Preliminary Study On The Paleolake Evolution Of Middle And South Hebei Plain Since Late Pleistocene

As an important part of the North China Plain,the Hebei Plain is a deep coverage area of the Quaternary strata that is only small spatial changes and good continuity.It is a continuous lacustrine facies deposit in the Late Pleistocene and Holocene.The rich sedimentary information of the paleoclimate and the paleoenvironment in the lake sediments of the Hebei Plain provides original and valuable information for studying the changes of continental paleoclimate and paleoenvironment,thus becoming an important information carrier for studying climate and environmental change.However,scholars in the past lacked a systematic analysis of the lake development characteristics of the Hebei Plain since the late Pleistocene.Based on this,this article investigated 4 sedimentary profiles in Ningjinbo and Baiyangdian areas,combined with 13 sedimentary profiles studied by some scholars,discussed the expansion and contraction process of ancient lakes in the Hebei Plain since the late Pleistocene,and reconstructed since the late Pleistocene The temporal and spatial evolution of ancient lakes in the Hebei Plain.The knowledge gained is as follows:(1)By comprehensively comparing the stratigraphic characteristics of the two large lakes in the Hebei Plain,the sequence of the lake strata in the central and southern Hebei Plains since the late Pleistocene is divided.In the early period of late Pleistocene,the sedimentary fluvial facies mainly consisted of silt,silty clay,and clay silt;in the late period,the fluvial facies and shallow lake facies mainly consisted of clay silt,silty clay,fine silt,clay Sedimentary with lakeside facies.In the early Holocene,the sediments were fluvial facies and shallow lacustrine mainly composed of clay silt,fine silt,and silt;in the mid-term,they were composed of shallow lacustrine and deep lacustrine sediments mainly composed of clayey silt,silty clay,and clay;Late period is the sedimentation of shallow lake facies and river facies mainly composed of clayey silt,silty clay and fine silt.The stages of the Holocene in the southern lake area of the Hebei Plain started earlier than in the middle.(2)According to the analysis of stratigraphic characteristics and particle size parameters,it is concluded that the climatic and environmental evolution stages of Baiyangdian and Ningjinpo are basically synchronized,and the climatic and environmental evolutions are divided into 5 major stages: the early Pleistocene is slightly cooler than the early-early Mid-term warm and humid-mid-late cold and drought-late cold-warm cycle changes-Holocene warm and wet to warm and dry transition.And the evolution process of Ningjinpo and Baiyangdian lakes was reconstructed.Lakes in the central and southern Hebei Plains had accumulated water as lakes as early as the middle and late Pleistocene,and with the cold and warm climate fluctuations,they appeared to develop and shrink in the late Pleistocene.The evolutionary process of re-development in the early Holocene,maximum development in the middle,and contraction and even drying up in the late period.(3)According to the evolution stages and climatic characteristics of the two lakes,combined with the profile position and sedimentary characteristics,a brief summary of the lake's various development stages is briefly summarized;the dominant factors of lake development are discussed-under the influence of climate and environmental changes and human activities Changes in the pattern of water systems.