Fate and preservation of lipids in the soils of archaeological and experimental burials

Archaeological grave soils from two mass burials and a selection of individual burials have been examined as part of a larger study combining soil micromorphology and chemical analysis to recover signatures relating to burials from around the skeletal remains. A strategy involving sampling from up to 17 anatomical positions was employed in the collection of soil samples for chemical analysis. Analysis was performed using combinations of elemental analysis, gas chromatography and gas chromatography mass spectrometry, liquid chromatography mass spectrometry and pyrolysis gas chromatography. Soils from a series of experimental burials of piglets were similarly examined. The analyses reveal notable effects of the burial environment on the preservation of organic signatures from the remains. Anoxia and hydrology emerge as key controls on preservation and the nature of the burial matrix can exert strong influences both on the preservation and on the pathways by which organic residues are transformed. Clear distinction was apparent in a number of graves between the organic signatures from the soil background organic content and those originating from the remains. Distributions of n-alkanes, n-alkanols and long chain fatty acids attributed to plant matter were differentiated from triacylglycerols, diacylglycerols, monoacylglycerols, fatty acids and n-alkanals some of which reveal distributions similar to those of human adipose tissue, reflecting preservation of signatures of the human remains in the soils. Distributions of short chain components, n-alkanals and fatty acids, attest to the reduction of adipose-derived fatty acids and their release from triacylglycerols by hydrolysis.
The grave soils also contained a range of ‘exotics’ including signatures relating to personal effects, dye from clothing and treatments applied to the coffin. Steroidal components from the gut regions also provide broad indications of the dominant nature of last meals, with potential indications of differences relating to social standing. The studies demonstrate the wealth of information contained in organic signatures of burial soils and recommendations for sampling are made for later studies.