Mesozoic Radiolarians from Rhythmically-Layered Deposits in the Islands of the Rimsky-Korsakov Archipelago (Peter the Great Bay, Japan Sea) and their Implications for the Triassic–Jurassic Boundary

The results of biostratigraphic study based on the radiolarian analysis of the rhythmically-layered terrigenous deposits developed in the islands of the Rimsky-Korsakov Archipelago (Peter the Great Bay) are presented. These deposits are most similar to medium-grained turbidiites (according to [21]). In the study region, the development and stratigraphic subdivision of the Upper Triassic and Lower Jurassic boundary deposits, separated by the marking layer, have been validated for the first time. Based on the comparison with the isochronic zonal subdivision of the Pacific and Tethys paleo areas, the layers with Globolaxtorum tozeri (Upper Rhaetian) are distinguished in the Upper Triassic deposits of the studied sections, while the Pantanellium tanuense Zone (Hettangian) is traced and the layers with Parahsuum simplum (Sinemurian–Pliensbachian) are revealed in the Lower Jurassic deposits.