Cretaceous Radiolarians from Sedimentary-Volcanogenic Deposits of the Sredinny Range of the Kamchatka Peninsula

A radiolarian-based scheme of stratigraphy and correlation of Upper Cretaceous deposits of the Sredinny Range is proposed. A synchronous accumulation of sedimentary-volcanic deposits of the Ening Series and the Irunei Formation took place in the Campanian in a single sedimentation basin in moderate-high latitudes, in the area currently in the north of the Sredinny Range. Here the Beds with Phaseliforma carinata–Prunobrachium articulatum are recognized on the western and eastern slopes of the range. In the south of the Sredinny Range, Campanian radiolarians are recorded in the Khozgon Formation; The Irunei Formation is dated Coniacian–Maastrichtian. A conclusion is made about the synchronous deposition of the Khozgon and Irunei formations from the Santonian—possibly beginning of the Maastrichtian. The deposits of the Irunei and Andrianovka formations are found to be coeval: it is assumed that the rocks of the Andrianovka Formation are a metamorphosed analogue of the Irunei Formation. The age of the Kirganik Formation is limited to the late Campanian (?)–Danian. Albian–Cenomanian and Santonian–Campanian radiolarians have been identified in pebbles of the Baraba Formation. During the formation of the Baraba conglomerates in the erosion area, along with metamorphites of the Malka Group, Santonian–Campanian siliceous rocks (equivalents of the Irunei Group on the eastern slopes of the Sredinny Range and Western Kamchatka) were exposed. The Albian–Cenomanian siliceous rocks either reflect the age of the lower horizons of the eroded Irunei Formation or are redeposited.