Reflections on the genesis of the serra geral and the paulista peripheral depression: the example of the region of São Pedro and the lower Piracicaba river, SP

Abstract

The genesis of the Serra Geral Ridge and Paulista Peripheral Depression has been a fundamental problem regarding the landforms of the State of São Paulo since the 1920s, and a final solution is still far from any consensus. Previous studies highlight erosional and tectonic factors related to the formation of these areas; however current research has shown that several hypotheses are only feebly supported. In this sense, this study presents an hypothesis on the genesis of the São Pedro Ridge, regional name of Serra Geral, and tests the validity of this proposition in the context of the formation of the Serra Geral Ridge as a whole. The results point to the hypothesis of an origin for the São Pedro Ridge by erosion as a consequence of the excavation process of the Paulista Peripheral Depression. This process took place with the establishment of large drainage patterns upon old structural lines that were reactivated during fragmentation of Gondwana. This excavation process and the formation of the proto-escarpment of the São Pedro Ridge must have begun between the Paleocene and Eocene, under a wet climate, after deposition of the Itaqueri Formation and establishment of the Cristas Médias Surface, having the geomorphological configuration of these areas transformed by neotectonic activity. Thus, this research confirms Margarida Penteado's proposition that the São Pedro Ridge had a hybrid erosional/tectonic genesis, which qualifies it as a complex cuesta.