Relation between geomorphology and paleoclimate change of the Guiana shield
Université Paris-Saclay, CNRS, GEOPS, Orsay, France
Through the dating of hematite and goethite in Fe-duricrust sampled on high elevation surfaces from the Guiana Shield, Northern Brazil, we identified several phases of weathering and erosion that affected the topography. We identified four weathering phase not well characterized in time during the Jurassic to the Cretaceous, in three younger well characterized during the Eocene and the Early and the Late Miocene.
The Guiana shield is characterized by different remnant surfaces where weathering lateritiic soils have been developed (Fig. A). The indurated upper part of the lateritic profile, better known as a “duricrust”, is used as a stability marker through time. In order to reconstitute the Guiana shield geomorphological evolution through time we performed (U-Th)/He dating on iron oxide and hydroxids combined to their mineralogical analysis from
three surfaces at different elevation in the North of Brazil (UIR, SAN and LIL, Fig. B). We obtained 153 dating on hematite and goethite minerals which age distribution allow us to identify several weathering phases (Jurassic-Cretaceous? – Eocene – Early and Late Miocene, Fig. C) which can have both climatic or geodynamic origins as the rise of the Andes.
Results of (U-Th/He) datings on iron oxides in duricrusts of the Roraima area.