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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]

The main purpose of this study is to investigate the accuracy of single-grain quartz OSL SAR dating for samples with known absorbed natural doses in the 150-200 Gy range. There exists some evidence that at least multi-grain quartz OSL ages tend to underestimate the true burial age in this dose interval by ~10- 15% (e.g. [1,2]). It has been hypothesized that single-grain data are superior to multi-grain data, because the latter must contain signals from `aberrant' grains (e.g. grains failing SAR procedural tests and/or grains in saturation), which can be excluded in single-grain analysis. Here we test this hypothesis using five known-age Eemian (MIS 5e, ~125-130 ka) sediment samples collected in northern Russia (Sula [1]) and in Denmark (Gammelmark [2]); conventional multi-grain methods using quartz gave results consistent with expectations for both sites, although there appeared to have been a small systematic age underestimate. Preliminary single-grain measurements show that ages are in poor agreement with the age control when using the conventional frequentist approach; the expected dose is underestimated by ~50%. Applying commonly used rejection criteria (e.g. recycling, OSL IR depletion and recuperation) does not improve this significant underestimation. However, a significant fraction (~40- 50%) of the detectable grains have natural sensitivity corrected OSL signals which cannot be interpolated on to the individually constructed laboratory dose response curves to give finite dose values, i.e. the grains are said to be in saturation. Previously, it has been argued that discarding such grains has the potential to significantly bias the resulting dose distributions towards low doses. In an attempt to circumvent this bias, it has been suggested that all grains with dose response curves with low characteristic doses (Dc values) compared to the natural dose ought to be rejected. Here we test if the so-called Dc criterion suggested by [3] in combination with Bayesian modelling using the specifically designed software tool BayLum [4] can help overcome this bias. [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]