Fluid seepage associated with slope destabilization along the Zambezi margin (Mozambique)

Type Article
Date 2020-10
Language English
Author(s) Deville Eric1, Scalabrin CarlaORCID2, Jouet Gwenael2, Cattaneo AntonioORCID2, Battani Anne1, Noirez Sonia1, Vermesse Hélène1, Olu KarineORCID3, Corbari Laure4, Boulard Marion3, Marsset TaniaORCID2, Dall'Asta Massimo5, Torelli Martina1, Pastor Lucie3, Pierre Delphine2, Loubrieu Benoit2
Affiliation(s) 1 : IFP-Energies Nouvelles, Rueil-Malmaison, France
2 : IFREMER, Géoscience Marines, Plouzané, France
3 : IFREMER, Unité Étude des Écosystèmes Profonds, Plouzané, France
4 : MNHN-UPMC, Paris, France
5 : TOTAL-CSTJF, Pau, France
Source Marine Geology (0025-3227) (Elsevier BV), 2020-10 , Vol. 428 , P. 106275 (13p.)
DOI 10.1016/j.margeo.2020.106275
WOS© Times Cited 8

Evidences for active fluid seepages have been discovered along the Zambezi continental slope (offshore Southern Mozambique). These seepages are mostly associated with pockmarks which are aligned along a trend parallel to the slope and running closely upstream of the headwall scarp of a wide zone of slope destabilization. Fluid seepages are interpreted as a potential trigger for the slope destabilization. Acoustic anomalies within the water column have been interpreted as related to moderate bubble seepages mostly located outside and only punctually inside the destabilization zone. Exploration with the SCAMPI towed camera system in the widest pockmark (diameter 200 m wide) has shown fluid seepages associated toauthigenic carbonate crusts and bacterial mats. These fluid seepages are also associated to the presence of chemiosynthetic organisms (Vesicomyidae and Thyasiridae bivalves, Siboglinidae tubeworms). The sampled gas in the sediment corresponds mainly to CH4 of microbial origin, generated by hydrogenotrophic methanogenesis from a substrate of organic origin, i.e. a conventional process of genesis of microbial gas in the marine domain. No evidence for thermogenic gas was detected. Another type of pockmarks has been observed within the core of the slope destabilization zone. Most of these pockmarks are inactive in terms of fluid seepage at present time and are associated to carbonate buildups forming chimney geometries. They probably correspond to diagenetic chimneys of former fluid migration pathways that have been exhumed during the mass sliding and the surrounding depression are related to recurrent activity of strong lateral slope currents which have scoured the sediments around. The spatial organization of the slope destabilization features is considered as representative of the temporal evolution of the landslide giving information about the dynamics of slope instability processes. This proposed evolution started by scattered seepages of formation water with dissolved gas. Then free gas seepages appeared notably in the upper part of the slope. This was followed by progressive shallow deformation in the sediments downslope of the main gas seepages. Finally, the whole slope was destabilized forming imbricated landslides exhuming locally former diagenetic chimneys.

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Deville Eric, Scalabrin Carla, Jouet Gwenael, Cattaneo Antonio, Battani Anne, Noirez Sonia, Vermesse Hélène, Olu Karine, Corbari Laure, Boulard Marion, Marsset Tania, Dall'Asta Massimo, Torelli Martina, Pastor Lucie, Pierre Delphine, Loubrieu Benoit (2020). Fluid seepage associated with slope destabilization along the Zambezi margin (Mozambique). Marine Geology, 428, 106275 (13p.). Publisher's official version : https://doi.org/10.1016/j.margeo.2020.106275 , Open Access version : https://archimer.ifremer.fr/doc/00635/74690/