| Abstract |
Nineteen radiolarian assemblage-zones have been established in the Jurassic to Cretaceous sequences in the Kanto Mountains, central Japan. They consist of the Parahsuum simplum (Hettangian - Pliensbac...hian), Parvicingula gigantocornis (Toarcian), Hsuum hisuikyoense (Aalenian), Unuma echinatus (early – middle Bajocian), Dictyomitrella(?) kamoensis (emended herein: late Bajocian – early Bathonian), Guexella nudata (emended herein: middle - late Bathonian), Mirifusus guadalupensis (emended herein: early Callovian), Stylocapsa(?) spiralis (newly defined: late Callovian – early Oxfordian), Tricolocapsa yaoi (middle – late Oxfordian), Pseudodictyomitra primitiva (Kimmeridgian – middle Tithonian), Pseudodictyomitra carpatica (late Tithonian – early Valanginian), Sethocapsa uterculus (emended herein: Valanginian), Eucyrtis tenus (emended herein: Hauterivian – early Barremian), Thanarla conica (newly defined: Barremian), Holocryptocanium barbui (late Albian – Cenomanian), Dictyomitra Formosa (newly defined: Coniacian – Santonian), Amphipyndax enesseffi (emended herein: early – middle Campanian), Amphipyndax tylotus (late Campanian – early Maastrichtian), and Clathrocyclas(?) gravis (emended herein: Maastrichtian) Assemblage-zones in ascending order. As a result, significant stratigraphic gaps are recognized in the Aptian – Middle Albian and the Turonian. It is noteworthy that these mid-Cretaceous time-stratigraphic hiatuses are widely observed not only in the Kanto Mountains but also in the Outer Zone of Southwest Japan. These stratigraphic gaps may be ascribed to the global mass extinctions and the deteriorated accretion or accretionary hiatus due to the change of movement directions of subducting Plates.show more
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