Thermal characterisation of Bronze Age hearths from the cave of Les Fraux (Dordogne, France) by thermoluminescence and magnetic susceptibility techniques

In the cave of Les Fraux (Dordogne, France) numerous traces of fires are visible in the galleries. A multidisciplinary investigation was carried out to study these fires. This paper presents the methodology applied for the hearth study. It is based on the examination of the thermoluminescence (TL) of quartz and the magnetic susceptibility of iron oxides. First of all, magnetic susceptibility was measured on the surface of hearths. Based on both susceptibility mapping and visible sediment characteristics, small sediment samples (1-2 g) were taken. Subsequently, quartz grains were extracted from the sediment samples. Fourteen thermal references were obtained by heating (from 200 to 650°C) fractions of the pristine unfired cave sediment. Comparing the TL signal of anciently heated quartz to the reference samples allowed to obtain the maximum equivalent temperature attained for each sample extracted from ancient fires. Consequently, the correspondence between magnetic susceptibility and temperature allowed for the reconstruction of a paleotemperature map of the study area. This research provides information about fire intensity in the cave, which can help to understand its function.