TRACE ELEMENT BEHAVIORS DURING THE END PERMIAN MASS EXTINCTION AT THE DEEP SEA FLOOR

We describe the variations of trace-elemental compositions that took place in the deep seafloor of paleo-super-ocean “Panthalassa” during the end-Permian mass extinction, based on the sedimentary rock samples from one of the most continuous Permian-Triassic boundary section of pelagic deep-sea, exposed in the northeastern Japan area. Our measurement shows high concentrations of redox-sensitive elements such as Vanadium, Molybdenum coinciding with low concentration of Manganese are present in the Upper Permian to end-Permian strata in the study section. Vanadium concentration shows two significant peaks in the section. First one is in the uppermost chert beds just below the overlying siliceous claystone beds without any co-increase of another trace elements. Second one is recognized in the uppermost part of siliceous claystone and the overlying basal black claystone which lithologic transition which accords the end-Permian mass extinction. Molybdenum shows increases in concentrations from the upper part of uppermost Permian siliceous claystone beds and overlying the base of the black claystone. The highest peaks of Molybdenum coincide with that of Vanadium. Above the horizon that is characterized by high concentrations of these trace elements, these elemental concentrations decrease and maintain low values within 0.7 m of the black claystone ranging to basal Triassic.Especially Molybdenum is activated to insoluble form in H₂S rich condition. While Vanadium has two step-reduction in the chemical valency, first-step reduction of Vanadium require relatively weaker reduced condition than that of Molybdenum. Hence, the single peak of Vanadium from Upper Permian chert beds suggest mildly reduced bottom water condition, assuming first step reduction of Vanadium. The high concentrations in Molybdenum and Vanadium at the basal black claystone coinciding with the microfossil disappearance suggest maximum reduced condition with much H₂S at that time. The low values of Vanadium and Molybdenum with low Manganese concentration after these highest values imply　element-depleted condition in Vanadium and Molybdenum at the Panthalassic seawater.