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Which parts of North America were covered by an epicontinental sea during the Cretaceous Period?

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Cretaceous paleogeography — Cretaceous Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cretaceous Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Cretaceous Period, significantly higher global sea levels led to the widespread inundation of continental landmasses by shallow epicontinental seas. In North America, these marine waters covered the western interior, creating a vast seaway that at times connected Arctic waters to the Tethys Sea.1

Geological evidence, such as the deposition of chalk, marine limestone, and carbon-rich black shales, confirms the presence of this interior sea across the region. This seaway was bordered to the west by rising mountains, which supplied abundant clastic sediments to the basin. The extent of these marine conditions is further evidenced by volcanic ash deposits, such as the "X" bentonite layer, which has been traced over 2,000 kilometers from central Manitoba to northern Texas.23