Distribution of dominant species and abundance of nannofossils in surface sediments of the central and northern parts of the South China Sea——Comparison and discussion

The distributional trends and their controlling factors of dominant species and nannofossil abundance in surface sediments of marginal and coastal seas in low to middle latitudes and high latitudes are discussed on the basis of the analysis of 146 samples from the nothern and central parts of the South China Sea and of comparison between the results of current work and data from other seas.
Despite significant variations in taxonomic composition between seas or between areas within one sea, there are some general trends in nannofossil distribution of marginal and coastal seas.All those nannofossil assemblages in middle and low latitudes are dominated by two species:Gephyrncapsa oceanica and Emilurnur huxleyi.Although the relative abundance of these species may vary greatly from area to area.Gephynxapsa creznica in general prevails in nearshore or semiclosed environments, increasing in number towards the shoreline, while Emiliania hurleyi increases in relative abundance towards continental slope and open ocean environments, decreasing in abundance again only in very deep-water, i.e., near the CCD.Similarly, the abundance of calcareous nannofossils, as a whole, is lower nearshore, increasing with water depth towards the continental slope, and then decreasing again towards and near the CCD.In high latitudes, the dominant species are Emilianui huzleyi and Cacmlithus pelagicus.
There are two groups of factors controlling the nanno (ossil distribuoon in surface sediments:ecological factors, including particularly water temperature, supply of nutrients; and sedimentological factors, including influx of terrigenous materials and deep-rwater carbonate dissolution.