Anthropogenic units fingerprinted by REE in archaeological stratigraphy: Mas d'Is (Spain) case

On occasions, archaeologists have to deal with serious difficulties to differentiate between processes that ultimately are responsible for the formation of stratigraphic units.Sometimes we face problems related with depositional units in multilayered deposits and other times, we ask for the character of some dark surface soils, very similar to natural paleosols and usually associated with archaeological findings. In both cases, the problems we must address concern the relative impact of human activities.The imbalance between anthropic and natural processes in the formation of archaeological deposits is crucial for a correct interpretation of the processes involved in the formation of archaeological sites, but also of their occupation-abandonment dynamics and the understanding of their spatial behaviors and relationship with the environment.In this paper we propose a new methodological approach for the identification of anthropogenic fingerprints in stratigraphic units through Rare Earth Elements (REE) soil analysis. The role of REE for the effective identification of sediment provenance due to their coherent behavior during weathering, erosion and fluvial transportation and their high resistance to chemical mobilization is well known in other areas of knowledge. We try to explore its potentiality in a challenging archaeological context. Our purpose was to identify human traces in stratigraphic units where archaeological materials are scarce or absent intertwined with others richer in archaeological remains by the determination of multiple elements and statistical studies. We believe that Rare Earth Elements (REE) soil analysis provides unique insights for a better characterization of natural and archaeological sediments but more importantly to recognize different stages of the gradient. We expect to discern between natural versus anthropic units and between primary versus secondary deposits (redeposition), using the case of the Neolithic site of Mas d'Is (Alicante, Spain) as an example. The application of the Principal Component Analysis (PCA) remarks differences in REE values, those analysis show differences between units of undoubtedly anthropogenic origin and control samples taken from natural sediments –including marls bedrock–, in their vicinity, but also we could notice finer nuances like the degree of human contributions to paleosols formation.