Jan Zalasiewicz, Maria Bianca Cita, Frits Hilgen, Brian R. Pratt, André Strasser, Jacques Thierry, Helmut Weissert

1 Dept. of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK
2 Dept. of Earth Sciences, University of Milano, via Mangiagalli 34, 20133 Milano, Italy
3 Stratigraphy/Palaeontology, Dept. of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, the Netherlands
4 Dept. of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
5 Département de Géosciences, Université de Fribourg, Chemin du Musée 6, CH-1700 Fribourg, Switzerland
6 Université de Bourgogne et UMR CNRS 5661 Biogéosciences Dijon, 6 Bd Gabriel, 21000 Dijon, France
7 ETH Zürich, Geologisches Institut, Sonneggstrasse 5, 8092 Zürich, Switzerland

Abstract

We propose a realignment of the terms geochronology and chronostratigraphy that brings them broadly into line with current use, while simultaneously resolving the debate over whether the Geological Time Scale should have a “single” or “dual” hierarchy of units: Both parallel sets of units are retained, although there remains the option to adopt either a single (i.e., geochronological) or a dual hierarchy in particular studies, as considered appropri-ate. Thus, geochronology expresses the timing or age of events (depositional, diagenetic, biotic, climatic, tectonic, magmatic) in Earth’s history (e.g., Hirnantian glaciation, Famennian-Frasnian mass extinction). Geochronology can also qualify rock bodies, stratified or unstratified, with respect to the time interval(s) in which they formed (e.g., Early Ordovician Ibex Group). In addition, geochronology refers to all methods of numerical dating. Chronostratigraphy would include all methods (e.g., biostrati-graphy, magnetostratigraphy, chemostratigraphy, cyclostrati-graphy, sequence stratigraphy) for (1) establishing the relative time relationships of stratigraphic successions regionally and worldwide; and (2) formally naming bodies of stratified rock that were deposited contemporaneously with units formally defined at their base, ideally by a GSSP (Global Boundary Stratotype Section and Point = “golden spike”) that represents a specific point in time. Geochronologic units may be defined and applied generally by either GSSPs or—as currently in most of the Precambrian—by Global Standard Stratigraphic Ages (GSSAs). Geochronologic units would continue as the time units eons/eras/periods/epochs/ages, and chronostratigraphic units as the time-rock units eonothems/erathems/systems/series/stages. Both hierarchies would remain available for use, as recommended by a formal vote of the International Commission on Stratigraphy in 2010. Geological context helps determine the appropriate usage of the component units.

Manuscript received 16 July 2012; accepted 13 Dec. 2012

DOI: 10.1130/GSATG160A.1