Provenance of sediments in the northern shelf of the South China Sea: Insights from Pb isotopes in detrital K-feldspar

Abstract

The South China Sea is the largest collection area of fluvial sediments among the semi-closed marginal seas, offering a desirable geological window for studying the source-to-sink transport process of terrigenous sediments in global marginal seas. K-feldspar is a common rock-forming mineral that is likely representative of the source terranes and could offer a more unbiased constraint on the sediment routing system. Moreover, its susceptibility to weathering prevents it from undergoing more than one sedimentary cycling, thereby providing a better indication of the material's primary source. In this study, Pb isotopes in detrital K-feldspars were analyzed on the northern shelf of the South China Sea with the aims of tracking the provenance of sediments and understanding the sedimentary process in the continental margin. The results show that the compositions of ²⁰⁶Pb/²⁰⁴Pb isotopes in detrital K-feldspars are mainly concentrated in the range of 18.5 to 19.0, with a wide range of ²⁰⁷Pb/²⁰⁴Pb ratios from 15.1 to 16.7. Quantitative provenance results indicate that the detrital K-feldspar primarily originated from the Pearl River catchment (55 %) and southeastern Chinese mainland (37 %), with minor contributions from Taiwan Island (8 %). For the Pearl River system, the Xi River is the most important sediment contributor, while the Bei River also provides a large amount of sediments. In contrast to detrital zircons, conspicuous differences in provenance were discerned for the two distinct proxies. This discrepancy arises from variations in the density and volume of K-feldspar and zircon grains, leading to their distinct sedimentary patterns during transportation. The study emphasizes the limitations of relying solely on a single proxy and highlights the utility of Pb isotopes in detrital K-feldspar for understanding the sedimentary processes within the marginal source-to-sink systems.