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Rock surface luminescence exposure dating (RSLED) is an evolving tool in dating prehistoric rock surfaces. In this study, we explore and compare current and new models and calibration methods using optically stimulated luminescence (OSL) depth profiles from quartz grains and Infrared Stimulated Luminescence (IRSL; IR 50 , pIRIR 225 , and MET 290) from feldspar grains found in granite and sandstone samples. This study shows that, although correct model assumptions improve the quality of exposure age estimates, significant discrepancies between observed and expected fitting parameter values remain, and these discrepancies leads to inaccurate age estimation. This is particularly the case when post-IR signals from feldspar are used. Here, the spectral dependency of luminescence signals is examined to better understand these problems. The demonstrated depth dependency of fitting parameters, previously assumed to be constant with depth, also gives rise to discrepancies in parameter values. The surprising observation that, in rocks, the IR 50 signal is apparently more easily bleached than the quartz fast-component OSL signal is explained in terms of the wavelength dependence of light attenuation increasing the effective path length for shorter wavelengths, and so changing the shape of the light spectrum with penetration depth. This complicates parameter estimates in exposure dating even more. Alternative approaches (rather than parameter estimation) for estimating how long a rock surface has been exposed to light are considered, based on modelling the shape and position of the measured luminescence-depth profile. It is concluded that the most accurate exposure age is derived by interpolating the depth of an unknown profile onto a curve of profile depths from known age profiles (the Exposure Response Curve, or ERC, approach). • Investigating calibration methods for rock surface luminescence exposure dating. • Rock surface luminescence exposure dating experiments on quartz and feldspar. • Correct model assumptions improve the quality of exposure age estimates. • Discrepancies in exposure age estimations exist using current calibration methods. • The most accurate exposure age is derived by interpolation of bleaching depth (ERC). [ABSTRACT FROM AUTHOR]

Located in the mountain range of the Pyrenees, ~100 km from the current coastline, the archaeological site of Gatzarria -- in and around a karstic cave -- has yielded an important Palaeolithic sequence, spanning from the Middle to the Upper Palaeolitic. The lithic industries identified correspond to several Middle Paleolithic technocomplexes, based either on the Levallois, the Discoid or the Quina technology, and a few Châtelperronian elements have also been identified. Several chronological variants of Aurignacian superpose the Middle Palaeolithic sequence, and the Gravettian completes the Upper Palaeolithic sequence [1]. Whereas both the Aquitaine Basin (SW France) and the Cantabrian region (North of Spain) are very rich in archaeological sites from these periods, the northwestern foothill of the Pyrenees, where Gatzarria is located, is less well known, despite a non-negligible number of sites. Similarities do however exist with the archaeological record of all three areas and raw material sourcing supports long distance movements, of objects and/or people, between them. Obtaining a numerical chronology at Gatzarria cave will thus enable us to describe population dynamics and interactions in a key region of SW Europe, the "Basque crossroads", during several key moments of the Upper Pleistocene. Here we present OSL ages obtained from 34 sediment samples collected for OSL dating and processed in the usual manner using sand-sized (180-250 µm) quartz and feldspar grains. Preliminary multigrain quartz measurements using the single-aliquot regenerative-dose (SAR) protocol show that quartz is fast-component dominated, has satisfactory luminescence characteristics and dose response curves have an average characteristic dose (Dc value) of ~70 Gy. Single-grain quartz measurement show that only about 2% of the grains give detectable luminescence signals and a significant fraction of these are in saturation on the laboratory dose response curve. Only very little K-rich feldspar is present in these samples, but comparison with quartz age will be made where possible. Age modelling will be undertaken using both the commonly applied frequentist approach as well as Bayesian modelling using the specifically designed software tool BayLum [2]. [ABSTRACT FROM AUTHOR]

