Belgium

Abstract The Chalk in Belgium was deposited mainly during Cretaceous times. The only exception is in the Mons Basin, where chalks of early Tertiary age (Danian and Montian) occur. The formation is found in the northern part of the country, but it crops out in only two areas—near Mons in the west and near Liege in the east (Fig. 8.1). During the Cretaceous, a major transgression led to marine sedimentation over almost the entire country. The transgression was not uniform and all regions were not affected simultaneously. Cretaceous marine sedimentation, comprising calcareous and glauconitic sands and sandstones, glauconitic marls and limestones and conglom erates, began in the west of the country during Albian times. Near the city of Mons, regional transgression along a north-south line can be recognized as extending east from the sedimentation centre of the Paris Basin (Fig. 8.2). During Albian and Cenomanian times, many transgressions and regressions of the sea occurred. In the Late Cenomanian, a major advance covered the western part of the country. The sediments deposited were not chalk but green, clayey marls, the lateral equivalents of the chalky marls of the Pas de Calais. This transgression continued during Turonian times when pure chalk was deposited for the first time in the western part of Belgium. During the early Cretaceous, Cenomanian and Turonian, the northern and north-eastern parts of the country were not submerged by the Cretaceous sea.