Abstract
Seismoacoustic profiling and sonar survey of the North Caspian water area revealed in some areas signs of intense release of methane from the sedimentary sequence. This fact was also supported by submarine videorecording data. Such sites are characterized by hummocky and ridgy morphologies, which accommodate local cone-shaped bodies (up to 1.3–1.5 m high) overgrown with algae, Balanus, and shelly material. Based on dredging data, these rises are composed of hard sandstones and shells. They can cover the seafloor or make up separate interlayers in the bottom sediments down to a depth of 2.7 m. Mineralogical studies demonstrated that the coarse-grained sediments are cemented with Mg-calcite, with δ13C reaching −32.6‰. They also include microcrystalline barite and globular iron sulfides. The results of investigation suggest that the local activation of authigenic mineral formation is related to gas discharge sources.
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