Holocene paleoflood stratigraphy in the lower Yellow River floodplain, China

The lower Yellow River has experienced enormous floods, levee breaches, and channel avulsions over the last 4000-year history, resulting in the deposition of extensive paleoflood sediments across the North China Plain. However, a comprehensive investigation of paleoflood stratigraphy in alluvial plains is still lacking. Here, representative paleoflood profiles along the abandoned channel areas in the lower Yellow River have been comprehensively and systematically analyzed in terms of sedimentology, stratigraphy, and chronology. Our findings reveal that the subsurface stratigraphy is mainly formed by twelve lithological facies and four facies associations. The facies associations are interpreted to represent lowland, paleosol, overbank and channel environments. Compared with the mutable overbank and channel deposits, lowland and paleosol facies that have been developed during relatively stable periods without flood aggradation can be utilized to refine stratigraphic correlations. By combining stratigraphic evidence and radiometric dating results, four sedimentary units are consistently identified in the study area: Unit I related to the early geomorphic surface before the ∼8.0 ka, Unit II represents stability period during the middle Holocene, Unit III with different sequences of overbank flood deposits and paleosols suggesting an abrupt environmental change since ∼4.0 ka, and Unit IV of widely distributed indicating the frequent cycles of flood and interflood since the last millennium. Furthermore, a sedimentary model of paleofloods with a distinct upward-coarsening sequence along the abandoned channel areas is proposed, illustrating the multi-stage deposition of the flooding process. In particular, the thick layer of uniform silt and clay in the lower Yellow River demonstrates distinct features of slack water deposits, which explores the potential of applying the traditional method to more populated and higher-risk areas on floodplains and similar lower rivers.