Evidences of early to late fluid migration from an upper Miocene turbiditic channel revealed by 3D seismic coupled to geochemical sampling within seafloor pockmarks, Lower Congo Basin

Type Article
Date 2006-04
Language English
Author(s) Gay A1, Lopez M2, Cochonat Pierre3, Levache D4, Sermondadaz G4, Seranne M2
Affiliation(s) 1 : Natl Oceanog Ctr Southhampton, Challenger Div Seafloor Proc, Southampton SO14 3ZH, Hants, England.
2 : Univ Montpellier 2, Lab Dynam Lithosphere, Montpellier, France.
3 : IFREMER, Dept Geosci Marines, Lab Environm Sedimentaires, Brest, France.
4 : TOTAL, Pau, France.
Source Marine and Petroleum Geology (0264-8172) (Elsevier), 2006-04 , Vol. 23 , N. 3 , P. 387-399
DOI 10.1016/j.marpetgeo.2006.02.004
WOS© Times Cited 58
Keyword(s) Pipes, Seismic chimneys, Polygonal faults, Fluid migration, Turbiditic channels, Pockmarks
Abstract Using high quality 3D seismic data within the Lower Congo Basin (LCB), we have identified pockmarks that are aligned above the sinuous belt of a buried turbiditic palaeo-channel, 1000 m beneath the seafloor. Geochemical analyses on cores (GC traces), taken in the centre of four of these pockmarks along this channel, show no clear evidence for migrated oil. But, some features of the GC traces, including elevated baselines (UCM > 34 mu g/g) and a broad molecular weight range of n-alkanes with little odd-even preference, may be interpreted as indicating the presence of thermogenic hydrocarbons in the cores.

Seismic profiles show that these pockmarks developed above two-main features representative of pore fluid escape during early compaction: (1) closely spaced normal faults affecting the upper 0-800 ms TWT of the sedimentary column. This highly faulted interval (HFI) appears as a hexagonal network in plane view, which is characteristic of a volumetrical contraction of sediments in response to pore fluid escape. (2) Buried palaeo-pockmarks and their underlying chimneys seem to be rooted at the channel-levee interface. The chimneys developed during early stages of burial and are now connected to the HFI.

This study shows that the buried turbiditic channel now concentrates thermogenic fluids that can migrate through early chimneys and polygonal faults to reach the seafloor within some pockmarks. Using a multidisciplinary approach within the Lower Congo Basin, combining 3D seismic data and geochemical analyses on cores, we trace the fluid history from early compaction expelling pore fluids to later migration of thermogenic hydrocarbons.
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Gay A, Lopez M, Cochonat Pierre, Levache D, Sermondadaz G, Seranne M (2006). Evidences of early to late fluid migration from an upper Miocene turbiditic channel revealed by 3D seismic coupled to geochemical sampling within seafloor pockmarks, Lower Congo Basin. Marine and Petroleum Geology, 23(3), 387-399. Publisher's official version : https://doi.org/10.1016/j.marpetgeo.2006.02.004 , Open Access version : https://archimer.ifremer.fr/doc/00000/1673/