The Frasnian-Famennian mass extinction is one of the most significant biocrises in Phanerozoic, which is characterized by the collapse of marine ecosystems, widespread oceanic anoxia, and hence, profound perturbations in global iron deposition. This critical interval witnessed a transition in ocean chemistry, including intensified continental weathering, enhanced nutrient supplies and huge amounts of ferruginous flux mobilization. These factors collectively produced the widespread deposition of sedimental iron formations in Late Devonian.
In South China, the Late Devonian Xiejingsi Formation, whose Ningxiang-type iron deposits known as the most important sedimentary iron ore in China, preserves a set of complete record throughout this transition. The oolitic ironstones, comprising hematite, siderite and their mixtures, exhibit a distinct signature of rhythmic stratigraphic architecture, suggesting that iron deposition was not a simple precipitation, but more connected to the fluctuating redox and sediment supply during this unstable period, indicating an intimate association with the F-F mass extinction.

 

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