Reading the climate signals hidden in bauxite

The dynamics of tropical weathering through time with the formation and long-term evolution laterite associated climatic geodynamic forcing is still a poorly explored issue. To better access this, we focused on lateritic-bauxitic duricrusts from well-explored, 300 m high Kaw mountain in northeastern French Guiana. Macroscopically homogeneous Fe (oxyhydr)oxides-rich subsamples were separated 10 bulk samples. Bulk- investigated by mineralogical geochemical analyses (U-Th)/He geochronology. samples show large heterogeneity macro- microscopic scale reflecting different stages duricrust processes dissolution (re)precipitation (oxyhydr)oxides. 284 ages obtained for goethite α-(Fe, Al)OOH hematite α-Fe2O3 range 30.5 ± 3.1 to < 0.8 Ma variability within sample. oldest Al-poor precipitated since 30 formed while kaolinite was stable. Precipitation Fe-minerals increased ∼ 14–12 but happened under ferruginous lateritic, non-bauxitic conditions. minerals, Al-substitution goethite, overall enrichment Th, as well gibbsite precipitation indicate an intensification shift towards bauxitic conditions end Miocene. Th-, U-, Al-rich phases this late episode intense partially replace oldest, often Th- U-poor leading considerable age spread. We claim that intensified weathering, which had its peak at ca. 6–2 Ma, corresponds bauxitization lateritic cover mountain. Our proposed model lateritization least Miocene provides new constraints timescale intensity onset Guiana (Kaw region) potentially older than possibly synchronous development bauxites neighboring countries, differences Paleogene might be due drainage capacities parental material. Late Neogene suggests regional increase precipitations linked incision owing local uplift. Finally, confirm detailed combination geochronological results coupled improves our understanding placing into temporal framework.