PAst deNudation raTEs in the tRopical Africa – PANTERA

Denudation is a key parameter in controlling the dynamics of the Earth’s surface and understanding "how, when, and where" denudation rates respond to climate change is critical. One of the major climate changes that have occurred in the past is the global cooling that took place during the late Neogene. It is characterized by the onset of the Quaternary glaciations and its oscillations and represent one of the most rapid and significant cooling at geological timescales. Synchronously with this cooling, over the last 3-4 Ma, sediment volume exported in marine and continental basin display an apparent 3-fold increase. Because it has been observed in various tectonic settings in both glaciated and non-glaciated regions, one research hypothesis is that this denudation increase is linked to the onset of the high-frequency Quaternary climate cycles, and not to erosion by the glaciers themselves. However, the reality of this Pleistocene denudation enhancement still needs to be confirmed. Methodological bias may explain part of this increase, and the signal linked to the climate oscillations themselves may have been obliterated by tectonics and/or glacier dynamics in some records. Unraveling this signal needs accurate and robust quantification of past denudation rates in regions that were neither glaciated nor tectonically active during the Quaternary.
The goal of the PANTERA project is therefore to test this research hypothesis by providing a reliable, detailed and direct record of denudation during the late Neogene, in a region that has been neither covered by ice nor significantly tectonically active during the Quaternary: the western tropical Africa. To achieve these objectives the project will reconstruct past denudation rates during the last 10 Ma, with a Pleistocene focus, from the analyzes of cosmogenic nuclide concentrations (14C, 10Be, 21Ne, 26Al) in present and ancient sediments shed from three main river basins -from North to South, the Ogooue, the SE Congo and the SW Madagascar. We will analyze sediments sampled in offshore cores drilled by SHOM and IFREMER. We will also analyze several continental archives including inland Neogene outcrops, Pleistocene fluvial terraces, cores drilled in Neogene sediments in the center of the Congo basin. As a benchmark, we plan to constrain the recent denudation rates, by analyzing cosmogenic nuclide concentrations (10Be, 21Ne, 26Al) in modern river sand. The goal of the project is to provide denudation rates record at the short time scale (0-900ka) and at the long time scale (0-10Ma) in order to study the impact, on the denudation rates of the Quaternary cycles and the onset of glaciations, respectively. Our project also includes a reconstruction of the rock source and uplift history using U-Pb/U-Th/4He double dating on zircon grains and other geochemical analyses. It will also quantitatively study sedimentary transfer processes via the analyses of muttilpel nuclide together and landscape evolution models incluidng a formulation for clasts transports with calculation of the comsogenic nuclide evolution. The PANTERA project will provide critical results to better understand the impact of the Quaternary glaciations on denudation rates. Its scientific reach goes also beyond and should raise the interest of a large audience either interested in sedimentary processes, tectonics, paleoenvironnemental changes in Africa and anthropogenic impact.