undifferentiated rock units

Paleontology and geology

Through the Cambrian, the warm, shallow seas spread over eastern Yukon Territory, submerging the entire territory under water. In the north and southeast, two deeper basins continued to fill with shales, while the shallower areas around them accumulated sandstones, siltstones, and limestones. Archeocyathids built up reefs in these tropical seas, which were also home to trilobites, brachiopods, graptolites, and early molluscs. The Cambrian rocks in Yukon preserve fossils of these animals, and one location has yielded rare, three-dimensional fossils of eggs and embryos, possibly from some of these early animals.