High-precision Dating of Abrigo de La Boja (Murcia, Spain): Implications for the Middle-to-Upper Palaeolithic Transition and the Culture-stratigraphy of Upper Pleistocene Iberia

La Boja is a rock-shelter located in Murcia (Spain) whose c.7 m infilling spans the last 50,000 years of the Pleistocene. Though punctuated by a few episodes of stasis or erosion, sediment accumulation proceeded at a regular rate, while human occupation was intermittent and light. This pattern allowed for the preservation of 31 well-separated Occupation Horizons whose stratigraphic integrity is demonstrated by stone tool refitting, the pristine preservation of hearths and earth ovens, and the age-depth consistency of dating results. Verification of these criteria warranted Bayesian modelling of the sequence, which was carried out under OxCal and delivered a high-resolution chronostratigraphy based on 56 age measurements obtained by OSL and radiocarbon. Our main conclusions are as follows: substantial human use of south-east Spain’s arid interior during MIS 2 and MIS 3 was restricted to interstadials; during stadials, visits were fleeting and left behind an exceedingly scant record (except perhaps in the Solutrean, when harsh conditions prevailed globally but short-lived pulses of increased humidity occurred locally); the Mousterian’s basal metre, featuring Levallois reduction and Soyons points, formed through the 50-55 ka (thousands of years ago) interval; the region’s earliest Upper Palaeolithic is the Evolved Aurignacian, which replaced the Middle Palaeolithic during the 37.1-37.4 ka interval (thereby supporting that, in southern and western Iberia, Neandertals persisted for longer than elsewhere in Eurasia); the transition to the Gravettian occurred within the 34-35 ka interval and there is no evidence that it was demic rather than simply technological; the existence of a distinct Lower Solutrean phase spanning the 25.0-25.5 ka interval is confirmed; in the region, the 20-22 ka slot is occupied by the Solutreo-gravettian, which implies that claims for the French Badegoulian to have extended as far south as the Spanish Levant cannot be supported.