Particle-size Distribution and Content of Calcium Carbonate in Marine Sediments in the Northern Part of the Goto-nada Sea, Nagasaki Prefecture, Japan

摘要

The particle-size distribution and the content of calcium carbonate of 47 surface bottom sediment samples collected from the northern part of Goto-nada Sea by the Geological Survey of Japan on September, 1976 were examined. The bottom sediments of this area were classified into three main sediment types according to the grain-size distribution. Type V sediment are definitely coarse-grained gravely sand with the high content of calcium carbonate. This sediment type distributes mainly on the Sakito-Hirashima Ridge. The accumulation of rich organic shell fragments in this area is apparently due to the warm current generated by the inflow of the branch of the Tsushima Current. The sandy sediment defined as sediment type II a is consisted of moderately sorted coarse-grained sand with negative skewness and distributes in the narrow belt along the southern margin of the area of the sediment type V. The sediment type II is defined by well sorted fine-grained sand and covers on the offshore deep sea floor. The bottom sediment samples were also examined by the Q-mode cluster analysis and classified into eight groups. The relationship between the sediment types and the cluster groups is well correponding each other.