Modern sedimentation in the Japan Trench: implications of the mineralogy and chemistry of clays sampled from sediment traps

Abstract

To determine the mineralogical and chemical characteristics of clay minerals, the composition of the clay-sized fraction and the sedimentological processes which affect these clay particles, two sediment traps were moored at depths of 8700 and 4000 m at the triple junction of the Japan Trench. Six types of clay minerals and nine types of non-clay minerals were identified by transmission electron microscopy. Smectite and illite were the most important clay minerals whereas quartz and plagioclase were the major non-clay minerals. Chemical analyses of the clay minerals showed that the smectite was an Fe–Al beidellite, illite a di-octahedral type rich in potassium and chlorite an Fe–Mg type. Two major mechanisms govern the transportation of the lithogenic mineral particles in the Japan Trench: (1) transportation by the turbidity currents in the neighbouring trough and canyon and (2) wind-borne transport of loess from mainland China. The settling time of clay-sized minerals to the bottom of the Japan Trench was roughly estimated to be 1 year.