Work

Tracing distinct Late Eocene to Miocene weathering events: Insights from ferruginous duricrusts of the Brazilian Central Plateau

Year: 2025

Type: article

Abstract: Supergene minerals preserve a record of protracted exposure and weathering, rendering them valuable for understanding and reconstructing continental surface evolution and palaeoclimatic history. Determining when and how these minerals precipitated is fundamental for reconstructing the timing, nature, and controlling factor of weathering processes recorded in weathering profiles. In this study, we investigate a well‐preserved, 5‐m‐thick lateritic ferruginous duricrust developed on low‐relief uplands (~1100‐m elevation) of the Brazilian Central Plateau (BCP). The BCP represents a high‐standing postorogenic surface in southeastern Brazil, where numerous geochronological data provide a framework for regional comparison. Using (U–Th)/He geochronology on 100 haematite and goethite grains from nodular, pisolitic, and protopisolitic facies at three depths (~0.5 to ~5 m), we provide new constraints on the timing and possible controls of discrete weathering episodes in the BCP. Two successive weathering phases during the Cenozoic Era were identified. The older phase, recorded predominantly by haematite, occurred between ca. 35 and 24 Ma (Late Eocene–Oligocene) under seasonally contrasted tropical conditions. The younger phase, dated between ca. 17 and 8 Ma (Middle to Late Miocene), is characterized by widespread goethite precipitation under more humid and cooler climatic conditions that influenced the entire profile. These findings are consistent with (U–Th)/He datasets from nearby sites and confirm the spatial extent and synchronicity of these weathering events across the BCP. Comparison with geochronological data from different lithologies reveals a strong control of basement composition on weathering style and age distribution: duricrusts developed over igneous and sedimentary rocks yield well‐clustered ages, whereas profiles over complex lithologies, such as cangas formed on Banded Iron Formations, show scattered and broadly distributed ages. This study contributes to refining the understanding of Cenozoic weathering dynamics and long‐term landscape evolution across the BCP.

Source: Earth Surface Processes and Landforms

DOI: 10.1002/esp.70192