The Paleontology of North America

the Cretaceous - 144 to 65 million years ago

World Paleogeography: The second major episode of continental rifting in the breakup of Pangea began in the Early Cretaceous. South America and Africa separated slowly from south to north creating the South Atlantic Ocean, while India and Madagascar rifted away from the western margins of Australia and Antarctica to form the Indian Ocean. At the same time, rifting between North America and Europe began, and Iberia turned counter-clockwise away from France. Throughout the Cretaceous, sea level was an average of 100 meters higher than today due to continental rifting and sea-floor spreading. Shallow seaways spread over many of the continents, including North America, South America, Africa, and Eurasia. Climate was globally warm during the Cretaceous, partly due to the mediating climatic effects of the shallow seas, and partly because the continental positions allowed warm waters to circulate around the globe. North American Paleogeography: During the Cretaceous, North America was moving northwest, closer to its present position. A large inland sea spread over much of central and southern North America. Low mountains stood out along the modern Appalachian Mountains and lowlands dominated from the modern Great Lake States into eastern Canada. Subduction along the western continental margin accelerated, adding intrusive and extrusive igneous rocks to the ancestral Sierra Nevada. The ancestral Rocky Mountains were uplifted, and exotic terranes were being added to its western margin. Paleontology: The Cretaceous Period may be best known for its ending. Marking the boundary between the Mesozoic and Cenozoic Eras, the end of the Cretaceous is defined by one of the most famous mass extinctions in the history of life on Earth. It has been estimated that over 60-70% of all marine species and nearly 15% of all terrestrial genera, including many mammals, went extinct at the end of the Cretaceous. Perhaps the most famous victims were the dinosaurs— only their descendents, the birds, survived. In fact, all land animals larger than about 20 kg (50 lbs., about the size of a large dog) died out. Gone too were many species of echinoderms, brachiopods, and molluscs, including ammonites and the reef-building rudist bivalves.

North America Today

Much of northeastern North America has been above sea level since the Cretaceous. These highlands have been shedding sediment into lower areas instead of accumulating it. Therefore, there are few rocks of this age in northeastern states. Exposures of Cretaceous rocks can be found in New Jersey, around the Appalachians from North Carolina to Tennessee, and west of the Mississippi River (from Texas north to Montana and west to California).

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