Central Asia is a key migratory route for the peopling of Asia during the Palaeolithic. Unfortunately, chronological information is limited, leaving a geographical and temporal gap in our knowledge of human migrations. One of the aims of the transdisciplinary project THOCA ("Timing and Ecology of the Human Occupation in Central Asia") is to determine the chronology of the first settlements in Central Asia over time through the study of three major archaeological sites (Khonako, Obi Mazar and Kuldara) located in the Khovaling Loess Plateau of Tajikistan [1]. Luminescence dating is being used to date the upper part of the sections, providing a chronological framework for palaeoenvironmental, palaeoecological, and palaeoclimatic studies over the past ~250 ka. Here we present the first detailed luminescence chronology of the Khonako sites. These sections consist of an alternation of thick loess units and up to 16 well-developed pedocomplexes (PC), providing a sedimentary record presumably back to MIS 31. Lithic assemblages excavated in the upper PC 1 and PC 2 are among the best representatives of the regional Middle Palaeolithic industries. About 320 samples were taken to establish a chronological model down to at least PC 2. Because of the high dose rates (~ 3 Gy/ka), the OSL signal from quartz can only be used to date the last ~30 ka, and so only the upper part of the section (~ top of L1). Quartz OSL and feldspar pIRIR200,290 ages are compared to evaluate the completeness of bleaching of the pIRIR200,290 signal and evaluate the size of the presumed residual dose that was present at deposition. First IR stimulation temperature tests are used to confirm the suitability of our pIRIR protocol. Because of the fine-grained nature of the sediment, only very small amounts of 63-90 µm K-rich feldspar grains could be extracted. Therefore, measurements using a pIRIR200,290 protocol were also carried out on the polymineral 63-90 µm fractions (i.e. no HF treatment or heavy liquid separation). All these measurements were made using a test dose approximately equal to the measured De. Dose recovery ratios (of between 0.91 ± 0.09 and 1.07 ± 0.02) are satisfactory for 6 samples ranging from ~ 20 ka (given dose of ~ 90 Gy) to ~ 250 ka (given dose of ~ 770 Gy) after the subtraction of residual doses (from 16 Gy to 54 Gy). Our preliminary test results also show that the polymineral 63-90 µm fraction yields the same De values as purified K-rich feldspar extracts. The new chronology for the Khonako sites confirms that PC 2 and PC 1 can be associated with MIS 7 and 5, respectively. The sedimentary record appears to be almost continuous through the last 250 ka, although there may be a hiatus in sedimentation at the bottom of PC 1 (end of MIS 6/beginning MIS 5). [ABSTRACT FROM AUTHOR]

In this study we present the first luminescence ages for the upper part of the Kuldara loess-palaeosol sequence, in the Khovaling Loess Plateau in Southeast Tajikistan. This study is part of the THOCA project ("Timing and Ecology of the Human Occupation in Central Asia", www.thoca.org) in which we aim to reconstructthe timing of hominin arrival in Central Asia, and the environmental and palaeoclimatic conditions under which they lived and evolved. The Kuldara site is located ~15 km from the famous Khonako site complex (see Challier et al., these proceedings) and is close to the Obi-Mazar/Lakhuti palaeolithic site [1,2]. The upper ~20 m of the stratigraphy at Kuldara is made up of a Holocene soil (~1.4 m thick), a thick (~10 m) L1 loess and two pedocomplexes (PC1 and PC2) separated by only ~2 m of (L2?) loess; the latter suggests that part or most of the presumed MIS6 loess was eroded at this site. In general, Tajik loess sequences consist of more than 40 pedocomplexes and cover a sedimentary history of the last 2 Ma; they are presumed to be complete. Even though previous studies noted that most parts of the sequences have no distinguished hiatuses, many sections have shortened loess layers between PC1 and PC2, and in some cases these two PC's are sitting immediately on top of eachother. This phenomenon suggests a regional erosional event, which could be activated by wind/water/ slope processes or tectonic uplift. For understanding this important event we need to identify the chronological range of this regional hiatus. In order to provide an independent timescale for palaeoclimatic studies using grain size, magnetic mineral assemblages, etc., and to check the completeness of the sedimentary record, 70 luminescence samples were collected using stainless steel tubes down to below the PC2 complex. A higher spatial sampling density was used in S0 and L1 (~15 cm) compared to the lower part of the sequence where it was ~50 cm. Quartz and feldspar in the coarse-silt and/or fine sand (40-63/63-90 µm) range were extracted using conventional sample preparation techniques. Quartz was purified using HF only, no heavy liquid separation was attempted and so the feldspar fraction must have contained significant quartz. Dose rates were determined using high resolution gamma spectrometry and are typical for loess in Tajikistan (~3-3.5 Gy/ka to silt-size d quartz grains). Quartz OSL dating is used to constrain the timing of loess deposition for the upper part of the sequence (De ≤ 150 Gy) and to determine a residual dose for the pIRIR200,290 signal. We apply pIRIR200,290 dating to the bottom part of the sequence using a relatively large test dose as suggested by the results of dose recovery tests. It appears that we can obtain reliable pIRIR200,290 De estimates up to ~800 Gy allowing us to provide a detailed luminescence chronology for the Kuldara site back to ~250 ka. [ABSTRACT FROM AUTHOR]

