Study On The Magnetic Characteristics And Environmental Evolution Of Xiashu Loess In Nanjing

Due to the large thickness, complete stratum and continuous formation, Chinese loess is the ideal information carrier for quaternary climate reconstruction. As an important part of the eastern loess, Xiashu loess is the southern edge of loess, but also the northern edge of the red soil of south. As in the triangular area of the eastern monsoon, Xiashu loess is very sensitive to the East Asian monsoon evolution. In this paper, we select a typical profile of Xiashu loess in Xianlin (XL profile), Nanjing for the study. Based on the systematic study and the comparative analysis of environmental magnetic, geochemical and granularity, we draw the following conclusions:(1) The results show that the main magnetic minerals of XL profile mainly are magnetite and maghemite, it also contains different levels of lepidocrocite, pyrrhotite and hematite. The main magnetic mineral particles of palesoil are superparamagnetic particles and the main feature of loess is paramagnetic (single and multi-domain) material.The magnetic characteristics of XL profiles is affected by climate change for the magnetic susceptibility is affect by the magnetic material formed under different environmental.(2) The results show that the pedogenic environment of XL area is wetter than Luochuan loess and similar to Luochuan paleosoil and Zhenjiang Xiashu loess, and was underwent moderate chemical weathering.(3) The results show that the curve of susceptibility, weathering and granularity has a good relationship with the stratum.The results of the index analysis show that during about250-100ka, the chemical weathering intensity is increasing and the pedogenic environment of Xianlin profile is divided into four intervals: cold and dry, warm and wet, cold and wet, warm and wet. At the same time, the East Asian summer monsoon was gradually increased and the winter monsoon gradually weaker during these period. It also shows that the middle and lower valley of the Yangtze River area has gradually become warm-wet during about250-100ka.(4) By comparative analysis of the average particle size and magnetic susceptibility index with other typical sediments, it shows that during about250-100ka period, there is a good consistency between the climate change in the Yangtze River region and the global climate change, which indicats that the climate change in Yangtze River region greatly affected by global change. In addition, the climate change showes a greater instability in this period, especially in the penultimate glaciation.This study enrich the loess research in eastern China, and it also provide reference information for the study of paleoclimate and environmental changes in eastern China. It’s important for the study of paleoclimate of the Yangtze River, especially for monsoon evolution.