Postdepositional remobilization

The nodules that form at rates on the order of tens of millimeters per million years appear to have been produced primarily by postdepositional remobilization under oxic conditions. These nodules have relatively high copper and nickel contents. The nodules that accrete at the fastest rates (200 mm per million years) appear to have formed primarily via postdepositional remobilization under suboxic conditions. Despite these rapid accretion rates, the suboxic diagenesis -type nodules account for only half of those found in areas where biological productivity is high. The other half appear to have been formed primarily by oxic remobilization. Hydrogenous precipitation appears to play the dominant role in forming only a small percentage of the nodules. 

Several factors may account for large resuspension rates. The retrieval and deployment of the trap at the sediment surface may resuspend some particulate matter. Natural resuspension may result from storms and sediment-focusing mechanisms. Postdepositional remobilization may increase the sedimentation rate of210 Pb at the deepest point of Lake Sempach (41). Because we cannot discriminate among different resuspension processes, we assumed that the Mn concentration in the resuspended material is equal to that in the sedimenting particles at a depth of 86 m. Particulate MnO, is rapidly reduced at the sediment surface therefore, this procedure tends to overestimate the resuspension term. 

Vertical profiles, by themselves, are generally insufficient to identify sources or to rule out postdepositional rearrangement. Simple deposition, for example, cannot be credibly distinguished from deposition modified by mixing or remobilization. 

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