Three series of pyrolysis experiments, anhydrous pyrolysis in helium-flow open system, hydrous pyrolysis in closed system and compaction-hydrous pyrolysis in open/closed system were performed to obtain a better understanding of organic metamorphism. Changes in the vitrinite reflectance, petrographic texture, ¹³C-NMR spectra, and Raman spectra of a Japanese subbituminous coal and oil/gas generation from three kerogen types in the above pyrolyses were correlated with the experimental conditions, and the process and mechanism of organic metamorphism is demonstrated as follows:
(1) The major driving force of organic metamorphism is heat subjected to sediments. The pressure, ambient condition, and reaction system do not promote the organic metamorphism itself. However, they affect the migration of products and the interaction between sedimentary organic matter (SOM) and pyrolysate, resulting in the differences in organic petrography and position of bond cleavage/re-coupling in the chemical structure.
(2) Hydrogen poor macerals as vitrinites/inertinites, and the aromatic carbon bond species in the chemical structure of SOM are relatively stable through organic metamorphism. They are fixed in sediments and aromatized with increasing organic metamorphism, and finally change to graphite. On the other hand, hydrogen rich macerals as alginites and exinites, and the aliphatic carbon bond species in the chemical structure of SOM are not stable, and are removed from SOM through organic metamorphism. Those hydrogen rich macerals are assumed to be the main source of the generated oil and gas, and are affected by pressure, ambient condition and reaction system.
(3) The reaction in the organic metamorphism begins from hydrogen rich macerals with lower bond energy, and it proceeds gradually to hydrogen poor macerals with higher-bond energy. SOM is roughly divided into two categories; the stable portion remaining in sediments to preserve geological record and the reactive portion converting to oil and gas.

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Specific feature of mono methyl-branched long-chain hydrocarbons, fatty acids and alcohols (anteiso compounds) was found in some moderately acidic (pH=3-5) Japanese freshwater lake sediments. Structural similarities of these compounds suggested that they should have originated from the same kind of organism tolerable to such a restricted habitat. Following investigations revealed that their abundance showed a significant vertical variation in the sediment core of the lakes, where evident pH fluctuations are known in the past. Another work demonstrated that majority of those compounds are contained in aquatic microorganism associated with fine particles suspending in the lake water, whose diameter ranges from 0.6μm to 40μm. Since the anteiso compounds were detected only within the lake system, these findings strongly suggested their possibility as a novel and sensitive biomarker reflecting the pH condition of the lake water.

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Hydrothermally-altered organic-rich lake sediment was collected from Lake Usori, Osorezan. The biomarker composition and carbon isotopic composition of individual n-alkanes were examined on this sample, and the characterization was carried out to compare with reservoir petroleum and hydrothermal petroleum.
The studied lake sediment is characterized by odd dominant n-alkane, a little amount of isoprenoid alkane and alkylaromatic hydrocarbon, and lack of UCM. These characteristics are different to the composition of both reservoir and hydrothermal petroleum. A significant amount of heterocyclic compounds and 17β(H)-hopane in this sample are similar to the composition of hydrothermal petroleum, but the concentration of PAHs, hopene and sterene in studied sample are much lower than those of hydrothermal petroleum.
Carbon isotopic compositions of individual n-C₁₇-C₃₀ alkanes decrease with increasing carbon number. The decrement of δ¹³C value is about 10‰.

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There are many inorganically acidic freshwater lakes in Japan. In some of those moderately acidic (pH=3-5) lake sediments (e.g., Lakes Kussharo, Tazawa, Usori and Inawashiro), significant amounts of long-chain anteiso-compound series (3-methylalkanes, (ω-2)-methylalcan-1-ol and (ω-2)-methyl-alkanoic acids) have been identified. Based on the analysis of the particulate matter collected both from the river water which makes the lake water acidic, and from the lake water, it was concluded that the source organism(s) of theanteiso-compounds is aquatic biota inhabiting the moderately acidic lake water (Miki and Fukushima, 1996). But the source organisms were not specified. The purpose of this study is to provide further evidences on the origin of the anteiso-compounds. The particulate matter (0.6-40μm) and planktons (>40μm and >100μm) were separately collected by using plankton nets and a glass fiber filter from L. Tazawa (pH=4.8-5.2) and L. Inawashiro (pH=4.4-5.0) water and analyzed for lipid compounds. In both lakes, the quantity of theanteiso-compounds in the fine particulate matter (0.6-40μm) was obviously larger than those in the planktons (>40μm), indicating that the true source may be finer bacteria dispersed in the lake water.

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Elemental composition of humic acids in the marine sediments collected from Hakata Bay near Muromi River lies within a range reported for those humic acids of marine origin in the literature. FT-IR spectra of the humic acid indicated the presence of such functional groups as hydrogen-bonded -OH, aromatic and aliphatic -CH, -COOH, C=O, C-O-C and amid band. ¹H-NMR also showed aliphatic and aromatic characters, which are important for anticipating the presence of humic substances. Pyrolysis-GC/MS suggested that the components of the humic acids are constructed from a wide range of biologically related materials such as proteins, carbohydrates, lipids and phenols. The results suggested that aquatic plants, algae and animal biomasses, mainly compose the humic acids and the contribution of terrestrial source materials such as lignin is small.

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