Dating oxalate minerals 20-45Â ka

We report a test of the dating of oxalate minerals near the radiocarbon limit. Oxalate salts are used for estimating the ages of prehistoric rock paintings and carvings, but uncertainties have existed about the origin of the carbon they contain. Sediments at the Carpenter's Gap 1 rockshelter, Western Australia, have been conventionally radiocarbon dated at about 34 000 years old, providing independent evaluation for the ages of buried oxalate crusts associated with them. Accelerator mass spectrometry radiocarbon (AMS 14C) assays of carbon in rapidly oxidized oxalate ions from these crusts produce age estimates marginally older than the covering sediments.