Pacing of the Toarcian Oceanic Anoxic Event (Early Jurassic) from astronomical correlation of marine sections |
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| Institution: | 1. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan 430074, China;2. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;3. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK;1. Institut des sciences de la Terre, Université de Lausanne, Bâtiment Géopolis, CH-1015 Lausanne, Switzerland;2. Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Quebec G5L 3A1, Canada;3. Geotop Research Centre, Université du Québec à Montréal, Montréal, Quebec H3C 3P8, Canada;4. Institut des dynamiques de la surface terrestre, Université de Lausanne, Bâtiment Géopolis, CH-1015 Lausanne, Switzerland;5. Laboratoire Géosystèmes, UMR-8217, Université Lille 1, CNRS, Villeneuve d’Ascq, France;6. UMR CNRS 5276 LGLTPE, Université Lyon 1, Campus de la Doua, Bâtiment Géode, F-69622 Villeurbanne Cedex, France;1. Paleomagnetic Laboratory ‘Fort Hoofddijk’, Department of Earth Sciences, Utrecht University, Netherlands;2. Stratigraphy/Paleontology, Department of Earth Sciences, Utrecht University, Netherlands;3. Nordic Centre for Earth Evolution, University of Copenhagen, Denmark;1. Environment, Earth and Ecosystems, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK;2. Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan |
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| Abstract: | The Early Toarcian Oceanic Anoxic Event (OAE) in the Early Jurassic Period is associated with a major negative carbon isotope excursion (CIE), mass extinction, marine transgression and global warming. The Toarcian OAE is thought to have been caused by flood basalt magmatism, and may have been a trigger for mass extinction. However, these proposed causes of the Toarcian OAE and associated biotic crisis are not adequately resolved by a precise chronology. The duration of the Toarcian OAE has been estimated to be anywhere from ~ 0.12 to ~ 0.9 Myr, most recently 0.74 to 3.26 Myr from U–Pb dating. The CIE associated with the Toarcian OAE has a similar pattern at numerous localities, and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals. Here we estimate a duration of ~ 620 kyr for the main negative CIE, ~ 860 kyr for the polymorphum zone and > 1.58 Myr for the levisoni zone based on 405-kyr astronomical eccentricity tuning of the marine section at Peniche (Portugal). This 405-kyr tuned series provides a ~ 2.5 Myr continuous high-resolution chronology through the Early Toarcian. There are 6, or possibly 7 short eccentricity cycles in the main CIE interval at Peniche. To confirm this astronomically based estimate, we analyzed three other sections at Yorkshire (UK), Dotternhausen (Germany), and Valdorbia (Italy) from marine carbon isotopic series. These four stratigraphic sections from Early Jurassic western Tethys record the Toarcian OAE with ~ 6 prominent carbon isotope cycles in the CIE that span a 600 ± 100 kyr duration. The Peniche 405-kyr tuned series indicates that the pre- and post-CIE intervals experienced strong precession–eccentricity-forced climate change, whereas the CIE interval is marked by dominant obliquity forcing. These dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the Early Toarcian paleoclimate system that was directly linked to the global carbon cycle. |
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