2. GEOLOGICAL AND PALEOGEOGRAPHICAL SETTING
The Dinantian Subsystem of southern Belgium and southwestern England lies in the northwestern part of the Rheno-Hercynian Fold Belt. In southern Belgium, outcrops are distributed on both sides of the Midi-Eifel fault zone and occur in two main structural units (Fig. 2A). From north to south these are: (1) the Brabant Parautochthon of Hance et al. (1999) and Mansy, et al. (1999), also formerly known as the Namur Synclinorium, (2) the Ardenne Allochthon of the same authors. These structural units were part of the Namur-Dinant Basin during the time of deposition. The following sedimentation areas (Fig. 2B) can be recognized (Poty, 1997; Hance et al., 2001):
- The Hainaut sedimentation area (HSA) (“Auge Hennuyère” of Paproth et al., 1983) was an area in which subsidence allowed accumulation of about 2500 m of Dinantian rocks, including several thick evaporitic intercalations (Groessens et al., 1982, Rouchy et al., 1993).
- The Namur sedimentation area (NSA) displays an incomplete stratigraphic succession characterized by proximal facies. The total thickness increases locally from south to north due to tectonic tilting in the eastern part of the area (Poty, 1997). The Dinantian succession of the Boulogne area (northern France) is similar (Hoyez, 1971; Poty, 1994).
- The Condroz sedimentation area (CSA) also exposes proximal facies with stratigraphic gaps in the east and a more complete succession to the west.
- The Dinant sedimentation area (DSA) (“Auge dinantaise” of Paproth et al., 1983) was strongly influenced by the development of thick Waulsortian buildups which formed a discontinuous barrier, during the Late Tournaisian. Relatively deep water sedimentation occurred in the depression lying between the transition to the inner shelf to the north and the Waulsortian buildups to the south.
- The Visé-Maastricht sedimentation area (VSA) was of local extent and suffered block faulting during Devono-Carboniferous. It was connected with the NSA during the Upper Devonian and Tournaisian and evolved to a graben which was open to the Campine Basin during the Viséan but separated from the NSA by the Booze – Val-Dieu ridge (Poty, 1997). The Dinantian of this area outcrops only in the vicinity of Visé where the succession includes numerous stratigraphic gaps.
- The southern Avesnois sedimentation area (ASA), northern France, of which the eastern extent is unknown, displays facies similar to those in the CSA. The northern Avesnois, where Dinant-type facies occur, belongs to the Dinant sedimentation area.
After the late Devonian regression, the depositional setting was that of a carbonate platform which evolved from a ramp in the early Tournaisian to a rimmed shelf during the early Viséan and then to a regionally extensive shelf during the middle and late Viséan (Hance et al., 2001). The shoreline was situated along the southern border of the Brabant emergent area.
