undifferentiated rock units

Paleontology and geology

The oldest Precambrian rocks in Yukon Territory are 1.7 Ga igneous and metamorphic rocks that belong to the ancient North American continent (Laurentia). After these rocks formed, Laurentia collided with other continents to form a supercontinent, and this territory was near the center. About 750 Ma, the supercontinent began to break up, and eastern Yukon was at the edge of the continent. Shallow seas covered most of the territory, and sandstones and shales formed as sediments eroded off the land. A few times, glaciers developed on land, scraping up larger rocks, carrying them to the sea, and dropping them over the usual marine deposits. The oceanic crust continued to rift, and as more sediment accumulated, basins dropped down in the north and southeast, which filled with deeper water shales and cherts. In the shallow areas, some of the earliest multicellular animals could be found, such as Ediacaria flindersi, Sekwia excentrica, and Cyclomedusa. Their fossils have been found in siltstones and sandstones in the south.