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Message: <blockquote data-quote="Davy Crockett" data-source="post: 291934" data-attributes="member: 367"><a href="https://www.dmr.nd.gov/ndfossil/poster/pierre/Pierre.pdf" target="_blank">https://www.dmr.nd.gov/ndfossil/poster/pierre/Pierre.pdf</a>   NORTH DAKOTA’S UNDERWATER WORLDDuring the Cretaceous, from about 90 million to 65 million yearsago, North Dakota was either completely or partially covered by subtropicalto warm temperate, shallow epicontinental seas. These seas occupied whatwas called the Western Interior Seaway, essentially the North Americanmid-continent. The seas were never very deep, perhaps a few hundred feetat most, and at their greatest extent they connected the Arctic Ocean withthe Gulf of Mexico. During low sea level, the Hell Creek Delta coveredwestern North Dakota and Fox Hills Sea shoreline habitats occurred incentral North Dakota. Fine grained sediments, mostly silt and clay,deposited on the floor of these oceans are now rocks of the Carlile,Niobrara, and Pierre Formations. These are the oldest rocks exposed inNorth Dakota. Entombed in these rocks are fossils of the animals andplants that inhabited the seas. Remains of marine reptiles, including themosasaur Plioplatecarpus, plesiosaurs, and the sea turtle, Archelon; fish(such as sharks, rays, and ratfish); birds; and invertebrates (including clams,cephalopods, snails, corals, and crabs) have been recovered from theserocks.</blockquote>