The Namurian age lasted from 331 to 319 million years ago. It is preceded by the Visean stage/age (which corresponds to the upper Carboniferous Limestone of Great Britain) and succeeded by the Westphalian stage/age (which corresponds to the lower and middle Coal Measures of Great Britain).
In the official geologic timescale of the International Commission on Stratigraphy (ICS), the Namurian straddles the boundary between the Mississippian subperiod (359-323 Ma) and the Pennsylvanian subperiod (323-299 Ma).[1] The upper part of the (regionally defined) Namurian stage corresponds to the (internationally used) Bashkirian stage whilst the lower part is assigned to the preceding Serpukhovian stage.[1] Frequent references appear in scientific literature to a Namurian epoch or Namurian series, reflecting the stage's earlier status.
The boundary between the global Serpukhovian and Bashkirian stages (and thus the Mississippian and Pennsylvanian subperiods) occurs within the Chokierian substage.[2][1]