The seismic stratigraphy of Quaternary subsurface sediments around Kobe area has been analyzed from selected seismic profiles, namely Toga-gawa, Juniken-doro, and Shuku-gawa lines. The lithostratigraphic condition from the nearest boring cores, namely Maya (MY), GS-K1 and Minami-Ashiyahama (SA), is considered as a basis to identify the characteristics of reflections in each profile. The seismic profile is then divided to produce zonation. The result shows that there are 2 major seismic zones. The seismic zone N shows non-parallel, very poor to non-continuity and non-clarity reflections, which can be correlated with the Miyakojima Formation. The seismic zone P shows parallel, good to poor continuity and clarity reflections, which can be correlated with the Tanaka Formation. Based on the amplitude and interval of reflections, the seismic zone P is divided to become sub-seismic zones P1 and P2. The sub-seismic zone P1 is correlated with the intercalation of sand, silt, volcanic ash layers and thin marine clay beds within Ma-1 to Ma 2 beds. And the sub-seismic zone P2 is correlated with the intercalation of gravel, sand, silt, volcanic ash layers and thin marine clay beds within Ma 2 to Ma 12 beds. This result shows similarity with seismic stratigraphy division in the neighborhood of the Osaka Plain.

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The area of East Mikabo Mountain and West Mikabo Mountain is underlain by the Mikabu Greenstones, which belong to the Mikabu Unit in the Sambagawa Belt in the northern Kanto Mountains. Late Jurassic clastic beds overlie the Mikabu Greenstones. We name this clastic beds the Nishimikabo Formation. This Formation is composed of red mudstone, siliceous rocks, alternating beds of sandstone and siltstone, and siltstone in ascending order. There are three cases for the sedimentary relationship between the red mudstone of the Nishimikabo Formation and the basaltic pyroclastic rocks of the Mikabu Greenstones. The first case is that the red mudstone conformably overlies the basaltic pyroclastic rocks. Second case is the alternation of the red mudstone and the basaltic pyroclastic rocks. Thirdly, the siliceous rocks of the Nishimikabo Formation and the basaltic pyroclastic rocks of the Mikabu Greenstones are accompanied by the red mudstone. This observation indicates that the Nishimikabo Formation has a comformable relationship with the underlying Mikabu Greenstones. The red mudstone includes a large amount of hematite and opaque minerals, suggesting that the red mudstone was deposited in a hydrothermal oxgenated environment. The Mikabu volcanic activity took place before the late Jurassic time based on the age of the Nishimikabo Formation. A few euhedral quartz grains are found in the red mudstone. There is a possibility that these quartz grains in the red mudstone and the siliceous tuff of the Nishimikabo Formation were derived from intermediate-felsic volcanic activities on the eastern margin of the Asian Continent in the Late Jurassic Yanshanian epoch. We infer that the region of the Mikabu volcanic activity and the deposition of the Nishimikabo Formation took place near the eastern margin of the Asian Continent.

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Lots of current ripple marks were found from the Miocene Sakurai Formation in the Chichibu Basin, Saitama Prefecture, central Japan. The sedimentary facies of the study area are distinguished into five facies: Conglomerate, Pebbly Sandstone, Massive Sandstone, Interbeds of Sandstone and Mudstone, and Microinterbeds of Sandstone and Mudstone. The sedimentary environment is interpreted as the channel-levee system of upper to mid submarine fan by the characteristics of these facies. Since the ripple marks distribute intensively in the Interbeds of Sandstone and Mudstone, the ripple marks are considered to have been formed in the levee sediments and the sediments over the fully-covered channel. The ripple marks correspond to the division C of Bouma sequence. The directions of paleocurrents of the ripple marks and current marks are the same. Therefore, the ripple marks were formed by the sedimentation of the low-density currents.

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The OD-5 borehole core is one of the nine deep borehole cores named OD series for measurement of ground subsidence in the Osaka Plain. The core was drilled at Tonouchi (34°44'03.69"N, 135°27'23.89"E, JGD 2000), Amagasaki City. The OD-5 borehole core intercalates sixteen marine clay beds and seventeen volcanic ash layers at least. However, enough analysis of volcanic ash had not done yet. In this study, author describes the characteristics of those volcanic ash layers and correlate with volcanic ash layers of the Osaka Group, the Plio-Pleistocene. As the result of this study, five new marine clay beds and two undescribed volcanic ash layers are found. Seventeen samples from fifteen volcanic ash layers are described with grain-size composition, mineral assemblage, and shape and refractive index of volcanic glass. The twelve samples of volcanic ash layers are identified with Yellow (as two layers), Pink (as two units), Komyoike III (as two units) and IV, Yamada II and III, Azuki, Bonnoike, and Naruohama IV volcanic ash layers. And author suggests that two volcanic ash layer horizons are correlated among those of only in deep borehole cores. Stratigraphical positions of twenty-one marine beds are identified as Ma-1 to Ma 13 on the basis of tephrostratigraphy. Correlation of volcanic ash layers only in deep borehole cores yielded in the Osaka Plain should make one step for progress to more detail tephrostratigraphy of the Osaka Group.

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