SEDIMENTARY RECORDS OF VOLCANIC ACTIVITIES IN THE SOUTH CHINA SEA OVER THE PAST 480 ka

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.