Single-grain Optically Stimulated Luminescence Research Articles

Investigations on single and multi-grain optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals in quartz derived from sandstones: Insights on provenance of quartz in ancient depositional systems

Trapped charge techniques of luminescence and electron spin resonance (ESR) are classic tools for dating Quaternary deposits. Over the past decade, these techniques have been routinely applied to investigate provenance and/or the sedimentary history of quartz grains based on their different luminescence and ESR characteristics. Of these, optically stimulated luminescence (OSL) sensitivity is one of the most widely investigated parameter for luminescence-based provenance approach. A majority of studies on this parameter are based on evaluation of multi-grain quartz OSL sensitivity of the samples. This is particularly concerning because single-grain quartz luminescence studies have shown that the luminescence signal of a multi-grain aliquot is contributed by less than ∼1–10% of the total grains. Since the sole criteria for discrimination of sources based on luminescence sensitivity relies on its intensity, therefore the results based on multi-grain analysis will most likely be skewed depending on the ‘proportion’ and ‘brightness’ of a few grains. This demands a need to evaluate the potential of single-grain quartz OSL sensitivity in provenance studies. In this study, we investigate single and multi-grain quartz OSL sensitivity from compositionally different sandstones with well-characterised sources based on U–Pb zircon ages. We further complement this analysis with characterisation of ESR centres commonly used in quartz provenance, namely E′1 and [AlO4]0 centres. Our study shows that single-grain quartz OSL sensitivity can help distinguish between sediments that have a predominant input from a single source as compared to those with contribution from multiple sources, which otherwise cannot be inferred from multi-grain studies. Moreover, our results on characterisation of quartz-based ESR intensity of E′1 and saturated [AlO4]0 centres successfully differentiates between sandstones and further complements the luminescence-based characterisation.

Underestimated single-aliquot quartz OSL ages of Late-Pleistocene sediments due to the dominance of medium component

Optically stimulated luminescence (OSL) dating technique has increasingly been employed to establish chronologies for coastal deposits since the Late Pleistocene. However, the commonly used single-aliquot quartz OSL dating method may yield inaccurate ages due to factors such as partial bleaching, luminescence characteristics, and the age limit of quartz. In this study, taking the Yangtze River Delta (YRD) as an example, single-aliquot and single-grain OSL dating using varying grain-sized quartz and K-feldspar were cross-checked to establish appropriate dating method for Late-Pleistocene sediments in coastal areas. The quartz OSL signals of the upper 24 m Holocene sediments were dominated by the fast component, and the ages obtained through OSL and AMS 14C ages agree. Conversely, the lower 24–91 m section, representing the last glacial-interglacial cycle, reveals a notable underestimation of quartz OSL ages, with a maximum underestimation of 250%, attributed to the influence of signal components. For samples within the dating limit of quartz (less than 70 ka), the single-grain method effectively mitigates the issue associated with the signal component. Single-grain K-feldspar technique proves valuable for accurately determining the age of those older sediments exceeding 70 ka. Through cross-checking between different OSL dating methods, sediments initially attributed to marine isotope stage (MIS) 3 (36–60 ka) are re-identified as deposited during MIS 5 (80–130 ka). This study highlights the necessity of assessing the variability in luminescence characteristics before applying a single OSL dating protocol to all samples from different sedimentary facies within a single core.

Tending to tradition: Dating stone arrangement maintenance in northwest Australia using optical methods

