Ammonite faunas from condensed Cenomanian-Turonian sections ('Tourtias') in southern Belgium and northern France.
Résumé
In southern Belgium (Mons Basin and Tournai region) and northern France (area between Lille, Valenciennes and Maubeuge), condensed sequences have been referred to as 'tourtias' since the start of the nineteenth century. These levels correspond to a succession of trangressive systems tracts and generally appear as dark green, glauconitic and microconglomeratic facies. They are distributed all along the base of the more important transgressive systems tracts of the Cenomanian and basal Turonian from the Boulonnais (northwest France) to the Mons Basin (southern Belgium), through the Artois and Douaisis. Their age can now be determined more accurately by identification of their ammonite content, as housed in museums such as the Institut royal des Sciences naturelles de Belgique (IRScNB, Brussels) and the Musée d'Histoire naturelle de Lille (MHNL). Here material from the IRScNB collections is described, illustrated and discussed; specimens contained in the MHNL collections were described in a previous paper.