2:00 PM - 2:15 PM
[HCG21-02] Spatio-temporal variation of the sedimentation process around the western slope of the Okinawa Trough during the Holocene
Keywords:East China Sea, Holocene, Sedimentary process
The East China Sea (ECS) is a marginal sea located in the eastern edge of the Eurasian continent. It is characterized by the geomorphological feature of the shallow shelf in the northeastern side and the Okinawa Trough (OT) in the southeastern side, and the oceanographical features of the existence of the Kuroshio Current and the seasonal variation of the current and water mass. These features make the transportation and sedimentation process of grains complicated. However, the comprehensive studies combined the observation of the transportation with the sedimentation are limited to few areas, such as the PN-Line between the Okinoerabu Island and the Changjiang rivermouth. In OT, the changes in the grain composition and provenance have been reconstructed based on the various proxies in the many sedimentary cores. However, they mainly focus on the transportation process across the whole ECS. Accordingly, the consistency of the sediments between the provenance and the coring sites and the reconstructed process in those cores are rarely considered.
In this study, the sedimentary core recovered from the western slope of the OT were used for the visual core description, the grain-size analysis, and the radiocarbon dating, and the seismic structure around these cores were observed using the sub-bottom profiler (SBP). As a result, in the southern site near PN-Line, the silt-sized grains are deposited continuously through the Holocene, suggesting the sedimentation process like the modern. The core around the middle of the study area shows the coarsening of grain-size, the changes in the composition of the grain, and the lower sedimentation rate. In the further north, the core adjacent to the Oki-Danjo Hills (ODH) around 30°N shows the coarsening of grain-size after around 11 ka from silt to sand, and the contribution from the reworked grains based on the reversal of the radiocarbon ages. It is estimated that these changes of the sedimentary facies were basically formed under the weakening of the coastal water during the sea-level changed and the following strengthening of KC. On the other hand, because the coring sites in this study are located the slope without the clear sub-marine valley and the geomorphological difference are relatively small, the difference of the sedimentary faces among these sites should be formed under the local geomorphology or the local process.
In this study, the sedimentary core recovered from the western slope of the OT were used for the visual core description, the grain-size analysis, and the radiocarbon dating, and the seismic structure around these cores were observed using the sub-bottom profiler (SBP). As a result, in the southern site near PN-Line, the silt-sized grains are deposited continuously through the Holocene, suggesting the sedimentation process like the modern. The core around the middle of the study area shows the coarsening of grain-size, the changes in the composition of the grain, and the lower sedimentation rate. In the further north, the core adjacent to the Oki-Danjo Hills (ODH) around 30°N shows the coarsening of grain-size after around 11 ka from silt to sand, and the contribution from the reworked grains based on the reversal of the radiocarbon ages. It is estimated that these changes of the sedimentary facies were basically formed under the weakening of the coastal water during the sea-level changed and the following strengthening of KC. On the other hand, because the coring sites in this study are located the slope without the clear sub-marine valley and the geomorphological difference are relatively small, the difference of the sedimentary faces among these sites should be formed under the local geomorphology or the local process.