western interior seaway

8/9/2019 Western Interior Seaway

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Kanook Tlingit NationMarch 2010

Approximately 100 million years ago a massive sea split the North AmericanContinent from the Arctic Ocean in the north to the Gulf of Mexico in the south.

A seaway teaming with life, not as you and I know today but life forms that whenthey passed into the ages, laid down the fossil fuel base we are just beginning totap, some extractions quick and profitable such as in the Texas and Oklahoma, whileothers are proving to be expensive and the process harmful to the environment.

The Western Interior Seaway (Cretaceous Seaway) as you can see in the above mapwas a massive waterway that covered much of the interior of North America duringthe early and mid Cretaceous epoch from 100 to 65 million years ago, and wasamong the largest continental seas of all time, stretching from Utah in the west tothe western Appalachians in the east, a total of 621 miles wide, with an deepestdepths of 2,624 feet to 2,953 feet (averaging a little over mile), overall it was a

relatively shallow sea. It covered most of the shallow southeastern United States,including every state adjacent to todays Gulf of Mexico.

It was created during the period when the Atlantic Ocean was experiencing thespreading of its seafloor, whereas so much new rock was created that it displacedthe water increasing sea-levels worldwide for millions of years, along with the nownon-existent Farallon 1 and North American Plates colliding, which caused the Rocky

1 http://en.wikipedia.org/wiki/Farallon_Plate
http://en.wikipedia.org/wiki/Farallon_Platehttp://en.wikipedia.org/wiki/Farallon_Plate


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Mountains to form in western North America 2 , the resultant action created adepression or Foreland Basin in the middle of America. This depression and thehighly variable sea-levels existing during the Cretaceous allowed the waters fromthe Arctic Ocean in the north and the waters from the Gulf of Mexico in the south tomeet and flood the central lowlands, forming this sea that ebbed and flowed over

the course of the Cretaceous epoch.Before the Western Interior Seaway was the Mowry Sea, whereas during the early

Cretaceous period (145 135 mya), was formed as the North American plate driftedwestward forcing the eastern edge of the Pacific plate deep into the earths mantle.

This subduction created a chain of volcanoes from Mexico to southwestern Canadathat hurtled large quantities of ash and lava, where the ash billowed high into theprevailing winds scattering the ash eastward. As it fell it accumulated across theland, with generous amounts falling into the Mowry Sea that occupied much of thecentral United States. Closed at its southern end it stretched northward in a narrowbody until it reached the Arctic Ocean. Because of its closed southern end it isfigured that it was a shallow calm sea, and somewhat stagnant due to the lack of currents from being closedthus diminishing it overall circulation. In addition to theash fall, it accumulated minerals that eroded from the surrounding landforms.

During the late Cretaceous the Mowry eventually joined with the Tethys Sea 3 ,which complete the Western Interior Sea, from that time two continental watershedsdrained into it from the east and from the west, diluting its saline waters and addingmore resources in the manner of eroded silt that formed shifting delta systems allalong its low-lying coasts. There was little sedimentation on the eastern shores,whereas the western coasts consist of a thick clastic wedge 4 which eroded eastwardfrom the Sevier orogenic belt 5 . The western shore was thus highly variable,depending on the variations of the sea-level, and the sediment accumulation,whereas this sediment accumulation suggests that the Western Interior Seaway waswarm and tropical with abundant algae computer models of late demonstrate acounter-clockwise circulation on the Seaway, with the cooler waters from the Arcticflowing south along the eastern seacoasts of Wyoming and Colorado.

At the end of the Cretaceous the continued uplift of a mountain-building episodecalled the Laramide orogeny 6 , lifted the sandbanks (sandstone) and muddy brackishlagoons (shale), the thick sequences of silt and sandstone still seen today as theLaramie Foundation 7 , while low-lying basins like the Powder River Basin in Wyomingbetween them gradually subsided. In time the Western Interior Seaway dividedacross the Dakotas and retreated south to the Gulf of Mexicothis shrinking

regressive phase of the Western Interior Seaway is referred to by some as the PierreSeaway.

