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Paleosols are an under-utilized tool for paleoenvironmental and paleoclimatic reconstruction in Brazilian intracontinental basins. The Itapecuru Formation, from the Lower Cretaceous of the Parnaíba Basin, consists of a 600-m-thick succession of interbedded very fine-to-fine-grained sandstone, mudstone, and paleosols containing rich fossil assemblages. This paper provides a detailed description of the macro and microscopic pedogenic features of a hydromorphic paleosol profile whithin the Itapecuru Formation. Analyses of clay mineralogy and whole-rock geochemistry in the hydromorphic paleosols at the Prata locality are used to infer pedogenic processes, paleoclimate, paleohumidity and paleovegetation. Estimates of paleoprecipitation and paleotemperature using climofunctions, chemical index of alteration without potassium, and paleosol weathering index proxies (PWIs) show values ranging from 810 to 1042 mm/yr (SE = ±78.1 mm/yr) and 10.9 to 11.8 °C (SE = ±0.23 °C), respectively. Climofunction values (MAP and MAT), paleohumidity, Kӧppen aridity index, and pedogenic clay mineral content suggest a humid paleoclimate during soil-forming and weathering processes. Based on these climate data and previously published paleogeographic and palynological studies, the Cretaceous (Albian) Prata pedotype was formed within the equatorial humid belt with vegetation of wet tropical forests. • Alluvial paleosols are characterized in the Parnaíba Basin. • Based on mineralogy and geochemistry analysis, six pedogenic processes were recognized along the Prata pedotype. • Climofunctions values suggest a humid paleoclimate during paleopedogenic modification. • The Albian paleolatitude of Brazil, along with studied climate data, suggests the influence of the Equatorial Humid Belt. • The soil taxonomy following paleoclimate data and pedogenic processes define the Prata pedotype as Ultisol Aquults. [ABSTRACT FROM AUTHOR]

In arid and semi-arid climates, soil development is strongly influenced by seasonal patterns and biogenic activity, and often results in pervasive pedogenic horizons consisting of highly concentrated carbonate. In Brazil, such horizons enriched in calcium carbonate are common and relatively well-studied in paleosols of the Upper Cretaceous Marília Formation. However, detailed analyses on the sequence of mineral precipitation phases and the role of organisms in these processes are still lacking. The present work describes eight argillic and calcic horizons characterized by different degrees of carbonate accumulation. Argillic horizons show translocation clay structures and weak to moderate cementation by calcium carbonate. Calcic horizons contain moderate to high carbonate accumulations ranging from powdery coatings to nodular masses of micrite. Carbonate distribution in these horizons is preserved largely as carbonate-cemented macropores produced by such ichnofossils as Planolites, Taenidium, Naktodemasis, Skolithos, Palaeophycus and calcareous rhizocretions. Moreover, stable isotope data, respired soil CO 2 function, and cathodeluminescence (CL) of the paleosol samples were used to evaluate soil paleovegetation, paleoproductivity, and the distinctive stages of calcite precipitation. Stable isotopic analysis suggests that paleovegetation cover in the paleosols was predominantly C 3 -photosynthsizing plants. The relationship between bioturbation indices and soil respiration suggests a positive pattern of paleoproductivity controlled by higher moisture conditions and the increased activity of soil fauna. Finally, CL imaging shows that there were multiple stages of carbonate precipitation with both α-type and β-type fabrics that are interpreted as abiotic and biotic processes during pedogenesis. • Calcic and argillic horizons are described in detail according with carbonate content; • C3 plants are recognized by carbon isotope composition; • Terraphilic and Hygrofillic trace fossils form the paleosols biota; • The relation of substrate colonization and paleosols organisms respiration represent positive paleoproductivity; • Abiotic processes and biotic activities control the pedogenic carbonate accumulation. [ABSTRACT FROM AUTHOR]