Pressure solution-fracturing interactions in weakly cohesive carbonate sediments and rocks: Example of the synsedimentary deformation of the Campanian chalk from the Mons Basin (Belgium)

This paper documents the pressure solution-fracturing interactions in weakly cohesive carbonate sediments and rocks by studying the synsedimentary deformation of the Campanian chalk from the Mons Basin (Belgium). The present work shows that the development of a normal fault in a near-surface marine environment can promote significant mass transfers and volume changes in weakly cohesive micritic carbonate materials. The deformation corresponds to a mass redistribution from the deformed zones adjacent to the fault plane towards the outermost deformed zones. These mass transfers result from a faster return of the interstitial fluid pressure to an initial state within the outermost deformed zones. The deformation is rapidly controlled by the volume gains caused by the diffused rupture of grain contacts inside the outermost deformed zones and not by fracturing. Within the deformed zones adjacent to the fault plane, the mass losses and the related chemical compaction lead to a decrease in reservoir qualities of the material and the growth of a permeability barrier that rapidly restricts the flow of interstitial fluids towards the active fractures. Within the outermost deformed zones, the transport properties and the reservoir qualities of the material are maintained or increased.