Testing the ABOx-SC method: Dating known-age charcoals associated with the Campanian Ignimbrite

Over the past decade several studies have shown the improvements to radiocarbon chronologies that arise when Acid Base Oxidation-Stepped Combustion (ABOx-SC, Bird et al., 1999) pretreatment methods are applied to the dating of charcoal thought to be >30 ka BP. However, few studies have examined whether the use of ABOx-SC produces dates that are not only older, but accurate on known-age charcoal samples that could not be decontaminated using the routine Acid Base Acid (ABA) pretreatment protocol. In this study we date 9 charcoal fragments found below the Campanian Ignimbrite (CI) tephra layer, dated by 40Ar/39Ar to 39,230 +/- 45 years (De Vivo et al., 2001; Rolandi et al., 2003), from three Palaeolithic sites. When treated with the ABOx-SC pretreatment protocol, the radiocarbon dates provide an accurate terminus post quem for the Cl. In contrast, the ABA protocol consistently underestimates the age of the tephra. These results serve as a warning against the use of consistency as an indicator for reliability, demonstrate that the routine ABA method is not sufficient to decontaminate charcoal samples from sites of Palaeolithic age, and show that ABOx-SC produces not only older, but accurate age estimates. (C) 2012 Elsevier B.V. All rights reserved.