Corridors of crestal and radial faults linking salt diapirs in the Espírito Santo Basin, SE Brazil

Abstract

This work uses high-quality 3D seismic data to assess the geometry of fault families around salt diapir in SE Brazil (Espírito Santo Basin). It aims at evaluating the timings of fault growth, and suggests the generation of corridors for fluid migration linking discrete salt diapirs. Three salt diapirs, one salt ridge, and five fault families were identified based on their geometry and relative locations. Displacement-length (D-x) plots, Throw-depth (T-z) data and structural maps indicate that faults consist of multiple segments that were reactivated by dip-linkage following a preferential NE-SW direction. This style of reactivation and linkage is distinct from other sectors of the Espírito Santo Basin where the preferential mode of reactivation is by upwards vertical propagation. Reactivation of faults above a Mid-Eocene unconformity is also scarce in the study area. Conversely, two halokinetic episodes dated as Cretaceous and Paleogene are interpreted below a Mid-Eocene unconformity. This work is important as it recognises the juxtaposition of permeable strata across faults as marking the generation of fault corridors linking adjacent salt structures. In such a setting, fault modelling shows that fluid will migrate towards the shallower salt structures along the fault corridors first identified in this work.

Folding and fracturing of rocks adjacent to salt diapirs

“…For example, in the Santos Basin, radial faults that extend beyond the limit of drape folding (Coleman et al, 2018) have two dominant trends that also exist in minibasins between the diapirs, and roof strata well above regional imply some contractional deformation. A similar situation occurs in the Espírito Santo Basin (Mattos and Alves, 2018;Maunde and Alves, 2020). Third, we find no field evidence, in the form of mesoscale structures or microscopic fabrics, of the shortening required if diapirs are expanding into the minibasins.…”

“…Radial extensional faults have been observed both over the crests of buried diapirs and around diapir flanks (Fig. 4d) (e.g., Hempel, 1967;Brinkmann and Lötgers, 1968;Davison et al, 2000a;Rowan et al, 2003;Stewart, 2006;Quintà et al, 2012;Carruthers et al, 2013;Salazar et al, 2014;Harding and Huuse, 2015;Coleman et al, 2018;Mattos and Alves, 2018;Maunde and Alves, 2020). Those above the diapirs have been attributed to doming and the consequent concentric tensile stress.…”

Salt Tectonics Versus Shortening: Recognizing Pre‐Orogenic Evaporite Deformation in Salt‐Bearing Fold‐And‐Thrust Belts on the Example of the Silica Nappe (Inner Western Carpathians)

“…Although the individual fault directions and fold vergencies show significant spatial scattering, they correlate well with the geometry of the interpreted former salt structures, that is, the local strike the paleoslope (inferred from the slump fold directions) and normal faults is always parallel to the strike of the nearby salt walls, or in case of the concentric structures, the slump folds verge radially away from the diapir (Figure 10a). We therefore connect the observed early to pre‐tilt structures to the former salt structures, and interpret them as normal faulting (Carruthers et al., 2013; Mattos & Alves, 2018; Rowan et al., 2003) and slump folding (Davison et al., 2000; Poprawski et al., 2014) associated to the stretching of the updoming sedimentary cover above growing salt diapirs.…”

Resolved stress analysis, failure mode, and fault-controlled fluid conduits

“…Faults and fractures often serve as conduits for fluid in lowpermeability rock (Barton et al, 1995;Caine et al, 1996;Zoback et al, 1996;Evans et al, 1997;Sibson and Scott, 1998;Ferrill and Morris, 2003;Faulkner et al, 2010;Alves and Elliott, 2014;Mattos et al, 2016;Mattos and Alves, 2018;Roelofse et al, 2020), including self-sourced oil and gas reservoirs (Ferrill et al, 2014a(Ferrill et al, , b, 2020Gale et al, 2014) or CO 2 reservoirs (Trippetta et al, 2013;Ward et al, 2016;Miocic et al, 2020), and reservoir cap-rock seals (e.g., Petrie et al, 2014;Roelofse et al, 2019). Permeability behaviorflow pathway versus seal -can be directly related to the deformation modes along a fault, fracture, or fracture network (Carlsson and Olsson, 1979;Sibson, 1996Sibson, , 1998Sibson, , 2000Sibson, , 2003Trippetta et al, 2017;Ferrill et al, 2019a).…”

“…These trapping depth estimates indicate that the faults analyzed here formed and remained active at these depths and are not near-surface phenomena. For comparison, these depths of normal fault formation and fluid movement are analogous to active fault-controlled fluid flow based on 3D seismic interpretation in the Barents Sea (Mattos et al, 2016), North Sea (Alves and Elliot, 2014;Ward et al, 2016) and the Gulf of Mexico (Roelofse et al, 2020).…”