Abstract: Analyzing the material sources of the black soil layer and parent material layer is crucial for understanding the formation and evolution of black soil. However, existing studies have primarily focused on the black soil layer itself, with limited research on the continuous evolutionary relationship between black soil and parent material layers. Furthermore, there is insufficient recognition of the sedimentary recycling processes of parent material in black soil regions. This study examines eight representative black soil profiles in the Xingkai Lake area of southern Sanjiang Plain. Through systematic collection of grain size analysis and geochemical testing samples, comparative analysis of the black soil layer and parent material layer reveals material source characteristics and climatic features associated with black soil formation. Grain size analysis indicates that both the black soil layer and parent material layer 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, reflecting weak hydrodynamic characteristics under the region's gentle topography. Geochemical analysis revealed that the CIA value (72.30) of the black soil layer was 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 studying the formation and evolution of Northeast China's black soil.