The coal-bearing formations of the Eocene Ishikari Group, Hokkaido, Japan, are supposed to be the petroleum source rock strata for the Yufutsu Field, Hokkaido, Japan. Geochemical and sedimentological analyses were performed for the Ishikari Group to clarify the relationships between petroleum source rock potentials and sedimentary facies and depositional sequences.
In the case of the Ishikari Group, coals have higher source rock potentials than coaly shales and shales. Back marshes in meandering fluvial systems that develop in the coastal plains near the sea are most suitable for the formation of coal source rocks. Coal beds rarely form in the upper transgressive systems tracts （TST） and lower highstand systems tracts （HST） due to marine incursions during the maximum flooding periods in the third order depositional sequences.
Thus, coal beds mainly develop in the middle to upper HST and lower to middle TST. Source rock potentials are higher in the TST than in the HST.
For the formation of the coal-bearing layers, balances between the relative sea-level change rates and peat accumulation rates are important for keeping the fluvial environment near the sea for a long time. Such sedimentary environment is likely to occur at two times in a sequence cycle, one is around a sequence boundary and the other is around a maximum flooding surface, in which the accumulation mode is prone to be aggradation. Among them, coals with high oil source rock potential tend to be formed in the transgressive periods. The raised bog model can be applied to the formation of the peat layers with high source rock potential. Higher contributions of herbaceous plants over woody plants and better preservation of organic matter in the raised bogs compared to the low-lying bogs should be the key factors for the formation of oil-generating coals
The gas seeps from the seafloor were presumed as a potential source of methane （CH4） to the atmosphere. Numerous gas plumes have also been reported around Japanese archipelago. During spring and summer in each 2014 and 2015, we have conducted the unique high-resolution measurements of CH4 in the atmosphere above the seas （eastern margin of Japan sea and sea around Hokkaido） where the gas hydrate expected to exist. To date, deepwater gas plumes are not assumed to contribute to the atmospheric CH4. Although atmospheric CH4 concentrations along the shipʼs track were almost 1.9 ppm, some observation sites with gas plumes were over 2.1 ppm. In addition to the gas plumes observed at depths shallower than 400 m in these areas, the TGHS （Top of Gas Hydrate Stability） was estimated to be shallow in contrast to earlier reports. These observations suggested that some gas plumes in the specific environment, where CH4 was easily transported to the ocean surface layer, contribute to increasing the atmospheric CH4 concentration.
Boron concentrations and B/Cl ratios of formation waters from oil and gas fields in Japan, which are mainly of fossil seawater origin, are graphically shown using published data. Most of the boron concentrations range from a little to 100 mg/l except for the Tempoku area and the B/Cl ratios are mostly between 0.001 and 0.1. Taking account of studies on hot springs and pore waters in deep sea sediments, sources of boron are probably derived from decomposition of organic matters and diagenesis of clay minerals in addition to the seawater.