Wenlock Epoch

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.^[5]

Wenlock
433.4 ± 0.8 – 427.4 ± 0.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chronology
−444 — – −442 — – −440 — – −438 — – −436 — – −434 — – −432 — – −430 — – −428 — – −426 — – −424 — – −422 — – −420 — – −418 — Paleozoic O Silurian D Late O Llandovery Wenlock Ludlow Přídolí Early D Rhuddanian Aeronian Telychian Sheinwoodian Homerian Gorstian Ludfordian             ← Lau event ← Mulde event^[1] ← Ireviken event^[2] Subdivision of the Silurian according to the ICS, as of 2021.^[3] Vertical axis scale: millions of years ago.
Etymology
Name formality	Formal
Name ratified	1980^[4]
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Epoch
Stratigraphic unit	Series
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, U.K. 52°34′52″N 2°38′20″W / 52.5811°N 2.6389°W / 52.5811; -2.6389
Lower GSSP ratified	1980^[4]
Upper boundary definition	FAD of the Graptolite Saetograptus (Colonograptus) varians
Upper boundary GSSP	Pitch Coppice, Ludlow, U.K. 52°21′33″N 2°46′38″W / 52.3592°N 2.7772°W / 52.3592; -2.7772
Upper GSSP ratified	1980^[4]

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).^[6] 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".^[7] He later modified this term to simply the "Wenlock rocks" in his book, The Silurian System in 1839.^[8]

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.^[9]

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.^[5]

References

1. Jeppsson, L.; Calner, M. (2007). "The Silurian Mulde Event and a scenario for secundo—secundo events". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 93 (02): 135–154. doi:10.1017/S0263593300000377.
2. Munnecke, A.; Samtleben, C.; Bickert, T. (2003). "The Ireviken Event in the lower Silurian of Gotland, Sweden-relation to similar Palaeozoic and Proterozoic events". Palaeogeography, Palaeoclimatology, Palaeoecology. 195 (1): 99–124. doi:10.1016/S0031-0182(03)00304-3.
3. "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
4. Holland, C. (1982). "The State of Silurian Stratigraphy" (PDF). Episodes. 1982: 21–23. Retrieved 11 December 2020.
5. "International Chronostratigraphic Chart 2013/01" (PDF). International Commission on Stratigraphy. Retrieved 10 July 2013.
6. Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. ISBN 9780521786737.
7. 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.
8. Murchison R.I. (1839). The Silurian System. Murray. p. 208.
9. The Geologic Time Scale 2012. Elsevier Science Ltd. 14 August 2012. ISBN 978-0-444-59425-9.