Paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite |
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| Institution: | 1. Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;2. Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Ministry of Land and Resources, Guangzhou 510075, China;3. Institute of Applied Geosciences, Technical University Berlin, Ackerstr. 76, 13355 Berlin, Germany;4. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;1. Department of Geology and Mineral Exploration, Institute of Natural Resources, National Research Tomsk Polytechnic University, 634050 Tomsk, Lenin Avenue, 30, Russia;2. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Maharashtra, India;1. School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;3. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510006, China;4. Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai 519000, China;5. Guangzhou Marine Geological Survey, Guangzhou 510075, China;6. State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510006, China;7. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China;8. Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA;1. School of Earth Sciences, Yunnan University, Kunming 650500, China;2. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;3. Engineering Research Center of Domestic High-resolution Satellite Remote Sensing Geology for University of Yunnan Province, Kunming 650500, China;4. MNR Key Laboratory of Sanjiang Metallogeny and Resources Exploration & Utilization, Kunming 650051, China |
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| Abstract: | Rare earth element concentrations in biogenic apatite of conodonts, fish debris and inarticulate brachiopods were determined in over 200 samples from Cambrian to modern sediments. Tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory, interexperiment or interspecies related variations clearly show that no resolvable fractionation of REE occurs. Incorporation of REE in biogenic apatite of Recent fish debris occurs near the sediment-water interface soon after deposition and reflects characteristics of seawater. The original REE signature apparently survives subsequent burial and diagenesis.Cerium variations in fish debris from modern environments are controlled by redox potential. Ce is fractionated by co-precipitation with metallic oxides under oxidizing conditions. This fractionation produces a negative Ce anomaly (Ceanom) in seawater that is reflected in the sedimented fish debris. Conversely, no fractionation of Ce occurs under reducing conditions, resulting in Ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions. Extrapolation of observations of the redox control of Ceanomin modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower Paleozoic and Lower Triassic oceans, whereas in the upper Paleozoic, the world ocean was generally oxidizing. |
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