Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea

Sixteen piston core samples collected from the Heuksan Mud Belt on the southeastern inner shelf of Korea were analyzed to characterize sediment property and distribution in relation to interpreted seismic units. The results from seven of 16 cores are presented in this study using core locations along a seismic track line. Variations in physical properties with depth gradually increased and/or decreased, depending on the characteristics of the specific property. Property patterns are primarily the result of dewatering caused by compaction and/or consolidation. Significant variations in depth are due to differences in sediment texture. In particular, core P03 is largely composed of sandy sediments below 170 cm. All core data come from three specific seismic Units: I, IIa and IIb, in descending order. The seismic patterns that define these units are interpreted as related to the rate of sea-level change during transgressions and depositional processes during the Holocene. Regionally, the variation of physical properties along the seismic profile is likely to reflect the relative characteristics of the seismic units. Unit I is characterized by low shear strength/wet bulk density and high porosity. Unit IIa appears to have higher shear strength than Units I and IIb. Unit IIb shows high wet bulk density and velocity. These observations suggest that the physical properties are mainly controlled by depositional processes related to sea-level change. Clay fabric analysis that uses a scanning electron microscope for two core samples shows the change of particle arrangement due to compaction caused by overburden loading with burial depth. In the upper part of the core, edge-to-edge and edge-to-face contacts dominate. In contrast, face-to-face contact characterized by the well-oriented arrangement of clay particles frequently occurs in the lower parts of the cores, indicating sediment compaction or initial consolidation caused by overburden pressure.