3.2.1. Nismes Formation - NIS

Authors: Bultynck, Casier, Coen, Coen-Aubert, Godefroid, Jacobs, Loboziak, Sartenaer & Streel, 1988; Bultynck & Coen, 1999.

 

Description:The Nismes Fm is an essentially greenish shaly unit with subordinate nodules, subnodular or nodular limestone beds and some limestone lenses mainly developed in the lower and middle members (Pont d'Avignon and Sourd d'Ave). The top of the shaly upper member (La Prée) is either below a marked bedded limestone bar or a sequence with interbedded shales and limestones. The two lower members contain rich atrypid and spiriferid brachiopod faunas.

 

Stratotype: Nismes, outcrops on the northern border of the Bois du Mousti.

 

Area: Southern, central and eastern part of the Dinant Synclinorium; some parts of the northern flank of the Dinant Synclinorium and the Vesdre Nappe.

 

Thickness: between 39 and 20 m in the three former areas, between 10 and 5 m in the two latter areas.

 

Age: Apart the Pont d'Avignon Mbr in the central part of the southern flank of the Dinant Synclinorium, the Nismes Fm is of early frasnian age (Lower falsiovalis to lower part of transitans conodont Zones) based on the first occurrence of the conodont Ancyrodella rotundiloba (see Bultynck et al., 1988). The formation corresponds to a major Devonian transgressive phase and its base becomes younger from the south to the north-east and the north.