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Institut de minéralogie, de physique des matériaux et de cosmochimie

PhD Thesis - Nina Zeyen

Study of modern microbialites from Mexican crater lakes

ERC Calcyan - Advisor K. Benzerara (Geobio-IMPMC)


Microbialites are organo-sedimentary rocks found in abundance throughout the geological record back to ~3.5 Ga. Interpretations on how and under which conditions ancient microbialites formed are based on actualism, i.e., a comparison with modern microbialites. Therefore, a better characterization of diverse modern microbialites is crucial to improve such interpretations. For this purpose, we studied modern microbialites from several Mexican alkaline crater lakes located in the Trans-Mexican Volcanic Belt. One of the objectives is to characterize microbialites and better understand the relationship between their composition and the chemical composition of the lakes as well as document the spatial associations of organic polymers with mineral phases down to the nm-scale and the possible traces of life preserved in the mineral part of the microbialites. For that purpose, we combined a geochemical characterization of the surface water of the lakes with bulk x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electron and x-ray microscopy analyses of the microbialites. Altogether, these analyses reveal the pervasiveness of an authigenic poorly crystalline silicate phase, rich in Mg and sometimes Fe and/or Mn Moreover, these results showed that organic carbon is pervasively associated with kerolite. Overall, it is suggested that the poorly-crystalline hydrated magnesium-rich silicate may result from a biomineralization process. The conditions and mechanisms of its formation as well as its importance in the fossilization of microbial communities in lacustrine microbialites are studied. Finally, the frequent occurrence of such an authigenic silicate phase in modern lacustrine microbialites calls for a reappraisal of its potential presence in ancient rocks.

Sylvain Bernard - 17/02/16

Traductions :

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    Institut de minéralogie, de physique des matériaux et de cosmochimie - UMR 7590

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    Geobio Team @ IMPMC

    The Geobio Team @ IMPMC brings together :

     - 10 permanent members

     - 3 postdoctoral fellows

     - 6 PhD students