Use of heavy liquid density separation to remove pyrite from sediment samples for radiocarbon dating

Abstract

Sample preparation protocols for concentrating organic material from sediments for radiocarbon dating often include a large number of steps and the use of hazardous chemicals. Thus, these protocols are often problematic for pollen-poor sediments as material can get lost or may become degraded. Pyrite in samples for radiocarbon dating hinders an effective graphitisation process and thus needs to be removed during sample preparation. Standard protocols require the use of nitric acid, a strong oxidant that corrodes organic material. Therefore, the use of nitric acid needs to be avoided when preparing pollen-poor but pyrite-rich sediments.We present a method that minimises the sample preparation steps by replacing acid treatment with heavy liquid separation. Using non-toxic LST at a density of 2.0gcm-3 is shown to be effective for separating the organic fraction from sulphides, silicates and carbonates. We applied this method to pyrite-rich and pollen-poor sediments from Western Australia that had previously been problematic to date. The successful AMS radiocarbon dating of all samples pre-treated with LST demonstrates the effectiveness of this method.