Abstract: This study investigated the shallow surface substrate in the Taonan area, western Songnen Plain. Accordingly, it revealed the elemental differentiation between surface (0~20 cm) and deeper (150~200 cm) soils in the shallow surface substrate layer, as well as the genetic mechanisms of salinization in this layer. The results show that compared to deeper soils, surface soils in the Taonan area are strongly enriched in organic carbon (Corg) and N and slightly enriched in Br, P, S, Se, and total carbon (TC). In contrast, no significant differences are identified in heavy metals, rare earth elements (REEs), and other trace elements. These findings suggest the primary causes of the enrichment of various element indicators in surface soils include agricultural activities, biogeochemical cycles, and water-salt migration. The factor analysis indicates that for surface soils, factor F1 is dominated by the heavy metal-REE combination (variance contribution rate: 26.66%), with its spatial distribution associated with fluvial deposition and agricultural activities. Furthermore, factor F2 for these soils is the salt-related element combination (including CaO and MgO; variance contribution rate: 11.24%), indicating the risk of salinization in low-lying zones. In contrast, for deeper soils, factor F1 is the combination of elements such as Al₂O₃, B, La, and Sc (variance contribution rate: 27.34%), reflecting the compositional characteristics of bedrocks or soil parent materials. Factor F2 for these soils is the combination of elements related to geological settings and salinity (variance contribution rate: 13.09%), indicating geological settings and salinization. The weathering and leaching coefficient, represented by the Ba value, shows significant spatial differentiation. Compared to deeper soils, surface soils manifest a larger range of high Ba values, primarily distributed in the zone south of Jubao Township and west of Datong Township, as well as the southern part of Erlong Township. This distribution, coinciding with the high-value zones of salt-related factor F2, is principally affected by topography and deep parent material types. In the low-lying plain area and the front of alluvial fans, the low-lying terrains, poor drainage, and intense evaporation lead to salt accumulation, causing a high risk of salinization. In the hilly area, the high values of factor F2 are associated with the bedrock lithology, with salts originating from weathered bedrocks. The results of this study will provide a geochemical basis for land resource optimization and ecological restoration in the Taonan area.