Keuper marl is a former and now deprecated term for multiple layers of mudstone and siltstone of Triassic age which occur beneath parts of the English Midlands and neighbouring areas e.g. Cheshire,[1] Nottinghamshire,[1] Devon, eastern Worcestershire and northern Yorkshire.[citation needed]
Typically red, or occasionally green or grey, these strata are generally featureless and contain few fossils. In basin formations, thick halite-bearing layers, or rock salt deposits, are sometimes present at the base of the marl.
In modern nomenclature, Keuper marl is included within the Mercia Mudstone Group.[1][2]