In the

geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronol ...

, the Roadian is an

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

or stage of the

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

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

Guadalupian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

Epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the Kungurian and followed by the Wordian.

Stratigraphy

In 1961, the regional timescale used for the southeastern US had the Wordian and Capitanian as subdivisions of the Guadalupian. Efforts to

correlate In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics ...

the Permian stratigraphy of the southeastern US with that of

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

led to the conclusion that between the Wordian stage and the Russian Artinskian stage, another stage needed to be introduced. This stage, the Roadian Stage, was established in 1968 and took its name from the Road Canyon Formation in Brewster County,

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

, formerly considered the lower (oldest) part of the

Word Formation In linguistics, word formation is an ambiguous term that can refer to either: * the processes through which words can change (i.e. morphology), or * the creation of new lexemes in a particular language Morphological A common method of word form ...

. The stage was added to the internationally used

IUGS The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Inte ...

timescale in 2001.; 1999: ''Proposal of Guadalupian and Component Roadian, Wordian and Capitanian Stages as International Standards for the Middle Permian Series'', Permophiles 34: pp 3–11. The base of the Roadian is defined as the place in the stratigraphic record where fossils of

conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...

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

(). 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).

References

Literature

External links

GeoWhen Database - RoadianUpper Paleozoic stratigraphic chart
at the website of the subcommission for stratigraphic information of the ICS {{Geological history, p, p Permian geochronology . Permian geology of Texas