Tropical Weathering History Recorded in the Silicon Isotopes of Lateritic Weathering Profiles

Damien Guinoiseau, Zuzana Fekiacova, Thierry Allard, Jennifer L. Druhan, Etienne Balan, Julien Bouchez

Research output: Contribution to journalArticlepeer-review

Abstract

Under tropical climates, mineral assemblages composing lateritic weathering profiles offer precious records of past weathering conditions. Silicon (Si) isotope signatures in the clay fractions of a deep lateritic profile in central Amazonia, Brazil, in combination with previously determined kaolinite ages, suggest that the surrounding region underwent two major weathering episodes, distinct in their intensity. The first episode (ca. 35–20 Ma) of moderate intensity produced well-crystallized kaolinites from the parent sediment with limited Si isotope fractionation. A more recent (8–6 Ma) and shorter phase caused the replacement, from top to bottom of the profile, of the first kaolinite generation by a new population characterized by higher crystallographic disorder and stronger Si isotope fractionation, suggesting weathering under conditions of rapid water percolation. These inferences are supported by results from an isotope-enabled reactive transport model, and they are consistent with paleoclimatic and paleogeographic evidences recorded over the Amazon Basin.

Original languageEnglish (US)
Article numbere2021GL092957
JournalGeophysical Research Letters
Volume48
Issue number19
DOIs
StatePublished - Oct 16 2021

Keywords

  • Amazon Basin
  • laterite
  • silicon isotopes
  • weathering intensity

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences

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