Dating of kaolinites by EPR to unravel the evolution of Amazonian laterite profiles

Kaolinite is a finely divided phyllosilicate which is widespread at the Earths’ surface. It is formed by intense weathering of aluminous silicates such as feldspars or micas and is extremely stable at Earth’s surface temperature conditions. Electron paramagnetic resonance (EPR) spectroscopy dating of kaolinite is a promising geochronological method for this clay mineral which cannot be dated by conventional radiometric [1]. Combined to (U-Th)/He dating of iron oxides and oxyhydroxides, it thereby enables deep insights into past and current surface processes and paleoclimatic evolution.
In this contribution we give an overview on the EPR method and its challenges and we present kaolinite EPR data from 28 samples deriving from two deep lateritic profiles developed throughout the Cenozoic on top of Paleoproterozoic schists of the Guiana shield. Comparison with geochronological constraints from (U-Th)/He dating on iron oxides and oxyhydroxides [2] of the same profiles allows a contextualization and a discussion of the ages, which enables a deeper insight into the evolution of the lateritic profiles.

[1] Allard, Thierry, et al.(2025) "EPR dating of clay minerals formation through geological times: benchmarking from the Quaternary to the Neoproterozoic era." American Journal of Science (325), 6

[2] Heller, Beatrix M., et al.(2022) "Reading the climate signals hidden in bauxite." Geochimica et Cosmochimica Acta (323), 40-73.