Preliminary analysis of grain-size populations with environ-mentally sensitive terrigenous components in marginal sea set-ting

Abstract

Terrigenous components were separated from the bulk sediment of Core A7 from the Okinawa Trough and Core A37 from the Ryukru Trench and grainsize distributions of these subsamples were analyzed. Based upon an analysis of the grainsize data of the two sedimentary sequences, grainsize populations are identified to be sensitive to sedimentary environmental changes. The modal values and size ranges of the two main grainsize populations in Core A7 are evidently different from those of Core A37, indicating the spatial variability of sediment sources and transport processes between the two places. The downcore variations in the content of the environmentally sensitive grain-size populations reveal that during the accumulation of sedimentary material the environment remained relatively stable at the site where Core A7 was collected, except for the apparent events for the formation of two turbidite layers and a volcanic ash layer. However, the sedimentary sequence of Core A37 shows six sedimentary cycles, indicating a highly variable sedimentary environment at this location.