View source for Earth:Western Interior Seaway

{{Short description|Large prehistoric inland sea that split the continent of North America}}
[[File:Map of North America with the Western Interior Seaway during the Campanian (Upper Cretaceous).png|thumb|Map of North America with the Western Interior Seaway during the [[Earth:Campanian|Campanian]]]]

The '''Western Interior Seaway''' (also called the '''Cretaceous Seaway''', the '''Niobraran Sea''', the '''North American Inland Sea''', and the '''Western Interior Sea''') was a large [[Earth:Inland sea (geology)|inland sea]] that split the continent of [[Earth:North America|North America]] into two landmasses. The ancient sea, which existed from the early [[Earth:Late Cretaceous|Late Cretaceous]] (100 million years ago) to the earliest [[Earth:Paleocene|Paleocene]] (66 [[Year#SI prefix multipliers|Ma]]), connected the Gulf of Mexico, through the {{wipe|United States}} and {{wipe|Canada}}, to the [[Earth:Arctic Ocean|Arctic Ocean]]. The two land masses it created were [[Earth:Laramidia|Laramidia]] to the west and [[Earth:Appalachia (Mesozoic)|Appalachia]] to the east. At its largest extent, it was {{convert|2500|ft|m}} deep, {{convert|600|mi|km}} wide and over {{convert|2000|mi|km}} long.

==Origin and geology==
[[Image:BrokenConcretion22.jpg|thumb|A broken concretion with fossils inside; late Cretaceous Pierre Shale near Ekalaka, Montana.]]
[[File:Monument rocks view.jpg|thumb|Monument Rocks (Kansas), located 25 miles south of Oakley.]]

By Late-Cretaceous times, Eurasia and the Americas had separated along the south Atlantic, and subduction on the west coast of the Americas had commenced, resulting in the [[Earth:Laramide orogeny|Laramide orogeny]], the early phase of growth of the modern Rocky Mountains. The Western Interior Seaway may be seen as a downwarping of the continental crust ahead of the growing Laramide/Rockies mountain chain.<ref name=stanley/> 

The earliest phase of the Seaway began in the mid-Cretaceous period when an arm of the [[Earth:Arctic Ocean|Arctic Ocean]] transgressed south over western North America; this formed the Mowry Sea, so named for the [[Earth:Mowry Shale|Mowry Shale]], an organic-rich rock formation.<ref name=stanley/> In the south, the Gulf of Mexico was originally an extension of the Tethys Sea. In time, the southern embayment merged with the Mowry Sea in the late Cretaceous, forming the "complete" Seaway, creating isolated environments for land animals and plants.<ref name=stanley/> 

Relative sea levels fell multiple times, as a margin of land temporarily rose above the water along the ancestral Transcontinental Arch,<ref name= Weimer84 >{{cite journal |author= R.J. Weimer  |year= 1984 |journal= AAPG Memoir |title= Relation of unconformities, tectonics, and sea-level changes, Cretaceous of Western Interior, U.S.A.; in |editor= J.S. Schlee  |publisher= [[Organization:American Association of Petroleum Geologists|American Association of Petroleum Geologists]] |issue= Memoir 36, Interregional unconformities and hydrocarbon accumulation |page= 7-35 |url=https://terra.rice.edu/department/faculty/morganj/ESCI536/Readings/Weimer_CretaceousSeaway.pdf |quote= [The url is to a Rice University-hosted pdf of a book chapter adapted from the original Weimer 1984 paper.] |access-date= March 6, 2021 }}</ref> each time rejoining the separated, [[Biology:Genetic divergence|divergent]] land populations, allowing a temporary mixing of newer species before again separating the populations.

At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachians, some {{Convert|1000|km|abbr=on}} wide. At its deepest, it may have been only {{Convert|800|or|900|m}} 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 [[Earth:Silt|silt]] that formed shifting delta systems along its low-lying coasts. There was little [[Earth:Sediment|sediment]]ation on the eastern shores of the Seaway; the western boundary, however, consisted of a thick [[Earth:Clastic wedge|clastic wedge]] eroded eastward from the [[Earth:Sevier orogeny|Sevier orogenic belt]].<ref name=stanley/><ref name=monroe>{{cite book|last=Monroe |first=James S. |title=The Changing Earth: Exploring Geology and Evolution |url=https://archive.org/details/changingearthexp00monr |url-access=limited |year=2009 |publisher=Brooks/Cole, Cengage Learning |location=Belmont, CA |isbn=978-0495554806 |page=[https://archive.org/details/changingearthexp00monr/page/n621 605] |edition=5th |author2=Wicander, Reed }}</ref> The western shore was thus highly variable, depending on variations in [[Sea level|sea level]] and sediment supply.<ref name=stanley/>

