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Radiocarbon dating of primary aragonite by sequential extraction of CO2
R. Bookman
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 lakes 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
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The Holocene, Vol. 17, No. 1,
131-137 (2007)
DOI: 10.1177/0959683607073295

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