Carbon isotope ratios (C13/C12) and biological markers are applied to problems of geochemical correlation of crude oil-source rock in Hidaka region, Hokkaido. Possible source rocks based on geological data include Phoronai shales (Paleogene Tertiary) and/or Urakawa shales (Cretaceous). The investigated crude oil produced from Phoronai Formation was separated into saturated, aromatics, heterocomponents and asphaltenes. δ-values of these fractions are -26.4%, -24.5%, -25.1% and -25.7%, respectively. Mean δ-values of Phoronai shales and Urakawa shales are -25.3% and -24.0%. From these results, Urakawa shales are regarded as source rock. Mass chromatography of the predominant fragments of biological markers is successful for the determination of internal ratios of individual components such as 5β/5α steranes and 17α/17β triterpanes. The results obtained on the mass chromatogram patterns and the ratios of geometrical isomers show that Urakawa shales are similar to the crude oil.
