REMOVAL OF CONTAMINANTS TO IMPROVE THE RELIABILITY OF RADIOCARBON DATES OF PEATS

Peat samples from Timaru Downs, New Zealand were subjected to a wide range of chemical treatments before radiocarbon assay. A step wise procedure was used in which each sample was radiocarbon dated before and after the treatments were applied. The criterion adopted for indicating the removal of young contaminants and thus resulting in the improvement in the reliability of radiocarbon dates is the increase in the radiocarbon age of the sample after treatment. When peat samples were radiocarbon dated without prior chemical treatments the results could not be used to accurately date the time of formation because of young contaminants. Contaminants could be removed by chemical treatment of peats with mineral acids, particularly 70% HNO₃ for the very old peat sample. The improvement brought about by acid treatment was greater than that from the classical humus extraction and fractionation method.