Scale models of salt tectonics during basement-involved extension

Abstract

Scaled experiments, w h o s e design was based on recently published low values for the viscosity of natural rocksalt, suggest that under typically low geological extension rates, a salt layer 500 m thick or thicker decouples the brittle overburden from the faulted basement. Because of its low viscosity, salt cannot transmit the large differential stresses necessary for basement faults to propagate upward as faults or abrupt forced folds into the brittle overburden, unless the salt layer is thin or has b e e n depleted. Thick salt diffuses localized deformation in the basement by flowing away from rising basement blocks, and toward sinking basement blocks. Basement extension is not transmitted to the overburden vertically but is laterally transmitted from the margins as the salt basin widens. Rather than being controlled by basement faults, the distribution of faults and diapirs in the overburden is controlled by lateral changes in overburden stratigraphy or thickness, preexisting faults, and faults that propagate laterally into the salt basin.

Tectonic inversion of salt-detached ramp-syncline basins as illustrated by analog modeling and kinematic restoration

“…The dry sand was chosen to simulate the brittle deformation of upper crustal sedimentary rocks (Horsfield, 1977;McClay, 1990), and the PDMS polymer was used as our salt analog (Weijermars, 1986), as in most analog modeling studies Nalpas and Brun, 1993;Vendeville et al, 1995;Withjack and Callaway, 2000;Dooley et al, 2005;Soto et al, 2007;Ferrer et al, 2014Ferrer et al, , 2016. Silica sand has a Mohr-Coulomb behavior at moderate values of normal stress, and its mechanical properties were measured using a ring shear tester at the Fault Dynamics Research Group Laboratory.…”

“…During the second extensional phase, the degree of decoupling between subsalt and suprasalt units and the salt withdrawal due to sediment loading mainly depends on salt thickness (e.g., Vendeville et al, 1995;Richardson et al, 2005). Although a thinner salt unit promotes the development of extensional fault-propagation folds and premature welds by salt depletion, a thicker salt unit allows a partially coupled deformation, which results in further salt migration and the development of wide salt-detached ramp-syncline basins (Figure 4).…”

“…Clearly, salt-detached ramp-syncline basins differ from the typical extensional minibasins because salt-detached ramp synclines can be a hundred times wider and the subsalt fault geometry is the main factor controlling these sedimentary basins, with or without the presence of salt. The salt acts as an effective décollement decoupling subsalt and suprasalt deformation (Vendeville, 1987(Vendeville, , 1988Nalpas and Brun, 1993;Vendeville et al, 1995;Steward and Clark, 1999;Withjack and Callaway, 2000;Ferrer et al, 2016), but such scenarios follow a partial coupling structural style, where the salt unit acts as a thin-skinned component in a thick-skinned deformation style. The basement fault does not penetrate the salt unit but is overlain by a draped fold over the master fault (Jackson and Hudec, 2017).…”

Analysis of gravity-driven normal faults using a 3D seismic reflection dataset from the present-day shelf-edge break of the Otway Basin, Australia

“…We have spatially constrained normal fault growth by providing evidence for along-strike and down-dip segment linkage, which highlights the complexity in fault plane geometric development. Studies have shown that the development of sub-parallel striking cover-restricted normal faults can be invoked by increased tilting, flexure and gravity gliding of cover sediments above basement normal faults (Vendeville et al 1995;Withjack and Callaway, 2000). Furthermore, analysis using 3D seismic datasets from the North Sea have shown a geometric and kinematic relationship between reactivation of sub-salt basement normal faults and the development of supra-salt normal fault systems, with extension in cover sediments instigated by basement normal fault reactivation Lewis et al 2013;Tvedt et al 2013).…”

“…Jackson and Rotevatn, 2013;Lewis et al 2013;Tvedt et al 2013). Studies have documented that tilting, flexure and gravity gliding increases in sedimentary rock located directly above basement normal faults and this may invoke the growth of sub-parallel striking, cover restricted normal faults (Vendeville et al 1995;Withjack and Callaway, 2000). We aim to temporally and spatially constrain the growth of a gravity-driven normal fault assemblage, imaged by 3D seismic data and located within Upper Cretaceous sedimentary rock at the present-day shelfedge break of the Otway Basin Australia (Figure 1).…”