We have developed new SIMS and NanoSIMS methodologies (Marin Carbonne et al., 2018, Decraene et al. 2019) to investigate the presence of metabolic isotope signatures recorded in ancient stromatolite and sediments. These protocols have been calibrated on different instruments and have been published. We also have discovered that a Fe isotope pyrite standard contains two different isotopic compositions (Pasquier et al., accepted at Geostandards), that have induced minor errors in two articles that have been corrected (Dupeyron et al., 2023, Decraene et al., 2023).
During the project, we conducted one field campaign in South Africa in 2019, the others were canceled due to the pandemic. However various collaborators have provided stromatolitic samples we have used, as the Malmani stromatolite for example. We also have conducted experimental diagenesis on different samples but we have not yet finished to characterize them.
We have demonstrated the presence of microbial sulfate reduction and iron dissimilatory reduction in the Tumbiana Formation (Australia, 2.7 Ga, Marin Carbonne et al. 2018, and Decraene et al., 2019), in the Mendon Formation (3.2 Ga. South Africa, Marin Carbonne et al., 2020). We have demonstrated that the Buck Reef Chert, despite its geological history, has preserved chemical heterogeneity in organic molecules (Alleon et al., 2021) and iron-mediated anaerobic ammonium oxidation (Pellerin et al., 2023). The study of modern stromatolite suggested the importance of microbial sulfate reduction in the biomineralization of the microbialite and that sulfide recorded near equilibrium isotope fractionation (Marin Carbonne et al., 2022). In a review article, we have identified the effect of metamorphism and diagenesis on the Fe isotope composition of sulfide (Dupeyron et al., 2023) but we were unable to identify the effect of the Great Oxygenation Event (GOE) on microbial metabolisms. We have published 18 research articles, three chapters that will be published in 2024 and 2025, and one special issue is ongoing. The results of the project have been presented at various conferences and workshops. One PhD student successfully defended her Ph.D another will finish in 2023, three post doc researchers have found permanent positions, one as a museum researcher in Japan, one as a CNRS researcher in France, and one as an assistant professor in US.
We have organized on workshop on Microbialite, M-Fed23 in October 2023 in Leysin Switzerland, this event internationally attended has been followed by an exhibition at the Palais de Rumine in Lausanne. The PI has given an opening conference, where the results of the project were presented.
