Western Interior Seaway

The Western Interior Seaway, also Cretaceous Interior Seaway, was an extensive epikontinentales shallow sea in the middle and late Cretaceous period, which ran through a broad estuary of the North American continent from north to south.

Historical Geology

The Western Interior Seaway was created when the Pacific and North American tectonic plates collided and it came to the formation of the Rocky Mountains in western North America. As the sea level during the Cretaceous period was high worldwide, flowed water from the north to the Arctic Ocean and south from the Gulf of Mexico into the central lowlands and formed a shallow sea, which during the Cretaceous times enlarged ( transgression ) and retired again (regression ).

The earliest phase of the Seaway began shortly before the end of the Early Cretaceous, when a southern foothills of the Arctic Ocean spread over western North America. He will Mowry Sea, named after a characteristic rock formation rich in oil shale. To the south stretched the Gulf of Mexico, then part of the Tethysozeans who joined in the mid-Cretaceous with the Mowry Sea and the full Seaway formed.

The Interior Seaway of the Rocky Mountains stretched to its greatest extent in the west to the Appalachian Mountains in the east and was about 1000 kilometers wide. Its greatest depth was about 800 to 900 meters, low compared to other seas. The rivers of two great continental watersheds resulted in him from the east and from the west, and encamped from fine-grained sediment ( silt ) in extensive river deltas along the flat shores. There was only a slight sedimentation on the eastern shores of the sea, the west bank, however, consisted of massive sediment packages that were removed during the Sevier orogeny - east. The coastline on the west bank was therefore be variable, depending on changes in sea level and sediment input to a high degree.

Widespread Carbonatablagerungen suggest a warm, tropical climate, developed in which mass of lime deposits forming algae. Rudy Slingerland of Penn State University calculated with the aid of a computer model that the flow in the Western Interior Seaway was counter-clockwise, with cooler water flowed southward along the eastern coasts in today's Wyoming and Colorado.

At the end of the Cretaceous period it came to Lara mixing orogeny and in low-lying basin sandstone and shale was deposited. The Western Interior Seaway divided and retreated southward back to the Gulf of Mexico. This shrinking regressive phase of the Western Interior Seaway is called the Pierre Seaway.

During the early Paleocene flooded parts of the Western Interior Seaway the lower reaches of the Mississippi to Memphis today.

Life in the sea

Numerous fossil evidence documenting the past life in the Western Interior Seaway. In the sea lived predatory reptiles, including the largest animals of the Cretaceous seas: mosasaur, which were up to 18 meters long, as well as ichthyosaurs and plesiosaurs. Even sharks came before, for example Squalicorax, further bony fish as Pachyrhizodus, Enchodus and Xiphactinus. There were molluscs, including ammonites and squid -like belemnites. Even single-celled plankton has been preserved fossil, including foraminifera, radiolarians and Coccolithophorales, an order of calcareous algae. These algae left behind when they die tiny disc-shaped lime platelets that coccoliths, which sank to the bottom and those mighty chalk deposits were formed, which owes its name to the Cretaceous period.

The Western Interior Seaway was also home earlier birds, including the flightless Hesperornis and seeschwalbenähnliche Ichthyornis. Both had occupied with teeth beaks.