The Keuper Formation is a geological unit within the Upper Triassic series, primarily exposed in central and western Europe. It is part of the larger Germanic Trias, which also includes the Buntsandstein and Muschelkalk formations. The Keuper Formation typically consists of sequences of mudstones, siltstones, evaporites (such as gypsum and rock salt), and occasionally carbonate beds and sandstones, reflecting deposition in predominantly continental to marginal marine environments, including playa lakes and shallow basins.
It was deposited during the Carnian to Norian stages of the Late Triassic, approximately 237 to 208 million years ago. The formation is widespread in countries such as Germany, France, the United Kingdom, and the Netherlands. In the UK, the Keuper Formation is known for its red-bed sediments and is associated with the Mercia Mudstone Group in some regional stratigraphic frameworks.
The Keuper Formation is economically significant in certain regions for its halite (rock salt) deposits, which have been mined historically. It also hosts various fossils, including reptiles, fish, and plant remains, contributing to paleoenvironmental reconstructions of the Late Triassic.
The name "Keuper" originates from the French term "Kéuper," borrowed into German geological nomenclature in the 19th century, itself derived from the Alsatian dialect word for a type of marl-rich clay.