The Western Interior Seaway: A Late Mesozoic Petroleum Province:

The Western Interior Seaway accumulated thick sediments which support hydrocarbon sources and reservoirs beginning in the Jurassic Period where the seaway was limited to the Canadian British Columbia and Saskatchewan Provinces. Seas retreated and advanced throughout the Northern Canadian Provinces up until the Early Cretaceous Period when the seaway began to invade the western U.S. states. By Late Cretaceous time, the seaway was at its maximum coverage throughout the Great Plains and along ...