Lithological Composition and Hydrocarbon Anomalies of Bottom Sediments of the Western Part of the East Siberian Sea

Abstract

On the basis of lithological and gas geochemical studies and a comprehensive interpretation of the available materials, the main factors of the formation and distribution of grain size distribution, water-physical properties, organic saturation, concentrations and geochemical parameters of hydrocarbon gases in seafloor sediments of geostructures of the western part of the East Siberian Sea are summarized and analyzed. It has been established that the sediments of the northern and central parts of the study area are represented by aleurite-pelites, the southern ‒ by aleurite-pelite-psamites with variations in Corg values ‒ 0.6–2.0%, natural humidity and density ‒ 18–43% and 1.5–2.0 g/cm3, open porosity ‒ 17–33%, the concentrations of methane and its homologues are 0.001–5.934 and 0.00003–0.0312 cm3/kg, the molecular mass of the hydrocarbons fraction, the “wetness”, “dryness” coefficients, and the coefficients of the transformation are 16.05–22.6 g/mol, 0.2–51%, 1–1999, 0.2–50.8 and δ13С‒СН4 (–82.7…–38.4‰). Based on the values of gas geochemical parameters, eleven types of gas sources were identified in bottom sediments. In the process of research, it was found that the formation of hydrocarbon anomalies in sediments is mainly associated with their reservoir properties, Corg content and depths of their sampling, as well as with the complex influence of geological factors, the main of which are the gas saturation of the underlying sediments and the type of gas sources, discontinuous and plicative tectonics, geostructures position, thickness of Quaternary deposits, coal and gas content and age of the folded base. To a lesser extent, anomalies of hydrocarbon gases are associated with the lithological composition and density parameters of sediments.