Three-dimensional consolidation of fine-grained sediments

Current theories of one- to three-dimensional consolidation are based on the concept of gravitational loading with concomitant expulsion of pore fluid as a result of mechanical rearrangements of particles and porosity reduction. However, the recent discovery of extensive networks of layer-bound fractures forming polygonal patterns in extremely fine grained smectitic clays and chalks suggests that current theory may not adequately explain the consolidation process in such sediments. These faults develop during shallow burial and often appear to have been active at the sediment-water interface. Radially isotropic strain suggests that the process of formation was nontectonic. Measured values of strain suggest that deformation resulted from volumetric contraction of the sediments. We argue that the formation mechanism for these fault systems is related to the colloidal properties of the constituent sediments and that, as such, stresses due to gravity may not be the only factor controlling pore-fluid expulsion during consolidation.