Abstract
This work presents a basinwide analysis on the Precarboniferous sequences of the Parana basin. Sufarce and well data have been used to update geological interpretation and to suggest a new stratigraphic proposal for the Ordovician-Silurian of the Parana basin. The diamictites, present in the Iapo, Vila Maria, and Rio Ivai Formations, play important role in the new proposal, for they are interpreted as time correlate horizons related to Neo-Ordovician Gondwanan glaciations. It is herein proposed a gradational contact between the Furnas and Ponta Grossa Formations, as well as, the existence of a conspicuous unconformity in the Upper Silurian. The Precarboniferous of the Parana basin is divided into two tectosedimentary sequences: 1. an Ordovician-Silurian sequence (Rio Ivai Group) composed of basal conglomerates and fluvial sandstones, overlain by coastal and marine sandstones (Alto Garcas Formation). This sandy unit is covered by diamictites (Iapo Formation), and transgressive marine shales/coastal sandstones (Vila Maria Formation). The Rio Ivai Group correlates with the Caacupe and Itacurubi Groups in Paraguay; 2. a Devonian sequence (Parana Group) composed of a sandy unit (Furnas Formation) deposited by braid deltas, ending in a marine shaly unit (Ponta Grossa Formation). The Ponta Grossa Formation has two maximum flooding surfaces bounded by prograding deltaic sandstones originating in East and Northeast sources.
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