长江河口三角洲区有孔虫沉降速度试验

SETTLING VELOCITY OF FORAMINIFERAL TEST: AN EXPERIMENT WITH SAMPLES FROM THE CHANGJIANG RIVER ESTUARY

作者对有孔虫壳体沉降速度进行了测试和研究,提出了不同属种有孔虫的壳径与沉降速度相关方程,引进了“当量直径”的概念,并用于长江口三角洲地层中的化石群,提出了解释潮汐河口有孔虫埋葬群的形成机理,从而定量的研究和辨别三角洲地层中的原地埋葬和异地埋葬化石群。

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.