Upper Cretaceous

Upper Cretaceous
Name	Upper Cretaceous
Time start	100.5
Time end	66.0
Unit	Epoch/Series
Color	#FFD700
Preceded by	Cretaceous
Followed by	Paleogene

Upper Cretaceous The Upper Cretaceous is the later epoch of the Cretaceous Period, spanning from about 100.5 to 66.0 million years ago and closing with the Cretaceous–Paleogene boundary. It is characterized by high global sea levels, widespread chalk and marine transgressions, and major radiations and turnovers among dinosaurs, mollusks, and angiosperms. Key figures, institutions, and localities such as Charles Darwin, Mary Anning, Louis Agassiz, Richard Owen, Adam Sedgwick, Royal Society, Smithsonian Institution, Natural History Museum, London, and Burgess Shale–era sites inform historical study and public collections of Upper Cretaceous fossils.

Definition and Chronostratigraphy

The chronostratigraphic subdivision defining the Upper Cretaceous rests on global stratotypes established by bodies like the International Commission on Stratigraphy, debated in symposia attended by scholars from University of Oxford, Harvard University, University of Cambridge, University of Paris, and California Institute of Technology. Boundary markers utilize ammonite biozones tied to outcrops at type sections near regions explored by Gideon Mantell, with magnetostratigraphy calibrated against cores collected under programs such as the Integrated Ocean Drilling Program and initiatives led by National Aeronautics and Space Administration scientists. Time scales incorporate radiometric dates from labs at Max Planck Society, Geological Survey of Canada, United States Geological Survey, and the British Geological Survey.

Geological and Paleogeographic Setting

Paleogeographic reconstructions rely on plate models developed by teams including researchers at Scripps Institution of Oceanography, Potsdam Institute for Climate Impact Research, Lamont–Doherty Earth Observatory, and the European Space Agency. Continental configurations during the epoch involved fragmentation of supercontinents with the opening of oceanic gateways noted near South America, Africa, India, Antarctica, and Australia, and seaways adjacent to Western Interior Seaway analogues documented in core studies by USGS and Geological Survey of India. Coastal chalk platforms and carbonate ramps around White Cliffs of Dover, Maastrichtian type locality, and Santonian outcrops illustrate interactions between tectonics and eustasy analyzed by researchers from University of Tokyo, University of Buenos Aires, and University of Cape Town.

Major Formations and Regional Stratigraphy

Prominent Upper Cretaceous formations include the Hell Creek Formation, Gosau Group, Niobrara Formation, Scaglia Rossa, Cenomanian–Turonian deposits of the Western Interior, Maastricht Formation, Benton Formation, Chalk Group, Liaoning beds, and Santonian strata of the Paris Basin. Regional studies feature fieldwork by teams from University of Alberta, University of Kansas, University of Montpellier, University of Salamanca, and University of Copenhagen, and collections curated at Paleontological Research Institution, Natural History Museum of Los Angeles County, and Royal Ontario Museum. Biostratigraphic correlations often cite index taxa described by historical figures like Alcide d'Orbigny and synthesized in atlases from Cambridge University Press and proceedings of the Geological Society of America.

Paleontology and Biotic Evolution

Upper Cretaceous faunas show diversification recorded in assemblages from plateaus and basins studied by expeditions linked to American Museum of Natural History, Field Museum of Natural History, Museo Nacional de Ciencias Naturales, and Chinese Academy of Sciences. Dinosaur genera such as Tyrannosaurus rex, Triceratops, Velociraptor, Hadrosaurus, Spinosaurus, Iguanodon-lineages, and Ankylosaurus coexist with marine taxa like Mosasaurus and ammonites described in monographs by Othniel Charles Marsh and Edward Drinker Cope. Flowering plants expand with angiosperm fossils curated by Kew Gardens, while microfossils including foraminifera, radiolaria, and dinoflagellate cysts feature in studies from Woods Hole Oceanographic Institution and Smithsonian Tropical Research Institute. Evolutionary patterns are discussed in works by Ernst Mayr, Stephen Jay Gould, Allan Wilson, and synthesized in volumes from Oxford University Press.

Climate and Sea-Level Changes

Paleoclimatic reconstructions for the epoch draw on isotope analyses from labs at University of Arizona, Massachusetts Institute of Technology, ETH Zurich, and University of Leeds, and on climate modeling by groups at NASA Goddard Institute for Space Studies, NOAA, Met Office Hadley Centre, and IPCC-affiliated researchers. The Cenomanian–Turonian Thermal Maximum and subsequent cooling events are compared with transgressive events recorded in the Western Interior Seaway and European basins, informing interpretations by scholars linked to Royal Society of London meetings and publications in journals from Nature Publishing Group and Science. Sea-level highstands produced chalk deposition in locales such as Dover, Saxon-Bohemian Basin, and Campanian beds studied by teams from University of Vienna and Uppsala University.

Tectonics and Sedimentation Patterns

Tectonic drivers include continued dispersal of Gondwana fragments and northward drift of India culminating in paleogeographic changes impacting sediment supply to basins like the Western Interior Basin, Paris Basin, and Ural Basin. Sedimentary regimes produced turbidites, marl, and chalk sequences investigated by the International Association of Sedimentologists and laboratories at ETH Zurich, University of Bergen, and Instituto Geológico y Minero de España. Orogenic pulses in regions adjacent to the Alps, Andes, and Rocky Mountains influenced provenance studies undertaken by teams from University of Salamanca, Universidad Nacional Autónoma de México, and CONICET.

Extinction and Legacy

The end of the epoch culminates in a mass extinction event recorded at globally distributed boundary sections examined by consortia including Chicxulub research teams, Gulf Coast Research Center, and investigators from Universidad Nacional Autónoma de México and MIT. Key contributors such as Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel advanced the impact hypothesis, which remains integrated with volcanism studies of the Deccan Traps researched by scientists at Indian Institute of Science and Geological Survey of India. The legacy of the Upper Cretaceous persists in modern vertebrate and plant clades assessed by researchers at institutions like Natural History Museum, London, Smithsonian Institution, and universities worldwide, and commemorated in exhibits at American Museum of Natural History and Natural History Museum of Los Angeles County.

Category:Cretaceous Period