SEDIMENTARY RECORDS OF VOLCANIC ACTIVITIES IN THE SOUTH CHINA SEA OVER THE PAST 480 ka
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摘要: 通过对南海西部越南岸外MD05-2901孔的研究,建立了48万年来高分辨率的氧同位素年代地层。针对磁化率结果显示的13层厚度超过4 cm的磁化率峰值层,将其年代和菲律宾巴拉望岛岸外的MD972142孔的火山灰层进行对比,发现其中10层完全对应,证明磁化率峰值层是由火山喷发作用造成的,说明48万年来菲律宾火山带喷发的粉尘可以沉积到南海西部。磁化率峰值层样品的粒度特征明显不同,呈双峰态分布,粗颗粒组分较多,空隙率高,密度和颜色反射率较小。由此证明,磁化率和粒度分析可用于寻找肉眼不可见的火山喷发作用的沉积学记录。研究发现的受火山喷发作用影响的特殊层位,可作为地层对比的参比标志,并为追溯48万年来大气和洋流的变迁提供了参考资料。Abstract: Magnetic susceptibility (MS) and grain size distribution of core MD05-2901, which is located in the upwelling area off eastern Vietnam in the South China Sea, were measured. Oxygen isotope stratigraphy indicates that the core spans a time period of 480 ka. Magnetic susceptibility curve displays glacial-interglacial variations in general, but with prominent peaks. Ten out of thirteen MS peak layers, which are thicker than 4 cm, correlate well with the volcanic ash layers recognized in core MD972142 offshore northwestern Palawan. The result indicates that the volcanic material from the Philippine seismic zone could have reached the western part of the South China Sea during the last 480 ka. The content of size fraction>16μm is relatively high in the layers of high MS values. In addition, grain size distribution of these layers shows distinct double-mode, indicating input from volcanic activities. MS and grain size features of the sediments can be used as an indicator of volcanic activities, which otherwise can't be examined easily by naked-eye. The MS peaks are also a useful tool for chronology and stratigraphic correlations.
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Keywords:
- volcanic ash /
- magnetic susceptibility /
- grain size /
- late Quaternary /
- South China Sea
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