Evaluating the suitability of extended-range luminescence dating techniques over early and Middle Pleistocene timescales: Published datasets and case studies from Atapuerca, Spain

The emergence of alternative luminescence dating techniques, such as thermally transferred optically stimulated luminescence (TT-OSL), post-infrared infrared stimulated luminescence (pIR-IRSL) and OSL dating of individual quartz ‘supergrains’, has opened up new possibilities for establishing numerical age control on sedimentary deposits that exceed the traditional upper age limits of quartz OSL dating. In this study, we evaluate the reliability of these ‘extended-range’ luminescence dating techniques over Middle and Early Pleistocene timescales using two approaches: (i) a broad-scale synthesis of extended-range luminescence chronologies published so far as part of known-age comparison studies; (ii) a series of new TT-OSL and pIR-IRSL case studies at the palaeoanthropological sites of Galería, Sima del Elefante and Gran Dolina (Atapuerca, Spain). The published known-age TT-OSL datasets (n = 82) and supergrain OSL datasets (n = 3) display good correspondence (i.e., suitably linear and proportion relationships) with associated age control. The known-age pIR-IRSL datasets (n = 228) display more inter-sample scatter, though there is general support for the reliability of more stringent pIR-IRSL protocols and multiple-elevated temperature pIR-IRSL approaches over Late and Middle Pleistocene timescales. While these reliability assessments are encouraging, there remains a clear need for more widespread, known-age empirical assessments of extended-range luminescence techniques beyond ∼300–400 ka. The ages obtained at Atapuerca using single-grain TT-OSL and pIR-IRSL measurement temperatures of 225 °C (pIR-IR225) are in agreement with independent age control over an age range spanning ∼240–930 ka. In contrast, the pIR-IRSL chronologies obtained using a more stringent measurement temperature of 290 °C (pIR-IR290) consistently overestimate the expected ages of the Atapuerca sequences. The single-grain TT-OSL ages obtained at Gran Dolina permit calculation of a new weighted mean age of 846 ± 57 ka for the Homo antecessor palaeoanthropological horizon (unit TD6). The known-age Atapuerca case studies highlight the feasibility, and advantages, of applying TT-OSL dating at the single-grain scale of analysis and demonstrate that the suitability of pIR-IRSL dating protocols can vary significantly at a site or regional scale. Together, our analyses show that no single extended-range luminescence dating technique is likely to be universally applicable to all samples. Collectively, however, these approaches offer good potential for obtaining reliable chronologies, and they are likely to offer the greatest benefits when applied in tandem to individual samples.