Biogenic silica content was determined in 25 surface sediment samples from the southern South China Sea to study its distribution and its modern oceanic environmental significance, which may provide further scientific evidence for paleoceanography explaination. This study showed that biogenic silica content in surface sediments and its water depth have evidently positive correlation, and the correlation coefficient was up to 0.782. Biogenic silica content was very low in continental shelf shallows and could not reflect the productivity of siliceous micropaleontology in surface waters, which may be affected by sedimentary types and terrigenous matter dilution. Distribution of biogenic silica content in surface sediments from deep water areas showed that it could not only reflect the paleoproductivity of siliceous micropaleontology in surface waters, but also indicate the strong or feeble upwelling. Thus, it was further confirmed that using biogenic silica content in sediments to trace upwelling and its change was effective and reliable. The analyzed result showed that radiolariia and poriferous specula have more contribution for biogenic opal, comparing with diatom in surface sediments from the northern studied area, probably owing to the diatom dissolved easily away and eaten by other organisms with little effort. In the upwelling areas, radiolarian, diatom and poriferous specula all approximately showed high abundance, which was consistent with high biogenic silica content.
A new approach to the basic composition char- acter of deep sea sediment is discussed in this paper for indi- cating its paleoenvironment meaning. For this purpose high precision grain size character of sediments from core NS93-5 was analysed by using the Laser Diffraction Particle Size Analyzer, combining with results of micropalaeontologic counting and trace element and calcium carbonate testing, to illustrate some main grain size indexes and their relationship with micropalaeontologic makeup and terrigenous input. It was showed that the grain sizes of deep sea sediment may reflect materials properties and their buildup framework. There are obvious relations between indexes of grain size ranges and abundances of different micropalaeontologic groups and terrigenous matters, in which grain size of <2 μm represents terrigenous composition, that of >5 μm is mainly made up of various microfossil shells, except for containing volcanic dust layers, and median diameter (MD) of grain size may be taken as proxy of paleoproductivity or paleoecologi- cal dynamic. These index and proxy were consistent with micropaleontologic records for well indicating important features of paleoceanographic ecology, showing that the mi- cropalaeontologic growth in the southwestern slope area of the South China Sea (SCS) was negatively correlated to ter- rigenous input since late Pleistocene and corresponded to glacial-interglacial global climatic changes incompletely, but had a regional particularity in this sea area.
