia

Work to apply luminescence dating to archaeological sites in the Lower Mekong Delta has continued with a programme aimed at dating ancient canal sediments and brick monuments in the vicinity of ancient city of Angkor Borei. Following the successful application of OSL dating to the Paris 2 canal near Angkor Borei further fieldwork and analysis has been undertaken. The infill and substrate of the larger Paris 4 canal connecting Angkor Borei to Oc Eo, some 80 km to the south in Vietnam has been sampled and subjected to luminescence analysis. Field spectroscopy and underwater bleaching experiments were also conducted in the Baray and Angkor Borei in 2004. The results show that both illumination intensities and spectral distributions are severely altered by as little as 1.5 m of turbid water, and that OSL bleaching rates for both quartz and feldspars are reduced. Since quartz resetting is heavily dependant on the UV components in daylight, which have preferentially attenuated the effects of turbid water on OSL zeroing rates are especially marked. The new data from the Paris 4 canal, which has been dated by OSL to be between the first millenium BC and the late first millenium AD are significant to understanding the archaeological development of the Fu Nan state in the Lower Mekong Delta, and the sequence of development of the canal network linking inland agrarian sites and coastal trading centres.     

Optical dating of flowstone and silty carbonate-rich sediments from Panxian Dadong Cave,Guizhou, southwestern China

Panxian Dadong Cave located in the western Guizhou is a very important Paleolithic site in China. At this site bone and stone artifacts, human teeth and mammalian fossils (known as Ailuropoda-Stegodon fauna) were found, and the site was previously dated to 120–300 ka using ESR/uranium-series methods. In this study, we successfully extracted fine quartz grains from flowstone and silty carbonate-rich sediments in the excavated area. The quartz extracts displayed excellent luminescence properties, and satisfied the SAR (single-aliquot regenerative dose method) acceptance criteria. The sensitivity-corrected OSL signals are not saturated at a dose up to about 1400 Gy. The cultural unit was OSL dated to 190–300 ka, corresponding to MISs 7–8. The flowstone deposits overlying the cultural unit were determined to be 13–190 ka and the silty carbonate-rich sediments underlying the cultural unit to be 300–360 ka. The optical ages are in general agreement with the coupled ESR/U-series and U-series ages.     

Optical dating of hydromagmatic volcanoes on the southwestern coast of Jeju Island, Korea

Jeju Island, the largest Quaternary volcanic island in Korea, has formed mostly since the early Pleistocene, but its latest chronology of volcanism and sedimentation is still poorly constrained. Here we report optically stimulated luminescence (OSL) ages for two hydromagmatic volcanoes on the southwestern coast of Jeju Island, i.e., the Songaksan and Suwolbong tuff rings. The basaltic tuffs of these volcanoes contain abundant quartz sands from underlying marine sedimentary sequences. Two samples collected from the middle part of the Songaksan Tuff yielded highly reproducible quartz single-aliquot regenerative-dose (SAR) OSL ages of 7.0±0.3 ka, providing the first direct age estimate of Holocene volcanism in Jeju Island. The quartz OSL age estimate of 5.1±0.3 ka for the younger reworked basaltic tuff (the Hamori Formation) is comparable with previous radiocarbon and U-series disequilibrium dating of fossil mollusk shells. Two samples from the Suwolbong Tuff show quartz OSL age estimates of 18.3±0.7 and 18.6±0.9 ka, which are identical within error ranges and younger than the quartz OSL age estimate of 23.2±1.0 ka for the underlying Gosan Formation. This study confirms that volcanism and attendant sedimentation were active in Jeju Island until very recently.     

Reliability of equivalent-dose determination and age-models in the OSL dating of historical and modern palaeoflood sediments

The challenge of accurately estimating the deposition age of incompletely-bleached samples in luminescence dating has motivated developments in the analysis of single grain dose distributions, and a number of statistical approaches have been proposed over the last few years. In this study, we compare the behaviour of the arithmetic average, so-called ‘robust statistics’, the Central Age Model (CAM), the Minimum Age Model (MAM) and the Internal–External Consistency Criterion (IEU) and lowest 5% method, when applied to single-grain dose distributions from a sequence of eight recent (40–1000 years) flash-flood deposits. These sediments are expected to be incompletely bleached, but all have age control from historical records. Modifications were made to allow the use of the standard CAM and MAM models with dose distributions containing near zero and negative dose values. An assessment of minimum over-dispersion (OD) is based on dose recovery tests based on gamma-irradiated samples. We then present a detailed analysis of the effect of an additional uncertainty added to the individual dose estimates on the burial dose estimates from the MAM and the IEU approach. The results of the various models are discussed in terms of the accuracy of the resulting age, and we conclude that, overall, the IEU approach generates the most accurate ages. We also demonstrate that accurate doses can be obtained for those older samples for which uncertainties of ∼40 years are unimportant by applying the IEU model to small aliquot (∼30 grains) dose distributions. From our study we conclude that these and similar young slack-water flood deposits can be accurately dated using quartz OSL, opening up the possibility of establishing time series of flood discharge in catchments for which no instrumental or historical record exists.     

