Calcretes and travertines from the Palaeocene Itaboraí Basin as evidence of the early evolution of the Southeastern Brazil Continental Rift

• DOI: 10.1111/sed.12788
• Publication Date: 2020-08-03T10:37:14Z
• Authors: Paula Braga Adler; Luiz Fernando De Ros; Kátia Leite Mansur; André Luiz Ferrari; Luiz Alberto Fern...; Alcides Nóbrega Sial
• Keywords: Alluvial fan

Abstract The Itaboraí Basin, located in Rio de Janeiro state, is the smallest segment of Southeastern Brazil Continental Rift, and first to open, during Palaeocene. Numerous studies focused on its fossiliferous content, but few systematically approached depositional diagenetic processes products. A detailed description basal sedimentary deposits that remained after nearly fifty years exploitation for cement production allowed an interpretation initial tectono‐sedimentary conditions responsible formation Basin. macroscopic petrographic outcrops well core samples calcretes travertines correspond basin infill was integrated with stable isotope geochemistry. were separated into different facies (powdery, nodular, massive, platy, laminated brecciated), classified according morphogenetic stages. Their main microscopic features include nodules, contraction cracks, vadose pisoliths, rhizocretions, infiltrated clays, corroded grains, expanded micas clay aggregates bimasepic–plasmic microfabric. exhibit diverse forms abiotic calcite crystal (plumose, lamellar prismatic‐radial, spherulitic) a minor proportion microbial microcrystalline precipitates (bacterial shrubs). Tectonically active periods, characterized by intense fault movements associated humid climate, promoted hydrothermal activity, modification alluvial calcrete ascending fluids. During periods tectonic stability under arid semi‐arid exposed influenced pedogenetic processes. Sulphide‐rich carbonate breccias occur zone at southern border. characterization extremely opening early evolution Basin essential understanding Rift. Additionally, some isotopic similarities carbonates vast South Atlantic Aptian Pre‐Salt lacustrine may offer interesting contribution important petroleum province.