Karst and Underground Landscapes in the Cretaceous Chalk and Calcarenite of the Belgian-Dutch Border—The Montagne Saint-Pierre

The eastern part of the Hesbaye plateau, which extends into the Dutch Limburg, was excavated by many underground quarries that mainly exploited the Cretaceous chalk of the Maastrichtian. In this area, the Meuse and its tributaries cut into the shallow dipping formations. Thus, entries of quarries usually are on hillsides. Most galleries sink horizontally along calcarenite layers, a coarse chalk also called «Tuffeau of Maastricht». The dimensions and extensions of these networks create real underground landscapes. These galleries intersect thousands of karst features and allow a privileged observation in three dimensions. These karst phenomena have dual characteristics: they mainly grow in a very porous lithology and outside fractures, so a context unfavourable to, a priori, a necessary concentrated weathering. Once dewatered, they cease to function, thus fossilizing a karst system in one of the rarely seen early genetic phases.