The wooden framework of Paris's Notre-Dame Cathedral was almost destroyed by fire on 15 April 2019. The remains of the charred timbers are not of any interest for the reconstruction, but they conceal within them more than 800-year history of this monument. Their investigation is therefore an extraordinary opportunity to get an insight into the construction process and learn more about relation between society and forest in the Central Middle Ages (11th-13th centuries). One of the key elements to better understand forestry management and the timber trade during this period is the provenance of the timber woods.
The aim of this thesis is to determine the geographical origin of wood used to build the Notre-Dame's framework with the help of geochemical tracers, in particular the multi-elemental composition and isotope ratios of strontium (Sr) and neodymium (Nd) in wood. The strength of geochemical tracing consists in discrimination of sites based on their geological and pedological contexts. During its development, the tree absorbs nutrients which are partially transferred to cell walls of wood. Mineral contents and isotopic signatures in wood thus reflect those of rocks and soils on which they grow. This approach is applied here for the first time to carbonized archeological wood. Before proceeding to identification of the origin of the Notre-Dame timber woods, 1) the conservation of geochemical tracers during carbonization was verified experimentally, and 2) a referential database of multi-elemental and isotopic signatures in present-day woods was built up at the scale of the Seine River catchment. Exposure to high temperature did not affect the isotopic composition of Sr and Nd, but provoked volatilization and loss of some of the elements. Elemental tracers were selected on the basis of the ratios of thermostable elements, i.e., those whose decrease in concentration was negligible (< 20 % at 800°C). The referential database was based on 12 forest sites, each representing a specific type of substrate, covering the geological and soil diversity within the Seine River catchment area. The origin of present-day wood was traced with an accuracy of around 80 %, and site discrimination was strongly controlled by the 87Sr/86Sr isotope ratio,and the Sr/Ca and Nd/Ca elemental ratios. The carbonized timbers from the Notre-Dame framework were characterized for the cutting dates of trees and their geochemical signatures were compared with each other and with those of potential source forests, as suggested by the historical sources. The geochemical signatures of most of the medieval woods are characteristic of forest stands growing on deep silty soils, in agreement with findings in archives which placed the origin on the south-east of Paris.

*corresponding author: e-mail: stulc@iic.cas.cz