|Budget Amount *help
¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1992 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1991 : ¥1,400,000 (Direct Cost : ¥1,400,000)
The late Cenozoic stratigraphic scheme of the Akita oil field was established in 1928 and has long been accepted by many geologists until recently without great changes. It is a composit succession of formations of the Oga and the Akita City areas: the Onnagawa, Fumakawa, Tentokuji, and Sasaoka Formations in ascending order. Thus the correlation of strata between both areas is the fundamental of this scheme.
The Onnagawa and Funakawa Formations whose types are in the Oga Peninsula have been widely applied in the Akita oil fields. Diatom biostratigraphy was examined in the two formations in several areas in the Akita oil fields. The results demonstrate that the Onnagawa Formation distributed in the inland area, east side of the present Akita coast, is correlated with the lower to middle part of the same formation of Oga, and the Funakawa of the inland area with the upper part of the same formation of the Oga Peninsula.
The Tentokuji and Sasaoka Formations, with their types in the Akita City area, have long been correlated with the Kitaura and Wakimoto Formations of Oga. The studies on diatom, planktonic foraminifera, and calcareous nannofossil of the Tenntokuji and Sasaoka Formations from several inland areas revealed that the two formations can be correlated with the Funakawa Formation of the Oga Peninsula, not with the overlying Kitaura and Wakimoto Formations.
According to these results, the Akita oil fields can be structurally devided into major areas separated by a line along the present Akita coast, where runs the Kitayuri thrust system. The east side of the thrust was rapidly uplifted during the deposition of the Sasaoka Formation and finally emerged. In contrast, in the western side of the thrust including the Oga Peninsula, a marine basin continued to exist, and the thick bathyal Kitaura and Wakimoto Formations were deposited. These results may reqire a future revision of a traditional concept of the structural deveropment of the Akita oil fields.