Stretching and Contraction of Extensional Basins With Pre-Rift Salt: A Numerical Modeling Approach

Abstract

We present a series of 2D thermo-mechanical numerical experiments of thick-skinned crustal extension including a pre-rift salt horizon and subsequent thin-, thick-skinned, or mixed styles of convergence accompanied by surface processes. Extension localization along steep basement faults produces half-graben structures and leads to variations in the original distribution of pre-rift salt. Thick-skinned extension rate and salt rheology control hanging wall accommodation space as well as the locus and timing of minibasin grounding. Upon shortening, extension-related basement steps hinder forward propagation of evolving shallow thrust systems; conversely, if full basin inversion takes place along every individual fault, the regional salt layer is placed back to its pre-extensional configuration, constituting a regionally continuous décollement. Continued shortening and basement involvement deform the shallow fold-thrust structures and locally breaches the shallow décollement. We aim at obtaining a series of structural, stratigraphic and kinematic templates of fold-and-thrust belts involving rift basins with an intervening pre-rift salt horizon. Numerical results are compared to natural cases of salt-related inversion tectonics to better understand their structural evolution.

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

“…The archetypal structural styles of the Northern Calcareous Alps include large panels of overturned stratigraphy, and steep mechanical contacts marked by severely deformed evaporites that can either repeat or omit significant parts of the stratigraphic sequence. Other parts of this fold-and-thrust belt conform to classical thrust contacts bringing older stratigraphy onto younger stratigraphy and constituting thrust sheets of significant lateral continuity (i.e., tens of kilometers; see Granado et al, 2021). Such complex structural styles of the Northern Calcareous Alps were interpreted as resulting from strong out of sequence thrusting and Cenozoic strike-slip overprinting a typical fold-and-thrust belt (e.g., Linzer et al, 1995Linzer et al, , 1997Frisch & Gawlick, 2003, amongst many others).…”

“…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).…”

“…As a result of shortening and erosion of these salt‐bearing rifted systems, salt can flare and be extruded to the actively deforming surface. Salt can also be driven downwards, back into its original source layer as diapirs are shortened, squeezed and shut‐off (i.e., Dooley et al., 2009; Granado et al., 2021). Salt extrusion points can be located at the emergent tips of salt‐detached thrust sheets (ref.…”

Reply to the comment of Schollnberger on ‘Subsidence analysis of salt tectonics‐driven carbonate minibasins’ (Northern Calcareous Alps, Austria), published on Basin Research 2020; 00: 1– 23 doi:10.1111/bre.12500

“…We assume similar lithological controls as those described by Jackson et al (2018) in the North Sea for the growth of the minibasins in the NCA and further insight to the salt composition in the NCA could be gained by adapting their analysis from the North Sea to the NCA. In fact, the authors have recently published numerical modelling works using variable salt rheologies, opening a new line of work for the NCA and other salt basins (Granado et al, 2021).…”

The Mechanical Behavior of Salt X

“…The deformation of a salt layer above an active normal fault has been investigated in numerous analogue, analytical, and numerical studies (e.g. Koyi et al 1993;Vendeville et al 1995;Burliga et al 2012;Warsitzka et al 2015Warsitzka et al , 2018Granado et al 2021). The differential vertical displacement around the tip of a basement fault leads to the formation of forced folds within the salt sequence, and it may also initiate the growth of salt pillows over the footwall.…”