Gas Chromatography–Mass Spectrometry Studies on Organic Matter Compositions of Bottom Sediments in Gas-Hydrate-Bearing Zones of the Sea of Okhotsk and Sea of Japan

We report here the results of the gas chromatography–mass spectrometry study of the organic matter composition of bottom sediments in gas-hydrate-bearing zones of the Sea of Okhotsk (Okhotsk–Kuril slope, western edge of the Kuril Basin) and the Sea of Japan (SE Tartar Strait). It was established that the organic matter of sediments from the western edge of the Kuril Basin is represented by n-alkanes with carbon chain lengths of C14–C31, has a mixed terrigenous marine genesis, and was formed in a weakly reducing environment in coastal or lagoonal settings. The organic matter of Tatar Strait sediments, which formed primarily under oxidizing conditions, is of terrigenous marine origin, with a higher production of marine hydrophytes and bacterially transformed material than along the Okhotsk–Kuril slope. One of the main sources of organic matter in the Tatar Strait is the flora of higher land plants, biomarkers of which were first identified in marine sediments.