Testing the capability of Rare Earth Elements to identify archaeological strata in an African site: The case of the terraced landscape at Konso, Ethiopia

Over the last twenty years Rare Earth Elements (REE) have started to be part of archaeometric studies. Due to their particular characteristics there have been several attempts to apply REE analysis to different archaeological scenarios including stratigraphically-controlled agricultural soils, demonstrating that this is an effective tool to understand how human activity is reflected in soil development. Our study proposes a new methodological approach for the identification of anthropogenic deposits through REE soil analysis, pushing current limitations of traditional chemical and sedimentology techniques. Our study represents the first application of REE concentrations in soils from tropical Africa within an archaeological context. The agricultural soils were captured in an artificial sediment trap that forms part of the terraced landscape in Konso, Ethiopia; a system thought to have developed over the last 500 years, and which was awarded World Heritage status in 2011. Forty samples were taken from successive alluvial layers down a c. 2m thick soil sequence that had accumulated behind a series of drystone walls. The samples were analyzed for trace elements and REE via ICP-MS. To understand the causes of enrichment or depletion of REE, the data were compared with soil organic matter, organic carbon and fire markers. To aid interpretation we crossreferenced our results with archaeobotanical and soil micromorphology data. Data were analysed using multivariate statistics. Taken together these results present a very different picture of landscape development to previous presented accounts; the REE analyses provide significant details regarding the source and transportation of sediments