Mineral assemblages of DSDP Holes 436 and 438A and the upper section of Hole 439 (871.5-911.0 m sub-bottom) resemble each other and are composed of montmorillonite (probably a small portion of montmorillonite/illite mixed-layer clays), illite, chlorite, kaolinite, quartz, plagioclase, hornblende, calcite, dolomite, siderite, gypsum, pyrite, and halite. In the middle section of Hole 439 (933.5-1041.0 m), clinoptilolite is also found. In the lower section of Hole 439 (1077.5-1150.0 m), montmorillonite is not confirmed, and clinoptilolite and mixed-layer illite are found. These assemblages, which also contain detrital kaolinite, are generally found in sediments from brackish-water environments. At Site 439, more than 1000 meters of sediment might have been removed by erosion at the base.

Supplement to: Aoyagi, Koichi; Kazama, Toshie (1980): Sedimentary mineralogy of argillaceous sediments from Deep Sea Drilling Project Holes 436, 438A, and 439, Japan Trench. In: Scientific Party, Initial Reports of the Deep Sea Drilling Project, 56/57 (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 56-57, 1011-1017