STRUCTURAL AND PALEOGEOGRAPHIC INFERENCES FROM A TEXTURE ANALYSIS OF ORDOVICIAN AND SILURIAN PELITES OF THE WEPION BOREHOLE (ARDENNES, BELGIUM)

A preliminary microfabric and texture analysis of shales, siltstones a nd a slate, collected in the Ordovician and Silurian of the Wepion bor ehole (Ardennes, Belgium), enables us to comment on the structural and paleogeorgraphic significance of the Caledonian Sambre-et-Meuse massi f as part of the Variscan front. The texture image in the massif only reflects a compaction strain, which is in accordance with the poorly e volved character of the fabric, in which no clear signs of a secondary cleavage can be distinguished. The shales and siltstones seem to have evolved within a shallow structural level under diagenetic circumstan ces. In this respect the Sambre-et-Meuse massif forms an exception wit h regard to the other Caledonian basement massifs in the Variscan fold -and-thrust belt in Belgium, which are all characterised by the develo pment of a slaty cleavage in low-grade metamorphic circumstances. Such a secondary cleavage also occurs at the bottom of the Wepion borehole in the Brabant basement.