undifferentiated rock units

Paleontology and geology

In the Early Tertiary, tectonic activity in the west uplifted the Northwest Territories, and the Western Interior Seaway drained away. In the northeast, Baffin Bay continued to open up as Greenland rotated and collided with islands in the north. This collision folded, faulted, and pushed up some areas into mountains, while other areas dropped down into basins. By the Middle Tertiary, most of the territory was above sea level, and deposition was restricted to lakes, rivers, and these small basins. Deposits of sandstone, siltstone, and shale preserve abundant wood, seed cone, and pollen fossils. One area even preserves tree stumps upright in growth position. These plant fossils show that relatives of modern plants from warmer, more southern areas were once common above the Arctic Circle. Forests and swamps were filled with Pinus (pine), Picea (spruce), Metasequoia (dawn redwood), Taxodium (cypress), Juglans (walnut), Liriodendron (magnolia), and many different mosses. By the end of the period, the climate became cooler, temporary ice caps developed to the north, and forests were restricted to lower elevations.