Numerical modelling study of mechanisms of mid‐basin salt canopy evolution and their potential applications to the Northwestern Gulf of Mexico

Abstract

Salt canopies are present in many of the worldwide large salt basins and are key players in the basins' structural evolution as well as in the development of associated hydrocarbon systems. This study employs 2D finite-element models which incorporate the dynamical interaction of viscous salt and frictional-plastic sediments in a gravity-spreading system. We investigate the general emplacement of salt canopies that form in the centre of a large, autochthonous salt basin. This is motivated by the potential application to a mid-basin canopy in the NW Gulf of Mexico (GoM) that developed in the late Eocene. Three different salt expulsion and canopy formation concepts that have been proposed in the salt-tectonic literature for the GoM are tested. Two of these mechanisms require pre-existing diapirs as precursory structures. We include their evolution in the models to assure a continuous, smooth evolution of the salt-sediment system. The most efficient canopy formation takes place under the squeezed diapir mechanism. Here, shortening of a region containing pre-existing diapirs is absorbed by the salt (the weakest part of the system), which is then expelled onto the seafloor. The expulsion rollover mechanism, which evacuates salt from beneath evolving rollover structures and expels it both laterally and to the surface, was not successfully captured by the numerical models. No rollover structures developed and only minor amounts of allochthonous salt emerged to the seafloor. The breached anticline mechanism requires substantial shortening of salt-cored, pre-weakened folds such that the salt breaches the anticlines and is expelled to the seafloor. The amount of shortening may be too large to occur in the central part of a salt basin, but may explain canopy evolution closer to the distal end of the allochthonous salt. When applying the different concepts to the northwestern GoM, none of the models adequately describes the entire system, yet the squeezed diapir mechanism captures most structural features of the Eocene paleocanopy. It is nevertheless possible that different mechanisms have acted in combination or sequentially in the northwestern GoM.

The Impact of Pre‐Salt Rift Topography on Salt Tectonics: A Discrete‐Element Modeling Approach

“…For simplicity and general applicability, we do not simulate syn‐kinematic sedimentation and assume a homogeneous overburden underlain by a salt interval with densities of, respectively, 2.3 g cm −3 and 2.16 g cm −3 . These values concur with nature and previous physical and numerical analogues (Albertz & Ings, ; Dooley et al, , ; Gemmer et al, ; Gradmann & Beaumont, ; Ings & Shimeld, ). The maximum and minimum salt thicknesses for each model are 2.1 km and 750 m respectively, due to gradual thinning of the salt across pre‐salt structural highs.…”

The influence of shortening and sedimentation on rejuvenation of salt diapirs: A new Discrete-Element Modelling approach

“…develops (Kupfer, 1968;Wagner and Jackson, 2011;Albertz and Ings, 2012;Cartwright et al, 2012;. Both densities are in agreement with previous physical and numerical analogues and natural examples (Gemmer et al, 2005;Ings and Shimmeld, 2006;Dooley et al, 2009, Albertz and Ings, 2012Gradmann and Beaumont, 2016). As both the thickness and density ratios of our models and natural prototypes are similar, stress in the elasto-plastic overburden are dynamically scaled (Weijermars et al, 1993).…”

“…The latest finite-element models (FEM), based on arbitrary Lagrangian-Eulerian formulations (Gemmer et al, 2004(Gemmer et al, , 2005Albertz and Ings, 2012;Gradmann et al, 2009;Gradmann and Beaumont, 2016) provide successful and numerically accurate results of local and regional scale salt tectonics (Fig. 1c).…”

“…For simplicity, an homogeneous overburden is assumed, with density of 2300 kg m -3 , representative of sediments not heavily compacted, and salt density of 2160 kg m -3 , representative of mobile salt, i.e. halite (Albertz and Ings, 2012;Gradmann and Beaumont, 2016), which is the main component of diapirs since the less mobile evaporites are preferentially left behind in the autochthonous layer as the structure…”

Topographic and Tectonic Evolution of Mountain Belts Controlled by Salt Thickness and Rift Architecture

“…Salt-rock deposits are common features of sedimentary basins, particularly the Triassic deposits of the Peri-Tethyan and Atlantic realms (Soto et al, 2017). Their physical properties offer a mechanical decoupling level, facilitate heat conduction, and result in complex geometries in rift basin deposits (Brun & Fort, 2011;Gradmann & Beaumont, 2017;Rowan, 2014) and fold-and-thrust belts (Callot et al, 2012;Granado et al, 2019;Legeay et al, 2018). In rift basins, numerical models show that mechanical decoupling due to a prerift salt layer leads to fast crustal extraction and mantle exhumation associated with the formation of sag basins and high thermal regime in overlying sediments (Duretz et al, 2019).…”