Structural and sedimentary discontinuities control vuggy porosity formation

Summary The epigenetic karstic systems in carbonate rocks are the result of the dissolution caused by meteoric waters during the geological time. The topic investigated in this study are the structural and sedimentary discontinuities that control the formation of vuggy porosity by epigenic fluids in carbonate units. These discontinuities include vertical fractures, horizontal and vertical stylolites and sedimentary discontinuities, such as cross stratifications. In this work, we studied these karst features in the Cretaceous carbonates of the Jandaira Formation, Potiguar Basin, Brazil. In order to describe these discontinuities, we performed four stratigraphic columns and collected Schimdt hammer data and horizontal and vertical plugs to analyse porosity and permeability in each layer and at the boundary between layers. We also investigated diagenetic features at the thin section and electronic microscopy scales. The findings indicate that vertical fractures and vertical stylolites were dissolved together by meteoric water percolation and cross cut all the layers, which allowed the horizontal fluid flow along sedimentary discontinuities. We conclude that structural and sedimentary discontinuities control fluid flow during diagenesis and influence the development of vuggy porosity.