Grain-size variation and sedimentary environment of HS1 borehole sediments in Jizhong Depression

The grain size analysis of HS1 borehole sediments in the Jizhong Depression was carried out, and the lithofacies paleogeographic evolution process in the depression area of North China Plain represented by Jizhong Depression since 3.5 Ma BP was discussed by integrating lithology, age and biomarkers.The results demonstrate that under the conditions the long-term turbulent decline of the neotectonic movement and continuous climate change, the river facies and unstable shallow lake depression facies alternate (Late Pliocene), river facies (Early Pleistocene), river facies, sheet flow facies and short-term flood facies (Middle Pleistocene), river facies and flood plain facies alternate (Late Pleistocene), flood plain facies (Holocene) five sedimentary evolution stages, and the hydrodynamic conditions of the sediment environment are weakening, and the fine particle components are increasing.The grain size fraction content of sediments was consistent with the climate change recorded by carbon-oxygen isotope and pollen.The acceptable grain fraction content increased under cold and dry climate conditions, while the coarse grain fraction content increased under warm and humid climate conditions.Under the climate conditions between them, the change of sediment particle size is relatively gentle, and the particle size range is vast.The cyclic variation of the sedimentary environment reflected by the grain size curve is well coupled with the cold and warm evolution stages of climate divided by pollen and carbon and oxygen isotope records.It is also consistent with the relevant documents of other boreholes in the same period in North China, which is of great significance to reconstruct the paleogeographic environment in the region.