Callovian Stage

the uppermost stage of the Middle Jurassic. The term was introduced in 1849 by the French geologist A. D. d’Orbigny, who named it after a locality in England. Callovian deposits (predominantly sandy-argillaceous) are widely developed in Great Britain, France, the Federal Republic of Germany, a number of regions of the USSR (Volga Region, Moscow vicinity, the Crimea, and the Caucasus), the USA, Mexico, and other countries. Based on the ammonites found in it, the Callovian stage is divided into six or seven zones (from the zone Macrocephalites macrocephalus to the zone Quenstedticeras lamberti).