Mid-Miocene palaeohydrology archived in palaeosols of La Tatacoa, Colombia

Abstract Mid-Miocene palaeosols of the Baraya Member (Villavieja Formation, La Tatacoa, Colombia) record contrasting pedogenic pathways developed within fine-grained floodbasin environments under subhumid tropical conditions. The Ferruginous Red Bed (FRB) and La Venta Red Bed (LVRB) form thick, cumulatively accreted palaeosol successions produced under low sedimentation rates, where pedogenesis proceeded contemporaneously with slow overbank deposition. Five pedotypes were differentiated using integrated field morphology, micromorphology, mineralogy, and geochemistry, allowing reconstruction of soil-forming processes governed primarily by soil moisture regime and hydropedological boundary conditions. The FRB succession is dominated by fersiallitisation, rubefaction, clay neoformation and illuviation, redoximorphic segregation, and limited carbonate cycling. Advanced chemical weathering (Al₂O₃ up to 26.7 wt%; CIA−K between 70 and 95), base-cation depletion, abundant clay coatings, and pervasive Fe–Mn nodules reflect sustained leaching and fluctuating saturation under persistently high water tables. These processes produced hydromorphic Alfisol-like palaeosols formed under udic to aquic moisture regimes, where pedogenic continuity was chiefly constrained by drainage. In contrast, the LVRB succession records a shift toward shrink–swell pedoturbation as the dominant pedogenic mechanism. Vertic fabrics—slickensides, wedge structures, accommodated planes, and crack-controlled clay infillings—overprint earlier argillic features and homogenise geochemical depth profiles (CIA−K ~85–90%), indicating intensified seasonal drying at the udic–ustic boundary. Secondary carbonates in both units reflect repeated wet–dry cycling, while the absence of gypsum confirms that arid conditions were not reached. Classification as Palaeo-Entisols, Palaeo-Inceptisols, Palaeo-Alfisols, and Palaeo-Vertisols reflects systematic variation in pedogenic processes rather than changes in sediment provenance or landscape position. Integration with the fossil record supports interpretation of La Venta as a heterogeneous riparian mosaic sustained by intermediate rainfall (~1000–2000 mm yr⁻1) and two pedogenetically effective dry seasons (~3 months each). the FRB–LVRB trajectories demostrate that regional hydropedological conditions—particularly drainage and moisture seasonality—exerted primary control on soil development, while situating Neotropical palaeosols within the broader framework of mid-Miocene climate dynamics and the Andean uplift.