晚更新世以来长江三角洲长尺度气候干旱事件 ——来自沉积物环境磁学的记录

选择位于长江三角洲南部区域的3个钻孔CSB4、CSB6和CSB8，开展环境磁学方面的研究，以揭示该地区晚更新世以来沉积物记录的显著气候事件。结果显示：3个钻孔都存在明显的S300低值区域，其变化规律为当S300为低值时，磁化率、ARM和SIRM的值较低，而IRMAF80mT/SIRM和ARM/SIRM的比值相对较高，表明磁性矿物浓度降低、粒度变细。同时S300低值区域沉积物以黄色粉砂质黏土为主，含铁锰质结核。IRM获得曲线定量分析结果揭示：沉积物中赤铁矿等高矫顽力组分的含量相对增加，指示长江三角洲区域3次显著的干旱气候事件。在磁性地层及其AMS 14C、光释光测年基础上，推断3次干旱事件发生的时间分别为163―121 ka B.P.（事件I）、57―42 ka B.P.（事件II）和14―10 ka B.P.（事件III），对应海平面相对较低时期，季风减弱，降水减少，气候干旱，形成以氧化作用为主的环境。

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

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.