The Cretaceous black shale developing in the Yamamombetsu district, Saru-gun, Hokkaido which has been refered to Urakawan or Hetonaian serieses, is proved to belong to Gyliakian series. Dips of the shale and overlying Takinoue formation, lower Neogene, look nearly parallel to each other, but the former is reversed; so before the Takinoue formation deposited, the Cretaceous sediments had returned nearly horizontally. In this report, I will describe these new knowledges, and based on them, represent my conclusion about reasons of existence of the "Nioi oil seapage", that is, it may be reapearance of oil trapped in sandstone of down-block of pre-Takinoue thrust and preserved by mudstone of upper-block.
The authors conducted laboratory tests on fluid phenomena in porous media, using the neutron source (Ra, Be) and radioisotope tracer (I131). And, radioisotope techniques on measuring fluid saturation and its gradients in small synthetic core were discussed.