The capability of rare earth elements geochemistry to interpret complex archaeological stratigraphy

In this study rare earth elements (REE) signatures (REE ratios, cerium and europium anomalies) are applied to a complex soil stratigraphic sequence from the site of Konso, Ethiopia, with the aim of determining whether REE can distinguish the strata observed in the field. Forty soil samples were taken from a depositional sequence that includes overlapping human induced and ‘natural’ erosional and depositional processes. The samples were analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to determine trace elements and REE, with concentrations of major elements determined using X-ray fluorescence (XRF). Cluster Analyses (CA) were used to observe differences between strata. The mechanisms that influenced REE values and fractionations were related to OM accumulation, pyrogenic SOM, redox and secondary CaCO3 precipitation, suggesting the addition of proxies to the REE, Sc and Y data processing. This produced a clustering of samples that more accurately reflected the stratigraphic field observations. It is expected that this approach, combining the analysis of REE concentrations with an understanding of the mechanisms driving them in a given site or profile, will be replicable for other stratigraphic sequences. The results demonstrate that REE signatures are not just able to detect stratigraphic differences defined through field observations but also highlight variations within the same deposits. REE analysis could therefore become a powerful geoarchaeological tool, even for studies of complex stratigraphies.