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Radiocarbon dating of primary aragonite by sequential extraction of CO₂

Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel, rbookman{at}syr.edu

B. Lazar

Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel

M. Stein

The Geological Survey of Israel, 30 Malkhei Israel Street, Jerusalem 95501, Israel

G. S. Burr

NSF-Arizona AMS Laboratory, Physics Building, 1118 East Fourth Street, PO Box 210081, University of Arizona, Tucson AZ 85721-0081, USA

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.

Key Words: Radiocarbon • dead carbon • aragonite • lacustrine carbonates • Dead Sea

The Holocene, Vol. 17, No. 1, 131-137 (2007)
DOI: 10.1177/0959683607073295


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