辽东半岛末次间冰期砂质沉积物的粒度端元特征与古环境演变

END-MEMBER CHARACTERISTICS OF GRAIN SIZE OF THE SANDY SEDIMENTS IN LIAODONG PENINSULA AND PALEOENVIRONMENTAL EVOLUTION OF THE LAST INTERGLACIAL PERIOD

辽东半岛作为东亚风成沉积系统的重要组成部分,受海-陆相互作用的影响,对气候变化表现出强烈的敏感性,蕴藏着中国东部沿海地区季风演变与古环境变迁的历史。本研究通过对大连长兴岛港华剖面362 cm厚的砂质沉积物的粒度数据进行参数化端元分析,探讨了该剖面沉积物的搬运方式、搬运动力及沉积环境,揭示了该地区末次间冰期(MIS 5a~5c)的古气候演变特征。结果表明:1)港华剖面沉积物粒度组分可以分解为4个端元:EM1代表高空西风作用下远距离悬浮搬运的细粉砂组分;EM2代表地方风系作用下低空短距离搬运的极细砂组分,在冬季风势力增强时可能被二次搬运;EM3和EM4代表以尘暴形式近地跃移搬运的砂粒组分;粗粒级组分EM3、 EM4含量变化对冬季风强度变化具有良好的指示意义。2)将各端元组分含量、中值粒径(Md)、 Fe_(2)O_(3)含量与深海氧同位素曲线对比,表明MIS 5c~5a期间港华剖面依次经历了相对暖湿→干冷→趋向于温湿化的气候旋回变化。3)根据光释光年代测定结果,港华剖面为末次间冰期的沉积物,通过与其他地区同时期的研究结果比对,港华剖面的环境演变信息与全球气候变化事件具有较好的对应,说明辽东半岛的风沙沉积在揭示中国东部沿海地区的环境演变方面具有重要价值。

The Liaodong Peninsula,as an important part of the East Asian aeolian deposition system,is one of the ideal regions for studying the evolution of the East Asian monsoon and palaeoenvironmental changes due to its sensitivity to climate change.In this study,an aeolian sand depositional profile 362 cm in thickness was obtained in the Liaodong Peninsula area,named Ganghua Profile(GH:39°32′13.94″N,121°20′01.63″E;30 m a.s.l),and sampled at 2 cm intervals.3 samples were collected at the depth of 152 cm,236 cm and 292 cm for OSL dating,and the age data obtained were 84.0±5.2 ka,78.8±4.98 ka and 96.7±5.2 ka,respectively.Considering the error range of the OSL dating,the grain size and geochemical elements of Ganghua profile and the deep-sea oxygen isotope curves were compared,and strong correspondence was found.Therefore,it is presumed that the profile determined to the period of the Last Interglacial period(MIS 5a~5c).Meanwhile,environmental proxy indicators such as grain size and chemical elements were also measured.The grain size data can be decomposed into 4 end-members:EM1 is composed of fine silt with a peak value of 5.7φ,which represents the component transported by the high-level westerly wind from long distance,and it usually exists in the form of floating silt and settles when winds weakens or with precipitation.The peak value of EM2 is 4.0φ,dominated by coarse silt and very fine sand,which transported in low altitude by the local wind system and its deposition of near-surface coarse grained sediments affected by dust storms;The peak values of EM3 and EM4 are respectively 2.6φand 2.2φ,mainly fine sand,which transported by near-surface saltation in the form of dust storms.In addition,both of them have high contents in the profile(62.52%),indicating that the EM3 and EM4 are the main sediments supply sources in the profile.Moreover,due to the significant positive correlation between EM3 and EM4 and the median size,we believe that the two are sensitive components affected by winter monsoon,indicating the intensity change of winter monsoon.On the basis of the existing research results,we have discussed the climate change in the study area during the Last Interglacial period(MIS 5c~5a).The results show that:The Last Interglacial climate change in the study area can be roughly divided into three stages:(1)During the MIS 5c,the winter monsoon was relatively weakened,the summer monsoon was stronger,the regional pedogenesis was enhanced,and the climate was relatively warm and humid.(2)From the MIS 5b to the early MIS 5a,the climate was dry and cold,and the climatic environment was very harsh.Meanwhile,the fall of sea level contributed to the exposure of the continental shelf in the Bohai Sea,providing sufficient supply of sandy sediments for the deposition.(3)During the MIS 5a,the climate fluctuated frequently and was in the transitional stage of mild and wet,but the climate was relatively colder compared with that of MIS 5c.