Mineralogy composition and texture indicative of fluid-assisted remobilization in carbonate units of the Irece Basin, Brazil

摘要

Carbonates of the Salitre Formation, IreceSIC 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 813C and 818O 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.