Iron Isotopes Reveal Fe Export Driven by Change of Tropical Weathering Regime
Z. Fekiacova‐Castanet, B. Heller, D. Guinoiseau, J. Bouchez, A. Duvivier, S. Cornu, A. Guihou, C. Quantin, T. Allard, S. B. Riffel, P. Deschamps, C. GautheronAbstract
Unraveling paleoenvironmental signals recorded in laterites is crucial for quantifying weathering‐driven elemental fluxes at the Earth's surface. New stable iron isotope data (δ 56 Fe), combined with (U‐Th)/He ages in Fe‐oxides from a ferruginous duricrust from French Guiana, reveal the response of Fe hosted in laterite to past changes in weathering intensity. The δ 56 Fe values increase with decreasing age, with a pronounced shift at around 6 Ma reflecting a change from a ferruginous laterization to a bauxitization regime. This shift indicates a transition from a weathering regime characterized by Fe redistribution within the laterite to one featuring significant Fe loss and redox processes. Isotope mass‐balance modeling reveals that intensified weathering during the bauxitization phase led to the loss of 35%–70% of Fe from the duricrust. Our work highlights the importance of lateritic profiles as environmental archives.