Analysis with confidence: distinguishing pre-Bondaian and Bondaian silicified mudstone artefact assemblages from the Cumberland Plain of Western Sydney, New South Wales

Abstract

Most Aboriginal open sites on the Cumberland Plain of Western Sydney were thought to have been occupied during the Bondaian phase after ca 7,000–8,000 cal. BP, based largely on the presence of backed artefacts, predominance of silcrete in assemblages and paucity of stratified sites and late Pleistocene dates. I propose here that sites with older pre-Bondaian artefacts are more common than that indicated by previous research. In the pre-Bondaian phase, silicified mudstone was the preferred raw material type. During the Bondaian phase people sometimes used silicified mudstone in addition to silcrete, but these assemblages have numerous backed artefacts and attributes relating to the manufacture of this artefact type. This paper proposes that differences between pre-Bondaian and Bondaian silicified mudstone assemblages can be detected by calculating the proportions of cortical-plus-plain platforms, faceted platforms and perhaps elongate flakes, in addition to the proportions of backed artefacts. Confidence intervals attached to those proportions take variation in sample size and the potential for random variation into account. The results indicate that sites with pre-Bondaian artefacts are more common than previously thought. This has implications for models which propose increased occupation of the Cumberland Plain during the Bondaian phase and for geoarchaeological studies of site histories.