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Published online June 15, 2022

Copyright © International Union of Geological Sciences.

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

Martin J. Head1*, Marie-Pierre Aubry2, Werner E. Piller3, Mike Walker4,5

1 Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
2 Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, USA
3 Institute of Earth Sciences, University of Graz, NAWI Graz Geocenter, Heinrichstrasse 26, 8010 Graz, Austria
4 School of Archaeology, History and Anthropology, Trinity Saint David, University of Wales, Lampeter, Wales, SA48 7ED, UK
5 Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, Wales, SY23 3DB, UK

Correspondence to:E-mail: mjhead@brocku.ca

Received: October 12, 2021; Revised: April 4, 2022; Accepted: April 4, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.