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 ...

stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...

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 ...

Series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used in ...

. The Roadian lasted between and million years ago (Ma). It was preceded by the

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 and million years ago (Ma). It was preceded by the Artin ...

and followed by the

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 and million years ago (Ma). It was preceded by the Roadian and foll ...

Stratigraphy

In 1961, the regional timescale used for the southeastern US had the Wordian and

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 million years ago. It was preceded by th ...

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 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 likely lasted between and million years ago (Ma) according to the most recent revision of the ...

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 The Road Canyon Formation is a geologic formation in Texas.Brewster County Brewster County is a county located in the U.S. state of Texas. It is in West Texas and its county seat (and only city) is Alpine. It is one of the nine counties that comprise the Trans-Pecos region, and borders Mexico. Brewster County is th ...

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 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 A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted b ...

) is located in Stratotype Canyon in the

Guadalupe Mountains The Guadalupe Mountains ( es, Sierra de Guadalupe) 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 ...

(). 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 Olson's Extinction was a mass extinction that occurred in the late Cisuralian or early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event. It is named after Everett C. Olson. There was a sudden change bet ...

, a worldwide loss of terrestrial vertebrate life occurred during the Early Guadalupian (Roadian,

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