Accelerator mass spectrometry radiocarbon ages of an oxalate accretion and rock paintings at Toca do Serrote da Bastiana, Brazil
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abstract
At the Toca do Serrote da Bastiana rock shelter in Brazil, a red iron ochre pictograph of an anthropomorphic figure had become coated with a 'calcite' accretion over time. Using X-ray diffraction and Fourier transform infrared spectroscopy, we determined that the accretion also contains whewellite, the monohydrate of calcium oxalate, in addition to calcium carbonate. An AMS radiocarbon date on the oxalate formed from contemporaneous carbon yielded a minimum date of 2490 30 years BP for the painting. An AMS radiocarbon age of 3730 90 years BP on organic material in the underlying paint layer is consistent with the oxalate result and four direct radiocarbon dates on organic matter extracted from other rock paintings in the same shelter. Our results strongly disagree with a 30,000-40,000 year old age obtained by electron spin resonance and thermoluminescence dating of the accretion.
