四国東部秩父累帯南帯北部（倉野亜帯）辺川セクションの海洋プレート層序と放散虫年代

The oceanic-plate stratigraphy (OPS) of the Jurassic accretionary complexes in the Kurano Subbelt of the Southern Chichibu Belt is investigated in the Hegawa Section, East Shikoku. The section is composed of bedded-cherts (A), siliceous-shale with the intercalation of chert beds (B), turbiditic sandstone and mudstone (C), distal turbidite with some sliding-blocks (D), and the deltaic sandstone (E) sedimentary units in ascending order. Among the units, lower part of the Unit B remains the intercalated vertical contact with the unit A, even the base of the unit is cut by a fault. The Unit B has gradual contact with the Unit C. The Unit Chas abrupt contact with the basal SBS-type coarse sandstone bed of the Unit D. The radiolarian zonation of the Hegawa Section is subdivided into the Parvicingula gigantocornis Assemblage Zone (Pg AZ: upper Lower Jurassic), Hsuum hisuikyoense AZ (Hh AZ: upper Lower Jurassic), Tricolocapsa plicarum AZ (Tp AZ: lower Middle Jurassic) and the Tricolocapsa conexa AZ (Tc AZ: upper Middle Jurassic) in ascending order. The units C and D include the exotic blocks of siliceous sediments that are the intercalation of siliceous mudstone, tuff and chert. The blocks derived from the Parahsuum takarazawaense AZ (Pt: upper Lower Jurassic) and the Pg AZ. The blocks fill the litho- and biostratigraphic gap between the Unit A and Unit B. Caused by the development of decollement along the lithological boundary between chert unit (A) and siliceous-shale unit (B), the blocks are probably derived from the preceding OPS-succession that has accreted just before the accretion of the units A to C of the Hegawa Section. Based on the correlation of the radiolarian zones, the units A to C of the section accreted during late Middle Jurassic.