Volgian and Santonian–Campanian radiolarian events of the Russian Arctic and Pacific Rim

Radiolarians are widely distributed in two siliceous intervals that coincide with the Tithonian–Berriasian and Santonian– Campanian boundaries in the Mesozoic of the Russian Arctic and Pacific Rim. The first level is rich in organic matter and typical of Jurassic–Cretaceous boundary strata from the Russian North European Margin (Barents−Pechora, Volga−Urals, and Siberian hydrocarbon provinces, as well as western Kamchatka). Abundant and diverse representatives of the family Parvicingulidae provide a basis for establishing the new genus Spinicingula (uppermost Middle Volgian–Lower Berriasian); another new genus, Quasicrolanium (Upper Volgian–Upper Berriasian) is also described. A Santonian– Campanian siliceous interval with radiolarians is documented from the margins of northern Asia (eastern Polar Ural, Kara Basin, Kamchatka). The Boreal genus Prunobrachium makes its first appearance at the Santonian–Campanian boundary and reaches an acme in Campanian strata. Radiolarian data can be used for basin biostratigraphy and correlation, as well as palaeogeographical interpretation of these hydrocarbon−rich facies. The Arctic and northern Pacific rims are well cor− related on the basis of parvicingulids, while in Sakhalin these are absent and calibrations are based on Unitary Associa− tions zones of the Tethys. In addition to the two new genera noted above, five new species (Parvicingula alata, Parvicingula papulata, Spinicingula ceratina, Lithostrobus borealis, and Spongurus arcticus) are erected, while 6