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

The mid-Miocene paleosols of the Baraya Member (Villavieja Formation, La Tatacoa, Colombia) preserve a detailed palaeohydrological record during the Middle Miocene Climatic Transition. Developed in distal flood basins of meandering fluvial system, the Ferruginous Red Bed (FRB) paleosols and La Venta Red Bed (LVRB) paleosols represent cumulative, polygenetic soils strongly shaped by alternating wet–dry cycles. Geochemical and micromorphological evidence reveal distinct pedogenic pathways. The FRB exhibits extreme weathering (Al₂O₃ up to 26.7%; CIA > 89), depletion of base cations, and abundant clay coatings, gley pedofeatures, and Fe–Mn nodules, reflecting illuviation and reduction–segregation processes under wetter udic conditions. In contrast, the LVRB shows vertic features, homogenized CIA values (~ 80–88%), and clay infillings within shrinkage cracks, recording pedoturbation and stronger seasonal drying (udic–ustic). Secondary carbonates in both profiles indicate periodic decalcification–reprecipitation, though aridic conditions were not reached. These paleosols classify as Alfisol (Udalf) and Vertisol (Udert/Ustert) respectively, both reflecting subhumid climates. Integration with the fossil record indicates a transitional riparian mosaic rather than a continuous rainforest habitat associated with the La Venta Fauna. The transition zone is determined by two intertwined factors rainfall (~ 1000–2000 mm/year) and at least one moderate dry season (~ 3 months). These findings underscore the role of soil geomorphological position and rainfall seasonality as primary drivers of redox processes and soil moisture balance, while situating Neotropical palaeosols within the broader framework of mid-Miocene climate dynamics and the northward migration of the Intertropical Convergence Zone.