记录:1 024 AD前后南中国海最强烈的灾难事件

在南海东岛牛塘海鸟粪土沉积层中发现一岩性明显不同于上、下层位的珊瑚砂夹层.通过对沉积柱DY4进行详细的粒度特征、元素地球化学和生物残留分析,结果表明58~69 cm深度的珊瑚砂夹层对应于一次突然的海洋沉积环境事件,很可能与历史时期一次最强台风袭击所导致的冲溢沉积有关.对临近该珊瑚砂夹层的上、下沉积物中(57~58 cm和70~71 cm)多粒陆地植物颖果进行8个样品的AMS14C测年分析,发现上、下两个年龄组非常接近,珊瑚砂夹层沉积大约发生在994~1 075 AD之间,平均中间年龄大约为1 024 AD史前的这次强台风袭击对东岛的生态环境很可能造成了严重的破坏.

Sedimentary records: catastrophic marine flooding event occurred on Dongdao Island of South China Sea around 1 024 AD

The sediment cores from "Cattle Pond" on Dongdao Island of South China Sea contain a coral sand sediment layer embedded by ornithogenic sediments with sharp stratigraphic contacts.The analyses of grain-size component,elemental geochemistry and biological remains in the sediments show that the interbedded coral sand layer corresponds to a sudden marine sedimentation event,very likely from extraordinary washover deposition.The ages,from AMS14C dating,of the terrestrial plant caryopsis(Urochloa paspaloides) well preserved in the ornithogenic sediments below and above this sand layer average around 1 024 AD,a further indication that the deposition of this interbedded coral sand layer is a precipitous incident.This marine flooding event recorded in these sediment cores may be the strongest among those reported so far in South China Sea,and,as seen from the biological remains in the sediments,may have caused catastrophic damage to the tropical eco-environment on Dongdao Island.This study shows that the lacustrine sediments influenced by seabird droppings on tropical coral islands can be used to reconstruct prehistoric intense cyclone records.