Despite the ubiquity of Aboriginal stone arrangements around the Australian continent, there is very little data-driven information about the antiquity or development of these sites. The lack of chronological controls for these sites has limited our understanding of the timing, development, and functions of stone arrangement culture. Here, we present geochronological investigations of a stone arrangement complex near the Packsaddle Valley in the Pilbara region of Western Australia using optically stimulated luminescence (OSL) dating. Sedimentary OSL samples were collected from directly beneath the boulders that comprise the stone arrangements to estimate the timing of their emplacement. The process of boulder erection by Aboriginal people involved partial removal of the topsoil, which would only have provided the sediments with brief periods of sunlight exposure. Hence, the OSL signals of our samples were not expected to have been fully bleached during boulder erection. Consequently, the single-grain OSL equivalent dose (De) data were modelled using the unlogged Minimum Age Model to identify those grains that reflect boulder emplacement. The OSL characteristics (proportion of zero-dose grains, skewness of De distribution, and Central Age Model De) from the stone arrangement OSL samples were compared to those from natural soil samples taken adjacent to the boulders, and results show that the stone arrangement samples retain a record of boulder emplacement and do not simply reflect natural soil processes. Consequently, ages for all samples were calculated to generate a chronology for boulder emplacement at the site.Boulder emplacement proceeded from ∼1,410 years ago until ∼420 years ago, with data from four recumbent boulders indicating they collapsed ∼380 years ago. The data clearly clusters into three discrete, self-consistent phases of boulder emplacement occurring at 1,360 ± 90 years ago, 800 ± 30 years ago, and 480 ± 20 years ago. We conclude that (i) the stone arrangement complex was constructed at least 1,360 years ago, (ii) the boulders tend to fall down by natural processes and, thus, the site was subsequently visited and maintained at least twice (800 and 480 years ago) when the fallen boulders were re-emplaced, and (iii) this process ended ca. 380 years ago after which the site has not been maintained. The maintenance of the stone arrangement complex over at least 900 years demonstrates a strong connection between people, the landscape, and their imprint on the landscape.

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.

Spatiotemporal variations and implications of luminescence sensitivity of quartz grains on the Chinese Loess Plateau since the last interglaciation

AbstractAlthough luminescence sensitivity of quartz grains of desert sands has been used in discriminating provenance, it still remains unclear about its spatiotemporal variations and climatic implications. In this paper, the luminescence sensitivity of quartz grains from the northern margin of the Chinese Loess Plateau (CLP) was studied using single-aliquot optically stimulated luminescence (OSL) and “pseudo” single-grain OSL measurements. Our results indicate that the OSL sensitivities have lower values in sand/loess beds and higher values in paleosols. We suggest that the variations in OSL sensitivity of quartz grains with depth on the CLP are mainly influenced by the origin of the quartz grains as they are related to the loess-sized material production processes and the migration of desert regions. More quartz grains of glacial origin with lower luminescence sensitivity, together with the reduced durations of irradiation and exposure cycles induced by shorter transport distance due to desert expansion, account for the lower luminescence sensitivity of glacial periods. Moreover, both the mountain processes and the retreat–advance of deserts are ultimately related to climatic changes, therefore, the orbital scale variations of luminescence sensitivity are controlled by glacial–interglacial oscillations on the CLP.

Single-grain OSL dating of fluvial terraces in the upper Hunter catchment, southeastern Australia

Abstract Fluvial terraces in the upper Hunter catchment, southeastern Australia provide a long-term record of river activity in response to climate change in the late Quaternary. Single-grain optically stimulated luminescence (OSL) dating of quartz was applied in this study to investigate the timing of the formation of three fluvial terraces in the upper Hunter catchment. A detailed examination of luminescence properties of individual quartz grains revealed some correlation between their OSL decay rates, intrinsic brightness and dose saturation characteristics. Some quartz grains containing a higher proportion of non-fast components exhibit low brightness in OSL signals and high dose saturation levels. Some grains with slow OSL decays pass the standard rejection criteria, but are likely to yield underestimated equivalent doses (Des) because of a higher contribution of non-fast components, which are shown to have low thermal stability. Different rejection criteria, including the fast ratio, the dose saturation level and the OSL sensitivity criteria, were tested on the single-grain De results. Application of a fast ratio rejection criterion is able to successfully identify thermally unstable grains. A new rejection criterion based on dose saturation property was also applied to improve the age of one sample with a large De. Our dating results identify multiple phases of river valley aggradation in the upper Hunter catchment since late Marine Isotope Stage (MIS) 6; at ∼ 138 ka, ∼90–94 ka, ∼65 ka, ∼26 ka and ∼18 ka. The aggradational episodes of the terraces in the upper Hunter catchment are correlated with glacial or stadial periods since MIS 6. These phases of valley-floor aggradation are inferred to be a function of increased sediment supply during the cold periods resulting from strong periglacial activities in the adjacent Australian highlands.

