Inversely graded pisolites of manganese oxide in the mid-Cretaceous manganese giant at Groote Eylandt, Australia, were deposited during a regional fall in sea level, as indicated by their relationships to wave-cut benches. Dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression. Ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal-lag mechanism.

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