Wenlock Epoch
| Wenlock | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chronology | |||||||||||||
| |||||||||||||
| 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 | ||||||||||||
| 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 | ||||||||||||
| Upper GSSP ratified | 1980[4] | ||||||||||||
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]
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
- ^ 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.
- ^ 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.
- ^ "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
- ^ a b c Holland, C. (1982). "The State of Silurian Stratigraphy" (PDF). Episodes. 1982: 21–23. Retrieved 11 December 2020.
- ^ a b "International Chronostratigraphic Chart 2013/01" (PDF). International Commission on Stratigraphy. Retrieved 10 July 2013.
- ^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. ISBN 9780521786737.
- ^ 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.
- ^ Murchison R.I. (1839). The Silurian System. Murray. p. 208.
- ^ The Geologic Time Scale 2012. Elsevier Science Ltd. 14 August 2012. ISBN 978-0-444-59425-9.
