From alluvial fans to lacustrine systems: trace fossils applied to paleoenvironmental analysis in the Taubaté Basin (Brazil)

Abstract Studies integrating ichnology and sedimentology in paleoenvironmental interpretations are rare in Brazilian rift successions. This study applies an integrated ichno-sedimentological analysis to a well core from the Resende and Tremembé Formations (Cenozoic Taubaté Basin) to reconstruct paleoenvironmental conditions. Three paleoenvironments were identified: alluvial fan, braided river, and lacustrine. The alluvial settings is characterized by coarse-grained deposits displaying bioturbation intensity and sporadic trace fossils, dominated by Palaeophycus and Skolithos, reflecting opportunistic colonization. Braided river deposits consist of stacked sandstones with trough cross-bedding and a trace-fossil assemblage with Palaeophycus, Skolithos, Macanopsis, and Taenidium. The lacustrine environment is characterized by dark shale interbedded with fine-grained sandstones, including ostracod-rich white beds. Sparse beds containing Planolites indicate a complex lacustrine system with potential variations in salinity and oxygenation. Comparison with previous studies suggests that ichnofossils and paleosols reflect water table fluctuations and humid conditions in the Resende Formation. For the Tremembé Formation, ichnofossil data, palynomorphs (Botryococcus and Pediastrum), and taphonomic signatures in fishes suggest a dynamic environment with fluctuating water levels, periodic salinity increases, and decreased oxygen levels.