Epochs in the Silurian
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Epochs of the Silurian Period.
Axis scale: millions of years ago.

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 that is comprehended between 438.5 ± 1.2 Ma and 433.4 ± 0.8 Ma (million years ago), approximately. The Telychian age succeeds the Aeronian age and precedes the Sheinwoodian age.[3]

It ended with the Ireviken event.

PalaeontologyEdit

AgnathansEdit

Agnathans of the Telychian
Taxa Presence Location Description Images
Rhuddanian-Telychian It had an elongated body and a dorsal fin and an anal fin near the back third of its body.
 
Jamoytius kerwoodi

ArthropodsEdit

Arthropods of the Telychian
Taxa Presence Location Description Images
Balizoma 440.8 million years ago to Pridoli epoch Dudley, England only been found in rocks of Silurian age.
 
Balizoma variolaris

CephalopodsEdit

Cephalopods of the Telychian
Taxa Presence Location Description Images
Dapingian-Homerian The shallow seas of Laurentia, Baltica and Siberia.[4] Head was soft muscular tissue at the opening of hard cone-like shell.
 
Cameroceras, shown feeding on a Aphetoceras, while a quartet of Cyclostomiceras swim by.

Ireviken eventEdit

The Ireviken event was the first of three relatively minor extinction events (the Ireviken, Mulde, and Lau events) during the Silurian period. It occurred at the Llandovery/Wenlock boundary (mid Silurian, 433.4 ± 2.3 million years ago). 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.

Anatomy of the eventEdit

The event lasted around 200,000 years, spanning the base of the Wenlock epoch.[2][5]

It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle.[5] The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.[5] The final two data are much further spaced, so harder to link with Milankovic changes.[5]

CasualtiesEdit

The mechanism responsible for the event originated in the deep oceans, and made its way into the shallower shelf seas. Correspondingly, shallow-water reefs were barely affected, while pelagic and hemipelagic organisms such as the graptolites, conodonts and trilobites were hit hardest.[2]

GeochemistryEdit

Subsequent to the first extinctions, excursions in the δ13C and δ18O records are observed; δ13C rises from +1.4‰ to +4.5‰, while δ18O increases from −5.6‰ to −5.0‰.[2]


ReferencesEdit

  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. ^ a b c d 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. ^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. ISBN 9780521786737.
  4. ^ Frey, R.C. 1995. "Middle and Upper Ordovician nautiloid cephalopods of the Cincinnati Arch region of Kentucky, Indiana, and Ohio" (PDF). U.S. Geological Survey, p.73
  5. ^ a b c d Jeppsson, L (1997). "The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events". In Brett, C.E.; Baird, G.C. (eds.). Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia University Press. pp. 451–492.