Meso-Cenozoic Source-to-Sink of the African margin of the Equatorial Atlantic
Résumé
The objective of the Transform Source to Sink Project (TS2P)
is to link the dynamics of the erosion of theWest 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.
For the Cenozoic, mapping and regional correlation of dated lateritic
paleo-landscape remnants allows us to reconstruct two physiographic
configurations of West Africa. These geometries show
that the present-day drainage organization stabilized by at least
29 Myrs ago (probably by 34 Myr) revealing the antiquity of the
Senegambia, Niger and Volta catchments toward the Atlantic as
well as of the marginal upwarp currently forming a continental
divide. The drainage rearrangement that lead to this drainage
organization was primarily enhanced by the topographic growth
of the Hoggar swell and caused a major stratigraphic turnover
along the Equatorial margin of West Africa. Elevation differences
between paleo-landscape remnants give access to the spatial and
temporal distribution of denudation for 3 time-increments since
45 Myrs. From this, we estimate the volumes of sediments and
associated lithologies exported by the West African Craton toward
different segments of the margin, taking into account the type of
eroded bedrock and the successive drainage reorganizations.
For the Mesozoic, we produced paleogeographic maps at the scale
of West Africa spanning the continental domain and offshore
basins since 200 Ma. Mapping spatial and temporal distribution
of domains either in erosion (sources) or in accumulation
(sinks) document the impact of the successive rifting of Central
and Equatorial Atlantic on the physiography of the area. We use
low temperature thermochronology dating along three transects
perpendicular to the margin (Guinea, Ivory Coast and Benin) to
determine periods of maximum denudation.
We compare these data to accumulation histories in passive margin
basins and discuss their stratigraphic expression according to
the type of margin segment they are preserved in.