Sequence stratigraphy of carbonate-evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea

The successions of carbonate-evaporite basins, which are periodically cut off from the world ocean, are considered in terms of their sequence stratigraphy. Two basin types are distinguished: those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation. It is argued that, following relative sea-level falls, sequences begin with the evaporites, precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin-centre halite fills in the second. The evaporites pass up into carbonate sediments which are mainly deposited on shallow-water platforms around the basin during transgressive and highstand systems tracts. The concepts and models developed are applied to the Zechstein (Upper Permian) strata of northeast England and adjoining North Sea. Seven sequences are proposed, with some containing thin parasequences. The sequence approach to carbonate—evaporite basins, which considers both basin margin and basin centre facies, gives a more encompassing perspective of sedimentation than the traditional cycle concept, with its emphasis on the basin centre.