Abstract
An Oligocene radiolarian fauna was recovered from silty mudstone within the Hyuga Group of the Shimanto accretionary complex in the Murasho district, central Kyushu, Southwest Japan. The fauna includes Artophormis gracilis, Lophocyrtis aspera group, Theocyrtis aff. setanios, and Theocorys bianulus. The radiolaria-dated Oligocene unit occupies the structurally lowest position in the imbricate stacks of the Hyuga Group. Previous workers reported middle Eocene to probably early Oligocene microfossils from structurally upper units, and thus these together imply the presence of the younging polarity toward a structurally lower unit.
