Diagênese, contexto deposicional e história de soterramento da Formação Rio Bonito, Bacia do Paraná

Abstract

Subsidence analysis and diagenetic processes in the sandstones of the Rio Bonito Formation was based on wells drilled in the Parana Basin. The main eodiagenetics products are pyrite, calcite, siderite and kaolinite. The main diagenetics products related to mesodiagenesis of the Rio Bonito Formation are ankerite, chlorite, quartz overgrowths and illita. The correlation between diagenetc products and sequence stratigraphy can not always be established. However, quartz overgrowths in the mesodiagenesis can be influenced by eodiagenetic alterations in quartzarenites with little influence of carbonatic cementation. In the analyzed wells the maximum burial depth of the Rio Bonito Formation was approximately 4000m and corresponds to temperature around 120oC. These conditions imply in mesodiagenetics modifications, such as chemical compacting, clay mineral transformation reactions and quartz overgrowths. With the burial history modeling and considering the age, selection and depth, the Rio Bonito Formation sandstones has porosity around 20% in burial depth of 3.000m. This indicates that despite the high burial depth, the sandstones might have good porosity, depending on depositional conditions. In general, compacting was more important than cementation, in reducing porosity. However, the eodiagenetic cementation was a positive factor in the sandstones framework preservation.