COMPARISON OF FOLDS IN THE CHEVLIPONT AND ABBAYE DE VILLERS FORMATIONS, NEAR THE ABBEY OF VILLERS, THYLE VALLEY, BRABANT MASSIF
Geological Survey of Belgium, Jennerstraat 13, B-1000 Brussel and U. Ghent, Krijgslaan 281-S8, B-9000 Gent.
Abstract
In a detailed structural study in the yle valley folds were studied in the Chevlipont and Abbaye deVillers formations. On the basis of cleavage/fold relationships and other criteria, the presence is demonstrated of both slump folds and tectonic folds. Apparently, a spatial relationship exists between the tectonic folds and slump folds. On the basis of the orientations of the slump folds the probable palaeoslope is determined for both formations: north-dipping for the Chevlipont Formation, south-dipping for the Abbaye de Villers Formation. This may refl ect a different basin geometry during deposition of these two formations. A structural cross-section is constructed on which a minimal thickness of 129.5 m is inferred for the Abbaye de Villers Formation. The cross-section also shows that the Abbaye deVillers Formation can be divided into a 119 m thick upper, southern part with thick, massive, S-dipping layers and a northern part of minimum 10.5 m thick, composed of thinner layers and containing numerous soft-sediment deformation features (slump folds and related features) as well as tectonic folds.