Structural and sedimentary geology of the Congo and Southern Gabon continental shelf; a seismic and acoustic reflection survey

Jansen, J H Fred; Giresse, Pierre; Moguedet, Gérard

doi:10.1016/0077-7579(84)90056-5

Cited by 28 publications

(10 citation statements)

References 5 publications

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“…The West African passive margin was initiated during the opening of the South Atlantic Ocean at Early Cretaceous (130 My) (Marton et al, 2000;Jansen et al, 1984). Subsequent to large accumulations of evaporites (up to 1000 m) during the mid-Aptian time (Valle et al, 2001), the post-rift stratigraphy is characterized by two superposed seismic architectures that reflect a major change in ocean circulation and climate (Séranne et al, 1992): (1) from Late Cretaceous to Early Oligocene time, an aggradational carbonate/siliciclastic ramp develops (greenhouse period) and (2) from Early Oligocene to Present time, the sedimentation is dominated by the progradation of a terrigenous wedge (Icehouse period) (Séranne, 1999).…”

Section: Geological Settingsmentioning

confidence: 99%

Seafloor facies related to upward methane flux within a Giant Pockmark of the Lower Congo Basin

et al. 2006

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The origin of the cold fluid venting from a Giant Pockmark within the Lower Congo Basin has been elucidated based upon results of precise mapping, submersible dives, gravity coring and isotopic analyses realized under a TOTAL-IFREMER cooperative project (ZAIANGO and BIOZAIRE projects).During four dives of the IFREMER ROV-Victor 6000, the bottom was filmed, hard and soft samples were lifted from the sediment, and water samples were collected with a CTD-rosette system. The detailed dip map shows that the 800 m wide Giant Pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological, mineralogical and chemical features on the seafloor, leading to a seafloor anomaly recorded on the multibeam imagery. Methane-rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate-rich circulating sea water to produce hydrogen sulphide and bicarbonate ions. This situation leads to a concentrical arrangement of the sedimentary facies, with methane-related features in the centre and sulphide-related features at the periphery. This organization is correlated with high levels of methane (up to 20 Amol/l) measured in the centre of the Giant Pockmark, responsible for the crystallization of gas hydrates at the bottom.In this model, the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux. D

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Section: Geological Settingsmentioning

confidence: 99%

Seafloor facies related to upward methane flux within a Giant Pockmark of the Lower Congo Basin

et al. 2006

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“…The lithostratigraphy of Late Neogene sediments suggests that turbidity currents played a minimal role in transporting sediment within the LCB (Giraudeau et al, 1998); (Pufahl and Wefer, 2001). Presumably, the sediments trapped into the canyon were carried far onto the lower fan, starving the shelf of coarse detritus (Jansen et al, 1984b); (Uenzelmann-Neben, 1998); (Savoye et al, 2000). Only fine muddy sediments not confined to the canyon are delivered to the LCB, perhaps from riverine plumes, through sedimentation by aggregates and in fecal pellets (Wefer et al, 1998); (Cooper, 1999) and mixed with hemipelagic sediments on the continental shelf and slope.…”

Section: Geologic Settingmentioning

confidence: 99%

Isolated seafloor pockmarks linked to BSRs, fluid chimneys, polygonal faults and stacked Oligocene–Miocene turbiditic palaeochannels in the Lower Congo Basin

et al. 2006

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Based on high-resolution 3D seismic data sets, we document the subsurface reservoir architecture and organization of a portion of the Oligocene-Miocene stratigraphy within the Congo Basin, offshore southwestern Africa. Within the 3D seismic volume, we have identified four levels of turbiditic palaeochannels, which are separated by low-amplitude continuous reflectors interpreted as hemipelagic sediments. Geochemical analyses on sediment samples taken within overlying seafloor pockmarks reveal the presence of thermogenic gases and oils, suggesting that deep-seated fluids have migrated through both the channel deposits and the impermeable layers between them, forming a conduit to the surface. Deep thermogenic fluids produced within Cretaceous source rocks are preferentially entrapped within coarse-grained turbiditic Oligocene-Miocene palaeochannels. We show in this study that the vertical stacking pattern of turbiditic palaeochannels allows the best pathway for fluids migration. Once the fluids migrate to the upper layer (i.e., Upper Miocene) of palaeochannels, they can reach the seafloor via migration along a highly faulted interval composed of polygonal faults. They are temporarily inhibited below an interpreted 300-m-thick gas hydrate layer marked by a strong BSR on seismic profiles. Fluids accumulate under the hydrate stability zone to form a thick layer of free gas. The generation of excess pore fluid pressure in the free gas accumulation leads to the release of fluids along faults of the highly faulted interval forming pockmarks on the seafloor. Ultimately, we show in this study that fluids are progressively concentrated in the sedimentary column and aligned pockmarks on the seafloor may represent a focused fluid flow from stacked turbiditic palaeochannels.

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“…Eisma and Van Bennekom (1978) were the first to describe the Congo River plume, finding it to be oriented generally towards northwest (see also Braga et al, 2004) rather than towards the south, as might be expected due to the location of the river (6°S) and the influence of the Coriolis effect. In the modeling study of Denamiel et al (2013) it was suggested that the northward extension of the plume can be explained as a buoyancy-driven upstream coastal flow that is influenced by the geomorphology of the Congo River estuary (see Jansen et al, 1984) and the combined influences of the ambient ocean currents and winds. Using Soil Moisture and Ocean Salinity (SMOS) satellite surface salinity and chlorophyll data, Hopkins et al (2013) also found that for most of the year, the main axis of the fresh water plume extends northwest between 400 and 1000 km along the coastline, extending to the Equator and even slightly further north.…”

Section: Introductionmentioning

confidence: 99%

Sea surface salinity variability in response to the Congo river discharge

Chao

Farrara

Schumann

et al. 2015

Continental Shelf Research

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Structural and sedimentary geology of the Congo and Southern Gabon continental shelf; a seismic and acoustic reflection survey

Cited by 28 publications

References 5 publications

Seafloor facies related to upward methane flux within a Giant Pockmark of the Lower Congo Basin

Seafloor facies related to upward methane flux within a Giant Pockmark of the Lower Congo Basin

Isolated seafloor pockmarks linked to BSRs, fluid chimneys, polygonal faults and stacked Oligocene–Miocene turbiditic palaeochannels in the Lower Congo Basin

Sea surface salinity variability in response to the Congo river discharge

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