Late Middle to Late Frasnian Atrypida, Pentamerida, and Terebratulida
Disponible en ligne sur www.sciencedirect.com Geobios 41 (2008) 493–513 http://france.elsevier.com/direct/GEOBIO/ Original article Late Middle to Late Frasnian Atrypida, Pentamerida, and Terebratulida (Brachiopoda) from the Namur–Dinant Basin (Belgium) Atrypida, Pentamerida et Terebratulida (Brachiopoda) de la partie supe´rieure du Frasnien moyen et du Frasnien terminal du Bassin de Namur-Dinant (Belgique) Bernard Mottequin a,b a Department of Geology, Trinity College, Dublin 2, Ireland b Paléontologie animale, université de Liège, bâtiment B18, 4000 Liège 1, Belgium Received 18 January 2007; accepted 17 October 2007 Available online 11 March 2008 Abstract In the Namur–Dinant Basin (Belgium), the last Atrypida and Pentamerida originate from the top of the Upper Palmatolepis rhenana Zone (Late Frasnian). Within this biozone, their representatives belong to the genera Costatrypa, Desquamatia (Desquamatia), Radiatrypa, Spinatrypa (Spinatrypa), Spinatrypina (Spinatrypina?), Spinatrypina (Exatrypa), Waiotrypa, Iowatrypa and Metabolipa. No representative of these orders occurs within the Palmatolepis linguiformis Zone. The disappearance of the last pentamerids, mostly confined to reefal ecosystems, is clearly related to the end of the edification of the carbonate mounds; it precedes shortly the atrypid one. This event, resulting from a transgressive episode, which induces a progressive and dramatic deterioration of the oxygenation conditions, takes place firstly in the most distal zones of the Namur– Dinant Basin (southern border of the Dinant Synclinorium; Lower P. rhenana Zone). It is only recorded within the Upper P. rhenana Zone in the Philippeville Anticlinorium, the Vesdre area, and the northern flank of the Dinant Synclinorium. It would seem that the terebratulids were absent during the Famennian in this basin, probably due to inappropriate facies.
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