Single-grain OSL dating at La Grotte des Contrebandiers (‘Smugglers’ Cave’), Morocco: improved age constraints for the Middle Paleolithic levels

Optically stimulated luminescence (OSL) measurements of individual quartz grains are reported for Middle Paleolithic (MP) or Middle Stone Age (MSA) deposits in La Grotte des Contrebandiers, Morocco. Single-grain measurements enable rejection of grains that may lead to under- or over-estimation of age due to malign luminescence properties or remobilisation of grains after burial. We identified the former using a range of experimental procedures and objective rejection criteria. Three post-depositional factors influenced the distribution pattern of equivalent dose (D_e) values for the remaining single grains: the disintegration of roof spall liberating unbleached, older grains into otherwise well-bleached sediments; the intrusion of a small number of younger grains from the overlying Upper Paleolithic deposits; and small-scale differences in the beta dose received by individual grains. Roof spall contamination was a significant problem, so we characterised the OSL signals and obtained D_e values for the calcareous sandstone in which the cave is formed, which allowed bedrock-derived grains in the MP/MSA deposits to be identified and rejected prior to age determination. We collected 31 samples from the MP/MSA deposits, and were able to calculate ages for 30 of them. These ages suggest that MP/MSA occupation of Contrebandiers was restricted to the interval between about 120 and 90 ka ago (Marine Isotope Stages 5d to 5b). Weighted mean OSL ages were obtained for samples associated with archaeologically sterile deposits at the base of the excavations (126 ± 9 ka), followed by two phases of the Moroccan Mousterian (122 ± 5 and 115 ± 3 ka), interspersed with archaeologically sterile deposits (112 ± 4 ka). The base and top of the Aterian were dated to 107 ± 4 and 96 ± 4 ka, respectively. Based on the grand weighted mean ages of 116 ± 3 and 103 ± 3 ka for the Moroccan Mousterian and Aterian at Contrebandiers, we suggest that these two industries may be separated by an occupation hiatus of up to 13 ± 3 ka at this site. Our single-grain OSL chronology confirms previous age estimates obtained for Contrebandiers and other sites in the vicinity, but are generally more precise and stratigraphically more coherent, due to the inherent advantages of measuring individual quartz grains and rejecting contaminant and other unsuitable grains before age determination.     

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza,Argentina)

Well constrained numerical ages of alluvial fan sediments are key to understanding the chronology of alluvial episodes and tectonic activity at the front of the Andean Precordillera. We tested the application of radiocarbon and optically stimulated luminescence (OSL) dating in the distal part of an alluvial fan five kilometers north of Mendoza. For OSL dating a large number of aliquots (n > 70) — each composed of ∼50 quartz grains — were measured in order to obtain reliable burial ages despite scattered dose distributions. Owing to a feldspar contamination in all samples, an infrared stimulation was inserted before each OSL measurement, which reduced the feldspar OSL signal successfully. By using the minimum age model we obtained stratigraphically consistent burial ages of alluvial deposits in a depth profile. The uppermost ∼1 m of sediment is composed of debris flow deposits buried 770±76 years ago. Three plant remnants used for radiocarbon dating from the same layer, however, yielded ages younger than 350 years, which are interpreted to underestimate the depositional age. Underneath the debris flow, a major unconformity cuts a series of distal alluvial fan sediments with interstratified floodplain deposits, which are composed of sandy and calciterich silt layers, respectively. Three samples from this unit which were distributed over one meter of sediment thickness yielded statistically concordant OSL ages of 12.3±1.2 ka, 12.3±1.2 ka, and 11.7±1.1 ka. The deposition of these sediments during the latest Pleistocene coincides with a phase of cool and humid climate, which occurred before the alluvial fan propagated farther into the foreland. The overlying debris flow sediments are associated with alluvial fan incision during the arid Late Holocene.     

