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AAPG Bulletin, Preliminary version published online Ahead of Print 1 April 2024.

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Accumulation of gas hydrates in mass transport deposit at Krishna-Godavari Basin, Bay of Bengal: Foraminiferal, sedimentological, and seismic evidence

Ajoy K. Bhaumik1 , Shiv Kumar2 , Swagata Chaudhuri13 , Satabdi Mohanty1 , Mrinal Kanti Mukherjee1 , K. Sain4 , Anil K. Gupta5 , and P. Kumar6

1 Department of Applied Geology, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand-826004, India
2 Geological Survey of India, State Unit: Telangana, Southern Region, Hyderabad-500068, India
3 Geological Studies Unit, Indian Statistical Institute, Kolkata-700108, India
4 Gas-hydrate Group, CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500007, India; Presently Director, Wadia Institute of Himalayan Geology, Dehradun, Uttarakhand - 248171
5 Department of Geology and Geophysics, Indian Institute of Technology Kharagpur – 721302, West Bengal, India
6 Institute of Engineering and Ocean Technology, Oil and Natural Gas Corporation, Panvel, Navi Mumbai-410 221

Ahead of Print Abstract

Gas hydrates have been reported from diverse environments ranging from marine sediments of continental margins and deep-sea fans to permafrost zones. However, they are scarcely reported from mass transport deposits (MTD). Here, we combine paleontological, grain size, stable isotopes, 2D seismic profile, and downhole log data from the Quaternary sediments of NGHP Site 10, Krishna-Godavari Basin, India, to identify a mid-depth MTD and accumulation of gas hydrates within it. Gas hydrates at Site 10 are present from 26 to 160 mbsf, with a change in hydrate saturation at 90 mbsf. The dominance of shelfal foraminifera (Ammonia spp., Bolivinita subangularis, Loxostomum amygdalaeformis, and Quinqueloculina seminulum) in deep-sea, the mixing of large rounded grains with clays, confirm the existence of shelf sediments within ~90 and ~153 mbsf, interpreted as MTD. The seismic profile also bears the signature of MTD within this interval. The gravity-driven MTD transported these shelf sediments to the continental slope environment and formed a different one from the topmost MTD. A higher abundance of Cibicides wuellerstorfi and the absence of Cassidulina carinata within the MTD suggest a change in the depositional environment. The usual range of δ13C of Bulimina marginata and a well-ventilated depositional environment indicates the formation of post-depositional gas hydrates within MTD. Mixing of sediments lowered the porosity in MTD. Gas hydrates within this zone are nucleated within intergranular/fracture pores by entrapment of upward-migrating methane through faults/fractures from deeper successions.

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Please cite this AAPG Bulletin Ahead of Print article as:

Ajoy K. Bhaumik , Shiv Kumar , Swagata Chaudhuri , Satabdi Mohanty , Mrinal Kanti Mukherjee , K. Sain , Anil K. Gupta , P. Kumar: Accumulation of gas hydrates in mass transport deposit at Krishna-Godavari Basin, Bay of Bengal: Foraminiferal, sedimentological, and seismic evidence, (in press; preliminary version published online Ahead of Print 01 April 2024: AAPG Bulletin, DOI:10.1306/03222423052.