Unifying Cenozoic chronostratigraphy and geochronology: applying the rules

The International Chronostratigraphic Chart (ICC), as the basis of the International Geological Time Scale, is the primary product of the International Commission on Stratigraphy (ICS), itself the principal commission of the International Union of Geological Sciences (IUGS). The ICC represents a sustained and concerted effort by Earth scientists worldwide to produce a temporal correlation framework that is both informative and practical. As with the International Stratigraphic Guide (Hedberg 1976, Salvador 1994, Murphy et al. 2021) published by the ICS Subcommission on Stratigraphic Nomenclature (ISSC), the ICC is designed to serve the broad scientific community effectively and efficiently. Inspired by the model provided by the Committee on the Silurian-Devonian Boundary (McLaren et al. 1977), the ICS established rules to ensure a consistent and objective approach to scientific procedures in implementing a common chronostratigraphic language (Cowie et al. 1986, Remane et al. 1996). While these rules have encouraged discussion, openness, and objectivity, tensions remain in some areas where compromises have not yet been achieved. We review here one such case concerning the subdivisions of the Cenozoic Era into subseries/subepochs, in which strong opinions have hindered the integration of Cenozoic chronostratigraphy into the accepted standard. In light of long historical precedent, logical consistency with units in the Neogene and Quaternary Cenozoic systems/ periods, broad applicability across marine, terrestrial and transitional strata, and wide acceptance and use by the Cenozoic Earth Sciences community, it is clear that Paleogene subseries/subepochs should be included in the ICC.