Mass transfers and volume changes related to pressure solution–fracturing interactions in carbonate rocks: Example of the Oligocene deformation of the Coniacian chalk from the Omey area (Paris Basin, France)

The present contribution documents the interactions between pressure solution and fracturing in carbonate rocks by studying the mass and volume changes caused by the Oligocene deformation of the Coniacian chalk from the Omey area. The isocon method allowed to establish that the decreases in interstitial fluid pressure resulting from the development of one normal fault and related tension gashes within a 11.4 m wide zone induced mass and volume changes within a 30.2 ± 3.5 m wide zone. In the hangingwall as well as in the footwall, the deformed zones adjacent to the fault plane exhibit mass gains (up to 58%) while the outermost deformed zones show mass losses (up to 36%). The pressure solution–fracturing interactions caused a mass redistribution from the most porous zones (outermost deformed zones) to the least porous zones (deformed zones adjacent to the fault plane) linked to differences in stress–strain energy of grain aggregates. The mass transfers strongly controlled the volume changes. Chemical compaction occurred only within the outermost deformed zones where mass losses took place in response to the reduction in solid–solid contacts. The zones affected by chemical compaction show equal mass and volume losses.