New luminescence dating results based on polymineral fine grains from the Middle and Upper Palaeolithic site of La Ferrassie (Dordogne, SW France)
In this study we compare different infrared stimulated luminescence (IRSL) signals for dating archaeological deposits. The IRSL and the more recently developed post-IR IRSL (pIR-IR) methods were investigated using polymineral fine grains extracted from the Middle and Upper Palaeolithic western excavation area in the site of La Ferrassie (Dordogne, SW France). The IRSL data measured at 50 °C (IR50) are compared to those obtained with the elevated pIR-IR signals measured for two stimulation temperatures, 225 °C (pIR-IR225) and 290 °C (pIR-IR290). The signals are documented in terms of bleaching and fading rates. In addition, comparisons of the IR50 ages corrected either with the H + L method (Huntley and Lamothe, 2001) or with the dose rate correction method (DRC, Lamothe et al., 2003) are presented. Results show that the polymineral fine grains give a reasonable estimate of the burial age of the samples. The IR50 and pIR-IR225 provide the most reliable ages when they are corrected using the DRC method (because of saturation effects). The polymineral ages are then compared with the previously obtained ages on K-feldspar coarse grains, quartz OSL (Guerin et al., 2015) and radiocarbon ages with the aim of accessing information on the depositional processes. It appears that further comparison of polymineral fine grains to coarse grains is beneficial to evaluate bleaching. Moreover, the polymineral results either confirm or refine the chronology of the La Ferrassie sequence proposed by Guérin et al. (2015), that is, the Mousterian layers range from marine isotope stage (MIS) 5 to the middle of MIS 3. In particular, i) the base of Layer 3 is pushed back to the end of MIS 4 or beginning MIS 3 and ii) the chronological attribution of Layers 4 and 5 is confirmed as MIS 3. Finally, the chronology of the Aurignacian layer (Layer 7) is strengthened by all the feldspars results.