Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

In this study, we conducted a comprehensive investigation of rock magnetic, mineralogical, and sedimentological records sediment cores supplemented by high resolution seismic data to elucidate the controls structural diagenetic ( early vs. late ) processes on magnetism in active relict cold seep sites Bay Bengal. Two distinct magnetic zones (Z-I Z-II) are defined based down-core variations properties. The is carried complex mineral assemblages detrital (titanomagnetite, titanohematite) authigenic (fine-grained greigite) minerals. Overall, susceptibility varies over one order magnitude with highest values found core. Uppermost zone (Z-I) characterized higher concentration magnetite as seen through elevated (? lf saturation isothermal remanent magnetization (SIRM). A systematic gradual decrease ? IRM 1T Z-I attributed progressive dissolution iron oxides subsequent precipitation sulfides. Magnetic grain size diagnostic (ARM/IRM parameter decreases initially due preferential fine-grained sulfidic (Z-I), increases later response formation greigite methanic (Z-II). Distinct low S-ratio core increased relative contribution from highly preserved coercive (titanohematite) grains origin which survived processes. strong linkage between occurrence carbonates observed. plausible mechanisms proposed explain preservation Z-II: 1) decline methane flux massive hydrate accumulation within fault system carbonate crust sub-surface sediments hindered supply upward migrating fluid/gas; thereby limiting sulfide production preferentially enhanced 2) restricted downward diffusing layers uppermost created deficient inhibited pyritization favoured