Cold seeps at the salt front in the Lower Congo Basin II: The impact of spatial and temporal evolution of salt-tectonics on hydrocarbon seepage

Wenau, Stefan; Spieß, V.; Pape, Thomas; Fekete, Noemi

doi:10.1016/j.marpetgeo.2014.09.021

Cited by 19 publications

(3 citation statements)

References 71 publications

(116 reference statements)

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“…Structural control on methane seepage at cold seep sites has been well reported using high resolution seismic and bathymetry data. For example Lomvi pockmark, Vestnesa Ridge, offshore Svalbard (Bünz et al, 2012;Berndt et al, 2014;Yao et al, 2019), Harstad Basin, southwest Barents Sea (Crémière et al, 2018), Bay of Bengal (Dewangan et al, 2020), Concepción Methane Seep Area, offshore Central Chile (Geersen et al, 2016), Taixinan Basin, South China Sea (Wang, et al, 2018) Central Nile deep sea fan (Römer et al, 2014), Nankai accretionary prism (Henry et al, 2002), Congo basin (Wenau et al, 2015) and Black Sea (Bohrmann et al, 2003). Extensive geological and geophysical studies established the presence of fracture-filled and massivetype gas hydrate deposits in the Krishna-Godavari (K-G) basin (Collett et al, 2008;Dewangan et al, 2010;Shankar and Riedel, 2010;Dewangan et al, 2011;Kumar et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

et al. 2021

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In this study, we conducted a comprehensive investigation of rock magnetic, mineralogical, and sedimentological records of sediment cores supplemented by a high resolution seismic data to elucidate the controls of structural and diagenetic (early vs. late) processes on the sediment magnetism in active and relict cold seep sites in the Bay of Bengal. Two distinct sediment magnetic zones (Z-I and Z-II) are defined based on the down-core variations in rock magnetic properties. The sediment magnetism is carried by complex magnetic mineral assemblages of detrital (titanomagnetite, titanohematite) and authigenic (fine-grained greigite) minerals. Overall, the magnetic susceptibility varies over one order of magnitude with highest values found in relict core. Uppermost sediment magnetic zone (Z-I) is characterized by higher concentration of magnetite as seen through elevated values of magnetic susceptibility (χlf) and saturation isothermal remanent magnetization (SIRM). A systematic gradual decrease of χlf and IRM1T in Z-I is attributed to the progressive diagenetic dissolution of iron oxides and subsequent precipitation of iron sulfides. Magnetic grain size diagnostic (ARM/IRM1T) parameter decreases initially due to the preferential dissolution of fine-grained magnetite in the sulfidic zone (Z-I), and increases later in response to the authigenic formation of magnetite and greigite in methanic zone (Z-II). Distinct low S-ratio and χlf values in methanic zone of relict core is due to increased relative contribution from highly preserved coercive magnetic (titanohematite) grains of detrital origin which survived in the diagenetic processes. A strong linkage between occurrence of authigenic carbonates and greigite formation is observed. Two plausible mechanisms are proposed to explain the formation and preservation of greigite in Z-I and Z-II: 1) decline in methane flux due to massive hydrate accumulation within the active fault system and formation of authigenic carbonate crust in the sub-surface sediments hindered the supply of upward migrating fluid/gas; thereby limiting the sulfide production which preferentially enhanced greigite formation in Z-I and 2) restricted supply of downward diffusing sulfide by the carbonate layers in the uppermost sediments created a sulfide deficient zone which inhibited the pyritization and favoured the formation of greigite in the methanic zone (Z-II).

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Section: Introductionmentioning

confidence: 99%

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

et al. 2021

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“…Equatorial margins with water temperatures above 20 o C are dominated by high organic productivity, resulting in the deposition of vast carbonate platforms (Testa and Bosence, 1999;Wilson, 2002;2012). On these carbonate platforms, fluid-flow features and seafloor cold seeps are often linked to the presence of underlying hydrocarbon reservoirs or, instead, relate to the presence of significant volumes of methane and gas hydrates in near-surface strata (Hovland, 1990;Hovland et al, 1985Hovland et al, , 1994Série et al, 2012;Prinzhofer and Deville, 2013;Wenau et al, 2015). Cold seeps may stimulate abnormal 'oases' of biological activity, leading to growth of chemosynthetic communities that accumulate authigenic carbonates on the seafloor (Hovland and Judd, 1988;Hovland et al, 1994;Løseth et al, 2009;Dondurur et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Fluid flow through carbonate platforms as evidence for deep-seated reservoirs in Northwest Australia

