Geochemical record of the sediments in the continental shelf of the northwestern South China Sea: Implications for the provenance and sedimentary evolution

Abstract

The marine stratigraphic record in the northwestern South China Sea provides an excellent case for understanding the provenance and sedimentary evolution of the marginal sea. However, considerable uncertainty exists in unraveling the geochemical record since the Oligocene due, in part, to a lack of systematic measurements of the sediments. In this study, the major and trace elements of sedimentary rocks from the northern Yinggehai-Song Hong Basin were analyzed to ascertain the provenance and reconstruct the sedimentary evolution in the northwestern South China Sea. The chondrite-normalized rare earth element (REE) patterns show fractionation between light REEs (LREEs) and heavy REEs (HREEs) with significant negative Eu anomalies (Eu/Eu* = 0.59–1.10), combining with discriminant function analysis, implies that the sediments were predominantly eroded from granitic rocks, which are mostly felsic igneous materials. The relatively high index of chemical variability (ICV) values (1.30–3.54) and low chemical index of alteration (CIA) values (36.2–61.5) indicate that these sediments are immature and might have experienced weak to intermediate chemical weathering during transportation and deposition. The geochemical data also show that the Red River catchment was the primary source region for the northern Yinggehai-Song Hong Basin since the late Oligocene. The variations in the element contents and ratios are consistent with the multi-stage tectonic activities of the basin and the provenance shift caused by the recombination of the Red River system in different sedimentary periods.