4000 years of trace metal record in a former iron-smelting district, West Bourgogne (France): multi-proxy paleoenvironmental assessment of human impacts on the landscape

The geochemical and palynological study of a well-radiocarbon-dated core from the “Les Comailles” peat bog, located in the vicinity of slag heaps in the former iron-metallurgy district of Puisaye (Bourgogne-Franche-Comté region, France), highlights the impact of metallurgical activities on vegetation cover from 2000 cal. BC to cal. AD 1740. The physico-chemical characterization of the peat bog demonstrated its reliability to be used as a chronological archive of past environmental changes. The study recorded evidence of atmospheric emissions of several metals, including arsenic, lead, or zinc, during the Late Bronze Age, even though no archaeometallurgical sites are currently known in the Puisaye district before the Early Iron Age, revealing the possible existence of punctuated bronze metallurgy in Puisaye. Forest clearance of Quercus was evidenced during the Second Iron Age and is related to the intensification of iron-metallurgy and crop cultivation. Comparison of palynological data from the Comailles core with charcoal analyses from slag heaps in the Puisaye district, supported the selection of wood for charcoal production during the Roman Empire and the Middle Ages, as some species present in the landscape are absent in anthracological spectra. We hypothesize that there was a spatial separation between metallurgy and crop activities in Puisaye. Compositional Data Analysis made on 13 trace elements (arsenic, cadmium, cobalt, chromium, copper, lanthanum, nickel, lead, rubidium, antimony, tin, zinc and zirconium) also highlighted two main changes of geochemical composition of peat samples, dated to the beginning of the Late Middle Ages and Modern Times, that could be related to archeologically known changes in iron-metallurgy processes and organization of iron-smelting sites at a regional scale. As forest cover inhibits identification of past settlements, further investigation is advised to identify former rural settlements.