| abstract
| - The Western Interior Seaway was a location in the United States of America during the Cretaceous, when an inland sea split the land that is the United States in half. The Cretaceous beach was possibly located in the seaway, due to the presence of Hesperornis. (Episode 1.3) Some Deinosuchus which appeared in Maidenhead presumably came through an Anomaly from the seaway. (Fire and Water)
- The Seaway was created as the Pacific and North American tectonic plates collided, causing the Rocky Mountains to form in western North America. With high eustatic sea levels existing worldwide during the Cretaceous, waters from the Arctic Ocean in the north and the Gulf of Mexico in the south met and flooded the central lowlands, forming a sea that transgressed (grew) and regressed (receded) over the course of the Cretaceous. The earliest phase of the Seaway began in the mid-Cretaceous, when an arm of the Arctic Ocean transgressed south over western North America; this formed the Mowry Sea, so named for the Mowry Shale, a characteristic rock formation that is rich in oil shale. In the south, the Gulf of Mexico was an extension of the Tethys Sea, which met with the Mowry Sea in the late Cretaceous, forming the "complete" Seaway. At its largest, the Western Interior Seaway stretched from the Rockies to the Appalachians in the east, some 1000 km wide. At its deepest, it may have been only 800 or 900 meters deep, shallow in terms of seas. Two great continental watersheds drained into it from east and west, diluting its waters and bringing resources in eroded silt that formed shifting delta systems along its low-lying coasts. There was little sedimentation on the eastern shores of the Seaway; the western boundary however, consists of a thick clastic wedge eroded eastward from the Sevier orogenic belt. The western shore was thus highly variable, depending on variations in sea level and sediment supply. Widespread carbonate deposition suggests that the Seaway was warm and tropical, with abundant calcareous algae. Rudy Slingerland of Penn State University has computer-modelled a counter-clockwise gyre for the Cretaceous Seaway, with cooler waters flowing south along the eastern seacoasts of Wyoming and Colorado. At the end of the Cretaceous continuing uplift in a mountain-building episode called the Laramide orogeny hoisted the sandbanks (sandstone) and muddy brackish lagoons (shale), the thick sequences of silt and sandstone still seen today as the Laramie Formation, while low-lying basins between them gradually subsided. The Western Interior Seaway divided across the Dakotas and retreated south towards the Gulf of Mexico. This shrunken, regressive phase of the Western Interior Seaway is sometimes called the Pierre Seaway. During the early Paleocene, parts of the Western Interior Seaway (marine waters) still occupied areas of the Mississippi Embayment, submerging the site of present-day Memphis. Later transgression however, was associated with the Cenozoic Tejas sequence, rather than with the previous event responsible for the Seaway.
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![[RDF Data]](/fct/images/sw-rdf-blue.png)