SETTLING VELOCITY OF FORAMINIFERAL TEST: AN EXPERIMENT WITH SAMPLES FROM THE CHANGJIANG RIVER ESTUARY
Zhu Xiaodong (Department of Geo and Ocean Sciences, Nanjing University, Nanjing. China,210008)
Majority of foraminiferal taphocoenoses in the Changjiang estuarine or deltaic area are allochthonous ones transported by tidal currents from sea and, hence, are controlled by transport process. In view of the fact that suspension and saltation are the main transport mechanisms for tests, settling velocities of foraminiferal tests should play a critical role in determining the transport distances and sorting effect. Therefore, for their settling velocities, foraminiferal tests of 12 dominant and representative species and forms from the area are measured, which have enabled us to establish the "test diameter/settling velocity equations" and also the "equivalent diameter equations" through relating test diameter to that of quartz grain. The results of the experiment have given rise to a quantitative interpretation of the causes of foraminiferal distribution in the area. As the results were proved to be applicable to foraminif eral taphocoenoses in known modern environments, they can be used to distinguish indigenous taphocoenoses from allochthonous ones with ease when sediment grain sizes are compared with equivalent diameters of foraminiferal tests-With the results of the present experiment, for example, a 30-meter long drilling core was analysed successfully.