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

Autor(es)

da Silva, Marcio Luiz ; Batezelli, Alessandro

• Tipo de documento: Artigo Científico
• Fonte: Journal of South American Earth Sciences; v. 152, p. 20-pg., 2024-12-05.

Resumo

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 Mar & iacute;lia 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 Mar & iacute;lia 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 Mar & iacute;lia Formation, was the most abundant and intense process and reflected periods with more arid conditions in the general context of the semi-arid palaeoclimate of the Late Cretaceous of the Bauru Basin. Calcification and silicification, processes that occurred in a conditioned, contemporary, or subsequent way in a precipitation-dissolution relationship, preceded the argilluviation process in the evolutionary framework of the Maastrichtian of the Basin. The argilluviation constitutes a process of superimposition over the calcification, favouring the formation of profiles with Btk, Bss, and Bt horizons. The argilluviation process indicates a high-water circulation rate in the profile, suggesting increased precipitation, desilication, leaching, and weathering. That process allows the advancement of pedoplasmation, the generation of textured coatings features, and the formation of grano-, mono- and porostriated b-fabrics at the micromorphological level. At a certain time, the calcification, silicification, and argilluviation coexisted, concomitantly or subsequently, during the variations of the semi-arid palaeoclimate that predominated in the Maastrichtian of the Bauru Basin. (AU)

• Processo FAPESP: 20/07997-4 - Explorando a diversidade dos dinossauros do Cretáceo Sul-Americano e suas faunas associadas
• Beneficiário: Max Cardoso Langer
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 15/17632-5 - Sedimentação e pedogênese das sequencias continentais Cretáceas das bacias Bauru, Sanfranciscana, Parecis e Neuquén.
• Beneficiário: Alessandro Batezelli
• Modalidade de apoio: Auxílio à Pesquisa - Regular