Investigation on the geochemical dynamics of a hydrate-bearing pockmark in the Niger Delta
Autor: | Jean-Pierre Donval, Jerome Adamy, Vincent Riboulot, Sylvie Grimaud, M. Voisset, Germain Bayon, Jean-Luc Charlou, Emmanuelle Rongemaille, Jean-Claude Caprais, Bertrand Chazallon, Patricia Pignet, Dominique Birot, Joel Etoubleau, Livio Ruffine |
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Rok vydání: | 2013 |
Předmět: |
010504 meteorology & atmospheric sciences
Stratigraphy Clathrate hydrate Carbonates Geochemistry Mineralogy 010502 geochemistry & geophysics Oceanography 01 natural sciences Methane chemistry.chemical_compound U/Th dating 0105 earth and related environmental sciences Pockmark Geology Tectonics Geophysics Active pockmark chemistry Anaerobic oxidation of methane Seismic surveys Carbonate Economic Geology Seawater Hydrate Gas hydrates Fault system |
Zdroj: | Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2013-05, Vol. 43, P. 297-309 |
ISSN: | 0264-8172 |
DOI: | 10.1016/j.marpetgeo.2013.01.008 |
Popis: | 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. |
Databáze: | OpenAIRE |
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