Abstract:
Hefei is located in the north bank of the middle and lower reaches of the Yangtze river and Xiashu loess is widely distributed. Through the analysis of lithology, oxide content and geochemical weathering parameters of BK2 borehole section in Hefei area, the geochemical characteristics and climate change rules of the eolian sediments in Hefei area are studied. The core section of the field borehole shows good continuity of the strata, and the quaternary sedimentary framework of the hole is divided according to the age data. The bottom boundary of Qh is 1.20 m, the bottom boundary of Qp3 is 5 m, and the depths range from 5 m to 35.10 m belong to middle and late Qp2. The values of SiO2 and TiO2 in Hefei loess gradually decrease with depth, whereas those of K2O, Na2O, CaO, MgO gradually increase and those of Al2O3, Fe2O3, P2O5, MnO show no obvious increase. The average content of the main chemical constituents (SiO2+Al2O3+Fe2O3) of Xiashu loess in Hefei is up to 88.99%, which indicates that the climate in this area is relatively humid. The degree of chemical weathering is relatively strong. Weathering index and residual coefficiency decline gradually from bottom to up while Bavalue and de-alkali increase from bottom to up, which demonstrate the weathering intensity decreases from bottom to up. These imply that the wetness degree decreased gradually during the sedimentation of Xiashu Formation; The average CIA value of Xiashu loess and the degree of removing Ca, Na and K of Xiashu loess are all higher than that of Luochuan loess, indicating that the paleoclimate of Xiashu loess was warmer and wetter than that of Luochuan at accumulational stage, drier and cooler than that of Xuancheng, and closer to that of Nanjing and Zhenjiang. Geochemical feature of sedimentary records from borehole section in Hefei shows that since 0.5Ma, it has experienced the change from wet heat to dry cold, which can be roughly divided into four stages:35 m to 14.50 m, 14.50 m to 4.50 m, 4.50 m to 1.20 m, and 1.20 m to 0 m. The climate has changed from warm wet-warm dry-cold dry-warm wet, indicating that the climate change in the region has a global consistency since the middle-late Pleistocene, which matches with MIS curve.