Recent deep drilling by Teikoku Oil Co. is adding much new subsurface geologic information, making possible an interpretation of the central portion of Shonai Plain. The present study is a report on the subsurface stratigraphy and the structure of that region, related to hydrocarbon deposit. Three matters in particular are reported.
1) There is a newly discovered Jurizuka Uplift which is gently descending to Sakata city and increasing the thickness of the tertiary formation to the north.
2) The gentle anticlinal structure is disclosed near Sagoshi and its core is composed of the pyroclastic sediment of green tuff formation. On the crestal part of this anticrine, a small amount of hydrocarbon is found, but not so productive as the lacking of the potential reservoir.
3) The writer discusses the petroleum accumulation in Narahashi-Ishinazaka oil field, related to the sedimentation and the growth history of each anticline in Shonai Basin.
