The stratigraphy of the so-called Keuper Sandstone Formation (Scythian–?Anisian) in the Permo–Triassic Cheshire Basin

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Abstract
The stratigraphy of the traditional Lower ‘Keuper’ Sandstone of Cheshire is reviewed. Two major lithofacies are defined: four Soft Sandstone sub-lithofacies are referred to fluvial, fluvial-lacustrine and aeolian origins; the seven Red Pebbly Sandstone sub-lithofacies to varying fluvial environments (channel-lag or race, migrating channel bars and megaripples, swales and flood-basins of both low and moderate-sinuosity streams), and possible intertidal lagoonal environments. Principles of stratigraphical classification are discussed, and the onset of Waterstones conditions and a widespread dune field taken as the datum below which lithostratigraphical correlation is attempted. Definition of the ‘Keuper’ Sandstone Formation and its constituent units, the Frodsham, Delamere, Alderley, Nether Alderley and Thurstaston Members, is made. The correlation suggests that following the mainly aeolian episode of the Bunter Upper Mottled Sandstone, low-sinuosity flood-waters of the ‘Keuper’ Sandstone entered the basin intermittently along certain directions, notably those of the Eastern (Midland–Congleton–Macclesfield and Alderley–Styal) and Central (Marston–Stockton) Rivers. Elsewhere aeolian activity continued, the rivers often drying out and being overwhelmed by blown sand. This was followed by the main fluvial period of the Delamere Member during which streams of moderate sinuosity were developed everywhere but in the south. The succeeding Frodsham Member represents a major aeolian episode which is terminated by low-energy aqueous sedimentation of the Waterstones. These correlations are partiularly open to testing by palaeomagnetic investigation and by spores.