The Whiterockian, often referred to simply as the Whiterock, is a earliest or lowermost stage of the Middle Ordovician.. 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.

The Whtetrock Stage was introduced by Cooper and Cooper (in Cooper, 1956, p. 6-7) "as a post-Canadian - pre-Chazyan chrono-stratographic unit" based on strata "in the Monitor

Monitor Range

The Monitor Range is located in south-central Nevada in the United States. The range lies west and northwest of the Hot Creek Range and north of Highway 6 in Nye County, and extends for approximately 106 miles into Eureka County at its northern end.The Forest Service is in charge of 83.6% of the...

 and Antelope Ranges, flanking Antelope Valley

Antelope Valley (Eureka County)

The Antelope Valley of southern Eureka County is a small 35 mi long valley, surrounded by four mountain ranges. Antelope Wash flows north, to endorheic flatlands at the valley's north end. Eureka, Nevada lies 20 mi east nestled among mountain ranges. From Eureka U.S...

, and in the Toquima Range

Toquima Range

The Toquima Range is a line of mountains in northwestern Nye County, in central Nevada in the western United States. From Hickson Summit on U.S. Route 50, the range runs for approximately 71 miles to the south-southwest. To its west are Big Smoky Valley, scenic State Route 376, and the large...

 of central Nevada", referred to as the Antelope Valley Limestone. The strato-type section in Whiterock Canyon in the northern Monitor Range and reference section at Meiklejohn Peak, Bare Mountain Quad. Nev. both show the boundary between the middle Ordovician Whiterock and underlying (mostly Canadian

Canadian Epoch

The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...

) Ibex series lies between the conodont Oepikodus evae, below, and Tripodus laevis, above, at the start of the Isograptus victoriae graptolite

Graptolite

Graptolithina is a class in the animal phylum Hemichordata, the members of which are known as Graptolites. Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous...

 lineage, seemingly coincident with the start of the Taconic Orogeny

Taconic orogeny

The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the United States...

.

The Whiterock Stage is given a range from 471.8 (ca 472) to 462 m.y.a, spanning close to 10 million years. 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

Cassinian

The Cassinian is the latest age of the Canadian Epoch when thought of temporally and the uppermost stage of the Canadian Series when thought of stratigraphically...

 and Ibexian stages and by the Canadian

Canadian Epoch

The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...

 Series and ICS Arenigian, overlaps with the slightly younger and newer ICS Darriwilian and is followed as orgiinally conceived by the Chazyan of North America.

References

• Cooper, G.A, 1965. Chazyan and related brachiopods: Smithsonian Misc. Coll. 127 ....