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Multiproxy reconstruction of oceanographic conditions in the southern epeiric Kupferschiefer Sea (Late Permian) based on redox-sensitive trace elements,molybdenum isotopes and biomarkers
Institution:1. Department of Organic Geochemistry, University of Kiel, Germany;2. Department of Earth Sciences, University of Oxford, Oxford, UK;3. WA-OIGC, Curtin University, Perth, Australia;1. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;2. Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China;3. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;4. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. Paleontological institute, University of Zürich, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland;2. BCG Parc de la Rouvraie 28, 1018 Lausanne, Switzerland;3. Institute of Earth Surface Dynamics, University of Lausanne, Géopolis, 1015 Lausanne, Switzerland;4. Department of Earth Sciences, University of Geneva, 13 rue des Maraîchers, 1205 Geneva, Switzerland;5. Guangxi Bureau of Geology and Mineral Resources, Jiangzheng Road 1, 530023 Nanning, China;1. School of Earth Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;2. School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa;3. Department of Geosciences, James Cook University, Townsville, QLD 4811, Australia;4. Edinburgh Ion Microprobe Facility, School of Geosciences, University of Edinburgh, Edinburgh, UK;1. Geological Studies Unit, Indian Statistical Institute, 203 Barrackpore Trunk Road, Kolkata 700108, India;2. Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock''s Close, BS8 1TS Bristol, United Kingdom;3. Polish Geological Institute, Rakowiecka 4, 00-975 Warszawa, Poland;4. Cabot Institute, University of Bristol, BS8 1UJ, Bristol, United Kingdom;5. School of Earth Sciences, University of Bristol, BS8 1RJ Bristol, United Kingdom
Abstract:The key drivers controlling the redox state of seawater and sediment pore waters in low energy environments can be inferred from redox-sensitive trace elements (RSTE), molecular biomarkers and trace metal isotopes. Here, we apply a combination of these tools to the Upper Permian Kupferschiefer (T1) from the Thuringian Basin, deposited in the southern part of the semi-enclosed Kupferschiefer Sea. Enrichment patterns of the RSTEs molybdenum (Mo) and uranium (U) as well as biomarker data attest to the rapid development of euxinic conditions in basin settings during early T1 times, which became progressively less extreme during T1 deposition. The evolution of redox conditions in basinal settings, and the associated delay in the onset of euxinia at more shallow marginal sites, can be attributed to the interaction of sea-level change with basin paleogeography. Euxinia in the southern Kupferschiefer Sea did not lead to near-quantitative depletion of aqueous Mo, possibly due to short deepwater renewal times in the Thuringian Basin, low aqueous H2S concentrations, the continuous resupply of RSTE during transgression and declining burial rates of RSTEs throughout T1 times. Drawdown of RSTE is, however, indicated for euxinic lagoon environments. Moreover, admixture of freshwater supplied to these lagoons by rivers strongly impacted local seawater chemistry. The highest Mo-isotope compositions of ~ 1.70‰ in basin sediments allow a minimum Kupferschiefer Sea seawater composition of ~ 2.40‰ to be estimated. This composition is similar to the ~ 2.30‰ estimate for the Late Permian open ocean, and confirms a strong hydrographic connection between the epeiric Kupferschiefer Sea and the global ocean. The substantial variation in Mo-isotope signatures is paralleled by diagnostic shifts in biomarkers responding to oxygenation in different parts of the water column. Water column chemistry has been affected by variation in sea level, hydrodynamic restriction, riverine freshwater influx and evaporitic conditions in shallow lagoons. Elucidation of the relative role of each driving factor by a single geochemical proxy is not feasible but the complex scenario can be disentangled by a multiproxy approach.
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