Conference Agenda

The primary objectives of the International Subcommission on Cretaceous Stratigraphy are to establish a standard global stratigraphic subdivision and nomenclature for the Cretaceous, and to produce a stratigraphic table displaying agreed subdivision to stage and substage level, with boundaries that are defined by a Global boundary Stratotype Section and Point (GSSP). The Cretaceous Period is the longest of the Phanerozoic with12 stages. In 2000, none of the stage boundaries of the Cretaceous System was defined using a GSSP, a concept initiated in 1977. Increasingly rapid progress has been made since the ratification of the Maastrichtian Stage in 2001, now under revision, with 5 GSSPs ratified over the last 6 years. These stratotypes will be reviewed to illustrate the requirements for formal recognition of stage and substage boundaries, with only the former requiring ratification by the ICS. Out of 12, only two stages, the Berriasian and Aptian, remain to be defined. No substages have yet been formalised. A range of criteria are being used as primary markers to define stage boundaries including macrofossils (ammonites, inoceramids), microfossils (planktonic foraminifera), a magnetic reversal, and a carbon isotope event. Additional secondary markers are essential to enable the wider placement of stage boundaries. Nonetheless, no single section will ever include the complete range of potential markers to define a stage boundary. Standard Auxiliary Boundary Stratotype (SABS) sections, approved by the IUGS in 2023, provide a basis to extend the correlative potential of a GSSP between continents, biogeographic provinces, climate zones, depositional facies and preservation states.