Characterisation of charred organic matter in micromorphological thin sections by means of Raman spectroscopy

Burned or charred organic matter in anthropogenic combustion features may provide important clues about past human activities related to fire. To interpret archaeological hearths, a correct identification of the organic source material is key. In the present work, Raman spectroscopy is applied to characterise the structural properties of char produced in laboratory heating- and open-fire experiments. This reference data set is compared to analyses of three different archaeological sites with Middle Palaeolithic combustion contexts. The results show that it is possible to determine whether a charred fragment is the product of burning animal-derived matter (e.g. meat) or plant-derived matter (e.g. wood) by plotting a few Raman spectral parameters (i.e. position of G and D bands, and intensity ratios H-D/H-G and H-V/H-G) against one another. The most effective parameters for discriminating animal- from plant-derived matter are the position of the G band and the H-V/H-G intensity ratio. This method can be applied on raw sample material and on uncovered micromorphological thin sections. The latter greatly compliments micromorphology by providing information about char fragments without any clear morphological characteristics. This study is the first of its kind and may provide archaeologists with a robust new method to distinguish animal- from plant-derived char in thin sections.

Automated summary

This study utilizes Raman spectroscopy to characterize the structural properties of char produced in laboratory heating- and open-fire experiments, finding that it is possible to distinguish between animal- and plant-derived char by plotting specific Raman spectral parameters against one another. The method can be applied to raw sample material and uncovered micromorphological thin sections, providing archaeologists with a robust new way to differentiate between animal- and plant-derived char.