GEOARCHAEOLOGY OF LAPA DO PICAREIRO: LINKING THE SEDIMENTOLOGICAL, PALEOENVIRONMENTAL, AND CULTURAL CHRONOLOGIES FROM A PALEOLITHIC CAVE IN PORTUGAL

Sedimentary processes in caves are driven by allogenic factors such as precipitation and vegetation, and by autogenic factors such as bedrock lithology and karst development. Climate change simultaneously initiates processes of both types, making them difficult to untangle from sedimentary evidence. Similarly, in caves occupied by prehistoric humans, an observed artifact pattern may or may not represent human responses to environmental change, and the pattern itself is often incomplete or altered by natural processes.

This poster presents geoarchaeological evidence from Lapa do Picareiro, a mountain-top limestone cave in central Portugal. Archaeological investigations at Picareiro have unearthed more than 10 m of sedimentary fill, primarily limestone eboulis derived from spalling and clayey silt derived from flow through fractures in the cave roof and walls. The sedimentary fill dates to roughly 9-70 kyr BP, with a fairly steady sedimentation rate of around 0.2 mm/yr during this period. The occupation history of the cave spans the Middle Paleolithic to the Bronze Age. Particularly abundant are lithics, bone tools, and hearth features from the Upper Paleolithic layers that represent the harsh climates of the last glacial stage.

Paleoenvironmental evidence in the cave sequence include: (i) faunal remains that reflect local ecological change (ii) clast size variations that reflect the strength of freeze-thaw cycles, (iii) trends in elemental geochemistry and magnetic susceptibility that are related to weathering intensity, (iv) stable C/N isotope trends that reflect changes in cave hydrology and biota, and (v) micromorphological evidence regarding the formation of occasional cemented layers. The sedimentary sequence is correlated with fluctuations in regional paleoclimate that are known from deep sea sediment core and Greenland ice core records. Especially evident are the impacts of cold/arid Heinrich events between roughly 14-60 kyr BP, which appear as large clast layers followed by deposition of muddy beds with elevated magnetic susceptibility.