A structural study in the Belgian Ardennes with sections constructed using computer based methods

Abstract

A 50 km2 area in the eastern part of the Hercynian Dinant synclinorium of the Belgian Ardennes containing sandstones, carbonates and shales is macroscopically folded and cut by several faults. Using numerical procedures the area was divided into five domains within which the folding is statistically cylindrical. The domains were examined with the aid of structural cross-sections. Each section was .constructed using a computer-plot showing the positions of outcrops projected parallel to the fold-axis onto the plane of section, together with the traces of bedding. A composite plot was obtained for all five domains by first rotating four domains separately so that their fold-axes became parallel to the fold-axis in the fifth domain. Such rotations, which affect the coordinates of outcrops as well as the direction cosines of bedding-poles, can be accomplished by matrix multiplication. Sections constructed in this way, particularly the composite section, display the structure to considerable depths. The competent rock-units within the map area have been deformed into rounded parallel folds. The intervening incompetent units appear to be zones of disharmony especially in the south. Several southdipping listric thrust-faults can be discerned in the sections.