Late Pleistocene aeolian reactivation in coastal barriers of southern Brazil: stratigraphic expression and paleoclimatic significance

Abstract

Pleistocene coastal barriers are important sedimentary archives of environmental and climatic change, although their internal stratigraphy is often obscured by pedogenesis or post-depositional reworking. Yet, these overprints can also preserve valuable evidence of superimposed climate variations. This study investigates the internal organization and late-phase aeolian activity of the Pleistocene-aged Barriers I, II, and III in the southern Brazilian Coastal Plain through a multiproxy approach integrating granulometry, magnetic susceptibility, geochemical markers (Fe₂O₃, TiO₂, Zr), luminescence sensitivity, and optically stimulated luminescence (OSL) dating. High-resolution profiles reveal vertically compartmentalized successions. In Barriers I and III, diffuse transitions separate two units, with upper layers showing geochemical depletion in Fe₂O₃ and TiO₂, improved grain-size sorting, and increased luminescence sensitivity. Barrier II, in turn, displays a clearer bipartite organization. Despite differences in expression, OSL ages from the upper units cluster in key intervals (38–34 ka, 22–16 ka, 12–8 ka), coinciding with Late Pleistocene–Early Holocene phases of climatic instability. These periods likely represent regionally widespread aeolian reactivation driven by reduced vegetation cover and atmospheric reorganization, followed by rapid stabilization under wetter conditions. Although post-depositional processes obscure some signals, OSL chronology provides the primary framework for identifying depositional hiatuses and late aeolian phases, while sedimentological, geochemical, and magnetic proxies reveal subtle internal boundaries within seemingly homogeneous deposits.