Using element geochemistry and detrital zircon geochronology to constrain provenance of the Eocene sediments in the deep-water area of the Pearl River Mouth Basin, South China Sea

Abstract

• The Eocene parent rocks formed in an island arc-active continental margin setting. • These sediments were mainly derived constantly from local topographic highs. • The Panyu Low Uplift began to receive sediments of South China since the late Eocene. As the largest sag in the Zhu II Depression within the Pearl River Mouth Basin, the Baiyun Sag (BYS) lies in an area of interaction among the Eurasian Plate, Pacific Plate, and Indian Plate. The BYS mainly experienced the Paleogene rift stage and Neogene–Quaternary post-rift stage. Thick syn -rift sediments in the BYS have recorded the nature of provenance and provide an excellent record of regional tectonic evolution prior to the opening of the South China Sea. In this study, elemental geochemical analysis combined with published zircon detrital U-Pb dating results are applied to better understand the provenance change and tectonic setting of the BYS during the Eocene. In this respect, the chondrite normalized REE patterns of Eocene samples from six wells are highly similar to upper continental crust (UCC) and post-Archean Australian shale (PAAS), particularly with respect to LREE enrichment, significantly negative Eu anomalies, and slight Ce anomalies. Geochemical results confirm that the BYS Eocene sediments were derived from a continental island arc to an active continental margin. In addition, the rock types of sources and the relatively narrow detrital zircon ages show that Mesozoic intermediate-felsic igneous and metamorphic rocks derived from local topographic highs contributed to infilling most of the BYS. Furthermore, the results show that the Panyu Low Uplift began to accept large sediments transported by the paleo-Pearl River from the South China coast during the active syn -rift stage, prior to the opening of the South China Sea.