西沙石岛末次冰期风成沉积序列新划分及其旋回特征

Last glacial aeolian sequence at the Shidao Island of Xisha Islands and its cyclic features

西沙石岛的风成碳酸盐岩是东亚季风末次冰期的产物,以砂丘与古土壤二元旋回的形式记录了东亚季风气候的干湿变化。利用西石2井钻井岩芯资料结合石岛野外地质剖面的详细考察,对石岛风成沉积序列进行了重新的地层划分,将石岛风成沉积分为三层砂丘与两层古土壤的沉积组合。通过对测年数据及东亚季风末次冰期气候变化特征的分析,认为石岛末次冰期风成沙丘与古土壤记录与黄土高原L1黄土的5个次级气候阶段一一对应,都是对东亚季风末次冰期气候背景下,气候干、湿变化在岁差尺度的沉积响应,是具有稳定周期的气候旋回。

The aeolian carbonate deposits cropped out at the Shidao Island of Xisha Islands are the product of the East Asian monsoon in last glacial stage.The dry and wet alternation of the East Asian monsoon has been recorded by the binary cycles of the deposits in the forms of dunes and paleosols.Using the drilling core of Xishi-2,combined with the detailed investigation of the geological sections at the Island,the aeolian sequence is re-divided into three layers of sand dune and two layers of palaeosol.Based on the dating data and the climatic changes in the East Asian monsoon,we believe that the vertical changes of the aeolian sequence or the alternation of dunes and paleosols correspond well with the second-order climatic sub-stages of L1 found at the Chinese Loess Plateau,indicating a cycle on precessional scale.