Control of tectonic setting and large-scale faults on the basin-scale distribution of deformation bands in porous sandstone (Provence, France)

From outcrops located in Provence (South-East France), we describe the distribution, the microstructures, and the petrophysical properties of deformation bands networks related to different tectonic events. In contractional setting, pervasively distributed networks of reverse-sense compactional-shear bands are observed in all the folded-sand units of the foreland, whereas localized networks of clustered reverse-sense shear bands are only observed close to a large-scale thrust. In extensional setting, networks of clustered normal-sense shear bands are generally observed adjacent to large-scale faults, although few and randomly distributed bands are also observed between these faults. Normal-sense cataclastic faults are also observed restricted to sand units, suggesting that faults can initiate in the sands in extension, which is not observed in contraction. Shear bands and faults show cataclastic microstructures of low-permeability whereas compactional-shear bands show crush microbreccia or protocataclastic microstructures of moderate permeability. This basin-scale analysis underlines the major role of tectonic settings (thrust-fault versus normal-fault andersonian-stress regime) and the influence of inherited large-scale faults on the formation of low-permeability shear bands. We also provide a geometrical analysis of the band network properties (spacing, thickness, shear/compaction ratio, degree of cataclasis, petrophysical properties) with respect to the host sand granulometry. This analysis suggests that granulometry, although less important than tectonic setting and the presence of large-scale faults, has however a non-negligible effect on the band networks geometry.