From downbuilding to contractional reactivation of salt-sediment systems: Insights from analog modeling

From Salt‐Bearing Rifted Margins to Fold‐And‐Thrust Belts. Insights From Analog Modeling and Northern Calcareous Alps Case Study

“…Mb1 attained as much as 50° of counterclockwise rotation around a sub‐horizontal axis (Figures 7b and 8c). Tilting was accompanied by the migration of the original position of its primary weld which is now situated in the landward flank of the minibasin (i.e., a rolled primary weld , sensu Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021). SW1 depicts a nearly vertical sigmoidal secondary weld rooted on a model salt accumulation.…”

“…Salt accumulations commonly localize deformation due to the inherent weakness of it (Weijermars et al., 1993; Vendeville & Nilsen, 1995; Letouzey et al., 1995; Rowan & Vendeville, 2006; Dooley et al., 2009; Ferrer, 2012; Duffy et al., 2018; Roma, Ferrer, et al., 2018; Roma, Vidal‐Royo, et al., 2018; Granado et al., 2021; Santolaria, Ferrer, et al., 2021, Santolaria, Granado, et al., 2021). As observed in other analog modeling programs, salt bodies represent weak discontinuities within the modeling sand package that absorb most of the horizontal contraction (e.g., Koyi, 1988; Vendeville & Nilsen, 1995; Nilsen et al., 1995; Roca et al., 2006; Rowan & Vendeville, 2006; Callot et al., 2012; Ferrer, 2012; Duffy et al., 2018, 2021; Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021; among others). All in all, our results evidence the role played by the inherited passive margin architecture and especially the distribution of the model salt: (a) thick, distal raft model salt promote decoupling of the sub‐ and supra‐salt deformation and the formation of a large‐transport, source fed‐thrust, (b) in the diapir‐minibasin province, salt‐walls localize deformation and account for most of the shortening accommodated in this area and (c) the distal model salt pinch‐out control the deformation in the foreland.…”

“…Onset of salt evacuation was triggered by pouring the first syn‐kinematic sand layer around the location of what‐would‐be the minibasin depocenters (minibasin seeding areas in Figure 2b). Sand deposited in such a way led to a localized sedimentary differential loading that triggered minibasins vertical sinking, while model salt is evacuated from below the minibasin depocenters toward flanking salt walls (e.g., Ferrer et al., 2022; Rowan & Vendeville, 2006; Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021; Warsitzka et al., 2013). Additional sand layers filled the accommodation space created by the minibasin's sinking which, in its turn, created positive feedback between sedimentary differential loading and sinking.…”

“…A 5 cm wide section along each side of the experiments was discarded to remove any possible border effects. Photographed sections were used to interpret the structural and stratigraphic architecture of the models and to generate voxels in image‐processing software to further constrain the 3D geometries of the model which allow the creation of virtual slices of the sandbox (Dooley et al., 2009; Ferrer et al., 2016; Granado et al., 2017; Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021). Section restorations (Roma, Vidal‐Royo, et al., 2018; Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021) have been used to reconstruct the pre‐shortening configuration inherited from the rifted margin stage (Models 2 and 3) and also the evolution during contraction of Model 3.…”

“…The main reasons for this are the inherent weakness of salt, the presence of pre‐shortening salt structures, and the inherited uneven stratigraphic thickness distribution related to salt‐sediment interaction (i.e., the so‐called non‐layer cake stratigraphy). Such inheritance represents a first order factor that controls deformation during contraction (Callot et al., 2012; Ferrer, 2012; Jackson et al., 2011; Moretti et al., 2013; Rowan & Vendeville, 2006; Santolaria, Ferrer, et al., 2021; Santolaria, Granado, et al., 2021). In those salt‐bearing rifted margins featuring a late syn‐rift to post‐rift salt basin, the salt‐sediment system evolves by gravitational collapse and by differential loading of sediments leading to salt evacuation and creation of accommodation space (e.g., Brun & Fort, 2004, 2011; Ge et al., 1997; Ge et al., 2020; Granado et al., 2016; Jackson & Hudec, 2017; Peel, 2014; Pichel et al., 2022; Rowan et al., 2012).…”