Performance of different luminescence approaches for the dating of known-age glaciofluvial deposits from northern Switzerland

Luminescence properties of two samples taken from sand lenses in proglacial outwash de-posits of a piedmont glacier that reached the Swiss midlands during the Last Glacial Maximum are investigated in detail. Deconvolution of CW-OSL decay curves shows that the fast component dominates the OSL signal of quartz. The chemistry of single feldspar grains, in particular the K content in different grains, is determined using wavelength dispersive spectrometry (electron microprobe), revealing an average 12.9 wt.% K of the grains contributing to the IRSL signal. D _e distributions are investigated in order to gain insights into partial bleaching, and agreement is found for quartz OSL and feldspar IR₅₀ and pIRIR₂₂₅ ages for small aliquots and single grains when applying the Minimum Age Model. These ages are also consistent with independent age control. For one sample, ages determined using the Central Age Model result in highly overestimated ages for both feldspar and quartz.     

An improved OSL chronology for the Still Bay layers at Blombos Cave,South Africa: further tests of single-grain dating procedures and a re-evaluation of the timing of the Still Bay industry across southern Africa

This paper presents a series of new single-grain optically stimulated luminescence (OSL) ages for the Still Bay at Blombos Cave, South Africa, and compares them to previously published OSL, thermoluminescence (TL) and electron-spin resonance (ESR) ages for this site. Details are provided about the measurement and analytical procedures, including a discussion of the characteristics of the OSL signals of individual quartz grains. This forms the basis for further investigations into the sensitivity of the equivalent dose (D_e) estimates to a range of different analytical approaches, including changes in the size of the test dose, the choice of signal integration interval, the subtraction of an appropriate background, and isolation of the most light-sensitive (‘fast’) component of quartz OSL. We also report the results of an inter-operator test of D_e determination using seven new samples from Blombos Cave, and demonstrate the reproducibility of results obtained for two samples that had been dated previously at another laboratory and were measured and analysed again in this study. Together, these tests validate the robustness of the Blombos Cave single-grain OSL age estimates to a variety of alternative OSL dating procedures. We have incorporated, for the first time, these ages for Blombos Cave into a data set of all single-grain OSL ages for Still Bay and Howieson's Poort sites across southern Africa, and have used a statistical model to re-evaluate the timing and duration of the Still Bay industry. We calculate the most plausible start and end dates of the Still Bay as 72.2 ka and 71.3 ka, respectively – amounting to a duration of 0.9 ka – and estimate (with conventional 95% confidence) that this industry began no earlier than 75.5 ka, ended no later than 67.8 ka and lasted no longer than 6.6 ka.     

Multi-method (TL and OSL), multi-material (quartz and flint) dating of the Mousterian site of Roc de Marsal (Dordogne,France): correlating Neanderthal occupations with the climatic variability of MIS 5–3

Roc de Marsal has yielded numerous remains of Mousterian occupations, including lithics, fauna and combustion features. It was made famous by the discovery of the skeleton of a Neanderthal child. Given the need to date the sequence, TL and OSL were applied on heated flints and quartz, and OSL on unheated quartz. Chronological results combined with palaeoenvironmental data – faunal remains and micromorphological features in the sediments from the cave, pollen proxies and faunal remains from the region – allowed us to place climate variations in southwest France on a numerical time scale. Denticulate Mousterian occupations were dated to the middle of MIS 4 (65–70 ka) and Quina layers either to the very end of MIS 4 or to MIS 3. Interestingly, a faunal pattern showing a mix of red deer, roe deer and reindeer was found to have occurred during MIS 4, which was shown to be consistent with data from other similar sites in southwest France.     

Bioturbation and the upward movement of sediment particles and archaeological materials: comments on Bueno et al.

The literature on bioturbation, both from the biological and archaeological points of view, is growing steadily. Available data suggests that ants and termites are responsible for the upward movement of soil/sediment particles and archaeological materials. It is argued that this could be the most parsimonious explanation for the stratigraphic data presented by Bueno et al. (2013), given the size range of displaced materials and the environmental setting, composed of a sandy soil in a savannah region.     

