What we do

Projects

Our group working hypothesis of the project is that laterite profiles record the long-term evolution of both climate (temperature, rainfall) and rates of weathering/erosion processes. We are concentrating our effort on the Guyana Shield and the Central Amazonia, where different lateritic sites have been identified according to their geomorphologic situation and their potential ancient age, i.e. up to a few tens or hundreds of million years. Another site in Namibia has also been investigated.
Our Way

Used methodologies

The first main objective will be to perform absolute dating of lateritic formation and evolution to date mineralogically well-identified populations of iron oxides and kaolinites by using (U-Th)/He and Electron Paramagnetic Resonance methods. These recently developed methods are appropriate because they can be applied to the most common secondary minerals found in laterites and span geological time scales. The inherent complexity of weathering materials, which may contain different populations of a same secondary mineral related to distinct stages of lateritization will be taken into account. The first objective is to provide a robust chronology lateritic formation that will constitute a reference for South America.
The second main objective is to determine the paleoclimatic conditions (temperature, rainfall) that led to the development of thick laterites, from a combination of geochemical or mineralogical indices and proxies. We are studying the weathering though different methodologies like the intensity of weathering assessed by the Chemical Index of Alteration; the ratio hematite/goethite that was proposed recently as a proxy for rainfall; and the O and H isotope composition of kaolinite and iron oxides that trace the conditions of formation including temperature. An exploratory task will associate "non-conventional" Li, Si and Fe isotopic systems that will help to decipher the specific weathering processes linked to the various stages of laterite formation. A final objective of the RECA project is to couple weathering budget with profile ages will provide average weathering and erosion rates, allowing comparison with other weathering environments or paleo-environments at the Earth surface.