Single-grain OSL dating of the Middle Palaeolithic site of Galería de las Estatuas, Atapuerca (Burgos, Spain)

This study presents single-grain optically stimulated luminescence (OSL) chronologies for the archaeological site of Galeria de las Estatuas – the first systematically excavated Middle Palaeolithic site within the karst system of the Sierra de Atapuerca archaeological complex, northern Spain. The single-grain OSL ages are compared with paired single-grain thermally transferred OSL (TT-OSL) dating results for a selection of samples in order to better assess quartz signal bleaching characteristics of endokarstic deposits preserved at Atapuerca. In total, seven luminescence dating samples were collected from four lithostratigraphic units exposed in two excavation pits (GE-I and GE-II). The single-grain OSL equivalent dose (De) distributions are characterised by generally low overdispersion (20–30%), suggesting appropriate bleaching at deposition. The resultant single-grain OSL ages reveal that the sediment sequence and archaeological remains excavated in pit GE-I accumulated 80–112 ka, while the upper layers of excavation area GE-II were deposited 70–79 ka. The replicate single-grain TT-OSL ages are in agreement with the OSL chronologies at 2σ for three of the four samples investigated; although in all cases the TT-OSL ages were systematically older than their single-grain counterparts. Apparent TT-OSL residual doses (i.e., TT-OSL De values in excess of their corresponding OSL De values) of 9–65 Gy were observed for all samples. These excess TT-OSL De values are generally low in comparison to the natural dose ranges of TT-OSL dating applications undertaken elsewhere in the Atapuerca karst system. The single-grain TT-OSL and OSL dating comparisons build on daylight bleaching experiments and modern analogue studies performed on other Atapuerca exogeneous infill deposits and suggest reasonable potential for TT-OSL signal resetting down to relatively low levels for at least some sediments preserved in the Atapuerca karstic cavities. The quartz single-grain OSL chronologies obtained in this study place the Middle Palaeolithic sequence of Galeria de las Estatuas within marine isotope stage (MIS) 5 and the beginning of MIS 4, and provide firm evidence for human occupation of the Sierra de Atapuerca during a previously unreported time period.

The chronology of a sediment core from incised valley of the Yangtze River delta: Comparative OSL and AMS 14C dating

Optically stimulated luminescence (OSL) dating has gained increased use in dating deltatic deposits, however, its application can be hindered by the problem of incomplete bleaching. To address this limitation, we test the single-grain OSL method for the first time in the Yangtze River delta. A total of eight OSL and 14 AMS 14C samples were obtained from a 50.8m long sediment core from the incised valley of the delta. Quartz extracted from eight OSL samples from the core was first measured with small multi-grain aliquots using medium- (45–63μm) and coarse-grained (90–125μm or 150–180μm) fractions to test the internal consistency of their respective ages. The results showed that four of five medium-grained quartz samples appeared to be well bleached. In contrast, the coarse-grained quartz samples revealed poor bleaching, except for two samples from the delta front facies. Five coarse-grained quartz OSL samples were further analyzed using a single-grain OSL technique. Only 0.5–0.7% of the grains passed the rejection criteria. Single-grain OSL dating is appropriate for age determination of coarse-grained sediments which have been affected by incomplete bleaching. However, it consumes a lot of instrument time. Central and minimum age models (CAM and MAM) were used to calculate the burial age of the samples; MAM ages fit best in the stratigraphic sequence. Small aliquots are recommended as effective in identifying incomplete bleaching for medium- or coarse-grained quartz. A comparison of AMS 14C dates and OSL ages shows that 14C values are 1–3ka older than OSL ages. According to the OSL ages, core SD experienced rapid accumulation 10–8ka and in the last 2ka. The former is linked to rapid sea-level rise in early Holocene, while the latter is primarily due to the migration of depo-center towards the core site, rather than entirely increased sediment delivery caused by human activities.

