Abstract
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 (<0.05μg/g) to provide useful ages. For this reason, we used a simple non-invasive beta-scanner imaging screening step to identify U-rich (≥1μg/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 ≥1μg/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 ± 0.052Ma) 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.
Original language | English |
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Pages (from-to) | 544-558 |
Number of pages | 15 |
Journal | Quaternary Geochronology |
Volume | 5 |
Issue number | 5 |
DOIs | |
Publication status | Published - Oct 2010 |
Keywords
- Beta-scanning imagery
- Calcite-aragonite
- Lead isotopes
- MC-ICP-MS
- Speleothems
- U/U ratios
- Uranium-lead dating
ASJC Scopus subject areas
- Geology
- Stratigraphy
- Earth and Planetary Sciences (miscellaneous)