Recent progress in oceanography, marine sedimentology, and organic geochemistry enables us to evaluate, quantitatively, factors which control the process of marine organic matter production and its degradation during settling through the water column as well as within the surface sediment. Since many of the factors could be evaluated through detailed geological observation and paleoceanographic reconstruction of the depositional setting, it seems possible to incorporate mathematical formulation of this process into the pre-existing models of source rock evaluation.In this paper, I will propose the mathematical formulation of the marine organic matter production-settling-degradation process based on recently accumulating oceanographic data, and try to apply this formulation to evaluate the source rock potential of the Miocene Onnnagawa Formation, northeast Japan.