<P> In many spots in Scandinavia basaltic dikes are found with ages between 670 and 650 million years . These are interpreted as evidence that by that time, rifting had started that would form the Iapetus Ocean . In Newfoundland and Labrador, the Long Range dikes are also thought to have formed during the formation of the Iapetus Ocean . It has been proposed that both the Fen Complex in Norway and the Alnö Complex in Sweden formed as consequence to mild extensional tectonics in the ancient continent of Baltica that followed the opening of the Iapetus Ocean . </P> <P> The southern Iapetus Ocean opened between Laurentia and southwestern Gondwana (now South America) about 550 Ma in the Ediacaran--Cambrian transition . At the time it did so the Adamastor Ocean further east closed . The opening of the Iapetus Ocean probably postdates the opening of the Puncoviscana Ocean with the Iapetus Ocean being separated from the Puncoviscana Ocean by the ribbon - shaped Arequipa - Antofalla terrane . However, the formation of both oceans seems unrelated . </P> <P> Southwest of the Iapetus, a volcanic island arc evolved from the early Cambrian (540 million years ago) onward . This volcanic arc was formed above a subduction zone where the oceanic lithosphere of the Iapetus Ocean subducted southward under other oceanic lithosphere . From Cambrian times (about 550 million years ago) the western Iapetus Ocean began to grow progressively narrower due to this subduction . The same happened further north and east, where Avalonia and Baltica began to move towards Laurentia from the Ordovician (488 - 444 million years ago) onward . </P> <P> Trilobite faunas of the continental shelves of Baltica and Laurentia are still very different in the Ordovician, but Silurian faunas show progressive mixing of species from both sides, because the continents moved closer together . </P>

Widespread deposition over most of new york along edge of iapetus ocean