In the geologic timescale, the Roadian is an age or stage of the Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

. It is the earliest or lower of three subdivisions of the Guadalupian epoch

Epoch (geology)

An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...

 or series

Series (stratigraphy)

Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...

. The Roadian lasted between 270.6 ± 0.7 and 268.0 ± 0.7 million years ago (Ma). It was preceded by the Kungurian

Kungurian

In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian epoch or series. The Kungurian lasted between 275.6 ± 0.7 and 270.6 ± 0.7 million years ago...

 and followed by the Wordian

Wordian

In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian epoch or series. The Wordian lasted between 268.0 ± 0.7 and 265.8 ± 0.7 million years ago...

.

Stratigraphy

The Wordian stage was introduced into scientific literature in 1916 and was named after the Word Formation

Word formation

In linguistics, word formation is the creation of a new word. Word formation is sometimes contrasted with semantic change, which is a change in a single word's meaning...

 of the North American Permian Basin. In 1961, the regional timescale used for the southeastern US had the Wordian and Capitanian

Capitanian

In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian epoch or series. The Capitanian lasted between and...

 as subdivisions of the Guadalupian. Efforts to correlate

Correlation

In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....

 the Permian stratigraphy of the southeastern US with that of Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 led to the conclusion that between the Wordian stage and the Russian Artinskian

Artinskian

In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Artinskian lasted between 284.4 ± 0.7 and 275.6 ± 0.7 million years ago...

 stage, another stage needed to be introduced. This stage, the Roadian stage, was established in 1968 and took its name from the Road Canyon Member, the lower (oldest) part of the Word Formation. The stage was added to the internationally used IUGS timescale in 2001.

The base of the Roadian is defined as the place in the stratigraphic record where fossils of conodont

Conodont

Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...

 species Jinogondolella nankingensis first appear. The global reference profile for the base (the GSSP) is located in Stratotype Canyon in the Guadalupe Mountains

Guadalupe Mountains

The Guadalupe Mountains are a mountain range located in West Texas and southeastern New Mexico. The range includes the highest summit in Texas, Guadalupe Peak, , and the "signature peak" of West Texas, El Capitan, both located within Guadalupe Mountains National Park, as well as Carlsbad Caverns...

, Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 (31° 52' 36,1" N, 104° 52' 36,5" W). The top of the Roadian (the base of the Wordian stage) is at the first appearance of fossils of conodont species Jinogondolella aserrata.

Biodiversity

Olson’s Extinction, a worldwide loss of terrestrial vertebrate life occurred during the Early Guadalupian (Roadian, Wordian)..

Literature

; 1961: The Permian ammonoids of Australia, Journal of Paleontology 35(4), pp 673-736.; 1999: Proposal of Guadalupian and Component Roadian, Wordian and Capitanian Stages as International Standards for the Middle Permian Series, Permophiles 34: pp 3-11.; 2004: A Geologic Time Scale 2004, Cambridge University Press; 1964: Pennsylvanian and Permian rocks in the Parry Islands Group, Canadian Arctic Archipelago, Report of activities, field

External links

• GeoWhen Database - Roadian
• Upper Paleozoic stratigraphic chart at the website of the subcommission for stratigraphic information of the ICS