ABSTRACT: The Ferromanganese System in the Ocean and Genesis of Ferromanganese Nodules

L. M. Gramm-Osipov

The genesis of ferromanganese nodules is one of the most complex problems of marine geology and geochemistry. To understand their genesis it is important to know whether the solid phase of the nodules can form with the concentrations of iron and manganese occurring in the water of the modern ocean. Consequently, it is necessary to clarify the physiochemical conditions in the environment of nodule formation, to estimate the solid phases and the reactions that determine the distribution and iron and manganese concentrations in the water column.

The author has done physiochemical analysis of the ferromanganese system in the ocean that pertains to nodule genesis. It is shown that the concentration and distribution of iron in the ocean depends on the aging of iron hydroxide (III), especially within the first 30 minutes of residence. Concentration and distribution of manganese is tied to the solid compound of Mn₃O₄ within the water depth interval of 150-600 m and on MnOOH at deeper water depths. MnOOH takes part in the reaction of disproportionation, which results in the formation of a MnO_1800-1.998 solid phase. In the pore water of the sediments supporting ferromanganese nodules, the concentration of manganese depends on the reaction of disproportionation.

The conducted physiochemical analysis of the ferromanganese system in the ocean indicates that the formation of nodules takes place at the same physiochemical conditions and iron and manganese concentrations that are observed in the modern ocean. Nodules appear to be of sedimentary-diagenetic origin.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990