Investigation on the geochemical dynamics of a hydrate-bearing pockmark in the Niger Delta

Type Article
Date 2013-05
Language English
Author(s) Ruffine Livio1, Caprais Jean-Claude2, Bayon Germain1, Riboulot VincentORCID1, Donval Jean-Pierre1, Etoubleau Joel1, Birot Dominique1, Pignet Patricia2, Rongemaille Emmanuelle1, Chazallon Bertrand3, Grimaud Sylvie4, Adamy Jerome4, Charlou Jean-Luc1, Voisset Michel1
Affiliation(s) 1 : IFREMER, Ctr Brest, Unite Rech Geosci Marines, F-29280 Plouzane, France.
2 : IFREMER, Ctr Brest, Unite Rech & Etud Environm Profonds, F-29280 Plouzane, France.
3 : Univ Lille 1, UMR CNRS 8523, CERLA FR CNRS 2416, Lab Phys Lasers Atomes & Mol PhLAM, F-59655 Villeneuve Dascq, France.
4 : TOTAL Oil Co, Pau, France.
Source Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2013-05 , Vol. 43 , P. 297-309
DOI 10.1016/j.marpetgeo.2013.01.008
WOS© Times Cited 13
Keyword(s) Active pockmark, Anaerobic oxidation of methane, Gas hydrates, Carbonates, Seismic surveys, Fault system, U/Th dating
Abstract A joint industrial project with IFREMER and Total provides insights into the tectonic setting and the geochemistry of a large active pockmark offshore W-Africa in the Niger Delta. The study combines both geophysical (seismic) and geochemical data to infer the dynamics of a 300 m wide pockmark located at 667 m water depth. Two Calypso cores, one at the centre and one outside the pockmark, along with three box-cores, two inside the pockmark and one outside, were collected to study the geochemistry of gas hydrates, carbonates and pore waters. Two seismic lines, a 3D high resolution random line and a 2D high resolution seismic line, provide a good description of the plumbing of the system. The integrated results depict a very active pockmark characterized by several gas charged-bodies, a well identified BSR marking a hydrate accumulation zone, charged from deeper sources via a network of faults. Hydrates and carbonate concretions have been detected inside the pockmark while only the latter has been found outside. The hydrate analyses show that the hydrate-forming gases are of thermogenic origin, albeit overwhelmingly composed of methane. Pore-water analyses reveal the occurrence of anaerobic oxidation of methane coupled with sulphate reduction at shallow depth (∼200 cm). The chloride concentration profile exhibits both values lower than that of seawater which is inherent to hydrate dissociation after core recovery and positive anomalies (values 7% higher than that of seawater background) at the lowermost part of the core. The latter evidence suggests current or recent hydrate formation at this area. The carbonate dating provides additional temporal information and indicates that this pockmark has been active since ∼21 kyr.
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Ruffine Livio, Caprais Jean-Claude, Bayon Germain, Riboulot Vincent, Donval Jean-Pierre, Etoubleau Joel, Birot Dominique, Pignet Patricia, Rongemaille Emmanuelle, Chazallon Bertrand, Grimaud Sylvie, Adamy Jerome, Charlou Jean-Luc, Voisset Michel (2013). Investigation on the geochemical dynamics of a hydrate-bearing pockmark in the Niger Delta. Marine And Petroleum Geology, 43, 297-309. Publisher's official version : https://doi.org/10.1016/j.marpetgeo.2013.01.008 , Open Access version : https://archimer.ifremer.fr/doc/00139/24981/