Chapter 5 - The Role of the Biosphere in Manganese-Ore Formation in the Geological History of the Earth

Abstract

The concentration of manganese in rocks of sedimentary and volcanogenic-sedimentary basins for the entire duration of the history of the formation of the Earth’s crust is closely connected with the organic matter of the biosphere. On the base of the isotopic composition of carbon in manganese carbonates in practically all Mn-carbonates, including ancient deposits of the land mass as well as sediments of modern water bodies (ocean, sea, and lake), is the participation of oxidized carbon of organic matter. The variation in the share (or degree) of participation by oxidized Corg in their formation is contingent upon several factors, chief among them are the quantity of organic matter in the sediments (bioproductivity of paleobasins) and the degree of activity of its microbial oxidation processes. Role of organic matter of biosphere in Mn-ore genesis is manifest at different stages of the formation of manganese rocks and ores: (a) in the participation in the composition of manganese carbonates by oxidized carbon of organic matter—that is, by CO2 formed during processes of microbial oxidation of Corg (sulfate-reduction and oxidation by the oxygen of manganese oxides); (b) in the mineralization by manganese carbonates of organogenic (microbial, etc.) remains; and (c) in processes of microbial oxidation of manganese rocks and ores in the zone of hypergenesis. Accumulation of manganese is closely connected with global biotic events (mass extinction of organisms).