Understanding Necrosol pedogenetical processes in post-Roman burials developed on dunes sands

Interaction between human remains and sediments starts after inhumation, leading to physico-changes and the development of a Necrosol, a type of soil seldom considered in archaeological research. In this study we analysed for physical (grain size, colour) and chemical (pH; LOI; elemental composition: FTIR-ATR, XRF, C and N) properties of soil samples from i) two graves from the post-Roman funerary area of A Lanzada (NW Spain) and ii) samples of a paleosol (coeval with the burials) from a nearby pedo-sedimentary sequence. The aim was to characterize Necrosol composition and pedogenesis and compare them with a reference soil. Principal component analysis of the dataset enabled to identify five pedogenetical processes: decalcification, melanization, acidification, neoformation of secondary minerals and enrichment in phosphorus. Overall, Necrosol pedogenesis was found to be of lower intensity than that of the reference soil (differing between burials), but some processes seem to be specific of the Necrosol formation (i.e., enrichment in phosphorous). Our results allow a proper description of the Necrosol and the funerary ritual followed by post-Roman inhabitants of A Lanzada. The characteristic Necrosol pedogenesis makes this soil a valuable archive that provides complementary information for the study of skeletal remains.