Early entombment within silica minimizes the molecular degradation of microorganisms during advanced diagenesis

Julien Alleon (1) , Sylvain Bernard (1) , Corentin Le Guillou (2, 1) , Damien Daval (3) , Feriel Skouri-Panet (1) , Sylvain Pont (1) , Ludovic Delbes (1) , François Robert (1)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 UMET - Unité Matériaux et Transformations - UMR 8207
3 LHyGeS - Laboratoire d'Hydrologie et de Géochimie de Strasbourg

Most ancient organic microfossils delicately preserved in 3D have been found in cherts. Although entombment within silica has been shown to promote morphological preservation, the impact of early silicification on the molecular evolution of fossilized microorganisms during burial remains poorly constrained. Here, we report results of advanced fossilization experiments performed under pressure (250 bars) and temperature (250 °C) conditions typical of sub-greenschist facies metamorphism for different durations up to 100 days on microorganisms experimentally entombed (or not) within a silica gel. The experimental residues have been characterized using XRD and XANES spectroscopy. The present study demonstrates that entombment within silica limits the degradation of microorganism molecular signatures, likely through specific chemical interactions, despite the progressive conversion of silica into quartz during the experiments. Extrapolation of the present results suggests that such protection may persist during geological timescales. The present experimental study provides molecular evidence that, in addition to morphologies, cherts may support the chemical preservation of remains of ancient life. The present results thus constitute a step forward towards the reconstruction of the original chemistry of pu-tative fossilized microorganisms.

Mots clés: Experimental silicification; Experimental fossilization; Organic microfossils; Molecular biosignatures; XANES spectroscopy

Domaines: Géologie appliquée

Julien Alleon, Sylvain Bernard, Corentin Le Guillou, Damien Daval, Feriel Skouri-Panet, et al.. Early entombment within silica minimizes the molecular degradation of microorganisms during advanced diagenesis. Chemical Geology, 2016, pp.98-108. ⟨10.1016/j.chemgeo.2016.05.034⟩. ⟨hal-01331276⟩