Paleoclimate reconstruction from Permian paleosols of the Rio do Rasto Formation, Paraná Basin, Brazil

Paleosols preserve critical evidence of past surface conditions and provide key insights into Earth’s environmental evolution. Pedogenetic processes, controlled by parent material, climate, topography, biological activity, and exposure time, record both the duration and intensity of weathering. Micromorphological features in paleosols are particularly valuable for establishing relationships between soil-forming processes and sedimentary structures, supporting robust paleoenvironmental and paleoclimatic interpretations. Permian paleosols from the Paraná Basin, southern Brazil, occur within the Rio do Rasto Formation, which is composed of lacustrine deposits of the Serrinha Member, overlain by aeolian systems, fluvial channels, and overbank successions of the Morro Pelado Member. This study integrates macro- and micromorphological observations with geochemical data (Chemical Index of Alteration – CIA) and mineralogical analyses (X-ray Diffraction – XRD) to reconstruct paleoclimate conditions during paleosol development. Microscale analyses show that variations in clay mineral assemblages and carbonate precipitates strongly control sample coloration, producing whitish, greenish, and grayish tones proportional to carbonate content. The results indicate a predominantly semiarid to arid paleoclimate, characterized by intense wetting–drying cycles, repeated waterlogging, and high evaporation rates. The clay fraction is dominated by expansive clay minerals, particularly smectite, reflecting reduced chemical leaching under seasonal drainage conditions. In contrast, subordinate kaolinite and illite suggest episodic phases of improved drainage and longer subaerial exposure. Pedogenic features such as desiccation cracks, slickensides, bioturbation structures (root traces and burrows), and redoximorphic mottling provide further evidence for soil development under a highly seasonal water regime. Carbonate nodules and evaporitic phases become increasingly abundant toward the top of the stratigraphic succession, indicating a progressive aridification trend associated with the continentalization of Gondwana during the Middle to Late Permian. CIA values demonstrate a regional climatic gradient within the basin, from semiarid conditions in intermediate areas to fully arid, locally evaporitic settings in more distal zones. These results reinforce the value of paleosols as reliable terrestrial paleoclimate proxies and provide new insights into the paleohydrological and climatic evolution of southern Gondwana during the Late Paleozoic. This study contributes to a better understanding of environmental dynamics prior to the Permo–Triassic transition.