Modeling the interaction between presalt seamounts and gravitational failure in salt-bearing passive margins: The Messinian case in the northwestern Mediterranean Basin

Abstract

The northwest Mediterranean Basin includes a thick Messinian salt sequence composed of three evaporitic units. From these, the intermediate unit, which is dominantly composed of halite, acted as a gravitational detachment favoring the downslope failure of the overlying sediments in a thin-skinned deformation regime. As a result, the structure of the margin is characterized by an upper extensional domain with basinward-dipping listric normal faults and a lower contractional domain that accommodates upslope extension by folding, salt inflation, or diapir squeezing. Lower to middle Miocene volcanic seamounts (presalt reliefs) located at the upper extensional domain locally disrupted the evaporitic units and produced salt flow perturbations. They acted as passive buttresses during the gravitational failure modifying the structural zonation of the margin. Using an experimental approach (sandbox models), we analyze the role played by seamounts during the kinematic evolution of passive margins and how they alter salt flow and suprasalt deformation during gravitational gliding. The experiments found that the seamounts locally interrupt the structural zonation of the margin because they hindered downdip salt flow during early deformation. Seamounts initially compartmentalize the margin architecture, resulting in the development of two gravitational subsystems with two extensional/contractional pairs that are subsequently reconnected when the accumulation of salt analog upslope of the relief is enough to overthrust it. From this point onward, the cover is passively translated downslope as a regional system. The changes in the viscous layer flow velocity related to the dip differences between the flanks and edges of the seamount determine the kinematic evolution of this system. Our experiments also provide geometric constraints to consider during interpretation of these structures, which are commonly poorly imaged in seismic data.

Obstructed minibasins on a salt‐detached slope: An example from above the Sigsbee canopy, northern Gulf of Mexico

“…The slope is thus partitioned into many extensional–contractional gravitational sub‐systems (or “flow cells”) developed between the obstructions, many of which only extend for 10–15 km along‐strike. This contrasts markedly with examples from the Liguro‐Provençal Basin (Ferrer et al, ) and the Nile Deep Sea Fan (Loncke et al, ), in which the base‐of‐salt has only a few major obstructions (in these cases, volcanic seamounts). These slope systems are partitioned into fewer and much larger‐scale extensional–contractional gravitational sub‐systems.…”

“…A population of minibasins have subsided or are actively subsiding into, and have translated downslope above, the extremely rugose base of the salt canopy. This structural setting differs from the salt‐detached slopes described in prior related studies in three key ways (e.g., Dooley et al, ; Dooley & Hudec, ; Ferrer et al, ; Gaullier et al, ; Granado et al, ; Loncke et al, ). First, rather than having a prekinematic supra‐canopy interval of fairly uniform thickness, the supra‐canopy is instead composed of minibasins of variable thickness.…”

“…In contrast, when the obstruction is defined by positive relief, such as an isolated base‐of‐salt high (this study) or a volcanic seamount (Ferrer et al, ; Loncke et al, ), it is possible that the translating supra‐salt may deform so that the obstruction may be fully or partly overcome (e.g., Figure b). Alternatively, under some circumstances salt may inflate to allow sediments to rise and translate across obstructions (e.g., Dooley et al, , ; Ferrer et al, ). We therefore suggest that negative relief is more likely to be a permanent obstruction than positive relief if a minibasin subsides deeply into it.…”

“…First, if a base‐of‐salt high fully protrudes above the salt at the onset of gliding, it may block downslope flow of salt and its overburden. This may partition the salt‐detached slope system into extensional–contractional sub‐systems (Figure b) (e.g., Ferrer, Gratacós, Roca, & Muñoz, ; Loncke, Gaullier, Mascle, Vendeville, & Camera, ;). Second, localized zones of contraction and extension can occur anywhere on a slope where salt and an overburden are gliding downslope above base‐of‐salt relief (Figure b) (e.g., Cobbold & Szatmari, ; Gaullier, Brun, Gue'Rin, & Lecanu, ; Dooley & Hudec, ; Dooley, Hudec, Carruthers, Jackson, & Luo, ; Dooley, Hudec, Pichel, & Jackson, ; Pichel, Finch, & Gawthorpe, ).…”

“…Note the simple extension–translation–contraction structural zonation (modified from Rowan et al, ). (b) Sketch of a physical model (modified from Ferrer et al, ) showing the structural styles developed when a mid‐slope seamount fully protrudes above top salt at the onset of gliding. Note how the slope system is partitioned into two extensional–contractional subsystems either side of the seamount.…”