2.1. INTRODUCTION
The Middle Devonian of the Ardenne was initially subdivided into Couvinian and Givetian stages. In a vote at Sigüenza (Spain) in 1979 a majority of the Devonian Subcommission was in favor of Eifelian as the name for the lower stage of the Middle Devonian. The base of the Eifelian is defined in the stratotype section of Wetteldorf in the Eifel area by the first occurrence of the conodont Polygnathus costatus partitus (Werner & Ziegler, eds, 1982). This boundary is well above the base of the Couvinian and is recognized in the upper part of the Eau Noire Fm. Because the underlaying St.-Joseph FM corresponds to the lowest part of the local Couvinian stage this formation is described here together with the Middle Devonian formations. The base of the Givetian is defined in the Global Stratotype Section and Point at Jebel Mech Irdane in the Tafilalt of Morocco and coincides with the first occurrence of the conodont Polygnathus hemiansatus (Walliser et al, 1995). This boundary is below the base of the Givet Limestone of the Ardenne as defined by Errera et al (1972) and within the lower part of the Hanonet Formation, representing the uppermost part of the Couvinian (Bultynck & Hollevoet, 1999).
Middle Devonian rocks of the Ardenne are exposed in the Dinant and Namur Synclinoria and in the Vesdre Nappe. The initial stratigraphic subdivisions of the Middle Devonian of the Ardenne were established by Gosselet (1860, 1873) and Maillieux (1912 to 1938). Recently the Middle Devonian formations of the Ardenne were described by Bultynck et al (1991) resulting from discussions within the Belgian Subcommission on Devonian Stratigraphy. The present summary description of the Middle Devonian formations is based on the latter paper.
Cross-sections of Middle Devonian formations of the Dinant Synclinorium are shown in figure 4 (southern and south-eastern border) and figure 5 (southern and northern border).
