Structure of the ocean–continent transition, location of the continent–ocean boundary and magmatic type of the northern Angolan margin from integrated quantitative analysis of deep seismic reflection and gravity anomaly data
L. Cowie, R. M. Angelo, N. Kusznir, G. Manatschal, B. Horn, 2017. "Structure of the ocean–continent transition, location of the continent–ocean boundary and magmatic type of the northern Angolan margin from integrated quantitative analysis of deep seismic reflection and gravity anomaly data", Petroleum Geoscience of the West Africa Margin, T. Sabato Ceraldi, R. A. Hodgkinson, G. Backe
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The crustal structure and distribution of crustal types on the northern Angolan rifted continental margin have been the subject of much debate. Hyper-extended continental crust, oceanic crust and exhumed serpentinized mantle have all been proposed to underlie the Aptian salt and the underlying sag sequence. Quantitative analysis of deep seismic reflection and gravity anomaly data, together with reverse post-break-up subsidence modelling, have been used to investigate the ocean–continent transition structure, the location of the continent–ocean boundary, the crustal type and the palaeobathymetry of Aptian salt deposition. Gravity inversion methods (used to give the depth to the Moho and the crustal thickness), residual depth anomaly analysis (used to identify departures from oceanic bathymetry) and subsidence analysis have all shown that the distal Aptian salt is underlain by hyper-extended continental crust rather than exhumed mantle or oceanic crust. We propose that the Aptian salt was deposited c. 0.2 and 0.6 km below global sea-level and that the inner proximal salt subsided by post-rift (post-tectonic) thermal subsidence alone, whereas outer distal salt formation was synrift, prior to break-up, resulting in additional tectonic subsidence. Our analysis argues against Aptian salt deposition on the Angolan margin in a 2–3 km deep isolated ocean basin and supports salt deposition on hyper-extended continental crust formed by diachronous rifting migrating from east to west and culminating in the late Aptian.
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The West Africa margin, formed by the progressive separation of the South American and African continents, has enjoyed a rich and varied exploration history and become a significant hydrocarbon-producing region. The amalgamation of hydrocarbon exploration approaches and imaginative ideas, leveraged with modern technologies, is yielding significant scientific and economic successes within the region.
The main objective of this Special Publication is to provide an overview of the advancement in understanding of the crustal structure, tectonic evolution and Mesozoic to Cenozoic stratigraphy of the West Africa margin both onshore and offshore, with a particular focus on the petroleum geology.