Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia

Abstract

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.

Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)

“…Bird et al, 1993;Muller et al, 1995;Girard et al, 2000Girard et al, , 2002Balan et al, 2005Balan et al, , 2007Fritsch et al, 2011). Absolute dating of laterites from previous studies revealed that they have Mesozoic and Cenozoic ages in India, Africa or South America (Vasconcelos et al, 1994(Vasconcelos et al, , 2015Balan et al, 2005;Bonnet et al, 2016;Allard et al, 2018). In case of the Amazon basin, absolute age records were consistent with those obtained from weathering mass balance calculations (about ten million years old, Lucas, 1989).…”

“…The occurrence of generations of other secondary minerals within a single weathering profile has also been reported for Mn oxides (Vasconcelos, 1999;Beauvais et al, 2008;Bonnet et al, 2016) and iron oxides (e.g. Allard et al, 2018). These generations are currently interpreted as a clue of an episodic evolution of the weathering profile, with the formation of a large amount of secondary minerals coinciding with short weathering pulse induced by optimum climatic conditions (Vasconcelos, 1999;Retallack, 2010;Bonnet et al, 2016).…”

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

“…Figure 10 depicts a typical lateritic profile and its mineralogical compartments, capped by a strong Fe-enriched weathering horizon, referred to as a duricrust horizon. Mesozoic to Cenozoic laterite chronology has enhanced our understanding of soil formation and opens new research (Allard et al, 2018;Monteiro, Vasconcelos, Farley, & Lopes, 2018;Shuster et al, , 2012. (e) Temperature variations based on δ 18 O isotopic composition over the Cenozoic (Zachos et al, 2001).…”

“…Tectonics avenues as laterites also record past climatic conditions (e.g., Vasconcelos et al, 2015) or landscape evolution (e.g., Bonnet et al, 2016). 40 Ar-39 Ar analysis of Mn oxides, and more recently, hematite and goethite He geochronology from laterites inform the timing, tempo, and geochemical processes of laterite formation via past climate change (Allard et al, 2018;Deng et al, 2017;Monteiro et al, 2014;Monteiro, Vasconcelos, Farley, & Lopes, 2018;Shuster, Vasconcelos, et al, 2005;Vasconcelos et al, 1994;Vasconcelos et al, 2013). For example, Figure 10d presents a compilation of published supergene goethite and hematite (U-Th)/He dates from northern Brazilian laterites.…”

Weathering history and landscape evolution of Western Ghats (India) from 40 Ar/ 39 Ar dating of supergene K–Mn oxides

“…Much work was done for dating weathering profiles on most continents of the tropical belt, using 40 Ar/ 39 Ar dating of K-rich Mn oxides (e.g., Vasconcelos, 1999;Vasconcelos et Conroy, 2003;Beauvais et al, 2008;Bonnet et al, 2016;Deng et al, 2016;Li et al, 2007;Riffel et al, 2015), or (U-Th)/He dating of iron oxy-hydroxides (e.g., Shuster et al, 2005;Vasconcelos et al, 2013;Monteiro et al, 2018;Allard et al, 2018). For instance, ages of cryptomelane formed in situ in lateritic regolith of West Africa and Brazil allowed calibrating continental denudation over geological time scales (Beauvais and Chardon, 2013;Vasconcelos and Carmo, 2018).…”