Beta dose variability and its spatial contextualisation in samples used for optical dating: An empirical approach to examining beta microdosimetry

Abstract Beta microdosimetry (BM) has long been considered a leading cause in the amount of spread that is observed within samples dated using optically stimulated luminescence (OSL). We examined two samples from the site of MacCauley's Beach, NSW, Australia that were considered to be influenced by BM but not quantifiably demonstrated. The beta dose rate (β-Dr) environment of both samples was investigated using a series of methods that employ common laboratory equipment. Beta counting and inductively coupled plasma optical emission and mass spectrometry (ICP-OES/MS) measurements of constituent components (e.g., coarse sand quartz, fine sand heavy minerals, etc.) of the bulk sediment samples was used to assess beta dose rate (β-Dr) variability within each sample. The result of this test showed significant variation in beta flux of sedimentary components, with the heavy mineral fraction of both samples having the highest β-Dr values (11.13 ± 0.40 Gy/ka, SP2; 22.03 ± 0.07 Gy/ka, SP5) of any of the measured components. Second, the spatial distribution of β-Dr was investigated using a geographic information system (GIS) analysis of sedimentary thin sections and portable x-ray fluorescence (pXRF) analysis of resin-impregnated sediments. The GIS results revealed a statistically significant non-uniform distribution of heavy mineral grains and associated hot- and coldspot regions. The pXRF results enabled the graphical display of a heterogeneous distribution of U, Th and K concentrations and also the resulting β-Dr map. However, the detection limit of the device meant that the lower β-Dr end of the distribution could not be resolved. It was concluded that BM plays a significant role in the OD of the single-grain OSL De distributions of those samples investigated, but could only be partially explained. It is recommended that characterisation of the beta dosimetric environment be carried out before assignation of BM is applied to De distributions.

SINGLE-GRAIN OPTICALLY STIMULATED LUMINESCENCE AGES OF BROWNWARE POTTERY IN THE MIDDLE ROCKY MOUNTAINS AND THE SPREAD OF NUMIC CERAMIC TECHNOLOGY

This study presents the results of a single-grain optically stimulated luminescence (SG-OSL) analysis of brownware pottery from four Late Prehistoric-period sites in the Middle Rocky Mountains, Wyoming, USA. SG-OSL of quartz ceramic temper provides improved age control for sites where radiocarbon dating has proven problematic due to old wood, recent wildfires, and calibration uncertainties. SG-OSL results are compared to fine-grain infrared stimulated luminescence (FG-IRSL) results from the same sherds and associated radiocarbon ages. We find that the single-grain technique applied to quartz sand temper provides improved accuracy and precision over both FG-IRSL and radiocarbon. We compare our results to directly dated brownwares from the southern and eastern Great Basin based largely on thermoluminescence analysis. While brownware ceramics appear earliest in the southwestern Great Basin, our data show that the technology spread quickly to the northeastern margin of the Numic homelands. We suggest that knowledge of ceramic technology in Formative (i.e., Ancestral Pueblo and Fremont) societies was important in the adoption of pottery by Numic hunter-gatherers and that, like in the southwestern Great Basin, this technological adaptation in the Middle Rocky Mountains may have occurred within a context of resource intensification during the last 800 years.

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

Abstract 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.

New ages for the Upper Palaeolithic site of Xibaimaying in the Nihewan Basin, northern China: implications for small-tool and microblade industries in north-east Asia during Marine Isotope Stages 2 and 3

It has been suggested that the ‘small-tool’ and microblade Upper Palaeolithic industries coexisted in the Nihewan Basin of northern China for about 8–14 000 years during Marine Isotope Stage (MIS) 2. This inference was based on uranium-series ages of around 15 and 18 ka for bovid teeth recovered from the ‘latest’ small-tool site of Xibaimaying – the youngest occurrence of such tools in the region – and optically stimulated luminescence (OSL) dating of the earliest typical microblade site (Youfang: ∼26–29 ka). In this study, we re-dated the Xibaimaying site using single-grain OSL methods and the resulting ages indicate that the cultural layer was deposited 46 ± 3 ka ago, during MIS 3 – more than 20 millennia earlier than previously thought and older also than the so-called earliest ‘primitive’ and typical microblade tools found at Zhiyu (∼31–39 ka cal BP) and Youfang. These new ages for human occupation of Xibaimaying remove support for the parallel development of the small-tool and microblade industries in the Nihewan Basin during the Upper Palaeolithic, but reliable age estimates from additional sites are needed to confidently infer the nature of the chronological relationship between these two Upper Palaeolithic industries and the associated toolmakers.

