Introducing Benzene Polycarboxylic Acid Analysis: potential of a molecular marker for the study of archaeological hearths and wildfires
Résumé
Since its development in 1998, benzene polycarboxylic acid (BPCA) analysis has become a powerful and frequently employed tool in environmental science research for its ability to elucidate the molecular characteristics of charred material on the entire combustion continuum from charcoal to condensates and soot. Applications of the method to ancient soils, sediments, and charred material are presently limited, yet the method holds great potential in archaeological research as a molecular marker for charred biomass, including cases where no or few macroscopic charcoal fragments remain. This study presents a multi-faceted approach to the implementation of the BPCA method in archaeological research. The interpretive potential of BPCA analysis—namely related to the aromaticity, aromatic condensation, and combustion temperature of the charred material—is first demonstrated through the statistical analysis of a BPCA database created for lab-produced charcoal. Variables hypothesized to influence the BPCA signal such as oxygen availability during pyrolysis are raised, highlighting future directions of research. Methodological considerations are elucidated through the presentation of pilot tests on experimental materials conducted to optimize the BPCA protocol for the analysis of archaeological samples. BPCA analysis is then applied to charcoal and charcoal-rich sediments from combustion residues directly overlying Levallois lithic remains in the Middle Palaeolithic (MIS 5) deposits of Ormesson (Seine-et-Marne, France), with the objective of characterizing the fire temperature reached in different zones in order to differentiate between the natural and anthropogenic origin of the fire. Lastly, complementary approaches such as polycyclic aromatic hydrocarbon analysis to permit source identification and the radiocarbon dating of isolated BPCAs are discussed to emphasize the interdisciplinary potential of this molecular marker for charring new to archaeological research.