Micro-archaeology of engraved and painted rock surface crusts at Yiwarlarlay (the Lightning Brothers site), Northern Territory, Australia

The formation of calcium oxalate (whewellite) on the encrusted surfaces at Yiwarlarlay, both over engravings and off-art, was dated using laser and permanganate oxidation techniques and ¹⁴C accelerator mass spectrometry. An age estimate of about 3160 BP was obtained for the start of crust formation over a painted engraving. Microscopic evidence of previous episodes of painting, in the form of bright red and yellow iron-oxide layers, is also observed in the crusts suggesting that rock painting traditions extend back at least 3000 years. Therefore, for defining rock art chronologies we recommend the use of micro-archaeological investigations combined with the dating of carbon-bearing components in layered rock surface crusts. This study has shown that the encrusted surface deposits on stable rock ledges can provide information about past human painting activities, weathering processes and climatic events. Direct correlations can also be made between micro-archaeological data extracted from laminations in painted crust over engravings and archaeological and ethnographic information. (C) 2000 Academic Press.