Thrust propagation through previously rifted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture, as it occurs in southern Italy. The Lagonegro units of the southern Apennines comprise a deformed pelagic basin succession showing variable stratigraphic characteristics, mainly lateral variations in both facies and thickness, interpreted to be due to a complex basin topography related to a Triassic rifting event. In contrast to previous studies, cross-section balancing and restoration indicate that the Lagonegro units exposed in the high Agri Valley area suffered relatively limited internal shortening (8 km, i.e. 35%). Early deformation of these rocks, later incorporated into a large-displacement thrust sheet, was dominated by folding around (present-day) roughly north–south-trending axes. The attainment of a regional décollement level was favoured by an early mild inversion of the basin, producing a roughly similar structural elevation of both hanging-wall and footwall successions to Mesozoic faults. Most of the contractional deformation was accommodated by buckling of the Mesozoic syn-rift strata between synsedimentary faults, which represented major mechanical interfaces. Early strain localization in the Lagonegro Basin ahead of the active thrust front was most probably mechanically controlled by a faulted crustal segment which originally lay, within the continental margin, between two massive carbonate platforms.
The process of faulting within a crustal-scale rift basin, subjected to transpression, is simulated in a series of small-scale experiments using sand and silicone layers. The structural scenario involved three stages: (1) extension; (2) sedimentation; (3) coeval shortening and strike-slip motion. A sandpack, placed above a basal silicone layer, was submitted to extension and produced a system of horst and grabens. Following the extension phase, the resulting surface topography was covered with silicone material, thus introducing a potential décollement between the pre- and post-rift sediments. These latter strata were made of sand. After sedimentation, deformation by transpression was applied using the same amount of shortening and an increasing strike-slip displacement in the different experiments. The strain partitioning increased with the amount of horizontal shear, and strike-slip faults developed at the more advanced stages of transpression. Two phases of faulting were observed before the horst and graben faults could be reactivated. The first phase was characterized by conjugate reverse faults, striking parallel to the rift-bounding faults, compatible with a stress regime in compression. A second phase of faulting was recognized at the end of transpression, leading to the generation of Riedel R-type strike-slip faults. The stress regimes responsible for the kinematics of fault generation and reactivation were interpreted using the Coulomb failure criterion and assumed a friction angle of 30° for the undisturbed sand. The reactivation of the steep normal faults in the horst and graben occurred only after a large strike-slip displacement. The general sequence of fault generation and reactivation suggested a temporal change in the stress regime. This change was caused by the permutation of the minimum and the intermediate principal stress axes and also by a progressive rotation, in the horizontal plane, of the axis of the maximum compressive stress. The spatial variation of the stress regime was also strongly controlled by the geometry of the interbedded silicone layer. A regular and undeformed post-rift silicone layer introduced a more efficient mechanical decoupling between the post-rift cover and the stretched basin. In summary, when a pre-existing graben was present, there was a succession of two distinct ‘tectonic phases’, whereas without a rift, the resulting fault kinematics reflected a single stress state and one tectonic phase.
The understanding of fluid flow in faulted sandstones is based on a wide range of techniques. These depend on the multi-method determination of petrological and structural features, porous network properties and both spatial and temporal variations and interactions of these features. The question of the multi-parameter analysis on fluid flow controlling properties is addressed for an outcrop damage zone in the hanging wall of a normal fault zone on the western border of the Upper Rhine Graben, affecting the Buntsandstein Group (Early Triassic). Diagenetic processes may alter the original pore type and geometry in fractured and faulted sandstones. Therefore, these may control the ultimate porosity and permeability of the damage zone. The classical model of evolution of hydraulic properties with distance from the major fault core is nuanced here. The hydraulic behavior of the rock media is better described by a pluriscale model including: 1) The grain scale, where the hydraulic properties are controlled by sedimentary features, the distance from the fracture, and the impact of diagenetic processes. These result in the ultimate porous network characteristics observed. 2) A larger scale, where the structural position and characteristics (density, connectivity) of the fracture corridors are strongly correlated with both geo-mechanical and hydraulic properties within the damage zone.
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