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In this study, we integrate environmental magnetic, sedimentological, and geochemical records of sediment core of Hole NGHP-01-10D overlying methane hydrate deposits to decipher the controls on the evolution of fracture-filled gas-hydrate system in the Krishna-Godavari (K-G) basin. Four distinct sedimentary units have been identified, based on the sediment magnetic signatures. An anomalous zone of enhanced magnetic susceptibility (Unit III: 51.9-160.4 mbsf) coinciding with the gas hydrate bearing intervals is due to the presence of magnetite-rich detrital minerals brought-in by the river systems as a result of higher sedimentation events in K-G basin and has no influence over hydrate formation. A strong to moderate correlation between magnetite concentration and chromium reducible sulfur (CRS) content indicates significant influence of sulfidization on the magnetic record and could be further exploited as a proxy to decipher paleo-H 2 S seepage events. Analysis of high-resolution seismic, bathymetry, and subbottom profiler data reveals the existence of a regional fault system in K-G basin. The opening and closing dynamics of the faults facilitated the migration and trapping of required gas concentrations resulting in accumulation of gas hydrates at the studied site. The seismic data provides support to the rock-magnetic interpretations. The observed variations in magnetic and geochemical properties have resulted from the episodic flow of methane and sulfide-enriched fluids through the fracture-filled network formed as a result of shale-tectonism. Our study demonstrated the potential of using an enviro-magnetic approach in combination with other proxies to constrain the evolution of gas-hydrate system in marine environments. Key Points:Magnetic signatures of detrital and diagenetic processes associated with evolution of gas-hydrate system. Changes in magnetic and geochemical properties controlled by underlying gas-hydrates. Magnetic proxy to decipher paleo-H2S seepage events in marine sediments.

In the present study, we have investigated the C–S–Fe systematics in a sediment core (MD161‐13) from the Krishna‐Godavari (K‐G) basin, Bay of Bengal. The core covers the late Holocene period with high overall sedimentation rate of ∼573 cm kyr−1. Pore fluid chemical analyses indicate that the depth of the present sulfate methane transition zone (SMTZ) is at ∼6 mbsf. The (ΔTA + ΔCa + ΔMg)/ ΔSO42− ratios suggest that both organoclastic degradation and anaerobic oxidation of methane (AOM) drive sulfate reduction at the study site. The positive correlation between total organic carbon content (TOC) and chromium reducible sulfur (CRS) content indicates marked influence of organoclastic sulfate reduction on sulfidization. Coupled occurrence of 34S‐enriched iron sulfide (pyrite) with 12C‐enriched authigenic carbonate zones is the possible records of paleo‐sulfate methane transition zones where AOM‐driven‐focused sulfate reduction was likely fueled by sustained high methane flux from underlying gas‐rich zone. Aluminum normalized poorly reactive iron (FePR/Al) and La/Yb ratios suggest increasing contribution from Deccan basalts relative to that of Archean‐Proterozoic granitic complex in sediment flux of Krishna‐Godavari basin during the last 4 kyr.

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