The Sedimentary Distribution and Evolution of Middle Jurassic Reefs and Carbonate Platform on the Middle Low Uplift in the Chaoshan Depression, Northern South China Sea

The Chaoshan Depression situated in the Dongsha Sea region, is an important Mesozoic residual depression beneath the Cenozoic Pearl River Mouth Basin in the northern South China Sea, showing significant potential for hydrocarbon exploration. However, current drilling efforts have not resulted in hydrocarbon finds due to the absence of high-quality reservoirs. Recent quasi-3D seismic data has allowed for the first identification of Mesozoic bioherms and carbonate platforms on the Middle Low Uplift of the Chaoshan Depression. A thorough analysis was performed on their horizontal sedimentary distribution and vertical evolution. The findings indicate that the seismic reflection patterns of reefs and carbonate platforms in this area are primarily characterized by high-amplitude discontinuous to chaotic reflections, sometimes showing blank reflections or weak, sub-parallel reflections, along with notable high-velocity anomalies. Atolls, stratiform reefs, and patch reefs are found on local topographic highs of the platform, with atolls mainly in the central part of the quasi-3D area, stratiform reefs in the northeast, and patch reefs in the central-eastern region. Four vertical evolutionary stages have been identified: initial development, flourishing, decline, and submergence. The spatial distribution of bioherms and carbonate platforms was influenced by paleotectonic topography, while their developmental scale was affected by changes in relative sea level. Furthermore, reefs limestone reservoirs within the upper part of the Middle Jurassic exhibit excellent conditions for hydrocarbon accumulation, following a "lower source, upper reservoir, and upper seal" model. These reservoirs have favorable geological conditions for the formation of medium- to large-scale hydrocarbon accumulations, suggesting significant exploration opportunities.