A Geomorphic explanation for apparent late Holocene 'intensification' in western New South Wales, Australia

The archaeological record of much of Australia is dominated by deposits that date to the mid to late Holocene. There are more locations from this time span compared with any other and these locations contain larger numbers of artefacts, a greater variety of artefacts and new forms of artefacts. Such changes in stone artefact abundance and diversity together with other evidence have given rise to theories of increasing social and economic complexity amongst Australian Aboriginal populations, often linked to speculation about increased social complexity and/or population density. However, amidst these claims an alternative hypothesis - that the apparent increase in late Holocene activity reflects more of a loss of records from earlier times rather than a dramatic recent increase in human population - has occasionally been aired. In this paper we report the results from research at three locations in the semiarid region of western NSW that demonstrate conclusively that the presence of an abundant archaeological record in the late Holocene is a consequence of geomorphological events and not human behaviour. The results of a dating program comparing OSL age estimates for valley floor sediments with radiocarbon age determinations from heat-retainer hearths inset into the valley floors indicate that, in nearly every case, the hearths were constructed after erosive events that removed sediments in which older archaeological materials might have been preserved. The results also provide an explanation for why there is a relative scarcity of archaeological deposits dating to the late Pleistocene in Australia, except in a few geomorphically persistent locations, such as caves and lunettes. Our results suggest that before models of social and/or population change are developed to explain the apparent increase in the frequency of archaeological remains during the late Holocene in Australia, the impact of Late Quaternary landscape change on the preservation and visibility of the archaeological record must be discounted.