苏北平原MIS 3阶段海侵事件的沉积记录

SEDIMENTARY RECORDS OF THE MIS 3 TRANSGRESSION EVENT IN THE NORTH JIANGSU PLAIN, CHINA

MIS 3阶段的气候与环境是古气候与古环境研究的热点,该阶段中国沿海地区的海侵过程是沿海平原环境演化的重要事件。根据苏北平原宝应By1钻孔的^(14)C年代结果和沉积特征、微体生物组合特点,确认苏北平原MIS 3阶段存在明显的海侵事件,潮滩与泻湖相沉积层的厚度约7m,深度在By1孔19～26m,海相层位于长江三角洲地区的典型末次冰盛期的硬粘土层之下,^(14)C年代在距今26～39ka之间,属于MIS 3阶段的沉积,岩芯沉积物的沉积构造以水平的薄层砂质粉砂沉积为主。沉积物中大量的海相有孔虫壳体在研究的岩芯段中是最丰富的;此外,还发现咸水环境下的Sinocytheridea impressa(Brady),Spinileberis pulchra与Spinileberis furuyaensis,Neomonoceratina chenae Zhao,Keijella bisanensis(Okubo)等形类壳体;该段岩芯中的植物残体、碳屑也很丰富,有机质含量丰富,显示比较封闭的弱动力环境,指示了潮滩、泻湖沉积环境。

Paleoclimate and environment studies of the Marine Isotope Stage 3 （MIS 3） of the Last Glacial cycle have attracted many researchers for the past decades. In China, the marine transgression of this stage has been considered to be highly important for the evolution of Chinese coastal plains. In this paper,we studied the upper part of 145 meters long Byl Core in Baoying in the North Jiangsu Plain by analyses of lithology, sedimentary stracture and fossil remains,by magnetostratigraphy,and by ^14C dating. The 7 meter long core sediments was collected from the depth interval of 19 - 26 meters of the borehole. They are mainly sandy silt layers with parallel bedding and contain a lot of foraminifera. Their sedimentary characteristics indicate a transgressional facies. Their ^14C dating given a range of 26 - 39ka, corresponding to the MIS 3. In addition, such marine fossils as Sinocytheridea impressa （Brady）, Spinileberis pulchra, Spinileberis furuyaensis, Neomonoceratina chenae Zhao, Keijella bisanensis （ Okubo ）, and marine ostracodes were also indentified in these core sediments. Plant remains and charcoal fragment are also abundant. These suggest a probably enclosed and shallow bay or lagoon environment, with relatively weak sedimentary dynamics. By the way, consolidated and hardened clayey sediments above the 7 meter long core sediments are typical units in the Yangtze Delta,indicating that they were deposited during the LGM period with the lowest seal level.