Principles of shortening in salt basins containing isolated minibasins

Abstract

AbstractShortening styles in salt‐influenced basins can vary markedly, with the volume and distribution of salt prior to shortening being a key control. Here, we use a suite of physical models to examine styles of thin‐skinned regional shortening in settings where the preshortening structure comprised minibasins surrounded by salt (‘isolated‐minibasin’ provinces). Our models show that the high volume of mechanically weak salt localizes lateral regional shortening, with shortening inducing salt flow towards the foreland that subsequently contributes to three key processes – translation, tilting and rotation of minibasins. First, we demonstrate that the flowing salt pushes against minibasins, propelling them in the regional shortening direction. Minibasin translation is enhanced by fast‐flowing salt streams and impeded by basal friction due to welding and base‐salt buttresses. Second, we show how minibasin tilt directions and magnitudes vary spatially and temporally during regional shortening. Minibasins tilt away from zones of pressurized salt, the locations of which may shift due to changes in salt flow regimes. Tilt directions may also change as minibasins pivot on primary welds, or due to forces associated with minibasin collision. Third, minibasins can rotate around sub‐vertical axes during regional shortening. We speculate that this rotation is caused by a combination of: (a) traction imparted on the minibasin boundary by differential horizontal flow of adjacent salt; and (b) pivoting on primary and secondary welds. We synthesize our results in a series of 3‐D conceptual models, before we compare and contrast regional shortening styles and processes in salt‐influenced basins with different preshortening salt configurations. Our findings contribute to the understanding of the geometry and kinematics of shortened salt basins, as well as a deeper understanding of the tectono‐stratigraphic evolution of minibasins.