Adeline Roche PhD thesis

Intrinsec and extrinsec controlling factors of microbialites

Fellowship: contrat doctoral, université de Bourgogne Franche-Comté

Supervisor: Emmanuelle Vennin

beginned in october 2016

 

Abstract

Microbial-mediated mineralization is considered as one of the main natural processes controlling CO2 levels in the atmosphere and a major structural and ecological player in the modern and in the past ecosystems. The result of this process is the formation of microbial deposits. Microbialites (organo-sedimentary structure predominantly accreted by sediment trapping, binding, and/or in situ precipitation as a result of the growth and metabolic activity of microorganisms) are found throughout the geological record and are the first bio-signatures of the early Earth and in the search for extra-terrestrial life potential. The oldest preserved fossil stromatolites in the geological record are about 3.4 billion years old and have been found in Australia and Canada. In modern natural systems, biological carbonates precipitation occurs in different forms, fabrics and in different environments (saline lagoons, hypersaline, alkaline lakes, freshwater rivers and lakes). The study of mechanisms of microbialite formation at different scales (km until nm) is critical for interpretation and understanding their origin and evolution. This multi-scale approach concern: (1) macro-scale (tectonics, climate); (2) meso-scale (hydrothermal circulation, water chemistry); (3) micro-scale (microbial - mineral interaction, mineralogy/morphology). Two fieldworks are chosen: modern (Great Salt Lake, USA) and ancient (Oligo-Miocene basin of Limagnes, France) microbialites. The results can help to answer important questions about i) carbonate formations in past (geological context) and present time (biogeochemical cycle and context of CO2 storage); ii) preservation in the fossil record of mineralization processes.

 

Keywords

microbialites, microbial mats, mineralization, preservation