Impact of faulting in siliciclastics: a case study in a turbidite succession

Turbidite successions are commonly composed of alternating layers of various thickness and grain size, forming multilayers with contrasting mechanical properties. The alternation of sandstone and mudstone layers is responsible for the concurrent occurrence of brittle (fractures) and ductile (clay smearing) deformation. When these alternating layers are faulted, they produce corresponding fault cores which act as conduits or barriers for fluid migration. In this case study, the turbidite succession is composed of multilayers of tight sandstones, siltstones and black shales strata. They are highly fractured and affected by several sets of normal to strike-slip faults with different degrees of development (from incipient simple discontinuities with mm-offset to fault zones with tens of meters offset and well-developed fault cores and damage zones) and various stages of reactivation. Varied fault zone properties in different turbidite-lithofacies associations were examined in order to analyze the architecture of the fault zone. The damage zone is characterized by means of fracture analysis (scan lines) and modeling implementing different approaches, for instance the discrete fracture network model, the continuum model, and the channel network model. In general, the fault core is more difficult to characterize because it is normally composed of fine grain material generated by friction and wear. With laboratory analyses including thin section analysis and X-ray mCT Synchrotron microtomography, we characterized the grains of the fault core, their geometrical and morphological properties (e.g. size, shape, specific surface area), and the fluid flow properties of various fault cores along the fault plane passing through the multilayers. The three dimensional pore network of a given rock takes into account porosity, pore connectivity, and specific surface area. By using the X-ray mCT microtomography images and fracture analysis, we are able to give a quantitative analysis and characterize the micro-structural properties of rocks within the varying siliciclastic damage zones and subsequential varying fault cores and document how diverse thickness, grain size and mechanical properties of alternating beds influence the fault zone properties and architecture.