Luminescence characteristics and dose distributions for quartz and feldspar grains from Mumba rockshelter,Tanzania

Mumba rockshelter is a key archaeological site for the Middle and Later Stone Age occupation of East Africa, but its chronology has remained unresolved. We report the results of a dating study, focussing on the characterisation of the optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) properties of quartz- and potassium-rich feldspar grains. Quartz has previously proven troublesome for dating in East Africa. We identified five general types of quartz grain behaviour, based on the shapes of their OSL decay and dose–response curves. Dose recovery experiments and measurement of the natural samples revealed particular problems with quartz grains that had hyperbolic dose–response curves, low characteristic saturation doses and anomalously large changes in sensitivity between regenerative-dose cycles. The use of pulsed irradiation during measurement and standard and additional quality-assurance criteria during data analysis reduced the number of grains that suffered from these problems. We applied these procedures to individual grains of quartz from eight samples and, using appropriate statistical models, identified post-depositional mixing in three samples. The remaining samples had scattered equivalent-dose distributions typical of quartz grains that had received variable beta dose rates during burial. Stratigraphically consistent OSL ages were obtained for all but the deepest sample. Feldspar ages were estimated for the latter sample and three other samples, using the elevated temperature IRSL signal that exhibited low rates of anomalous fading. Fading-corrected feldspar ages for the latter three samples are consistent with their single-grain quartz ages, but single-grain dating is needed to address problems of post-depositional mixing.     

The formation process of a paleoindian open-air site in Central Brazil: integrating lithic analysis,radiocarbon and luminescence dating

Lithic analysis, radiocarbon dating and luminescence dating are applied to a stratified open-air Paleoindian site in Central Brazil, lending some balance to a published record dominated by rock shelter sites. Most lithics are found in two discrete occupation layers. Lithics found outside these layers are attributed to post-depositional movement of small flakes mainly upwards. Single-grain luminescence dating on quartz grains also suggest post-depositional movement. Both wind and bioturbation are suspected mechanisms. The luminescence analysis does not provide precise depositional dates in this situation but does support such dates suggested by radiocarbon.     

Dating the Ramat Saharonim Late Neolithic desert cult site

The Ramat Saharonim site, located in the central Negev desert, Israel, consists of four shrines in a shallow valley and 30 tumuli, aligned on two cuesta cliffs on the valley's sides. Previous assessments based on site surveys suggested a general chronological span from Late Neolithic period (ca. 5000–5500 BC) through the Early Bronze Age (third millennium BC). Excavations in one shrine and three tumuli revealed a well-constructed double wall at the shrine and seven primary adult burials in the three tumuli. Quartz from sediment samples post-dating the construction of the burials and shrine was dated by optically stimulated luminescence (OSL) using the single aliquot regenerative dose (SAR) protocol, and charcoal and leather samples were dated by ¹⁴C. The OSL results for a burial in one tumulus are 7500 ± 700 to 6000 ± 600 years. In a second tumulus, OSL ages of 2000 ± 200–1800 ± 170 years and a ¹⁴C age on leather of 390–200 BC (2340–2150 cal BP) imply that this burial is Nabatean and that the site was used also in the Hellenistic period. Two ¹⁴C ages on charcoal from the shrine give an age between 5280 and 4710 BC (7230–6660 cal BP). OSL single aliquot ages for sediment from the shrine are highly scattered and far too old (60,000 to 12,000 years). The unlikely old ages are due to insufficient resetting of the OSL signal of some of the quartz grains when sand was blown onto the site. Indeed, single grain measurements for six samples of sediment postdating the shrine show a very large range of grain ages, but with a distinct young population in all samples. Ages calculated from these young populations average 5400 ± 800, in better consistence with the ¹⁴C dates and confirming our supposition that only some of the transported grains were reset at the time of deposition. The combined OSL and ¹⁴C dating shows that the shrines and tumuli are contemporaneous and attributes the complex to the Late Neolithic. This has clear ramifications for our understanding of the period and the rise of desert pastoral societies.     

