IVORIAN
Carmeuse Coordination Center, Bd de Lauzelles, 65 – B-1348 Louvain-la-Neuve, Belgium; E-mail: luc.hance@skynet.be
Service de Paléontologie animale, Université de Liège, Bâtiment B18, Allée du 6 août, Sart Tilman, B-4000 Liège; E-mail: e.poty@ulg.ac.be
Department of Geology, Trinity College, Dublin 2, Ireland; E-mail: devuyst@hotmail.com
Abstract
ABSTRACT. The Ivorian Substage is the upper division of the Tournaisian. Its base, emended in this paper, corresponds to the first appearance of the conodont Polygnathus communis carina in the Yvoir railway station section. Its top is defined by the base of the Moliniacian Substage which corresponds now to the base of the Viséan. The Ivorian is characterized by a rich and diversified conodont fauna throughout and by a diversification of the foraminifers in its upper part. It is therefore very well zoned and precisely correlated across the Franco-Belgian Basin and beyond. Its upper boundary is marked by a drastic reduction of the conodont fauna and the disappearance of selected Tournaisian foraminiferal taxa. Ivorian sedimentation reflects the evolution of the Namur-Dinant Basin from a homoclinal ramp in the early Tournaisian to a broad shelf of regional extent in the late Tournaisian. Waulsortian buildups started growing in the distal part of the ramp during early Ivorian and formed a discontinuous barrier over the southwestern part of the Dinant Sedimentation Area. Distal peri-Waulsortian facies are dominated by cherty crinoidal wacke- to packstones, thick-bedded crinoidal packtsones, grainstones and dolostones. An oolitic grainstone, the Avins Mbr of the Longpré Fm, caps the Ivorian succession in the inner shelf. Proximal peri-Waulsortian facies are cherty crinoidal wacke- to packstones and purplish blue, poorly fossiliferous wacke- to packstones.