The Limagne Basin: a journey through modern and fossil microbial deposits

Abstract

The 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 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 approach the controlling processes at the origin of the mineralization involved in the formation of the microbialites and their preservation in the fossil record.

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

“…The upper limit of the water level elevation can be estimated from the maximum vertical development of the buildups, until the formation of an erosion or emersion surface, i.e. when the buildups reach the water surface (Bouton et al ., 2016a,b; Roche et al ., 2018; Vennin et al ., 2019, 2021). A similar distribution of the hemispheroids and crusts is found along the shorelines of the Bonneville and GSL phases (Fig.…”

“…2; Benson et al ., 2013b; Adams & Rhodes, 2019). This drop in lake water level was regional as it is observed in the Bonneville Basin (Oviatt, 1997; Bouton et al ., 2020; Vennin et al ., 2021) and in the Estancia Lake (New Mexico; Allen & Anderson, 2000). This decrease in water level coincided with the beginning of the warm Bølling–Allerød climatic event (Godsey et al ., 2011).…”

“…In the Great Basin, two different carbonate buildups have been described as shoreline‐tufa and spring‐associated tufa (Benson et al ., 1995; Bouton et al ., 2016a,b; Vennin et al ., 2019; DeMott et al ., 2019b). The carbonate buildup distribution is non‐random (Bouton et al ., 2016b; Roche et al ., 2018; Baskin et al ., 2021; Vennin et al ., 2021) and reflects specific climatic, geodynamic and physiographic parameters. Climate‐driven water level fluctuations may explain palaeoshoreline migrations as well as the distribution of some buildups in both sides of the Great Basin [Lahontan lacustrine system: Benson, 1994; Adams & Rhodes, 2019; Lake Bonneville and Great Salt Lake (GSL): Bouton et al ., 2016a,b; Vanden Berg, 2019; Vennin et al ., 2019].…”

“…In addition, the substrate lithology can drive the development of the carbonate buildups because firm and stable substrates have been shown to play a physical and chemical role (i.e. through ion availability) in the microbialite development in French rivers (Roche et al ., 2019) and in GSL (Bouton et al ., 2016a; Vennin et al ., 2021). The role of the substrate on the development of the buildups has not been addressed in the western Great Basin.…”

Facies distribution and depositional cycles in lacustrine and palustrine carbonates: The Lutetian–Aquitanian record in the Paris Basin

“…Outcrops and boreholes have been described in detail using the classifications of Dunham (1962) and Embry and Klovan (1971) for texture, and the commonly used terminology for non-marine facies based on the structure of specific facies such as calcretes or microbial carbonates (Platt, 1989;Platt & Wright, 1991;Alonso-Zarza & Wright, 2010a;Gierlowski-Kordesch, 2010;Alonso-Zarza et al, 2011;Roche, 2020). Classification of microbial-rich build-ups after Vennin et al (2021) is used for the description of microbial features in sedimentary facies. Facies and microfacies have been characterised based on their lithology, texture, sedimentary structures and component grains observed on macro samples and on 205 thin sections.…”