This view shows a typical fluvial interval (in thin section). Observe that the fining-upward general trend is in some cases cut by higher frequency small cycles of coarser-grained sandstones which present better petrophysical properties. High proportion of volcanic fragments enhanced the formation of authigenic smectite. Again, there is no direct relationship between porosity and permeability, probably due to diagenetic imprint. It is possible that the higher permeability layers had its original porosity preserved due to the very early mechanical infiltration of smectite. The general grain size is fine to medium.