|433.4 ± 0.8 – 427.4 ± 0.5 Ma|
|Regional usage||Global (ICS)|
|Time scale(s) used||ICS Time Scale|
|Time span formality||Formal|
|Lower boundary definition||Imprecise. Currently placed between acritarch biozone 5 and last appearance of Pterospathodus amorphognathoides. See Llandovery for more info.|
|Lower boundary definition candidates||A conodont boundary (Ireviken datum 2) which is close to the murchisoni graptolite biozone.|
|Lower boundary GSSP candidate section(s)||None|
|Lower boundary GSSP||Hughley Brook, Apedale, United Kingdom|
|Upper boundary definition||FAD of the Graptolite Saetograptus (Colonograptus) varians|
|Upper boundary GSSP||Pitch Coppice, Ludlow, United Kingdom|
The Wenlock (sometimes referred to as the Wenlockian) is the second epoch of the Silurian. It is preceded by the Llandovery epoch and followed by the Ludlow epoch. Radiometric dates constrain the Wenlockian between 433.4 and 427.4 million years ago.
Naming and history
The Wenlock is named after Wenlock Edge, an outcrop of rocks near the town of Much Wenlock in Shropshire (West Midlands, United Kingdom ). The name was first used in the term "Wenlock and Dudley rocks" by Roderick Murchison in 1834 to refer to the limestones and underlying shales that underlay what he termed the "Ludlow rocks". He later modified this term to simply the "Wenlock rocks" in his book, The Silurian System in 1839.
Definition and subdivision
The Wenlock is divided into the older Sheinwoodian and the younger Homerian stage. The Sheinwoodian lasted from 433.4 to 430.5 million years ago. The Homerian lasted from 430.5 to 427.4 million years ago.
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- Murchison R.I. (1833–1834). "On the Structure and Classification of the Transition Rocks of Shropshire, Herefordshire and part of Wales and on the Lines of Disturbance which have affected that Series of Deposits, including the Valley of Elevation of Woolhope". Proceedings of the Geological Society of London 2 (33): 14. https://archive.org/details/proceedings218331838geol.
- Murchison R.I. (1839). The Silurian System. Murray. pp. 208. https://books.google.com/books?id=cKlAAAAAcAAJ&q=murchison+wenlock+limestone&pg=PA209.
- The Geologic Time Scale 2012. Elsevier Science Ltd. 14 August 2012. ISBN 978-0-444-59425-9.
Original source: https://en.wikipedia.org/wiki/ Wenlock epoch. Read more