四国東部秩父累帯南帯中生界の地質と放散虫年代

The zonal distribution, the lithostratigraphy and the radiolarian ages of the Mesozoic flysch-olistostrome formations distributed in said area were discussed in context with the Mesozoic basin development of the South Zone of the Chichibu Belt. The results can be summarized as follows: (1) The studied area is divided into eight subzones Ia to V from the north to the south and is bounded by E-W trending reverse faults (Figs. 2,3). (2) These formations are divided into three stratigraphic units i.e. the Middle Jurassic to Lower Cretaceous Nakagawa Group, the formation correspond to the Lower Cretaceous Torinosu Group and the uppermost Lower to lowest Upper Cretaceous Tochidani Formation (Table 1). (3) On the basis of lithology and its age, the Tochidani Formation is considered to belong in the northern Shimanto Belt. Therefore the reverse fault which bounds the southern limit of the subzone IV is suitable for the Butsuzo Tectonic Line. (4) The olistostrome component of the Nakagawa Group changes in each subzone, and the ages of this group become younger toward the southern subzones (Tables 1-3). (5) Based on the directions of paleocurrent and slumping, the terrigenous sediments of the Nakagawa Group were transported from northwards and westwards, and the olistoliths of chert slided from both northwards and southwards (Fig. 2, Tables 4-6). (6) These sedimentary and tectonic features suggest that the deposition of the terrigenous sediments advanced from the northern basin to the southern ones in Middle Jurassic to Early Cretaceous age, and the olistoliths of limestone, chert and greenstone derived from some rows of topographic high which bound these sedimentary basins in the South Zone of the Chichibu Belt.