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Fluid seepage associated with slope destabilization along the Zambezi margin (Mozambique)
Marine Geology ( IF 2.9 ) Pub Date : 2020-06-23 , DOI: 10.1016/j.margeo.2020.106275
Eric Deville , Carla Scalabrin , Gwenael Jouet , Antonio Cattaneo , Anne Battani , Sonia Noirez , Hélène Vermesse , Karine Olu , Laure Corbari , Marion Boulard , Tania Marsset , Massimo Dall'Asta , Martina Torelli , Lucie Pastor , Delphine Pierre , Benoit Loubrieu

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 to authigenic carbonate crusts and possibly 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.



中文翻译:

与赞比西河边缘(莫桑比克)边坡失稳相关的渗流

在赞比西河大陆斜坡(莫桑比克南部海岸)发现了活跃的流体渗漏证据。这些渗漏大多与沿与斜坡平行的趋势对齐并在宽阔的斜坡失稳区域的顶壁陡峭上游延伸的麻点有关。流体渗漏被解释为边坡失稳的潜在诱因。水柱内的声音异常已被解释为与中等程度的气泡渗漏有关,气泡渗漏大多位于不稳定区域外,而只是在稳定区域内。用最宽的麻点(直径200 m宽)的SCAMPI拖曳相机系统进行的勘探显示,流体渗漏与自生的碳酸盐结皮和可能的细菌垫有关。这些液体的渗漏还与化学合成生物的存在有关(Vesicomyidae和Thyasiridae bivalves,Siboglinidae tubeworms)。沉积物中的采样气体主要对应于CH微生物来源的4,由有机来源的底物通过氢营养甲烷化作用产生,海洋领域微生物气成因的常规过程。没有检测到热气的证据。在斜坡失稳带的核心区域内还观察到了另一类麻点。就目前的流体渗漏而言,这些麻子大多数都不活跃,并且与形成烟囱几何形状的碳酸盐堆积有关。它们可能对应于先前的流体运移路径的成岩烟囱,该流体运移路径在质量滑动过程中被挖掘出,周围的凹陷与强侧向洋流的经常性活动有关,后者掠夺了周围的沉积物。边坡失稳特征的空间组织被认为是滑坡随时间变化的代表,给出了有关边坡失稳过程动力学的信息。该提议的演化始于地层水与溶解气体的零散渗漏。然后,在斜坡的上部明显出现了自由气体渗漏。其次是主要气体渗流的沉积物下坡逐渐浅变。最后,整个斜坡失去稳定性,形成带斜坡的滑坡,挖掘出局部成岩作用的烟囱。

更新日期:2020-06-23
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