Santa Bárbara Formation (Early Paleozoic, Caçapava do Sul, southern Brazil): Petrographic and Sm–Nd isotopic provenance parameters

Integrated petrographic and Sm–Nd isotopic data were applied in order to constrain the provenance of the Early Paleozoic Santa Bárbara Formation, Sul-rio-grandense Shield, southern Brazil. This unit comprises continental sandstones, conglomerates and siltstones deposited under semi-arid climate in a rift or pull-apart basin. Samples were collected within a stratigraphic framework composed of three sequences, in which the two basal ones present northeastwards paleoflow, and the third one marks the inversion of basin filling. Samples from sequence I show, in the south, a strong influence of intermediate volcanic (Hilário Formation) sources, and a significant increase in quartz and metamorphic fragments upsection. In the northern deposits, there is a possible influence of juvenile units (Cambaí/Vacacaí), and a more significant input of Paleoproterozoic-sourced sedimentary rocks (e.g. Maricá Formation) upsection. Samples collected from the topmost deposits of sequence II present a clear increase in the amount of volcanic fragments (mostly acidic), reflecting denudation of the “Caçapava high”. Data obtained in sequence III (Pedra do Segredo) show a progressive decrease in quartz content and a significant increase in feldspathic, plutonic fragments. A more evolved phase of denudation of the “Caçapava high”, exposing leucogranitoids of the Caçapava do Sul complex, is proposed for this interval.