There were higher rates of sea floor spreading and an increased length of the spreading ridges. By the Late Cretaceous the South Atlantic basin had opened, creating a north-south oriented Atlantic Ocean. The magmatic arc extended from Alaska to Baja California. It extended from the Gulf of Mexico to the Arctic and was 1000 miles wide at its widest point. There was abundant volcanic activity.
Sediments are red and brown because of better oxygenation.
The Western Interior Seaway collected clastics that were shed off the growing mountains to the west. This is the deepest part of the basin.