Marine evaporites such as the Zechstein (Permian, NW Europe) consist of thinning-upward sulphate–halite–potash cycles whose origin is poorly understood. An intra-basinal mechanism presented here explains well their mineral composition and cycle development. It involves the progressive obstruction of ocean connections by sulphate-platform progradation, causing a chain reaction of outflow reduction and subsequent accelerated sulphate precipitation. Numerical modelling shows this to be a self-accelerating process that ultimately triggers halite and potash precipitation. Isostatic compensation of the salt load explains the formation of accommodation space for subsequent cycles, each about half the thickness of the previous cycle.