The Whiterockian, often referred to simply as the Whiterock, is an earliest or lowermost stage of the Middle Ordovician.
[1][2][3] Although the Whiterockian or Whiterock Stage refers mainly to the early Middle Ordovician in North America, it is often used in the older literature in a global sense.
Nev. both show the boundary between the middle Ordovician Whiterock and underlying (mostly Canadian) Ibex series lies between the conodont Oepikodus evae, below, and Tripodus laevis, above, at the start of the Isograptus victoriae graptolite lineage, seemingly coincident with the start of the Taconic Orogeny.
Officially its start is defined by the potentially lowest occurrence of the conodont Protoprioniodus aranda or Baltoniodus triangularis.
The Whiterockian is preceded by the North American Cassinian and Ibexian stages and by the Canadian Series and ICS Arenigian, overlaps with the slightly younger and newer ICS Darriwilian[6] and is followed as originally conceived by the Chazyan of North America.