Abstract: The paper presents the results of multidisciplinary studies in the carbonate–barite mineralization area revealed on the western slope of the Kuril deep-water basin in the Sea of Okhotsk. Findings of carbonate concretions and barite in different age (Miocene–Holocene) deposits indicate that the bottom of this area hosted a long-lived center of gas–fluid emanations over several million years. The age of the host deposits was determined based on the diatom analysis: the oldest age corresponds to the Late Miocene (7.67‒6.57 Ma). The carbonate–barite mineralization originated due to the migration of hydrocarbon (mainly methane) and Ba-containing gas–fluid flows derived from both near-surface reservoirs and deep sources. The flows were most likely associated with mud volcanism. Hydrocarbon gases in pore fluids of the sediment are enriched in heavy methane homologues, while carbonate concretions are characterized by a heavier oxygen isotope composition. The Sr isotope composition (⁸⁷Sr/⁸⁶Sr) is significantly lower (0.708581) compared to the water of modern sea basins, which may also indicate the deep nature of fluids. Modern activity is expressed in the episodic manifestation of gas flows as strong hydroacoustic anomalies in the water core.