A unified radiolarian zonation for the Late Cretaceous and Paleocene of Japan

Previous radiolarian zonations for the Late Cretaceous and Palcocene of Jap an are reviewed in terms of species identifications and age determinations. With adoption of a consistent identification scheme, a remarkably uniform succession of radiolarian assemblages is evident throughout Southwest Japan . Sufficient species range into higher northern latitudes (Hokkaido, easter n Russia) to permit the establishment of a single radiolarian zonation for the Northwest Pacific. The new zonation consists of six Late Cretaceous and two Palcocene interval zones: Theocampe urna zone (Tu, Coniacian), Dictyomitra koslovac zone (Dk, Santonian to early Campanian), Amphipyndax tylotus zone (At, late Campania n), Pseudotheocampe abschnitta zone (Pa, early Maastrichtian), Clathrocycla s gravis zone (Cg, mid-Maastrichtian), Lithostrobus wero zone (Lw, early Pa lcocene), Buryella foremanae zone (Bf, mid-Palcocene). Zone Dk may be subdi vided into Santonian and early Campanian subzones based on the first appear ances of Archaeospongoprumun hueyi gr., Protoxiphotractis perplexus and Lit hocampe wharanui. Previous workers' recognition of an Amphipyndax pseudoconulus or A. enessef fi assemblage in Japan is found to be erroneous. Careful examination of ill ustrations of the A. pseudoconulus-tylotus complex reveals that A. pseudoco nulus s.s. (= A. enesseffi of Foreman 1966) is very rare in Japan and restr icted to the late Campanian, its first appearance coinciding with that of A . tylotus.