Late Holocene distal mud deposits off the Nakdong delta, SE Korea: evidence for shore-parallel sediment transport in a current-dominated setting

The distal mud deposits (DMDs) off the Nakdong delta represent a subaqueous delta on the inner continental shelf aligned parallel to the southeast coast of Korea and displaying a clinoform geometry. Hydrographically, the coast is characterized by a micro-tidal regime, the strong Korean Coastal Current (KCC) and the East Korean Warm Current (EKWC). Age models and sedimentary facies related to the clinoform geometries are based on high-resolution chirp subbottom profile data and have provided information on shore-parallel sediment transport and accumulation during the late Holocene sea-level highstand. The highest sedimentation rates (6.19–9.17 cm/year) produced steep foresets in the central DMDs at water depths of 35–50 m. Here, vertical burrows are repeatedly truncated by laminated mud packages displaying erosional surfaces. This region represents the main depocenter of the Nakdong subaqueous delta. The topset sediments of the southern DMD at ~40 m water depth closer to the river mouth show relatively low sedimentation rates (0.01–0.12 cm/year). Here, the muds have a predominantly mottled character. Similarly, the foreset sediments of the northern DMD at ~71–80 m water depth with sedimentation rates of 0.10–2.03 cm/year are also predominantly characterized by mottled muds. The spatial dispersal pattern of the DMDs is consistent with the coast-parallel front between the KCC and EKWC along the southeast Korean coast. In addition, the depocenter of the Nakdong subaqueous delta clinoform is affected by the near-bed turbulence generated by episodic storm events.