International audienceThe Lower Cambrian Pardailhan Formation of the Montagne Noire (Southern France) has yielded a diverse fossil assemblage including bivalved arthropods (the bradoriids Monceretia erisylvia gen. et sp. nov., Cambria danvizcainia sp. nov. and Matthoria? sp., together with Isoxys sp.) associated with trilobites, hyolithids, inarticulate brachiopods, sponge spicules, ichnofossils and chancelloriid sclerites. This assemblage provides new evidence about the biodiversity of Early Cambrian marine communities in palaeocontinentalGondwana. The bradoriids are Cambriidae, a familywith widespread distribution in offshore shelf marine environments during Early Cambrian times. The present study confirms the presence of cambriids within a subtropical latitudinal belt that encompasses Laurentia, Siberia and the Gondwanan margins from Southern France to South China. Although knowledge of the distribution of fossil cambriids is patchy, at the generic level they appear to be provincial, with Petrianna from Laurentia, Shangsiella and Auriculatella from South China, Cambria from Siberia and Gondwana (Armorica), and Monceretia gen nov. from Gondwana (Armorica). The presence of Isoxys in the Montagne-Noire confirms the cosmopolitan distribution of this genus in the Early and Middle Cambrian tropics. Cambriid bradoriids occupy a biostratigraphically narrow time interval, probably equating to part of the Atdabanian and Botomian stages of Russian terminology. Their presence in the Pardailhan Formation supports the notion of a Botomian age, determined from archaeocyathan evidence. The North American bradoriid genus Matthoria, also possibly present in the Pardailhan Formation, is reassigned to the Cambriidae

International audienceThe Cambrian–lower Ordovician volcanic units of the South Armorican and Occitan domains are analysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Cambrian–Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases: (1) basal Cambrian rhyolites, (2) upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, (3) upper lower–middle Cambrian continental tholeiites, (4) Tremadocian rhyolites, and (5) upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic continental rift is termed the “Tremadocian Tectonic Belt” underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that forecasted the South Armorican–Medio-European Ocean as a part of the Palaeotethys Ocean

A carbonate bed of the Pardailhan Formation, early Cambrian, southern Montagne Noire (southern France), provided microfossils such as Hyolithellus sp., Torellella cf. mutila and Torellella sp. along with numerous disarticulated pieces of composite skeletons such as valves of the brachiopod Eoobolus priscus and of the bradoriid Monceretia erisylvia, and chancelloriid sclerites (Chancelloria sp.). The assemblage also furnished a rich set of sclerites from the tommotiid Kelanella altaica. Five morphological variations of the latter have been identified. The presence of concentric ribs formed by distal inflation of selected shell laminae in Kelanella supports its assignment to the camenellans. More particularly, the presence of transverse structures within the internal cavity (septa) of Kelanella suggests a close relationship with the Lapworthellidae. However, the latter differ from Kelanella by the continuous morphological variation along their scleritome which is also composed of simple conical elements with uniform ornamentation. Several forms of Kelanella are similar to mitral and sellate sclerites of Camenella, whereas some other forms are comparable to Kennardia. The new material suggests that Kelanella occupies a transitional position between Lapworthellidae and the grouping of Tommotiidae and Kennardiidae. Such a phylogenetic position also implies that the number of sclerite morphotypes tends to decrease within the camenellan scleritome during evolution.

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The Ibero-Armorican Arc is the main Variscan macrostructure inSWEurope. Its branches preserve the Cambrian record of a continuous margin of West Gondwana, from its southwestern edge (West Asturian-Leonese and Cantabrian zones and their lateral continuity into the Iberian Chains) to its northeastern extension (basement of the Cenozoic Aquitaine basin, Montagne Noire, southern Cévennes, and Sardinia). These Variscan relics allow the reconstruction of a Cambrian Epoch 2 carbonate belt that developed intermittently along West Gondwana. Facies associations show that the main centres of carbonate productivity were nucleated in ooidal and sand shoals, together with microbial and microbial- archaeocyathan reefs, developed in high energy regimes under subtropical arid conditions. Outside the inner carbonate belt, carbonate production was episodic and related to deposition of kerogenous black shales and phosphogenesis in the Central Iberian Zone and northern parts of Montagne Noire and Cévennes. Development of carbonate platforms along the margin was diachronous and discontinuous, due to poleward drifting and tectonically induced drowning and flooding. Biogeographic connection with similar subtropical carbonate platforms from East Gondwana (mainly South China) favoured the migration of equatorial and subtropical trilobite genera, such as <i>Dolerolenus</i>, <i>Eoredlichia</i>, <i>Metaredlichia</i>, <i>Protolenus</i>, <i>Redlichia</i>, and <i>Sardaspis</i>