West Philippine Sea Sediments Since The Late Pleistocene Fossil Assemblages And Their Provenance

The sedimentology and mineralogy from the cores ph03 and ph04 in the West Philippine Sea are studied systematically and comprehensively. The mineral assemblages, sources of the sediments, sedimentary characteristisc and environmental evolvement from the latest Pleistocene were discussed.The grain size of the sediments are fine in the core and consist mainly of silt and clay. The XRD analyses of the content of clay minerals are carried out after the extraction of fractions smaller than 2μm in size from sediment samples. The results indicate the clay assemblage characters in this area: smectite is the most abundant(average percentage content is about 50%) and of high content at the tephra layers; chlorite and kaolinite contents are less than smectite's, and with accordant variation; illite contents is the lowest. The whole rock mineral assemblage characters: calcite content is highest and increase gradually upward to keep stable; quartz, plagioclase and amphibole content have a reverse trend.The origins of sediments in the region fall into four categories: terriginous clastic sedimentation, marine organic sedimentation, volcanic sedimentation at the sea bottom, and authigenesic sedimentation. The sources of terriginous are Philippine islands and Asia continent. The origin rock of submarine volcanic deposition is basalt. The marine biological deposition and authigenesis deposition are influenced by the marine environment, however, terrigenous deposition, and submarine volcanic deposition are related to the tectonic region.The studied sediments are divided into two intervals, based on the sedimentary environmental evolution after the latest Pleistocene. (1)latest Pleistocene:terriginous clastic sedimentation with sediments of coarse grains predominated over marine organic sedimentation, during the low global sea level; (2)Holocene: marine organic sedimentation dominated this area because of the high sea level and stable sedimentary environment, on the contrary, terriginous clastic sedimentation weakened. So we can see that the sea level changes after the latest Pleistocene define the sedimentary environment of this area.