Radiocarbon dating of primary aragonite by sequential extraction of CO2

This paper describes the potential of correcting the C-14 age shift resulting from the contamination of primary aragonites by detrital carbonates using online sequential extraction of CO2. The experiments were carried out on laminated lacustrine aragonites collected from Holocene Dead Sea sediment sections. X-ray diffraction analysis revealed the presence of detrital calcite interpreted to originate from the watershed and transported to the lake with runoff. The contamination could not be separated physically from the sample, potentially contributing decayed C-14 ('dead carbon') and increasing the age of the aragonite. Sequential extraction of successive fractions of CO2 unveiled the effect of detrital material on the C-14 ages, and showed that the first CO2 extract represents the least contaminated C-14 fraction that provides the best approximation for the true C-14 age (which includes the lake's reservoir age). We calculated the age offset contributed by the contamination range encountered in this study (1-21%) to be about 900 years per 10% contamination. The sequential extraction procedure is recommended for C-14 dating of Holocene age lacustrine carbonates suspected to be contaminated with extraneous carbon-bearing materials.