Rockshelters and stone procurement in the Kimberley: evidence from the Lower Mitchell River Yinika Perston and Mark W. Moore Archaeology and Palaeoanthropology, University of New England Introduction Stone procurement was a challenge to Kimberley stoneworkers because quartzite, although abundant, mostly outcrops as bedrock unsuitable for flaking (Figure 1). The best-quality material usually occurs as a gradational seam with indistinct boundaries and is sporadically accessible at broken-down bedrock edges. Procuring quartzite entailed high venture costs (after Elston 1992) to prospect for stone, detach it from bedrock, and process the stone into usable sizes or finished tools. Bedrock flaking Percussion flakes were struck directly from acute-angled platforms on bedrock edges. Chunks were broken from bedrock by heavy percussion on attenuated edges to detach angular chunks. Substantial amounts of bedrock were processed at some sites, producing dense concentrations of stoneworking debris (Figure 2). In other areas, isolated flake scars suggest that stoneworkers were assaying the bedrock to test for flaking suitability. Relative age of bedrock flaking Walsh (1994:282) argued that bedrock flaking in the Kimberley dated prior to his ‘Aborigine Epoch’. Our 2010 fieldwork suggests that the history of bedrock flaking extended to relatively recently. Bedrock flaking and iron staining Sandstone surfaces in the Kimberley are often stained naturally with a red iron oxide wash. Flaking on these surfaces exposed fresh stone and the process of iron staining began anew. Differential degrees of oxide staining between adjacent scars indicates a hiatus between flaking events. Some scars have not yet developed an iron stain and date to the relatively recent past (Figure 3). Bedrock flaking and rock art motifs Rock art motifs and flaking can co-occur near the edges of bedrock. Flaking often removed parts of rock art panels, including Gwion Gwion (Figure 6) and Wanjina-style motifs. Wanjina-style art panels sometimes overlapped bedrock flaking scars (Figure 7) probably because these images were more likely to extend over bedrock edges. One Wanjina-style image was both painted over and partly removed by bedrock flaking (Figure 8). This demonstrates that some bedrock flaking dates to the Wanjina period. Conclusion Future work will explore the nexus between bedrock flaking as technology and ritual and the time-depth of each. This will involve diacritical analysis of the size, nature, and placing of flake scars on bedrock and the flaking represented in adjacent flaking areas and in excavated sequences. Acknowledgments The 2010 Kimberley fieldwork was supported by a collaborative project between the Australian Research Council (LP0991845, DP1096558), Kimberley Foundation Australia, Kandiwal Aboriginal Corporation, WA Department of Environment and Conservation and Slingair Heliwork WA. We wish to thank Mike Morwood, June Ross, John Goonak, Greg Goonak, Gavin Goonak, Myron Goonak, Joey Karadada, John Heywood and Kim Newman. Thanks also to Jon Harman for providing free DStretch software used to enhance the images in Figure 6 (available at www.dstretch.com) Literature Cited Elston, R.G., 1992. Modelling the economics and organization of lithic procurement. In Archaeological Investigations at Tosawihi, edited by R.G. Elston and C. Raven, pp. 31-70. Intermountain Research, Silver City, Nevada. Ross, J., 2008. Associated rock art traditions: Marking practices found at rock art complexes in the central Australia desert. Paper presented at the Australian Archaeological Association Annual Conference, Noosa, Qld. Walsh, G.L., 1994. Bradshaws: Ancient Rock Paintings of North-West Australia. The Bradshaw Foundation, Geneva, Switzerland. Bedrock flaking and oxalate crusts Oxalate crusts formed when oxalic acid produced by biological activity reacted with calcium and cations to produce a shiny, laminated surface coating. Crust formation depends on microenvironmental conditions. Oxalate crusts sometimes cover bedrock flaking scars, suggesting a relatively greater age than scars in the same area that lack a coating (Figure 4). Figure 1 Quartzite in the Kimberley region outcrops as massive bedrock exposures. Figure 2 Abundant flaking debris. Figure 4 Oxalate crusts occur over some flaking scars, suggesting a relatively great age. Figure 5 Block collapse can create new platforms for flaking. These blocks of quartzite were originally attached to the rock face and both were knapped (1 & 2) before they fell (A & B). The larger block was then knapped at least twice after it fell. The older scars have iron staining (3) while the more recent scars do not (5). The rock face was knapped after the blocks collapsed (4). An unstained biface was found nearby, made from the same quartzite. Figure 6 Flaking removed part of some Gwion Gwion figures on blocks of collapsed bedrock. Details have been digitally enhanced. Figure 8 This Wanjina-style motif overlaps some flake scars and is partly removed by others. Figure 7 The foot of this Wanjina-style motif extends over several flake scars. Figure 9 ‘Large-scar’ flakes were usually >100 mm long and well-spaced. They would have been suitable for macroblade and biface manufacture. Scale 10cm. Technology and ritual Bedrock flaking reflected two strategies. The ‘large-scar’ approach involved heavy percussion blows to detach large flakes, often >100 mm long. Stoneworkers spaced the blows to avoid striking into hollows left by prior flake removals. Large-scar knapping often occurs as a few flake scars in isolation on the edge or end of a boulder (Figure 9). The ‘small-scar’ approach involved lighter blows that detached flakes <100 mm. Blows were spaced close together, sometimes forming flaked edges spanning several linear metres (Figures 10, 11). Bedrock quarrying produced chunks or flakes for macroblade and biface manufacture. While many small-scar products were suitable for biface manufacture, most were too small for macroblade manufacture. Bedrock-struck flakes of all sizes would have been suitable for unmodified use or retouching. Physical interaction with the fabric of important spiritual sites is well-documented among Indigenous groups (Ross 2008). The long bedrock edges flaked by small-scar knapping that sometimes border rock art panels may be a local manifestation of this. Scars in these series are the ones that most frequently remove parts of motifs or are painted over. Figure 11 ‘Small-scar’ flaking sometimes extended over several linear metres. Bedrock flaking and wall collapse Sandstone shelters in the Kimberley region are in a slow but continuous process of collapse. Block collapse can create new potential platforms for further bedrock reduction, or it can obscure former platform surfaces and make them difficult or impossible to exploit further. Stratified flaking episodes were sometimes created by this process (Figure 5). Figure 10 ‘Small-scar’ flakes were usually <100 mm long and were closely spaced. They were too small for macroblade manufacture. Scale 10 cm. Sequence: 1/2 A B 3/4 5/biface biface scars with iron staining scars without staining 1 2 3 4 5 A B stencils Figure 3 The differential degrees of iron staining on scars indicates a hiatus between flaking events. Older flake scars with iron oxide staining. More recent scars lack staining.