Evolution of the Angolan passive margin, West Africa, with emphasis on post-salt structural styles

Marton, L. GyöRgy; Tari, Gábor; Lehmann, Christoph

doi:10.1029/gm115p0129

Cited by 91 publications

(23 citation statements)

References 20 publications

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“…These coquina reservoirs are located in the Brazilian and West African continental margins, and were deposited on shallow lacustrine platforms created during the breakup of West Gondwana in the Early Cretaceous (Thompson et al, 2015). The Congo-Angola margin is a passive continental margin that resulted from the opening of the South Atlantic Ocean in the Early Cretaceous (Marton et al, 2000). Three main units can be distinguished in the sedimentary series of the lower Congo basin, which are related to three tectonic phases: prerift continental deposits (Jurassic), synrift fluviolacustrine deposits and sag phase (Lower Cretaceous), and postrift unit with large accumulation of salt (Middle Aptian) covered 10.1029/2019JB018434 by thick marine successions (Albian to present) (Savoye et al, 2009).…”

Section: Presalt Coquina From Offshore Congomentioning

confidence: 99%

Seismic Dispersion and Attenuation in Fluid‐Saturated Carbonate Rocks: Effect of Microstructure and Pressure

et al. 2019

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The frequency dependence of seismic properties of fully saturated rocks can be related to wave‐induced fluid flows at different scales. The elastic dispersion and attenuation of four fluid‐saturated carbonate rocks, with different microstructures, have been measured over a broad frequency range in the laboratory. The selected rocks were a presalt coquina from offshore Congo, an Urgonian limestone from Provence (France), and an Indiana limestone either intact or thermally cracked. The selected samples present a variety of pore types characteristic of carbonates, and their link with potential squirt flow dispersion was investigated. To cover a broad frequency range, forced oscillations (0.004 to 100 Hz) and ultrasonic (1 MHz) measurement techniques were performed in a triaxial cell, at various differential pressures, on the samples saturated by fluids of different viscosity. Both hydrostatic and axial oscillations were applied in order to get the different dynamic moduli. For all our samples, the drained/undrained transition and the squirt flow mechanisms were characterized experimentally, in terms of amplitude of dispersion, amount of viscoelastic attenuation, and frequency ranges. Biot‐Gassmann's theory was found to apply mainly at seismic frequencies (10–100 Hz). A potential correlation between pore type and possible squirt flow dispersion was investigated. Intragranular microporosity, with either a rimmed or uniform distribution, does not seem to generate any substantial dispersion. On the other hand, cracked intergranular cement and uncemented grain contacts seem to generate substantial squirt flow dispersion, at respectively seismic and sonic log frequencies.

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Section: Presalt Coquina From Offshore Congomentioning

confidence: 99%

Seismic Dispersion and Attenuation in Fluid‐Saturated Carbonate Rocks: Effect of Microstructure and Pressure

et al. 2019

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“…Despite uncertainties regarding the precise tectonic setting of Aptian salt deposition, there is a general consensus with regard to the water depth within which the salt was deposited. Except for Karner and Gambôa (2007) and Montaron and Tapponnier (2010), who suggested salt deposition in relatively deep waters (1.5-3 km), others support a shallow-water depositional environment based on the following evidence: (1) the stratigraphic context of the salt, above continental and/or lacustrine deposits and below shallow-water limestones (e.g., Szatmari et al, 1979;Moreira et al, 2007;Palagi, 2008); (2) subaerial exposure and karstification of the pre-salt sag sequence (Gomes et al, 2009); and (3) paleon tological evidence from the base of Aptian carbonates capping the salt on the Angolan margin, suggesting water depths of <500 m (Marton et al, 2000).…”

Section: Early Cretaceous Salt Of the South Atlantic: Previous Studiementioning

confidence: 99%

Dual tectonic-climatic controls on salt giant deposition in the Santos Basin, offshore Brazil

