The sedimentary facies and dynamic environment of the Diaokou lobe in the modern Huanghe River Delta of China

The Huanghe River captures the Diaokou River in 1964 and forms a deltaic lobe in the subsequent 12 a. The progradational process of the Diaokou lobe is in associated with complicated evolution of riverine sheet flooding, merging, and swinging. On the basis of 11 borehole cores and 210 km high resolution seismic reflection data set, the sedimentary sequence and dynamic environment of the Diaokou lobe (one subdelta lobe of the modern Huanghe River Delta) are studied. The stratigraphy of the lobe is characterized by an upward-coarsening ternary structure and forms a progradational deltaic clinoform. Totally six seismic surfaces are identifiable in seismic profiles, bounded six seismic units (SUs). These SUs correspond to six depositional units (DUs) in the borehole cores, and among them, SUs 4–6 (DUs D to F) consist of the modern Diaokou lobe. Lithological and seismic evidences indicate that the delta plain part of the Diaokou lobe is comprised primarily by fluvial lag sediments together with sediments from sidebanks, overbanks, fluvial flood plains and levees, while the delta front part is a combination of river mouth bar sands (majority) and distal bar and deltaic margin sediments (minority). As a result of the high sedimentation rate and weak hydrodynamic regime in the Huanghe River Delta, the sediments in the delta front are dominated by fine-grained materials. The grain size analysis indicates the Huanghe River hyperpycnal-concentrated flow shows the suspension, transportation and sedimentation characteristics of gravity flow, and the sediment transportation is primarily dominated by graded suspension, while uniform suspension and hydrostatic suspension are also observed in places. The strength of the hydrodynamic regime weakens gradually offshore from riverbed, river mouth bar, sidebank, distal bar subfacies to delta lateral margin and flooding plain subfacies.