On gas hydrates of East Asian marginal seas: patterns of genesis and distribution (review)

Abstract

The reviewed results on the genesis and distribution of gas hydrates in the marginal seas of Eastern Asia have been presented. Hydrate-forming gas in the continent–ocean transition zone, in general, is a mixture of the thermogenic and microbial components with the characteristic isotopic composition of methane from –40 to –75 ‰ PDB. Gas hydrates were found also within the areas of magmatic and coal-metamorphogenic gases fluxes into the host sediments. The Okhotsk and Japan Seas gas hydrate-bearing provinces have a signs of gas hydrocarbon zonality (in accordance with the classical oil and gas formation pattern). Multilevel (stratified) gas hydrates accumulations in the western part of the Pacific Ocean have been revealed, which is an important factor in the methane and carbon cycle. The genetic and spatial correlation of gas hydrate-bearing sediments with oilgas and coal-bearing strata is traced. The most important factor in the formation of gas hydrates is the geological structure of the regions under favorable temperature, pressure and geochemical conditions. Neotectonics is the most important factor controlling relict gas hydrates, located below the sea floor up to 2000 meters, and modern tectonics – gas hydrates in the near-bottom interval. The nodes of active faults intersections, especially those controlled by deep zones, are the subject to permeability and are in close proximity to petroleum-bearing forms, which are the most promising patterns for the massive aggregates of gas hydrates. The gas hydrates of the East Asian marginal seas are insufficiently studied, and this requires the long-term international research programs.