LAUSR

The analysis of the recognized Late Cretaceous radiolarian assemblages from various structural and formation zones of the Olyutor and Algan terranes of the Koryak Highland has revealed a significant difference in their taxonomic composition, the quantitative content of radiolarians, and their morphological features. The radiolarian assemblage of the Olyutor terrane, which occupies the southern part of the Koryak Highland, consists of almost 100% Californian radiolarian species. The radiolarian assemblage of the Algan terrane, which is located in the northwestern part of the Koryak Highland, contains 50% or more species described from sections of the Russian Plate and Western Siberia and no more than 50% Californian species. These data clearly show the relationship between the Algan paleobasin and the paleo-Arctic and West Siberian Sea under the simultaneous influence of the Pacific currents, following which Californian species could pass to the basin. The Olyutor terrane had a close connection with the Paleopacific in Late Cretaceous. At the same time, most of the taxa which are most characteristic of the Olyutor zone were also distributed in the Upper Cretaceous/Paleocene of New Zealand. Among them are both cosmopolitan and probably bipolar species, which most likely include Stichomitra livermorensis, Theocampe altamontensis, T. vanderhoofi, Bathropyramis sanjoaquinensis, Praestylosphaera pusilla, and P. hastata. A biostratigraphic division in the rank of beds with fauna—the beds with Prunobrachium articulatum—was first identified in the Algan Zone (northwestern part of the Koryak Highland). Currently, the level with Prunobrachium articulatum is subglobal and is traced from Western Siberia, where it was first established, both to the west to the Russian Plate and the east to the Pacific margin inclusive. Several levels are suggested in the Olyutor zone (southern part of the Koryak Highland): the first occurrence of Praestylosphaera pusilla (F.O.) and Phaseliforma meganosensis (F.O.) and the last occurrence of Orbiculiforma quadrata (L.O.) at the Santonian–Campanian boundary; the first occurrence and abundance of Dictyomitra densicostata in the Lower Campanian; an abundance of Phaseliforma carinata, Stichomitra livermorensis, and Archaeodictyomitra regina and the first appearance of Clathrocyclas hyronia and Lithomespilus mendosa in the upper Campanian/Maastrichtian. The biostrata distinguished in the Koryak Highland were correlated with biostratons of adjacent territories in the Pacific region.