Absence of Evidence or Evidence of Absence? Understanding the Chronology of Indigenous Occupation of Western New South Wales, Australia

Article excerpt

Abstract

Radiocarbon determinations obtained from heat retainer hearths in four sampling locations in western New South Wales, Australia are reported, with age estimates ranging from the mid Holocene until the last few centuries BP. Hearths are first considered in their geomorphic setting to determine the likely age of the surfaces into which they were dug and the reasons why they are still extant today. Second, the radiocarbon determinations are analysed not to date single events in the past, but to construct a regional chronology of Indigenous Australian occupation. In this chronology, periods when hearths were not constructed are as important as periods when radiocarbon determinations indicate sustained hearth formation. Third, comparisons are made among the four sampling locations to determine regional patterns. Results suggest both regional and local patterns of occupation and abandonment, or at least very much reduced hearth construction, over the last two millennia. The increasing frequency of radiocarbon determination results from hearths as one approaches the present is likely to be a result of the relative abundance of well preserved recent surfaces in the locations we have studied and the consequent lack of relatively ancient surfaces.

Keywords: archaeology, radiocarbon, chronology, hunter-gatherers, Australia

Introduction

Antiquarians and archaeologists have long been aware of the rich surface archaeological record that is exposed in many areas of western New South Wales (NSW), Australia (Figure 1). This record is dominated by flaked stone artefacts, but also includes ground stone (axes and grinding dishes), mounds, middens, burials, rock art sites, scarred trees, and what are commonly termed 'heat retainer hearths'. The remains of heat retainer hearths are frequently exposed at the surface by erosion and then deflated, so that the depression into which they were originally excavated erodes away, leaving behind a dome of heat fractured hearth stones (Figure 2) that in some cases protect a layer of charcoal sufficient to obtain a radiocarbon determination. Here we report the results of radiocarbon determinations on charcoal from 96 heat-retainer hearths from western NSW, and our efforts to establish a chronology of Indigenous Australian occupation based on interpretation of these determinations in the light of geomorphic landscape change.

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The research has been conducted by the Western New South Wales Archaeological Program (WNSWAP) with field sites located on the southeast margin of the Australian arid zone in far western NSW, extending from Broken Hill north to Tibooburra near the NSW/Qld border and east as far as Peery Lake near the opal mining town of White Cliffs (Figure 1). Rainfall in this region averages less than 300 mm per annum, pan evaporation exceeds 2000 mm per annum, and prolonged droughts, where annual rainfall is below the first decile of the annual average for several successive years, are the norm. At the same time, intense storm cells can result in places receiving twice their average annual rainfall in less than 24 hours. Vegetation cover is naturally sparse and patchy, resulting in a high level of surface visibility. In addition, the introduction of sheep and cattle grazing in the nineteenth century led to accelerated topsoil erosion over a large proportion of the region, aiding surface exposure of stone artefact scatters and associated heat retainer hearths (Fanning 1994, 1999, 2002). Valley floor incision associated with these changes has also exposed sedimentary sequences in the creek banks. Analysis and dating of sediments of these valley fills allows a longer-term geomorphic history of the valley floor, and how preservation of the archaeological record may have been affected by past environmental change, to be determined. Two chronological techniques have been employed concurrently, namely radiometric and AMS dating of fluvially deposited charcoal buried with the sediments, and Optically Stimulated Luminescence (OSL) dating of quartz grains, which directly dates the depositional event which is responsible for the sedimentary unit. …