Neogene Paleogeography of the Surrounding Dewa Hilly Lands

Abstract

Abstract:Oil occurence in basins may generally be related to the relief of basins bottom and to the sedimentary environments.To clarify the process of the oil accumulation, the study of paleography is a important method and a basic information for the oil exploration.The writer studied on the stratigraphy of the Neogene strata developed in the surrounding area of the Dewa hilly lands, which include the southern part of the Akita and Yamagata, the eastern part of Miyagi prefectures, and introduced several time-stratigraphic units and its formations. The strgtigraphical relationships of each province are discussed, and inter-provincial correlation are shown in Table 1. As the result of the study, the Dewa Hilly lands was situated on the subsiding zone during the Onnagawa stage, but in the late Funakawa stage, was slowly uplifted from south to north.Oil occurence is closely related to the paleogeographical aspects. Submarine ridges in the deeper stagnant sea are one of the most favorable places for the oil accumuration. The Amarume and Fukura oil fields may be an example of this relationship.The Innai-Katsurazaka and Horiuchi oil fields are situated in the hinge belt, where the sand-shale ratio is bitween 1/8 to 1.