SOURCE TO SINK STUDY AT CONTINENT-SCALE (AFRICA): MANTLEDYNAMICS CONTROLS AND IMPLICATIONS FOR THE SEDIMENTROUTING SYSTEM

International audienceA source to sink approach was performed at the scale of a continent – African the frame of theTopoAfrica project, with three main objectives (1) the characterization of the relative importance ofdeformation (uplift) and climate (precipitation) (2) the quantification of the deformation, its nature and causes,(3) the effect of those deformations on the past African topography and on the sediment routing system. Wemainly focused on Western, Central and Austral Africa, characterized by anorogenic relief (plains andplateaus) record of long (several 100 km) to very long (several 1000 km) wavelength deformations,respectively of lithospheric and mantle origin.The sink measurement was based on the seismic stratigraphic analysis of numerous regional seismiclines (from the upstream part of the margin to the abyssal plain) merge of industrial and academic data,calibrated in ages and lithologies on reevaluated wells to get the best possible ages. Volumes measuredbetween successive time-lines, were compacted for a comparison with solid eroded volumes. Uncertaintieswere calculated (including ages, time-depth conversion law, porosities...) using the Volume Estimatorsoftware.The source study was performed using dated stepped planation surfaces (etchplains and pediplains) keymorphological features of Africa mappable at catchments-scale. During Late Paleocene to Middle Eocenetimes, Africa experienced a very hot and very humid climate leading to the formation of an African-scaleweathering surface (etchplain) known as the African Surface. This surface today deformed and preserved aslarge plains, domes or plateaus, can be used as (1) a marker of the very long wavelength deformations and (2)a reference level to measure eroded volumes since 40 Ma. Some other younger planation surfaces were alsomapped of (1) Early Oligocene and (2) Late Miocene ages.(1) Deformation (uplift) is the dominant control of the sediment budget. Climate (precipitation) changesonly enhance or inhibit a deformation-controlled flux.(2) The sources of clastic sediments are or closed marginal bulges or far field domes due to mantledynamics with by-pass (transfer zones) along long-lasting polygenic surfaces located in between.(3) Africa-scale deformations occurred during Late Cretaceous (Turonian-Coniacian) and around theEocene-Oligocene boundary with a break contemporaneous of intense chemical erosion from 75 Ma andmainly from 65 to 40 Ma. Most of the African relief and topography are younger than 40 Ma. Late Cretaceousrelief are only preserved in the Guinea Rise and the Southern African Plateau