Impact des écosystèmes microbiens sur la sédimentation. Impact of microbial ecosystems on sedimentation

Abstract

The microbial communities which often give rise to the fine lamination in sediments are very diverse both in species composition (e.g. phototrophic and chemotrophic bacteria, fungi, algae) and metabolism (e.g. oxygenic and anoxygenic photosynthesis, organic and inorganic chemosynthesis, anaerobic and aerobic respiration, organic and inorganic fermentation). These microbial ecosystems have separated for more than 3.5 Ga (3500 m.y.). They intervene in the biostructuration of sediments by active mineral deposition, particle trapping and sediment stabilisation. They build bioconstructions (stromatolites, oncolites, oolites and microbial bioherms). Further they are active in a number of biogeochemical biomineralisation processes including phosphatogenesis, carbonate genesis and the formation of iron ore and sulfur deposits, and petroleum and kerogen. They are also active agents in the biocorrosion and bioerosion of sedimentary rocks under marine and terrestrial conditions. Since they have an enormous capacity for proliferation, microbial laminated communities invade new habitats, practically instantaneously where suitable energy sources and gradients for electron flow are available. In addition such microbial systems are excellent and sensitive paleoecological indicators. In order to study their impact on sedimentation and fossilisation a close collaboration between geologists and microbiologists is needed. Only in this way can the nature of fossil microbial ecosystems and the metabolisms that were at work be recognized and reconstructed.