2 http://en.wikipedia.org/wiki/North_American_Plate 3 http://en.wikipedia.org/wiki/Tethys_Sea 4 http://en.wikipedia.org/wiki/Clastic_wedge 5 http://en.wikipedia.org/wiki/Sevier_orogeny 6 http://en.wikipedia.org/wiki/Laramide_orogeny 7 http://en.wikipedia.org/wiki/Laramie_Formation
http://en.wikipedia.org/wiki/North_American_Platehttp://en.wikipedia.org/wiki/Tethys_Seahttp://en.wikipedia.org/wiki/Clastic_wedgehttp://en.wikipedia.org/wiki/Clastic_wedgehttp://en.wikipedia.org/wiki/Sevier_orogenyhttp://en.wikipedia.org/wiki/Laramide_orogenyhttp://en.wikipedia.org/wiki/Laramie_Formationhttp://en.wikipedia.org/wiki/North_American_Platehttp://en.wikipedia.org/wiki/Tethys_Seahttp://en.wikipedia.org/wiki/Clastic_wedgehttp://en.wikipedia.org/wiki/Sevier_orogenyhttp://en.wikipedia.org/wiki/Laramide_orogenyhttp://en.wikipedia.org/wiki/Laramie_Formation


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This sea teamed with life, albeit life that you and Idont see hanging around anymore, some say to ourbenefitmost of these creatures weighted more thantwo modern day locomotives, and stretch from hereto tomorrow. Albeit was a shallow sea it had

numerous predatory marine reptiles, like theMosasaurs (lizard in Greek) who were a serpentinereptile these ferocious predators are now consideredto the closest relatives of snakes due to symptomatic similarities in jaw and skullanatomies, they were lepidosaurs, reptiles with overlapping scales. It is believedthey evolved from semi-aquatic squamates 8 known as the aigialosaurs 9 closerelatives of modern-day monitor lizards, in the Early Cretaceous Period. During thelast 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with theextinction of the ichthyosaurs and pliosaurs, the Mosasaurs became the dominantmarine large 60 foot reptile,

They shared the sea with the Squalicorax (crow shark) of the extinct lamniform 10 shark,evidence points to this predator reaching 16.5feet in length, classified as a predator he wasalso a scavenger, but his main food wasturtles, mosasaurs, ichthyodectes and otherbony fishes and

sea creatures. His distant cousin also roams theWestern Interior Seaway, whereas the PtychodusMortoni a giant (33 feet) shell-fish eating shark slipsthrough the water like a bullet making short work of any shellfish it encounters.

And the food for theSqualicorax consists of theadvanced bony fish like the Pachyrhizodus which bearsomewhat of a resemblance to the ever popular Salmon of theday, these guys swim in schools as do they buddies theEnchodus , a small fish around 2.5inches in length modern day sardine,

or herring? The larger of the species, bony fish is the 16-foot Xiphactinus , making him a

sizeable foe against theSqualicorax.Additional sea life included

invertebrates, like the mollusks,ammonites and squid like belemnites and of course the

8 http://en.wikipedia.org/wiki/Squamates 9 http://en.wikipedia.org/wiki/Aigialosaur 10 http://en.wikipedia.org/wiki/Lamniformes
http://en.wikipedia.org/wiki/Squamateshttp://en.wikipedia.org/wiki/Squamateshttp://en.wikipedia.org/wiki/Aigialosaurhttp://en.wikipedia.org/wiki/Lamniformeshttp://en.wikipedia.org/wiki/Lamniformeshttp://en.wikipedia.org/wiki/Lamniformeshttp://en.wikipedia.org/wiki/Squamateshttp://en.wikipedia.org/wiki/Aigialosaurhttp://en.wikipedia.org/wiki/Lamniformes


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plankton which gave the Cretaceous epoch its name, the coccolithophores 11 , as theysecreted the chalky platelets, along with the foraminiferans 12 and radiolarians 13 .

Wandering around on its shorelines you wouldcommonly find a Claosaurus (broken lizard), thatreached a height of 16 feet and weighted in at 1,050

lbs, he was a well knownplant eater.

There was manyHesperornis swimmingaround, they were a large wingless bird (feet in length)

that hunted for its subsistence in the sea, swimming about using its powerful legs.It has lobed toes as found in todays grebes, rather than webbed this determinedbased on their ability to rotate, webbed toes would have hindered this ability. Now Inot sure at what corner video store this ability was found, but someone way smarterthan I made a determination.

The Ichthyornis seabird was as pesky as the common seagullis today, flying about and scavenging for its daily bread. Thistwo foot bird had one major difference than most birds today,the jaws had numerous small, sharp teeth along with its largewinds and breastbone that suggests they had strong flightability.

