Evidence of synsedimentary tectonic movements in the Triassic halite of Cheshire

During the Triassic, north-west Europe was subjected to tensional stresses which resulted in the formation of a complex system of rapidly subsiding grabens and wrench-faulted basins. This pattern of regional crustal extension, which is part of the larger scale Mesozoic break-up of the Pangean megacontinent, is related to the Triassic opening of the Tethys Ocean in southern Europe and rifting in the Arctic North Atlantic, and is a prelude to the Jurassic opening of the southern North Atlantic¹. Great thicknesses of generally continental sediments, often with salt deposits, accumulated in the Triassic basins, which were mainly avolcanic. In western Britain, a complex series of fault-bounded basins extended from the Western Approaches and Channel area northwards to the Irish Sea, and includes the Worcester graben and the Cheshire Basin. The present study of the halite formations in the Cheshire Basin shows evidence for penecon-temporaneous fault movements; these were a feature of Triassic times but it is rare that such movements can be detected so precisely as is the case here.