The aim of the RECA project is to combine chronometric, weathering and climatic proxies developed in the recent years in order to build a comprehensive and predictive scenario of laterite formation and evolution. We will concentrate our effort on geodynamically stable Guyana Shield and Central Amazonia regions, where laterites formed through the whole Cenozoic and can be associated with major geomorphological units.
This ambitious multidisciplinary project proposes, for the first time, to perform absolute dating of lateritic duricrusts associated to the episodes of planation in the South American subcontinent. We will date mineralogically well-identified populations of iron oxi(hydroxi)des (hematite, goethite) and clays (kaolinites), as illustrated in the following figure.
The timing of duricrust formation will then be related to paleoclimatic conditions (temperature, rainfall) derived from a combination of geochemical or mineralogical indices and proxies :(i) at global scale, through, e.g., the known continental drainage curves;(ii) at a more regional scale through the intensity of weathering, the ratio hematite/goethite or O and H isotope systems of kaolinite and iron oxi(hydroxi)des.
A second task will associate non-conventional Li, Si and Fe isotopic methods that will help to decipher the evolution of weathering processes linked to the various stages of laterite formation. Coupling weathering budget and the ages of weathering profiles will yield average weathering and erosion rates, allowing comparison with other weathering environments or paleo-environments at the Earth surface.