The Silurian in Ontario, Canada

Paleontology and geology

Central Ontario was above sea level throughout the Silurian, but parts of the north and south were covered by shallow seas for at least part of this period. In the Early and Middle Silurian, southeastern Ontario was under water. Limestones, sandstones, and shales in this area contain crinoid and eurypterid fossils, as well as abundant traces and burrows. One locality is famous for its preservation of soft tissues of jawless fish, arthropods, marine plants, and annelids, including velvet worms. These rocks are unique because they also preserve animals with hard skeletons, such as brachiopods and corals, which are rarely found alongside soft-bodied fossils. From the Middle to Late Silurian, the seas dried up, giving way to tidal flat, beach, and delta environments. Deposits of dolostone, salt, and gypsum formed in lagoons that occasionally got so shallow the seawater evaporated. Thick shales were deposited in mudflats, which in some areas preserve brachiopods oriented upward, in life position.

In the Late Silurian, the seas began to flood the northern part of Ontario. Stromatoporoids and corals built up reefs in these warm, shallow waters, which flourished with trilobites, brachiopods, gastropods, cephalopods, bryozoans, and crinoids. Fossils of these animals are preserved in the limestones, sandstones, and shales in many areas in the north.