The Standard Auxiliary Boundary Stratotype: A proposed replacement for the Auxiliary Stratotype Point in supporting a Global boundary Stratotype Section and Point (GSSP)

Auxiliary boundary stratotypes have unquestionable value in extending the knowledge of a Global boundary Stratotype Section and Point (GSSP) between continents, biogeographic provinces, climatic zones, depositional facies and preservational states. Two kinds of such stratotypes are in use, the Auxiliary Stratotype Point and the Auxiliary Stratotype Section, although only the Auxiliary Stratotype Point is recognised by the International Commission on Stratigraphy (ICS). The Standard Auxiliary Boundary Stratotype, which is based on the Auxiliary Stratotype Section, is proposed here as a formal replacement for the Auxiliary Stratotype Point. As such, it would provide a detailed complementary expression of the boundary interval without the designation of a specific point – no such points can replicate the precise level defined by a GSSP either conceptually or in practice. We recommend that requirements for future Standard Auxiliary Boundary Stratotypes broadly follow ICS guidelines for GSSPs but be applied with greater flexibility. Past practice reveals inconsistency in the protocols used for approving such auxiliary boundary stratotypes. We propose that in future they require approval by the respective ICS subcommission. More than one Standard Auxiliary Boundary Stratotype may support a single GSSP but restraint should be exercised in approving them, and each will always be subordinate to the GSSP itself.