Laurentia

Laurentia is an old continent incorporating much of what is now North America and Greenland. Like any well-run corporation, it seems to have been built slowly, by gradual accretion and merger, from a truly ancient (Archean age) region around modern Quebec. We aren't yet sure what to make of the recent profusion of supposed Paleo- and Mesoproterozoic supercontinents. See Sankaram 2003) for a brief review. However, through most of Proterozoic and Phanerozoic time, Laurentia also seems to have been associated with Baltica and Siberia, forming the continental assemblage sometimes called Nena. Much more variably, Laurentia has also had ties with Africa and South America.

We can be reasonably confident that Laurentia was the core of the Stenian assembly of Rodinia. After the failure of the Rodinian enterprise in the early Neoproterozoic, most of the cratons tore off to the south pole to sign on with Gondwana. Laurentia, however, drifted thoughtfully to the southwest, pondering its next move and gradually rotating counterclockwise. During Cambrian and Ordovician time Laurentia was approached by its old associates, Baltica and Siberia, which had likewise been suspicious of the Gondwanan venture. Having reassembled its old management team, Laurentia merged with Baltica to form Euramerica d/b/a the Old Red Continent (ORCo), a conglomerate engaged in the production and distribution of many success lines of fishes and land plants from a variety of convenient shallow sea locations.

The success of this strategy seems to have attracted defectors from Gondwana, so that Euramerica was soon assimilating a talented group of Gondwanan veterans collectively known as Avalonia and Armorica. This expansion seems to have caused a series of shake-ups and mountain-building events in the Silurian and Devonian, ultimately requiring the closure of the Iapetus Sea location, with serious erosion in some up-scale Eastern territories. However, this reorganization also drove ORCo to develop some radically new technology, including tetrapods and trees, which rapidly created a vast new internal market for terrestrial products.

During the Late Ordovician and Early Silurian the Iapetus plate then began to subduct under Laurentia causing further mountain building. The collision between the plates resulting in telescoping of the continental crust and a period of volcanism. This event marks first episode of the Appalachian Mountain building. Erosion of the highland area led to development of thick clastic wedges. At the same time there occurred on other side of Iapetus Ocean a similar period of mountain building, the Caledonian Orogeny.

During the Late Silurian and Devonian the Iapetus Ocean closed as Laurentia collided with the continent of Baltica to form the supercontinent Laurussia/Euramerica.

Links

Inter. Subcommission on Cambrian Stratigraphy

Laurentia-Kalahari collision and the assembly of Rodinia

Sankaran, AV (2003), The supercontinent medley: Recent views. Curr. Sci.85: 1121-1124.