Carbonaceous fraction contents of soil cultural layers from different ages from the area of Verona (NE Italy)

Cultural layers are deposits resulting from settlement and human activity on natural soil in the past. Materials from past domestic activities that become buried in the soil can be used to reconstruct human impact in a specific area in the past. The use of fire from early human societies since our times produced an enrichment of fire-related products such as charcoal. The presence and fluxes of charcoal particles in soils and sediments have been associated with the human occupation of a site in specific periods. But not only does the presence of charcoal permits us to infer the presence of human populations, but, in addition, assessing the abundance and degradation level of charcoal fragments can clarify anthropic activities in cultural deposits. In European towns, cultural layers with similar characteristics, have been defined as urban “Dark Earth” (DE) but their age, formation, and composition often differ significantly across sites. This study examined three archaeological sites in Verona, Italy, where DE layers with similar characteristics had been identified. The primary aim of this research was to understand the anthropogenic influence on the development of DE layers, by characterizing their geochemistry and the carbonaceous materials. To pursue this goal, we provided a micromorphological description of the soil and the abundance of charred material. The characterization of the amorphous/crystalline degree through µ-Raman spectroscopy was also investigated. Bulk material was described in terms of amounts of total organic carbon (TOC), recalcitrant organic carbon (ROC), total inorganic carbon (TIC), and trace element concentration. Radiocarbon dating of charred and humin fractions was performed to clarify the dynamics underlying DE origin. The different aspects studied were compared to outline the behavior and the development of the soil under the conditions of human exploitation, investigating the correlations and relationships of the variables. The results showed that a diverse pattern of human activities, including metal tools and/or ceramic manufacturing, was related to the formation of DE layers in urban contexts. Moreover, the investigation of carbonaceous fractions highlighted differences in soil organic carbon and charred material fraction, even if both of which were correlated with human influence.