Ramp syncline basins were identified above thick salt in the São Paulo Plateau, Santos Basin  They form by translation over a thick salt detachment with basal relief due to viscous drag and salt flux variations  They record 28-32 km of SE translation during the Late Cretaceous to Paleocene  They form by translation over basinward-dipping and landward-dipping basesalt ramps  Stratal terminations and architecture vary along-dip and strike within these

Salt is sensitive to the geometry of the substrate it flows across. We use physical models to investigate the impact of base-salt relief on deformation patterns. First, we investigate early-stage gravity gliding across base-salt relief. Salt flowing onto structural high blocks forms a zone of thickened salt and associated shortening owing to a flux mismatch. On the downdip edge of the basement high another flux mismatch generates a topographic monocline (ramp-syncline basin) with associated extensional and contractional hinges. With multiple base-salt high blocks, this structural pattern was repeated down the entire slope. Laterally discontinuous base-salt relief generated additional complexities such as major rotations of raft blocks and intervening diapirs as salt is channelled around and between base-salt relief. At the allochthonous level, regional dip, salt budget and base-salt relief influence flow patterns. Individual salt sheets spread sub-radially with streamlines skewed down the regional slope. As the canopy coalesced along allosutures, inward flow from the canopy peripheries dominated, driven by more vigorous flow from outer feeders owing to less competition for source-layer salt. Subsequent shortening returned flow patterns to grossly dip-parallel. However, salt flows fastest where it is thickest and thus chains of feeders channel rapid intracanopy flow.

This study employs a novel Discrete-Element Modelling approach to investigate the interplay of sedimentation with rejuvenation of diapirs by shortening. The inherent complexity of salt tectonics, the complications encountered when imaging structures beneath salt, and the lack of outcrop analogues, coupled with its importance to petroleum systems, make salt tectonics one of the most interesting and debated topics in basin studies. Model results successfully reproduce the geometric and dynamic behaviour of active diapirism and show the effects of sedimentation thickness, rate and timing on the generation of distinct diapir geometries, including i) salt tongues and ii) squeezed upright diapirs. Models with late sedimentation or a lower sedimentation rate relative to salt mobility show development of asymmetric diapirs with allochthonous salt tongues; whereas models with earlier sedimentation or a faster sedimentation rate generate upright squeezed diapirs. Early sedimentation at a moderate rate results in a symmetrical hour-glass shaped structure, resembling a tear-drop diapir. Results are fully reproducible and comparable with many natural examples, and include overburden deformation which is difficult to simulate using other numerical techniques. Extending this approach to different problems and basinal contexts could improve our understanding of deformation mechanisms and sediment distribution around salt structures.

Gravity‐driven salt tectonics along passive margins is commonly depicted as comprising domains of updip extension and downdip contraction linked by an intermediate, broadly undeformed zone of translation. This study expands on recently published physical models using discrete‐element modeling to demonstrate how salt‐related translation over pre‐salt rift structures produce complex deformation and distribution of structural styles in translational salt provinces. Rift geometries defined by horsts and tilted fault‐blocks generate base‐salt relief affecting salt flow, diapirism and overburden deformation. Models show how flow across pairs of tilted fault‐blocks and variably‐dipping base‐salt ramps associated with pre‐salt faults and footwalls produce abrupt flux variations that result in alternation of contractional and extensional domains. Translation over tilted fault‐blocks defined by basinward‐dipping normal faults results in wide, low amplitude inflation zones above footwalls and abrupt subsidence over steep fault‐scarps, with reactive diapirs that are squeezed and extrude salt as they move over the fault. Translation over tilted‐blocks defined by landward‐dipping faults produces narrow inflation zones over steep fault‐scarps and overall greater contraction and less diapirism. As salt and cover move downdip, structures translate over different structural domains, being inverted and/or growing asymmetrically. Our models allow, for the first time, a detailed evolution of these systems in cross‐section and demonstrate the effects of variable pre‐salt relief, salt sub‐basin connectivity, width and slope of base‐salt ramps. Results are applicable to syn‐ and post‐rift salt basins; ultimately improving understanding of the effects of base‐salt relief on salt tectonics and working as a guide for interpretation of complex salt deformation.

