Uâ€“Pb dating of calciteâ€“aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS
- Permanent Link:
- Uâ€“Pb dating of calciteâ€“aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS
- Series Title:
- Quaternary Geochronology
- Pickering, Robyn
Kramers, Jan D.
- Springer Nature
- Publication Date:
- Subjects / Keywords:
- Uranium-Lead Dating ( local )
Speleothems ( local )
Calciteâ€“Aragonite ( local )
Mc-Icp-Ms ( local )
Beta-Scanning Imagery ( local )
Lead Isotopes ( local )
234U/238U Ratios ( local )
- serial ( sobekcm )
- 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 Uâ€“Th dating and, although Uâ€“Pb geochronology presents a suitable alternative, bulk U concentrations are typically too low (<0.05 Î¼g/g) to provide useful ages. For this reason, we used a simple non-invasive beta-scanner imaging screening step to identify U-rich (â‰¥1 Î¼g/g) domains that could be analyzed with MC-ICP-MS techniques to provide Uâ€“Pb ages. We demonstrate the technique using samples from Sterkfontein cave that exhibit infrequent <1 cm-thick layers with U concentrations â‰¥1 Î¼g/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 Uâ€“Pb age of âˆ¼2.3 Ma that agrees well with their estimate of 2.24 ± 0.09 Ma. We also obtained similar Uâ€“Pb (0.164 ± 0.026 to 0.200 ± 0.052 Ma) and Uâ€“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 Uâ€“Pb ages.
- Original Version:
- Quaternary Geochronology, Vol. 5, no. 5 (2010-10).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
- Rights Management:
- This object is protected by copyright, and is made available here for research and educational purposes. Permission to reuse, publish, or reproduce the object beyond the bounds of Fair Use or other exemptions to copyright law must be obtained from the copyright holder.
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