Geologic Evolution Model for the Atibaia Municipality Region. São Paulo State, Brazil, during the Cenozoic.

Abstract

This paper aims to present a geologic evolution model to the Cenozoic scenery of the Atibaia region, based in geologic, geomorphologic e paleontologic data. This region is characterized by a Precambrian basement formed by migmatites, gnaisses, granites, granulites, and metasedimentary and metaigneous rocks, highly deformed, encompassed by Amparo Complex, Socorro Domain, and Atibaia Pluton. Locally, this basement is covered by Cenozoic sediments that include Recent fluvial deposits, terraces, coluvion aprons, and Neogenic and Paleogenic remain deposits, with an expressive paleontologic record. The geomorphology of the region is characterized by a hilly terrain, with some ridges that could attain relatively high altitudes (more than 1.400 m in the Itapetinga Ridge). The basement rocks are cut by high dip shear zones that appear to control the Cenozoic deposits occurrences and seem suffering vertical movements during Cenozoic, in a revitalized tectonic behavior, also known as ´resurgent tectonics´. The proposed evolution scenery comprises four stages, as folow: (1) Aptian-Albian times – the area was covered by a thin sedimentary and igneous rock sheet correlated to the Paraná Basin and the tectonic regime had tensional style; (2) Late Cretaceous – uplifting and erosion are the predominant effects that resulted in the huge South- American pediplane, that, probably developed until Early Paleogene times; (3) Paleogene – The South-American surface was dissected and some small taphrogenic basins were developed (e.g., Tanque deposits); and (4) Miocene – Recent – the tectonic regime has a compressional style due to the Andes Cordillera appearance, that counterbalances the westward drift of the South- American plate, resulting in a more complex tectonic action, with some tiny sedimentary deposition areas. As considered in this paper, this 4th stage corresponds to the Neotectonics realm.