n-Alkyl nitriles and compound-specific carbon isotope analysis of lipid combustion residues from Neanderthal and experimental hearths: Identifying sources of organic compounds and combustion temperatures

Molecular and isotopic approaches offer the chance to identify combustion residues and substrate components of archaeological combustion features to infer past fire-related activities. Analysis of fatty acid methyl esters by gas chromatography-combustion-isotope ratio mass spectrometry have been successfully used to distinguish among different animal fat groups. However, plant oils from different tissues have not been widely investigated even though organic residues from leaf, root, and wood tissues are preserved in sediments from archaeological combustion structures. Our analyses of plant residues from controlled laboratory heating sequences and experimental hearths involving wood and animal residues, provide references to discern anatomical parts of fresh and charred plants and to differentiate contributions of terrestrial plants and animal sources in open air hearths. This information is compared with charred organic residues from combustion structures from three Middle Palaeolithic sites: El Salt (Spain), Abric del Pastor (Spain) and Crvena Stijena (Montenegro). The occurrence of n-alkyl nitriles in our samples corroborates their potential as combustion temperature biomarkers and the δ13C16:0 and δ13C18:0 values allow us differentiate between charred and fresh plant anatomical parts and between fresh plant oils and animal fats.