Late Cretaceous hydrotermal silicification in the southern part of the Bauru Basin - São Paulo, Brasil

Abstract

Many occurrences of silicified sandstones were found in areas of exposition of the Caiuá and Bauru groups (Bauru Basin, Late Cretaceous), in the northwest part of the states of Paraná and extreme west of São Paulo, Brasil. Silicification occurs sometimes as pore lining, sometimes as partially or totally filling the intergranular space. Four different but often coexistent types of silicification were identified: (a) microcrystal growth in palisades, (b) sintaxial overgrowth (megaquartz), (c) pore filling by silica in mosaic polygonal texture, and (d) pore filling by silica in microcrystalline texture. Silicification developed in two different settings: (a) in a framework without compaction and (b) in mechanical compaction framework. Geological features of the occurrences and petrographic analyses indicate a hydrothermal origin for the silicification. It is very likely that such a hydrothermal event could have been associated with the Late Cretaceous alkaline magmatism. The silicification developed at the end of sedimentation and closing of the Bauru Basin