The Whiterockian, often referred to simply as the Whiterock, is an earliest or lowermost stage of the

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Ma (milli ...

. 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 Whitetrock 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 or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, Wes ...

and Antelope Ranges, flanking

Antelope Valley The Antelope Valley is a valley primarily located in northern Los Angeles County, California, United States and the southeast portion of Kern County, California, Kern County, and constitutes the western tip of the Mojave Desert. It is situated ...

, and in the

Toquima Range The Toquima Range is a mountain range, located primarily in Nye County with a small extension into Lander County, in Nevada, United States. Most of the range is included within the Humboldt-Toiyabe National Forest. The range reaches a maxim ...

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 Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...

) Ibex series lies between the

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

''Oepikodus evae'', below, and ''Tripodus laevis'', above, at the start of the ''Isograptus victoriae''

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

lineage, seemingly coincident with the start of the

Taconic Orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago (Ma) 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 ...

. 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 ''Baltoniodus'' is an extinct genus of conodonts. Use in stratigraphy The base of the Dapingian, the first stage of the Middle Ordovician, is defined as the first appearance of ''Baltoniodus triangularis''. The Whiterock Stage refers mainly ...

''. The Whiterockian is preceded by the North American Cassinian and Ibexian stages and by the

Series and ICS Arenigian, overlaps with the slightly younger and newer ICS

Darriwilian The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species ' ...

GeoWhen Database.
/ref> and is followed as originally conceived by the

Chazyan The Chazy Reef Formation is a mid-Ordovician limestone deposit in northeastern North America. It consists of some of the oldest reef systems built by a community of organisms rather than the deposit of a limited range of similar organisms, such ...

of North America.

''References''

{{Reflist *Cooper, G.A, 1965. Chazyan and related brachiopods: Smithsonian Misc. Coll. 127 .... Middle Ordovician North America Ordovician geology of Nevada Ordovician geochronology