A revised, Last Interglacial chronology for the Middle Palaeolithic sequence of Gruta da Oliveira (Almonda karst system, Torres Novas, Portugal)

Abstract

Based on previous radiocarbon and U-series (Diffusion/Adsorption) dating of bone samples, the Middle Palaeolithic has been thought to persist at Gruta da Oliveira until ∼37 thousand years (ka) ago. New U-series ages for stratigraphically constraining speleothems, coupled with new luminescence ages for sediment infill, show that the site’s ∼6 m-thick archaeological stratigraphy dates entirely within a <30 ka interval spanning substages 5a-5b of Marine Isotope Stage (MIS) 5. Significant technological change is observed across the sequence, akin to that seen in the Upper Palaeolithic over similar timescales. Flake-cleavers and bifaces, normatively definitional of the Vasconian facies, are restricted to a short interval correlated with Greenland Stadial (GS) 22, 85.1–87.6 ka ago. In cave and rock-shelter sites of southern and western Iberia, intact archaeological deposits securely dated to the ∼37–42 ka interval remain elusive. Geological dynamics (e.g., erosion, sedimentation hiatuses, palimpsest formation) and human adaptive responses to climate-driven environmental change (e.g., abandonment of now forest-covered low- and mid-altitude karst areas, concentration of settlement in alluvial plains and coastal settings) are possible explanations for this pattern.