Cenozoic deposits and deforming structures in the Depressão Periférica Paulista, Campinas, São Paulo

Abstract

The study area is located in the Metropolitan Region of Campinas, on the contact between the Depressão Periférica Paulista and the Atlantic Plateau. The work here presented aims at mapping the Cenozoic deposits and also the tectonic structures that deform them. Three Cenozoic deposit units, associated to hill tops and slopes, were identified; from the oldest to the youngest, they correspond to: Rio Claro Formation (Trc), planation surface deposits (TQsp), and gravitational flow deposits (Qfg). The Trc deposits consist of meandering fluvial facies intercalated, or in lateral contact, with gravitational flow facies. The TQsp occurs at the top or on gently sloping divides of gentle and rolling hills. It consists of sandy-clayey or sandy deposits underlain by a stone line. The Qfg occurrences are very restrict, associated to the lower portion of slopes, and its thickness increases towards current valleys; it consists of both colluvial, with a basal stone line, and fluvial terrace deposits. This stone line sometimes contains ferruginous fragments originated from ferricretes of the Trc sediments. Two older strike-slip Cenozoic events and a younger extensional one affect the Cenozoic deposits. The older, with σ1 trending around EW, has generated strike-slip NE and NW faults, and normal EW ones. It was probably contemporaneous with the deposition of the Trc. The second event, whose σ1 trends around NW, has generated EW to WNW and NS to NNW faults, and is probably of transtensional nature. This event affects the Trc and TQsp deposits and has produced vertical tectonic offsets of the basal surface of the Trc totalizing at least 50m. The younger event, with a sub-horizontal σ3 trending around NE, has generated NE normal faults, which affect the Trc and TQsp sediments.