Physical properties and geoacoustic provinces of surficial sediments in the southwestern part of the Ulleung Basin in the East Sea

Abstract

A total of 157 piston and box core samples were collected and analyzed to characterize physical properties and geoacoustic provinces of surficial sediments in the southwestern part of the Ulleung Basin in the East Sea. The results and distribution patterns of surficial sediment texture, physical and acoustic properties reflect well the sedimentary environment like distribution and composition of sediment in the study area. The inner shelf and basin slope in this study are dominated by fine-grained sediments and show high porosity and water content, with low bulk density and velocity as well. The trough of the Korea Strait and outer shelf, which is composed of coarse-grained sediments, shows low porosity and water content and high bulk density and velocity. Based on in-situ velocity and sediment properties, the study area is divided into five provinces: (1) Province IA is hemi-pelagic mud partially mixed with intermittent sandy sediments which are derived from the outer shelf due to slide/slump or mass flows (in-situ velocity: 1445 m/s, mean grain size: 8.4Φ, porosity: 84%, and bulk density: 1.24 g/cm3), (2) Province IB is covered with muddy sediments that were deposited during the Holocene (in-situ velocity: 1445 m/s, mean grain size: 7.9Φ, porosity: 78%, and bulk density: 1.35 g/cm3), (3) Province II is marked by mixed recent and relict sediments (in-situ velocity: 1477 m/s, mean grain size: 6.1Φ, porosity: 68%, and bulk density: 1.53 g/cm3), (4) Province III is dominated by coarse-grained relict sediments formed during the Pleistocene (in-situ velocity: 1564 m/s, mean grain size: 3.8Φ, porosity: 54%, and bulk density: 1.77 g/cm3), and (5) Province IV consists of coarser sediments than Province III (in-situ velocity: 1671 m/s, mean grain size: 3.0Φ, porosity: 46%, and bulk density: 1.91 g/cm3). The compressional wave velocity, mean grain size, and bulk density increase from Province IA to Province IV, whereas the porosity and water content decrease from Province IA to Province IV. Variability of the physical and acoustic properties tends to follow the general trend of the mean grain size. The classification of each province using the in-situ velocity corrected with the temperature and pressure provides a better reflection of the sediment properties and sedimentary environment.