海南岛东南部海岸砂丘风暴冲越沉积记录

A Coastal Dune Overwash Record of Typhoon Storm Events from Southeastern Hainan Island

通过海南岛东南部海岸详细的古风暴学考察,在尖岭海岸发现了含有风暴冲越沉积物的海岸沙丘剖面,分别命名为JL-1和JL-2剖面,试图从海岸沙丘沉积记录中提取历史上的风暴事件信息。沉积物粒度、磁化率等参数的指标分析表明,这两个剖面含有典型的风暴冲越沉积物,利用放射性核素AMS14C测年、OSL测年分析,并结合历史文献记载,确定这些风暴沉积层是多次台风作用的产物,其形成机制与风暴浪越过海岸沙丘的堆积有关,风暴流越过沙丘顶部后不能回流,导致风暴流携带的沉积物迅速沉积。此外,依据Stockdon经验公式计算结果,该地点沉积记录所代表的最大风暴事件相当于100到200年一遇的重现期。研究表明,该处海岸沙丘冲越沉积含有南海台风强度与重现期的重要信息。

In the present study,coastal dune deposits are analyzed to derive the information on historical storm events.Paleotempestology investigations were carried out for the southeastern part of Hainan Island. The storm deposits identified are interbedded within the aeolian coastal dune proles on the Jianling coast. They are characterized by coarsegrained overwash deposits during the extreme storm events,as revealed on the basis of detailed stratigraphic division,grain size and magnetic susceptibility analyses. The age of the storms events was determined using the14 C and OSL dating methods,in combination with historical documents. When a storm surge hits the coast,the coastal dune may be overtopped or breached,and a low-lying dune associated with a large,flat terrain at the backshore is suitable for trapping the storm sediment to form a thick-bedded,sandy washover deposit. The Stockdon empirical equation was used to calculate the overwash height,indicating that the storm record at the Jianling site represents the product formed by several storms,with their return periods being 100 to 200 years. The result obtained implies that the coastal dune here contain important information on the intensity and frequency of occurrence of the South China Sea typhoons.