APPLICATION OF CENTRIFUGATION TO CLASSIFICATION OF MARINE CLASTIC SEDIMENTS

The grain size of sediments, as a result of complex geological processes of weathering, transportation and deposition, is one of the most important physical indicators in sedimentological study. The size of sediment particles may document detailed information on both provenance and hydrodynamics. It is very important for paleoenvironmental study to separate sediments into different groups of grains size effectively and rapidly. Pipette method is one of the methods often used by sdedimentologists for this purpose, but for marine sediments, which are usually too fine, this method is not satisfactory enough due to its time-consuming process, much loss and low separation efficiency. Centrifugation can accelerate the settling velocity of fine particles and increase the separation efficiency. Therefore, 27 surface sediments collected from the mud area along the inner continental shelf of the East China Sea is separated into four grades (< 2 μm, 2-10 μm, 10-63 μm, >63 μm) using the centrifugal method. Microscopic observation of the samples after sizing shows that there is no mixture between different grades, indicating that the separation using the centrifugation was effective and feasible. The average recovery rate for all samples is about 94%, and the highest is over 97%. The loss of each sample is positively correlated with the content of fine particles (< 10 μm), that is, the more the fine particles contained, the greater the loss. Further comparison with the results from the laser diffraction particle size analyzer is also carried out. It shows that the laser analyzer has a poor discrimination of particles < 10 μm, underestimating of < 2 μm particles and overestimating of 2-10 μm particles. This study shows that the centrifugation can effectively and rapidly separate fine marine sediments into grain size groups.