Salt-basin margins commonly host extensional fault systems above landward-thinning salt wedges, yet the mechanisms governing fault persistence or abandonment during salt withdrawal remain debated. Observations from global salt basins show contrasting behaviours. In some settings, extensional deformation ceases once salt is evacuated and welded, while in others, faults remain active despite complete salt removal beneath them. These contrasting observations suggest that salt can play a dual mechanical role at basin margins, either as a passive detachment surface enabling gravitational sliding of the overburden, or as an active carrier that couples the overburden to basinward salt flow.
Here we investigate the factors controlling the transition between coupled and decoupled deformation above salt wedges using two-dimensional numerical modelling. Our models simulate the mechanical interaction between salt and overburden across a migrating salt wedge, systematically varying salt-top dip, wedge geometry, and basal friction along evacuated zones. This approach allows us to track how each deformation mode initiates, evolves through time, and ultimately wanes as salt geometry and mechanical conditions change.
The results show that strong coupling between salt and overburden promotes the initiation of upslope extension driven by salt flow, followed by basinward migration of deformation as the wedge retreats, ultimately leading to abandonment of older faults. In contrast, efficient detachment along salt-evacuated surfaces enables early decoupling, sustained gravitational sliding, and long-lived fault activity that persists even after salt withdrawal, before gradually diminishing as detachment efficiency decreases. These outcomes reproduce both end-member behaviours documented in natural systems and clarify their full evolutionary trajectories.
The Levant Basin provides a unique natural laboratory to test these mechanisms, as its young, shallow Miocene salt system preserves both coupled and decoupled deformation styles side by side. Our findings demonstrate how subtle mechanical differences at the salt–sediment interface govern the birth, growth, and decay of extensional systems above salt pinch-outs, with broad implications for the structural evolution of salt-basin margins worldwide.