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Volcanoes and Coral Reefs

Colour image of globe showing changing position of continents 435 million years agoRocks from the Silurian Period in New Brunswick include sedimentary and igneous rocks located mostly in the western half of the province. The sedimentary rocks were deposited in an ocean environment 443 to 416 million years ago and added to New Brunswick’s complex geology during the final closure of the Iapetus Ocean. Intrusive igneous rocks and extrusive volcanic rocks are a complex mix of formations formed in volcanic island arc and subduction zone settings as the Rheic Ocean closed and the Meguma Terrane, comprising much of Nova Scotia, began its collision with North America. Volcanic rocks (rhyolite to dacitic tuff) on the Kingston Peninsula record this event as remnants of the Kingston (volcanic island) Arc.

Colour graphic illustrating how volcanic island arcs are created above a subducting platePlumes of magma (molten rock) generated by the subduction and closing of the Iapetus Ocean rose like giant bubbles in the crust and solidified into features called plutons. The plutons from the Silurian and Devonian are found between Bathurst and Woodstock and in southwestern New Brunswick where the Saint George Plutonic Suite is comprised of a cluster of intrusive rocks, including the Bocabec Gabbro and Utopia Granite, well known as building stones.

During the Silurian, the pieces of New Brunswick were located near the equator. In the warm tropical waters off the coast, coral reefs developed around volcanic islands, similar to present-day South Pacific. The fossilized remains of these coral reefs and the animals that lived in them are preserved in limestones found today in northern New Brunswick near places like Jacquet River and Quinn Point, and in the south near Brown’s Flat. Sediments deposited in shallow ocean waters or lagoons also record the oldest fish fossils in New Brunswick, jawless fish known as heterostracans and anaspids, and our oldest sea scorpion remains.

Although new evidence for Ordovician land plants is now being discovered, it was during the Silurian Period that plants and animals emerged from the earth's oceans to gain a firm hold on land. The emergence of life on land was the biggest event in the history of life since the Cambrian Explosion. While New Brunswick has a good record of Devonian age land plants our Silurian fossil record is sparse. The Cripps Stream Formation near Beaver Harbour contains one of several fossil plant localities near the Bay of Fundy coast. Poorly preserved remains primitive plants were described in the 1960s, but little is known about them.