Comparison of 14C and luminescence chronologies at puritjarra rock shelter, central Australia

Abstract

At Puritjarra rock shelter a long comparative sequence permits detailed comparisons of luminescence and radiocarbon chronologies over 35,000 years. Both techniques produce self-consistent chronologies for the Puritjarra deposit, but observed discrepancies between luminescence dates on unburnt sediments and 14C, assays on charcoal are greater than reported elsewhere. TL ages are generally older than 14C ages but dates converge at depths below 70 cm, dating first significant human occupation of the rock shelter ∼35,000 years ago. The discrepancies are not removed by calibrating 14C dates or adjusting TL ages for lower water content of sediments. The 14C chronology is broadly supported by sedimentary or palaeobotanical evidence, stone artefact typology and other archaeological data. Radiocarbon dates on intact hearths agree with those on detrital charcoal. TL ages were arrived at using both ‘total bleach’ and ‘selective bleach’ methods and the latter agree with optical ages for the same samples. Incomplete bleaching of sediments during deposition can be ruled out. Incorporation of old material into the luminescence samples via in-situ disintegration of local sandstone remains a possibility and will be an important issue to resolve as luminescence techniques are increasingly deployed to date archaeological deposits in rock shelters.