The Late Permian in the British Isles was ushered in by rapid and widespread marine transgressions which brought into being the partly enclosed and moderately deep Zechstein Sea in the east, and the more restricted Bakevellia Sea in the west. In the Zechstein Sea, normal marine conditions existed during the first two of four major sedimentation cycles, and a full and varied marine fauna is present in thick marginal carbonates. Conditions were generally less favorable in the Bakevellia Sea, and sparse faunas in marginal carbonates and clastics are dominated there by bivalves. In both basins deposition in the early cycles was concluded by barren evaporites, which are particularly thick in the second cycle in the Zechstein basin.

The original basins are thought to have become almost completely filled by the end of the second cycle and space for subsequent sedimentation in the Zechstein Sea was provided mainly by continued differential subsidence. In this paleogeographic setting, the sediments of the third Zechstein cycle are almost everywhere of shallow-water, intertidal or supratidal origin, and this is reflected in the specialized and restricted gastropodbivalve fauna of the third cycle carbonates. The trend to increasing impoverishment is continued in the sediments of the fourth and a minor fifth cycle, none of which have yielded recognizable marine fossils and which may not be of truly marine origin. Sediments of the third and subsequent cycles of the Bakevellia Sea basin have so far yielded no fossils, with the exception of a few bivalves in a marginal sub-basin which might have been flooded from the east rather than the west.

Subsequent sediments in both basins, and in areas not inundated by the Zechstein and Bakevellia seas, are mainly continental-margin red beds, predominantly red sandstones (some eolian) in areas marginal to the former basins, but passing basinwards into siltstones and mudstones. These sediments are mainly of very shallow water origin, and bear abundant evidence of repeated subaerial exposure. Apart from a few reptilian remains in sandstones near Elgin, in Scotland, these Upper Permian sediments have yielded no stratigraphically significant fossils, and appear to pass upwards, without a break, into similar continental sediments customarily assigned to the Triassic.

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