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南沙海域万安盆地是南海西南部一重要的新生代沉积盆地。经地震勘查,盆地盖层厚度达12.5km。据少数钻井揭示及与其它盆地进行地震地层对比,认为万安盆地奠基于中生代基底之上,发育有晚始新世-第四纪地层。盆地大致呈近SN向展布的菱形,它是张性特征非常明显的走滑拉张盆地。盆地自形成至今,其古地理受全球海平面升降和区性构造运动影响,经历了从四面环陆的内陆湖泊到北西南三面环陆的海湾,再到滨、浅海的演化。古地理控制了盆地的古环境和沉积相带的分布。
Wan’an Basin in the Nansha Sea is an important Cenozoic sedimentary basin in the southwestern South China Sea. After seismic exploration, the thickness of the cover of the basin reaches 12.5km. According to a few wells drilled and compared with other seismic stratigraphy strata, it is concluded that the Wanan Basin was founded on Mesozoic basalts and developed late Eocene-Quaternary strata. The basin is roughly in the shape of a nearly SN-spread diamond, which is a strike-slip stretch basin with pronounced traits. Since the formation of the basin, its paleogeography has been affected by global sea-level rise and regional tectonic movements. It has undergone the evolution from inland lakes surrounded by the four sides to the gulf surrounded by three sides in the northwestern South China Sea, to the coast and the shallow sea. Paleogeography controlled the distribution of paleoenvironment and sedimentary facies in the basin.