Widespread [[Chemistry:Carbonate|carbonate]] deposition suggests that the Seaway was warm and tropical, with abundant calcareous [[Earth:Phytoplankton|planktonic algae]].<ref name="oceansofkansas1">{{cite web|title=Oceans of Kansas Paleontology |publisher=Mike Everhart |url=http://www.oceansofkansas.com/index2.html |access-date=2007-02-06}}</ref> Remnants of these deposits are found in northwest Kansas<!-- The Flint Hills limestones far predate the seaway. -->. A prominent example is Monument Rocks, an exposed chalk formation towering {{Convert|70|ft}} over the surrounding range land. It is designated a National Natural Landmark and one of the Eight Wonders of Kansas. It is located {{Convert|25|mi}} south of Oakley, Kansas.<ref>{{cite web|url=http://www.kansastravel.org/monumentrocks.htm|title=Monument Rocks, the Chalk Pyramids - Kansas|first=Keith|last=Stokes|website=www.kansastravel.org|access-date=7 April 2018}}</ref> The Western Interior Seaway is believed to have behaved similarly to a giant estuary in terms of water mass transport. Riverine inputs exited the seaway as coastal jets, while correspondingly drawing in Tethyan waters from the south and Boreal waters from the north.<ref>{{cite journal |last1=Slingerland |first1=Rudy |last2=Kump |first2=Lee R. |last3=Arthur |first3=Michael A. |last4=Fawcett |first4=Peter J. |last5=Sageman |first5=Bradley B. |last6=Barron |first6=Eric J. |date=1 August 1996 |title=Estuarine circulation in the Turonian Western Interior seaway of North America |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/108/8/941/183171/Estuarine-circulation-in-the-Turonian-Western?redirectedFrom=fulltext |journal=Geological Society of America Bulletin |volume=108 |issue=8 |pages=941–952 |doi=10.1130/0016-7606(1996)108<0941:ECITTW>2.3.CO;2 |access-date=5 April 2023}}</ref> During the late Cretaceous, the Western Interior Seaway went through multiple periods of anoxia, when the bottom water was devoid of oxygen and the water column was stratified.<ref>{{cite journal |last1=Lowery |first1=Christopher M. |last2=Leckie |first2=R. Mark |last3=Bryant |first3=Raquel |last4=Elderbak |first4=Khalifa |last5=Parker |first5=Amanda |last6=Polyak |first6=Desiree E. |last7=Schmidt |first7=Maxine |last8=Snoeyenbos-West |first8=Oona |last9=Sterzinare |first9=Ericfa |title=The Late Cretaceous Western Interior Seaway as a model for oxygenation change in epicontinental restricted basins |journal=[[Earth:Earth-Science Reviews|Earth-Science Reviews]] |date=1 February 2018 |volume=177 |pages=545–564 |doi=10.1016/j.earscirev.2017.12.001|bibcode=2018ESRv..177..545L |url=https://findresearcher.sdu.dk:8443/ws/files/143467468/Manuscript_REVISED.pdf }}</ref>

At the end of the Cretaceous, continued Laramide uplift hoisted the sandbanks (sandstone) and muddy brackish lagoons (shale), thick sequences of silt and sandstone still seen today as the [[Earth:Laramie Formation|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, and final regressive phase is sometimes called the '''Pierre Seaway'''.<ref name=stanley>{{cite book |last=Stanley |first=Steven M. |title=Earth System History |location=New York |publisher=W.H. Freeman and Company |year=1999 |isbn=0-7167-2882-6 |pages=487–489}}</ref>

During the early [[Earth:Paleocene|Paleocene]], parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment, submerging the site of present-day Memphis. Later transgression, however, was associated with the Cenozoic [[Earth:Tejas sequence|Tejas sequence]], rather than with the previous event responsible for the Seaway.<ref name="Stanley">{{cite book |last1=Stanley |first1=Steven M. |title=Earth system history |date=1998  |publisher=W.H. Freeman |location=New York |isbn=0716728826 |page=516}}</ref><ref>{{cite book |last1=Monroe |first1=James S. |date=1997 |title=The changing earth: exploring geology and evolution |location=Belmont, Calif. |publisher=Wadsworth Pub |isbn=0314095772 |page=643 |edition=2nd}}</ref><ref>{{cite book |last1=Frazier |first1=William J. |last2=Schwimmer |first2=David R. |title=Regional Stratigraphy of North America |chapter=The Tejas Sequence: Tertiary—Recent |date=1987 |pages=523–652 |doi=10.1007/978-1-4613-1795-1_9|isbn=978-1-4612-9005-6 }}</ref>

