Sea-level change and free gas occurrence influencing a submarine landslide and pockmark formation and distribution in deepwater Nigeria

Type Article
Date 2013-08
Language English
Author(s) Riboulot VincentORCID1, 2, Cattaneo AntonioORCID1, Sultan Nabil1, Garziglia Sebastien1, Ker StephanORCID1, Imbert Patrice3, Voisset Michel1
Affiliation(s) 1 : IFREMER, Ctr Brest, Inst CARNOT EDROME, Brest, France.
2 : Univ Perpignan, F-66025 Perpignan, France.
3 : TOTAL, Pau, France.
Source Earth And Planetary Science Letters (0012-821X) (Elsevier Science Bv), 2013-08 , Vol. 375 , P. 78-91
DOI 10.1016/j.epsl.2013.05.013
WOS© Times Cited 41
Keyword(s) pockmarks, fluid seepage, submarine landslide, sea-level changes, piezocone, Niger Delta
Abstract A series of pockmarks observed at the seabed matches well the perimeter of a large submarine landslide, called NG1, located on the outer shelf and continental slope of the Eastern Gulf of Guinea. NG1 extends over 200 km2, is covered by a 120-m thick sedimentary layer which tapers downslope, and has an internal structure clearly identified in 3D seismic data consisting of three adjacent units on the upper continental slope. The pockmarks above NG1 have a diameter of several tens of meters and reveal distinct origins: (1) linked to >500 m deep fluid reservoirs, (2) rooted in NG1 internal discontinuities between NG1 units, and (3) well above NG1, superficially rooted in a regional conformity (D40), which marks the lowest sea level of the Marine Isotope Stage 6.

The regional stratigraphic pattern of the study area is composed of muddy sedimentary sequences separated by correlative conformities and transgressive condensed units of coarser grain size. Mud-confined coarser-grained units constitute transient gas reservoirs favoring lateral gas migration and formation of pockmarks rooted in the condensed units. The buried NG1 landslide modifies the layered structure of the sedimentary column providing (1) overall, a barrier to fluid migration, and (2) localized pathways for fluid migration. The triggering factor for the formation of pockmarks above NG1 can be the variation of hydrostatic pressure driven by relative sea-level fall during Marine Isotopic Stages 6 and 2 and consequent gas exsolution and fluid flow. We anticipate our result to be a starting point for understanding the role of gas seeps on climate change worldwide. Furthermore, gas release intensifies during lowstands with relevant implication on global warming after ice ages.
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Riboulot Vincent, Cattaneo Antonio, Sultan Nabil, Garziglia Sebastien, Ker Stephan, Imbert Patrice, Voisset Michel (2013). Sea-level change and free gas occurrence influencing a submarine landslide and pockmark formation and distribution in deepwater Nigeria. Earth And Planetary Science Letters, 375, 78-91. Publisher's official version : https://doi.org/10.1016/j.epsl.2013.05.013 , Open Access version : https://archimer.ifremer.fr/doc/00159/27031/