A soil organic matter (SOM) was evaluated using a multiproxy approach integrating thermal, elemental, isotopic, and phytolith-based analyses. Differential scanning calorimetry and thermogravimetric analysis revealed distinct exothermic and endothermic reactions associated with the progressive decomposition of organic compounds, with the third exothermic event (3 % peak Exothermic) contributing a substantial proportion of total mass loss around 500 °C, indicating the presence of thermally stable organic fractions. Elemental composition and C/N ratios varied among profiles and horizons, reflecting differences in organic matter sources and degrees of decomposition. Stable carbon isotope ratios (δ¹³C) showed a wide range of values, suggesting mixed contributions of C₃- and C₄-derived organic inputs and possible vertical redistribution of organic carbon within the soil profiles. Phytolith assemblages were dominated by morphotypes indicative of terrestrial vegetation, with variable proportions of aquatic organism remains and charcoal, pointing to changes in vegetation structure, hydrological conditions, and fire activity over time. Multivariate analysis of phytolith indices highlighted clear compositional gradients among modern and fossil assemblages, supporting shifts in environmental conditions and organic matter dynamics. Overall, the combined thermal, elemental, isotopic, and phytolith evidence provides robust insights into the composition, stability, and environmental controls on soil organic matter in soils from Catimbau National Park, northeastern Brazil.