Using portable X-ray fluorescence (pXRF) spectrometry to discriminate burned skeletal fragments

Abstract

Identifying the individuals who make up burned and commingled skeletal assemblages represents a labour-intensive challenge. Portable X-ray fluorescence (pXRF) is a potential tool for reconciling fragmented and mixed individuals using the unique elemental content of bone. While the method’s usefulness has been demonstrated with unburned bone, further work is needed to identify if the elemental signatures embedded in bone remain consistent enough, regardless of exposure temperature, to allow the discrimination of burned individuals. We test whether pXRF can discriminate between individuals with variable degrees of burning and further, whether the elemental profiles reliably reflect burning temperatures. Tibiae and femora from five fresh lambs (Ovis aries) were sectioned and experimentally burned for 30 min at 200 °C, 400 °C, 600 °C, 800 °C and 900 °C. Elemental profiles from the unburned and burned fragments were analysed using discriminant function analysis. Whether burned, unburned or variably exposed to heat, fragments from the five individuals were successfully distinguished using aggregate elements (more than 80% of fragments correctly classified). The elemental profiles did vary by degree of burning allowing the distinction of fragments burned at < 200 °C, 400 °C, 600–800 °C and 900 °C (> 90% correctly classified). Collectively, these results show the promise of pXRF in the analysis of burned and commingled assemblages if the elements used are carefully considered and aggregated. However, further work considering diagenetic effects needs to be undertaken.