Howarth

Alves

2016

Marine Geology

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Fluid flow features in carbonate platforms of the outer Browse Basin, Northwest Australia, are investigated using 3D seismic and borehole data. During the Cenozoic, the study area evolved from a carbonate ramp to a rimmed platform with isolated carbonate build-ups; as such it played a key role in focusing fluid on their buoyant flow to the surface. Statistical analyses of direct hydrocarbon indicators show fluid flow to be focused in elevated areas i.e., the greater is the focusing of fluid, the larger is the carbonate platform or isolated build-up. Locally, karst systems created regions of enhanced permeability through the evolving carbonate stratigraphy. Karstified horizons are located on the top of carbonate build-ups and platform clinoforms as fluid buoyantly concentrates and diffuses up into topographic highs. In turn, the putative migration of gas and fluid generated hypogenic karst systems, enhancing permeability in otherwise lower permeability rock. Based on the interpreted data, we suggest a pivotal relationship between the presence of carbonate build-ups (and karsts) in the Browse Basin and hydrocarbon accumulations at depth. Areas of elevated topography focus sub-surface fluid, enhancing the permeability of carbonate successions. In turn, focused fluid flow can lead to the generation of methanogenic carbonates, enhancing the growth of isolated build-ups and leading to further generation of elevated features. This grants the identification of similar features on seismic data from Northwest Australia, and other Equatorial margins in the world, as a valid proxy for the recognition of hydrocarbon accumulations below thick carbonate successions.

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“…Especially the Lower Congo Basin (LCB) has been investigated extensively with respect to the fluid flow systems in its upper and middle slope setting (Andresen & Huuse, ; Andresen et al, ; Gay et al, , ; Gay, Lopez, Cochonat, et al, ; Gay et al, ; Ho et al, ; Lucazeau et al, ; Maia et al, ; Serié et al, ). The lower slope and the salt front, however, received less attention although hosting abundant fluid flow phenomena (Olu et al, ; Ondréas et al, ; Sahling et al, ; Wenau et al, , ).…”

Section: Geological Settingmentioning

confidence: 99%

Active Seafloor Seepage Along Hydraulic Fractures Connected to Lateral Stress From Salt‐Related Rafting: Regab Pockmark, Congo Fan

Wenau

Spieß

2018

JGR Solid Earth

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Seafloor seepage is a widespread phenomenon within salt‐influenced basins as the deformation provides pathways for hydrocarbons to reach the seafloor. However, only minor attention has been given to the distal parts of such systems where the impact of salt tectonic deformation is relatively unpronounced. The stress put on the sedimentary column by moving salt on a continental margin may influence fluid flow systems even outside of the salt province. This stress may lead to overpressure formation within reservoirs and determine the orientation of overpressure‐induced fractures. Seepage in the Congo Fan has been discovered in such a distal position at the Regab pockmark, about 35 km west of the salt front, and its geology and biology have been studied extensively in recent years. We present high‐resolution multichannel seismic data from the Regab pockmark that reveal the underlying migration pathways from a buried channel flank 300 m below seafloor to the seafloor via hydraulic fractures in the sealing overburden. Local doming of the reservoir and the remobilization and uplift of sedimentary strata along the migration pathways are interpreted as the result of overpressure within the reservoir. The orientation of the hydraulic fractures is WSW‐ENE, and the fracture outline corresponds to the area of most intense seepage activity within the seafloor pockmark. Along with a similar orientation of other fractures in the vicinity, we propose that this alignment is due to the stress imposed on the sedimentary column in the fan by the seaward moving salt and rafting sedimentary packages of the salt province further east.

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Cold seeps at the salt front in the Lower Congo Basin II: The impact of spatial and temporal evolution of salt-tectonics on hydrocarbon seepage

Cited by 19 publications

References 71 publications

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

Fluid flow through carbonate platforms as evidence for deep-seated reservoirs in Northwest Australia

Active Seafloor Seepage Along Hydraulic Fractures Connected to Lateral Stress From Salt‐Related Rafting: Regab Pockmark, Congo Fan

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