first recognized in the Gulf of Lyon, offshore France (e.g. Benedicto et al. 1999; 57 Sanchis and Séranne, 2000) and the Kvamshesten Basin, onshore Norway 58 (Osmundsen et al. 2000). They were initially described through conceptual (Gibbs, 59 1984) and physical models (Ellis and McClay, 1988; McClay, 1990 McClay, , 1996 McClay 60 and Scott, 1991), as forming above the hangingwall of ramp-flat extensional faults 61 whose basal detachments dip in the direction of tectonic transport. The hanging 62 wall is warped down above the ramp to create a relatively narrow basin. As the 63 hangingwall block moves, the locus of subsidence (located above the footwall 64 ramp) remains fixed in space, but its previous sediment fill is progressively moved 65 away from it, producing a characteristic asymmetric, shingled stratal unit b). 67A second type of RSB has been identified above salt-detached systems in which 68 the base of the moving unit is a salt layer ( Fig. 1c-d) (e.g. Kwanza Basin, Angola, 69 Peel et al. 1998; Marton et al. 1998; Jackson et al. 2001). Jackson and Hudec 70(2005) reviewed the processes and kinematics of RSBs on the Angolan margin 71 using highly schematized sections and 2D seismic data. These authors described 72 salt-detached RSBs as being formed by translation of sediments above a salt layer 73 with a basinward-dipping ramp at its base ( Fig. 1c-d 202In order to constrain the geometry, and to understand the 3D kinematics and 203 tectonostratigraphic evolution of RSBs, 3D seismic mapping of key surfaces within 204 the RSBs were produced to generate thickness maps of key stratigraphic intervals. 205We did not use primary well data, with the identification of key seismic stratigraphic ( Fiduk and Rowan, 2012; Guerra and Underhill, 2012; Jackson et al. 2015). Intra- 209RSB horizons were chosen based on their reflectivity and continuity. 24735% of total post-salt succession (Fig. 12a). 248The base-salt steps associated with the RSBs trend mainly NNE-NE, parallel to the 249 RSBs, although the northernmost high trends NNW and, thus, slightly oblique ( higher degree of translation and rotation of older RSB strata. 339A landward shift from abrupt to subtle transitional limits along the upper and lower 340 boundaries of the RSBs (Fig. 12b-c) is explained by an increase in the 341 aggradation/translation ratio (Ȧ/Ȧ). This is evidenced by landward steepening of 342 the depositional axial-trace in areas where the RSBs are less folded ( Fig. 7-11). (Figs. 10 and 11), typically in their uppermost sections (Fig. 12c). 362By summing the offsets between the thickest points on each isochron map in fig. 363 13, a total translation of 26.9 km was obtained for RSB 5. This, however, 364represents a minimum distance as we were not able to include isopachs of the first 365 and last onlapping intervals, due to intense faulting and folding at both their eastern estimated at 32 (+ 2) km ( Fig. 11 and 13). In many other examples, we were only 371 able to determine a minimum translation because they are l...

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 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 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. K E Y W O R D S base-salt relief, Brazil, diapirism, gravity-driven deformation, minibasins, ramp-syncline basins, salt tectonics, Santos Basin, São Paulo Plateau, translation 454 | EAGE PICHEL Et aL. 456 | EAGE PICHEL Et aL. | 457 EAGE PICHEL Et aL.FIGURE 3 Static-corrected base-salt (BoS) structure map illustrating the main base-salt highs and associated ramps in (a), and overlay of different structural domains of the SPP and location of sections presented in this study in (b). LW and BW refer to landward-and basinwarddipping base-salt ramps, respectively. The black polygon in (a) corresponds to the location of the depth base-salt structure map adapted from Alves et al. (2017) shown in (c) for comparison 458 | EAGE PICHEL Et aL. F I G U R E 4 (a) TWT top-salt structure map showing the framework of salt walls and minibasi...

Thick evaporite deposits are common in many sedimentary basins, where they can flow to form a range of salt structures (e.g. diapirs) (e.g.