Black shale, grey shale, fossils and glaciers: Anatomy of the Upper Ordovician–Silurian succession in the Tazzeka Massif of eastern Morocco
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Ordovician conodont collections from several Argentinian basins including the Eastern Cordillera, Famatina and Precordillera allow recognition of a group of conodonts that comprise a new genus here named Condorodus n. gen. Species of this genus have an apparatus composed of six elements recovered so far: Pa, Pb, Sb1, Sb2, Sc and Sd. The differences mainly between the P elements support recognizing three species, from the older to younger: C. diablensis n. gen., n. sp., C. gracielae n. gen., n. sp. and C. chilcaensis n. gen., n. sp., that appeared in the upper Floian (Lower Ordovician) and vanished in middle Darriwilian time (Middle Ordovician). The Eastern Cordillera is here assumed as the place of origin of the Condorodus n. gen. lineage during the late Floian, and then this genus dispersed through the western margin of Gondwana, reaching the Precordillera in the early Darriwilian, from there it could have dispersed to different regions of Gondwana, Perigondwana and Laurentia during the late Darriwilian, and probably give rise to conodont apparatuses of similar morphology in the Late Ordovician.
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Panderodus nogamii LEE, (formerly Scolopodus nogamii), first described from North Korea, occurs also in the Lower Ordovician of Thailand, Malaysia, North and South China, Australia and Argentina. It ranged through the Middle and early Upper Ordovician and was restricted to shallow water carbonates in tropical to subtropical palaeolatitudes of Greater Gondwana. Its distribution is similar to that of the Ordovician gastropod Peelerophon oehlerti and the Ordovician trilobite Asaphopsoides sp.
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The family Harknessellidae Bancroft, 1928 (Orthida, Dalmanellidina) was designed to embrace an assemblage of species referred previously to Harknessella Reed, 1917, and included five genera known mainly from the Middle and Upper Ordovician of England.Herein, we suggest reassigning to this family the genus Cacemia Mitchell, 1974, widespread in the middle Darriwilian (upper Middle Ordovician) of the Iberian and Armorican massifs.Since its designation, Cacemia was placed among the dalmanellidin heterorthids, in spite of its strongly mucronate hinge line, which is totally unknown within this Mediterranean family.A new harknessellid has been identified from the upper Darriwilian beds of the Central Iberian Zone (Central Spain): Isabelella fascicostellata Reyes-Abril & Villas gen.et sp.nov.It is similar to Horderleyella Bancroft, 1928 for its coarsely fascicostellate radial ornamentation and obtuse cardinal angles, although its convexoplane to convexoconcave profile allows discrimination from the typically dorsibiconvex Horderleyella.A phylogenetic analysis of the family places both Cacemia and Isabelella in basal positions of their clades, which fits with their early stratigraphic record.Based on our study, the family Harknessellidae appears to have originated in the high latitude Mediterranean margins of Gondwana during pre-Darriwilian times, before the detachment of Avalonia from Gondwana.The family reached its highest diversification in Avalonia throughout the Late Ordovician, keeping connections with the Mediterranean and Proto-Andean margins of Gondwana, as well as with the mid-latitude palaeocontinents of Baltica and South China.
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Late Ordovician-early Silurian chitinozoans from the Upper Member of the Salar del Rincón Formation of northwestern Argentina are described.The study area belongs to the Central Andean Basin situated on the western Gondwana margin during the Early Palaeozoic.Chitinozoan assemblages correlate with those from Northern Gondwana, where the effects of the glacial and postglacial events that occurred around the Ordovician-Silurian boundary, are quite welldocumented.The recovered chitinozoan associations from the upper part of the Salar del Rincón Formation record the uppermost Ordovician-lowest Silurian deposits representing the postglacial stage of the late Hirnantian glaciation.Similar strata are usually absent in other parts of the Central Andean Basin.Tasmanites tzadiaensis is recovered for the first time outside of the northeast of Africa, supporting the northern Gondwana affinities.Associated land-derived components indicate a nearshore environment with terrestrial input.The other associated palynomorphs support the latest Hirnantian-earliest Rhuddanian postglacial stage correlation, as well.The ranges of several Late Ordovicianearly Silurian Spinachitina and Cyathochitina species are discussed in terms of the Ordovician-Silurian boundary.Five new species are formally described: Spinachitina titae sp.
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Abstract The Ordovician successions of France and neighbouring areas of Belgium and Germany are reviewed and correlated based on international chronostratigraphic and regional biostratigraphic charts. The same three megasequences related to the rift, drift and docking of Avalonia with Baltica can be tracked in Belgium and neighbouring areas (Brabant Massif and Ardenne inliers), western (Rhenish Massif) and northeastern Germany (Rügen). The remaining investigated areas were part of Gondwana in the Ordovician. The Armorican Massif shares with the Iberian Peninsula a Furongian–Early Ordovician gap (Toledanian or Norman gap), and a continuous Mid–Late Ordovician shelf sedimentation. The Occitan Domain (Montagne Noire and Mouthoumet massifs), eastern Pyrenees and northwestern Corsica share with southwestern Sardinia continuous shelf sedimentation in the Early Ordovician, and a Mid Ordovician ‘Sardic gap’. In the Ordovician, the Maures Massif probably belonged to the same Sardo-Occitan domain. The Vosges and Schwarzwald massifs display comparable, poorly preserved Ordovician successions, suggesting affinities with the Teplá-Barrandian and/or Moldanubian zones of Central Europe.
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Abstract: Lower Ordovician faunas of Bohemia (Perunica), Baltica and North China include the oldest known representatives of the Order Craniida, but otherwise in Gondwana and associated terranes, the record of craniides is sparse. Pseudocrania insperata sp. nov. from the Lashkarak Formation of the Eastern Alborz Mountains is the first and as yet only record of the occurrence of craniides in the Middle Ordovician (Darriwilian) of Iran and temperate to high latitude peri‐Gondwana. Pseudocrania was known hitherto only from the Middle Ordovician of Baltoscandia and the Chu‐Ili terrane of Kazakhstan.
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The last two decades have seen the publication of a large number of papers dealing with Palaeozoic acritarchs including many devoted to the description of Ordovician assemblages. It has become clear that, these microfossils have considerable potential for correlation and that they are frequently recovered From sequences otherwise devoid of fossil material. In Britain, acritarchs have been described in detail from the Cambrian (Potter 1974 M. S.); Tremadoc (Rasul 1971 M. S., 1974, 1977a, l977b) and from the Silurian (Lister 1966 M. S., 1970; Hill 1974 M. S.) Until the recent work of Booth (l979 M. S.) dealing with Arenig-Llanvirn assemblages, no detailed systematic investigation of British Ordovician acritarchs had been attempted. The primary objective of the present study is to provide a comprehensive description of acritarchs from the Middle and Upper Ordovician of Britain, with particular emphasis on the type-areas of the Llandeilo and Caradoc. In conjunction with the work of Booth it is hoped that this account will go some way towards providing a biostratigraphical framework which will facilitate the use of these microfossils for the purposes of correlation in the Ordovician.
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