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Radiocarbon dates for earth mounds on the Adelaide River, Northern Australia.

Article Excerpt
Abstract

This paper reports new dates for mid to late Holocene occupation of the lower Adelaide River in northern Australia. Earth mounds located on the margins of the floodplains provide a series of radiocarbon determinations that suggest continuous settlement from at least 4000 years BP until recently. During that time the floodplains have undergone a dramatic environmental evolution from extensive mangrove swamps in the mid Holocene, through a variable mosaic of estuarine and freshwater conditions c.3000 years ago, to the freshwater floodplains extant since 2000 BP. These results have implications for the chronology of earth mounds elsewhere in northern Australia.

Keywords: northern Australia, chronology, Holocene, floodplains, earth mounds

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The Adelaide River earth mounds are located on the western side of the lower Adelaide River, 60 km south east of Darwin in the Northern Territory (Figure 1). They lie 50 km from the sea, on the edge of a vast freshwater floodplain.

[FIGURE 1 OMITTED]

Earth mounds in northern Australia can be divided into two types based on their location and contents. The first type is 'coastal/estuarine' and is composed of earth and marine and/or estuarine shell. There is usually little stone and few organic remains, apart from shell, contained in these sites. The second 'freshwater' type is found inland, in ill-drained areas associated with freshwater swamps and the floodplains of fiver systems, and is composed mainly of earth. Any shell remains are likely to be freshwater species and there are usually more stone artefacts associated with these mounds.

Chronology

Unlike their counterparts in southern Australia, the chronology of earth mounds in northern Australia is not well established. Prior to the Adelaide River study, there were few published dates available from the Northern Territory.

The oldest coastal/estuarine type mounds recorded are on the South Alligator River in western Arnhem Land, where a sample of mangrove shell returned a date of 4600[+ or -]80 years BP (ANU-3992). Four other sites in the area were dated between 4170[+ or -]100 (ANU-3991) and 1950[+ or -]100 years BP (ANU-4047) (Woodroffe et al. 1988:97). Samples of Anadara taken from earth mounds on the Reynolds River, western Northern Territory, returned dates of 4330[+ or -]60 years BP (Wk-7432) and 3480[+ or -]50 years BP (Wk-7170) (Guse 2005:112; Guse and Majar 2000:34, 35-37). At Hope Inlet near Darwin, HI97 was dated to 1830[+ or -]100 years BP (Wk-6525) (Bourke 2000:228). On the Mary River east of Darwin, two mounds were dated to 920[+ or...

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