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Ordovician period dating

The Panthalassic Ocean covered much of the northern hemisphere, and other minor oceans included Proto-Tethys, Paleo-Tethys, Khanty Ocean which was closed off by the Late Ordovician, Iapetus Ocean, and the new Rheic Ocean.

As the Ordovician progressed, we see evidence of glaciers on the land we now know as Africa and South America.

Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, and invertebrate faunas with dominantly calcitic skeletons.

The small continent Avalonia separated from Gondwana and began to head north towards Baltica and Laurentia.

The Rheic Ocean between Gondwana and Avalonia was formed as a result.

Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole.

Early in the Ordovician, the continents Laurentia (present-day North America), Siberia, and Baltica (present-day northern Europe) were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move towards Laurentia later in the period, causing the Iapetus Ocean to shrink between them.

At the time these land masses were sitting at the South Pole, and covered by ice caps.

ordovician period dating-20

For most of the Late Ordovician, life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected planktonic forms like conodonts, graptolites, and some groups of trilobites (Agnostida and Ptychopariida, which completely died out, and the Asaphida which were much reduced).As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician.Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts.The Ordovician Period in Britain was traditionally broken into Early (Tremadocian and Arenig), Middle (Llanvirn [subdivided into Abereiddian and Llandeilian] and Llandeilo) and Late (Caradoc and Ashgill) epochs.The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column.These volcanic island arcs eventually collided with proto North America to form the Appalachian mountains.By the end of the Late Ordovician these volcanic emissions had stopped.It received international sanction in 1906, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress.The Ordovician Period started at a major extinction event called the Cambrian-Ordovician extinction events some time about 488.3 ± 1.7 Ma (million years ago), and lasted for about 44.6 million years.This second period of the Paleozoic era created abundant fossils and in some regions, major petroleum and gas reservoirs.The boundary chosen for the beginning both of the Ordovician Period and the Tremadocian stage is highly useful.

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