Abstract
The Aonomine Group in the Toba area comprises muddy and sandy matrixes, containing numerous blocks of sandstone and chert, and a small amount of siliceous mudstone, greenstone and limestone blocks. The Aonomine Group is distributed in the Futaji, Shiranezaki and Aonomine zones from north to south. The Futaji and Shiranezaki zones had been considered to be the Permian complexes of the Kurosegawa Belt. In the Futaji zone, early-middle Early Jurassic radiolarian fossils were extracted from siliceous mudstone blocks and Late Permian radiolarians from chert blocks. In the Shiranezaki zone, early-middle Early Jurassic radiolarians were found from acidic tuff and mudstone, and Late Paleozoic to Late Triassic radiolarians from chert blocks. In the Aonomine zone, early Middle Jurassic radiolarians were obtained from black mudstone. The radiolarian age determinations suggest that the Aonomine Group is the Lower to Middle Jurassic accretionary complexes, and it may belong to the Chichibu Belt.
