U-Pb dating of calcite-aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS

Robyn Pickering, Jan D. Kramers, Tim Partridge, Janos Kodolanyi, Thomas Pettke

Research output: Contribution to journalArticlepeer-review

61 Citations (Scopus)

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 languageEnglish
Pages (from-to)544-558
Number of pages15
JournalQuaternary Geochronology
Volume5
Issue number5
DOIs
Publication statusPublished - 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)

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