Permo-Triassic rocks formed at a time of low sea level and consist almost entirely of continental red beds. Away from active fault scarps, sandstones and mudstones were laid down in deltas and lakes and the arid climate allowed the formation of dunes and playa lakes.

An important set of sedimentary basins occur adjacent to Shetland. St Magnus Bay may hold up to 1 km of Permo-Triassic strata of which the upper parts comprises anhydrite-bearing siltstone and well-rounded conglomerate. Other basins occur off Fetlar and Unst and west of Fair Isle.

During the Jurassic the area drifted northwards from 35ºN to 45ºN. The desert climate of the Triassic gave way to much more humid conditions with the development of lush vegetation. The Jurassic strata of the West Shetland and Unst basins contain thin coals, lignites and abundant plant debris. In the Unst Basin, the Upper Jurassic strata are 680m thick and include over 300 m of black Kimmeridge Clay.

The West Shetland Platform acted as a sediment source during the Early Cretaceous, suggestive uplift and erosion. Shetland may later have subsided and the margins of the land area may once have been covered by Late Cretaceous chalk and mudstones, prior to removal in response to early Tertiary uplift.