Computer-aided maturity modeling and reconstruction of thermal history of the rock have become important and routine parts of sedimentary basin analysis and petroleum exploration. In performing simulations of organic maturation, it is extremely important to have a more reliable information about the thermal history of the rock. Various kinetic and non-kinetic thermal indicators have been proposed and applied to the reconstruction of thermal history. Among several organic thermal indicators, sterane isomer ratio and vitrinite reflectance are the most typical molecular and macromolecular thermal indicators, respectively. Many studies on their kinetic modeling have been performed in the 1980s to the early 1990s.
Sterane epimerization, which had once impressed us as an ideally simple uni-molecular reaction useful for paleo-temperature analysis, is now considered not to occur in nature. Various complex reactions concern the evolution of sterane isomer ratio in the sedimentary basin. However, this does not deny the value of sterane isomer ratio as a useful thermal indicator, since complex reaction process can often be simply expressed by the first order reaction kinetics. The same is true in modeling evolution of macromolecular organic matter. Maturation of kerogen or vitrinite can be modeled simply by the pseudo-first order kinetic reactions.
Geochemical model for organic maturation represents gross simplifications of what must be an enormously complex natural system. Numerical model does not express real geochemical process in nature, but expresses geochemical concept of organic maturation. Model construction itself can enhance insight into organic geochemistry. Our increasing knowledge on organic geochemistry can be linked with knowledge of other geological sciences by geochemical modeling. Geochemical modeling can expand the potential of organic geochemistry.

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In order to investigate the origin of non-marine oils in southeast Asia, especially the oils which indicate high oleanane/C₃₀ hopane index, the occurrence of unsaturated oleanenes, possible precursor of oleanane, was studied in two onshore Malaysian wells. Four isomers were identified in the same samples from these wells. Among these isomers, olean-13 (18) -ene was the most dominant in m/z=191, 218 and 410 mass chromatograms. Rapid decrease of olean-13 (18) -ene and 18α-olean-12-ene with increasing depth suggests that these isomers may be precursors of oleanane. These unsaturated oleanenes were still observed at 2500m depth with vitrinite reflectance of 0.75%. The conversion from oleanenes to oleanane has not completed in upper oil generation window.
Effect of molecular-sieving on the analysis of oleanenes was also investigated. This treatment is often applied to fluvio-deltaic source rock to remove n-alkanes. Experimental results indicated that oleanenes abundance decreased with increasing the amount of molecular sieve and the duration of the treatment. Degradation and/or conversion of unsaturated oleanenes can proceed faster due to catalytic effect of the sieve. Oleanenes are important compounds in the fluvio-deltaic petroleum system. However, the analysis of oleanenes with molecular-sieves should be conducted carefully.

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In order to investigate chemical fingerprints of different combustion sources, polycyclic aromatic hydrocarbons (PAHs) of airborne particulate samples were collected on three different occasions in Beijing (China), Tokyo (Japan) and Malaysia. Total-PAHs concentrations, including methyl- and dimethylphenanthrenes and sulfur containing hetero-aromatics (PASHs), were found to be the highest in Beijing (winter) samples followed by Beijing (summer), Tokyo, and Malaysia with readings of (405, 437), (20.4, 41.1), (8.43-43.1), and (2.64-42.6)ng/m³, respectively. Some of compositional differences observed could be due to the difference in combustion sources among the three countries rather than environmental alterations. Using ratios of benzo[ghi]perylene to benzo [e] pyrene (BghiP/BeP) and dimethylphenanthrenes to fluoranthene (DMP/Flu), Malaysian aerosols were elucidated from Tokyo and Beijing samples, suggesting high BghiP/BeP and DMP/Flu ratios as potential molecular markers of biomass-burning in the tropical region. Retene and 1,7-DMP/2,6-DMP ratio had previously been suggested as molecular markers for wood- or conifer-burning, were found to be useless in tropical region. Although PASHs were expected as molecular markers for the burning of sulfur-rich coal in China, ratios of PASHs to total-PAHs had showed only a slight enrichment in Beijing (winter) samples which was significantly affected by coal-combustion as compared to other samples in this study.

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A newly developed method was employed for separately extracting carbonate- and noncarbonate-assciated lipids. The sample examined was a lime mud from the inner Great Barrier Reef. Unsaturated n-fatty acids and phytol were enriched in the carbonate fraction, indicating that the carbonate-associated organic matter was derived primarily from marine algae. In contrast, saturated n-fatty acids, n-heptadecane, labdane and C_25:1 highly branched isoprenoid alkene were enriched in the noncarbonate fraction, indicating that the source of the noncarbonate-associated organic matter includes higher plants and diatoms. Iso-and anteiso-fatty acids of bacterial origin occurred both in the carbonate and noncarbonate fractions. The method used in this study was unsuccessful for the separate determination of sterols. A portion of the carbonate-associated sterols was presumably recovered in the noncarbonate fraction.

