Quaternary sedimentary evolution and source apportionment in the northwestern South China Sea: Evidence from geochemical and zircon U-Pb data

Abstract

The sedimentary basins in the northwestern South China Sea (SCS) preserve crucial records regarding the evolution of the Qinghai-Tibet Plateau and exhibit significant potential as hosts for natural gas hydrate resources. However, the limited availability of Quaternary stratigraphic samples in this region has impeded a more comprehensive understanding of the Quaternary sedimentary evolution within the area. This study integrates new and published detrital zircon U-Pb ages with geochemical analyses to elucidate the provenance and transport pathways of Quaternary sediments in the Qiongdongan Basin (QDNB) in the northwestern SCS, providing new insights into its evolution. Analyses of major and trace elements in Quaternary sediments, along with detrital zircon U-Pb age spectra, indicate that the QDNB primarily received sediment supply from the Red River source, with significant characteristics of the Pearl River source also observed in the eastern and northeastern parts of the basin. The contribution from Hainan Island was limited, even in the northern shelf areas closer to the island. Quantitative analysis reveals a gradual increase in the contribution of the Pearl River source from the western to the eastern deep-water regions of the QDNB, ranging from 46.05 % to 65.74 %. It is inferred that deep currents transport fine-grained sediments, predominantly from the Pearl River source, from the eastern side of the Xisha Trough to the QDNB. However, within the QDNB, the Quaternary sediments are primarily influenced by the Red River source. Topography is the primary factor controlling the large-scale migration of sediments in the northwestern SCS, while ocean currents have a significant impact on the transport of fine-grained sediments. The rapid uplift of the Qinghai-Tibet Plateau during the Quaternary was a primary driver of accelerated sedimentation rates in the northwestern SCS basin. This study elucidates the spatial variations in sediment provenance across different regions of the northwestern SCS, providing crucial geological evidence for understanding the Quaternary sedimentary evolution.