4. GENERAL EVOLUTION OF THE NAMUR-DINANT BASIN DURING THE DINANTIAN

The Hastarian succession displays rather similar facies throughout the Namur-Dinant Basin, reflecting a homoclinal ramp setting. Lithostratigraphic correlations are well documented. Towards the north, formations thin and stratigraphic gaps increase.

During the Ivorian, the facies pattern was more varied. Inner ramp facies cover the Namur-Condroz and southern Avesnois areas, whereas outer ramp facies are restricted to the Dinant area where a discontinuous barrier of Waulsortian buildups developed. During the upper Ivorian, the ramp evolved to a shelf and a break of slope separating the inner and outer shelf facies prograded southward and reached the Ciney-Yvoir line during the earliest Viséan. A deep-water basin with culm facies may have existed to the south, as in southwest England and southwest Ireland, but this is not exposed.

Submarine topographic irregularities produced during the Tournaisian by varying sedimentation rates including, notably, growth of Waulsortian buildups, were smoothed out by late Moliniacian times. After that time, middle and late Viséan sedimentation across the area from western Germany to southern Ireland was governed by an aggrading shelf with parasequences of wide extent.

During the Livian, open marine facies were restricted to the north, while evaporites developed in the south. This inversion of the normal pattern was probably related to an early phase of Variscan shortening.

Warnantian deposits are locally missing. In the DSA this gap only includes the uppermost Warnantian and basal Namurian (E1 goniatite Zone), whereas in the northern part of the NSA it extends stratigraphically downwards to the uppermost Livian. Silesian siliciclastic deposits overlie the Visean limestones.