On the age of the sedimentary cover of the Kurile Basin, Sea of Okhotsk

A velocity model of the upper Earth’s crust of the Kurile Basin, Sea of Okhotsk, is constructed using experimental seismic data. Four layers are distinguished in the sedimentary cover with the maximum thickness of 3000 m. The lower layer, up to 1100 m thick with layer velocity of 3.2–3.5 km/s, is observed only in the abyssal part of the basin. This layer pinches out near the foot of the basin slopes, is never exposed on the sea floor, and is not available for dredging. The cross-section of sedimentary cover contains seismic boundaries—markers, which mark the regional sedimentation gaps in the Middle Eocene, Late Oligocene, and Late Miocene. It is shown that an extensive sedimentary basin existed within the Kurile Basin as early as the Late Mesozoic. The sediments were accumulated in an environment of synsedimentary subsidence on the continental margin, where a paleobasin with almost present-day boundaries was formed by the end of the Oligocene.