During the time of the Western Interior Seaway, a few milesaway another important landform today was coming into itsownthe Bryce Canyon in Utah, where it has been determined that its make upwas determined by the ebb and flow of the levels of the sea.

The same forces that occurred during the Laramide Orogeny, which began some70 mya and that created the Rocky Mountains were at play in the Bryce areastretching the area into the high plateaus this majestic force uplifting the ColoradoPlateaus and changing the course of the Colorado River and opening the Gulf of California about 5 mya, created the hoodoos, badlands, and monoliths we find in theBryce Canyon National Park.

11 http://en.wikipedia.org/wiki/Coccolithophore 12 http://en.wikipedia.org/wiki/Foraminifera 13 http://en.wikipedia.org/wiki/Radiolarian
http://en.wikipedia.org/wiki/Coccolithophorehttp://en.wikipedia.org/wiki/Coccolithophorehttp://en.wikipedia.org/wiki/Foraminiferahttp://en.wikipedia.org/wiki/Foraminiferahttp://en.wikipedia.org/wiki/Radiolarianhttp://en.wikipedia.org/wiki/Radiolarianhttp://en.wikipedia.org/wiki/Coccolithophorehttp://en.wikipedia.org/wiki/Foraminiferahttp://en.wikipedia.org/wiki/Radiolarian


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Grand Canyon (A), Chocolate Cliffs (B), Vermilion Cliffs (C), White Cliffs(D), Zion Canyon (E),

Gray Cliffs (F), Pink Cliffs (G), Bryce Canyon (H)The Grand Staircase

The oldest sequence of these super-sequence of rocks are exposed in the GrandCanyon, the intermediate in Zion National Park and the youngest parts are laid barein the Bryce Canyon region, whereas a small amount of overlap occurs in andaround each park. Keep in mind that the formation of the Grand Staircase tookover 2000 million years of our Blue Marbles history, whereas the rocks exposed inthe Bryce Canyon are about 100 million years younger than those in nearby ZionNational Park and likewise the rock in the Zion National Park are younger thanthose in the Grand Canyon.

As the shoreline of the Western Interior Seaway moved back and forth, the Bryceregion alternated from being part of the Sevier landmass to being under theCretaceous Seaway, creating therefore alternating layers of non-marine, inter-tidal,and marine sediments that layer on top of each other.

Conglomerate 14 , siltstone 15 and fossil-rich sandstone add up to approximately 300feet, mark the arrival of the Western Interior Seaway. In addition there is foundwhat is known as Dakota Sandstone 16 , marked as the oldest formation exposed in

the Bryce Canyon region, and as mentioned is the youngest one exposed in the Zionand Kolob canyons area to the southwest.

Found in the Dakota Sandstone are copiousamounts of petrified wood , oyster bedscontaining millions of fossils and large amount of coal. These formations can be seen in the PariaValley 17 where you can find sand that accumulatedon beaches and lagoons, and vast coal-producingswamps as the Western Interior Seaway advancedand later retreated this area sits on much older

Jurassic formations that are not exposed in theimmediate region.As the Western Interior Seaway became deeper and calmer it deposited mud and

silt on top of the Dakota Formation which eventually produced the black Tropic

14 http://en.wikipedia.org/wiki/Conglomerate_%28geology%29 15 http://en.wikipedia.org/wiki/Siltstone 16 http://en.wikipedia.org/wiki/Dakota_Sandstone 17 http://www.americansouthwest.net/utah/grand_staircase_escalante/paria.html
http://en.wikipedia.org/wiki/Conglomerate_(geology)http://en.wikipedia.org/wiki/Conglomerate_(geology)http://en.wikipedia.org/wiki/Siltstonehttp://en.wikipedia.org/wiki/Siltstonehttp://en.wikipedia.org/wiki/Dakota_Sandstonehttp://en.wikipedia.org/wiki/Dakota_Sandstonehttp://www.americansouthwest.net/utah/grand_staircase_escalante/paria.htmlhttp://www.americansouthwest.net/utah/grand_staircase_escalante/paria.htmlhttp://en.wikipedia.org/wiki/Conglomerate_(geology)http://en.wikipedia.org/wiki/Siltstonehttp://en.wikipedia.org/wiki/Dakota_Sandstonehttp://www.americansouthwest.net/utah/grand_staircase_escalante/paria.html


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Shale that is found in parts of Utah and is up to 985 feet thick in the PariaAmphitheater, whereas it forms the un-vegetated badlands seen in the TropicValley 18 , known as perhaps the most fossil-rich formation in the area containinguncounted numerous straight-shelled and coiled ammonites.

