The Ordovician of France and neighbouring areas of Belgium and Germany

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 compa-rable, poorly preserved Ordovician successions, suggesting affinities with the Teplá-Barrandian and/or Molda-nubian zones of Central Europe.This paper is a contribution to the International Geoscience Programme (IGCP) projects 653 "The onset of the Great Ordovician Biodiversification Event" and 735 “Rocks and the Rise of Ordovician Life: Filling knowledge gaps in the Early Palaeozoic Biodiversification". The authors are particularly grateful to Annalisa Ferretti, David A.T. Harper and Petr Kraft for their careful and constructive reviews, comments and suggestions, which greatly improved the quality and relevance of the paper

First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician stages

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity

Field guide to the geology of the Brabant Massif: the outcrops of the Dyle and Senne Basins

This field guide will provide a good insight into the Lower Palaeozoic geology of the Dyle (first day) and Senne (second day) basin areas, which are among the most important and extensive outcropping zones of the Brabant Massif. Fifteen selected outcrops are visited. They cover all the stratigraphic range observed in the Brabant Massif from the Lower Cambrian (Blanmont Formation) to the upper Silurian (Ronquières Formation) and also the Brabantian unconformity. An up-to-date geological introduction syntheizes the most recent publications and the results of the recent 1/25,000 scale mapping of the Brabant. In each stop, a detailed description is provided of the location, stratigraphy, lithology and structural architecture, followed by interpretations. The observations and their implications are placed in the broader context of the Cambrian to Devonian odyssey of the Brabant Massif within the wandering history of the Avalonia microplate

Stratigraphy of the Lower Palaeozoic of the Brabant Massif, Belgium, part II : the Middle Ordovician to lowest Silurian of the Rebecq Group

Multidisciplinary researches in the last 25 years and recent geological mapping of the Brabant Massif have completely changed our knowledge about one of the most poorly known parts of Belgian geology. The sedimentary succession is now surprisingly complete compared to what was written in the literature before the 1970s. It ranges in age from the lower Cambrian to the top of the Silurian, and is very thick (>13 km). This highlights the need to produce an up-to-date stratigraphy. In this second part about the Middle Ordovician to lowest Silurian, we describe in detail the formations, which are combined into a new group, how the description of the units evolved through time, their lithology, sedimentology, boundaries and contacts, thickness, fossil content and type seCtions or most typical outcrop areas. The new Rebecq Group comprises 10 formations from the Abbaye de Villers to the Brutia formations. The sedimentation in Megasequence 2 begins in a shelf environment with the Abbaye de Villers and Tribotte formations. The Rigenee Formation marks a rapid deepening that leads to the slope and/or deeper water deposits of the Rigenee, Ittre, Bornival, Cimetiere de Grand Manil, Huet and Fauquez formations. Thereafter, an abrupt change of bathymetry marks the top of Megasequence 2 and leads to the shallow shelf deposits of the Madot and Brutia formations. The igneous activity, represented by interbedded volcanic to volcano-sedimentary rocks and magmatic intrusions, reached a peak in the Madot Formation, which forms the base of Megasequence 3. This group shows a moderately thick, between 1500 to 2000 metres, mostly siliciclastic succession. Some shelly facies in the Upper Ordovician show the rapid drift of Avalonia to low latitude and the warm Boda Event that precedes the Hirnantian glaciation. A chronostratigraphic comparison with the Central Condroz Inlier shows that the succession there is also almost complete from the Middle Ordovician (Huy Formation) to the lowermost Silurian (Bonne-Esperance Formation) and that a short stratigraphic hiatus marks the top of Megasequence 2. This comparison shows that, since the early Cambrian, the sediments of the Brabant Massif and the Condroz Inlier were deposited in the same Brabant-Condroz sedimentary Basin

La Terre en éclaté: III: Du continent à l'océan: transferts de matière

Fondation L. de Brouckèreinfo:eu-repo/semantics/publishe