Luminescence dating of rock surfaces is an emerging absolute chronological technique that has the potential to determine how long a rock surface has been exposed to daylight and/or how long it has been buried. By measuring the OSL signal as a function of depth into the rock surface, it is possible to determine how long the rock surface has been exposed to daylight by fitting a luminescence kinetic model to the measured luminescence-depth profile. Despite increasing use of this technique, the possible dependence of derived ages on the chosen model has not been examined. Existing studies are based on the assumption that first-order kinetics apply and a first order model (F.O.M.) has been used. In this study, we use (i) a general-order kinetics model G.O.M., (McKeever and Chen, 1997) and (ii) a localised recombination model here referred to as the fading model, F.M., (Jain et al., 2015) to develop new analytical expressions for luminescence-depth profiles in rocks. These models are tested using both simulated and experimental data based on the IR 50 signal. Based on these tests it is concluded that the derived apparent exposure ages are dependent on the chosen model. This model dependence occurs despite the fact that the speed of progression of the bleaching front into the rock surface is model independent. The reasons for this apparent discrepancy are discussed in details. Calibration with a single known-age sample (Sohbati et al., 2012b) gives inaccurate exposure ages for all investigated models unless the appropriate model is applied and/or the age of the calibration profile is of the same order of magnitude as the age of the unknown profile, but using the G.O.M. improves the accuracy of age estimates for IRSL profiles. An alternative approach to exposure dating is presented here as "Exposure Response Curve" calibration. We conclude that using inflection points, to avoid the difficulties caused by fitting parameter correlation, proves model-independent, and is a promising method for further investigation in Rock Surface Luminescence Exposure dating. • Develop new analytical expressions for luminescence-depth profiles in rocks. • Testing models using simulated and experimental data based on the IR50 signal. • Model dependence occurs despite that the speed of progression is model independent. • The general order model improves the accuracy of age estimates for IRSL profiles. • Calibrating by using Exposure Response Curve (ERC) proves model independent. [ABSTRACT FROM AUTHOR]

Luminescence dating is one of the most promising technique available for studying bioturbation on pedological timescales. In this study, we use multi-grain and single-grain quartz OSL to quantify termite bioturbation processes ( Macrotermes natalensis ) in a savannah ecosystem in Ghana. Termites transport soil from depth to the surface to construct termitaria. Over time, erosion levels these mounds and returns the sediment to the soil surface. These two processes of construction and erosion together represent an upward “conveyor belt” sediment transport process. We find that the sediment is effectively bleached during the erosion process allowing us to quantify retrospectively, for the first time, the surface deposition rate, the inverse of the upwards transport rate. At this site, this is ~0.28 mm year −1 and began about 4.000 years ago. Downward mixing through subsurface galleries may replace 10–20% of the volume ka −1 below the unit formed by reburied termite deposits. [ABSTRACT FROM AUTHOR]

Luminescence dating is used extensively to provide absolute chronologies for Late Pleistocene sediments. Nowadays, most optical dates are based on quartz optically stimulated luminescence ( OSL). However, the application of this signal is usually limited to the last ∼100 ka because of saturation of the quartz luminescence signal with dose. In contrast, the feldspar infrared stimulated luminescence ( IRSL) dose-response curve grows to much higher doses; this has the potential to extend the datable age range by a factor of 4-5 compared with quartz OSL. However, it has been known for several decades that this IRSL signal is unstable, and this instability often gives rise to significant age underestimation. Here we test against independent age control the recently developed feldspar post- IR IRSL approach to the dating of sediments, which appears to avoid signal instability. A physical model explaining our observations is discussed, and the method is shown to be accurate back to 600 ka. The post- IR IRSL signal is reduced by exposure to daylight more slowly than that from quartz and low-temperature IRSL, preventing its general application to young (e.g. Holocene) sediments. Nevertheless, this new approach is widely applicable (feldspar of appropriate luminescence behaviour is even more ubiquitous than quartz). These characteristics make this a method of great importance for the dating of Middle and Late Pleistocene deposits. [ABSTRACT FROM AUTHOR]

