Cenomanian
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| Cenomanian | |
|---|---|
| Name | Cenomanian |
| Color | #a0d0ff |
| Time start | 100.5 |
| Time end | 93.9 |
| Time unit | Ma |
| Former names | Neocomian (part) |
| Chronology | Late Cretaceous |
Cenomanian The Cenomanian is the earliest age of the Late Cretaceous, spanning roughly 100.5 to 93.9 million years ago in the International Commission on Stratigraphy timescale. It succeeds a boundary with the Albian and precedes the Turonian, and is recognized across lithostratigraphic sequences in Europe, North America, Africa, Asia, and Australia. The interval records major tectonic reorganizations tied to plate motions involving the North Atlantic, South Atlantic, Tethys and associated basins.
Definition and Stratigraphic Boundaries
The age was formally ratified by stratigraphic work anchored in type sections in northern France and southern England, and is tied to biostratigraphic markers such as the first occurrence of specific ammonite taxa used in studies by paleontologists working with the International Commission on Stratigraphy. Boundary definition integrates chemostratigraphy exemplified by carbon isotope excursions, magnetostratigraphy correlated with polarity chrons identified in marine cores from the North Sea and Gulf of Mexico, and radiometric calibration using zircons from volcanic ash beds in the Western Interior Seaway and Betic Cordillera. Global correlation invokes index fossils from genera recorded in sections at locales investigated during expeditions funded by institutions like the British Geological Survey and the United States Geological Survey.
Geology and Paleoenvironments
Sedimentary facies of the age include chalks, limestones, marls, sandstones and black shales deposited in epicontinental seas such as the Western Interior Seaway, the Tethys Ocean margins, and the Eromanga Basin. Plate tectonic reconstructions by groups at the University of Cambridge and Scripps Institution of Oceanography link Cenomanian subsidence to rifting between the North America and Eurasia plates and to passive margin development along the South Atlantic opening between South America and Africa. Volcaniclastic layers associated with the Kerguelen Plateau and Ontong Java Plateau are recorded in deep-sea cores retrieved by the International Ocean Discovery Program and bear on nutrient flux and ocean chemistry. Facies analysis in the Paris Basin and Benton Shale demonstrates lateral shifts in depositional environments influenced by eustasy and regional tectonics studied by researchers at the University of Oxford and Harvard University.
Paleontology and Biotic Events
The age witnessed diversification and provincialism among ammonites, bivalves, belemnites, and rudistid reef builders documented by specialists associated with the Natural History Museum, London and the Smithsonian Institution. Vertebrate assemblages include marine reptiles recorded in strata of the Cretaceous Western Interior Seaway and terrestrial dinosaurs described from formations such as the Kem Kem Beds and the Cedar Mountain Formation; notable taxa were reported in papers from the American Museum of Natural History and the Royal Society. Major biotic events include turnover episodes linked to oceanic anoxic intervals recorded in the Gabon and Hauterivian sequences and discussed in syntheses by the European Geosciences Union. Palynological records from cores in the Sahara and Boreal Realm illustrate floral shifts contemporaneous with angiosperm radiations documented by botanists at the Royal Botanic Gardens, Kew.
Climate and Oceanography
Paleoclimatic reconstructions indicate greenhouse conditions with high atmospheric CO2 inferred from proxies analyzed at laboratories affiliated with ETH Zurich and Lamont–Doherty Earth Observatory. Sea-level highstands produced extensive epicontinental seas comparable to those studied in modern analog work at the Woods Hole Oceanographic Institution. Ocean circulation models developed by groups at the Max Planck Institute for Meteorology and Princeton University simulate weakened polar gradients and stratified water columns that promoted widespread anoxia, as evidenced by black shale occurrences in the South Atlantic and isotope excursions recorded in cores from the IODP expeditions. Monsoon-like precipitation patterns linked to the paleogeography of India and Madagascar are inferred from sedimentary records examined by teams from the University of Cape Town.
Regional Subdivisions and Correlation
Regional stage equivalents and subzones have been defined across continents: boreal and subboreal ammonite zonations used in the North Sea and Scandinavia; Mediterranean biozones established in the Betic Cordillera and Calcaire de Beien exposures; and provincial schemes applied to the Western Interior Seaway of North America and the Afro-Arabian basins including the Benue Trough. Correlation employs conodont, foraminiferal and nannofossil zonations refined by teams at the Paleontological Society and cross-referenced with magnetostratigraphic frameworks from the Ocean Drilling Program.
Economic Significance and Resources
Cenomanian strata are economically important as hydrocarbon source and reservoir rocks in basins such as the Gulf of Mexico, the North Sea, the Saharan basins and the Caspian Basin; exploration and production are led by companies like BP, ExxonMobil, and Shell. Chalk and limestone units serve as aquifers and building stone quarried in regions overseen by the Monuments Men legacy projects and local heritage agencies. Phosphorite and metal-enriched phosphatic horizons in deposits studied by the United Nations Educational, Scientific and Cultural Organization and national geological surveys provide mineral resources exploited in Morocco and Jordan. Environmental assessments of resource extraction reference guidelines produced by the International Energy Agency and the World Bank.