Mudstones of the Middle to Upper Miocene Teradomari Formation are considered to be the main petroleum source rocks for the oil fields in Niigata and, at the type locality, are classified as turbidite (Et) and (hemi) pelagic (Ep) mudstones, according to Bouma sequence division.
Hopanes, steranes and other alkanes extracted from the mudstones were analyzed by GC and GC-MS. Oleanane/hopane ratios and sterane composition suggest that Et contains more terrestrial organic matter than Ep. This result is consistent with the maceral composition (Watanabe and Akiyama, 1996).
Pristane/phytane ratios indicate more anoxic depositional environment of Ep than Et in the Upper Teradomari Formation, while there is no difference between Et and Ep in the Lower Teradomari Formation.
Chemical composition of the pyrolysates of kerogens is different between Et and Ep in the Upper Teradomari Formation in n-alkene/n-alkane ratios and relative amounts of trisnorhopene and C₁₇ isoprenoid. These results are also consistent with the maceral composition of the kerogens.

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Vitrinite reflectance (Re%, mean random reflectance) was measured on the collinite macerals separated from the Neogene clastic sediments distributed in the Nishikubiki area of the northern Fossa Magna region. In this study, samples were collected from two regions, the North (N) and the South (S), along the limbs of the Nambayama anticline in the western part of Joetsu City.
The regression lines between log Re(%) and stratigraphic horizon based on thickness of the sediments in the study area show similar gradients with those of the MITI exploratory test wells around this area. This result suggests that the nearly same maximum paleotemperature gradient prevailed in the Nishikubiki area.
Vitrinite reflectance values between the two regions show that the South region is about 0.6% higher than the North region at the same stratigraphic horizon of the Nambayama Formation, suggesting about 1700m difference in original burial depth.

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The Yabase oil field in the Akita Prefecture is the largest oil field in Japan, and it has produced approximately 35 million barrels of cumulative oil by the end of 1995. Relationship between characteristics of extracted steranes and mineral compositions was studied for the Neogene source rock samples from four wells in the northern part of the field. Gas Chromatography-Mass Spectrometry for saturated hydrocarbons from the rock extracts, X-ray fluorescence and X-ray diffraction analyses were carried out.
Diacholestanes/cholestanes ratio tends to increase westward among the four wells. Detritus content calculated from SiO₂ and Al₂O₃ contents, and the total content of clay minerals also tend to increase westward. Therefore, positive correlation was observed between the detritus content and the diacholestanes/cholestanes ratio, and between the total clay content and the ratio. The diacholestanes/cholestanes ratio relates to thermal maturity and generally increases with increasing maturity. Positive correlation was observed between the ratio and 20S/(20S+20R) ratio of stigmastanes. The diacholestanes/cholestanes ratio is also influenced by the depositional environment of source rocks. The ratio will become more useful to the quantitative estimation of clay content in their source rocks, by taking the environmental influence as well as the maturity influence into account.

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Some type of macerals in sediments fluoresces under ultraviolet light. According to an increase of their maturity level, the wavelength of fluorescence maximum sifts toward longer wavelength, and intensity of the fluorescence diminishes. This property allows the fluorescence spectra to be a good maturity indicator for low immature sediment samples whose maturity can be hardly determined by vitrinite reflectance. However, correlations between thermal alteration of the fluorescent substances and the "red-shift" in the spectra are not clarified well.
In this investigation, we examined thermal alteration of fluorescence spectra and chemical structures of fluorescent substances in the resinite from Latrobe Valley (Victoria, Australia). The samples were heated stepwise from 100℃ to 320℃ at 20℃ intervals for 15min at each temprature. We observed fluorescence spectra and ultraviolet-visible (UV-VIS) absorption spectra of the samples cooled after maintaining for 15min at each temperature. The "red-shift" in the fluorescence spectra was associated with alterations of UV-VIS absorptions. The IR spectra of the original samples and of the samples obtained after heating at the final temperature were also determined. No IR absorption bands due to aromatic rings appeared after the heating. These facts indicated that elongations of conjugated double bonds caused the "red-shift" of fluorescence.