Quartz-tipped arrows older than 60 ka: further use-trace evidence from Sibudu,KwaZulu-Natal,South Africa

This paper discusses the results of a detailed functional study of 16 microlithic backed tools made on quartz, and newly excavated at Sibudu Cave, KwaZulu-Natal, South Africa. The layers associated with the artefacts have OSL ages of 61.7 ± 1.5 ka, 63.8 ± 2.5 ka and 64.7 ± 1.9 ka and represent the Howiesons Poort Industry at the site. I show that more than 50% of the pieces could hardly have been used in any way other than to tip arrows in a transverse position. This outcome supports previous inferences that some of these small stone tools, and perhaps a bone point from the same context, signify the use of bow and arrow technology during the Middle Stone Age. In addition to transversely hafted arrow tips, there is also evidence that some of the tools could have been hafted diagonally. Such tools could have been used equally successfully as arrow tips or barbs, or as barbs for hand-delivered spears. The variation in hafting configuration for these geometric shapes signifies hunting technologies that were flexible and most likely adapted according to need, preference, season and/or prey type.     

OSL dating as an alternative tool for age determination of relic charcoal kilns

Chronometric studies of charcoal production remains are largely based on ¹⁴C-dating of associated charcoal. Owing to intrinsic limitations, however, this method provides no meaningful time resolution for post-1650 CE features. We investigate the potential of optically stimulated luminescence (OSL) dating of heated sandy sediments as an alternative and complementary tool for dating charcoal kiln remains. Seven samples from five relic charcoal kilns and 11 complementary samples from the underlying sandy substrate are used. Through a range of procedural tests, we demonstrate that the single-aliquot, regenerative-dose procedure in combination with OSL signals from quartz allows determining equivalent doses both accurately and precisely. For four of the five investigated kilns, OSL ages are consistent with independent age information from ¹⁴C-dating and written sources. Especially for post-1650 CE features, the precision can be significantly better than that of ¹⁴C-dating, and we highlight the potential of OSL dating for distinguishing, relatively, between charcoal production phases with an unprecedented time resolution. We conclude that the approach is a promising alternative to ¹⁴C.     

Optically stimulated luminescence dating of young fluvial deposits of the Middle Elbe River Flood Plains using different age models

In the last few decades optically stimulated luminescence (OSL) dating has become an important tool in geochronological studies. The great advantage of the method, i.e. dating the depositional age of sediments directly, can be impaired by incomplete bleaching of grains. This can result in a scattered distribution of equivalent doses (D_E), leading to incorrect estimation of the depositional age. Thoroughly tested protocols as well as good data analysis with adequate statistical methods are important to overcome this problem. In this study, samples from young fluvial sand and flood plain deposits from the Elbe River in northern Germany were investigated to compare its depositional ages from different age models with well-known historical dates. Coarse grain quartz (100–200 μm and 150–250 μm) and polymineral fine grains (4–11 μm) were dated using the single aliquot regenerative (SAR) dose protocol. The paleodose (D_P) was calculated from the DE data set using different approaches. Results were compared with the development of the Elbe River, which is well-documented by historical records and maps covering the last 1,000 years. Depending on the statistical approach it can be demonstrated that depositional ages significantly differ from the most likely depositional age. For the investigated coarse grain quartz samples all ages calculated from the MAM-3_UL, including their uncertainties, are within the historical documented age. Results of the polymineral fine grain samples are overestimating the historically documented depositional age, indicating undetectable incomplete bleaching. This study shows the importance of using an adequate statistical approach to calculate reliable OSL ages from fluvial sediments.     

