The Ammonoidea of the Plenus Marls and the Middle Chalk

Abstract

The ammonite fauna of the Plenus Marls and Middle Chalk (Upper Cenomanian and Turonian) is described; it comprises 49 species and subspecies (8 new), referred to 27 genera. These provide a basis for revision of the ammonite zonation of the Upper Cenomanian and Turonian of Great Britain and correlation with the sequences in the Paris Basin and the stratotype areas in Sarthe and Touraine. It is demonstrated that the Cenomanian—Turonian boundary is best taken between the Neocardioceras juddii Zone below and the Watinoccras coloradoense Zone above.