The global reference profile for the base (the GSSP or golden spike) is located in the valley of the Aidaralash River, near Aqtöbe in the Ural Mountains of Kazakhstan.
There is some debate over the exact sequence of species; one option, according to Henderson (2018),[6] lists the following biozones, from youngest to oldest: In North America, the regional equivalent of the Asselian is the Nealian stage.
[7][8] In South China, the Asselian is equivalent to at least the lower part of the regional Zisongian stage of the Chuanshanian Series.
[9][10] Both the Nealian and Zisongian are defined by fusilinid assemblages, so their precise correlation to the conodont-based global timescale is uncertain.
The Asselian occupies a portion of major terrestrial sediment units in Europe, namely the Autunian series of France and the lower Rotliegend of Germany.