A new process of reconstructing archaeological fires from their impact on sediment: a coupled experimental and numerical approach based on the case study of hearths from the cave of Les Fraux (Dordogne, France)

A novel approach to the intensity of archaeological fires is proposed, based on a combination of archaeological observations and analyses of sedimentary hearths with relevant proxies obtained from using experimental combustion structures. In this work, two different structures were built and monitored. They aimed at reproducing two types of archaeological hearth morphology encountered at the Bronze Age site of the cave of Les Fraux (Saint Martin de Fressengeas, Dordogne, France). A series of fires was constructed and a large amount of data was collected: temperature curves, wood consumption and observations on substratum evolution. A numerical code for heat transfer was developed to model heat propagation from the surface to the underlying sedimentary layers, the input parameters of which were adapted to fit the thermal evolution observed with the experimental fires. We found that two archaeological parameters are fundamental to characterise the intensity of the fire: the paleotemperature reached at the surface of the burnt sediment (which in our case was determined by thermoluminescence analyses) and the depth of the rubefaction front as an indicator of a 250 A degrees C isothermal surface. We then estimated the duration of an equivalent single fire that would correspond to one of the archaeological hearths investigated. Finally, with the wood consumption recorded during the fire experiments, and the estimated firing duration, the energy involved was evaluated. When generalised to the study of archaeological hearths, this approach could be of great interest in firing intensity evaluation (temperature/time/energy).