四国東部の領石・物部川層群チャート礫と細粒砕屑岩から産した中・古生代放散虫化石

Radiolarian fossils from the conglomerates and fine elastics in the Lower Cretaceous brackish and shallow-marine formations of the Kurosegawa Terrane in East Shikoku are studied with reference to their genesis and basement conditions. The Late Permian, Mid-Late Triassic and the Earliest Jurassic radiolarians are extracted from the chert pebbles in the conglomerates of the Lower Cretaceous Ryoseki and Monobegawa Groups. The Early, Middle and Late Jurassic and the Earliest Cretaceous Radiolarians are extracted from black mudstone pebbles, mudstone grains in the matrices, and the sandy mudstone beds of the groups. They are accompanied with autochthonous radiolarian and molluscan tests of the Barremian age. In the Chichibu Superterrane, the pelitic beds of the Torinosu Group and the equivalents commonly yield the Mid-Late Jurassic and Early Cretaceous radiolarian assemblages. The Group and its equivalents lie over the Triassic molluscan formations and the Paleozoic complex in the southern Kurosegawa Terrane. They also lie over the Mid-Late Jurassic accretionary prisms and melanges in the South Chichibu Terrane. Whereas, the Group and equivalents are never distributed in the North Chichibu Terrane that is composed of the Lower to Middle Jurassic accretionary complex. From the point of subducting oceanicplate stratigraphy, in the stratigraphic sequences of the North Chichibu Terrane, the lithofacies change from chert to detrital clastics in the Latest Triassic to Earliest Jurassic. Judging from the above-geological properties, the Upper Permian, Middle and Late Triassic and the Earliest Jurassic chert pebbles in the Ryoseki and Monobegawa Groups probably have originated from the chert-clastics sequences and/or complex of the North Chichibu Terrane. It also indicates the possibility that the Lower to lower Middle Jurassic accretionary complex of the North Chichibu Terrane was already cropped out as a fenster in the Early Cretaceous.However, the small-sized mudstone grains with radiolarian tests of the late Middle and Late Jurassic and the Earliest Cretaceous age probably originated from the Torinosu Group and its equivalents. The author indicates a possibility that the Torinosu Group and its equivalents were depositted widely in the northern Kurosegawa Terrane, as well as the southern Kurosegawa and the South Chichibu Terranes.