The end-Ordovician glaciation and the Hirnantian Stage: A global review and questions about Late Ordovician event stratigraphy |
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| Authors: | A Delabroye M Vecoli |
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| Institution: | 1. Universidade do Porto, Faculdade de Ciências, Departamento de Geociências, Ambiente e Ordenamento do Território, Centro de Geologia, Rua do Campo Alegre 687, 4169-007 Porto, Portugal;2. University of the Witwatersrand, School of Geography, Archaeology and Environmental Studies, Private Bag 3, Wits 2050, Johannesburg, South Africa;3. Universidade do Porto, Reitoria, Centro de Geologia, Praça Gomes Teixeira, 4099-002 Porto, Portugal;1. Rue des Jonquilles, 35235 Thorigné-Fouillard, France;2. Géosciences-Rennes, CNRS UMR 6118, Université de Rennes 1, 35042 Rennes, France;3. Research Unit of Paleontology, Department of Geology and Soil Sciences, Ghent University, Krijglsaan 281/S8, 9000 Ghent, Belgium;4. IRF Group, Inc., 2357 East 23rd street, Tulsa, OK 74114, USA;5. Saudi Aramco, Exploration Technical Services Department, 31311 Dhahran, Saudi Arabia;6. Saudi Aramco, Gas Fields Characterization Division, 31311 Dhahran, Saudi Arabia;7. Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry of CAS, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;5. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA;6. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;1. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;2. Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark;3. Nordic Center for Earth Evolution (NordCEE) and Institute of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark |
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| Abstract: | This paper proposes a global review of Hirnantian event stratigraphy. The Hirnantian GSSP in south China is tentatively correlated with latest Ordovician strata from the peri-Gondwanan “glacial” regions. Problems of biostratigraphical correlation are highlighted. At a worldwide scale, the major biostratigraphically useful fossil groups (graptolites, chitinozoans, brachiopods, conodonts, acritarchs) are analysed and their limits for global correlation of the uppermost Ordovician are discussed. Palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective Late Ordovician global biostratigraphical scheme. As an alternative correlative tool, the HICE (Hirnantian Isotopic Curve Excursion) event is often put forward in the literature. However, carbon isotope chemostratigraphy shows, like biostratigraphy, some limits to the present state of knowledge. No good independent biostratigraphical control of the HICE exists in both shallow carbonate deposits and deeper shaly ones. Recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic (δ13Corg) and inorganic (δ13Ccarb) carbon species, further complicating the use of the HICE as an isochronous benchmark.All of these difficulties for Hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future. Precise Late Ordovician and early Silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the “Big Five” extinctions. |
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