Experimentally Derived Sedimentary, Molecular, and Isotopic Characteristics of Bone-Fueled Hearths

Abstract

Molecular and isotopic analysis of sediments from archaeological combustion features is a relatively new area of study. Applications can inform us about ancient pyrotechnologies and patterns of animal exploitation in a wide range of human contexts, but may be particularly informative with regard to ancient hunter-gatherers. Our analyses of sediments from experimental bone and wood fires, and from controlled laboratory heating sequences, provide fine-grained data on the formation and location of biomarkers from pyrolyzed animal fats in hearths. Integrating microstratigraphic, molecular, and isotopic data can improve recognition of bone fires in archaeological contexts, perhaps even where bone preservation is poor. Experimental bone fires produced an upper layer of calcined bone above a thin layer of tarry black amorphous material coating mineral sediments. Mineral sediments beneath the black layer showed little alteration but high lipid content. Sampling for molecular and isotopic analysis should target the black layer as the bulk of pyrolyzed biomarkers are located here and stable isotope values are less affected than in the overlying layer of ash or calcined bone. The combined presence of certain symmetric and slightly asymmetric saturated long-chain ketones (14-nonacosanone, 16-hentriacontanone 16-tritriacontanone, and 18-pentatriacontanone), especially together with heptadecane (C 17 n-alkane), are molecular indicators of the thermal degradation of terrestrial animal fat. Formation and relative dominance of these molecules in hearth sediments relates to the initial prevalence of specific precursor fatty acids and can provide broad separations between sources. We suggest that separations could be further supported and expanded by combining stable isotope analysis of the same compounds.Thermal processing and combustion of animal bone, fat, and oil for food and fuel has been critical to human survival in a wide range of contexts. Fat is an important source of energy and allows for efficient use of protein in carbohydrate-poor environments (Outram 2002;

Micro-contextual identification of archaeological lipid biomarkers using resin-impregnated sediment slabs

“…Their formation is related with thermal alteration, resulting from ketonic decarboxylation of fatty acids 44 . They are biomarkers of vegetable cooking practices 21 and also have been reported in experimental fireplaces fueled with fresh bone 45 . Long-chain n-ketones were not detected in our resin control samples and we did not find any literature about their use in polyester resins.…”

Ancient arctic pyro-technologies: Experimental fires to document the impact of animal origin fuels on wood combustion

“…Comparing driftwood and nondrifted wood fuels provides further data on the properties of woody fuels. Recently, a number of experiments have examined the use of bone as a main or secondary fuel source (Théry-Parisot, 2002;Théry-Parisot et al, 2005;Costamagno et al, 2005;Crass and Behm, 2005;Crass et al, 2011;Lejay et al, 2016;Lejay, 2018;Buonasera et al, 2019;Hoare, 2020). Even more limited are experiments focused on animal fat as fuel (Odgaard 2003).…”

An experimental approach to the preservation potential of magnetic signatures in anthropogenic fires

“…Experimental approaches to the study of prehistoric fire have been fruitful (e.g. : [2,11,24,32,37–53]). They have provided valuable information on combustion structure formation aspects with particular emphasis on observable features such as temperature ranges, size and morphology, heat penetration and internal stratigraphy in relation to variables such as fuel type, combustion duration or different post-combustion actions (trampling, relighting…etc.).…”