undifferentiated rock units

Paleontology and geology

In the Early Silurian, basins in the northeast and southwest of Manitoba continued to accumulate sediment from the central portion of the province and reefs continued to build up in the shallow seas. Many different invertebrates thrived in the warm waters, including corals, brachiopods, trilobites, cephalopods, gastropods, and bryozoans. They left their traces alongside stromatolites in the very shallow areas. However, as sea level dropped in the Middle Silurian, some of these areas became extremely shallow, and dolostones, salt, and gypsum deposits replaced the limestones. Other areas were left exposed above sea level and erosion began to wear them down. For the rest of the period, sea level continued to fluctuate, and sediments were alternately deposited and removed depending on whether the areas were under water or exposed. The remaining sandstones, shales, limestones, dolostones, and evaporites outcrop in the northeastern and southwestern parts of the province, with more rocks below the surface.