Editing Cretaceous (section)

== Paleogeography ==
During the Cretaceous, the late-[[Paleozoic]]-to-early-Mesozoic [[supercontinent]] of [[Pangaea]] completed its [[Plate tectonics|tectonic]] breakup into the present-day [[continent]]s, although their positions were substantially different at the time. As the [[Atlantic Ocean]] widened, the convergent-margin mountain building ([[orogeny|orogenies]]) that had begun during the [[Jurassic]] continued in the [[American cordillera|North American Cordillera]], as the [[Nevadan orogeny]] was followed by the [[Sevier orogeny|Sevier]] and [[Laramide orogeny|Laramide orogenies]].

[[Gondwana]] had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. [[South America]], [[Antarctica]], and [[Australia]] rifted away from [[Africa]] (though [[India]] and [[Madagascar]] remained attached to each other until around 80 million years ago); thus, the South Atlantic and [[Indian Ocean]]s were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising [[Sea level#Dry land|eustatic sea levels]] worldwide. To the north of Africa the [[Tethys Sea]] continued to narrow. During most of the Late Cretaceous, North America would be divided in two by the [[Western Interior Seaway]], a large interior sea, separating [[Laramidia]] to the west and [[Appalachia (landmass)|Appalachia]] to the east, then receded late in the period, leaving thick marine deposits sandwiched between [[coal]] beds. Bivalve palaeobiogeography also indicates that Africa was split in half by a shallow sea during the Coniacian and Santonian, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater.<ref>{{cite journal |last1=Moussavou |first1=Benjamin Musavu |date=25 September 2015 |title=Bivalves (Mollusca) from the Coniacian-Santonian Anguille Formation from Cap Esterias, Northern Gabon, with notes on paleoecology and paleobiogeography |url=https://bioone.org/journals/geodiversitas/volume-37/issue-3/g2015n3a2/Bivalves-Mollusca-from-the-Coniacian-Santonian-Anguille-Formation-from-Cap/10.5252/g2015n3a2.short |journal=Geodiversitas |volume=37 |issue=3 |pages=315–324 |doi=10.5252/g2015n3a2 |s2cid=128803778 |access-date=28 December 2022}}</ref> Yet another shallow seaway ran between what is now Norway and Greenland, connecting the Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans.<ref>{{cite journal |last1=Mutterlose |first1=Jörg |last2=Brumsack |first2=Hans |last3=Flögel |first3=Sascha |last4=Hay |first4=William |last5=Klein |first5=Christian |last6=Langrock |first6=Uwe |last7=Lipinski |first7=Marcus |last8=Ricken |first8=Werner |last9=Söding |first9=Emanuel |last10=Stein |first10=Rüdiger |last11=Swientek |first11=Oliver |date=26 February 2003 |title=The Greenland-Norwegian Seaway: A key area for understanding Late Jurassic to Early Cretaceous paleoenvironments |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001pa000625 |journal=[[Paleoceanography and Paleoclimatology]] |volume=18 |issue=1 |pages=10-1-10-25 |doi=10.1029/2001pa000625 |bibcode=2003PalOc..18.1010M |access-date=14 May 2023}}</ref> At the peak of the Cretaceous [[transgression (geology)|transgression]], one-third of Earth's present land area was submerged.<ref>{{cite book |first1=Dougal |last1=Dixon |first2=M J |last2=Benton |first3=Ayala |last3=Kingsley |first4=Julian |last4=Baker|title=Atlas of Life on Earth |location=New York |publisher=Barnes & Noble Books |year=2001 |page=215 |isbn=9780760719572}}</ref>

The Cretaceous is justly famous for its [[chalk]]; indeed, more chalk formed in the Cretaceous than in any other period in the [[Phanerozoic]].{{sfn|Stanley|1999|p=280}} [[Mid-ocean ridge]] activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in [[calcium]]; this made the oceans more saturated, as well as increased the [[bioavailability]] of the element for [[Coccolithophores|calcareous nanoplankton]].{{sfn|Stanley|1999|pp=279–281}} These widespread [[carbonate]]s and other [[sedimentary rock|sedimentary deposits]] make the Cretaceous rock record especially fine. Famous [[Geologic formation|formations]] from North America include the rich marine fossils of [[Kansas]]'s [[Smoky Hill Chalk]] Member and the terrestrial fauna of the late Cretaceous [[Hell Creek Formation]]. Other important Cretaceous exposures occur in [[Europe]] (e.g., the [[Weald]]) and [[China]] (the [[Yixian Formation]]). In the area that is now India, massive [[lava bed]]s called the [[Deccan Traps]] were erupted in the very late Cretaceous and early Paleocene.