A review of radiolarian biostratigraphy for the oil-bearing Neogene of Japan. Application to petroleum geology

This article reviews history and current status of Neogene radiolarian biostratigraphy in Japan, with an emphasis on its applicability for petroleum exploration.A collective database of Neogene radiolarian biostratigraphic records from various localities through Japan is also presented.In earlier days, radiolarian biostratigraphic subdivisions of the Neogene in Japanese oil-fields were due much to the work of Nakaseko and his co-workers. They recognized a lot of radiolarian assemblages which were then classified into several types of assemblages on the basis of dominant species. As a consequence, four assemblage zones were defined for the Neogene. By using these biostratigraphic criteria, subdivisions and correlation of the Neogene sequences were performed in most of the major sedimentary basins during the past thirty years from the mid-1950's to the mid-1980's.The radiolarian zones in current use are essentially worked out in deep sea cores and are potentially useful for more refined correlation of the oil-bearing Neogene of Japan. Possible minor limitation of their use due to biogeographic provincialism and burial diagenetic alteration of siliceous tests is also discussed.