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Organic matter in rock samples can be found in various forms: interspersed in inorganic matrix, absorbed onto mineral surfaces, and incorporated into crystal defects and inclusions of authigenic minerals. In the present paper, extractable organic matter in the phosphorite, consisting mainly of apatite, from the Middle Miocene Monterey Formation, California was classified into the following four groups. (a) Free bitumen; conventional extracted from the powder sample. (b) Bound bitumen; extracted by saponification of solvent extracted residue. (c) Trapped free bitumen; extracted by solvent after HCl demineralization of saponified residue. (d) Trapped bound bitumen; extracted by saponification of solvent extracted residue after HCl treatment. Molecular distributions of hydrocarbons, fatty acids, and some typical ketones in four bitumen fractions were analyzed to clarify the characteristics of organic matter incorporated into authigenic apatite crystals.
Trapped bitumen comprises 28% of the total bitumen. n-Alkane distribution of free bitumen is similar to that of trapped bitumen, but the later is characterized by higher relative abundance of higher molecular weight alkanes and higher odd number carbon preference index. The pristane/phytane ratio of free bitumen is much lower than that of trapped bitumen. Although sterane distribution from four bitumen fractions are nearly similar to each other, relative abundance of cholestane tends to increase significantly in the order of free, bound, HCl/free, and HCl/bound fractions. Hopenes and ββ hopanes are major hopanoids in free bitumen. While hopanoids in trapped bitumen are characterized by αβ hopanes and a little hopene. Ketones of all bitumen fractions are dominated by 6,10-dimethylundecan-2-one and 6,10,14-trimethylpentadecan-2-one. Fatty acids from bound bitumen ranges from C₉ to C₃₀ with a maximum at C₁₆, while those from trapped bitumen exhibits a narrower range of carbon number with dominant C₁₄, C₁₅ and C₁₆ acids. Hopanic acids from bound bitumen are rich in ββ hopanic acids and 28-norhopanic acids. On the contrary, trapped bound bitumen is characterized by βα hopanic acids and little 28-norhopanic acids.
These compositional differences among free, bound, HCl/free, and HCl/bound have not been fully interpreted at present. Inner crystal stress due to increasing crystanity of apatite during diagenesis could be one of essential causes for the discriminative alteration of trapped bitumen.

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The Aga-oki oil and gas field, offshore Niigata, Japan, consists of two parallel anticlinal structures, which are called the West and East structures.
The geochemical data of oils from the Shiiya Formation such as light hydrocarbons and biomarkers indicate that the oil from the West structure is more degraded and less mature than that from the East structure.
The difference in maturity of oils probably reflects a difference in the kitchen area: the geochemical data of oil and condensate from two exploratory wells suggest that the oil from the West structure has migrated from the southwest kitchen area, while the oil from the East structure has migrated from the east kitchen area.

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The Aptian to Albian sediments of the Yezo Supergroup in the northern Oyubari area are well-laminated, being affected little by macrobioturbation. A positive peak of carbon isotope excursion, high organic carbon contents and high sulfur contents are detected in the middle Albian. The redox environmental indices, S2/S3, pristane/phytane and bisnorhopane/hopane ratios, show a reducing condition in this stratigraphic level. The good correlation of S2/S3 ratio vs. TOC indicates that the high organic carbon contents in this basin depend primarily on the reducing conditions. Therefore it is apparent that a reducing environment (i.e. anoxic to dysoxic environment) prevailed in this basin, and this regional event is correlated with the global OAE1c.

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Lake Saroma is the biggest coastal lagoon in Japan and the bottom water is generally oxic in recent years, while Lake Abashiri is characterized by an anoxic bottom water even in winter season. In order to characterize the oxic and anoxic surface sediments in the coastal lagoons, distributions of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) contents have been investigated in the two lake sediments. TOC, TN and TS contents, as well as C/S and C/N ratios, seem to reflect the oxic-anoxic condition, primary production and salinity in the lakes. In the oxic environment, TOC, TN and TS contents are low, and the C/S and C/N ratios are high. On the other hand, in the anoxic environment, TOC, TN and TS contents are high, and the C/S and C/N ratios are low. These results suggest that fleshly deposited planktonic organic matter was preserved and was effectively used by sulfate reducing bacteria in the anoxic environment.

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Several strains of thermoacidophilic archaea were isolated from a water sample taken from the hot spring "Kamado-Jigoku 4 Chome" at Beppu in Oita, Japan. The original temperature of the hot spring was 78.3℃, and the pH was 2.48. In the original water sample, spherical microbes with a diameter of about 1μm were mainly observed by fluorescence microscopy.
An isolate (tentatively designated as BK4-K1) grows optimally at 70〜75℃ and pH 2〜3. Although the shape of the strain BK4-K1 was observed as spherical with a diameter of about 1μm by optical microscopy, it was observed as irregular (0.8〜1.2μm) by scanning electronmicroscopy. The strain was gram-negative and nonmotile. Susceptibility to antibiotics indicated that the strain BK4-K1 belongs to archaea domain. Lack of long chain fatty acids in the total cellular lipid also supported the classification. The strain BK4-K1 was identified as being of a close relative of the genus Sulfolobus, on the basis of fair agreement of its total characteristics with those of the archaeon, Sulfolobus acidocaldarius. The TLC analysis, however, showed that the strain has different total cellular lipid constituents from those reported for the close relative of the genus Sulfolobus isolated from Owaku-dani at Hakone in Japan.

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