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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 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.
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.
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.
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.
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.
In the geologic timescale, the Telychian is the third and final 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 Burgsvik Beds are a sequence of shallow marine limestones and sandstones found near the locality of Burgsvik in the southern part of Gotland, Sweden. The beds were deposited in the Upper Silurian period, around 420 million years ago, in warm, equatorial waters frequently ravaged by storms, in front of an advancing shoreline. The Burgsvik Formation comprises two members, the Burgsvik Sandstone and the Burgsvik Oolite.
The Lau event was the last of three relatively minor mass extinctions during the Silurian period. It had a major effect on the conodont fauna, but barely scathed the graptolites, though they suffered an extinction very shortly thereafter termed the Kozlowskii event that some authors have suggested was coeval with the Lau event and only appears asynchronous due to taphonomic reasons. It coincided with a global low point in sea level caused by glacioeustasy and is closely followed by an excursion in geochemical isotopes in the ensuing late Ludfordian faunal stage and a change in depositional regime.
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 became extinct in this interval.
The Fröjel Formation is a ten-metre thick siliciclastic unit lying in the carbonate sequence of Gotland, Sweden. Deposited some 424 million years ago during the mid Homerian, the sediments represent an unusually high supply of terrigenous sediment into the shallow carbonate platform that was to become the island of Gotland. Their deposition is coincident with a δ13C excursion of +3‰.
Gotland is made up of a sequence of sedimentary rocks of a Silurian age, dipping to the south-east. The main Silurian succession of limestones and shales comprises thirteen units spanning 200–500 m (660–1,640 ft) of stratigraphic thickness, being thickest in the south, and overlies a 75–125 m (246–410 ft) thick Ordovician sequence. Precambrian shield rocks that underlie these sediments are found 400 to 500 meters sea level. Sedimentary rocks cropping out in Gotland were deposited in a shallow, hot and salty sea, on the edge of an equatorial continent. The water depth never exceeded 175–200 m (574–656 ft), and shallowed over time as bioherm detritus, and terrestrial sediments, filled the basin. Reef growth started in the Llandovery, when the sea was 50–100 m (160–330 ft) deep, and reefs continued to dominate the sedimentary record. Some sandstones are present in the youngest rocks towards the south of the island, which represent sand bars deposited very close to the shore line.
In the geologic timescale, the Přídolí 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.
The Wenlock 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.
The Lundgreni Event, also known as the Mid-Homerian Biotic Crisis, was an extinction event during the middle Homerian age of the Silurian period. Evidence for the event has been observed in Silurian marine deposits in the Iberian Peninsula, Bohemia, and Poland.
The Šilalė Event was an extinction event affecting conodonts during the Přídolí, the final stage of the Silurian period.
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.
- 1 2 Samtleben, C.; Munnecke, A.; Bickert, T. (2000). "Development of facies and C/O-isotopes in transects through the Ludlow of Gotland: Evidence for global and local influences on a shallow-marine environment". Facies. 43 (1): 1–38. doi:10.1007/BF02536983. S2CID 130640332.
- ↑ Jarochowska, Emilia; Ray, David C; Röstel, Philipp; Worton, Graham; Munnecke, Axel (2017). "Harnessing stratigraphic bias at the section scale: Conodont diversity in the Homerian (Silurian) of the Midland Platform, England". Palaeontology. 61: 57–76. doi: 10.1111/pala.12326 . S2CID 135200300.
- ↑ Biebesheimer, Ellie J.; Cramer, Bradley D.; Calner, Mikael; Barnett, Bruce A.; Oborny, Stephan C.; Bancroft, Alyssa M. (2021). "Asynchronous δ13Ccarb and δ13Corg records during the onset of the Mulde (Silurian) positive carbon isotope excursion from the Altajme core, Gotland, Sweden". Chemical Geology. 576: 120256. Bibcode:2021ChGeo.576l0256B. doi:10.1016/j.chemgeo.2021.120256. ISSN 0009-2541. S2CID 234817512.