TROPICAL GEOGRAPHY ›› 2016, Vol. 36 ›› Issue (3): 427-437.doi: 10.13284/j.cnki.rddl.002852

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Long Scale Climatic Drought Events in the Yangtze River Delta since the Late Pleistocene: Environmental Magnetic Records from the Sediment

ZHOU Qixian1,YANG Xiaoqiang1,LI Jian2,LIN Qinglong2,PENG Jie1, WENG Yuanzhong1,DING Jieying1,LIU Chunlian1   

  1. (1. School of Earth Science and Geological Engineering,Sun Yat-sen Univeristy,Guangzhou 510275,China; 2. Zhejiang Institute of Geological Survey,Hangzhou 311203,China)
  • Online:2016-05-05 Published:2016-05-05

Abstract: Since the late Pleistocene, the Yangtze River Delta region affected by both the sea level and the East Asian monsoon, resulting in complex regional climate, has brought a lot of uncertainty for recovery of its long-term history and evaluation of future climate evolution. This article selected three long boreholes in the south Yangtze River Delta, CSB4, CSB6 and CSB8, to be studied. The analysis of environmental magnetism was for revealing the region's significant climate events recorded from the sediments since the late Pleistocene. The results showed that there were three significant low S300 areas in the three boreholes, when S300 was a low value, the magnetic susceptibility, ARM and SIRM values were low, and the ratio of IRMAF80mT/SIRM and that of ARM/ SIRM relatively were high, indicating that the concentration of magnetic minerals were reduced, particle size became small. Their sediments mainly were yellow silty clay containing ferromanganese tuberculosis. IRM acquisition curves and spectral quantitative analysis results revealed that the relative increase in the content of hematite high coercivity component in the sediments indicated that three significant dry events happened in the Yangtze River Delta. Based on the magnetic strata, AMS14C dating and optically stimulated luminescence dating, the three drought events happened in 163-121 ka B.P. (Event I), 57-42 ka B.P. (Event II) and 14-10 ka B.P. (event III), respectively. The three dry events were corresponding to a relatively low sea level, while the monsoon weakened, rainfall decreased, climate became dry, forming an oxidation-based environment.

Key words: the Yangtze River Delta, environmental magnetism, droughts, East Asian summer monsoon, sea level, the Late Pleistocene