Origin of deep-water sediment waves in the Ulleung Interplain Gap, East Sea

Abstract

A detailed analysis of Chirp (2-7 kHz) subbottom profiles and a long (ca. 10 m) piston core reveals origin of deepwater sediment waves in the Ulleung Interplain Gap (UIG). On the basis of acoustic and lithologic characters, the sediments are divided into two units: 1) upper transparent unit (UTU) and 2) lower wavy stratified unit (LWSU). The LWSU is characterized by a few regular wavy reflectors with upslope migration. Also, it gradually decreases downslope in wave height, wave asymmetry and thickness, and consists dominantly of fine-grained turbidites with subordinate pelagic and hemipelagic sediments. These sedimentary features indicate that the LWSU was most likely generated by turbidity currents, rather than bottom currents. The UTU, discordant to the reflectors of the underlying LWSU, mostly comprises muddy contourites and manganiferous contourites with rare fine-grained turbidites, reflecting intensified bottom-current activity and infrequent input of turbidity currents from the slopes of the Oki Bank and Dok Island. Under these conditions, a thin (3-6 m thick), elongate mound of bottom-current deposits (UTU) formed on the fine-grained turbidity current waves (LWSU).