Calcified Fungal Filaments in the Petrocalcic Horizon of Eutrochrepts in Beauce, France
Résumé
Calcified filaments could be responsible for the induration of petrocalcic horizons, although they are absent or very rare in petrocalcic horizons with a porosity filled by needle-fiber and micro-rod calcite. The aim of this study was to show that calcified filaments were also numerous in these petrocalcic horizons, thus ensuring their high cohesion. Samples were collected in petrocalcic horizons of Eutrochrepts in Beauce, France. They were studied by scanning electron microscopy, and chemical analyses were performed using an energy dispersion spectrometer microprobe. Observations of fragments in the secondary electron mode showed a close packing of needle-fiber calcite with micro-rod calcite without any visible calcified filament. In the backscattered electron mode, observations showed numerous rounded voids, 0.5 to 1.0 µm in diameter within the packing of microrods. These voids and their walls exhibited similar morphological characteristics to those of the calcified filaments described earlier and interpreted as the remains of fungal hyphae. Chemical analysis of the rounded voids' walls, needle-fiber calcite, and micro-rod calcite revealed the presence of C and Ca as main elements and secondarily of Al and Si, but their respective compositions were not significantly different (P = 0.05). The C/Ca atomic ratio indicated that the analyses did not avoid resin, and that they cannot be used for discussion of calcite or calcium oxalate presence.