Title

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

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Publisher

Springer Nature

Publication Date

October 2010

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 (<0.05 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.

Notes

Quaternary Geochronology, Vol. 5, no. 5 (2010-10).

Keywords

Uranium-Lead Dating, Speleothems, Calcite–Aragonite, Mc-Icp-Ms, Beta-Scanning Imagery, Lead Isotopes, 234U/238U Ratios

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1 online resource

Subject: topical

Uranium-Lead Dating; Speleothems; Calcite–Aragonite; Mc-Icp-Ms; Beta-Scanning Imagery; Lead Isotopes; 234U/238U Ratios

Type

Article

Genre

Serial publications

Identifier

SFS0062955_00001

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