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 and 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.