Oil-source rock correlation in the Tempoku basin of northern Hokkaido, Japan

Geochemical correlation studies of seven oils and source rocks from the onshore Tempoku basin of northern Hokkaido were carried out. Low sulfur, high wax and high pristane/phytane ratios of the oils suggest that they were generated mainly from nonmarine source rocks. Source rock evaluation and hydrous pyrolysis data show that coals and coaly shales in the Paleogene Haboro Formation and Cretaceous Hakobuchi Group have oil-generating potential. These nonmarine source rocks are correlated as the major source of the Tempoku oils, using sterane and triterpane distributions and carbon isotope compositions. Correlation studies also suggest a minor contribution from marine source rocks of the Neogene Onishibetsu or Paleogene Magaribuchi Formations to the oils of the Yuchi and Wakkanai fields located in the western part of the basin