| dc.description.abstract | In this study, we identified a near surface regional sequence boundary in the continental slope of the northeastern South China Sea. This regional sequence boundary can be used as an important indicator for distinguishing the sequences which formed before or after the Last Glacial Maximum in the continental slope environment. We employed multiple marine geophysical and geological methods, including deep-towed sonar system, sediment core analysis, and radiocarbon dating, to investigate the formation mechanism of the regional sequence boundary and reconstruct the sedimentary environment change history in the study area.
According to the sub-bottom profiler interpretations, we found the regional sequence boundary predominantly occurs in topographically flat areas, such as terraces on the flanks of the Good-Weather Ridge, bathymetric troughs between ridges, and atop the Palm Ridge and the Pointer Ridge. Based on grain size analysis, radiocarbon dating and core images of the core MD18-3545, we propose four sedimentary periods in the last 35,000 years in the study area. The Period 1 was in the stage before the regional seafloor erosive process. The relative sea-level was approximately -60 meters, and the sediment facies present a stable depositional hemipelagite facies with weak bottom current. The Period 2 started in the sea-level lowstand stage of the Last Glacial Maximum (LGM), and ended in about 11,900 year BP. The strong bottom current in this period transformed the sedimentary environment from depositional to erosive. Following the Period 2, the relative sea-level in the Period 3 has rose to -60 m and the sedimentary environment returned to depositional, forming the regional sequence boundary. Bottom current intensity increased with rising sea-levels. The sediment facies also shifted from hemipelagite to contourite, which controlled by strengthened bottom current. The Period 4 started in around 6,500 year BP. The relative sea-level is in stable highstand. Although bottom current intensity decreased compared to the previous period, it still played a significant role in shaping the seafloor environment and developing the contourite system. We propose that global climate changes and sea-level fluctuations have impacted bottom current intensities, sedimentary environments, and seafloor morphologies in the northeastern slope of South China Sea over the past 35,000 years. | en_US |