Anisian

 ( Geological Ages ) 

In the geologic timescale, the Anisian is the lower stage or earliest geologic age of the Middle Triassic series or geologic epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Epoch) and precedes the Ladinian Age.

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Stratigraphic definitions The stage and its name were established by geologists Wilhelm Heinrich Waagen and Carl Diener in 1895. The name comes from Anisus, the Latin name of the river Enns. The original type locality is at Großreifling in the Austrian state of Styria.

The base of the Anisian Stage (also the base of the Middle Triassic series) is sometimes laid at the first appearance of conodont species Chiosella in the stratigraphic record. Other stratigraphers prefer to use the base of magnetic chronozone MT1n. There is no accepted global reference profile for the base, but one (GSSP) was proposed at a flank of the mountain Deșli Caira in the Dobruja.The GSSP was proposed by Grădinaru et al. (2007)

The top of the Anisian (the base of the Ladinian) is at the first appearance of ammonite species Eoprotrachyceras and the ammonite family Trachyceratidae. The conodont species Neogondolella appears at the same level.

Especially in Central Europe the Anisian Stage is sometimes subdivided into four substages: Aegean, Bythinian, Pelsonian and Illyrian.

The Anisian contains six ammonite :

• zone of Nevadites
• zone of Hungarites
• zone of Paraceratites
• zone of Balatonites
• zone of Kocaelia
• zone of Acrochordiceras

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Selected formations

• Ashfield Shale (New South Wales, Australia)
• Lower and middle Besano Formation (Switzerland and Italy)
• Upper Ermaying Formation (Shaanxi and Shanxi, China)
• Favret Formation / Prida Formation (Fossil Hill Member) (Nevada, US)
• Grès à Voltzia (France)
• Guanling Formation (Guizhou and Yunnan, China)
• Moenkopi Formation (Holbrook and Anton Chico members) (SW US)
• Lower and Middle Muschelkalk (central Europe)
• Röt Formation / Upper Buntsandstein (Germany)

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Sources

• ; 2005: The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale, Episodes 28(4), pp. 233–244.
• ; 2007: The Global Boundary Stratotype Section and Point (GSSP) for the base of the Anisian Stage: Deşli Caira Hill, North Dobrogea, Romania, Albertiana 36, pp. 54–71.
• ; 2004: A Geologic Time Scale 2004, Cambridge University Press.

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External links

• GeoWhen Database - Anisian
• Lower Triassic timescale at the website of the subcommission for stratigraphic information of the ICS
• Lower Triassic timescale at the website of Norges Network of offshore records of geology and stratigraphy.

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