Origin and evolution of the genera Lonsdaleia and Actinocyathus:Insights for the Mississippian palaeogeography from the western Palaeotethys

Representatives of the subfamily Lonsdaleiinae Chapman,1893 are common in the Mississippian of the western Palaeotethys.A general analysis of the origin,distribution and evolution of that subfamily has been undertaken.The most probable hypothesis for the origin of the genus Lonsdaleia McCoy,1849 is to acquire colonialism via the genus Axophyllum Milne Edwards and Haime,1851.Actinocyathus d'Orbigny,1849 would be a descendant of Lonsdaleia by increasing integration in the colonies.The first occurrences of Lonsdaleia have been recorded in the lower Visean from northern Britain and northern Tianshan Mountains of northwestern China,but the diversification and migration to the whole Palaeotethys only happened in the late Visean.Three hypotheses are proposed on that matter.The Serpukhovian was also a period of migrations and diversification for these genera.Both Lonsdaleia and Actinocyathus have been recorded in Bashkirian refuges,the Sverdrup Basin in northern Laurasia and the Tindouf Basin in northern Africa,respectively.The division of the western Palaeotethys into six subprovinces based on the distribution of corals is proposed.

Uneven Distribution of Pseudotormentus De Wever et Caridroit(Radiolaria,Protozoa):Provincialism of a Permian Planktonic Microorganism

The Permian planktonic distribution is not well known,in contrast to other fossil distributions of nekton and benthos.Radiolaria are representative microfossils of plankton in the Permian palaeocean.This study compares both correlated radiolarian occurrences（Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston） in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China.Pseudotormentus distributions are concentrated in the Panthalassa,whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys.The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins,indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys.In other words,this study infers the provincialism of Permian planktonic microorganisms.The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current.

Cambrian-early Ordovician volcanism across the South Armorican and Occitan domains of the Variscan Belt in France:Continental break-up and rifting of the northern Gondwana margin

The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Camhrian-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： （I） 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 conti- nental 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 fore- casted the South Armorican-Medio-European Ocean as a part of the Palaeotethys Ocean.