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| Cenomanian–Turonian Oceanic Anoxic Event (OAE2) | |
|---|---|
| Name | Cenomanian–Turonian Oceanic Anoxic Event (OAE2) |
| Date | ~94.1 million years ago |
| Location | Global |
| Type | Oceanic anoxic event |
Cenomanian–Turonian Oceanic Anoxic Event (OAE2) occurred near the Cenomanian–Turonian boundary ~94.1 million years ago and represents one of the most pronounced mid‑Cretaceous global carbon cycle perturbations, involving widespread marine anoxia, rapid carbon isotope excursions, and extensive black shale deposition. The event is tied to coeval activity at large igneous provinces and is recorded in stratigraphic sections across palaeocontinents such as Europe, North America, Africa, South America, Asia, and Australia, with stratigraphic markers used by chronostratigraphers and palaeontologists.
The interval corresponds to the late Cretaceous greenhouse climate during the Cenomanian and Turonian stages and is framed by global sea‑level highstands recognized in sequence stratigraphy linked to the transgressive systems tracts of passive margins like the Western Interior Seaway and the proto‑Atlantic basins such as the South Atlantic Ocean. Tectonically, the time overlaps with the emplacement of the Ontong Java Plateau, Kerguelen Plateau, and the onset of activity related to the Caribbean Large Igneous Province and is recorded in marine sections correlated by biostratigraphic markers such as ammonite and foraminiferal zonations used by paleontologists like Alcide d'Orbigny and modern chronostratigraphers following the International Commission on Stratigraphy. Paleogeographic reconstructions by groups at institutions like the Paleomap Project and researchers associated with the Geological Society of America depict expanded epicontinental seas and restricted basins promoting water‑column stratification.
Leading hypotheses implicate intensified volcanism from large igneous provinces such as the Ontong Java Plateau and magmatic events recorded in the High Arctic Large Igneous Province that released CO2 and volatiles, with cascading effects described in publications from research teams at institutions like Lamont–Doherty Earth Observatory and Scripps Institution of Oceanography. These greenhouse forcings interacted with palaeogeography and ocean circulation changes influenced by seaway configurations like the proto‑Atlantic gateways, producing enhanced thermal stratification and oxygen minimum zone expansion documented by investigators affiliated with the British Geological Survey and the Max Planck Society. Feedbacks involving enhanced nutrient delivery via weathering of volcanic provinces, intensified runoff from landmasses such as Laurasia and Gondwana, and possible methane release from clathrates have been proposed in studies from researchers at the University of Cambridge and the University of California. Modeling efforts by groups at the National Center for Atmospheric Research and the European Centre for Medium-Range Weather Forecasts simulate combinations of CO2 rise, ocean stratification, and productivity that reproduce aspects of the event.
The event is characterized by a pronounced positive carbon isotope (δ13C) excursion recorded in bulk carbonates, organic carbon, and belemnite rostra from marine sections described in literature from the Geological Society of London and depositional records archived by the United States Geological Survey. Elevated total organic carbon (TOC) contents and enrichments in molybdenum, uranium, and vanadium are reported from cores studied by researchers at the Institut de Physique du Globe de Paris and the GFZ German Research Centre for Geosciences, indicating widespread anoxia and euxinia in some basins. Paired δ18O, Sr isotopes, and osmium isotope shifts measured by teams at ETH Zurich and the University of Tokyo provide constraints on temperature, weathering rates, and mantle‑derived inputs, while mercury spikes linked to volcanic emissions have been documented by scientists at the University of Massachusetts Amherst and the Chinese Academy of Sciences.
Marine biota show major turnovers with extinctions and radiations documented in ammonite, inoceramid bivalve, and planktonic foraminiferal assemblages studied by paleontologists at the Natural History Museum, London and the Smithsonian Institution, and reef ecosystems including rudist and scleractinian communities experienced declines reported in regional syntheses by the Royal Belgian Institute of Natural Sciences and the Australian National University. Marine vertebrates, including some lineages of teleost fishes and marine reptiles, show distributional and diversity shifts recorded in collections at the American Museum of Natural History and described by researchers associated with the University of Oxford. Organic‑rich sediments became substrates for exceptional fossil preservation in localities curated by the Museo Nacional de Ciencias Naturales and the Canadian Museum of Nature, influencing interpretations by evolutionary biologists and paleoecologists at institutions such as the University of California, Berkeley.
Black shales of OAE2, such as the Faxe Formation analogues, display lamination, high TOC, and pyrite framboid populations analyzed by sedimentologists from the University of Texas at Austin and the University of Barcelona, reflecting low oxygen bottom waters and limited bioturbation. Organic facies vary across basins from laminated sapropelic deposits in the Tethys Ocean margins to hemipelagic shales in the Western Interior Seaway, with basin architectures interpreted using seismic data provided by energy sector collaborations and academic studies from Imperial College London and Utrecht University. Diagenetic overprints, sulfur isotope systematics, and trace metal partitioning studied by geochemists at the California Institute of Technology inform models for burial efficiency and long‑term carbon sequestration.
High‑resolution cyclostratigraphic and astrochronologic studies conducted by teams at the University of Milan and the Vrije Universiteit Amsterdam estimate the main δ13C excursion lasted on the order of 200–600 kyr within a broader perturbation spanning ~1 Myr, with U‑Pb zircon ages from bentonites and ash layers tied to geochronologists at the Massachusetts Institute of Technology and the University of Geneva providing absolute age anchors. Magnetostratigraphy correlated by researchers at the Institute of Geology, Chinese Academy of Geological Sciences and biostratigraphic tie‑points using index fossils maintained by curators at the Natural History Museum, Vienna improve temporal resolution for regional correlation.
Records of OAE2 appear across shallow and deep marine settings in regions including the Anglo‑Paris Basin documented by the British Geological Survey, the North African basins curated in studies at Cairo University, the Brazilian offshore basins studied by the Petróleo Brasileiro S.A. research groups, and the South China Block investigated by teams at the Nanjing Institute of Geology and Palaeontology. Integrated datasets from drilling programs such as those of the Integrated Ocean Drilling Program and the International Ocean Discovery Program supply long sedimentary records that, combined with regional field sections studied by universities like Uppsala University and Kyoto University, delineate the spatial heterogeneity of anoxia, productivity, and sedimentation during this key mid‑Cretaceous event.
Category:Geologic events