Structural and paleogeographic inferences from a texture analysis of Ordovician and Silurian pelites of the Wepion borehole (Ardennes, Belgium)

Abstract

A preliminary microfabric and texture analysis of shales, siltstones and a slate, collected in the Ordovician and Silurian of the Wépion borehole (Ardennes, Belgium), enables us to comment on the structural and paleogeographic significance of the Caledonian Sambre-et-Meuse massif as part of the Variscan front. The texture image in the massif only reflects a compaction strain, which is in accordance with the poorly evolved 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 circumstances. In this respect the Sambre-et-Meuse massif forms an exception with regard to the other Caledonian basement massifs in the Variscan fold-and-thrust belt in Belgium, which are all characterised by the development of a slaty cleavage in low-grade metamorphic circumstances. Such a secondary cleavage also occurs at the bottom of the Wépion borehole in the Brabant basement.