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This paper presents a multicomponent early diagenetic model which explicitly accounts for the coupling of the redox cycles of Fe and Mn to those of oxygen, carbon, sulfur, and nitrogen. Rate expressions are used to represent the oxidation of organic carbon, the oxidation of secondary reduced species formed as byproducts of organic matter oxidation, and the precipitation and dissolution of sulfide and carbonate minerals. The net rate of organic carbon oxidation is broken down into the contributions of aerobic respiration, denitrification, dissimilatory Mn (IV) reduction, dissimilatory Fe (III) reduction, sulfate reduction, and methanogenesis. The computational algorithm is based on a modified Monod kinetics formulation for the organic matter degradation pathways. The non-specific adsorption of ammonia, the surface complexation of Fe** and Mn** cations, and the homoge-neous interconversions within the dissolved …