==Fauna==
The Western Interior Seaway was a shallow sea, filled with abundant marine life. Interior Seaway denizens included predatory marine [[Biology:Reptile|reptile]]s such as plesiosaurs, and [[Biology:Mosasaur|mosasaur]]s.  Other marine life included [[Biology:Shark|shark]]s such as ''[[Biology:Squalicorax|Squalicorax]], [[Biology:Cretoxyrhina|Cretoxyrhina]],'' and the giant shellfish-eating ''[[Biology:Ptychodus mortoni|Ptychodus mortoni]]'' (believed to be {{Convert|10|m}}&nbsp;long);<ref>{{cite news|last=Walker |first=Matt |url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8530000/8530995.stm |title=Giant predatory shark fossil unearthed in Kansas |newspaper=BBC Earth News |date=24 February 2010 |access-date=16 April 2013}}</ref> and advanced bony fish including ''[[Biology:Pachyrhizodus|Pachyrhizodus]]'',<ref>{{cite web |title=''Pachyrhizodus''. A Large Predatory Fish from the Late Cretaceous Western Interior Sea |author=Mike Everhart |date=February 2, 2010 |work=Oceans of Kansas Paleontology |url=http://www.oceansofkansas.com/pachyrhi.html |access-date=May 5, 2011}}</ref> ''[[Biology:Enchodus|Enchodus]]'', and the massive {{Convert|5|m|adj=on}} long ''[[Biology:Xiphactinus|Xiphactinus]]'', larger than any modern [[Biology:Osteichthyes|bony fish]].<ref>{{cite journal |last1=Cumbaa |first1=Stephen L. |last2=Tokaryk |first2=Tim T. |title=Recent Discoveries of Cretaceous Marine Vertebrates on the Eastern Margins of the Western Interior Seaway |journal=Saskatchewan Geological Survey Summary of Investigations |date=1999 |volume=1 |pages=57–63 |url=http://publications.gov.sk.ca/documents/310/88504-Cumbaa-Tokaryk_1999_volume1_MiscRep99-4.1.pdf |access-date=27 August 2021}}</ref> Other sea life included [[Biology:Invertebrate|invertebrate]]s such as mollusks, ammonites, squid-like [[Biology:Belemnitida|belemnites]], and [[Earth:Plankton|plankton]] including [[Biology:Coccolithophore|coccolithophore]]s that secreted the chalky platelets that give the [[Earth:Cretaceous|Cretaceous]] its name, [[Biology:Foraminifera|foraminifera]]ns and radiolarians.<ref>{{cite journal |last1=Boyles |first1=M.J. |last2= Scott |first2=A.J. |year=1982 |title=Comparison of Wave-Dominated Deltaic Deposits and Associated Sand-Rich Strand Plains, Mesaverde Group, Northwest Colorado |journal=AAPG Bulletin |volume=66 |number=5 |pages=551–552}}</ref><ref>{{cite book |last1=Kauffman |first1=E.G. |year=1984 |chapter=Paleobiogeography and evolutionary response dynamic in the Cretaceous Western Interior Seaway of North America |title=Jurassic-Cretaceous biochronology and paleogeography of North America |volume=27 |pages=273–306 |publisher=Geological Association of Canada |url=http://mmtk.ginras.ru/pdf/Kauffman,1984_K2_N_America.pdf |access-date=27 August 2021}}</ref>

The Western Interior Seaway was home to early [[Biology:Aves|birds]], including the flightless ''[[Biology:Hesperornis|Hesperornis]]'' that had stout legs for swimming through water and tiny wings used for marine steering rather than flight; and the [[Biology:Tern|tern]]-like ''[[Biology:Ichthyornis|Ichthyornis]]'', an early avian with a toothy beak. ''Ichthyornis'' shared the sky with large [[Biology:Pterosaur|pterosaur]]s such as ''[[Biology:Nyctosaurus|Nyctosaurus]]'' and ''[[Biology:Pteranodon|Pteranodon]]''. ''Pteranodon'' fossils are very common; it was probably a major participant in the surface ecosystem, though it was found in only the southern reaches of the Seaway.<ref name=bennett1994niobrara>Benton, S.C. (1994). "The Pterosaurs of the Niobrara Chalk." ''The Earth Scientist'', '''11'''(1): 22-25.</ref>

