Extended-range luminescence and ESR dating of Iberian fluvial terraces (Duero and Guadiana basins) associated with the Lower Palaeolithic sites of La Maya I, II, III, Burganes and Albalá (west-central Spain)

Abstract

The major river basins of the Iberian Peninsula that drain towards the Atlantic coast contain extensive Lower Palaeolithic (Acheulean) records associated with well-preserved fluvial terrace sequences. These open-air archaeological records are often difficult to constrain chronologically due to a lack of suitable material for dating (e.g., faunal remains) or because their Middle Pleistocene antiquity precludes the use of otherwise routinely applicable geochronometric techniques such as conventional optically stimulated luminescence (OSL) dating. As a result, many important Iberian Acheulean sites lack precise and accurate chronologies, and their existing temporal frameworks are based solely on morphostratigraphic correlations with regional fluvial terrace systems. Here we present the first application of extended-range luminescence dating – namely multi-grain post-infrared infrared stimulated luminescence (pIR-IRSL) dating of K-feldspars and single-grain thermally transferred-OSL (TT-OSL) dating of quartz – to a series of terrace sequences in the Duero basin (central sector) and Guadiana basin, as well as associated Lower Palaeolithic sites of La Maya I, II and III along the Tormes River, Burganes (and related sites) along the Tera River, and Albalá along the Guadiana River. Additionally, we present results of a parallel electron spin resonance (ESR) quartz dating study of the Tormes River terrace (Duero basin), which has been undertaken independently on the same samples to enable stratigraphically paired dating comparisons. Our study indicates that sedimentary quartz from this sector of the Duero basin produces very weak TT-OSL signals, variable Al signal repeatability and below-average Ti signal fitting uncertainties, though it is still possible to determine consistent comparative ages using the measurements protocols employed here. For samples where both pIR-IRSL and TT-OSL signals were measured, the paired luminescence dating ages are in agreement at 1σ. Agreement between the quartz ESR and TT-OSL ages is also observed for one sample from the Tormes River. However, the ESR signals (both Al and Ti) of a second sample showed insufficient bleaching and age overestimation in comparison to the paired TT-OSL dataset. Comparison of our latest dating results with published chronological datasets point to some fluvial terraces of the Duero basin potentially having diachronous formation histories. Despite this, our combined chronological results show that the terrace systems are chronologically ordered and suggest that, regionally, the +8 to +34 m terraces likely post-date marine isotope stage (MIS) 10, whilst the +50 m terraces formed prior to, or during, MIS 10. The related Acheulean sites that contain lithic material in stratigraphic position are dated to MIS 9–7 (193–314 ka at 2σ age range), and temporally overlap with the early Middle Palaeolithic records in the Duero basin, also dated here to MIS 8–7 (or 159–259 ka at 2σ). Our results are consistent with previous observations regarding the chronological overlap of these two technologies in the region, and support the possibility of a non-linear pattern of replacement for the Acheulean in the Iberian Peninsula during the Lower to Middle Palaeolithic transition.