Rhuddanium

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system series step ≈ age ( mya )
higher higher higher younger
Silurian Pridolium 419.2
⬍
423
Ludlow Ludfordium 423
⬍
425.6
Gorstium 425.6
⬍
427.4
Wenlock Homerium 427.4
⬍
430.5
Sheinwoodium 430.5
⬍
433.4
Llandovery Telychium 433.4
⬍
438.5
Aeronium 438.5
⬍
440.8
Rhuddanium 440.8
⬍
443.4
deeper deeper deeper older

The Rhuddanium is in the Earth's basal stratigraphic level of Llandovery series and thus the basal level of the Silurian system's. Geochronologically, this unit corresponds roughly to the period from approx. 443.4 to approx. 440.8 million years. The Rhuddanium follows the Hirnantium , the highest level of the Ordovician, and is replaced by the Aeronium .

Naming and history

The stage is named after the small town of Cwm Rhuddan , south of Llandovery ( Wales ). The stage (and name) was proposed in 1971 by a British group of geologists under LRM Cocks.

Definition and GSSP

The lower limit (and thus the lower limit of the Silurian) is defined by the first appearance of the graptolite species Parakidograptus acuminatus and Akidograptus ascensus . The end of the Rhuddanium is defined by the first appearance of the graptolite species Monograptus austerus sequens . The official reference profile (GSSP = "Global Stratotype Section and Point") for the Rhuddanium is located in Dob's Linn , Moffat ( Scotland ).

literature

  • Felix Gradstein, Jim Ogg, Alan Smith: A Geologic timescale. Cambridge University Press, 2004, ISBN 0-521-78673-8 .
  • LRM Cocks: The Ordovician-Silurian Boundary. In: Episodes. 8 (2), 1985, pp. 98-100.
  • LRM Cocks: The Llandovery Series in the Llandovery area. In: CH Holland, MG Bassett (Ed.): A global standard for the Silurian System. (= National Museum of Wales. Geological Series. 9). Cardiff 1989, ISBN 0-7200-0308-3 , pp. 36-50.

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