Inoceramids (oyster-like bivalve molluscs) were well-adapted to life in the oxygen-poor bottom mud of the seaway.<ref>{{cite journal |last1=Da Gama |first1=Rui O.B.P. |last2=Lutz |first2=Brendan |last3=Desjardins |first3=Patricio |last4=Thompson |first4=Michelle |last5=Prince |first5=Iain |last6=Espejo |first6=Irene |title=Integrated paleoenvironmental analysis of the Niobrara Formation: Cretaceous Western Interior Seaway, northern Colorado |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=November 2014 |volume=413 |pages=66–80 |doi=10.1016/j.palaeo.2014.05.005|bibcode=2014PPP...413...66D }}</ref> These left abundant fossils in the Kiowa, [[Earth:Greenhorn Limestone|Greenhorn]], [[Earth:Niobrara Formation|Niobrara]], [[Earth:Mancos Shale|Mancos]], and [[Earth:Pierre Shale|Pierre]] formations. There is great variety in the shells and the many distinct species have been dated and can be used to identify specific beds in those rock formations of the seaway. Many species can easily fit in the palm of the hand, while some like ''Inoceramus (Haploscapha) grandis''<ref>{{Cite journal |last=Moss |first=Rycroft G. |date=May 2004 |orig-year=1 December 1932 |title=Bulletin 19: The Geology of Ness and Hodgeman Counties, Kansas |url=http://www.kgs.ku.edu/General/Geology/Ness/04_expos.html |journal=Bulletin of the University of Kansas—Lawrence |volume=33 |issue=18 |page=Stratigraphy: Rocks Exposed |access-date=2020-11-17}}</ref> could be well over a meter in diameter. Entire schools of fish sometimes sought shelter within the shell of the giant ''[[Biology:Platyceramus|Platyceramus]]''.<ref>{{cite book |last1=Prothero |first1=Donald R. |title=Bringing fossils to life : an introduction to paleobiology |date=2013 |publisher=Columbia University Press |location=New York |isbn=9780231158930 |edition=Third |page=172}}</ref>  The shells of the genus are known for being composed of prismatic calcitic crystals that grew perpendicular to the surface, and fossils often retain a pearly luster.<ref>{{cite book |last1=Ludvigsen |first1=Rolf |last2=Beard |first2=Graham |year=1997 |title=West Coast Fossils: A Guide to the Ancient Life of Vancouver Island |url=https://archive.org/details/westcoastfossils0000ludv |url-access=registration |pages=[https://archive.org/details/westcoastfossils0000ludv/page/102 102–103]|publisher=Harbour Pub. |isbn=9781550171792 }}</ref>

<gallery widths="200px" heights="200px">
Image:Kansas sea2DB.jpg|Artist's impression of a ''[[Biology:Cretoxyrhina|Cretoxyrhina]]'' and two ''[[Biology:Squalicorax|Squalicorax]]'' circling a dead ''Claosaurus'' in the Western Interior Seaway
File:Elasomosaurus Face Clean.png|''[[Biology:Elasmosaurus|Elasmosaurus]] platyurus'' in the Rocky Mountain Dinosaur Resource Center in Woodland Park, Colorado
Image:InoceramusCretaceousSouthDakota.jpg|''[[Biology:Inoceramus|Inoceramus]]'', an ancient bivalve from the Cretaceous of South Dakota.
</gallery>

== See also ==
* {{Annotated link|Geology of the Bryce Canyon area}}
* {{Annotated link|Hudson Seaway}}
* {{Annotated link|Lake Agassiz}}
* {{Annotated link|Sundance Sea}}
* {{Annotated link|Zuñi sequence}}

==References==
{{Reflist|2}}

==Further reading==
* {{Cite book |last1=Kauffman |first1=Erle G. |last2=Caldwell |first2=W.G.E. |date=1993 |chapter=The Western Interior Basin in Space and Time |editor-last1=Caldwell |editor-first1=W.G.E. |editor-last2=Kauffman |editor-first2=Erle G. |title=Evolution of the Western Interior Basin |url=https://www.researchgate.net/publication/248065566 |series=Volume 39 of Geological Association of Canada Special Paper |location=St. John's, NL |publisher=Geological Association of Canada |access-date=2022-02-13}}

==External links==
* [http://www.northern.edu/natsource/earth/Marine1.htm Marine Reptiles of South Dakota]
* [http://www.scotese.com/ Paleo Map Project]
* [http://www.elasmo.com/frameMe.html?file=paleo/fauna/ut_cret.html&menu=bin/menu_fauna-alt.html Cretaceous paleogeography, southwestern US]


[[Category:Cretaceous paleogeography]]
[[Category:Historical oceans]]

{{Sourceattribution|Western Interior Seaway}}