Evolutions of sedimentary facies and palaeoenvironment and their controls on the development of source rocks in continental margin basins: A case study from the Qiongdongnan Basin, South China Sea

Abstract

Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China. However, the development of high-quality source rocks in this basin, especially in its deep-water areas, are still not fully understood. In this study, evolutions of sedimentary facies and palaeoenvironment and their influences on the development of source rocks in diverse tectonic regions of the Qiongdongnan Basin were investigated. The results show that during the Oligocene and to Miocene periods, the sedimentary environment of this basin progressively varied from a semi-closed gulf to an open marine environment, which resulted in significant differences in palaeoenvironmental conditions of the water column for various tectonic regions of the basin. In shallow-water areas, the palaeoproductivity and reducibility successively decrease, and the hydrodynamic intensity gradually increases for the water columns of the Yacheng, Lingshui, and Sanya-Meishan strata. In deep-water areas, the water column of the Yacheng and Lingshui strata has a higher palaeoproductivity and a weaker hydrodynamic intensity than that of the Sanya-Meishan strata, while the reducibility gradually increases for the water columns of the Yacheng, Lingshui, and Sanya-Meishan strata. In general, the palaeoenvironmental conditions of the water column are the most favorable to the development of the Yacheng organic-rich source rocks. Meanwhile, the Miocene marine source rocks in the deep-water areas of the Qiongdongnan Basin may also have a certain hydrocarbon potential. The differences in the development models of source rocks in various tectonic regions of continental margin basins should be fully evaluated in the exploration and development of hydrocarbons.