Geochemistry and provenance of Oligocene to middle Miocene sandstones in the Qiongdongnan Basin, northern South China Sea

Abstract

The Qiongdongnan Basin (QDNB) is a petroleum-bearing basin in the northern margin of the South China Sea (SCS). Provenance analysis is an important tool in petroleum exploration and is helpful in predicting the distribution of good reservoirs in areas with less drilling. However, the provenance of the QDNB remains controversial, and further research is needed. Here, we apply whole-rock geochemistry, petrography, and heavy minerals combined with published detrital zircon U-Pb ages to constrain the provenance of Oligocene to middle Miocene sandstones in the QDNB and the tectonic environment of their deposition. The Oligocene to middle Miocene sandstones from the QDNB are geochemically immature. These sandstones were derived from a weakly weathered source area characterized by dominantly felsic igneous rocks, with a particular slight addition from recycled sedimentary sources. And the Lingshui Formation underwent less weathering than the upper and lower strata. The tectonic setting of the sandstones in the basin belongs to a continental island arc (CIA) or an active continental margin (ACM). Heavy mineral assemblages and detrital zircon U-Pb ages reveal sediment input from multiple sources. Hainan Island was a major and continuous source area contributing to the basin from the early Oligocene to the middle Miocene. In addition, intrabasinal uplift regions could have supplied material to local areas. While these sedimentary source patterns appear to have changed very little in the late Oligocene, a provenance from central Vietnam was explicitly discerned in the western QDNB in the late Oligocene. It is possible that the paleo-Pearl River supplied large volumes of sediment to the eastern QDNB from the late Oligocene to the early Miocene.