U-Th dating of cave carbonate overgrowths: indicators for establishing closed system reliability

Summary

This is an abstract from the "New approaches to the intractable problem of dating rock art" session, at the 90th annual meeting of the Society for American Archaeology.

Uranium-thorium dating of speleothem calcite has become a spectacularly effective geochronometer underpinning important Quaternary climate records. The method is at its strongest on clean, macrocrystalline calcite, typically stalagmites found deep underground. U-Th depends on closed-system accumulation of thorium, as a decay product of a fixed initial amount of uranium. If a sample is contaminated with thorium at its time of formation this effect can be corrected for, up to a point, at the expense of reduced precision of the age. But if a sample has not remained closed to chemical migration of uranium then it become all but impossible to accurately date, and this error cannot be detected internally. Clean, well-preserved stalagmites are usually reliable in this regard, but other speleothem types can be susceptible to uranium migration, usually loss to the environment giving erroneously old U-Th ages. U-Th dating of thin carbonate coatings over rock art can be reliable, but might not be. Hence assemblages of age determinations should be carefully assessed for internal consistency. Micro-drilled or in-situ investigations of spatial variability apparent age can be especially effective in this regard. Single, unsupported ages of any crust material, including coralline speleothem, should be treated with caution.

This Resource is Part of the Following Collections

• Society for American Archaeology 90th Annual Meeting, Denver, CO (2025)   •
• New approaches to the intractable problem of dating rock art

Keywords

Record Identifiers

Abstract Id(s): 52394