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

Abstract

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 nearbed turbulence generated by episodic storm events.

Upslope migrating sand waves on sediment-starved shelves: An example from the southeastern continental margin of the Korean Peninsula

“…Sediment texture and composition on the southeastern continental shelf of Korea vary spatially with increasing water depth (Koo et al, 2014). Extensive clay-rich terrigenous muddy sediments, named as the Korea Strait shelf mud (KSSM; Chun et al, 2015), occur above 100 m on the inner shelf parallel to the coastline. In contrast, the outer shelf is mainly covered by coarser relict sediments that are thought to have been deposited during lowstand sea level (Koo et al, 2014).…”

“…Peak non-tidal currents vary spatially along the margin, exceeding 30 cm/s in the middle of the Korea Strait (Teague et al, 2001). Strong typhoons originating from the northwestern Pacific Ocean are common in the Korean Peninsula (Choi et al, 2012) and are significant agents in sediment movement and deposition (Chun et al, 2015).…”

Quaternary mud deposits on the Korean shelf—processes, facies, stratigraphy: an introduction and future challenges

“…Off the Nakdong delta along the southeastern coast of Korea, Chun et al (2015) evaluate the subaqueous delta clinoform deposits on the inner shelf on the basis of high- Fig. 3 Summary of the history of partitioning of the HMB.…”

Holocene sedimentation in the Hupo Trough of the southwestern East Sea (Japan Sea) and development of the East Korea Warm Current

“…Consequently, the EKWC transports the river-derived sediments through the Korea Strait into the Ulleung Basin. A distal mud deposit (Korea Strait shelf mud) along the southeastern coast of Korea in a modern-type depositional environment might be formed by shore-parallel sediment transport (Bahk et al, 2004; Chun et al, 2015; Lee et al, 2010).…”

“…Consequently, the thick accumulation of Holocene sediments in the inner shelf around the Korea Strait indicated that the Nakdong River had played an important role in supplying the fine-grained sediments into the East Sea. Additionally, the EKWC led to the deposition of Nakdong River-derived sediments along the southeastern coast of Korea after the breaching of the Korea Strait during the postglacial sea level rise (Chun et al, 2015;Kong and Park, 2007;Lee et al, 2010). Among the three branches of the TWC, the evolution of the EKWC flowing along the southeastern coast of Korea has not been studied in detail, compared with the OB and NB.…”