U–Pb dating of calcite–aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS
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Speleothems are found in association with hominin fossil-bearing cave deposits in South Africa and can be used to provide valuable chronological constraints. Such material is generally too old for U–Th dating and, although U–Pb geochronology presents a suitable alternative, bulk U concentrations are typically too low (<0.05 μg/g) to provide useful ages. For this reason, we used a simple non-invasive beta-scanner imaging screening step to identify U-rich (≥1 μg/g) domains that could be analyzed with MC-ICP-MS techniques to provide U–Pb ages. We demonstrate the technique using samples from Sterkfontein cave that exhibit infrequent <1 cm-thick layers with U concentrations ≥1 μg/g. Relict aragonite needles are found exclusively in these U-rich layers. We analyzed material from the same flowstone suite as Walker et al. (2006) and obtained a U–Pb age of ∼2.3 Ma that agrees well with their estimate of 2.24 ± 0.09 Ma. We also obtained similar U–Pb (0.164 ± 0.026 to 0.200 ± 0.052 Ma) and U–Th (0.148 ± 0.003 Ma) ages for another sample exhibiting U-rich layers. We recognize that open-system behaviour during the partial transformation of aragonite to calcite is a potential problem and argue, on the basis of geochemistry and age consistencies, that recrystallization took place rapidly after speleothem formation and did not significantly affect the U–Pb ages.
Quaternary Geochronology, Vol. 5, no. 5 (2010-10).
Uranium-Lead Dating, Speleothems, Calcite–Aragonite, Mc-Icp-Ms, Beta-Scanning Imagery, Lead Isotopes, 234U/238U Ratios
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Uranium-Lead Dating; Speleothems; Calcite–Aragonite; Mc-Icp-Ms; Beta-Scanning Imagery; Lead Isotopes; 234U/238U Ratios
Pickering, Robyn; Kramers, Jan D.; Partridge, Tim; Kodolany, Janos; and Pettke, Thomas, "U–Pb dating of calcite–aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS" (2010). KIP Articles. 5512.