Paleoclimate-driven depositional dynamics of Western Gondwana Endorheic Basins during the Middle to Late Permian.

The sedimentation patterns within endorheic basins are primarily controlled by climate. These basins are sensitive to atmospheric circulation patterns that influence the distribution of moist and dry air masses. During the Middle to Late Permian period, Western Gondwana underwent continentalization, during which fluvial, lacustrine, and aeolian deposits formed the stratigraphic framework of several basins. Field data from the Rio do Rasto Formation of the Paraná Basin in southern Brazil reveal a highly complex depositional architecture within this broad endorheic basin. By analyzing vertical facies succession and paleocurrent patterns, we identified two distinct catchments that feed distributive fluvial systems (DFS) anchored in different source areas within a large paleogeographic depositional area. The Rio do Rasto Formation's stratigraphic framework reveals the intercalation of medial-to-distal DFS deposits that form tens of meters of progradational cycles. These cycles consist of basal deltaic lobes and lacustrine deposits. Ephemeral fluvial channels, aeolian deposits, and red beds are recognized toward the top. Additionally, linking paleocurrent data with facies associations suggests that the two distinct catchments were influenced by different atmospheric circulation mechanisms. The more perennial basal deposits were supplied with sediment and water from southern and southeastern African terrains. In contrast, ephemeral streams and arid-related deposits were fed by west-northwestern catchments associated with the Asunción Arch. When analyzing the vertical patterns of facies in progradational cycles, ephemeral deposits tend to dominate perennial ones toward the top. This indicates an increasing trend of aridization in the Late Permian. Comparative sedimentological and paleontological data from the Karoo Basin reveal similar depositional patterns, with basal deposits influenced by a moisture-rich center. Paleoclimatic models from the Middle to Late Permian suggest that the moisture center migrated southward. This migration caused an intensification of arid conditions and a decrease in precipitation in southern Africa. Consequently, this climatic shift likely diminished the supply of water and sediment to fluvial and deltaic systems in the northern Paraná Basin, reinforcing an aridification trend across western Gondwana on a regional scale. High discharge variability in western and northwestern catchments may have been exacerbated by orographic barriers producing rain shadows. The Asunción Arch and the volcanic belt along the western margin of South America, associated with the Sierras Pampeanas, further restricted moisture-bearing air masses from reaching the continental interior. Observed stratigraphic patterns reflect endorheic basins' sensitivity to shifts in atmospheric circulation and hydrological regimes. The increasing aridity recorded in the upper portions of the Rio do Rasto Formation aligns with global climatic trends recognized in other Permian basins. Such widespread aridization may have contributed to the paleoenvironmental instability preceding the End-Permian mass extinction. This highlights the broader significance of basin-scale sedimentary records in reconstructing climatic and ecological change.