Magnetic Mineral Diagenesis in a Newly Discovered Active Cold Seep Site in the Bay of Bengal

Abstract

Diagenetically formed magnetic minerals at marine methane seep sites are potential archive of past fluid flow and could provide important constraints on the evolution of past methane seepage dynamics and gas hydrate formation over geologic time. In this study, we carried out integrated rock magnetic, and mineralogical analyses, supported by electron microscope observations, on a seep impacted sediment core to unravel the linkage between greigite magnetism, methane seepage dynamics, and evolution of shallow gas hydrate system in the K-G basin. Three sediment magnetic zones (MZ-1, MZ-2, and MZ-3) have been identified based on the down-core variations in rock magnetic properties. Two events of intense methane seepage are identified. Repeated occurences of authigenic carbonates throughout the core indicate the episodic intensification of anaerobic oxidation of methane (AOM) at the studied site. Marked depletion in magnetic susceptibility manifested by the presence of chemosynthetic shells (Calyptogena Sp.), methane-derived authigenic carbonates, and abundant pyrite grains provide evidences on intense methane seepage events at this site. Fracture-controlled fluid transport supported the formation of gas hydrates (distributed and massive) at this site. Three greigite bearing sediment intervals (G1, G2, G3) within the magnetically depleted zone (MZ-2) are probably the paleo-gas hydrate (distributed-type vein filling) intervals. A strong linkage among clay content, formation of veined hydrate deposits, precipitation of authigenic carbonates and greigite preservation is evident. Hydrate crystallizes within faults/fractures formed as the methane gas migrates through the gas hydrate stability zone (GHSZ). Formation of authigenic carbonate layers coupled with clay deposits restricted the upward migrating methane, which led to the formation of distributed-type vein filling hydrate deposits. A closed system created by veined hydrates trapped the sulfide and limited its availability thereby, causing arrestation of pyritization and favored the formation and preservation of greigite in G1, G2, G3.

Greigite Formation Modulated by Turbidites and Bioturbation in Deep‐Sea Sediments Offshore Sumatra

“…Greigite is considered to be metastable but has been reported to be generated and preserved in diverse environmental settings with ages ranging from the Ediacaran to the Holocene, although the greigite could be younger than its host sediment. Environments include organic‐rich lacustrine and marine sediments, restricted anoxic basins, gas hydrate systems, and hydrothermal/cold seep environments (e.g., Badesab et al., 2020; Dewangan et al., 2013; Dong et al., 2013; Greve et al., 2021; Horng, 2018; Housen & Musgrave, 1996; Kars, Greve, & Zerbst, 2021; Kars, Köster, Henkel, et al., 2021; Kelder et al., 2018; Krs et al., 1990; Larrasoaña et al., 2007; Reynolds et al., 1994; Roberts et al., 1996; Sagnotti & Winkler, 1999; Snowball, 1991; Vasiliev et al., 2007, 2008).…”

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

“…Rock magnetic properties of methanic sediments from active cold seep and gas hydrate dominated sedimentary systems have been extensively studied to understand the magnetic mineral diagenesis. For example in Nankai trough, Japan (Kars and Kodama, 2015), Cascadia Margin (Housen and Musgrave, 1996;Larrasoaña et al, 2007), continental margin offshore of south-western Taiwan (Horng and Chen, 2006), continental margin off Argentina and Uruguay (Riedinger et al, 2014), Bay of Bengal (Badesab et al, 2017;Badesab et al, 2019;Badesab et al, 2020a;Badesab et al, 2020b;Badesab et al, 2020c), Southern Eastern Mediterranean continental shelf (Amiel et al, 2020), Niger deep-sea fan (Dillon and Bleil, 2006), Bulls eye vent off Vancouver Island, Canada (Novosel et al, 2005), and North-western Weddell Sea (Reilly et al, 2020).…”

“…For example, a magnetic based proxy for deciphering paleo-methane seepage events and sediment dispersal patterns, tracking of the rapid sedimentation events and its control on the magnetic mineral diagenesis and evolution of gas hydrate deposits was developed (Usapkar et al, 2014;Badesab et al, 2017;Badesab et al, 2019;Badesab et al, 2020b). Furthermore, the mechanism of formation and preservation of greigite in deep methanic sediments were unravelled by Badesab et al (2020c). The occurrence of silicate-hosted greigite inclusion were reported by Badesab et al (2020a).…”

“…They further highlighted its importance in understanding magnetic mineral diagenesis in the gas hydrate system. More recently, Badesab et al (2020c) conducted a comprehensive rock magnetic and mineralogical investigation on a seep-impacted sediment core from a newly discovered site and successfully delineated the processes governing the methane seepage dynamics and evolution of shallow gas hydrate (2-3 mbsf) system in the K-G basin. However, a dedicated rock magnetic study focussing on understanding the complex diagenetic (early and late) processes controlled by variability in methane fluxes and underlying fault/fractures at active and relict seep dominated sedimentary systems is still lacking.…”