Initiating Salt Tectonics by Tilting: Viscous Coupling Between a Tilted Salt Layer and Overlying Brittle Sediment

Salt basins often exhibit a shelf/slope region of extension and a deeper domain of contraction. The up-slope normal faults in such salt tectonics systems are often associated with the pinch-out edge of the buried salt layer. Although the spatial correlation between the normal faults and the salt pinch-out was previously observed, the mechanism was not fully explained. The Levant basin, which is a young and mildly deformed salt basin with a relatively thin overburden, provides an opportunity to analyze a simple salt tectonics system driven by basin margin tilt, and the formation of the normal faults. This work presents analytical and numerical modeling of the coupled viscous salt and overlying visco-plastic sediment layer. Results suggest the viscosities of both the sediment overburden and salt, as well as their thicknesses, control the deformation of the coupled layers. The visco-plastic deformation mechanism explains quantitatively the position of faulting and observations of the temporal evolution of brittle deformation in the Levant basin margin. It predicts that the largest stress in the overburden arises above the salt edge, driving normal faulting at that location. Our model also places quantitative constraints on the effective viscosity of the overburden (>2 × 1020 Pa s), which is consistent with experimentally-determined creep laws. Our results contribute to the understanding of halokinematics in salt basins during the early stages of deformation and will allow better assessment of geological hazards related to salt related deformation.