Giant ferralsol genesis in Brazilian dry forest

• A six-meter Ferralsol was described in the Brazilian semiarid; • Umbric horizons were formed in past dry conditions; • Carbon isotopic variation indicates climate fluctuation in the last 8 kyr cal BP; • Fractionation and anomalies of REE are sensitive to soil genesis; Brazilian semiarid dominantly hosts thin and incipient soils. These soils have limited information about landscape evolution. This study investigates the formation and paleoenvironmental significance of a six-meter Ferralsol in the Araripe Plateau, Brazilian semiarid region. Through a multi-proxy approach, we analyzed soil morphology, micromorphology, geochemistry, carbon isotopes, and rare earth element (REE) fractionation. Deep weathering and leaching processes formed acidic, clay-rich Ferralsols under past climatic oscillations. Buried umbric horizons at 70 cm and 150 cm depth suggest organic matter accumulation in wetter climatic phases. Radiocarbon dating and δ 13 C analyses indicate significant climatic fluctuations over the last 8 cal kyr BP, with alternating wet and dry periods influencing vegetation composition and soil formation. Micromorphological and geochemical data indicate a polygenetic soil formed under contrasting conditions and remobilized materials. Negative Ce anomalies in umbric horizons suggest past reducing conditions, while positive Ce anomalies in high-crystalline Fe oxides indicate oxidative environments. A negative Eu anomaly across most horizons reflects deep leaching, whereas a positive Eu anomaly in organic fractions suggests localized metal–organic complexation. Sedimentation rates and isotopic shifts highlight climate-driven geomorphic processes, including colluvial deposition and slope instability. These findings support the hypothesis that Ferralsols in the Araripe Plateau are not strictly formed in situ but have been influenced by erosion, transport, and redeposition processes. Our findings underscore the interplay between climate, geomorphology, and soil genesis in the Neotropical dry forest. The Araripe Plateau’s Ferralsols serve as paleoenvironmental archives, capturing Holocene climate variability and its influence on vegetation and landscape evolution.