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[1] Three primary salt tectonic structural styles of the Scotian Basin are compared with plane strain finite element models in order to investigate their origin. Here, we focus on simplified model salt basins with initial rectangular cross-sectional geometries and follow their evolution in the context of tectonic and parametric thermal subsidence and under various sedimentation regimes. Structural style A, an open-ended roho system with a synkinematic wedge, is reproduced by models including deltaic progradation and seaward spreading/ gliding of sediments above a salt detachment. Structural style B, a linked salt tectonic system with landward regional normal faults and allochthonous salt sheets climbing seaward over Late Cretaceous and Paleogene strata, is shown to be a consequence of early aggradation followed by progradation. Structural style C is characterized by salt diapirs and intervening minibasins and is reproduced by models with Rayleigh-Taylor instabilities requiring compaction driven density inversions, weak sediments, and initial perturbations of the overburden-salt interface. Citation: Albertz, M., C. Beaumont, J. W. Shimeld, S. J. Ings, and S. Gradmann (2010), An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 1. Comparison of observations with geometrically simple numerical models, Tectonics, 29, TC4017, doi: 10.1029/2009TC002539.

We investigate the evolution of rifted continental margin shale tectonics using 2D finite-element models that couple sediment deformation to compaction-driven Darcy fluid flow via the effective stress. Fluid overpressures are generated in the models by a combination of mechanical compaction (grain rearrangement) and viscous compaction (grain dissolution and local reprecipitation), and lead to failure and flow of viscoplastic Bingham shale. Model results indicate that pore fluid pressures must be 90-95% of the lithostatic pressure to cause shale failure and delta destabilization. Mechanical compaction alone is insufficient to generate fluid overpressures required for failure in the models and viscous compaction is the primary source. The numerical models include delta progradation, lateral lithology variation, and flexural isostatic compensation. Seaward shale flow and associated overburden deformation results in the formation of landward regional and counter-regional fault-bounded extensional basins, a transitional domain of thickened and folded shale beneath the continental slope, and a seaward fold and thrust belt at the delta toe. The structural styles generated by the preliminary numerical models are compatible with features observed in unstable Cenozoic deltas (e.g. the Niger Delta) and provide additional insight into the fundamental relationships between deltaic sedimentation, fluid pressure generation, and margin-scale gravity spreading. doi: 10.1144/0016-76492009-052.

Salt 'withdrawal' sedimentary minibasins, common features of salt tectonic provinces, are typically subcircular or polygonal, 10-30 km in diameter, and contain as much as 10 km of sediment above evaporite that has been expelled into surrounding diapiric structures. The early development of minibasins typically is not buoyancy driven (Rayleigh-Taylor instability) because thin sediment overburden is usually less dense than salt (strictly, halite) or other evaporites. We analyze an alternative mechanism that applies in compressional regimes involving sedimentation onto salt, lateral flow and shortening of sediment and salt to form viscous pressure ridges (VPRs) (the key process). Loading by sediment ponded between VPRs provides a positive feedback that grows the pressure ridges. We show using lubrication theory and numerical models that this mechanism quantitatively solves the enigma and grows minibasins until the compacting sediment is sufficiently thick and dense for Rayleigh-Taylor instabilities to take over. doi: 10.1130/G30520.1