FIFTY YEARS OF LUMINESCENCE DATING*

Luminescence techniques for dating both heated materials (e.g., pottery and burnt stone) and sediments have gone through three phases in the past 50 years. The first 22 years, from 1957 to 1979, were devoted to thermoluminescence (TL) techniques applied to heated material. In the next six years, from 1979 to 1985, it was found that TL dating could be applied to sediments. However, the TL signals of both quartz and feldspar grains observed for modern sediments were small, but were not zero, thus making them useful only for older sediments. A new luminescence signal that was totally zeroed by exposure to sunlight for a relatively short period of time, a few hours or less, was found; this led to the development of optically stimulated luminescence (OSL) dating techniques in 1985. Further developments have continued to the present day. Within the past 22 years, 1999 was also a year with major developments. A reliable procedure for single aliquots of quartz that have a rapidly bleached (‘fast’) OSL component was formalized and an instrument that allowed rapid measurement of equivalent doses for single grains was constructed. These developments have led to OSL becoming a major dating tool in Quaternary geology, at least for the past 100 000 years, and in archaeology, particularly as related to the dispersal of modern humans.     

Optically stimulated luminescence dating of heated materials using single-aliquot regenerative-dose procedure: a feasibility study using archaeological artefacts from India

Optically stimulated luminescence (OSL) dating of heated/fired materials of archaeological importance from various parts of India was attempted. A single-aliquot regenerative-dose (SAR) procedure was used for palaeodose determination in the quartz grains extracted from the heated materials using the luminescence produced by blue light stimulation. In most pottery samples, the palaeodose obtained using SAR-OSL is ∼6% lower than the palaeodose measured using thermoluminescence (TL) method. Broadly, there is good agreement between the SAR-OSL and TL ages of the artefacts and their archaeologically expected ages. The results suggest that routine dating of heated/fired materials using the SAR-OSL procedure is more practicable, especially when the TL sensitivity of the quartz grains is poor and availability of datable material is limited.     

The effect of fluvial environments on sediment bleaching and Holocene luminescence ages — A case study from the German Alpine Foreland

This study investigates the potential of luminescence to date deposits from different fluvial sedimentary environments; namely point bar deposits, sandy and silty channel fills and floodplain sediments. Samples were taken from Holocene (<5 ka) terraces of the Lech and Danube rivers, for which independent age constraint is available through ¹⁴C ages, archaeological data and historical maps. OSL-ages were obtained using small aliquots of coarse grain quartz for the majority of samples. Two further samples were dated by the IRSL-signals of polymineral fine grain extracts, as no sufficient number of coarse grains could be extracted from these sediments. In order to detect and ac-count for incomplete bleaching, we used the decision process suggested by Bailey and Arnold [Statistical modelling of single grain quartz De distributions and an assessment of procedures for estimating burial dose. Quaternary Science Reviews 25, 2475–2502, 2006]. Although their model was designed for single grains of quartz, our study shows that it is also applicable to multiple grains of quartz, pro-vided that a low number of luminescent grains is present on one aliquot. Luminescence ages of point bar deposits and a sandy channel fill correspond most closely to the independent age control. In the floodplain, sand-striped floodplain channel deposits were incompletely bleached to a moderate degree, yielding ages with acceptable overestimations, while fine-grained floodplain deposits were worst bleached. One crevasse splay deposit was so severely incompletely bleached that none of the age models was able to yield accurate ages.     

An assessment of the luminescence sensitivity of Australian quartz with respect to sediment history

This study provides a preliminary systematic characterisation of OSL sensitivity, with respect to sediment history, of single grains of Australian quartz from a variety of source rocks and depositional contexts. Samples from two distinct lithologies and with relatively short modern sedimentary histories were compared in an examination of the influence of rock type on OSL sensitivity. Sediments derived from weathered sandstone were found to be brighter than those from metamorphosed schists, suggesting that sensitivity may be inherited from the source rock and its earlier sedimentary history. Secondly, quartz from the same source, but different modes of deposition, was compared to assess the effect on sensitivity of nature of exposure to light during the most recent bleaching event. Quartz grain sensitivity appears not to vary depending on the mode of sediment deposition, suggesting that the nature of exposure to light during deposition is less important in the sensitisation process. This study highlights the complexity and variety of natural sedimentary quartz, demonstrating the limitations of an investigation based solely on OSL sensitivity. Further systematic investigation into the physical, geological and geomorphological characteristics of sediments is proposed to better understand the mechanisms of luminescence sensitisation in quartz.     