We report on quartz Optically Stimulated Luminescence (OSL) dating of the infill of 14 relict sand wedges and composite-wedge pseudomorphs at 5 different sites in Flanders, Belgium. A laboratory dose recovery test indicates that the single-aliquot regenerative-dose (SAR) procedure is suitable for our samples (measured to a given dose ratio 0.980 ± 0.005; n=139). Completeness of resetting of the wedge infill of two samples was confirmed by single-grain analyses. The suite of optical ages indicates that repeated thermal contraction cracking, degradation and infilling with wind-blown sediment appear to have been commonplace in Flanders during the Late Pleniglacial (Oxygen Isotope Stage 2; OIS2); more specifically, around the Last Glacial Maximum (LGM, ∼21 kyr ago) and the transition period between the LGM and the start of the Lateglacial (∼15 kyr ago). Optical dating at one site has revealed two significantly older wedge levels, the younger inset into the older; the younger wedge has an age of 36 ± 4 kyr (Middle Pleniglacial; OIS3), the older wedge 129 ± 11 kyr, which points to formation during the Late Saalian (OIS6). Our OSL ages of the wedges and host sediments bracket formation of the BGB (Beuningen Gravel Bed: a widespread deflation horizon in northwestern Europe) at between ∼15 and 18 kyr; this is in good agreement with previous OSL dating studies. We conclude that optical dating using quartz SAR OSL establishes an absolute chronology for these periglacial phenomena and allows secure palaeoenvironmental reconstructions to be made. [ABSTRACT FROM AUTHOR]

Located in southwest France, Roc de Marsal is a cave with a rich Mousterian stratigraphic sequence. The lower part of the sequence (Layers 9–5) are characterized by assemblages dominated by Levallois lithic technology associated with composite faunal spectra (including red deer, roe deer and reindeer) that shows a gradual increase in the frequency of reindeer. The top of the sequence (Layers 4–2) are characterised instead by Quina lithic technology (both in terms of technology and typology) with the faunal remains dominated by reindeer. Roc de Marsal thus provides a very interesting case study to place behavioural changes in a context of changing climates and environments in western Europe during the late Pleistocene. To link the occupations at Roc de Marsal with global and regional climatic conditions known independently, a robust chronology is needed. With this aim in mind, we applied three luminescence dating methods (TL, OSL and IRSL) on different minerals (flint, quartz and K-feldspar extracts). Here the results of two of these methods are presented in detail (TL and OSL) and compared with preliminary IRSL data. At Roc de Marsal, a comparison of methods was necessary to overcome a complex sedimentary history, with very heterogeneous dose rate distributions, both at the beta (mm) and gamma (dm) dose rate scales. The results indicate that the lower Levallois layers are dated to ∼65–70 ka, while overlying Quina layers are dated to ∼49 ka. These ages for the lower layers fit well with some models that place mixed faunal assemblages in the initial MIS 4; however, while the Quina ages overlap with several other Quina assemblages from the region, they place the reindeer dominated fauna well after the peak cold of MIS 4 and suggest a more extended and complex period of contemporaneous lithic techno-complexes than posited by some current models. [ABSTRACT FROM AUTHOR]

A new interdisciplinary project was initiated to excavate a portion of the Palaeolithic site of La Ferrassie left intact by earlier excavations. One of the aims of this project was to provide chronological information on the succession of Middle and Upper Palaeolithic layers, as well as on the skeletons unearthed by Capitan and Peyrony in the early 1900's. We report here preliminary results on the lithics, faunal remains, site formation processes, and on the stratigraphic context of the La Ferrassie 1 and 2 skeletons that were found adjacent to our excavations. Finally, results from luminescence dating of the sediments and a preliminary set of radiocarbon ages are presented. Quartz OSL, both at the multi-grain and single-grain levels of analysis, and post-IR IRSL of feldspar at various stimulation temperatures are compared. The quartz/feldspar comparison revealed a bleaching problem for the quartz OSL (and the feldspar pIRIR signals) from Layer 2; as a consequence, the age of this Layer was determined using a minimum age model. A Mousterian industry with bifaces, at the base of the sequence, has been dated between 91 ± 9 and 44 ± 3 ka. The Ferrassie Mousterian layers are attributed to MIS 3, between 54 ± 3 and 40 ± 2 ka, and thus appear very late in the final Middle Palaeolithic of the region; furthermore, these ages constrain the chronology of the La Ferrassie 1 and 2 skeletons, which have been attributed to one of these Ferrassie Mousterian layers. The Châtelperronian layer is dated to 42 ± 3 ka and the Aurignacian to 37 ± 2 ka. Implications of the ages for the La Ferrassie 1 and 2 skeletons, and for the variability of late Mousterian, are discussed. [ABSTRACT FROM AUTHOR]