Analysis of biomarkers for the characterization of phosphatic crusts of compacted herbivore dung from a Middle Bronze Age settlement in the northeast Italy

Phosphatic crusts found in archaeological sites are orangish deposits with hard texture composed of microlaminated plant fragments embedded in a cement of hydroxyapatite (Ca₅(PO₄)₃OH), considered as indicators of animal penning. They generally derive from compacted dung and bedding material enriched in liquid animal waste that partially transforms organic matter and carbonates into Ca-phosphates. In this study, the phosphatic crusts collected at the Middle Bronze Age (1650-1300 BCE) site of La Muraiola di Povegliano (Verona, northeast Italy) were investigated by means of separation techniques coupled with mass spectrometry. The chemical analysis of biomarkers like faecal steroids from these crusts revealed high concentrations of 5β-phytostanols (5β-stigmastanol and epi-5β-stigmastanol) which are indicative of plant material digested by herbivores. 5β-phytostanols form, in fact, from the reduction of Δ5physterols (campesterol, β-sitosterol, stigmasterol) mediated by enteric bacteria in the intestinal tracts of herbivore mammals, especially in ruminants such as cattle, sheep, and goats. The identification of these compounds, combined with field observations and data derived from soil micromorphology, as well as pollen and phytolith analyses, offers valuable insights into husbandry practices in Bronze Age settlements. Acting as archives for microbotanical assemblages and chemical compounds that are rarely preserved to such a high degree in other deposits, this study highlights phosphatic crusts as critical features for exploring the interactions between humans, domestic animals, and their surrounding environment.
This research is part of the DIANE project (DIrt ANd Excrements: Integrating high-resolution sediment analysis and advanced biomolecular archaeology, 2022-2027) and it is strictly correlated to the ERC GEODAP project (GEOarchaeology of DAily Practices: extracting Bronze Age lifeways from the domestic stratigraphic record, 2021-2026). Both the projects aim to reconstruct domestic activities of ancient communities with a multidisciplinary approach that involves geoarchaeology, archaeobotany and organic chemistry.