The Western Interior Seaway splits North America
A shallow sea runs from the Arctic to the Gulf of Mexico, cutting the continent in two.
- When
- —
- Duration
- 30 million years
- Known to
- ± 5 million years
- Era
- Cretaceous, Mesozoic
High sea levels and a subsiding foreland basin flood the middle of North America, creating a seaway up to a thousand kilometres wide and several hundred metres deep that separates Laramidia in the west from Appalachia in the east. It moderates the continental climate, isolates dinosaur faunas on either side long enough for them to diverge, and fills with the chalk, shale and superbly preserved marine reptiles and fish of Kansas and the Dakotas. It drains away as sea levels fall towards the end of the period.