The Place of the Trimingham and Norwich Chalk in the Campanian-Maestrichtian Succession

Abstract

AbstractThe Maestrichtian is considered an independent stage younger than and equal in rank to the Senonian stage; in its type-area it includes, besides the Maestricht Tuff, such older formations as the Chalk of Ciply and of Spiennes, the Kunrade Limestone, upper beds of the Gulpen Chalk, and even some part of the Hervian Greensands. The zone of Pachydiscus egertoni forms the base of the Maestrichtian stage.In its type locality the Campanian stage includes the zone of Bostrychoceras polyplocum; at the same time its uppermost beds are at any rate not older than the uppermost beds of the Senonian stage in its type area. The zone of B. polyplocum thus forms a part of the Senonian stage.The true Belemnella lanceolata (Schloth.) is restricted to the Trimingham Chalk. Belemnitella ex. gr. mucronata (including “Belemnites lanceolatus” von Sharpe and Blackmore non Schloth.) are, on the contrary, all but confined to the Norwich Chalk and older beds of the English Upper Chalk. Accordingly, a new zonal name “Zone of Belemnella lanceolata” is recommended for the Trimingham Chalk, and the zone of Belemnitella mucronata should, in the opinion of the writer, be restricted to beds older than the Trimingham Chalk.The Trimingham Chalk is assigned to the Lower Maestrichtian, while the Norwich Chalk represents the Upper Campanian (including the B. polyplocum zone).