Heavy-mineral assemblages in the cored sediments from DSDP Legs 56 and 57 show a distinct change of source rocks, from older sedimentary rocks during the Oligocene to volcanic rocks during the Miocene through Pleistocene. The former might have been supplied by the "Oyashio ancient landmass," and the latter from the volcanic areas in Hokkaido and northeast Honshu. This indicates a shift of the Japanese Islands toward the continent.

Supplement to: Miki, Takashi; Takahashi, Ryohei (1980): Heavy-mineral analysis of sediments from the Deep Sea Drilling Project transect of the Japan Trench, Legs 56 and 57. 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, 1019-1025