The pilot application of geochemical sourcing to an inland Pilbara archaeological landscape in north-western Australia

Past human mobility, often reconstructed using stone artefact assemblages, is an important component of Australian archaeology. Tracing the transport of stone artefacts enables direct measures of the direction and distance of past Aboriginal movement across landscapes. Sourcing transported stone artefacts to their geological point of origin therefore has the potential to significantly improve our understanding of human mobility. Beyond this, the identification of artefact source locations is also critical for stone artefact analyses since raw material factors strongly condition assemblage formation. However, relatively little stone sourcing has been completed in Australia. This is particularly the case for the inland Pilbara, north-western Australia, where almost no sourcing work has been published. This paper presents the results of a limited pilot study which aimed to test the application of petrographic and in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analytical techniques to the sourcing of transported artefacts from three Pilbara quarried outcrops to two non-quarried open surface sites. The results indicate that geochemical interelement ratios (e.g., La/Nd and U/Th) can discriminate between both quarry sites and artefacts. A clear petrographic and geochemical match between a quarry and one stone artefact discarded at a non-quarried site was found, and different samples collected from the same quarry yielded overlapping geochemical signatures. This suggests that LA-ICPMS has the potential to elucidate artefact transport (as a proxy for the movement of people) between locations, effectively linking these places as part of a behavioural system. While a larger database of artefact and quarry specimens is needed to fully explore both the efficacy of the approach and the archaeological implications, this study suggests that sourcing techniques hold significant promise for reconstructing past human mobility in the Pilbara and for demonstrating landscape-scale connections between sites.