Artículos de revistas
Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia
Fecha
2018-02-20Registro en:
Chemical Geology, v. 479, p. 136-150.
0009-2541
10.1016/j.chemgeo.2018.01.004
2-s2.0-85041602816
2-s2.0-85041602816.pdf
Autor
Université Pierre et Marie Curie
Université Paris-Saclay
Federal University of Rio Grande do Sul
Pontifícia Universidade Católica de Minas Gerais - Pós Graduação de Geografia
Federal University of Goias
Universidade Estadual Paulista (Unesp)
Institución
Resumen
This study focuses on the dating of millimetric pisoliths from ferruginous duricrusts located in central Amazonia (Brazil), by coupling detailed mineralogy and two relevant dating methods: (i) (U-Th)/He analysis of goethites by mass spectrometry; (ii) analysis of radiation-induced defects of kaolinites embedded in duricrusts by electron paramagnetic resonance spectroscopy (EPR). Three samples collected at different elevations in the landscape were selected. The goethite corrected ages range from 1.1–15.2 Ma and consistently increase with elevation. EPR was performed on kaolinites after several cycles of a deferration procedure. Considering extreme geochemical scenarii, the ages of kaolinites are 1.7–7.1 Ma for a closed system and 4.0–16.7 Ma for an open system with 100% Rn loss. Ages of goethites and kaolinites are close, in the limit of the uncertainty of the methods. They show important periods of duricrust formation at Middle Miocene and at Late Miocene/Pliocene. Data allow the estimation of lowering rates between 3 and 8 m/Ma, in agreement with independent data available in the literature for the central Amazonia region or even for erosion of other cratons in the world. The two dating methods can be compared on common duricrust samples. By revealing single or multi-step weathering/erosion episodes related to relictual paleosurfaces, they also bring promising contributions to an advanced knowledge of ancient and complex lateritic geosystems.