Fuelling the Roman salt industry. Developing a new multiproxy approach to identify peat fuel from archaeological combustion residue

Abstract

In Europe, especially the Low Countries, peat was intensively used as a fuel source. Yet, the identification of peat as a fuel source from archaeological combustion residues is challenging. Nevertheless, detecting peat fuel in archaeological contexts would significantly contribute to broader socio-economic questions, such as fuel and landscape management strategies. To achieve this goal, this study developed a new multiproxy approach by combining several analytical methods (light microscopy, scanning electron microscopy, analytical pyrolysis, phytolith, faecal spherulite and ash pseudomorphs analyses and micro X-ray fluorescence spectroscopy) to identify fuel types, predominantly peat, from combustion residues. This methodology was successfully applied to combustion residues discovered at 6 Roman salt production sites situated along the southern North Sea coast. Not only was peat, specifically Sphagnum sp. and Ericaceae peat, identified as the predominant fuel source, but the use of fossil coal as a secondary fuel source could also be hypothesised. This paper demonstrates the high potential of the proposed methodology to identify not only the use of peat in combustion residues, but potentially also the specific type of peat used as well as other fuel sources.