Aridity and Settlement in Northwest Australia
Veth, Peter, Antiquity
An element in the changing pattern of Australian archaeology has been the filling-in of great blanks on the archoeological map, once survey and excavation has begun to explore them. The dry lands of the great central and western deserts of Australia, a hard place for humans to this day, have in the lost couple of decades come to find a large place in the transitional story.
The arid northwest
This paper focusses on the northwest portion of Australia incorporating the Gascoyne, Pilbara, Western Desert and Kimberley regions (Figure 1). This huge area has changed over the last 20 years from the archaeological `blackhole' reviewed by Dortch (1977), to one providing some of the oldest occupation sequences for both the continent and its offshore islands (O'Connor in press, pers. comm.; Veth 1994). These results are not unexpected given the region's propinquity to proposed entry routes for colonizers out of island southeast Asia and into Sahul (Birdsell 1977).
This huge region has many diverse landform, vegetation and climate types (Brown 1987; Harrison 1993; O'Connor 1993; Veth 1993. The Gascoyne and Western Desert, generally semi-arid to arid, have highly weathered and often subdued landscapes, with locally prominent ranges. In the major difference between the two regions, the Gascoyne has numerous and sometimes major ephemeral water-courses that harbour important concentrations of food and water resources, while the Western Desert is characterized by uncoordinated drainage, and resource distribution is more scattered. The Pilbara region, also with an arid to semi-arid climate, contains a major upland system (e.g. the Hamersley and Chichester ranges) which gives rise to substantial drainage courses, such as the Fortescue and de Grey. These discharge over extensive coastal plains to enter the Indian Ocean along an otherwise featureless arid coastline. Vegetation of these arid areas is predominantly tree/shrub steppe and hummock grassland.
In contrast to these regions, which experience as little as 250 mm of rain per annum, the Kimberley is characterized by substantially higher rainfall (up to 1400 mm) with a markedly seasonal distribution. The lowest rainfall occurs in the southwest Kimberley, which is generally featureless and flat; it increases substantially as the numerous and sometimes massive ranges to the north and east are encountered. Drainage is well co-ordinated, and in many cases, the discharge volumes of rivers are very high (Lau et al. 1987). Vegetation is much more dense and includes extensive woodlands, major mangrove forests and even patches of rainforest.
An intriguing pattern in the prehistoric record of these varied regions is the evidence for a changing nature of occupation in stratified sites spanning the Pleistocen - Holocene transition. Varied interpretations of these changes have given rise to a number of demographic models (e.g. Hiscock 1988; Morse 1993a; O'Connor 1990; O'Connor et al. 1993; Smith 1988; Veth 1993).
Climates and environments
These varied models see major changes in climate and sea-levels associated with the Last Glacial Maximum as restructuring resources significant to human ecology. Changes in demography and settlement behaviour ensued, with implications for prehistoric exchange systems, local social organization and dietary composition. The period 15,000-7000 b.p. is the time of greatest change in certain archaeological signatures (after Gould 1980), as witnessed in marked fluctuations in regional cultural discard rates, long-distance exchange systems and inferred alterations to resource catchments.
While palaeoclimatic reconstructions for northwest Australia are sketchy, it is reasonable to propose that the arid conditions experienced today were exacerbated during the Last Glacial Maximum with climatic amelioration possibly occurring as late as the early Holocene. Areas almost certainly affected include the Gascoyne, Pilbara and Western Desert. …