Sedex brine expulsions to Paleozoic basins may have changed global marine 87Sr/86Sr values,triggered anoxia,and initiated mass extinctions |
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| Institution: | 1. Section of Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Geneva, Switzerland;2. GNS Science, Wairakei Research Centre, Taupo, New Zealand |
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| Abstract: | Sedimentary-exhalative (sedex) ore deposits were formed by discharge of metal-rich brines into ancient ocean basins. Chemical, isotopic, and geologic data from several Paleozoic sedex districts suggest that the brine discharges also supplied enormous quantities of radiogenic Sr and biolimiting nutrients to the oceans. Seven middle Paleozoic sedex events appear to coincide with short-duration positive excursions (“spikes”) in the global marine Sr-isotope record that are not explained by current oceanic models. These strong temporal correlations, combined with mass balance evidence and oceanographic modeling, suggest the flux of radiogenic Sr-rich sedex brines may have been sufficient to cause these prominent spikes. If these sedex hydrothermal events are recorded in the secular record, then the 87Sr/86Sr record may provide a unique tool for ore genesis studies and for assessing the mineral potential of sedimentary basins of different ages.The apex of these enigmatic 87Sr/86Sr spikes correlate with global δ13C and δ18O spikes, periods of global anoxia, deposition of metal-rich black shales, deposition of ironstones, climate change, metal-induced malformation (teratology) of marine organisms and significant mass extinctions. While the relationships among these phenomena remain poorly understood and diverse models for these events have been proposed, most invoke an increased flux of biolimiting nutrients resulting in ocean eutrophication. Evidence that the flux of key biolimiting nutrients and metals contained in sedex brines may have been equivalent to or surpass that of the total modern riverine flux to the ocean suggests that these sedex brine exhalations may have triggered global chemical and biological events. |
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| Keywords: | Sedex deposits Brine Anoxia Strontium isotopes Carbon isotopes Mass extinction |
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