Abstract
Synsedimentary and early diagenetic oxygen levels are estimated by evaluating celadonite–smectite formation in Jurassic marine black shale-hosted manganese carbonates. Celadonite formed under suboxic–dysaerobic conditions, Al-rich Fe-smectite formed under suboxic–anaerobic conditions, and nontronite formed under anoxic-anaerobic conditions during sedimentary burial. A genetic pathway by direct precipitation from solution is proposed for the enormous mass of celadonite based on mineral and textural evidence. Lamination of the manganese ore is independent of clay-mineral composition and was created by a series of mineralized Fe-rich biomats.
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