Early Jurassic climatic trends in the south-Tethyan margin |
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| Institution: | 1. Université de Lyon, UCBL, ENSL, CNRS, LGL-TPE, 69622 Villeurbanne, France;2. Laboratoire de Recherche n° 25 « PRHPM-LECT », Université de Tlemcen, 13000 Tlemcen, Algérie;3. Institut Universitaire de France, Paris, France;4. Institute of Earth Surface Dynamics (IDYST), University of Lausanne, Building Géopolis, CH-1015 Lausanne, Switzerland;1. UMR CNRS 5276 LGLTPE, Université Lyon 1, Campus de la Doua, Bâtiment Géode, F-69622 Villeurbanne Cedex, France;2. Departamento de Ciências da Terra and IMAR-CMA, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Largo Marquês de Pombal, 3000-272 Coimbra, Portugal;1. Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany;2. Department of Geology, University of Rajasthan, 302004 Jaipur, India;3. GeoZentrum Nordbayern, Fachgruppe PaläoUmwelt, Friedrich-Alexander-Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany;4. Geology Department, Faculty of Science, Minia University, 61519 Minia, Egypt;5. Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 11, 24118 Kiel, Germany;1. MARE - Marine and Environmental Sciences Centre, Faculty of Sciences and Technology, Department of Earth Sciences, University of Coimbra, Rua Sílvio Lima, 3030-790 Coimbra, Portugal.;2. Laboratório de Palinofácies e Fácies Orgânica (LAFO), Departamento de Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira, 274, prédio do CCMN, sala J1020, Campus Ilha do Fundão, Cidade Universitária, CEP 21.949-900 Rio de Janeiro, RJ, Brazil;3. Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées, Université de Toulouse, CNRS, IRD, 14 avenue E. Belin, F-31400 Toulouse, France;4. Centre d''ACP, 47 rue Théron Périé, BP 30205, F-81104 Castres Cedex, France;5. Muséum d''Histoire naturelle de Toulouse, allées Jules-Guesde, F-31000 Toulouse, France |
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| Abstract: | The Early Jurassic period was characterized by extreme environmental changes, as reflected by major global carbon isotope anomalies and abrupt changes in oxygen isotope and elemental records of marine organisms. Available data suggest an overall warm Early Jurassic climate interrupted by periods of severe cooling, with a climatic optimum during the early Toarcian. Available geochemical studies, however, have mainly focused on the northern margin of the Tethys Ocean, so that the palaeogeographic extent of these environmental perturbations, latitudinal palaeotemperature gradients and climate belt boundaries remain poorly constrained. Here we report the first stable isotope records of brachiopod shells (δ13C and δ18O values) from the Upper Sinemurian-Middle Toarcian interval in the southern margin of the Tethys Ocean (northwest Algeria). These data were used to better constrain the palaeoenvironmental evolution of the North Gondwana margin during the Early Jurassic, which likely played an important role on supra-regional climate. The diagenetic history of the analysed brachiopod shells was monitored using scanning electron microscopy, and elemental (manganese and strontium) compositions. The brachiopod δ13C and δ18O data show very similar trends as those reported for various Tethyan regions, and record negative carbon and oxygen isotope excursions near the Sinemurian–Pliensbachian and Pliensbachian–Toarcian transitions and during the Toarcian oceanic anoxic event (T-OAE). Despite these similarities, the carbon and oxygen isotope records are systematically offset towards more positive δ13C values (average +0.5‰) and more negative δ18O values (?1.0‰) compared to those obtained from sites of higher palaeolatitudes in the northern Tethyan margin. These offsets suggest a spatial heterogeneity in the stable isotope composition of dissolved inorganic carbon in the Early Jurassic Ocean and a marked latitudinal temperature gradient between the southern and northern margins of the Tethys. |
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