Radiocarbon dating of primary aragonite by sequential extraction of CO ₂

This paper describes the potential of correcting the ¹⁴C 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 ¹⁴C ('dead carbon') and increasing the age of the aragonite. Sequential extraction of successive fractions of CO₂ unveiled the effect of detrital material on the ¹⁴C ages, and showed that the first CO₂ extract represents the least contaminated ¹⁴C fraction that provides the best approximation for the true ¹⁴C 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 ¹⁴C dating of Holocene age lacustrine carbonates suspected to be contaminated with extraneous carbon-bearing materials.