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Carcassonne, France

Javier Alvaro J.,Complutense University of Madrid | Colmenar J.,Copenhagen University | Monceret E.,18 rue des Pins | Pouclet A.,3 rue des foulques | Vizcaino D.,7 Jean Baptiste Chardin
Tectonophysics | Year: 2016

Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing.The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances. © 2015 Elsevier B.V.

Alvaro J.J.,CSIC - National Institute of Aerospace Technology | Bauluz B.,University of Zaragoza | Clausen S.,Lille University of Science and Technology | Devaere L.,Lille University of Science and Technology | And 3 more authors.
Stratigraphy | Year: 2014

The northern Montagne Noire possesses one of the most complete Cambrian-Lower Ordovician successions of West Gondwana. The strata are poorly fossiliferous, metamorphized and disturbed by Variscan tectonism, and their stratigraphic nomenclature dramatically multiplied by the designation of numerous informal units exclusively identifiable in their ownVariscan thrust slices and nappes. This paper presents an updated revision of lithostratigraphic units and volcanic complexes. Special attention is given to crosscutting relationships of the latter and the setting and age of fossiliferous phosphorites, such as the Watsonella crosbyi-bearing phosphatic limestones of the Marcou Formation. This mollusc is key to defining in the next future the Global Standard Cambrian (Terreneuvian) Stage1/Stage2 boundary. The absence of Cadomian tectono-thermal events is documented by meso-and microstructural and metamorphic analyses.

Pouclet A.,3 rue des foulques | Alvaro J.J.,Complutense University of Madrid | Bardintzeff J.-M.,University Paris - Sud | Imaz A.G.,University of Zaragoza | And 2 more authors.
Geoscience Frontiers | Year: 2016

The 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. © 2016 China University of Geosciences (Beijing) and Peking University.

Alvaro J.J.,CSIC - National Institute of Aerospace Technology | Zamora S.,Natural History Museum in London | Vizcaino D.,7 Jean Baptiste Chardin | Ahlberg P.,Lund University
Geological Magazine | Year: 2013

In the carbonate-siliciclastic strata of West Gondwana (e.g. in the Montagne Noire, France), the aftermath of the mid Languedocian (mid Cambrian) regression is characterized by a late Languedocian major turnover of trilobite families and a Furongian-early Tremadocian radiation related to the stepwise immigration of trilobite invaders from East Gondwana under persistent transgressive conditions. The scarcity of upper Languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the Iberian Chains (Spain), where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions. These have yielded the trilobites Peronopsis cf. insignis, Oidalagnostus trispinifer, Proampyx difformis (= Proampyx aculeatus), Bailiaspis? glabrata (= Holocephalina agrauloides, by ontogeny), Holasaphus cf. centropyge and a paradoxidid gen. et sp. indet. Despite preservation and sampling biases, the identification of this taphonomic window in offshore clayey substrates of West Gondwana allows the recognition of a strong biogeographical link with Baltica, and the correlation of the global Guzhangian Stage and the Solenopleura? brachymetopa Zone of Scandinavia with part of the Mediterranean upper Languedocian Substage. Copyright © 2012 Cambridge University Press.

Alvaro J.J.,CSIC - National Institute of Aerospace Technology | Monceret E.,18 rue des Pins | Monceret S.,18 rue des Pins | Vizcaino D.,7 Jean Baptiste Chardin
Bulletin of Geosciences | Year: 2010

The Ibero-Armorican Arc is the main Variscan macrostructure in SW Europe. 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 Dolerolenus, Eoredlichia, Metaredlichia, Protolenus, Redlichia, and Sardaspis.

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