The plant derived solid organic matter in sediments bears the two geological evidences of sedimentary conditions and diagenetical to metamorphic grade of the host sedimentary rock if it is analyzed or measured properly. The object to study precise grade of organic metamorphism has to be restricted to a certain maceral in order to avoid variation of the values caused by the diversity of the matter. The most applicable effective method at present after identifying or separating the macerals is the coal microscopic measurements of vitrinite reflectance and sporinite fluorescence spectra under incident light. The two methods are applicable not only for dealing with coal seam but also with phytoclasts or kerogen, and the latter is the more effective for analyzing the lowest stage of the organic metamorphism including diagenesis and the former is for the diagenetical to the more higher stages where the fluorescent substance vanished. X-ray diffraction method for analyzing the degree of graphite crystalization is effective for grading the highest stage of organic metamorphism, but the contamination and dilution by other macerals than vitrinite affect the diffraction pattern in the lower stages, consequently the additional maceral analysis or concentration of vitrinite in the object matter is required for the more minute and exact analysis by this method.
It is suggested that present geological subject by applying the methods of analyzing the organic metamorphism to the Japanese Islands as a part of neotectonic island arc system is a precise analysis of stratigraphic and regional variation of the pattern in the Cenozoic group in connection with the present geophysical data around the islands. Practical application of the methods has been executed by the author to reveal a pair of organic metamorphism (AIHARA, 1980) between the forearc and backarc Paleogene coal-bearing groups in the island arcs reflecting a good coincidence with the Cenozioc terrestrial heat flow condition. Standing on a view point that the lower stage of organic metamorphism including diagenetical alteration implicates the succeeding more higher grade of metamorphism, the latter of the older ages will be analyzed and deduced analogically by this geological reasoning.