[H-TT35_1PO1] Developments and applications of AMS techniques for earth and human environmental research

[HTT35-P02] Radiocarbon dating of charcoal by the ABOX-SC method

*Shinji TOMIYAMA¹, Masayo MINAMI², Toshio NAKAMURA² (1.Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya Uni, 2.Center for Chronological Research, Nagoya University)

Keywords:Radiocarbon, Charcoal, ABOX-SC method

Charcoal is one of the most important samples for radiocarbon dating. It is necessary to remove contaminants from charcoal sample to obtain the reliable date. ABA (acid-base-acid) method is usually used for chemical pretreatment of charcoal: First, a sample is treated with HCl to remove carbonate contaminant. Next, the sample is treated with NaOH to remove organic contaminants derived from soil during burial. After then, the sample is treated with HCl again to remove absorbed atmospheric carbon dioxide during NaOH treatment. The residue is combusted with CuO at 850?C and graphitized to be 14C-dated. However, the ABA treatment often cannot completely remove contaminants from poorly-preserved and/or old charcoals (>about 30 ka). Bird et al. (1999) showed that the ABOX-SC (acid-base-oxidation stepped combustion) method removes organic contaminants more efficiently than the ABA treatment. The age of the charcoal sample treated with the ABOX-SC was reported to be older than that of the charcoal sample treated with the ABA (Brock et al., 2010).The ABOX-SC method consists of 3 step chemical pretreatments: HCl and NaOH treatments followed by K2Cr2O7-H2SO4 treatment in a sealed tube at 60?C for 20 hr (Brock et al., 2010). The mixed solution of K2Cr2O7 and H2SO4 removes organic contaminants effectively from charcoal samples, and can extract carbon fraction of oxidation resistant elemental carbon, OREC, which is resistant to oxidation and is less affected by contamination during burial (Bird et al., 1999). After the ABOX chemical treatment, the OREC is heated at 630?C with CuO for 2 hr to remove atmospheric CO2 contaminants adsorbed during sample treatment and contaminants remained after the ABOX treatment. Finally, the residue of OREC is oxidized completely into CO2 at 850?C for 1 hr, and the CO2 is graphitized to be 14C-dated.In this study, we apply the ABOX-SC method to some charcoal samples of known age to measure 14C ages. The charcoal samples, which were excavated from Tang-e Sikan cave in Arsanjan city, Iran, have been dated at about 40 ka and 26 ka by the ABA method, and are considered to be attributed to Upper Paleolithic period. In this study, we confirm the age difference of Paleolithic charcoal samples by the two pretreatment methods of ABA and ABOX-SC.