5:15 PM - 6:45 PM
[SCG48-P34] Distribution of the sedimentary facies in the northern East China Sea during the late Holocene
Keywords:East China Sea, Holocene, sediments
The East China Sea (ECS) is a marginal sea located at the eastern side of the Eurasian continent, having the shelf in the northwestern side and the Okinawa Trough (OT) in the southeastern side. It is well known that the surface sediments in ECS shows complex distribution due to the various component such as the provenance and type of grains, the current with the seasonal variability, the tidal current, the water mass, and the climate. In addition, because a part of ECS became exposed during the last glacial period, it is necessary to understand the transition of sedimentary facies since the Last Glacial Maximum for establishment of the modern sedimentary environment.
In the northern ECS, most of the cores studied in detail are located around the “mud patch” at the southwest of the Jeju Island and the Danjo Basin at the northernmost part of OT. On the other hand, there are only a few studies on the cores recovered from the outer shelf of ECS or the western slope of OT with a detailed age constraint. This study aims to understand the type and distribution of the sedimentary facies around the outer shelf of the northern ECS during the late Holocene, using cores recovered from a wide area.
The visual core description, radiocarbon age analysis, grain size analysis are conducted on the cores recovered from the outer shelf of the northern ECS by Japan Coast Guard. These cores are categorized into four facies as below; (1) sandy silt, (2) mixture of the fine sand, silt, and molluscan shells, (3) well sorted sands, and (4) mixture of the fine to medium sand and molluscan shells. All of four facies have mottled facies without a clear alteration or laminae, and could be separated geographically. Also, the radiocarbon age of foraminifera shows that these facies were formed during the last 5-6 ky without notable reverse of ages. The linear sedimentation rates are up to 10 cm/ky. The modern transportation and sedimentation processes in the outer shelf were formed after the sea level reached to the modern position.
In the northern ECS, most of the cores studied in detail are located around the “mud patch” at the southwest of the Jeju Island and the Danjo Basin at the northernmost part of OT. On the other hand, there are only a few studies on the cores recovered from the outer shelf of ECS or the western slope of OT with a detailed age constraint. This study aims to understand the type and distribution of the sedimentary facies around the outer shelf of the northern ECS during the late Holocene, using cores recovered from a wide area.
The visual core description, radiocarbon age analysis, grain size analysis are conducted on the cores recovered from the outer shelf of the northern ECS by Japan Coast Guard. These cores are categorized into four facies as below; (1) sandy silt, (2) mixture of the fine sand, silt, and molluscan shells, (3) well sorted sands, and (4) mixture of the fine to medium sand and molluscan shells. All of four facies have mottled facies without a clear alteration or laminae, and could be separated geographically. Also, the radiocarbon age of foraminifera shows that these facies were formed during the last 5-6 ky without notable reverse of ages. The linear sedimentation rates are up to 10 cm/ky. The modern transportation and sedimentation processes in the outer shelf were formed after the sea level reached to the modern position.