Single-grain OSL chronologies for the Still Bay and Howieson's Poort industries and the transition between them: Further analyses and statistical modelling

The chronology of the Still Bay (SB) and Howieson's Poort (HP) lithic industries remains an issue of keen interest because of the central role of these two phases of technological and behavioural innovation within the Middle Stone Age of southern Africa. Several dating studies have been conducted on SB and HP sites, including a pair published by the present authors and our colleagues in 2008 and 2013. These reported the results of systematically applying single-grain optically stimulated luminescence (OSL) dating procedures to 10 sites in South Africa, Lesotho and Namibia to constrain the timing of the start and end of the SB and HP and reveal the existence of a gap of several millennia between them. Alternative ages for these two industries have since been proposed by others for one of these South African sites (Diepkloof Rockshelter) and some concerns have been raised about the procedures used in our earlier studies to estimate the beta dose rates for a small number of samples. Here, we provide an update on our chronology for the SB and HP and address the issues raised about the methods that we used previously to estimate the beta dose rates and their associated uncertainties. To test the sensitivity of our new SB and HP ages to different underlying assumptions, we have run the same statistical model as that used in our 2008 and 2013 studies under three different scenarios. We show that the ages for the different samples are insensitive to how we analytically process or statistically model our data, and that our earlier conclusions about timing of the start and end of the SB and the HP and the probability of a gap between them remain true for two of the three scenarios. We conclude by bringing our study into the context of additional chronometric, stratigraphic and lithic technology studies that have been conducted in the intervening decade.

Additional evidence for early modern human morphological diversity in Southeast Asia at Tam Pa Ling, Laos

Despite its geographic primacy as the intersection of dispersal paths to Australasia, mainland Southeast Asia has played little role in scenarios of early human migrations. Tam Pa Ling (TPL), a cave site in northern Laos, is the source of early modern human fossils – a partial cranium (TPL1) and a complete mandible (TPL2) – that represent the earliest anatomically modern humans in continental Southeast Asia and introduce new migration routes into the region during Marine Isotope Stage 3. In the current analysis, a new partial mandible from the site, TPL 3, is introduced, described, and evaluated using geometric morphometrics in the context of Pleistocene archaic, early modern and Holocene humans. In addition, the sedimentary context of TPL3 is described and refined through further quartz single-grain optically stimulated luminescence (SG-OSL) measurements and additional feldspar post-infrared infra-red stimulated luminescence (pIR-IRSL) techniques.The TPL3 mandible has discrete traits similar to eastern Asian early modern humans, including a well-developed chin and a lack of lateral corporal robusticity. It does, however, retain a relatively broad anterior mandibular arch that is more commonly associated with archaic populations. In this way, it is similar to the TPL2 mandible as well as other similarly-aged fossils from the region that show a mixture of archaic and derived traits. The combined quartz SG-OSL and feldspar pIR-IRSL techniques provide an age range of 70 ± 8–48 ± 5 ka for the depositional age of the layer containing the TPL3 mandible. This upper age estimate is ∼20 ka older than the depositional ages for the TPL1 and 2 fossils, extending the upper limit for the currently excavated sedimentary and associated fossil evidence.

OSL dating of individual quartz ‘supergrains’ from the Ancient Middle Palaeolithic site of Cuesta de la Bajada, Spain