et al. 2018

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The stratigraphic evolution of ancient salt giants is controversial, mainly due to the absence of modern analogues that are of comparable scale and thickness and that occur in similar tectonic and hydrological settings. Fur thermore, investigating the original stratigraphy of salt giants is often made difficult by postdepositional flow and dissolution. Layered evaporites of the Ariri Formation in the Santos Basin (offshore Brazil), deposited during open ing of the South Atlantic Ocean, form part of one such salt giant. Despite being well imaged in seismic data and being penetrated by more than 50 boreholes, little work has explored the stratigraphic architecture of this unit and what this may tell us about the syndepositional tectonics, basin physi og raphy, and variations in climate and sea level. Here we integrate threedimen sional seismic and borehole data from the São Paulo Plateau, deepwater Santos Basin, to document the intrasalt stratigraphy of the Ariri Formation. Our analysis suggests a combination of an arid paleoclimate, lowamplitude local sealevel variations, and basin physiography controlled the deposition of this thick (2.5 km) salt sequence during a short time span (<530 k.y.). The Ariri Formation records at least 12 cycles of basin desiccation and filling, re sulting in the deposition of four key units (A1-A4) that have a distinct com position and therefore seismic expression; i.e., lowfrequency, transparent, chaotic seismic facies represent relatively haliterich (>85%) units (A1 and A3), whereas highfrequency, highly reflective seismic facies represent still relatively haliterich (65%-85% halite) units, but contain relatively high pro portions (15%-35%) of anhydrite and bittern salts (i.e., K and Mgrich salts; A2 and A4 units). Our findings suggest that during salt deposition the Santos Basin was characterized by a series of subbasins of varying water depth; as a result the thickness and composition of these units vary laterally and are spa tially related to structural domains. Overall, thinner salt (~1.8 km) and higher anhydrite net thickness (~350 m) occur toward the structurally high Sugar Loaf domain, compared to flanking, structurally lower domains where the mean salt thickness is >2.2 km and anhydrite net thickness are less (~180 m). In addition, stratigraphic variations in the basin suggest that seawater incur sions came from the south, through the São Paulo and Walvis Ridges; conse quently, more anhydrite was deposited closer to the ridge, whereas more bit tern salts were deposited in more distal and restricted locations. The results of our study, although based on an analysis of Aptian salts preserved offshore Brazil, offer valuable insights into the sedimentology and stratigraphic archi tecture and evolution of other ancient salt giants.

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“…Gravity-driven thin-skinned salt tectonic activity is typically characterized by linked upslope extension and downslope contraction (e.g., Brun and Fort, 2011;Rowan et al, 2004), which significantly affect the tectonostratigraphic evolution of salt-bearing passive margins (e.g., the South Atlantic margins; Marton et al, 2000;Mohriak et al, 2008) and intracratonic rift basins (e.g., the Central Graben, North Sea; Karlo et al, 2014). Sediment loading and margin tilting associated with thermal subsidence and tectonic activity are two major controls of gravity-driven salt tectonics (e.g., Brun and Fort, 2011;Rowan et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Progressive tilting of salt-bearing continental margins controls thin-skinned deformation

Warsitzka

Rosenau

et al. 2019

Geology

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As a primary driving force, margin tilting is crucial for gravity-driven thin-skinned salt tectonics. We investigated how instant versus progressive margin tilting mechanisms influence salt tectonics using an analogue modeling setup where tilting rate could be controlled. Instant tilting resulted in initially high deformation rates, triggering widely distributed upslope extension and downslope contraction. Later, both the extensional and contractional domains migrated upslope as early extensional structures were successively deactivated, while deformation rates decreased exponentially. In contrast, progressive tilting led to downslope migration of the extensional domain by sequentially formed, long-lived normal faults. Contraction localized on a few, long-lived thrusts before migrating upslope. We attribute the distinct structural evolution of thin-skinned deformation, especially in the extensional domain, in the two tilting scenarios mainly to mechanical coupling between the brittle overburden and underlying viscous material. The coupling effect in turn is largely controlled by the deformation rate. By demonstrating the spatiotemporal variations of structural style and kinematic evolution associated with instant versus progressive tilting, we suggest that such variation is identifiable in nature and therefore can provide a new way to analyze margin tilting histories.

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Evolution of the Angolan passive margin, West Africa, with emphasis on post-salt structural styles

Cited by 91 publications

References 20 publications

Seismic Dispersion and Attenuation in Fluid‐Saturated Carbonate Rocks: Effect of Microstructure and Pressure

Seismic Dispersion and Attenuation in Fluid‐Saturated Carbonate Rocks: Effect of Microstructure and Pressure

Dual tectonic-climatic controls on salt giant deposition in the Santos Basin, offshore Brazil

Progressive tilting of salt-bearing continental margins controls thin-skinned deformation

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