Wenlock Epoch
{{short description|2nd Series (Epoch) of the Silurian}}
{{Infobox geologic timespan
| name = Wenlock
| color = Wenlock
| time_start = 433.4
| time_start_uncertainty = 0.8
| time_end = 427.4
| time_end_uncertainty = 0.5
| image_map = Mollweide Paleographic Map of Earth, 430 Ma (Homerian Age).png
| caption_map = A map of Earth as it appeared 430 million years ago during the Wenlock Epoch, Homerian Age
| image_outcrop =
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| timeline = Silurian
| name_formality = Formal
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| celestial_body = earth
| usage = Global (ICS)
| timescales_used = ICS Time Scale
| formerly_used_by =
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| chrono_unit = Epoch
| strat_unit = Series
| proposed_by =
| timespan_formality = Formal
| lower_boundary_def = Imprecise. Currently placed between acritarch biozone 5 and last appearance of Pterospathodus amorphognathoides. See Llandovery for more info.
| lower_gssp_candidates = None
| lower_def_candidates = A conodont boundary (Ireviken datum 2) which is close to the murchisoni graptolite biozone.
| lower_gssp_location = Hughley Brook, Apedale, U.K.
| lower_gssp_coords = {{Coord|52.5811|N|2.6389|W|display=inline}}
| lower_gssp_accept_date = 1980
| upper_boundary_def = FAD of the Graptolite Saetograptus (Colonograptus) varians
| upper_gssp_location = Pitch Coppice, Ludlow, U.K.
| upper_gssp_coords = {{Coord|52.3592|N|2.7772|W|display=inline}}
| upper_gssp_accept_date = 1980
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The Wenlock Epoch (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 {{Period start|Wenlock}} and {{Period start|Ludlow}} million years ago.{{cite web|title=International Chronostratigraphic Chart 2013/01|url=http://www.stratigraphy.org/ICSchart/ChronostratChart2013-01.pdf|publisher=International Commission on Stratigraphy|access-date=10 July 2013}}
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).{{cite book |isbn=9780521786737|title=A Geologic Time Scale 2004|last1=Gradstein|first1=Felix M.|last2=Ogg|first2=James G.|last3=Smith|first3=Alan G.|year=2004}} 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".{{cite journal | url=https://archive.org/details/proceedings218331838geol | title=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 | author=Murchison R.I. | journal=Proceedings of the Geological Society of London | year=1833–1834 | volume=2 | issue=33 | pages=[https://archive.org/details/proceedings218331838geol/page/14 14]}} He later modified this term to simply the "Wenlock rocks" in his book, The Silurian System in 1839.{{cite book | url=https://books.google.com/books?id=cKlAAAAAcAAJ&q=murchison+wenlock+limestone&pg=PA209 | title=The Silurian System | publisher=Murray | author=Murchison R.I. | author-link=Roderick Murchison | year=1839 | pages=208}}
Definition and subdivision
The Wenlock's beginning is defined by the lower boundary (or GSSP) of the Sheinwoodian. The end is defined as the base (or GSSP) of the Gorstian.{{cite book|title=The Geologic Time Scale 2012|date=14 August 2012|publisher=Elsevier Science Ltd|isbn=978-0-444-59425-9}}
The Wenlock is divided into the older Sheinwoodian and the younger Homerian stage. The Sheinwoodian lasted from {{Period start|Sheinwoodian}} to {{Period start|Homerian}} million years ago. The Homerian lasted from {{Period start|Homerian}} to {{Period start|Gorstian}} million years ago.
References
{{Reflist}}
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