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.     

Optical dating of liquefaction features to constrain prehistoric earthquakes in Upper Assam, NE India—some preliminary results

Optical dating of liquefied sand structures formed during major earthquakes in Upper Assam, northeast of India, has been carried out to constrain the timing of prehistoric earthquakes in this seismically active region. The bleaching of source material and of the same material during the creation of a liquefaction feature was tested using quartz extracted from 21 samples associated with two different liquefaction structures in Upper Assam. Due to the poor sensitivity of quartz from this region, a sensitisation procedure was used in our SAR protocol to reduce the scatter in optical ages. Various internal consistency tests of the measurement protocol and the excellent reproducibility of the OSL ages indicate that the dose estimates from the quartz are accurate and the optical ages reliable. The preliminary OSL ages indicate that the liquefaction features were formed between 1430 AD and 1630 AD. This study demonstrates that using OSL, ‘direct dating’ of prehistoric earthquakes may be possible, if sand blows from liquefied dykes are preserved.     

Impact of millennial mining activities on sediments and microfauna of the Tinto River estuary (SW Spain)

In this paper, we analyze two short cores collected in the Tinto estuary (SW Spain), and describe the palaeoenvironmental evolution of this area during the last two millennia, along with the influence of historical mining activities and recent industrial pollution on sediments and microfauna (foraminifera and ostracoda). Although there were no significant changes in the distribution of microorganisms, a first pollution period (0-150 AD) was recorded in high sediment pollution by Cu in the shallow palaeochannels of the middle estuary. During this period and the following 1700 years, tolerant pioneer species of both foraminifera and ostracoda were found predominantly in the inner, protected areas of the estuary, while the bottom sediments were subjected to high hydrodynamic gradients, and consequently showed lower density and diversity of organisms. In the last 150 years, acid mine drainage processes, introduction of a new mining period, and the polluted inputs derived from two industrial processes resulted in increased heavy metal contamination of the bottom sediments, and corresponding extirpation of ostracodes and restriction of foraminifers to the inner zones of the estuary.     

Towards dating Quaternary sediments using the quartz Violet Stimulated Luminescence (VSL) signal

Quartz optically stimulated luminescence (OSL) dating is widely used to determine the time of deposition and burial of Late Quaternary sediments. Application of the method is usually limited to the past 150,000 years due to early saturation of the OSL signal. Here we explore the potential to date Quaternary sediments using the violet (402 nm) stimulated luminescence (VSL) signal of quartz. We develop and test a new post-blue VSL single aliquot regenerative dose dating protocol, and demonstrate that the VSL signal originates from a deep trap at about 1.9 eV with a thermal lifetime of 10¹¹ years at 10 °C, and that this trap is bleachable by sunlight. The VSL signal grows with dose to ∼6400 Gy, a factor ∼20 higher than the conventional quartz OSL signal, and with the proposed protocol we recover a known dose of 1000 Gy in three out of four samples. The potential of the VSL protocol for dating Quaternary sediments is highlighted by its successful application to a suite of geological samples ranging in age between 13 and 330 ka. Based on our investigations, we propose that the VSL protocol has the potential to extend the quartz dating range to cover the full Quaternary.     

Thermally re-distributed IRSL (RD-IRSL): A new possibility of dating sediments near B/M boundary

This study attempted to probe a geologically more stable IR stimulated luminescence signal (IRSL) that explored so far. IRSL, probes the proximal pairs and, pIRSL measurements at elevated temperatures consume more distant pairs. We surmised that the residual IRSL after pIR-IRSL should arise from most distant pairs and hence should be more stable. A thermal stimulation after pIR-IRSL leads to redistribution of charges including distant pairs and this can be probed by further IRSL and pIRSL (post IR IRSL) measurements. This post IRSL following a thermal treatment is termed as redistributed IRSLs (RD IRSL and RD pIRSL) and contributes about 10% of total IRSL counts from a pristine sample. As expected RD, IRSLs are poor to be solar bleachable. Burial age of around 800 ka(with 30–40 %) using RD-IRSL and RD-pIRSL were comparable with the palaeomagnetic dating and were a factor of three higher than conventional pIR-IRSL, TRL, IR-RL and VSL ages.     

ESR dating of fluvial quartz: Estimate of the minimal distance transport required for getting a maximum optical bleaching

An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.

In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated.     

Potential use of Ti-center in ESR dating of fluvial sediment

The titanium centers of quartz (Ti–Li and Ti–H) were used to date fluvial sediments, together with the aluminum-center (Al). The response of these centers to the light from a solar simulator suggests that these centers are sensitive only to the UV component of the sunlight. Ti–Li and Ti–H proved to be totally bleachable by the sun and the necessary time was, respectively, 520 and 240 h. The multiple-center method was then applied on several alluvial sediments of the Creuse Valley (France). Equivalent doses and ages were calculated and Ti–Li center proved to be suitable for dating Middle Pleistocene fluvial terraces sediment. The use of both Ti–Li- and Al-centers is also recommended to determine if the sediment was well bleached at the time of deposition.     

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.