Seismic sequence and evolution model of isolated carbonate platform—A case from Yongle Atoll, Xisha Islands

The Yongle Atoll is a typical modern isolated carbonate platform, which has recorded a complete evolutionary history of biological reefs and carbonate platforms in the Xisha Area. Based on the newly acquired high-resolution multi-channel seismic data, combined with the research results of Well CK-2 in the Yongle Atoll and Well XK-1in the east of Yongle Atoll, the sequence stratigraphy of the Yongle Atoll is studied, the evolution of the Atoll discussed, and the evolutionary model for the Xisha isolated carbonate platform established. Based on the change in seismic reflection isophase characteristics, five sequences, i.e. Sq1 (Lower Miocene), Sq2 (Middle Miocene), Sq3 (Upper Miocene), Sq4 (Pliocene), and Sq5 (Quaternary) were divided from the bottom up, And the chronostratigraphic framework of the Yongle Atoll was established upon the basis. The depositional environment of the platform dominated by lagoons has been relatively stable since Miocene. The platform slope used to be a neritic environment in Early Miocene where biological reefs well developed. It has been a bathyal sedimentary environment since Miocene up to the present. Gravity flow deposits originated from the top of the platform, as Quaternary contour current deposits are also observed on the western slope of the platform. The development and evolution of the isolated carbonate platform in the Xisha may be divided into four stages: initiation in Early Miocene, large-scale carbonate platform growth in Middle Miocene, drowning period in Late Miocene-Pleistocene, and an atoll at present. This study makes up the shortcomings of previous studies on the development and evolution of isolated carbonate platforms in the Xisha Islands.