Base-Salt Relief Controls on Salt-Tectonic Structural Style, São Paulo Plateau, Santos Basin, Brazil

Abstract

Base-salt relief influences salt flow, producing three-dimensionally complex strains and multiphase deformation within the salt and its overburden. Understanding how base-salt relief influences salt-related deformation is important to correctly interpret salt basin kinematics and distribution of structural domains, which have important implications to understand the development of key petroleum system elements. The São Paulo Plateau, Santos Basin, Brazil is characterized by a >2 km thick, mechanically layered Aptian salt layer deposited above prominent base-salt relief. We use 3D seismic reflection data, and physical and conceptual kinematic models to investigate how gravity-driven translation above thick salt, underlain by complex base-salt relief, generated a complex framework of salt structures and minibasins. We show that ramp-syncline basins developed above and downdip of the main pre-salt highs record c. 30 km of Late Cretaceous-Paleocene basinward translation. As salt and overburden translated downdip, salt flux variations caused by the base-salt relief resulted in non-uniform motion of the cover, and the simultaneous development of extensional and contractional structures. Contraction preferentially occurred where salt flow locally decelerated, above landward-dipping base-salt ramps and downdip of basinward-dipping ramps. Extension occurred at the top of basinward-dipping ramps and base-salt plateaus, where salt flow locally accelerated. Where the base of the salt layer was broadly flat, structures evolved primarily by load-driven passive diapirism. At the edge of or around smaller base-salt highs, salt structures were affected by plan-view rotation, shearing and divergent flow. The magnitude of translation (c. 30 km) and the style of salt-related deformation observed on the São Paulo Plateau afford an improved kinematic model for the enigmatic Albian Gap, suggesting this structure formed by a combination of basinward salt expulsion and regional extension. These observations contribute to the long-lived debate regarding the mechanisms of salt tectonics on the São Paulo Plateau, ultimately improving our general understanding of the effects of base-salt relief on salt tectonics in other basins.

Base‐salt relief controls salt‐related deformation in the Outer Kwanza Basin, offshore Angola

“…We interpret that the landward-thickening and -dipping packages described in Section 4.3 ( Figure 6) form a series of stacked 'ramp-syncline basins' (RSBs) that developed in response to the progressive downdip translation of the salt and its overburden across the major base-salt ramp located along the updip edge of the study area ( Figure 5a) (Peel et al, 1998;Marton et al, 1998;Jackson et al, 2001;Jackson and Hudec, 2005;Pichel et al, 2018;Pichel et al, 2019). A RSB is defined as a "translating growth syncline that gradually moves seaward on a dipping detachment as if on a conveyor belt" by .…”

“…Previous translation estimates using RSBs used 2D seismic sections and were therefore unable to determine any syn-translation rotation; we think this is the first time this phenomenon has been quantified from a salt basin. Plan-view rotation of salt structures associated with salt flow over base-salt relief has been suggested from analysis of seismic reflection data in the Santos Basin, offshore Brazil (Pichel et al, 2019), and documented in physical models . RSB 2 overlies RSB 1 ( Figure 6), and is now located c. 11.3 km seaward from, and has rotated clockwise 12° from, its causal ramp (Figure 8f), whereas the youngest, RSB 3, is located 5.4 km seaward of the ramp and has undergone 5° of clockwise rotation (Figure 8g).…”

Salt-magma interactions influence intrusion distribution and salt tectonics in the Santos Basin, offshore Brazil

“…Salt tectonics continued throughout the Late Cretaceous and early Cenozoic as the basin-margin clastic sediments prograded south-eastwards across the salt (Fig. 1c) [Davison et al, 2012;Guerra and Underhill, 2012;Jackson et al, 2015b;Pichel et al, 2019b]. Post-Albian up-dip extension involved continuous development of salt rollers and reactive (i.e.…”

“…Intermediate translation during this period was characterised by the development of ramp-syncline basins, passive diapirs, and localized contraction and extension occurring in response to salt movement over a prominent base-salt relief (Fig. 1c) [e.g., Dooley et al, 2020;Pichel et al, 2019b;Pichel et al, 2018]. Down-dip contraction was associated with salt thickening, development of salt-cored folds, thrusts, and squeezed (active) diapirs, as well as the advancement of a salt nappe beyond the south-eastern edge of the salt basin (Fig.…”

“…suggesting salt flow and related deformation was greatest where magma was being emplaced (Figs 2-4, 7, and 11). Albian-to-Santonian salt movement above the Merluza Graben may have been instigated by (Figs 11a and b): (i) the presence of an inherited base-salt low, containing thicker, more halite-rich, and thus more mobile salt than adjacent areas [e.g., Dooley et al, 2017;Dooley et al, 2020;Pichel et al, 2019a;Pichel et al, 2019b]; and/or (ii) heat-enhanced salt flow driven by igneous activity within the Merluza Graben [Schofield et al, 2014;Underhill, 2009].…”