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

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.

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The evolution of the Massif Central Rift; spatio-temporal distribution of the volcanism

BSGF - Earth Sciences Bulletin ◽

10.2113/172.2.201 ◽

2001 ◽

Vol 172 (2) ◽

pp. 201-211 ◽

Cited By ~ 66

Author(s):

Laurent Michon ◽

Olivier Merle

Keyword(s):

Central Area ◽

Temporal Distribution ◽

Rift System ◽

The South ◽

Volcanic Event ◽

Quaternary Volcanism ◽

Massif Central ◽

Lithospheric Thinning ◽

The North ◽

Magmatic Event

Abstract The Massif Central area is the largest magmatic province of the West-European Rift system. The spatial-temporal distribution of Tertiary-Quaternary volcanism in the Massif Central, France, shows that three magmatic phases can be defined, each of them characterized by different volumes and different locations. The first event, termed the pre-rift magmatic event, is very scarce and restricted to the north of the Massif Central. It is suggested that this could result from lithospheric bending of the European lithosphere ahead of the incipient Alpine chain during the Paleocene. The second event, termed the rift-related magmatic event, is located in the north of the Massif Central only and is spatially connected with zones of high crustal thinning (i.e. the Limagne graben). It immediately follows Oligocene graben formation and associated sedimentation, and is represented by more than 200 scattered monogenic edifices. This second event can be attributed to partial melting as a consequence of lithospheric thinning that affected the north of the Massif Central during the rifting event. The lack of volcanism in the south during the same period of time is probably related to the very slight lithospheric thinning during the Oligocene. The third event, termed the major magmatic event, started first in the south in the upper Miocene at about 15 Ma, well after the end of the sedimentation. It is unrelated to any extensional event. This major magmatic event reached the north of the Massif Central at about 3.5 Ma, following a pause in volcanism of about 6 Ma after the rift-related magmatic event. These two episodes of the major magmatic event are spatially and temporally associated with the two main periods of uplift, suggesting a common origin for volcanism and uplift processes. The major magmatic event can be attributed to late thermal erosion of the base of the lithosphere above a mantle diapir, as suggested by seismic tomography data. This general magmatic evolution drawn from data at the Massif Central scale may apply to the Eger graben as well, as the three magmatic events described in this study (pre-rift magmatic event, rifting event and post-Miocene volcanic event) are also reported in the literature. This suggests that a single cause should explain the formation of the entire western European rift surrounding the Alpine mountain belt.

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A Characterisation of Alpine Mesocyclone Occurrence

10.5194/wcd-2021-53 ◽

2021 ◽

Author(s):

Monika Feldmann ◽

Urs Germann ◽

Marco Gabella ◽

Alexis Berne

Keyword(s):

Temporal Distribution ◽

Radar Data ◽

Detection Algorithm ◽

Data Set ◽

Additional Information ◽

Detection And Tracking ◽

Synoptic Weather ◽

Southern Side ◽

The Alps ◽

Spatio Temporal

Abstract. This work presents a characterization of mesocyclone occurrence and frequency in the Alpine region, as observed from the Swiss operational radar network. Five years of radar data are processed with a thunderstorm detection and tracking algorithm and subsequently with a mesocyclone detection algorithm. A quality assessment of the radar domain provides additional information on the reliability of the tracking algorithms throughout the domain. The resulting data set provides the first insight into the spatio-temporal distribution of mesocyclones in the Swiss domain, with a more detailed focus on the influence of synoptic weather, diurnal cycle and terrain. Both on the northern and southern side of the Alps mesocyclonic signatures in thunderstorms are frequent. The regions with highest occurrence are predominantly the Southern Prealps and to a lesser degree the Northern Prealps. The parallels to hail research over the same region are discussed.

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Life history of three catfish species (Siluriformes: Ariidae) from southeastern Brazil

Biota Neotropica ◽

10.1590/s1676-06032012000400008 ◽

2012 ◽

Vol 12 (4) ◽

pp. 74-83 ◽

Cited By ~ 12

Author(s):

Márcia Regina Denadai ◽

Eduardo Bessa ◽

Flávia Borges Santos ◽

Wellington Silva Fernandez ◽

Fernanda Motta da Costa Santos ◽

...

Keyword(s):

Organic Matter ◽

Temporal Distribution ◽

Reproductive Period ◽

Southeastern Brazil ◽

Spatial Distributions ◽

Fish Scales ◽

Fish Bones ◽

History Of ◽

Spatio Temporal ◽

Small Overlap

This study evaluated the spatio-temporal distribution, reproduction and diet of the catfishes Genidens genidens, G. barbus and Aspistor luniscutis in Caraguatatuba Bay. Their sizes were recorded and the sex and reproductive stage identified. The abundance was compared between areas (South and North) and among months (August 2003 - October 2004). The species had different spatial distributions, allowing them to coexist. The temporal distribution reflected their tendencies to migrate in the reproductive period, as evidenced by the dominance of small immature individuals in the bay. G. genidens tended to reproduce in winter, and A. luniscutis in spring. The diet of G. genidens consisted of crustaceans, mollusks (shells), fish scales, ostracods, and bivalve siphons. G. barbus consumed a high proportion of mysids, followed by fish (bones and scales). For A. luniscutis, the diet was based on fish scales and crustaceans. High quantities of particulate organic matter were observed in the diet of all three species, as previously known for estuarine catfishes. The consumption of fish scales may reflect a lepidophagic habit. A small overlap was observed among the diets, reflecting differences in their environments as well as in the proportions of each item ingested.

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