Influence of total organic carbon deposition on the inventory of gas hydrate in the Indian continental margins

Johnson, Joel E., Phillips, Stephen C., Torres, Marta E., Piñero, Elena, Rose, Kelly K. and Giosan, Liviu (2014) Influence of total organic carbon deposition on the inventory of gas hydrate in the Indian continental margins Marine and Petroleum Geology, 58 . pp. 406-424. DOI 10.1016/j.marpetgeo.2014.08.021.

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Total organic carbon (TOC) content of marine sediments represents residual carbon, originally derived from terrestrial and marine sources, which has survived seafloor and shallow subseafloor diagenesis. Ultimately, its preservation below the sulfate reduction zone in marine sediments drives methanogenesis. Within the gas hydrate stability zone (GHSZ), methane production along continental margins can supersaturate pore fluids and lead to the formation of gas hydrate. In this paper we examine the inventory and sources of TOC in sediments collected from four regions within the GHSZ along the Indian continental margins. The recovered sediments vary in age from Oligocene to recent. Mean TOC abundance is greatest in the Krishna-Godavari (K-G) Basin and decreases progressively to the Mahanadi basin, Andaman wedge, and Kerala-Konkan (K-K) Basin. This decrease in TOC is matched by a progressive increase in biogenic CaCO3 and increasing distance from terrestrial sources of organic matter and lithogenic materials. Organic carbon sources inferred from C/N and delta C-13(TOC) range from terrestrial (K-G Basin) to mixed marine and terrestrial (Mahanadi Basin), to marine dominant (Andaman wedge and K-K Basin). In the K-G Basin, variation in the bulk delta C-13(TOC) is consistent with changes in C-3 and C-4 vegetation driven by monsoon variability on glacial-interglacial timescales, whereas in the Mahanadi Basin a shift in the delta C-13(TOC) likely reflects the onset of C-4 plant deposition in the Late Miocene. A large shift the delta C-13(TOC) in the K-K basin is consistent with a change from C-3 to C-4 dominated plants during the middle Miocene. We observe a close relationship between TOC content and gas hydrate saturation, but consider the role of sedimentation rates on the preservation of TOC in the zone of methanogenesis and advective flow of methane from depth. Although TOC contents are sufficient for in situ methanogenesis at all the sites where gas hydrates were observed or inferred from proxy data, seismic, borehole log, pressure core, and gas composition data coupled with relatively high observed gas hydrate saturations suggest that advective gas transport may also play a role in the saturation of methane and the formation of gas hydrates in these regions. Although TOC content may be a first order indicator for gas hydrate potential, the structural and stratigraphic geologic environment along a margin will most likely dictate where the greatest gas hydrate saturations will occur.

Document Type: Article
Additional Information: WOS:000347577000024
Keywords: TOC; C/N; Organic carbon isotopes; Bay of Bengal; Krishna-Godavari; Mahanadi; Andaman accretionary wedge; Kerala-Konkan
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: Yes
DOI etc.: 10.1016/j.marpetgeo.2014.08.021
ISSN: 0264-8172
Date Deposited: 19 Feb 2015 10:26
Last Modified: 05 Oct 2017 12:02

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