Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.
Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 precedes Cambrian Stage 4, although neither its base or top have been formally defined yet. The lower boundary is loosely defined as the first appearance of trilobites which happened around ~521 million years ago. The upper boundary and beginning of Cambrian Stage 4 is informally defined as the first appearance of the trilobite genera Olenellus or Redlichia around ~514 million years ago.