Influence of Diagenesis on Nodule Growth

Perhaps the most comprehensive explanation of the role of hydrogenetic and diagenetic processes on manganese nodule accretion has been presented by Dymondetal (1984). On their classification, hydrogenous deposition involves the direct precipitation or accumulation of colloidal metals oxides from seawater. Strictly, this involves deposition of manganese oxides on surfaces in contact with seawater such as involved in the formation of manganese crusts. In practice, manganese nodules formed on red clays have charac- 

From the above comments, it will be seen that the principal factor driving the diagenetic milieu in the sediments is the biological productivity of the oceanic surface waters. A map of biological productivity of Pacific ocean surface waters shows that the productivity of the northern sector of the Southwestern Pacific Basin is 50-100 gC m yr, in the C-C F.Z. is in the range 100-150 gC m yr and in the Peru Basin is 

Fortius purpose, we may therefore consider hydrogenous deep-sea nodules to be a baseline. When oxic diagenesis takes place, Mn, Ni and Cu are released into the sediment pore waters and are ultimately incorporated into the nodules. Ni + and Cu + substitute in the phyllomanganate lattice (see below). This explains the high Mn/Fe ratios and Ni+Cu contents of oxic nodules. When sub-oxic diagenesis takes place, Mtf+ is remobilized into the reducing sediments and 

Biotuibation is an essential requirement for benthic lifting of manganese nodules and maintaining the nodules at the sediment surface. In both the C-C F.Z. and the Pern Basin, the biological productivity of the oceanic surface waters is high enough that the amount 

In addition to the above, Calvert and Piper (1984) have proposed a diagenetic source of metals derived from sediments far away for nodules occurring in an erosional area with thin sediment cover in the C-C F.Z. The metals were thought to be transported to the site of deposition by oceanic bottom water, probably AABW. Although this process is well known in shallow-water continental margin areas such as the Baltic Sea, only limited evidence to support this hypothesis has been presented for the deep-sea enviromnent. 

---