undifferentiated rock units

Paleontology and geology

The Jurassic was a time of substantial tectonic activity in Yukon Territory. Subduction in the southwestern part of the territory began to push the volcanic islands in that area over the continental shelf that covered the rest of the territory. This activity folded, faulted, and metamorphosed many rocks while pushing them up into mountain ranges and moving them farther to the east. It also brought magma to the surface, which formed large blocks of granite under the territory. As mountains rose up, the shallow seas were replaced by narrower, deeper basins where underwater avalanches were common. By the end of the period, the volcanic islands were part of the high mountains that covered much of the territory, while other parts were approaching from the west. The limestones, sandstones, shales, and conglomerates from the Jurassic seas contain fossils of ammonites and bivalves. Some rocks form this period may be included in the undifferentiated Mesozoic rocks on this map because the substantial alteration and movement they experienced makes them difficult to date.