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 engraving and off-art, was dated using laser and per manganate oxidation techniques and C-14 accelerator mass spectrometry. An a ge estimate of 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 3 000 years. Therefore, for defining rock art chronologies we recommend the u se of micro-archaeological investigations combined with the dating of carbo n-bearing components in layered rock surface crusts. This study has shown t hat the encrusted surface deposits on stable rock ledges can provide inform ation about past human painting activities, weathering processes and climat ic events. Direct correlations can also be made between micro-archaeologica l data extracted from laminations in painted crust over engravings and arch aeological data extracted from laminations in painted crust over engravings and archaeological and ethnographic information.