Facies association and depositional environment of shallow-water contourite deposits in the Hupo Basin, East Sea of Korea

This study focus on the depositional environment of the Hupo Basin shelf. We used sedimentary facies, grain size, textures, sediment color, as well as optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) age data.  A long sediment core (19ESDP-101, about 120 m) has been interpreted to be the product of shallow water contourites. The sediments in the core are divided into seven sedimentary facies grouped into four facies associations (FA): FA1) contourite drift, FA2) contourite drift and channel transition, FA3) contourite channel and drift transition, and FA4) contourite channel. FA1 resulted from the interaction between hemipelagic fallout, low-density gravity flow, and sedimentation under low velocity bottom currents. Compared to FA1, both FA 2 and FA3 are indicative of higher velocity bottom currents, owing to their relative increase in grain size and the presence of subtle indicators of bed-load transport. FA 4 portrayed massive to slightly bedded sand,  representing a contourite channel environment with high-energy conditions. The sedimentary facies stacking patterns observed at the study area site suggested that the depositional processes changed at the area where the core was optained. Therefore, the FA stacking pattern suggests the lateral migration of the contourite depositional system and continuous flow of the North Korean Cold Current (NKCC). Fluctuations in the bottom current activity, related to the intensification and deceleration of the NKCC, have caused fluctuations between contouritic and hemipelagic dominated periods. Our findings and interpretations can serve as a much needed reference for shallow-water contourite recognition in modern environments.