南沙海区更新世以来的火山灰及其地质意义

PLEISTOCENE VOLCANIC SHARDS AND THEIR GEOLOGICAL SIGNIFICANCE IN THE NANSHA AREA OF THE SOUTH CHINA SEA

南沙海区 1795 7和 1795 9柱状样中含有丰富的火山灰 ,它们可以分成 3种类型 ,即块状玻屑、泡状玻屑和微泥球 ,自下而上构成 8个火山灰层 (NM1— NB5 ) ,记录了 8次明显的火山活动 ,年龄从 0 .135 Ma到1.34 Ma,化学成分的分析显示这些火山灰可能来自南沙海区南面的巽他火山带 ,这些火山灰层具有时间标志作用 ,可以作为一种有效的地层划分和对比的工具。

Abundant volcanic shards were found dispersed in sediments in Cores 17957 and 17959 from the Nansha Area of the South China Sea.They have been divided into three forms,namely,lump,cellular and micro mudsphere shards.Eight volcanic shard layers(NM1—NB5)have been recognized in the two cores in an ascendant order,in ages from 0 135 to 1 34 Ma.The age assignment of the layers is based on a direct correlation with the paleomagnetic and oxygen isotopic records.Core 17957 is 1 37 Ma old at the bottom, while Core 17959 is 0 80 Ma old at the bottom Of the 8 volcanic shard layers,3 from Matsuyama epoch are named NM1—NM3,and 5 from Brunhes epoch named NB1—NB5 Chemical analysis indicates that these volcanic shards may come from the Sunta volcanic zone south of the Nansha sea area The layers can be used as an efficient tool for further dating of Pleistocene sediments in the South China Sea.