OSL dating of the Middle Palaeolithic Hotel California site, Sierra de Atapuerca, north-central Spain.

In this study we present optically stimulated luminescence ( OSL) dating results obtained at one of the most important open-air Middle Palaeolithic sites in the Sierra de Atapuerca foothills - Hotel California. We also assess the possibility of obtaining extended-range OSL chronologies for a nearby Middle Pleistocene fluvial deposit using several novel methods, namely OSL dating of individual quartz 'supergrains', multi-grain aliquot thermally transferred OSL ( TT-OSL) dating and the first application of a single-grain TT-OSL dating procedure. Four single-grain OSL ages constrain the Middle Palaeolithic occupation of Hotel California to between 71±6 and 48±3 ka. The Hotel California single-grain equivalent dose ( D_e) distributions are highly overdispersed and contain several dose populations, which are probably attributable to post-depositional sediment mixing, partial bleaching and intrinsic scatter. The reliability of multi-grain aliquot OSL dating is compromised by the complex underlying D_e dispersion affecting these samples, as well as by biasing multi-grain averaging effects. Extended-range OSL and TT-OSL chronologies for the nearby Pico River terrace are consistent with each other and with broad independent age control. These experimental approaches yield a weighted average age of 348±16 ka for terrace T_A9 of the Arlanzón River sequence. Our results highlight the benefits of comparing ages obtained using several OSL methodologies to improve the robustness of luminescence chronologies. They also demonstrate the potential that single-grain OSL techniques offer for establishing improved age constraints on the many other Middle Palaeolithic sites found at Atapuerca and elsewhere across north-central Spain. [ABSTRACT FROM AUTHOR]