Stratigraphy: gateway to geohistory and biohistory

Concerned with the ordination, correlation and age determination of the rock record and the events entombed therein, stratigraphy is the central discipline in geohistory and biohistory. We consider (from our Cenozoic perch) changes in stratigraphy since the gestation of the International Stratigraphic Guide—changes in response to the “revolutions" of plate tectonics, bolide theory, sequence stratigraphy and cyclostratigraphy, and a cultural shift away from Lyellian gradualism. We discuss certain strictly stratigraphic matters in terms of the “Hedberg triad" of lithostratigraphy, biostratigraphy and chronostratigraphy, which triad has had its day as the core structure of the Guide. Sequence stratigraphy challenges both the lithostratigraphic formation and the notion of pervasive diachrony. Biostratigraphy flourishes in both its oppelzone and phylozone modes and is integrated increasingly with geomagnetic (the Cenozoic spine) and radiometric evidence in a sequence-and cyclostratigraphic context. Chronostratigraphic classification is hierarchical but rigid nesting is questioned.