It is ordinarily considered that hydrocarbons production from kerogen in nature is carried out in reduced environments. Heating experiments on living pollen and spores as a simulation of organic maturation have been generally conducted in open system under the air and nitrogen gas. In order to investigate the influence of air and nitrogen gas on thermal alteration of pollen, living pollen grains of Pinus thunbergii were heated in open system to 290℃ under the air and to 453℃ under the nitrogen gas. The temperature to begin abrupt weight loss, contraction and color darkening (decrease in statistical Thermal Alteration Index) of pollen grains heated under the air is lower than that heated under the nitrogen gas. The pollen grains heated at the temperature higher than 180℃ under the air might be oxidized by atmospheric oxygen, because atomic O/C ratio of those grains are higher than those heated under the nitrogen gas. Our results support that inert gas including nitrogen gas is better than the air as the atmosphere of heating experiments for simulation of organic maturation.

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To reconstruct prehistoric human diets, we studied pottery excavated from the Hamanaka 2 archaeological site, Rebun Island, Hokkaido, Japan, where marine mammals were cooked (boiled) in pottery vessels to obtain animal oils and fats. We analyzed lipids adhering to the pottery and demonstrated that cholesterol made up more than 80% of the detected sterols, suggesting that they were of animal origin. The stable isotopes of carbonized material adhering to the inner surfaces of potsherds indicated that the charred materials likely reflected a diet of marine mammals or finfishes. Radiocarbon dates on the same charred materials showed a large marine reservoir effect, which supported the interpretation that they were derived from marine products cooked in the pottery vessels. The apparent radiocarbon age differences between the charred materials on the inner surfaces of the potsherds and charred wood from the same layer that the potsherds came from indicated a correction value for the marine reservoir effect (ΔR) in the northwestern Pacific of 444±55 ¹⁴C years at 3010BP. The results of these three analyses, namely, sterol analysis, stable isotope analysis, and radiocarbon dating, are consistent with the archaeological hypothesis that during the latter half of the Late Jomon period (1300-1200cal BC), sea mammals were cooked in pottery vessels to obtain animal oils and fats at the Hamanaka 2 archaeological site.

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After the development of compound-specific isotope analysis (CSIA) by gas chromatograph/pyrolysis/isotope ratio mass spectrometer (GC/pyrolysis/IRMS) in the end of the 1990s, stable hydrogen isotopic composition of organic compounds has been employed for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and as a potential proxy for reconstructing paleoclimatic, paleohydrological, and paleosalinity changes. However, sample amount required for accurate and precise determination of the isotopic composition is generally 10-50nmol H for each compound, which is much larger than that of stable carbon (0.1-5nmol C) and nitrogen (1-10nmol N) on the isotope analysis by gas chromatograph/combustion/isotope ratio mass spectrometer (GC/combustion/IRMS). Here, I demonstrate the performance of GC/pyrolysis/IRMS on the small amount of samples, and suggest a mathematical correction for preventing systematic errors in the measured isotopic composition due to different sample amounts. By using this correction, the hydrogen isotopic composition of organic compounds can be determined with a standard deviation (1σ) of better than 7‰ on the sample amount of 4nmol H and even 13‰ on the sample amount of 2nmol H. This correction thus allows us easy access to the hydrogen isotopic composition of organic compounds containing with small concentration in samples.

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The distribution and behavior of tri-aromatic hydrocarbons (especially alkylphenanthrenes) have been investigated in twenty-four mudstones from the Tertiary succession in the Sylhet Basin of Bangladesh. Phenanthrene (P) and methylphenanthrenes (MP) were abundant in most samples, whereas anthracene and methylanthracene (MA) were detected only in some samples. Abundances of the 1,7-dimethylphenanthrene (DMP) isomer are significant relative to other DMP isomers. Overall correlation between the methylphenanthrene index 3 (MPI 3) and T_max (426-449℃) is poor in this basin. Abundances of MA, pimanthrene (1,7-DMP) and 1-MP are relatively high in the lower part of the succession. Higher plant organic matter is abundant in the lower part of the succession (middle Eocene to early Miocene), whereas planktonic organic matter is relatively abundant in the middle and upper parts (middle Miocene to Pleistocene). These alkyl-isomers thus originated from terrigenous sources. High phenanthrene/alkylphenanthrene ratios in the mudstones can be related to oxic environmental conditions. Based on detailed aromatic distribution patterns and their isomer ratios, we conclude that the compositions of P, MP and DMP isomers in the Sylhet Basin were probably controlled by organic matter sources, rather than by thermal maturity in the early stage of the oil window.

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Laboratory cultured strains of Emiliania huxleyi EH2 (identical to NIES-837) and Gephyrocapsa oceanica GO1 (NIES-838) were grown at 20℃ under various salinity conditions ranging from 15‰ to 34‰, and were analyzed for long-chain (C₃₇-C₃₉) alkenones and (C₃₇-C₃₈) alkyl alkenoates. In both E. huxleyi EH2 and G. oceanica GO1, there were no tetra-unsaturated (C_37:4) alkenones, which were frequently identified at low salinity waters in literatures. The alkenone unsaturation index (U^k'₃₇) in E. huxleyi clearly changed under lower salinities such as 27‰ and 32‰, while the values in G. oceanica were almost constant in various salinities. From these results, the U^k'₃₇ variations affected by salinity should be paid attention in paleotemperature reconstruction from natural samples that E. huxleyi predominates, especially in lower saline environments. Interestingly, our culture experiments also showed that the alkenone chain-length ratio (K₃₇/K₃₈) for E. huxleyi and G. oceanica increased with decreasing salinities, although the ranges of these variations were small. These results suggest that the K₃₇/K₃₈ values were affected by the cellular and physiological factors in a single haptophyte cell, although this value varies mainly depending on the changes of haptophyte species and/or strains in natural environments. Hence, we suggest that the K₃₇/K₃₈ ratio can be more reliable as a paleosalinity indicator.

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