Abstract. Current models of gravitational tectonics on the structural styles
of salt-influenced passive margins typically depict domains of upslope
extension and corresponding downslope contraction separated by a mid-slope
domain of translation that is rather undeformed. However, an undeformed
translational domain is rarely observed in natural systems as extensional
and contractional structures tend to interfere in the mid-slope area. In
this study, we use sandbox analogue modelling analysed by digital image
correlation (DIC) to investigate some of the factors that control the
structural evolution of translational domains. As in nature, experimental
deformation is driven by slowly increasing gravitational forces associated
with continuous basal tilting. The results show that a translational domain
persists throughout the basin evolution when the pre-kinematic layer is
evenly distributed. However, a thin (1 mm in the experiment, 100 m in
nature) pre-kinematic layer can render the translational domain relatively
narrow compared to settings with a thicker (5 mm) pre-kinematic layer.
In contrast, early differential sedimentary loading in the mid-slope area
creates minibasins separated by salt diapirs overprinting the translational
domain. Similarly, very low sedimentation rate (1 mm per day in the
experiment, < 17 m Ma−1 in nature) in the early stage of the
experiment results in a translational domain quickly overprinted by
downslope migration of the extensional domain and upslope migration of the
contractional domain. Our study suggests that the architecture of passive
margin salt basins is closely linked to the pre- and syn-kinematic cover
thickness. The translational domain, as an undeformed region in the
supra-salt cover, is a transient feature and overprinted in passive margins
with either low sedimentation rate or a heterogeneous sedimentation pattern.
How Topographic Slopes Control Gravity Spreading in Salt-bearing Passive Margins: Insights from Analogue Modelling