Dose saturation represents a fundamental limitation for obtaining finite optically stimulated luminescence (OSL) quartz ages over Middle Pleistocene timescales. Single-grain OSL studies typically reveal significant intra- and inter-sample variability in quartz dose saturation properties at the individual grain level. This enhanced variability may offer the potential to obtain extended-range chronologies exceeding the traditional upper age limits of multiple-grain OSL dating. However, there have been relatively few detailed assessments of single-grain OSL properties over high dose ranges. In this study we investigate extended-range single-grain OSL dating potential at Cuesta de la Bajada, one of the most important Ancient Middle Palaeolithic sites in the Iberian Peninsula. The quartz samples from this site exhibit exceptional dose saturation properties and contain significant populations of individual ‘supergrains’ with bright OSL signals, very high characteristic saturation dose (D0) limits of 200 to >600 Gy, and dose-response curves that closely conform to single saturating exponential functions. Assessments of OSL signal composition and the ability to successfully recover a known laboratory dose of 470 Gy support the potential for obtaining high equivalent dose (De) values with reasonable fitting uncertainties. A series of novel sensitivity tests are used to assess potential biases in supergrain De estimation over high dose ranges related to (i) thermally transferred signal contributions, (ii) choice of dose-response curve fitting function, and (iii) insufficient dose saturation properties of individual grains. The single-grain De values obtained using the standard quality assurance criteria and novel sensitivity tests are consistent at 2σ, and are in agreement with quartz Ti-centre ages obtained on two of three paired electron spin resonance (ESR) samples collected from Cuesta de la Bajada. These comparisons support the suitability of our single-grain OSL results and suggest there may be good potential for using quartz supergrains to establish extended-range chronologies at some Middle Pleistocene sites. Comparisons with other single-grain OSL studies across the Iberian central plains suggest that favourable dose saturation properties may be influenced by regional-scale geological controls. The importance of undertaking single-grain OSL dating at Cuesta de la Bajada is also demonstrated by the results of synthetic aliquot experiments, which reveal multiple-grain age offsets of 60–170 ka when unsuitable grain types are inadvertently included in the final age calculations. The single-grain OSL results indicate that the main archaeological horizon at Cuesta de la Bajada (unit CB3) accumulated between 264 ± 22 and 293 ± 24 ka. These ages are consistent with the chronologies of other key early Middle Palaeolithic sites in the region (Ambrona AS6 and Gran Dolina TD10) and indicate that the Ancient Middle Palaeolithic techno-complex likely spread across Iberia from at least Marine Isotope Stage 9 onwards.

The age of three Middle Palaeolithic sites: Single-grain optically stimulated luminescence chronologies for Pech de l'Azé I, II and IV in France

Optically stimulated luminescence (OSL) measurements were made on individual, sand-sized grains of quartz from Middle Palaeolithic deposits at three sites (Pech de l'Azé I, II and IV) located close to one another in the Dordogne region of southwest France. We were able to calculate OSL ages for 69 samples collected from these three sites. These ages reveal periods of occupation between about 180 and 50 thousand years ago. Our single-grain OSL chronologies largely support previous age estimates obtained by thermoluminescence dating of burnt flints at Pech IV, electron spin resonance dating of tooth enamel at Pech I, II and IV and radiocarbon dating of bone at Pech I and IV, but provide a more complete picture due to the ubiquitous presence of sand-sized quartz grains used in OSL dating. These complete chronologies for the three sites have allowed us to compare the single-grain ages for similar lithic assemblages among the three sites, to test the correlations among them previously proposed by Bordes in the 1970s, and to construct our own correlative chronological framework for the three sites. This shows that similar lithic assemblages occur at around the same time, and that where a lithic assemblage is unique to one or found at two of the Pech sites, there are no deposits of chronologically equivalent age at the other Pech site(s). We interpret this to mean that, at least for these Pech de l'Azé sites, the Mousterian variants show temporal ordering. Whether or not this conclusion applies to the wider region and beyond, the hypothesis that Mousterian industrial variation is temporally ordered cannot be refuted at this time.

Single-grain and multi-grain OSL dating of river terrace sediments in the Tabernas Basin, SE Spain

River terraces represent important records of landscape response to e.g. base-level change and tectonic movement. Both these driving forces are important in the southern Iberian Peninsula. In this study, Optically Stimulated Luminescence (OSL) dating was used to date two principal river terraces in the Tabernas Basin, SE Spain. A total of 23 samples was collected from the fluvial terraces for dating using quartz OSL. Sixteen of the samples could not be dated because of low saturation levels (e.g. typical 2xD0 < 50 Gy). The remaining seven samples (5 fossil and 2 modern analogues) were investigated using both multi-grain and single-grain analysis. Single grain results show that: (i) measurements from multi-grain aliquots overestimate ages by up to ∼ 4 ka for modern analogues and young samples (<5 ka), presumably because (ii) the presence of many saturated grains has biased the multi-grain results to older ages. Despite the unfavourable luminescence characteristics we are able to present the first numerical ages for two terrace aggradation stages in the Tabernas Basin, one at ∼16 ka and the other within the last 2 ka.

