undifferentiated rock units

Paleontology and geology

For most of the Devonian, shallow to deep seas covered Yukon Territory. Deeper waters existed in basins in the north and southeast, as well as on the continental slope in the southwest, but the rest of the territory was covered by shallow waters. These warm, tropical seas were home to many different invertebrates, including brachiopods, graptolites, corals, bryozoans, trilobites, and gastropods. Pollen and spore fossils of lycopsids and ferns have also been found in marine sediments, indicating that plants covered low-lying areas near the sea. By the Late Devonian, subduction began to form volcanic islands in the southwest. This activity forced magma up to the surface to the east, opening a new ocean between the islands and continent and forming large blocks of granite.