Hoodoos in Claron Formation, Bryce Canyon The Western Interior Seaway was already retreating east and to the south when

the Straight Cliffs Foundation wasdeposited, whereas it layers representvarious stages of the retreatThe cliff-forming sandstone of the TibbetCanyon Member was deposited ontop of the Tropic Shale in a shallowmarine and later near shore

environments and then shale andsandstone from the Smokey HollowMember were deposited on top of itsbasal layer of coal-rich mudstone incoastal swamps and lagoons on the

shore of the Seaway. While the alternating layers of shale and sandstone mixedwith massive coal deposits of the John Henry Member were laid down in theswamps, lagoons and rivers and streams and their associated depositsenvironments as one member. The formation eventually erodes into almost un-climbable cliffs and escarpments of whitish to yellow-gray sandstones that arerelatively thin inter-bedded with layers of shale and mudstone, numerous sharkteeth have been found in the lower parts of the formation.

Lakes and east-flowing rivers became common as the Seaway retreated,themselves a dominant settling place for sediment following its retreat. Such as theflow that created the Wahweap Foundation found in southern Utah and northernArizona in and around the Lake Powell area, whereas dinosaur fossils have been

18 http://www.brycecanyoncountry.com/tropic.html
http://www.brycecanyoncountry.com/tropic.htmlhttp://www.brycecanyoncountry.com/tropic.htmlhttp://www.brycecanyoncountry.com/tropic.html


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located amongst other types of fossils. The Wahweap is part of the Grey Cliffs of the Grand Staircase, dinosaur remains include some of the Hadrosauroideas.

Family tree of the Hadrosauroidea.Representative genera of each tribe are shown to scale

As the retreat continued a flood plain crossed by rivers and lakes developed in theBryce Canyon, where mud and sand accumulated in this to become gray sandstoneand mudstones of the Kaiparowits Formation, located in the Kaiparowits Plateau.


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further to the west were the Sevier Highlands. Erosion from the Highlandsdeposited around 1500 feet of what is now the Straight Cliffs Formation.Remnants in the interior are now seen as beds of coal, whereas later deposits in theCretaceous formed higher sandstone layers, known as the Wahweap andKaiparowits Formations.

Found in eastern Wyoming was another largedinosaur, its length at over 30 feet named theNedoceratops , a plant eating fellow this speciesthrived in North America and Asia during theCretaceous epoch, all are known to have ceased theirexistence after the K-T extinction event.

Between 68 mya and 65 mya you would have foundroaming around in Wyoming the most famous of alldinosaurs, the infamous Tyrannosaurus Rex , or the T-rex , that lived exclusively in Western North America

and had an extremely wide range in itssearching for subsistence. It has thedistinction of being the last non-aviandinosaur to exist prior to the K-T extinctionevent 65 million years age. The T-rex wasthe largest known tyrannosaurid and thelargest know land predator measuringsome 42 feet in length, 13 feet tall, at thehips and weighting 7.5 tons, it is believedhe may have preyed on hadrosaurs andceratopsians, while some scholars believe he was a scavenger.

And although more commonly identified with Europe and the British Islands therehave been some types of Plesiosaurs found in the Western Interior Seaway

footprint, this was a marine carnivoreclassified as a reptile and they are said toresemble a snake threaded through theshell of a turtle, albeit they had no shell.

From the Arctic Ocean to the Gulf of Mexico this ancient sea containednumerous species of life, and its ancientseabeds left a record of all this and the

floraand fauna that was in its life. Some 65.5million years ago a large piece of rock slammedinto the Yucatan Peninsula near today thevillage of Chicxulub and the beginning of theend happened to the non-avian dinosaurs of the world. I imagine on that day, theearthbound beasts of the land in that Western


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Interior Sea looked south and watched a massive fire ball mushroom high into theatmosphere, later to be followed by high velocity blast of air and still later a wall of water reaching high above their heads washing over them. The end had come tothe Cretaceous epoch.

western interior seaway

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