Characteristics Of Geochemical Elements And Magnetic Susceptibility Of Huahonggou Loess Section In Dalian City And Their Environmental Significance

During the last interglacial period of the Late Pleistocene,the global climate experienced many cycles of cold and warm,and the last interglacial period reached its peak in the deep-sea oxygen isotope MIS5e stage,which had an impact on the sedimentary environment and sedimentary characteristics.The fluctuating changes in the content of geochemical elements and various geochemical indicators have good indications for the climatic evolution of sediments.Magnetic susceptibility characteristics can reflect the degree of dryness,wetness,coldness and warmth of paleoclimate,and it is an important indicator to study temperature and precipitation in paleoclimate.This paper takes the loess section of Huahonggou Village,Xijiao National Forest Park,Ganjingzi District,Dalian City as the research object,through qualitative description and quantitative analysis of the loess geochemical characteristics,magnetic susceptibility characteristics and absolute geological age data,and compares Huahonggou loess with my country's The typical aeolian loess Luochuan loess is compared with the loess geochemical element characteristics of the Liaodong Peninsula area,and the climatic background and sedimentary environment evolution law during the development and formation of the profile are inferred,and the sedimentary characteristics of the sediments are discussed.(1)The characteristics of geochemical elements show that the chemical elements of Huahonggou loess are mainly composed of SiO₂ and Al₂O₃,followed by Fe₂O₃,and the average content of the three is as high as 84.92%.The fluctuations of the contents of major and trace elements showed obvious periodic characteristics.The contents of SiO₂ and Al₂O₃ showed an opposite trend with the change of depth,and the contents of Al₂O₃ and Fe₂O₃ showed a relatively consistent fluctuation trend with the change of depth,which was in line with the general soil-forming process.law.Geochemical indicators Chemical alteration index(CIA),weathering leaching coefficient(Ba),regression coefficient(TJXS),residual coefficient(CJXS),silicon aluminum iron ratio(S/AF),potassium-sodium ratio(K/N),calcium-magnesium ratio(C/M),and rubidium-strontium ratio(R/S)all showed good correlations,and the weathering degree experienced a change trend of weakening weathering-increasing weathering-weakening weathering-increasing weathering-weakening weathering.Corresponding weathering and leaching process,calcium and magnesium migration degree,aluminum and iron enrichment degree,weathering pedogenesis and soil cohesion degree also showed the same stage changes.The A-CN-K graphic analysis shows that the overall weathering degree of the profile is not very high,just entering the medium weathering stage,and the climate environment during the deposition of loess is relatively cold and dry.(2)Through the comparative analysis of the typical aeolian loess in my country,the Luochuan loess,the Huahonggou loess,the Malanhe terrace loess,the Changxing Island loess,the Zhoujiagou loess,and the Qidingshan loess of the Liaodong Peninsula,the constant element UCC curves and constants The ratios of stabilizing elements SiO₂/Al₂O₃,SiO₂/TiO₂,TiO₂/Al₂O₃ show that the Huahonggou loess contains more fine particles and lower quartz content,which is similar to the provenance of the Malanhe terrace loess.The main source,the source is the secondary source.By comparing and analyzing the chemical alteration index of the loess profile in southern Liaoning,it is found that the overall climatic environment of the Huahonggou loess during the depositional period is similar to that of the Qidingshan loess.(3)Magnetic susceptibility characteristics show that:the overall value of loess in Huahonggou is low and the coefficient of variation of mass susceptibility is small,the change trend of low-frequency mass susceptibility and high-frequency mass susceptibility curves are basically the same,and the frequency susceptibility curve fluctuates more frequently,the three curves all show obvious fluctuations and decreases at the depth of 300cm?245cm,indicating that the profile was formed in a relatively dry and cold stable environment.In the early depositional period,the climate environment changed abruptly,and the depositional environment changed from warm and humid to dry and cold.Using the linear regression equation,it is estimated that the annual average temperature during the depositional development period of the Huahonggou profile is between 3.64°C and 5.69°C,and the average annual precipitation is between 295.14mm and 400.91mm.The temperature and precipitation are much lower than those of modern times.The paleoclimate environment of the period was colder,arid,and the winter monsoon was stronger than that of modern times.(4)Optical luminescence(OSL)dating results show that the age of the loess in the Huahonggou loess section is concentrated at 124 ka B.P.,which is a relatively cold period in the last interglacial period of the Late Pleistocene,and the corresponding deep-sea oxygen isotope stage is the last interglacial period The glacial stage MIS5d after the heyday of MIS5e.Compared with the deposition rate in the early stage of the Jinchenglu section in southern Liaoning,it is found that the deposition rate of the Huahonggou loess is extremely fast.The appearance of the environmental event of rapid deposition of loess in the profile.