Sea level controls on the provenance of fine-grained sediments in the Xisha Trough, northwestern South China Sea over the last ~30 ka

Abstract

The Xisha Trough situated in the northwestern South China Sea (SCS), plays a pivotal role in transporting sediments from the Red River into the deep-sea basin of the SCS, and thus is a critical place to examine variations in source-to-sink process of the Red River-derived sediments associated with past climate and oceanography changes. In this study, we analyzed clay minerals, grain size composition, and specific XRF core scanning elements of sediment core XT-1, retrieved from the northern slope of the Xisha Trough, to assess changes in sediment provenance and their primary influencing factors in the studied area over the last ~30 ka. The results show that clay minerals are primarily composed of illite+chrolite with a mean of 89%, followed by kaolinite with a mean of 9%; smectite occurs as a minor component. The mean grain size and XRF core scanning elements exhibit a three-phase change that corresponds well to variations in sediment source since the last glacial period. Over the last 29.8 ka, sea level fluctuations are the primary factor controlling changes in provenances and their contributions in the northern slope of the Xisha Trough. During the last glacial from 29.8 to 20.2 ka with lower sea levels, both the Red River and Taiwan were the primary contributors of fine-grained sediments in the lower continental slope of the Xisha Trough. However, with marine transgressions from the last deglaciation, Taiwan gradually became the dominant source of fine-grained sediments, followed by the Red River. Additionally, during the Last Glacial Maximum and the early to middle Holocene periods, the strengthened deep-water current (DWC) and East Asian summer monsoon, respectively, exerted strong impacts on the contribution of Taiwanese sediments to the Xisha Trough. The changing pattern of primary provenance in the studied core is roughly in line with those observed in the northern SCS, while differing from those in the southern regions of the western Xisha Trough. This discrepancy is likely caused by varying influences of the DWC on these regions.