Development and controlling factors of Neogene reefs in Xisha sea area

During the Neogene a large number of reefs developed in the Xisha sea area with a great potential for oil and gas exploration. High-resolution seismic data and extensive well drilling data provided an opportunity to understand the evolution of reefs in this area. A few reefs initially developed on a basement high in the early Miocene. In the early Middle Miocene, the reefs, such as point reefs, platform-edge reefs, and pinnacle reefs, flourished on the western slope of Xisha Uplift. They gradually back stepped to the elevated topographic highs in response to a relative sea level rise. In the late Middle Miocene, reefs began to wither and mainly grew on the Xisha Uplift represented by horse toe reefs and platform-edge reefs. Since the Late Miocene, many reefs formerly developing on the edge of the Xisha Uplift were submerged and only some atolls survived around the islands on the Xisha Uplift. Tectonics and eustasy controlled the development of Neogene reefs in the Xisha sea area. Tectonics controlled the topography for the initial growth of reefs, and tectonic subsidence combined with rapid relative sea-level changes controlled reef evolution during the Neogene. In addition, the rhythm of relative sea-level changes in a short time also influenced the sedimentary cycles of reefs.