199.6 – 145.5 MILLION: JURASSIC
- Pangea supercontinent begins to split with significant mountain-building and volcanism;
- seas fill rift zones, Panthalassa and Tethys oceans begin shrinking;
- Climate warm and humid with vast tropical forests;
- The plankton that lived in the Jurassic period made our crude oil;
- Dinosaurs dominate the land;
- First birds arise from small dinosaurs;
- Marine reptiles flourish;
- Gymnosperm trees form global forests with vast ‘prairies’ of ferns.

Name | Diameter (km) | Age (megayears) | Dating method | Morphological type | Notes |
---|---|---|---|---|---|
Viewfield, Saskatchewan | 2.5 | 190 ± 20 | Geological dating | CONFIRMED Simple | Jurassic-Triasic post-impact deposit |
Cloud Creek, Wyoming | 7 | ~190 ± 30 | Geological dating | CONFIRMED Complex | Chronostratigraphic |
Hartney, Manitoba | 6 | <190 ± 20 | Geological dating | PROBABLE Complex? | Structurally uplifted centre |
Upheaval Dome, Utah | 2.57 | <170 | Geological dating | PROPOSED | Younger than the Jurassic Navajo Sandstone |