中国东部中新世风尘沉积的发现及其研究意义

黄土高原红粘土古气候与古环境研究取得巨大进展。已知最老的红粘土时代达到22 Ma，在亚洲晚新生代环境演变研究，特别是在指示亚洲内陆干旱荒漠化、高原隆升的环境效应等方面有重要意义。结合野外实地调查和室内粒度、磁化率、扫描电镜和地球化学实验分析结果，对南京附近灵岩山剖面的沉积特征与风尘沉积证据进行了探讨。在灵岩山剖面玄武岩下覆的松散沉积层中有厚度超过4 m的风尘沉积层，时代在12 Ma以前，为迄今中国东部发现的新生代最老的风尘沉积物，是中新世季风气候出现之后的产物，推测与秦安红土剖面记录的15～13 Ma快速强烈粉尘沉积阶段一致，并和南极冰盖15 Ma开始扩大造成的全球降温事件有关联。

The Discovery of Miocene Aeolian Sediments and Its Paleoenvironmental Significance in East China

The researches on the paleoclimatology and paleoenvironment recorded by the red clay have made much progress in the region of China's loess plateau during the past decade. The earliest red clay in the western part of the loess plateau is about 22 Ma old. While in the eastern region to Liupanshan Mountain, the bottom part of the red clay sequences is no more than 9 Ma. Red clay was regarded as the result of aeolian sedimentation which is similar to the loess-paleosol sequences. Red clay records have important significance in the studies on Asian environmental evolution in the Era of Cenozoic, especially on the fields of inland desertification and the impacts of the Tibetan Uplifting. But no aeolian sediments older than the early time of Pleistocene has found in East China. On the basis of field investigation in the northern suburb of Nanjing, East China, the section of Lingyan Hill was discovered and the loess-like sediment layer was covered by basalt layers with the age of 12.17Ma. Field investigation and sampling was carried out and the whole sedimentary section was about 19 meters high not including the covered basalt layers. Under the basalt layer was the loess-like sediments. A general analysis about the loess-like sediments was carried out on the proxies of grain size, magnetic susceptibility, quartz SEM and geochemical elements. According to the sedimentary characteristics of the sediments and the laboratory analysis results, the 4-metre thickness loess like deposits in the section of Lingyan Hill was regarded as the aeolian sediments with the age of more than 12 Ma, which is the earliest aeolian deposits in East China. The deposit is the result of climatic event in the mid-Miocene, which was corresponding with the 15-13Ma rapidly strong deposition of aeolian sediments in the Qin'an section in Loess Plateau and the enlargement of ice sheet in Antarctic after 15Ma.