Carbonate mud production in lakes is driven by degradation of microbial substances.

International audienceCarbonate mud is crucial in the global carbon cycle and serves as a key sedimentary archive for paleoclimate reconstruction. Understanding the mechanisms behind its formation is crucial for explaining long-term carbon storage, including atmospheric carbon dioxide transfer to the hydrosphere and variations in mud production over geological timescales. Various mechanisms explain carbonate mud formation in both lake and marine sediments. Using bio-physicochemical methods on deep sediments of Lake Ilay, Jura, France, we propose a model of micrite formation. Our study shows that micrite mineralization occurs in sediments due to the degradation of ooze rich in exopolymeric substances throughout the sediment core’s depth. This mineralization continues as long as exopolymeric substances are present, persisting for at least 2000 years. Cryo-Scanning electron microscope imaging reveals calcite nucleation at degraded exopolymeric substance nodes, advancing with substance degradation and calcium release. These findings provide insights into fossil carbonate mud origins and formation processes

Le bassin des Limagnes : une excursion à travers les dépôts microbiens modernes et fossiles.

35 pagesInternational audienceThe Limagne Basin (Massif Central, France) originated during a major, European-scale, extensive event (European Cenozoic Rift System), which led to the formation of several rift systems in the foreland of the Alps between the Upper Eocene and Pliocene. A fluvio-lacustrine system emplaced in the basin and resulted in a mixed carbonate-siliciclastic sedimentation in which microbial and metazoan buildups occupy an important place. However, microbial deposits are not exclusive to the Cenozoic history of the Limagne Basin; nowadays, in the basin, they still form in association with thermal spring systems. A fieldtrip was carried out in the Limagne Basin as part of the Microbialites: formation, evolution and diagenesis (M-Fed) meeting (October 2019). The objective of this excursion was to assess the diversity of modern and fossil (Chattian to Aquitanian) microbial sediments and structures in three prime locations (the Jussat and Chadrat outcrops and the Grand Gandaillat quarry). A detailed description of the morphologies and fabrics of the buildups and their associated biotic components can be used to discuss the spatio-temporal distribution pattern. Different basin margin models are proposed based on the changes in the distribution, morphology and size of the microbial and metazoan-rich deposits through time. The Jussat outcrop offers novel perspectives to unravel the evolution of the lacustrine/palustrine cycles over time and to establish a long-term paleoenvironmental history of the western margin of the basin during the Aquitanian. These cycles are composed of (i) lacustrine sedimentation comprising microbial and metazoan buildups and organic matter-rich marls reflecting a period of high accommodation, and (ii) palustrine deposits made of mudstones and clayey paleosoils, indicative of a period of low accommodation. It is suggested that climatic, tectonic, volcanic and local parameters (physiography, substrate) control the deposition of the buildups in each of the different cycles. In addition, the modern microbial mats of the Sainte-Marguerite and La Poix outcrops offer an opportunity to constrain the controlling processes at the origin of the mineralization involved in the formation of the microbialites and their preservation in the fossil record.Le bassin des Limagnes (Massif Central) est issu de la mise en place d’une phase de rifting liée à la géodynamique Ouest-Eropéenne (Rift Ouest Européen) entre l’Eocène Supérieur et le Pliocène. Il représente un lieu privilégier pour étudier les bioconstructions à microbialites et métazoaires qui s’inscrivent dans une sédimentation mixte carbonate-terrigène fluvio-lacustre. Ce secteur bénéficie par ailleurs de la présence de tapis microbiens modernes. L’excursion organisée en octobre 2019, à l’occasion du colloque Microbialites: formation, evolution and diagenesis , dans cette région permet d’observer et d’approcher la diversité et la structuration de sédiments microbiens modernes et fossiles. Une description détaillée de la morphologie, des fabriques des bioconstructions chattiennes et aquitaniennes et de leurs composants biotiques, des affleurements de Jussat et Chadrat et dans la carrière de Grand Gandaillat, fournit un éclairage concernant leur organisation spatio-temporelle. Les changements de distribution, de morphologie et de taille des bioconstructions à microbialites et métazoaires à travers le temps permettent de proposer plusieurs modèles de rampe lacustre. Les cycles palustre/lacustre ont fait l’objet de publication récente, toutefois le site de Jussat offre des conditions d’affleurement exceptionnelles qui soulignent le rôle du climat et de la tectonique dans la mise en place de cette cyclicité. Ces cycles sont organisés en une succession de dépôts : (1) lacustres composés de bioconstructions à microbialites et métazoaires et de marnes riches en matière organique qui indiquent des périodes de forte accommodation et (2) de dépôts palustres boueux et argileux à paléosols soulignant des périodes de faible accommodation. Le climat, la tectonique, le volcanisme mais également des paramètres locaux tels que la physiographie des lacs et le substrat sont impliqués dans la formation des bioconstructions et leur organisation au sein des différents cycles sédimentaires. De plus, les tapis microbiens modernes de Sainte-Marguerite et de La Poix viennent offrir une opportunité de comprendre les processus de minéralisation à l’origine de la formation des microbialites et de leur préservation dans le registre fossile

Quaternary lacustrine carbonate deposits of the Great Basin, USA : impact of climate, tectonics and substrate.

International audienceThe Great Basin included several lacustrine systems that accommodated extensive carbonate buildups: the Lahontan on the western side (dating back to 48 kyr cal bp), and the Bonneville (from 30 to 11.5 kyr cal bp) and Great Salt Lake (starting 11.5 kyr cal bp) on the eastern side of the basin. The eastern lakes show a transition from freshwater to hypersaline conditions. In contrast, the western lakes do not show any significant change from the originally prevailing freshwater conditions. Mapping of the carbonate buildups in the different lakes settings enables a comparison of a biotic versus an abiotic composition of the carbonate buildups, their morphologies and their specific spatial distributions. The morphology, size and distribution of the carbonate deposits are predominantly governed by seasonal to long-term water level fluctuations, particular geomorphological heritage, fault-induced processes, groundwater seepage and substrates. All of the lakes show a palaeoshoreline distribution with some buildups containing crusts, hemispheroid domes, and parts of complex domes resulting from climate-induced lake level variations. However, the presence of columns and complex domes made up of mixed biotic/abiotic carbonates in the western Great Basin is related to the influx of groundwater. Winnemucca Lake and Pyramid Lake contain bigger buildups than the ones observed in the eastern Great Basin lakes. The presence of these large size buildups and thinolites in the Lahontan lacustrine system are a consequence of local hydrological processes associated with influenced groundwater flows through specific sedimentary structures (for example, from springs and delta fronts) and faults. This contrast in the distribution, composition and size of the buildups between the two sides of the Great Basin suggests local changes in water chemistry (for example, [Ca2+]) and groundwater influxes. This work provides a novel conceptual model for the formation of abiotic and/or biotic carbonate buildups in lacustrine settings

Les Huguenots. Conjuration ; Les Huguenots. Bénédiction des poignards / Meyerbeer, comp. ; Marthe Bakkers, S (Valentine) ; Pierre d'Assy, B (St Bris) ; Boussagol, BAR (Nevers) ; Choeurs et orchestre ; Alfred Fock, dir.

Titre uniforme : Meyerbeer, Giacomo (1791-1864). Compositeur. [Les Huguenots]. ChoixEnregistrement : 08-12-1908Diffusé grâce à la générosité de Monsieur Ludovic MathiezDiffusé grâce à la générosité de Monsieur Ludovic Mathie