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The deep core samples (site name: 21ESDP-203, drilled depth: 200.3m) collected from the southeastern shelf (Korea strait) of Korea were used to characterize physical property with sedimentary depth. Laboratory analysis (i.e., velocity and physical properties) was conducted on core samples. The physical property data were readily classified in good agreement with the lithological units alternating sandy mud and muddy sand with sedimentary depth. Based on compressional wave velocity data, the geoacoustic units are divided by 11 units with sedimentary depth. In particular, the upper sediments above 15 meter are characterized by high compressional wave velocity (greater than 1700 m/s) and high wet bulk density (∼2.2g/cm3 in maximum). Whereas, the porosity is very low (25% in minimum). This is due to the abundance of sandy sediments in this interval. The shear wave velocities of sediments are calculated from the compressional wave velocity and the effect of burial depth (Hamilton, 1980). The range of shear wave velocity is from 267 to 1345 m/s. However, most of data are less than 400 m/s. The velocity ratio (Vp/Vs) and the velocity gradient with sedimentary depth are calculated and estimated. The patterns are slightly different from those of Hamilton (1980). These results suggest that the physical properties are not only controlled by lithology and compaction caused by dewatering with burial depth, but also by different sedimentary environment after deposition.

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.

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley reveals that the Nakdong River valley deposits, approximately 60 - 70 m thick, consist of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuary, coastal/shoreface, and delta. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed approximately before 12 ka. The transgressive systems tract (TST) can be divided into two depositional systems (Unit II and III). The river-derived sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 6 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the recent deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 6 ka.