Late Jurassic ocean anoxic event: evidence from voluminous sulphide deposition and preservation in the Panthalassa

The historically productive copper-bearing Besshi-type sulphide deposits in the Japanese accretionary complex were formed as volcanogenic massive sulphide deposits on the deep-sea floor of the Panthalassa Ocean. Here we report that eleven typical Besshi-type deposits yielded Re-Os isochron ages around 150 Ma (148.4 +/- 1.4 Ma from the composite isochron) in Late Jurassic time. This date coincides with the lowest marine Sr-87/Sr-86 ratio and highest atmospheric CO2 concentration of the past 300 million years. We infer that intense mid-ocean ridge hydrothermal and volcanic activity in the Late Jurassic produced huge sulphide deposits and large emissions of CO2 gas, leading to global warming and a stratified Panthalassa Ocean with anoxic deep seas that favored preservation of sulphides in the pelagic environment. The emergence of ocean anoxia triggered by seafloor volcanism is also consistent with a positive delta C-13 excursion and widespread deposition of petroleum source rocks and black shales.