The organic maturity of four samples from the Recent marine sediments in Japan Sea off southwestern Hokkaido was evaluated by means of statistical Thermal Alteration Index (stTAI). The scale of stTAL was determined by the brightness or grey level, of pollen of Pinus, Podocarpus, Abies, Picea and Tsuga using a microscope (Ujiie, 1996b). The maturity of these samples lies below the lowest limit of vitrinite reflectance (Ro=0.30%). stTAI is a useful parameter to evaluate early maturation, especially of very immature sediments which can not be measured by vitrinite reflectance.

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Many oils in Southeast Asia region exhibit non-marine characteristics. Among these oils, some indicate high oleanane index (oleanane/C₃₀ hopane), which are supposed to generate in terrestrial source rocks deposited in fluvio-deltaic setting. Geochemical data on source rocks indicated that the rocks with high oleanane index are only found in prodelta shales. However, source rock potential of these prodelta shales is poor; TOC<2% and HI<200mgHC/gTOC. It is difficult for oils to be expelled out from the source rocks with these lean potential and the oils are cracked to be gas in the source rocks with additional heat energy. The oleanane index of the rocks appears to increase as the source rock potential decreases. The oleanane indices of the oils from Southeast Asia were plotted against Ts/Tm ratios. This diagram clearly separated the oils into two groups. With geological background and other geochemical parameters such as Pr/Ph and carbon isotope, these two groups are interpreted as; 1) algal oils which are supposed to generate in lacustrine source rocks in Oligocene, and 2) terrestrial oils which are supposed to generate in fluvio-deltaic source rocks in Miocene. In each group, the oleanane index increases as the Ts/Tm ratio increases. The Ts/Tm ratio is supposed to be affected by maturity and depositional environment. However, even in each group, the oleanane index increases as the Ts/Tm increases, which suggests that the oleanane index could be affected by maturity.

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Phosphatic mudstone layers have been found from the depth 465-485mbsf, ODP Site 797, Japan Sea. The only phosphatic mineral detected by XRD was apatite. Total organic carbon (TOC), total sulfur and lipids were determined for 17 siliceous mudstone and 9 phosphatic mudstone samples.
Phosphatic mudstone are characterized by (1) higher TOC content relative to that of the siliceous mudstone; (2) the C/S ratio was observed to exhibit a significant increase at the phosphatic mudstone layer, defining the lower siliceous with a low value from the upper siliceous zone with a high value; (3) n-alkane distribution consisting of a mixture of high molecular weight components with odd predominance (land plant origin) and low molecular weight homologs without odd predominance (bacteria origin); (4) pristane/phytane ratios in the range 1.14-2.30 with an average of 1.67; (5) high C₂₇/C₂₉ and C₂₇/C₂₈ sterane ratios showing relatively large input of diatoms; (6) abundant of neohop-13(18)-ene and hop-17(21)-ene originated from bacteria.
CPI (Carbon Preference Index) and hopanoid based ββC₃₁/(ββ+βα+αβ)C₃₁ ratio do not change at the zone boundary of diagenetic silica minerals. The maturation of organic matter has not been affected by diagenetic silica mineral zoning, and quartz does not act as a catalyst.

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Organic rich black shale around Permian/Triassic boundary from Kinkazan and Guzyo-hachiman area are consistent with typical pelagic sedimentary environment, being dominated by rich in amorphous organic matter, lack of woody material. n-Alkanes isolated from both of the samples maximize at C₁₆, decreasing in relative abundance with increasing carbon number. The pristane/phytane ratios are lower than1. 0. Polycyclic Aromatic Hydrocarbons (PAHs) in black shale dominated by non-alkylated PAHs are thought to be a pyrolytic origin. The total amount of PAHs from Kinkazan and Guzyo-hachiman are 60.0 and 41.6μg/g-dry sample, respectively. It is suggested that there was a large natural fire at Permian/Triassic boundary time.

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It is generally accepted that most petroleum hydrocarbons are generated from kerogen by cracking of alkyl chains. Infrared spectroscopy can analyze the hydrocarbon generation by decreasing absorbance bands of alkyl CH₂ stretching vibration (2930cm^-1) during heating experiments of kerogen samples. The objective of this paper is to study hydrocarbon generation characteristics of each maceral of immature kerogen using micro-FTIR equipped with a heating unit, and to describe kinetics of kerogen decomposition.
As a result of heating from 30 to 550℃ at several different heating rates, the temperature of the maximum point in decreasing rate of the alkyl CH₂ absorbance is defined as "IR2930Tmax". IR2930Tmax values appear about 300℃ (10℃/min). This evidence means that maximum hydrocarbon generation occurs around 300℃ by decomposition of alkyl chains.
Activation energy distribution at the cracking of alkyl CH₂ chains falls between 35 and 60kcal/mol (maximum values between 45 and 50kcal/mol) at the frequency factor A=10¹⁶(1/s). This activation energy value seems to be too low for the direct cracking of alkyl chains, and is possible related with free radical reaction mechanism.

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Mudstones of the Shiiya Formation distributed along the Gomoto River, Niigata Pref. are classified into turbidite (Et) and hemipelagic (Ep) mudstones of a Bouma sequence. However, both Et and Ep kerogens from the Shiiya Formation consist mainly of terrigenous macerals (vitrinite and non-fluorescent amorphous organic matter: NFA), i.e., no evident differences are found in the maceral composition between Et and Ep, whereas the differences are obvious in the Teradomari Formation (Watanabe and Akiyama, 1996). On the other hand, the biomarker analysis of the Shiiya Formation indicates that Et mudstones contain abundant terrigenous triterpenoids, while those triterpenoids are absent or quite scarce in Ep mudstones. This characteristic biomarker composition suggests that Et mudstones contain more organic compounds of terrestrial origin than Ep, and that the kerogen macerals of marine origin in Ep should have been selectively decomposed during deposition. The difference between the Teradomari and Shiiya Formations in the organic matter composition is thought to be due to the different sedimentary environments: the Shiiya Formation was deposited at the more proximal, shallower and more oxic submarine fan environment than the Teradomari Formation.

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Molecular sieve treatment for separation of sterane and triterpane compounds from n-alkanes leads to isomarization of oleanenes in the bitumen extracted from the Shiiya Formation, where 24-norolean-12-ene and olean-12-ene decrease with increasing of Δ¹³⁽¹⁸⁾, Δ¹⁸isomers at room temerature.

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