Keuper marl

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]