L'évènement de Kačák (Eifelien Supérieur, Dévonien Moyen) sur la plate-forme Belge et ses effets sur la paléobiodiversité des coraux rugueux

The Devonian is a period that recorded many biocrises. One of them, known as the Kačák event ranges through the Polygnathus ensensis Zone immediately before the Eifelian-Givetian boundary (Middle Devonian). This crisis has been identified in many localities worldwide, mostly in bathyal settings. The event, divided into two phases (otomari event and Kačák event s.s.), is typically marked by a turnover among pelagic faunas, especially conodonts, dacryoconarids and ammonoids. This turnover result from a transgression associated with anoxia that generally corresponds to the deposition of black shale in deep-water settings. In Belgium, the Kačák event s.s. corresponds to a time window equivalent to the deposition of the Lomme and Hanonet formations. New stratigraphic and palaeontological (rugose corals) data show that the Kačák event had a moderate to weak impact on the Belgian carbonate shelf ecosystem. The Old World Realm faunal assemblages show no significant variation in diversity across the Kačák event. Nevertheless, the remarkable and unexpected occurrence of some rugose corals typical of the East American Realm (siphonphrentids and heliophyllids) in the lower part of the Hanonet Formation helps identify the event as the latter is also marked by a short phase of cosmopolitanism of benthic fauna. This is a proposed criterion useful to recognize the Kačák event where the typical pelagic guides are missing.Le Dévonien est une période ayant enregistré de nombreuses crises biologiques. L'une d'entre elles, connue sous le nom d'événement de Kačák correspond à l’entièreté de la Zone à Polygnathus ensensis située immédiatement avant la limite Eifelien-Givetien (Dévonien Moyen). Cette crise à été identifiée dans de nombreuses localités à travers le monde, essentiellement en environnements bathyaux. Cet événement, subdivisé en 2 phases (l'événement otomari et l'événement de Kačák s.s.), est typiquement marqué par un turnover au sein des faunes pélagiques, essentiellement chez les conodontes, dacryoconarides et ammonoïdes. Ce turnover résulte d'une transgression associée à une anoxie correspondant généralement au dépôt de black shales dans les environnements profonds. En Belgique, l'événement de Kačák s.s. correspond à une fenêtre temporelle équivalente au dépôt des formations de la Lomme et d'Hanonet. De nouvelles données stratigraphiques et paléontologiques (coraux rugueux) montrent que l'événement de Kačák à eu un impact modéré à faible sur l'écosystème de la plate-forme carbonatée Belge. Les assemblages faunistiques de l'Old World Realm ne montrent pas de variations significatives de diversité au passage de l'événement de Kačák. Cependant, la remarquable et inattendue présence de quelques coraux rugueux typiques de l'East American Realm (siphonophrentides et heliophyllides) dans la partie inférieure de la Formation d'Hanonet permet l'identification de l'événement car ce dernier coincide également avec une courte phase de cosmopolitanisme au sein de la faune benthique. Ce critère utile est proposé pour l'identification de l'événement de Kačák lorsque les indicateurs typiques au sein des faunes pélagiques sont absents

Building a robust Middle Cambrian astrochronology using deep-water rhythmites and parsequences in the Marjum Formation of western North America

peer reviewe

Assessment of left atrial shape and volume in structural remodeling secondary to atrial fibrillation.

PURPOSE: Assessment of volume in relation with left atrial (LA) shape alteration before and after PV isolation. METHODS: We compared trapezoidal modification of LA using echocardiography with the ellipsoid formula (EEL: ) and CT, with both ellipsoid (CTEL: ) and truncated cone formulas (CTTR: ), in 40 patients, before and +/-3 months after AF ablation. RESULTS: A trapezoidal shape was present in 76.3% of patients. The different volume measurements were statistically correlated (r = 0.603-0.837, p < 0.001) irrespective of the formula used. After reverse remodeling, with 77.5% of patients in stable sinus rhythm, correlation coefficient for volume remained significant (p < 0.001). CONCLUSIONS: In AF, dilation of the LA is associated with a geometrical trapezoidal change in many cases. The CT truncated cone formula applies best for precise evaluation of trapezoidal shape alteration in dilated AF atria. There is a good correlation between CTTR: and echocardiography which remains a valuable estimation for volume calculation in clinical practice

The Cabrières Biota (France) provides insights into Ordovician polar ecosystems

Early Palaeozoic sites with soft-tissue preservation are predominantly found in Cambrian rocks and tend to capture past tropical and temperate ecosystems. In this study, we describe the diversity and preservation of the Cabrières Biota, a newly discovered Early Ordovician Lagerstätte from Montagne Noire, southern France. The Cabrières Biota showcases a diverse polar assemblage of both biomineralized and soft-bodied organisms predominantly preserved in iron oxides. Echinoderms are extremely scarce, while sponges and algae are abundantly represented. Non-biomineralized arthropod fragments are also preserved, along with faunal elements reminiscent of Cambrian Burgess Shale-type ecosystems, such as armoured lobopodians. The taxonomic diversity observed in the Cabrières Biota mixes Early Ordovician Lagerstätten taxa with Cambrian forms. By potentially being the closest Lagerstätte to the South Pole, the Cabrières Biota probably served as a biotic refuge amid the high-water temperatures of the Early Ordovician, and shows comparable ecological structuring to modern polar communities

The Cabrières Biota (France) provides insights into Ordovician polar ecosystems

Early Palaeozoic sites with soft-tissue preservation are predominantly found in Cambrian rocks and tend to capture past tropical and temperate ecosystems. In this study, we describe the diversity and preservation of the Cabrières Biota, a newly discovered Early Ordovician Lagerstätte from Montagne Noire, southern France. The Cabrières Biota showcases a diverse polar assemblage of both biomineralized and soft-bodied organisms predominantly preserved in iron oxides. Echinoderms are extremely scarce, while sponges and algae are abundantly represented. Non-biomineralized arthropod fragments are also preserved, along with faunal elements reminiscent of Cambrian Burgess Shale-type ecosystems, such as armoured lobopodians. The taxonomic diversity observed in the Cabrières Biota mixes Early Ordovician Lagerstätten taxa with Cambrian forms. By potentially being the closest Lagerstätte to the South Pole, the Cabrières Biota probably served as a biotic refuge amid the high-water temperatures of the Early Ordovician, and shows comparable ecological structuring to modern polar communities.</p