The sedimentary provenance of Upper Miocene Dongfang submarine fan, Yinggehai Basin: source-to-sink system unravelled through new detrital zircon U-Pb ages and heavy mineral analysis

Abstract

The Upper Miocene Dongfang submarine fan, developed in the Yinggehai Basin, is considered one of the most valuable reservoirs in the northern South China Sea. However, the provenance of the fan remains a controversy between the Red River drainage area and Central Vietnam, hindering hydrocarbon exploration in the basin. In this study, heavy mineral analysis and detrital zircon geochronology of samples from the Upper Miocene intervals in four boreholes were conducted for provenance analysis of the fan. The occurrence of Cr-spinel and high leucoxene contents (34.3 %–85.9 %) in heavy mineral assemblages from these wells suggest sediment contributions from the Red River drainage area and Central Vietnam. Detrital zircon grains from the fan exhibit a wide U-Pb age range, including Luliangian, Jinningian, Caledonian, Indosinian, Yanshanian, and Himalayan populations. Multidimensional scaling (MDS) robustly supports a dual-provenance model consisting of the Red River drainage area and Central Vietnam. Furthermore, we propose that the Red, Ma, Lam, Gianh, and Ben Hai rivers served as sediment pathways owing to the similarities in zircon age distributions between the fan and modern drainage systems. Unmixing models employing the Kolmogorov-Smirnov (K-S) test D statistic quantify the relative source contributions, indicating a potential internal evolution of the fan. Among these, the Red River drainage area dominated the samples D132h and D1310h, accounting for 94.3 % and 86 % of detritus, respectively. Central Vietnam predominantly contributed 99.5 % of sediments to the sample D134h. For the sample D136h, 45.7 % of sediments were derived from the Red River drainage area and 54.3 % from Central Vietnam. The reconstruction of the source-to-sink system reveals that the global forcings (the uplift of the Tibetan Plateau, the expansion of Antarctic ice sheets) and regional adjustments (the intensification of East Asian monsoon, the reversal of Red River Shear Zone) collectively controlled the formation and development of Dongfang submarine fan. Specifically, the activity on the Red River Shear Zone destabilized the deltaic sediments along the western margin of Yinggehai Basin, generating sediment gravity flows that accumulated in the depocenter and formed the Dongfang submarine fan. The source-to-sink system model may provide valuable insights into the prediction of Upper Miocene reservoirs and guides the future hydrocarbon exploration in the basin.