Argilluviation, calcification, and silicification in palaeosols from the Late Cretaceous of Brazil

• Published in: Journal of South American earth sciences 2025-02, Vol.152, p.105285, Article 105285
• Main Authors: Silva, Márcio Luiz da, Batezelli, Alessandro
• Format: Article
• Language: English
• Subjects: Argillic features; Carbonate-silica association; Micromorphology; Pedogenic carbonates; Semi-arid climate
• ISSN: 0895-9811
• DOI: 10.1016/j.jsames.2024.105285

Palaeosols are soils that have formed in past landscapes. They are used in palaeoenvironmental analyses and reconstitutions, as in stratigraphic correlations, because they indicate surface stability and represent moments of pause in erosion and deposition. In the Marília Formation (Upper Cretaceous of Bauru Basin), the palaeosols exhumed and buried were developed on sandstones and present argillic (Btk, Bt and Bss), hydromorphic (Cg), and calcic (Bk) horizons with different cementation degrees. During the Maastrichtian of the Bauru Basin, these palaeosols were conditioned by calcification, silicification, and argilluviation. The objective of the study was to analyse the relationship and palaeoenvironmental significance between the processes of argilluviation, calcification, and silicification in palaeosols developed in the proximal, medial, and distal zones of distributive fluvial systems (DFS) of the Upper Cretaceous of Brazil. Eleven sections (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, and S11) were described, comprising forty-three profiles. The description of facies and identification of architectural elements, characterisation of palaeosols, and micromorphological and geochemical analyses were performed according to the specialised literature. We identified well-drained (Bt horizon) and poorly drained or hydromorphic (Cg horizon) pedotypes that represent alternated periods of drier (Bkm horizon) and higher humidity (Bss horizon). The profiles were classified as Luvisols (Bt and Btk horizons), Calcisols (Bk and Ck horizons), Arenosols (C-horizons), and Vertisols (Bss-horizons). The palaeosols of the Marília Formation, Maastrichtian of Bauru Basin, developed in a distributive fluvial system (DFS) dominated by braided rivers and ephemeral lakes. The palaeosols with Bk, Btk, Bss, Bg, and Bt horizons suggest climate semi-arid during the Maastrichtian, with changes in precipitation and evapotranspiration patterns. Calcification and argilluviation were the main formation process responsible for the genesis and evolution of palaeosols during the Maastrichtian. Silicification, responsible for forming silcretes in some profiles, occurred subsidiary to the calcification process in semi-arid climate conditions and may have been affected by diagenetic processes. Calcification, responsible for the diversity of calcretes in the Marília Formation, was the most abundant and intense process and reflected periods with more arid conditions in the general context of the sem