Late Quaternary depositional characteristics and environment significance of the Xibozhang section in Baoding, central Hebei Plain, China

This paper aims to ascertain the depositional paleoenvironment since the late Quaternary in the central Hebei plain. We measured the 20.74 m-deep Xibozhang section and analyzed the collected samples for grain size and optically stimulated luminescence (OSL) tests. OSL dating results indicate that the deposits were formed during 102~8.67 ka, belonging to the late Pleistocene to early Holocene. Analysis of lithology and grain size show that, the section is fluvial deposit with typical binary structure, which can be further divided into channel deposit and floodplain deposit. The channel deposits are mainly medium-coarse sand containing mica fragments, with oblique bedding. Frequency curves is characterized by positive bias bimodal with moderate to poor sorting, and the probability cumulative curves are mainly two-stage dominated by jump components. The floodplain deposit is mainly clayey silt with well-preserved shell fossils and calcareous nodules. Most frequency curves are negative bias bimodal with poor sorting, and the probability cumulative curves are mainly two-stage dominated by suspension components. The C-M diagram shows that the Xibozhang section consists largely of uniformly suspended deposits, belonging to typical meandering river deposits. Comparing the measured section with the loess section of Jingyuan, we found that the Xibozhang section could be divided into three stages from the bottom up. The lower part, 16.14~20.74 m, is the deposits of the late stage of the last interglacial period, with warm and humid climate, dominated by silty deposits; The middle part, 3.18~16.14 m, is the deposits of the last glacial period, with dry and cold climate. The grain size shows the fine-coarse-fine characteristic, individually corresponding to the early interglacial stage, interglacial stage and maximum glacial stage of the last glacial period; The upper part, 0.2~3.18 m, is the deposits of the post glacial stage with similar characteristics of 16.14~20.74 m, dominated by clay and clayey silty sand deposits. Grain size analysis reveals that the late Quaternary depositional environment of the Baoding depression in central Hebei Plain is mainly of fluvial environment, and the distribution of grain size stage is the material respond to glacial-interglacial climate.