Luminescence Dating of Monumental Stone Architecture at Chavín De Huántar,Perú

Optically stimulated luminescence (OSL) is applied to quartz extracted from mud mortar collected from Chavín de Huántar, an early Andean monumental center. The samples appear to have been only partially exposed to sunlight during construction, so a minimum age model is applied to equivalent dose distributions. Complications, including complex radioactivity, low sensitivity of the quartz, and limited sample, prevent high precision, but the 14 dates obtained cluster around 1000 BC largely in agreement with radiocarbon assays on charcoal also collected from the mortar. Results suggest a relatively rapid construction for the monument. This work develops OSL as a method for directly dating architectural mortar.     

Roman mining on Exmoor: a geomorphological approach at Anstey's Combe,Dulverton

Abstract

A survey of valley fills in south-facing combes (headwater valleys) along the south side of the Exmoor massif revealed an anomalously deep infill in one valley. This infill of up to 5 m depth had been gullied revealing a complex stratigraphy. Studies of the stratigraphy, clast orientation and shape suggested several accumulation episodes under different environmental conditions commencing in a periglacial climatic regime. Later units included sandy silts which can be dated using optically stimulated luminescence (OSL) of quartz grains. The OSL dates, indicate that the inter-gravel silts accumulated in two periods, the Romano-British period and the 16th–17th centuries AD. A survey of the very small valley catchment revealed a linear trench of a type associated with early iron mining. Given the anomalously high volume of accumulated sediment from such a small catchment and evidence of mining on the slope above the site, the geomorphic mechanism is almost certainly the downslope transport of mining debris from the slope to the valley floor. This study suggests that the systematic survey of headwater valleys in metalliferous uplands may be one way of locating areas of early mining activity and that such deposits could provide a chronology of working and abandonment.     

Recent Excavation and Recording at the New Neolithic Rock Art Site of Vallée Aux Noirs,Buthiers (Seine‐et‐Marne,France)

Following the exceptional discovery of Neolithic engravings on a boulder at Vallée aux Noirs in the Fontainebleau forest, south of Paris, an excavation trench was opened in order to access the buried part of the decorated rock panel and explore the stratigraphic context of the artwork. A palaeosol was found two metres below the modern ground level, underneath multiple layers of sterile sandy soil forming a very compact sequence from which only one archaeological artefact was recovered – an Iron Age fibula (c.200–300 BC). Dating of the palaeosol was attempted through two different methods: AMS dates from charcoal suggest a significant span from the Early Bronze Age to the Iron Age, while two more consistent OSL dates point to formation of the palaeosol during the Late Neolithic (3500–3000 cal BC). The entire engraved rock surface (16 m²), including its buried part, was fully recorded. Four main semiotic groups were identified: a typical fifth‐millennium crook‐hafted axe with a ring, two boats with steering oars, and a central, very tall human figure dominating the composition from its 3.5‐metre height.     

An Early Islamic Inter-Settlement Agroecosystem in the Coastal Sand of the Yavneh Dunefield,Israel

This study examines the remains of an agricultural complex found in the Yavneh coastal dunefield, central Israel. Known as a plot-and-berm agroecosystem, the complex consisted of earthworks in a crisscross pattern of sand berms and sunken agricultural plots that were used for groundwater harvesting. The plots, which provided easy access to the high groundwater table and the berms around them, are overlaid by a gray sand unit covered by pottery sherds and artifacts. This gray sand is more fertile than the underlying sand, suggesting refuse enrichment. Artifactual similarity of the finds to those of inland (Tel) Yavneh suggests that Yavneh was the main source for the refuse additive. Based on artifacts and OSL ages it seems that this agroecosystem was active during the 10th to early 12th centuries a.d. The agroecosystem demonstrates an early example of an Early Islamic agrotechnological attempt in marginal and sandy regions of the Mediterranean basin.