The Oxfordian Stage was called "Clunch Clay and Shale" by William Smith (1815–1816); in 1818 W. Buckland described them under the unwieldy title "Oxford, Forest or Fen Clay".

The name is derived from the English city of Oxford,[4] where the beds are well developed, but they crop out almost continuously from Dorset to the coast of Yorkshire, generally forming low, broad valleys.

[5] The base of the Oxfordian Stage is defined as the point in the stratigraphic record where the ammonite species Brightia thuouxensis first appears.

A global reference profile for the base (a GSSP) had in 2009 not yet been assigned.

The top of the Oxfordian Stage (the base of the Kimmeridgian) is at the first appearance of ammonite species Pictonia baylei.