Abstract
This paper presents geochemical and some geological features of the presumed source beds of the Neogene Tertiary in Japan. Distribution patterns of total organic carbon, bitumen and hydrocarbon contents in the presumed source beds, variation of bitumen and hydrocarbon ratios, vitrinite reflectance with burial depth, the time-temperature relationship to the threshold of intense oil generation, negative evidence for primary migration in water solution and the depth-porosity curves of the Japanese oil-producing sedimentary basins were examined. The results show that primary migration, by oil phase transport of immature or mild mature hydrocarbons derived from primary bitumen takes place at a relatively shallow depth, c. 800–1300 m in Japanese Neogene oil fields.
