METHANE SEEPAGE IMPACT ON AUTHIGENIC PYRITE MORPHOLOGY IN SEDIMENTS OF THE LAPTEV SEA CONTINENTAL SLOPE

Abstract

Relevance. The paper presents the results of studying the morphology and size distribution of authigenic pyrite, both present in sediments and in carbonate nodules. From the point of view of studying the conditions of early diagenesis, authigenic pyrite is considered the most important iron sulfide mineral due to its greatest diagenetic stability relative to other iron sulfides. Numerous previous studies of the morphology and size of authigenic pyrite show the possibility of using this information to assess the redox conditions of sedimentation and early diagenesis in both modern and ancient sedimentary basins. The aim of the research was to study the morphology and size distribution of authigenic pyrite to assess the effect of sulfate-controlled anaerobic oxidation of methane on the conditions of early diagenesis. Methods: field hydroacoustic researches (Kongsberg EA600), X-ray diffraction (Bruker D2 Phaser), scanning electron microscopy with local energy dispersive analysis (TESCAN VEGA 3 SBU). Results. Morphologically, pyrite is represented by idiomorphic and hypidiomorphic crystals, framboids and their clusters, radial outgrowths, and also rod like aggregates. The mean diameter of framboids, as well as the high value of standard deviation, indicate the diagenetic origin of pyrite. Sulfate-driven anaerobic oxidation of methane is the dominant process that controls the formation of iron sulfides, which is confirmed by the presence of fairly large framboids up to 49 µm in diameter. The observed diversity of pyrite morphology may reflect the change in the diagenetic environment over time, due to the variability of the flow of methane-bearing fluids.

Keywords

• authigenic pyrite
• diagenesis
• cold methane seeps
• anaerobic oxidation of methane
• sulfate reduction
• laptev sea