undifferentiated rock units

Paleontology and geology

In the Early Devonian, Manitoba was above sea level and exposed to erosion, but toward the Middle Devonian, the seas in the southwest began to encroach again. In very shallow areas, sea water would occasionally evaporate, leaving behind deposits of salt and gypsum. In slightly deeper areas, corals and stromatoporoids built up reefs in the warm waters teeming with trilobites, brachiopods, gastropods, bryozoans, and crinoids. In the deep, low-oxygen basins, black shales formed as substantial amounts of organic material accumulated in the mud. Sea level fluctuated throughout the rest of the period, resulting in alternating deposits of shales, sandstones, limestones, and evaporites in many areas. By the Late Devonian, the water covered the southern half of the province, as well as the northeastern tip below Hudson Bay. While some of these Devonian rocks have been eroded away and others are buried below the surface, several exposures can be seen in the southwest and northeast.