In the inactive Ulleung back-arc basin, accumulation of turbidites was predominant over hemipelagic deposition since about Pliocene time. Most of the late Pleistocene turbidite layers deposited in the time interval between major volcanic eruptions (at about 9,300, 21,000 and 50,000 yrs B.P.) contain heavy minerals that were derived mainly from the stable craton of the East Korean Peninsula. During major eruptions, however, turbidites composed dominantly of unstable minerals originated mainly from the volcanic arc of northwestern Honshu. A few turbidite layers contain mineral assemblages common to both margins. Turbidites in the Ulleung interplain gap were derived from the adjacent islands and banks.--Modified journal abstract.