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Kerogens in sediments of different burial depth over a stratigraphic sequence in Neogene Shinjo sedimentary basin were heated from room temperature to 800℃ under a helium flow by a thermogravimetric analyzer (TG). Compounds released by the thermal decomposition of kerogen were introduced into and analyzed by a gas chromatograph-mass spectrometer (GC/MS). Two hundred and forty-nine compounds were identified and are mainly aliphatic and aromatic hydrocarbons. A release profile of each compound from kerogen with increasing heating temperature was obtained by TG-MS. In general, thermal release of compounds started around 350℃ which shifted to 450℃ with increasing burial depth of kerogen and ended roughly at 550℃. The release-peak width tended to become narrower with increasing burial depth of kerogen, which reflects the loss of a thermally more labile fraction of kerogen in sediments during diagenesis.

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Heating experiments of 1- and 2-methylnaphthalenes in the presence of Na-montmorillonite at 200 to 350℃, and three Neogene sediments at 300℃ were performed to examine time-course changes in amounts of naphthalenes, ratios of 2- to 1-methylnaphthalene and molar fractions of dimethylnaphthalenes. The experiments of 1- and 2-methylnaphthalenes produced mixtures of naphthalene, methylnaphthalenes and dimethylnaphthalenes by intermolecular and intramolecular methyl transfer reactions. A major portion (70 to 90%) of naphthalenes was changed to solvent-insoluble organic matter by the experiments. The heating experiments of two Neogene sediments produced mixtures of naphthalenes whose amounts increased with heating time, whereas those from the other sediment decreased. This difference might reflect the contents of precursors of naphthalenes in the sediments. The catalytic action of Na-montmorillonite was inactivated on heating at 250 to 350℃ within 24h. The inactivation of the mineral matrices in the sediments was also observed in the experiments. After the inactivation of the catalyst, amounts or molar fractions of isomers of naphthalenes were found nearly constant. The change of maturity parameters from their initial values to those at the inactivation time may provide a simulation of maturation process of naphthalenes in sediments. The ratios of 2- to 1-methylnaphthalene at equilibrium can be used for comparison of the chemical properties of the sediment matrices on the stability of methylnaphthalenes.

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Aliphatic and aromatic hydrocarbons, and fatty acids were detected from a stone excavated from an archaeological pit in Inadaira site, Aomori Prefecture, Japan. Polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin were not detected in carbonized material adhered on the surface of the stone sample and in soil (soil sample) which covered the stone. Shorter carbon-chain (<C₂₂) n-alkanes found on the stone sample were probably associated with allochthonous living organisms. Likewise, the tetradecanoic, hexadecanoic and cis-9 hexadecenoic acids were relatively abundant in the sample, indicating that the allochthonous materials were supplied and well preserved on the surface. In the soil sample, the molecular distribution patterns of n-alkanes and fatty acids were nearly similar to those reported for the typical forest soil and therefore, they were mainly derived from the terrestrial higher plants. These results indicate that the stone has not experienced high temperature heating and do not support the archaeologists' speculation that the pit was used as a kiln. It is presumed that the pit was possibly used as a non-heating place for storage of foods etc.

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Extraction and esterification conditions were examined for the analysis of dipeptides in sediments by gas chromatography (GC) coupled with mass spectrometry (MS). It was found that extraction by shaking with water at 60℃ for 1h and esterification in 1.5M HCl-methanol at room temperature for 3h were satisfactory conditions under which a small portion (<0.2%) of L-valylglycine (L-Val-Gly) decomposed as well as only a trace amount of hexaglycine (<0.04%) and polyglycine (<0.02%) decomposed to glycylglycine. We applied the method to the surface sediment sample (0-2.5cm) from Tokyo Bay. Stereoisomers of alanylalanine, Val-Gly and glycylvaline were separated by an optically active GC column and their identifications were made by GC-MS, showing apparent dominances of the L-isomers. The four dipeptide concentrations ranged from 1.6 to 5.3nmol g^-1. The dipeptides detected from the sediment sample are very likely those extant in the sediment mainly derived from proteins during the early stage of diagenesis but not those produced by the degradation of polypeptides in the course of the analytical procedure employed.

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