and the second one in the Xiaoyangqiao section, North China. Both ASSPs were approved by the Subcommission on Ordovician Stratigraphy in 2016 and 2019, respectively, but, in 2021, the International Union of Geological Sciences (IUGS) proposed to deny the use of specific points and replace them by Standard Auxiliary Boundary Stratotypes (SABS) for more "flexible" correlations with GSSPs.

Biostratigraphy

The global stages

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