undifferentiated rock units

Paleontology and geology

In the Triassic, shallow to deep seas of the continental shelf and slope covered Yukon Territory. In the southwestern part of the territory, subduction closed the ocean basin that separated the continent from a series of volcanic islands. This activity sliced off pieces of oceanic crust, added them to the islands, and began squeezing the islands against each other and the continental slope. Sediments eroding from the islands and the mainland to the east were deposited in the seas over Yukon, while large reefs built up in shallow areas. These reefs were home to sponges, brachiopods, echinoderms, corals, bivalves, gastropods, and conodonts. Closer to shore, animals left burrows and traces, and pollen and spores washed in from the land. Also during this period, other parts of the territory were forming out in the ocean to the west. Some rocks from 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.