Sedimentary and hydraulic characterization to identify hydrofacies in Barreiras Formation, Rio de Janeiro state - Brazil

Abstract

The use of analogous outcrops in characterizing hydrogeological heterogeneities is widespread worldwide. It is a powerful tool for sediment characterization and determination of hydraulic parameters in rural and urban areas lacking hydrogeological information. This study investigates and characterizes the depositional and post-depositional factors that control the quality of the porous aquifer of the Barreiras Formation, Campos Basin, Rio de Janeiro, Brazil. The integrated analysis between petrological and hydraulic parameters in two outcrops analogous to the Barreiras aquifer demonstrated the role of post-depositional processes, which altered the original deposition conditions. The two outcrops are predominantly composed of sandy and muddy facies, with hydraulic conductivity ranging between 10−4 to 10−5 cm/s and 10−5 to 10−8 cm/s, respectively. This allowed the definition of two hydrofacies, formed by sandy layers as reservoirs and by muddy layers acting as hydraulic barriers. In this context, the Barreiras Formation can be characterized as a poor aquifer, differing from the typical braided fluvial deposits. This evidence draws attention to the indiscriminate use of typical sedimentary models in environments with a high rate of chemical-biological weathering, not only in underground flow models but also in studies of underground resources protection and exploitation, such as the Barreiras aquifer, which consists of one of the main water sources for public, industrial and agricultural supply.