Roadian

In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian epoch or series. The Roadian lasted between 270.6 ± 0.7 and 268.0 ± 0.7 million years ago (Ma). It was preceded by the Kungurian and followed by the Wordian.[1]

Stratigraphy

The Wordian stage was introduced into scientific literature in 1916 and was named after the Word Formation of the North American Permian Basin. In 1961, the regional timescale used for the southeastern US had the Wordian and Capitanian as subdivisions of the Guadalupian.[2] Efforts to correlate the Permian stratigraphy of the southeastern US with that of Russia led to the conclusion that between the Wordian stage and the Russian Artinskian stage, another stage needed to be introduced.[3] 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.[4] The stage was added to the internationally used IUGS timescale in 2001.[5]

The base of the Roadian is defined as the place in the stratigraphic record where fossils of conodont species Jinogondolella nanginkensis first appear. The global reference profile for the base (the GSSP) is located in Stratotype Canyon in the Guadalupe Mountains, Texas (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.

References

Notes

1. ^ See Gradstein et al. (2004) for a detailed geologic timescale
2. ^ Glenister & Furnish (1961)
3. ^ Nassichuk (1964)
4. ^ Furnish & Glenister (1968)
5. ^ The current ICS' subdivision of the Guadalupian epoch/series was officially proposed by Glenister et al. (1999)

Literature

* Glenister, B.F. & Furnish, W.M.; 1961: The Permian ammonoids of Australia, Journal of Paleontology 35(4), pp 673-736.
* Glenister, B.F.; Wardlaw, B.R.; Lambert, L.L.; Spinosa, C.; Bowring, S.A.; Erwin, D.H.; Menning, M. & Wilde, G.L.; 1999: Proposal of Guadalupian and Component Roadian, Wordian and Capitanian Stages as International Standards for the Middle Permian Series, Permophiles 34: pp 3-11.
* Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press
* Nassichuk, W.W.; 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