Litho- and tephrostratigraphy of the Yuhigaoka boring cores from the Osaka Plain, central Japan

摘要

In 1996, 600-meter deep core boring was carried out at Yuhigaoka (Latitude 34 deg 39' 17", Longitude 135 deg 30' 54"), Osaka City in the central part of the Osaka Plain. The core samples mainly consist of unindurated sand, gravel, silt and clay, ranging in age from the late Pliocene to middle Pleistocene. The core sediments are lithologically divided into YU-A and YU-D Formations, in ascending order. The YU-A Formation is composed of fluvio-lacustrine gravel, sand and silt, with YU542, YU400 and YU384 volcanic ash layers. The YU542 volcanic ash layer correlates with the Fukuda volcanic ash layer, which exists at the horizon of the boundary between the lowermost and lower parts of the Osaka Group. The YU-B Formation is composed of alternating beds of marine clay and fluvio-lacustrine sand and silt, and intercalates eighteen volcanic ash layers. In these volcanic ash layers, YU261, YU210, YU173, YU163, YU1SS and YU65 layers correlate with the Yellow, Pink, Komyoike IV, Yamada II Azuki, Hacchoike I volcanic ash layers of the Osaka Group, respectively. On the basis of these correlations, nine marine clay-beds in the YU-B Formation have been identified as the Ma-1, Ma0, Ma1,------ Ma6 and Ma7, in ascending order.