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Dans le cadre de la manifestation M-Fed Microbialites: formation, evolution, diagenesis, Julien Curie présentera ses travaux de recherches : "The role and impact of microbialites in the depositional architecture of the Roman travertines of Jebel Oust (Tunisia)"Résumé The role and impact of microbialites in the depositional architecture of the Roman travertines of Jebel Oust (Tunisia)J. Curie1,*, C. Petit21 Laboratoire ArScAn, MAE René-Ginouvès, 21 Allée de l’Université, Nanterre, France2 Laboratoire ArScAn, Université Paris 1 Panthéon-Sorbonne, 3 rue Michelet, Paris, France* Email: julien.curie@sorbonne-université.frTravertines are terrestrial carbonates that develop various depositional geometries and facies. Their precipitation processes and origins are well-known since few decades (e.g. Guo &#38; Riding, 1998; Pentecost, 2005; Kele et al., 2011; Teboul et al., 2016) but still discussed nowadays, especially regarding the role of microbial communities (e.g. Riding, 2011; Della Porta et al., 2017; Valeriani et al., 2018). The hot travertine-depositing waters (54°C) of Jebel Oust in Tunisia, exploited during Roman Antiquity for cult and bath practices, offer a great model of travertine precipitation influenced by microbial communities. Indeed, the 2000 years-old channel – which starts its course just by the sacred spring vent and used to provide with hot waters the Roman baths complex located downstream - is filled in its proximal slope with a 2 meters-thick sequence of a very thin-laminated travertine deposit which shows stromatolitic structures and puff-pastry facies. This results from microbial mats activities developing a “hot water ice” – or “calcite ice” – phenomenon, as described for calcite rafts in few travertines from Central Italy (Gandin &#38; Capezzuoli, 2014). The biological induced aggradational unit, only disturbed by few detrital and ancient anthropic elements, show a cyclicity in isotopic composition, with δ13C and δ18O values around 3‰ PDB and -9‰ PDB, respectively. Moreover, δ13C and δ18O values depict a strongly negative correlation throughout the sedimentary sequence. These data may suggest variations of microbial activities probably linked to variations in precipitating-waters temperature. In the distal slope, i.e. in the Roman baths, travertine deposits preserved in water pipes and pools also show biological-induced precipitation. These are microbially crusts with shrub crystals, bush crystals and stromatolite features due to microbial activities.References:Della Porta, G., Capezzuoli, E., De Bernardo, A., 2017, Marine and Petroleum Geology, 87Gandin, A., Capezzuoli, E., 2014, Sedimentology, 61Guo, L., Riding, R., 1998, Sedimentology, 45Kele, S., Özkul M., Fóizis I., Gökgöz, A., Oruç Baykara, M., Cihat Alçiçek, M., Németh, T., 2011, Sedimentary Geology, 238Pentecost, A., 2005, Travertine, Springer, 445 p.Riding, R., 2011, Microbialites, stromatolites, and thrombolites. In J. Reitner and V. Thiel (eds), Encyclopedia of Geobiology. Encyclopedia of Earth Science Series, Springer, Heideberg, pp. 635-654Teboul, P. A., Durlet, C., Gaucher, E. C., Virgone, A., Girard, J. P., Curie, J., B. Lopez, Camoin, G. F., 2016, Sedimentary Geology, 334Valeriani, F., Crognale, S., Protano, C., Gianfranceschi, G., Orsini, M., Vitali, M., Romano Spica, V., 2018, New Microbiologica, 41, 2Mots-clés  : Géoarchéologie, Géologie, Carbonates, Eauhttps://www.microbialites2019.com/