Petroleum-like hydrocarbons have been occurred commonly associated with hydrothermal activity. The hydrocarbons, "hydrothermal petroleum", were generated by the interaction between a hot hydrothermal fluid and sedimentary organic matter in a deposit distributed around the hydrothermal systems such as the continental margin and volcanic systems in land areas. Until recently, the occurrences of a significant amount of the petroleum have been discovered in seven marine hydrothermal fields located on seafloor spreading axes and the submarine volcanoes of island-arcs. However, the occurrence of petroleum has not been reported from hydrothermal fields associated with back-arc rifting and spreading zone, except the King George Basin in Antarctica. Seafloor hydrothermal systems located in the back -arc basin are suitable for occurrence of a large amount of hydrothermal petroleum, because the back-arc basin is developed near the continent and expected to be covered with thick sediment. There are many hydrothermal fields in Okinawa Trough, although the occurrence of the hydrothermal petroleum has not been reported. In this paper, origins of oil and gas reserved in the volcanic rocks of the Green Tuff region in the northeast Japan were discussed, and the possibile occurrence of hydrothermal petroleum from such region is suggested. The Green Tuff terrene has been known as one of the active areas of submarine volcanisms, and thus hydrothermal activity had enhanced the maturation and improved the potential of the reservoir rocks. Further studies are necessary for investigation and identification of economically valid hydrothermal petroleum, which was generated during ancient age and reserved in the geological systems.

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Ruthenium tetroxide oxidation has been used as an aid to elucidating molecular structures in a type II kerogen. We have improved on the conventional method by characterizing some of the low molecular weight compounds present in the products. Aliphatic α, ω-dicarboxylic acids (C₂-C₂₃), normal monocarboxylic acids (C₂-C₂₉), branched α, ω-dicarboxylic acids (C₄-C₇), and benzene mono- to tetracarboxylic acids were detected as the main products. Carbon number distributions of the aliphatic α, ω-dicarboxylic acids indicate that the type II kerogen contains short polymethylene bridges in the macromolecular network. Isomer distributions of the benzene polycarboxylic acids show that naphthalene-/anthracene-type structures and biaryl-linkages are the dominant aromatic moieties in the network.
As minor compounds we detected a series of hopanoic acids (C₃₀-C₃₄) and carboxysteranes (C₂₈-C₃₀). Correspondence of the carbon number range of the steroid skeletons in the kerogen with those of steranes in the bitumen suggests that precursor molecules, such as sterols, were incorporated into the kerogen and attached with aromatic units during diagenesis. Comparison of the hopanoic acids and hopanes in the bitumen indicates that the hopanoids in the kerogen retained their carbon number distribution during the incorporation of their precursor molecules into the kerogen matrix; further, they are more stable towards isomerization compared to the bitumen hopanes.

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Living-pollen grains of angiosperm Styrax japonica were heated at 65 to 285℃ for 24 hours under the atmosphere in the laboratory to investigate the changes in physical and chemical properties of pollen by artificial heating experiments. It was shown that the heated pollen-grains have decreasing trends in weight, size, the atomic H/C ratio and brightness (stTAI) with increasing heating temperature, but an increasing trend in atomic N/C ratio as was known for fern spores and gymnosperm pollen. The decreasing trend of the atomic H/C ratio in the heating experiments indicates that hydrocarbon generation from pollen wall, sporopollenin, should take place in the range of heating temperature between 132 and 242℃. It is concluded that the features of angiosperm pollen, especially its brightness (stTAI) may be useful as a possible indicator for organic maturation like those of other kinds of plants.

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Compound-specific hydrogen isotope analysis of polycyclic aromatic hydrocarbons (PAHs) has been established at sub-nano molar level, using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). The analytical precision of δD value is generally less than a few ‰ at >2nmol (i.e. 20ng H) injection of pyrene and fluoranthene calibrated with co-injected 30ng H of phenanthrene and chrysene.
Hydrogen isotope exchange of pyrene and fluoranthene with water under neutral and acidic conditions was examined with relevance to hydrogen isotopic distribution of individual PAHs in carbonaceous chondrites. Hydrogen isotope exchange between PAH and water hardly occurred at 170℃ under neutral pH condition for 2 days. However, under acidic condition (pH=2), the isotope exchange reaction occurred, where hydrogens have exchanged more easily between pyrene and water relative to between fluoranthene and water. The kinetically different behavior between pyrene and fluoranthene coincides with the two-series PAH formation mechanisms in carbonaceous chondrites inferred from carbon isotopic compositions of PAH.

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Dissolved organic matter (DOM) comprises major part of aquatic organic matter, but is poorly understood, because of the difficulty in isolating a sufficient amount of DOM for the detailed chemical analyses. It is known that more than half of DOM is composed of a large molecular weight material, water humus. This study aimed to concentrate and isolate the high molecular weight DOM (HMW-DOM: MW>1000) using a tangential flow ultrafiltration (TFF), and to characterize the isolated solid organic matter. The water samples (80L〜100L) were collected from five lakes (Lakes Nakatsuna, Kizaki, Suwa, Misuma-ike and Shirakoma-ike) in Nagano Prefecture, Japan. DOM was concentrated from 100L to 1L by TFF, and then from 1L to 200mL by a conventional agitational ultrafiltration, equipped with filters of nominal molecular cut-off (MCO), 1000 dalton. The concentrated water was finally lyophilized to give DOM as a solid material. HMW-DOM thus obtained accounted for about 30〜40% of DOM in each lake water. Elemental and stable isotopic analyses gave the atomic C/N ratios: 10〜28, the δ¹³C: -28〜-25‰ and δ¹⁵N: 0.4〜8.6‰, respectively. Together with the lipid composition, these analytical data supported the assumption that the limnological properties reflect on the chemical nature of DOM.

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Lake Kai-ike (max. water depth: 11m) is a brackish meromictic lake, which is characterized by the occurrence of a dense "bacterial plate", inhabited by purple sulfur bacteria, Chromatium sp. at the mid-depth (ca. 4.5m). The lipids in the sediment core and particulate matter in the water column were analyzed to identify and quantify possible bacterial biomarkers.
Particulate materials collected from near the "bacterial plate" contained large amounts of alkenes, alkenols and alkenoic acids, in addition to C₂₅ and C₃₀ acyclic isoprenoid alkanes. The sediment of L. Kai-ike has a great deal of complicated compounds, including cyclic and acyclic isoprenoids. Phytane and PMI disappeared remarkably from surface layer of sediment to 3cm in depth. On the contrary, farnesol and alkenol (C_16:1: hexadec-9-enol) probably derived from bacteriochlorophylls c, d or e of green sulfur bacteria, once decreased and again increased in the bottom sections (>40cm) of the core. The concentrations of octahydrosqualene, a C₃₀acyclic isoprenoid alkene, did not show apparent decreasing or increasing trends. The sedimentary organic matter of the meromictic lake has a potential to estimate the changes of bacterial community in the past.

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