Nd isotope composition of conodonts: An accurate proxy of sea-level fluctuations |
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| Institution: | 1. Poznan Science and Technology Park, Adam Mickiewicz University Foundation, 61-612 Poznan, Poland;2. Isotope Laboratory, Adam Mickiewicz University, 61-680 Poznan, Poland;1. Department of Geology, State University of New York, College at Potsdam, Potsdam, NY 13676, USA;2. Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA;3. Department of Geology and Environmental Science, James Madison University, 395 South High St., MSC 6903, Harrisonburg, VA 22807, USA;4. Department of Geology and Geophysics, Coastal Studies Institute E301/302 Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, LA 70803, USA;1. SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX, UK;2. Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia;3. School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia;1. Institute of Geology, Adam Mickiewicz University, ul. Maków Polnych 16, 61-606 Poznań, Poland;2. Biogeochemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, 55020 Mainz, Germany;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;3. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;4. Wuhan Institute of Geology and Mineral Resources, Wuhan 430223, China |
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| Abstract: | Analyses of the Nd isotope composition of conodonts from the Anti-Atlas (Morocco), the Montagne Noire (France) and the Rhenohercynian domain (Germany) provide insight into the temporal and lateral variations in seawater geochemistry in the western part of the Variscan Sea during the Late Devonian. Most of the isotopic excursions accurately record changes in sea level. The εNd values decreased during regression phases when erosion accelerated supply of unradiogenic Nd from old continental sources. A rise in sea level generated a positive shift in εNd values due to input of more radiogenic oceanic water into the seawater reservoir of the shelf areas. The method has great potential for sea-level research, paleoceanography and correlation because sea-level changes can be precisely recognized even in successions with uniform, monotonous lithologies. However, it has a significant limitation being valid only in epeiric seas and shelf areas. We have used the Nd isotope record to reconstruct the eustatic sea-level changes in late Frasnian–early Famennian time. The onset of the organic-rich Kellwasser units coincides with negative trends in εNd values. This accords with oxygen deficiency at the sea bottom being initiated by short-term regressive events, which in turn would be consistent with cooling periods of glacial origin, as previous authors have suggested. |
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