Characterisation of iron (II) sulfides in wet archaeological woods: the wreck of Mandirac (IV th century, antique ports of Narbonne, France)

Céline Remazeilles (1) , Francois Leveque (2) , Maylis Minjacq , Philippe Refait (1) , Corinne Sanchez (3) , Marie-Pierre Jézégou (4)

1 LaSIE - Laboratoire des Sciences de l'Ingénieur pour l'Environnement - UMR 7356
2 LIENSs - LIttoral ENvironnement et Sociétés - UMR 7266
3 ASM - Archéologie des Sociétés Méditerranéennes
4 DRASSM - Département des Recherches Archéologiques Subaquatiques et Sous-Marines [Marseille]

The wreck of Mandirac (Narbonne, France, IV century) was excavated in 2013 and 2014 from waterlogged soil. A magnetic prospection campaign performed in 2014 revealed that the wood was abnormally magnetic. A plank extracted from the hull, containing an iron nail, was analysed using Environmental Scanning Electron Microscopy, micro-Raman spectroscopy, X-Ray diffraction and magnetic characterization methods in order to identify the mineral composition inside the wood and of the nail. Results revealed an accumulation of greigite and pyrite in the wood around the nail, where the pH was measured below 3. The nail was completely corroded into pyrite and siderite, with no metal left. Marcasite was also identified far from the nail, where the pH was measured around 5. Greigite was the only phase responsible of the magnetic signal emitted from the wood and proved to be present in varying amounts throughout the entire wreck. The iron sulfides were probably formed via anaerobic sulphidogenic bacteria influenced corrosion processes, which occurred on the nails. These results are very different from those obtained from more recent shipwrecks (XIX century). So the nature of these iron sulfides in wet archaeological woods is discussed.

Keywords: Waterlogged soil; archaeological wood; microbiologically influenced corrosion; iron sulfides; greigite; pyrite; Mandirac

Domains: Chemical Sciences; Analytical chemistry; Chemical Sciences; Inorganic chemistry; Chemical Sciences; Material chemistry; Physics [physics]; Condensed Matter [cond-mat]; Materials Science [cond-mat.mtrl-sci]

Céline Remazeilles, Francois Leveque, Maylis Minjacq, Philippe Refait, Corinne Sanchez, et al.. Characterisation of iron (II) sulfides in wet archaeological woods: the wreck of Mandirac (IV th century, antique ports of Narbonne, France). WOAM 2016, May 2016, Florence, Italy. ⟨hal-02345869⟩