The interval definitions in this timescale are derived from the following sources:

• K. M. Cohen, S.C. Finney, P.L. Gibbard and J.-X. Fan. 2023. The ICS International Chronostratigraphic Chart v2023/09. view
• J. A. Lillegraven and M. C. McKenna. 1986. Fossil mammals from the "Mesaverde" Formation (Late Cretaceous, Judithian) of the Bighorn and Wind River basins, Wyoming, with definitions of Late Cretaceous North American Land-Mammal "Ages". American Museum Novitates 2840:1-68 view
• F. M. Gradstein, J. G. Ogg, and A. G. Smith. 2004. A Geologic Time Scale 2004 1-589 view
• F. M. Gradstein, J. G. Ogg, M. D. Schmitz and G. M. Ogg. 2020. Geologic Time Scale 2020 view
• W. B. Harland, R. L. Armstrong, A. V. Cox, L. E. Craig, A. G. Smith and D. G. Smith. 1990. A Geologic Time Scale 1989. view
• B. D. Webby. 1998. Steps toward a global standard for Ordovician stratigraphy. Newsletters in Stratigraphy 36:1-33 view

There are 59 timescales which overlap this one. show

• Cenozoic Subepochs
• Obsolete Names for ICS Units
• Ten Million Year Bins
• Mesozoic Subages
• Cretaceous Subepochs
• Carboniferous Subepochs
• Devonian Subages
• Cambrian Epochs
• European Faunal Units
• European Faunal Zones
• Mammal Paleogene Zones
• Cenozoic Subepochs of Southern Europe
• Central Paratethys Stages
• Neogene Mammal Ages of China
• Paleogene Mammal Ages of Asia
• North American Land Mammal Ages
• North American Mammal Subages/Zones
• South American Land Mammal Ages
• Cretaceous North American Land-Mammal Ages
• Ammonite Chrons of Northwest Europe
• Ammonite Chrons of North America
• Permian of the Russian Platform
• Permian of the Pamirs
• Permo-Triassic Subages of Eastern Europe
• Permian Subages of Germany
• Permian of Western Europe
• Permian of the Salt Range
• Permian of China
• Permian of North America
• Carbo-Permian of the Russian Platform
• Carboniferous of Western Europe
• Carboniferous of China
• Obsolete Carboniferous Ages of China
• Carboniferous of North America
• Devonian of France
• Devonian of Germany
• Devonian of Czechoslovakia
• Devonian of Eastern North America
• Silurian of the Baltic
• Silurian Ages of Europe
• Silurian of England
• Silurian of North America
• Ordovician of Britain
• Ordovician of the Baltic
• Ordovician of Ibero-Bohemia
• Ordovician of Australia
• Ordovician of China
• Ordovician of North America
• Cambrian of China
• Cambrian of Australia
• Cambrian of Siberia
• Cambrian of Kazakhstan
• Cambrian of North America
• Cambrian of West Avalonia
• Cambrian of Britain
• Precambrian of Russia
• Obsolete Precambrian Ages
• Cretaceous-Cenozoic of New Zealand
• Permian-Jurassic of New Zealand

Interval boundaries marked with * have been interpolated based on the differences between the ages for international timescale boundaries quoted in the source and the currently accepted ages for those boundaries.

Interval names marked with † are no longer in current use.

This timescale is used in the definition of 127258 collections