Hexactinellid faunas in the Chalk of England and Ireland

Abstract

The Chalk of England contains three main Hexactinellid faunas, of Lower Cenomanian, Middle and Upper Turonian, and Lower Senonian to Maestrichtian age respectively. The third is also represented in Ireland. A number of minor faunal changes can also be recognized. The three main faunas have little in common, and their relationship is not evolutionary; the changes appear to be due to migrations. By analogy with modern forms, this is likely to reflect changes in the pattern of current circulation in the Upper Cretaceous ocean.