First Find of Manganese and Cadmium Sulfide Minerals in Pleistocene–Holocene Sediments of the Deryugin Basin in the Sea of Okhotsk (Pacific Ocean)

The article reports the results of studies on manganese and cadmium sulfide minerals found for the first time in Pleistocene–Holocene sediments of the marginal seas of the West Pacific Ocean. Manganese sulfide minerals (alabandite, αMnS, and rambergite, γMnS) from sediments of a mud volcanic edifice in the Deryugin Basin (Sea of Okhotsk) constitute the second find in the world (after the Baltic Sea basins) in marine sediments of the present-day ocean. There is currently there has been no evidence for the presence of cadmium sulfide minerals (greenockite) in Pleistocene–Holocene marine sediments. Manganese calcites and elemental sulfur are found in close association with these sulfides. The results of electron microscopic studies made it possible to characterize in detail the morphological types of the identified mineral phases and features of their chemical composition. It has been established that among the studied sulfide minerals, isomorphous substitutions in the MnS–ZnS–CdS solid solution system are widespread and in some cases accompanied by the formation of intermediate mineral phases of variable composition. The existence of a periodic oxygen minimum environment in the Deryugin Basin (up to the point of hydrogen sulfide contamination), combined with the episodic influx of elision gas-fluid components with hydrogen sulfide and a number of metals (manganese, cadmium, zinc) at local sites of the seafloor within mud volcanic edifices, contributed to the formation of this unusual paragenesis of authigenic sulfide minerals. A model for the formation of manganese-bearing mineral phases, characteristic of anoxic environments in local depressions of the Baltic Sea with periodic hydrogen sulfide contamination, was accepted as the main working hypothesis of authigenic mineral formation.