Usewear and phytoliths on bedrock grinding

Pacific rim archaeology, 35 75-87. Usewear and phytoliths on bedrock grinding patches, Pilbara, north-western Australia Bedrock grinding patches were recorded in the Fortescue Metals Group Ltd (FMG) Rail Corridor within the Wooodstock/Abydos Aboriginal Heritage Area 130 km south of Port Hedland, Western Australia. WA State Ministerial conditions required the salvage of representative samples, residue analysis and other detailed microscopic study to investigate the technology and function of these grinding patches. Following a pilot study and experimental work, we undertook microscopic study of 159 samples- including PVS (PolyVinyl Siloxane™) peels and water extractions- from 81 grinding patches, collected at six sites. The worn stone surfaces are microscopically similar to traces found on experimental and Aboriginal stone artefacts used for grinding seeds, although the development of wear patterns is variable. The most common residues were phytoliths, which indicate that grinding patches were utilised for grinding grasses of the Panicoid and Chloridoid sub-families, although the open nature of the sites means issues of taphonomy need to be considered. Spinifex phytoliths suggest seeds from this plant may also have been exploited. No traces of pigment or ochre were found. We suggest that the grinding patches are linked with food processing associated ceremonial gatherings and rock art