Mineralogy composition and texture indicative of fluid-assisted remobilization in carbonate units of the Irecê Basin, Brazil. (October 2021)

• Record Type: Journal Article
• Authors: do C. Couto, Diego Canídia; Barbosa, Paola F.; Santos, Roberto V.; Vieira, Lucieth C.; Dantas, Elton L.; Bezerra, Francisco H.R.; Taveira, Igor A.P.; Gomes Júnior, Cleber P.
• Is Part Of: Journal of South American earth sciences. Volume 110(2021)
• Publication Date: 2021-10
• Subjects: Carbonate units -- Hydrothermal fluids -- Mineral characterization -- Filled structures -- Dolomitization; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2021.103346
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: Carbonates of the Salitre Formation, Irecê Basin, Brazil, have been the focus of extensive stratigraphic and structural studies for several decades. Besides hosting phosphorites deposits, these rocks are analogues to fractured and certified oil reservoirs, such as those of the Cretaceous pre-salt oil system offshore Brazil. The present study presents an integration of X-Ray Diffraction (XRD), Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMScan), Optical Petrography, Cathodoluminescence (CL), and Charge Contrast Imaging (CCI) data that allows a high-resolution characterization of the mineralogy within the carbonate units. In addition, we also present carbon and oxygen stable isotope data to identify possible origins of the associated fluids. The mineral characterization revealed that calcite (50–70%), quartz (20–30%) and dolomite (10–20%) are the main post-sedimentary mineral phases found in veins, vesicle structures and cement of the carbonate units. The mineral phases of veins were formed by the interaction with hydrothermal fluids, which had an important role in the dissolution, karstification, and remobilization of carbonate units. Isotopic analysis shows that δ13C and δ18O are more negative in veins and vesicles when compared to host rock, indicating that there is no effective isotopic exchange between the host rock and the filled structures and that these structures were filled with hydrothermal fluids from an external source. Highlights: Hydrothermal processes in carbonate sequences lead to hypogenic carstification. The carbonate sequences of the Salitre Formation have structures filled with calcite, dolomite and quartz. Isotopes of carbon and oxygen show that the veins and vesicles have a different signature than the embedding rock. Fractures and faciological characteristics of carbonate sequences control the pervasive nature of hydrothermal fluids. Mineralogical characterization shows dolomitization and dolomitic cementation processes.