The first record of active methane (cold) seep ecosystem associated with shallow methane hydrate from the Indian EEZ

Abstract

Here we report the discovery of cold-seep ecosystem and shallow methane hydrates (2-3 mbsf) associated with methane gas flares in the water column from the Indian EEZ for the first time. The seep-sites are located in the Krishna-Godavari (K-G) basin at water depths of 900-1800 m and are characterized by gas flares in the water-column images. The occurrence of methane gas hydrates at very shallow depths (2-3 mbsf) at some of the seep-sites is attributed to high methane flux and conducive P-T conditions, necessary for the stability of methane hydrate. Chemosymbiont bearing Bivalves (Vesicomidae, Mytilidae, Thyasiridae and Solemyidae families); Polychaetes (Siboglinidae family) and Gastropods (Provannidae family) are also identified from seep-sites.

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

“…A high-resolution seismic data beneath the seep sites showed the presence of acoustic chimneys, and the overburden is heavily faulted (Dewangan et al, 2020). Deeprooted faults provide a conducive environment for the migration of methane from deep-seated gas reservoir and led to the development of a cold seep ecosystem and formation of shallow fracture-filled gas hydrate deposits at the studied site (Dewangan et al, 2020;Mazumdar et al, 2019;Sriram et al, 2020). High methane flux and favourable P-T conditions supported the accumulation of gas hydrates (Mazumdar et al, 2019).…”

“…Regulation of gas plumbing system due to opening/closing of the fractures/faults provides important constraints on the methane flux (Dewangan et al, 2011;Sriram et al, 2013;Mazumdar et al, 2019). Widespread occurrence (45-219 cmbsf) of authigenic carbonates in the studied core suggests that the multiple AOM driven by variability in paleomethane fluxes is controlled by the opening and closing dynamics of the fracture/fault system due to prevailing shale tectonism (Dewangan et al, 2010;Gullapalli et al, 2019;Mazumdar et al, 2019).…”

“…These deformed structures provide efficient migration pathway for methane-rich fluids through the deep-rooted faults, and hence these regions are preferred locales for the formation of gas hydrates deposits (Dewangan et al, 2010). The presence of sub-surface gas hydrate deposits in the K-G basin has been confirmed through well-logging, drilling and sediment coring activities, while paleo-methane seepage events are evident through the presence of methane derived authigenic carbonates and chemosynthetic community (Collett et al, 2008;Mazumdar et al, 2009Mazumdar et al, , 2019.…”

“…Deeprooted faults provide a conducive environment for the migration of methane from deep-seated gas reservoir and led to the development of a cold seep ecosystem and formation of shallow fracture-filled gas hydrate deposits at the studied site (Dewangan et al, 2020;Mazumdar et al, 2019;Sriram et al, 2020). High methane flux and favourable P-T conditions supported the accumulation of gas hydrates (Mazumdar et al, 2019). A recent rock magnetic study by Badesab et al (2019) on the long drilled sediment cores that overlie the deep-seated gas hydrate deposit provided the longest and most detailed sediment magnetic record in the K-G basin, Bay of Bengal.…”

“…The first evidence of active methane seepage and shallow methane hydrate from geological, geochemical and geophysical studies was reported by Mazumdar et al (2019) in the Krishna-Godavari (K-G) basin. Gas hydrate exploration cruise (SSD-045) of CSIR-National Institute of Oceanography (CSIR-NIO) onboard R/V Sindhu Sadhana discovered this active seep and associated shallow gas hydrates in 2018 ( Figure 1A).…”