Petrografia e gênese das rochas sedimentares do Aptiano e Albo-Aptiano da Bacia do Espírito Santo

Abstract

The Aptian and Alba-Aptian intervals are characterized by arkoses and subarkoses on the onshore portion of Espirito Santo Basin. These sandstones were deposited, together with a few shales and limestones, in a fluvial system of low energy. Source rocks were garnet-biotite-granulites which cropped out at the western margin of the basin in an area tectonically active and with high relief. The climate was warm and humid, during most of this time, propitiating a dense vegetation which accumulated partly as coal in the lowermost section. Sandstones of the Aptian and Albo-Aptian sections are separated by evaporite beds deposited in a restricted environment. Sandstones above evaporites are generally massive, montmorillonitic, and have a greater clay content than those sandstones below, which have a kaolinite matrix and parallel or crossed lamination. To the south the upper section changes to a carbonate facies deposited in a shallow marine shelf. This facies is composed of algal and pisolitic biosparites and biomicrites with some dolomitized zones. These limestones were deposited by a transgressing sea, advancing from south arid east which, after a small regression at the base of the interval, finished by covering all the basin at Albian time.