Estimating firing temperatures of pyrotechnological processes in the Neolithic site of Portonovo

Research aims – The abundant structural evidence for the use of pyrotechnology at the Neolithic site of Portonovo is an invaluable means of reconstructing fire-related activities, such as pottery firing, baking or toasting. The specific aim of this research is thus to obtain some information on the maximum temperatures reached during the firing cycles of the many ovens identified. We focused in particular on the transformation of CaO-rich sediments (Heimann 1989), structurally modified by exposure to low or high temperatures (as in Berna et alii 2007), which constitute the inner parts and hardened surfaces of the ovens. The 16 prehistoric structures were constructed within the colluvial layer and in the marl substratum (Schlier Formation), both very CaO-rich sediments (Cilla 2009). The Schlier Formation (Burdigalian pp - Langhian) consists of hemipelagic deposits characterized by an alternation of marls and clayey marls and, subordinately, of whitish grey marly limestone (Centamore, Deiana 1986). The identification of the temperature range at which a sediment was burned is based on characterizing the irreversible transformations that occur when silicate minerals, and in particular clay minerals are fired, using X-ray powder diffraction analysis (PXRD). Clays undergo several structural and compositional changes when exposed to increasing temperatures.