Abstract: Understanding the material sources of the black soil horizons and their parent materials is of great significance for elucidating the formation and evolutionary processes of black soils. However, previous studies have primarily focused on the black soil layer itself, with limited attention given to the continuous evolutionary relationship between black soil and parent material layers, as well as to the sedimentary recycling processes of parent material in black soil regions. This study examined eight representative black soil profiles in the Xingkai Lake area of southern Sanjiang Plain. Grain-size analysis and geochemical measurements were systematically conducted on both black soil and parent material layers to reveal provenance characteristics and climatic implications for black soil formation. Grain size analysis indicates that both the black soil and parent material layers in the study area are dominated by silt-sized particles (approximately 60%). Sedimentary environment discriminants and C-M diagrams indicate that both layers represent aquatic deposits, suggesting weak hydrodynamic characteristics under the region’s gentle topography. Geochemical analysis reveals that the CIA value (72.30) of the black soil layer is significantly higher than that of the parent material layer (64.06), indicating that the black soil formed under a warm and humid climate environment, consistent with the Holocene interglacial warming period background of Northeast China’s black soil development. Both the black soil layer and parent material in the study area share the same source material, medium-to-acidic igneous rocks from the Wanda Mountains, which were transported and deposited via fluvial alluvial processes, undergoing re-sedimentation during deposition. Preliminary findings suggest the formation of southern Sanjiang Plain black soil involved a complex sequence of “weathering in the source area → multi-stage transport → re-sedimentation”, providing geochemical evidence for understanding the formation and evolution of black soils in Northeast China.