Late Paleozoic glacial to postglacial stratigraphic evolution of the Rio do Sul depocenter, Itararé and Guatá groups, Pennsylvanian-Cisuralian, southern Brazil

Abstract

The transition from the Late Paleozoic Ice Age (LPIA) to fully postglacial conditions in SW Gondwana is under increasing discussion due to either the radiometric ages of its boundary or the stratigraphic nature of this transition. The record of this transition in the Paraná Basin is found in the glacial and glacially influenced deposits of the upper Mafra and Rio do Sul Formations (upper Itararé Group) and postglacial strata of the Rio Bonito Formation (Guatá Group). Here we address the depositional architecture and stratigraphic evolution of these deposits in the Rio do Sul depocenter, eastern Paraná Basin, Brazil, the main area of subsidence in the basin during this transition in Pennsylvanian-Cisuralian time, bringing an opportunity to examine the characteristics of glacial to postglacial transition. Analyses of facies, stratigraphic logs, stratigraphic correlations, and paleocurrent dispersal trends allowed us to define three evolutionary stages. The first stage registers glacial advance from the south-southwest represented by an erosive surface and subglacial tillites. Gravitational deposits covered the tillites in response to ice retreat (upper Mafra Formation), and the Lontras Shales (lower Rio do Sul Formation) correspond to the marine maximum flooding. The second stage comprises co-genetic deepwater (Rio do Sul Formation) to shallow (Rio Bonito Formation, Triunfo Member) progradational deposits after the Lontras Shale maximum flooding. Paleocurrent data and glacially related features point to glaciated source areas located to the NE, E, and SE for the Rio do Sul depocenter during this stage. The third stage corresponds to retrogradational stacking pattern upon a fluvial subaerial unconformity (incised valley), starting with fluvio-deltaic beds (Triunfo Member), followed by fine-grained deposits of the Paraguaçu Member of Rio Bonito Formation. No features related to glacial influence characterize this third stage. As previously suggested, tectonic uplift likely drove the additional NE source and created the space that allowed the transitional contact between Rio do Sul and Rio Bonito formations in the Rio do Sul depocenter.

A field guide to the sand-rich turbidite systems of the Taciba Formation, Itararé Group, Paraná basin, Brazil

“…Next to the outcrop there are two waterfalls where the turbidites are also exposed. This is the best-known outcrop in the area (D'Ávila et al 2008, D'Ávila 2009, Fallgatter 2015, Schemiko et al 2022). The most prominent feature is a mud diapir from the Lontras shale (Fig.…”

“…This connection is proposed by the relative positions of the two localities, the alignment of glacial striations (Rocha-Campos et al 1988;Puigdomenech et al 2014;Rosa et al 2021), and the similar facies distribution (Fallgatter et al 2023). Further north, a connection between the paleotrough and the Rio do Sul embayment (Canuto 1993;Santos et al 1996;Fallgatter and Paim 2019;Schemiko et al 2022) cannot be discarded.…”