This template gives the references for the data provided by {{Period start}} and related templates.
{{Period start ref|period name}}
outputs a <ref> tag with the reference.{{Period start ref|period name|noref}}
outputs a bare text of the reference without enclosing it in a <ref> tag.{{Period start ref|Cretaceous}}
→ [1]{{Period start ref|Cretaceous|noref}}
→ Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.-X. "International Chronostratographic Chart v 2020/01" (PDF). Stratigraphy.org. International Commission on Stratigraphy. Retrieved 22 March 2020.