The Study On The Characteristics Of Paleoenvironmental Evolution Since Late Pleistocene In Baiyangdian Area, Hebei Province

Baiyangdian Area has located in East Asian monsoon region since late Pleistocene, so it is sensitive to environment variation. The Quaternary deposition has a wide, thick and continuous distribution. It is a good record of the environmental changes. Studies of environmental effect of paleo-climate changes in this area primarily focused on the analysis of lithologic of sediment and the sporo-pollen assemblage. While this paper do the analysis in detail by grain size and magnetic susceptibility.This paper mainly studies three typical profiles around Baiyangdian Area by analyzing the formation of sediment. By analyzing the characters of grain size and magnetic susceptibility and using OSL and AMS14 C dating, this study reveals the law of environmental change in Baiyangdian Area.The main conclusions are as follows:1. Determine the age of deposition by using OSL and AMS14 C dating, as well it is reasonable and reliable after accounting for sedimentary environment and being modified. The max age of the bottom of profiles is 121.843 ka BP through the computer simulation, so we know that the sediment has begun piling up since late Paleocene.2. Based on the ages and analysis of deposit, it is possible to classify sequence stratigraph into three stages since Last Inter-glacial Stage. The bottom layer is from 121 ka BP to 75 ka BP.Sedimentary facies is fluvial and sediments include mainly medium, coarse and ultra-fine sand. The medium layer is from 75 kka BP to 10 ka BP.Sedimentary facies are fluvial and lakeside. Particle size ranges wildly from clay to fine sand. The top layer is from 10 ka BP to now. Particle size mainly ranges from clay to silt. Lake, swamp and river developed alternately. Black and grayish black peat developed well and the basis benthic fossils were found in some layers.3. Identification of distribution characteristics of magnetic susceptibility of sediments and its environmental significance indicates that the climate was warm and humid during the early stage of late Paleocene. The climate generally become dry and cold during the late stage of late Paleocene. While also underwent variations of three stages warm-humid or cold-dry. In early Holocene, it began to change warm and humid. In middle Holocene, climate become generally typical warm and humid, aquatic organism growth well and the level of the lake rose and fell.The curves of paleo-climate proxies since late Pleistocene generally accord well to Marine Isotope Stages 1 to 5a.