Reconstructing past fire traces through biomolecular approaches: the organic residue and benzene polycarboxylic acid analysis of Palaeolithic soils, sediments, and charred remains

The entanglement of Pleistocene and Palaeolithic hominins with fire is a long and convoluted process, which requires the mobilisation of multiproxy approaches to unravel. While significant developments have been made in recent years, the molecular dimension of these investigations remains relatively underexplored. This thesis investigates the capabilities and constraints of organic residue (lipid biomarker) and benzene polycarboxylic acid (BPCA) analyses to reconstruct past fire traces through the study of (pyrogenic) organic matter. Reconstruction is articulated around six axes: (i) the origins of combustion residues (i.e., natural versus anthropogenic); (ii) fuel sources; (iii) combustion conditions, namely heat treatment temperatures; (iv) the function(s) of anthropogenic fires; (v) the spatial organisation of combustion residues and pyrotechnic behaviours; and (vi) the palaeoenvironmental conditions in which the combustion events occurred. The potential of lipid biomarker and BPCA analyses to address these aspects of pyrotechnology is investigated through the study of combustion residues from the Palaeolithic sites of Les Bossats à Ormesson and La Grotte Bouyssonie.
Prior to archaeological applications, the BPCA protocol using microwave-assisted digestion is evaluated for possible procedural modifications. Moving from methodological development to interpretive potential, the utility of the BPCA method is then demonstrated through a proof-of-concept study involving the statistical analysis of BPCA results from modern charcoal. Using these data, random forest algorithms are constructed to predict heat treatment temperatures and precursor feedstock types in unknown samples.
At the open-air site of Ormesson, investigations focus on extensive combustion residues overlying Middle Palaeolithic deposits to determine whether these residues result from natural or anthropic actions. The findings support the interpretation that the residues derive from a previously undocumented wildfire in the Paris Basin region during Marine Isotope Stage 5. This case study raises broader epistemological challenges regarding the equifinality of archaeometric and geochemical data used to differentiate natural and anthropogenic fires.
At the cave site of La Grotte Bouyssonie, Aurignacian and Magdalenian combustion residues are analysed with the objective of elucidating human-environment relationships, as well as continuity and change in Upper Palaeolithic pyrotechnology. Geochemical data indicate significant contributions of higher terrestrial plants to soil organic matter, with fuel procurement strategies contingent upon environmental variability, and no evidence for the cooking of meat or the use of animal products (e.g., dung, bone) as fuel. This study raises important questions regarding the biases of anthracological and geochemical data for palaeoenvironmental reconstruction, as well as epistemological approaches to pyrotechnology in the absence of evidence for ‘specialised’ fire functions.
The unique archaeological contexts in which these methodologies were applied allow for nuanced reflections on their analytical and interpretive potential to reconstruct past fire traces, so critical to understanding the evolution of Palaeolithic pyrotechnology.