MESO-CENOZOIC ACCUMULATION HISTORY OF THE AFRICAN MARGIN OF THE EQUATORIAL ATLANTIC

Artiom Loparev (1) , Delphine Rouby (1) , Chardon Dominique (1) , Massimo Dall’asta (2) , François Guillocheau (3) , Cécile Robin (3) , Et Al.

1 GET - Géosciences Environnement Toulouse
2 TOTAL S.A.
3 GR - Géosciences Rennes

The objective of the Transform Source to Sink Project (TS2P) is to link the dynamics of the erosion of the West African Craton to the offshore sedimentary basins of the African margin of the Equatorial Atlantic at geological time scales. This margin, alternating transform and oblique segments from Guinea to Nigeria, shows a strong structural variability in the margin width, continental geology and relief, drainage networks and subsidence/accumulation patterns. We analyzed this system combining onshore geology and geomorphology as well as offshore sub-surface data. We defined offshore basins stratigraphic architectures of the 3 sub-basins (Sierra Leone /Liberia, Ivory Coast and Ghana / Togo / Benin) and used these to establish their terrigeneous accumulation histories including the whole depositional system (from the shoreline to the most distal deposits onto the oceanic crust). We then corrected these from remaining porosity after compaction as well as in-situ production (mainly carbonates) established from well-data. We included uncertainties related to the time to depth conversion, biostratigraphy, porosity and in-situ production corrections. We discuss our results in terms of Saddler effect for the most recent time periods. Accumulations in the three basins show increased rates during the Cenomanian, Maastrichtian and Oligocene. We compare these accumulation histories to paleogeographic maps established at the scale of West Africa spanning the continental domain and offshore basins since 200 Ma and discuss their source to sink implications during the opening of Equatorial Atlantic. The Cenomanian accumulation may be related to the erosion of the remaining rift-shoulder following continental break-up. The Maastrichian increase in accumulation could be related to either the tectonic inversion of western Africa at the time or to climatic change affecting erosion capacity in the continental drainage area. The Oligocene peak is contemporaneous of a major drainage reorganization in West Africa following the rise of the Hoggar and the major sea-level fall at the time. Some uncertainties remain to be addressed in the Ghana / Togo / Benin basin on the contribution of the neighboring Niger Delta developing throughout the Neogene as well as the shredding effect of Mass Transport Deposits affecting this segment of the margin.

Domaines: Stratigraphie; Géomorphologie

Artiom Loparev, Delphine Rouby, Chardon Dominique, Massimo Dall’asta, François Guillocheau, et al.. MESO-CENOZOIC ACCUMULATION HISTORY OF THE AFRICAN MARGIN OF THE EQUATORIAL ATLANTIC. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.553, 2017, Abstract book. ⟨insu-01718042⟩