Application of single-grain OSL dating to ice-proximal deposits, glacial Lake Benson, west-central Minnesota, USA

Glacial Lake Benson formed in west-central Minnesota as the Des Moines lobe of the Laurentide ice sheet retreated north of a small moraine in the Minnesota River lowland. Although previous research has constrained the timing of glacial Lake Agassiz immediately to the north, little age control is available for the formation of glacial Lake Benson and ice-marginal positions to the south. In order to constrain the age of glacial Lake Benson and test the application of single-grain optically stimulated luminescence (OSL) dating to ice-marginal deposits, seven OSL samples were collected from a variety of depositional settings. These included deltaic deposits linked to specific lake levels, pro-glacial fluvial, ice-contact and supra-glacial deposits. Single-grain OSL results indicate evidence for incomplete resetting (partial bleaching) of the luminescence signal, as expected for glacial environments, and therefore ages were calculated using a minimum age model. OSL results constrain the timing of ice-margin retreat and lake formation to 14.4–14.8 ka. Analysis of single-grain equivalent dose distributions indicates that deposits created by glacial-dominated processes typically had higher over-dispersion (>50%) and greater positive skew (>0.9) than deposits originating from fluvial processes. These results suggest that water-lain deposits should be targeted for OSL sampling over those created by glacial processes when dating ice-proximal settings.

A luminescence imaging system for the routine measurement of single-grain OSL dose distributions

In optically stimulated luminescence (OSL) dating and other retrospective dosimetry studies there is considerable demand for the ability to measure luminescence from individual dosimeters in the size range 50–500 μm diameter, either as separate grains or as part of a matrix. This work tests the potential of an electron multiplying charge-coupled device (EMCCD), providing extremely low level light detection. We characterize the performance of the device by discussing reproducibility and evaluating uncertainties in OSL signals. Finally we derive a typical single grain natural dose distribution with associated uncertainties.

Investigation of late and post-Fremont alluvial stratigraphy of Range Creek, east-central Utah: Use of OSL when radiocarbon fails

Range Creek in east-central Utah hosts a unique abundance of Fremont-aged archaeological sites. Although good age control is available for cultural artifacts and sites, radiocarbon ages from alluvial sequences along the valley floor have generally produced age overestimates. In order to provide an alternative dating technique and test the reliability of the radiocarbon results, samples for single-grain quartz optically stimulated luminescence (OSL) dating were collected from three alluvial profiles where 18 radiocarbon samples of charcoal and aggregated pollen had been analyzed. While AMS radiocarbon age results were more precise, the single-grain OSL ages were stratigraphically consistent and suggest radiocarbon age overestimation of up to 2–6 ka, with the greatest divergence observed in the results from aggregated pollen samples. OSL results and geochemical analyses suggest that hydrocarbon contamination may have affected the accuracy of the radiocarbon results; age overestimates are likely due to contribution from oil-shale deposits within the catchment.OSL and stratigraphic results suggest fluvial deposition began prior to 0.88 ka (AD 1130) at the site. Floodplain aggradation continued by conformable deposition of tabular flood packages, commonly capped with charcoal and ash-rich sediments, until interrupted by channel (arroyo?) entrenchment prior to 0.34 ka (AD 1670). Sandy flood packages filled this channel and re-aggradation continued until historic arroyo entrenchment of Range Creek in the late AD 1800's. OSL age constraints indicate that the alluvial sediments at the study sites were deposited during and immediately following Fremont occupation of Range Creek at AD 1000–1200 and may contain valuable archives of environmental conditions leading up to and following the abandonment of Fremont peoples from the region. Moreover, OSL results point to the importance of the use of multiple chronometers to date alluvial deposits, as the radiocarbon chronology alone would suggest that the study sites contained pre-Fremont-aged deposits and may lead to the misinterpretation of associated cultural and environmental records.