Paleontology and geology

For a relatively short time in the Early Tertiary, the last remnants of the Western Interior Seaway stretched from the Gulf of Mexico up to southwestern Manitoba. Shallow marine sandstones in this area contain fossils of single-celled marine organisms called dinoflagellates. As the sea withdrew, a vast swamp covered the area, which was filled with early evergreens, ginkgoes, and huge ferns. Over time, this plant material accumulated and was compacted into coal beds in between layers of sandstone and shale. These rocks are exposed in the southwestern edge of the province, but erosion has removed other Tertiary deposits.