The chronology of paleoenvironment: (U-Th)/He dating and δ13C of lateritic duricrusts from the Cuesta and Paulista Peripheral Depression sectors of São Paulo State, southeastern Brazil

Abstract

Lateritic duricrusts are key records of continental weathering processes, landscape evolution, and paleoclimatic conditions in tropical regions. This study aims to assess the timing and paleoenvironmental conditions of lateritic duricrust formation from sectors of the Cuesta and Paulista Peripheral Depression of São Paulo State, southeastern Brazil. The relationship between (U-Th)/He ages and δ¹³C signatures across different planation surfaces was established in hematite- and goethite-bearing samples from weathering profiles on the Cuesta, Urucaia, and Rio Claro Surfaces. Our results show that lateritic duricrusts on the Urucaia and Cuesta Surfaces, located at higher elevations, are hematite-predominant, whereas those on the Urucaia and Rio Claro Surfaces, situated at lower elevations, are goethite-predominant. The δ¹³C values indicate the predominance of C4 vegetation during the formation of lateritic duricrusts, associated with regional climatic conditions and the C3–C4 vegetation shift in the Late Miocene. In soils, δ¹³C values may reflect the effects of land use intensification. The (U-Th)/He ages of the lateritic duricrusts suggest three distinct formation events: Miocene (23–5.3 Ma), Pliocene (5.3–1.6 Ma), and Pleistocene (< 1.6 Ma), with a clear relationship between the chronology of planation surfaces and elevation. The results indicate that lateritic duricrusts on the Cuesta Surface yielded ages ranging from 18 ± 2 Ma to 3 ± 1 Ma, spanning the Miocene and Pliocene. On the Urucaia Surface, ages varied from 20 ± 2 Ma to < 1 Ma, encompassing both the Miocene and Pleistocene. In contrast, the relatively young Rio Claro Surface presented ages < 1 Ma, corresponding to the Pleistocene. The complexity of tectonic and climatic events over time resulted in an overlap of ages, reflecting the formation of lateritic duricrusts in different periods, as evidenced by the Miocene ages on the Urucaia Surface and Pliocene ages found on the Cuesta Surface.