FAULTING AND TEXTURE CHANGES IN CHALK - AN EXAMPLE IN A GRABEN OF THE MONS BASIN (BELGIUM)

Changes in texture of chalk are in close relationship with normal fault slips : porosity loss and decrease in pore size under compaction and pressure-solution and cementation. Fluids play a major part in the rearrangement of grains or in removal and deposition of calcite. The described deformation stage, reached under low tectonic stresses, followed a dilatant state characterized by increased porosity, pore size and permeability. At this stage pressure-solution was already a significant process of deformation.