Seismic characteristics and development of the Xisha carbonate platforms, northern margin of the South China Sea

The Xisha carbonate platforms, which include the modern-day Xisha Atoll, occur upon the northern continental margin of the South China Sea (SCS). In this study, we identify the seismic characteristics about various sedimentary facies of the carbonate platform and different types of reef in this area, based on the 2-D seismic data, reefs show high-amplitue moundy continuous reflection at the top and weak chaotic reflections inside. Carbonate platforms show high-amplitude continuous reflection at the top and high reflection alternative with weak reflection. The above analysis provided information about the influence of fluctuations in relative sea level, tectonic movements, paleotopography and the development mechanism of the carbonate platform. Based on the seismic data and data from drillholes (Xichen-1, Xiyong-1), we propose a schematic sedimentary model of the Xisha carbonate platforms at the northern margin of the SCS and outline five stages of development for the carbonate platform. Its sedimentary evolution consists of Initial establishment stage, development stage, exposure stage, drowning stage and large atoll reefs development stage. We also propose that several phases tectonisms supply proper environment and structural position for carbonate platform development, they can also destroyed the exist platforms. Besides, eustasy change was also the main influential factor on the development of the platforms.

Research highlights
► we combined the stratigraphic division plan in the adjacent area together to define the formation boundary in Xisha Islands, besides we also consulted and followed the result of early well on the islands.
► We used large quantity seismic profiles to show the seismic characteristics of carbonate platform and different types of reef in Xisha Islands and this can be a reference for the sequent relevant study in the South Asian area.
► We proposed a development model of Xisha carbonate platform and divided the develop process into five stages: 1. Initial establishment of the carbonate platform; 2. Development of the carbonate platform; 3. Exposure of the carbonate platform; 4. Drowning of the carbonate platform; 5. Development of large atoll reefs.
► We analyzed the main control factors about the development of Xisha carbonate platform: tectonic movements and sea level change.