The Chalk revolution

摘要

It is relatively common to see an issue of a journal dedicated to a particular topic; it is less common to have an entire issue written by a single author! Yet the latest issue of Proceedings of the Geologists' Association comprises two papers by Rory Mortimore on the Chalk of southern Britain and France. In the first of two papers, Mortimore reviews the revolution that has occurred in our understanding of the Chalk (Proceedings of the Geologists Association, 2011, v.122, pp.232-297). Several aspects are discussed. There is the recognition that through the use of marker beds, including marl seams and types of flint, it is possible to have a very precise stratigraphical framework for the Chalk (Fig. 18), with, for example, the 'Lewes Marls' and associated 'Lewes Tubular Flints' providing a marker that covers the whole Anglo-Paris Basin. Hand-in-hand with advances in Chalk lithos-tratigraphy are those in biostratigraphy, and particularly in the use of inoceramid bivalves, the shells of which are common throughout the Chalk, readily identifiable as fragments recovered from drill core. But these advances have led to what is perhaps the most significant revolution in our understanding of this major lithostratigraphical unit.