Wenlock Epoch

Last updated
Wenlock
433.4 ± 0.8 – 427.4 ± 0.5 Ma
Chronology
Etymology
Name formalityFormal
Name ratified1980 [4]
Usage information
Celestial body Earth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unit Epoch
Stratigraphic unit Series
Time span formalityFormal
Lower boundary definitionImprecise. Currently placed between acritarch biozone 5 and last appearance of Pterospathodus amorphognathoides . See Llandovery for more info.
Lower boundary definition candidatesA 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″N2°38′20″W / 52.5811°N 2.6389°W / 52.5811; -2.6389
GSSP ratified1980 [4]
Upper boundary definition FAD of the Graptolite Saetograptus (Colonograptus) varians
Upper boundary GSSP Pitch Coppice, Ludlow, U.K.
52°21′33″N2°46′38″W / 52.3592°N 2.7772°W / 52.3592; -2.7772
GSSP ratified1980 [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]

Contents

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]

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A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. Most, but not all, GSSPs are based on paleontological changes. Hence GSSPs are usually described in terms of transitions between different faunal stages, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2022, 77 of the 101 stages that need a GSSP have a ratified GSSP.

<span class="mw-page-title-main">Geologic time scale</span> System that relates geologic strata to time

The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy and geochronology. It is used primarily by Earth scientists to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.

<span class="mw-page-title-main">Silurian</span> Third period of the Paleozoic Era 444-419 million years ago

The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.

In the stratigraphy sub-discipline of geology, a Global Standard Stratigraphic Age, abbreviated GSSA, is a chronological reference point and criterion in the geologic record used to define the boundaries between different geological periods, epochs or ages on the overall geologic time scale in a chronostratigraphically useful rock layer. A worldwide multidisciplinary effort has been ongoing since 1974 to define such important metrics. The points and strata need be widespread and contain an identifiable sequence of layers or other unambiguous marker attributes.

In the geologic timescale, the Aeronian is an age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that began 440.8 ± 1.2 Ma and ended 438.5 ± 1.1 Ma. The Aeronian Age succeeds the Rhuddanian Age and precedes the Telychian Age, all in the same epoch.

<span class="mw-page-title-main">Ludfordian</span> Seventh stage of the Silurian

In the geologic timescale, the Ludfordian is the upper of two chronostratigraphic stages within the Ludlow Series. Its age is the late Silurian Period, and within both the Palaeozoic Era and Phanerozoic Eon. The rocks assigned to the Ludfordian date to between 425.6 ± 0.9 Ma and 423.0 ± 2.3 Ma. The Ludfordian Stage succeeds the Gorstian Stage and precedes the Pridoli Epoch. It is named for the village of Ludford in Shropshire, England. The GSSP for the Ludfordian is represented as a thin shale seam, coincident with the base of the Leintwardine Formation, overlying the Bringewood Formation in England.

<span class="mw-page-title-main">Gorstian</span> Sixth stage of the Silurian

In the geologic timescale, the Gorstian is an age of the Ludlow Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 427.4 ± 0.5 Ma and 425.6 ± 0.9 Ma, approximately. The Gorstian Age succeeds the Homerian Age and precedes the Ludfordian Age. The age is named after Gorsty village southwest of Ludlow. The base of the age is marked by Graptolites tumescens and Graptolites incipiens. The type section is located in a quarry in the Elton Formation at Pitch Coppice, Shropshire, United Kingdom.

<span class="mw-page-title-main">Homerian</span> Fifth stage of the Silurian

In the geologic timescale, the Homerian is an age of the Wenlock Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 430.5 ± 0.7 Ma and 427.4 ± 0.5 Ma, approximately. The Homerian Age succeeds the Sheinwoodian Age and precedes the Gorstian Age.

<span class="mw-page-title-main">Sheinwoodian</span>

In the geologic timescale, the Sheinwoodian is the age of the Wenlock Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 433.4 ± 0.8 Ma and 430.5 ± 0.7 Ma, approximately. The Sheinwoodian Age succeeds the Telychian Age and precedes the Homerian Age.

<span class="mw-page-title-main">Telychian</span> Third stage of the Silurian and last stage of the Llandovery

In the geologic timescale, the Telychian is the age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon. The Telychian Age was between 438.5 ± 1.2 million years ago (Ma) and 433.4 ± 0.8 Ma. The Telychian Age succeeds the Aeronian Age and precedes the Sheinwoodian Age. The name of the interval is derived from the Pen-lan-Telych Farm near Llandovery, Powys, Wales. The GSSP is located within the Wormwood Formation.

In the geologic timescale, the Rhuddanian is the first age of the Silurian Period and of the Llandovery Epoch. The Silurian is in the Paleozoic Era of the Phanerozoic Eon. The Rhuddanian Age began 443.8 ± 1.5 Ma and ended 440.8 ± 1.2 Ma. It succeeds the Himantian Age and precedes the Aeronian Age.

In the geological timescale, the Ludlow Epoch occurred during the Silurian Period, after the end of the Homerian Age. It is named for the town of Ludlow in Shropshire, England.

In the geological timescale, the Llandovery Epoch occurred at the beginning of the Silurian Period. The Llandoverian Epoch follows the massive Ordovician-Silurian extinction events, which led to a large decrease in biodiversity and an opening up of ecosystems.

The Ireviken event was the first of three relatively minor extinction events during the Silurian period. It occurred at the Llandovery/Wenlock boundary. The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species became extinct; 80% of the global conodont species also become extinct in this interval.

<span class="mw-page-title-main">Fröjel Formation</span>

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The Mulde event was an anoxic event, and marked the second of three relatively minor mass extinctions during the Silurian period. It coincided with a global drop in sea level, and is closely followed by an excursion in geochemical isotopes. Its onset is synchronous with the deposition of the Fröel Formation in Gotland. Perceived extinction in the conodont fauna, however, likely represent a change in the depositional environment of sedimentary sequences rather than a genuine biological extinction.

<span class="mw-page-title-main">Pridoli Epoch</span> Final Series (Epoch) of the Silurian

In the geologic timescale, the Pridolí Epoch is the uppermost subdivision of the Silurian Period, dated at between 423 ± 2.3 and 419.2 ± 3.2 mya. The Přídolí Epoch succeeds the Ludfordian Stage and precedes the Lochkovian, the lowest of three stages within the Lower Devonian geological epoch. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb, Slivenec, in the Czech Republic. The GSSP is located within the Požáry Formation, overlying the Kopanina Formation. Přídolí is the old name of a cadastral field area.

<span class="mw-page-title-main">Buildwas Formation</span>

The Buildwas Formation, formerly called Wenlock Shale and Buildwas Beds, is a geologic formation in Shropshire, England. It preserves fossils dating back to the Silurian period. The formation is the defining formation of the Sheinwoodian age of the Wenlock epoch, the Middle Silurian.

Conodonts are an extinct class of animals whose feeding apparatuses called teeth or elements are common microfossils found in strata dating from the Stage 10 of the Furongian, the fourth and final series of the Cambrian, to the Rhaetian stage of the Late Triassic. These elements can be used alternatively to or in correlation with other types of fossils in the subfield of the stratigraphy named biostratigraphy.

<span class="mw-page-title-main">Black Country Geopark</span> UNESCO Global Geopark in England

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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. 1 2 3 Holland, C. (1982). "The State of Silurian Stratigraphy" (PDF). Episodes. 1982: 21–23. Retrieved 11 December 2020.
  5. 1 2 "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.
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