CLIMATE VARIABILITY IN SOUTHWESTERN GONDWANA AT THE END OF THE LATE PALEOZOIC ICE AGE: A SEDIMENTOLOGICAL AND GEOCHEMICAL APPROACH

The Late Paleozoic Ice Age (LPIA) was the most significant glacial event of the Phanerozoic eon, followed by Permian global warming, making this time interval an important analogue for understanding climate dynamics during glacial cycles. In South America, the LPIA was divided into four climate stages: glacial, terminal glacial, post-glacial, and semiarid-arid. These four stages are recorded in the sedimentary succession of the Gondwana I Supersequence of the Paraná Basin, Brazil. The aim of this research is to reconstruct the climate history of the terminal glacial and post-glacial stages of the Gondwana I Supersequence, comprising the Rio do Sul (upper part of the Itararé Group) and Rio Bonito formations. Our methods include sedimentological and geochemical analysis (X-ray fluorescence) of a drill core located in the southern part of the Paraná Basin. Sedimentary elemental ratios were used to calculate paleoweathering indices, such as Al₂O₃/SiO_2, MgO/Al₂O₃, and chemical index of alteration (CIA). Sedimentological data from the lower section provides evidence of iceberg activity, including dump and dropstones structures preserved within in a turbidite succession, recording a deepening upward trend (from dominantly sandstone and siltstone to rhythmite). The upper interval begins with a predominance of dark gray mudstone, showing no glacial evidence, but grades upward to record dropstones. Geochemical tracers depict a significant change of chemical weathering intensity in the middle part of the Rio do Sul Formation interval. The basal part of the formation records lower chemical weathering intensity with CIA values varying from ~54 to ~70, higher values of MgO/Al₂O₃, and lower values of Al₂O₃/SiO₂. The upper part of the interval is characterized by higher chemical weathering intensity, with CIA values varying from ~77 to ~90, lower values of MgO/Al₂O₃, and higher values of Al2O3/SiO₂. According to these results, the climate condition in the lower Rio do Sul Formation is inferred to have been cold and arid, with temperature calculated from CIA varying between 4.6 to 13.7 °C, while the upper part was warm and humid (17.7 to 24.9 °C). However, the presence of dropstones at the top of the upper part still denotes a glacial influence.